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Page 1: Effect of Surface Finish on Concrete Properties · 2013-12-05 · 2.3.2 Measuring Fresh Air Content ... slabs were made in order to test the effect of the surface finish on concrete

Effect of Surface Finish on Concrete Properties

by

Ardavan Amirchoupani

A thesis submitted in conformity with the requirements for the degree of Master of Applied Science

Civil Engineering University of Toronto

© Copyright by Ardavan Amirchoupani 2013

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Effect of Surface Finish on Concrete Properties

Ardavan Amirchoupani

Master of Applied Science

Civil Engineering

University of Toronto

2013

Abstract

The purpose of this project was to evaluate two types of concrete surfaces and analyze the effect

of each finish on the air content, paste content, aggregate fraction and rate of absorption at

various depths from the surface. For this project, nine concrete mixtures were evaluated with

varying cement, water and air contents. Slabs were cast and two types of finishes were

considered: a trowel-finished made with a magnesium trowel and a form-finished from the

plywood molds used. Cores were taken from the slabs and tested at 0, 5, 10, and 20mm below

the surface.

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Acknowledgments

I would like to thank my supervisor Prof. Hooton for his guidance, encouragement and support.

I would also like to thank Prof. Peterson for his assistance and advice throughout this endeavor.

Additionally, this project would not have been possible without the help of Olga Perebatova and

the help of my colleagues in the Concrete Materials group at University of Toronto.

Special thanks to my officemates Eric, Majella, Mahsa, and Johnny for their help. Additional

thanks to all my friends especially Patrick and Amin for their company and their presence of

which was a pleasant distraction and without whom graduate school would not have been

anywhere as enjoyable. Lastly, I would like to thank my family for their love and support.

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Table of Contents

Acknowledgments .......................................................................................................................... iii

Table of Contents ........................................................................................................................... iv

List of Tables ................................................................................................................................ vii

List of Figures .............................................................................................................................. viii

List of Appendices .......................................................................................................................... x

Chapter 1 Introduction .................................................................................................................... 1

1 Background ................................................................................................................................ 1

1.1 Objective ............................................................................................................................. 1

1.2 Description of Experimental Work ..................................................................................... 1

Chapter 2 Literature Review ........................................................................................................... 3

2 Background ................................................................................................................................ 3

2.1 Concrete Components and Hydration ................................................................................. 3

2.2 Transport Mechanisms in Concrete .................................................................................... 4

2.2.1 Sorptivity ................................................................................................................. 5

2.3 Air Entrainment .................................................................................................................. 9

2.3.1 Air Entraining Agents ........................................................................................... 10

2.3.2 Measuring Fresh Air Content ................................................................................ 11

2.4 Methods for Measuring Air Content in Hardened Concrete ............................................. 12

2.5 Concrete Placement and Finishing .................................................................................... 16

2.5.1 Screeding ............................................................................................................... 17

2.5.2 Floating ................................................................................................................. 17

2.5.3 Troweling .............................................................................................................. 18

2.5.4 Curing ................................................................................................................... 18

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2.6 Related Studies .................................................................................................................. 19

Chapter 3 Experimental Procedures .............................................................................................. 26

3 Background .............................................................................................................................. 26

3.1 Materials ........................................................................................................................... 26

3.1.1 Cementitious and Supplementary Cementing Materials ....................................... 26

3.1.2 Fine Aggregate ...................................................................................................... 26

3.1.3 Coarse Aggregate .................................................................................................. 26

3.1.4 Chemical Admixtures ........................................................................................... 27

3.2 Concrete Mixture Design .................................................................................................. 27

3.2.1 Proportioning ........................................................................................................ 28

3.2.2 Casting Procedures ................................................................................................ 29

3.2.3 Curing Procedures ................................................................................................. 32

3.3 Testing Hardened Concrete Properties ............................................................................. 33

3.3.1 Compressive Strength ........................................................................................... 33

3.3.2 Resistivity and Permeability Tests ........................................................................ 33

3.3.3 Rate of Absorption Test ........................................................................................ 35

3.3.4 Hardened Air, Aggregate and Paste Content Analysis ......................................... 38

Chapter 4 Results and Discussion ................................................................................................. 45

4 Background .............................................................................................................................. 45

4.1 Compressive Strength Results .......................................................................................... 45

4.2 Resistivity and Permeability Results ................................................................................ 48

4.3 Sorptivity Results .............................................................................................................. 52

4.4 Aggregate Distribution Results ......................................................................................... 62

4.5 Hardened Air Content Analysis ........................................................................................ 67

4.6 Paste Content Analysis ..................................................................................................... 71

4.7 Cylinder Aggregate and Paste Distribution ...................................................................... 76

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Chapter 5 Conclusions and Recommendations ............................................................................. 77

5 Conclusions .............................................................................................................................. 77

5.1 Recommendations ............................................................................................................. 79

References ..................................................................................................................................... 80

Appendices .................................................................................................................................... 86

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List of Tables

Table 1: ASTM C457 Air Void Parameter Equations .................................................................. 14

Table 2: Summary of Concrete Mixtures ...................................................................................... 28

Table 3: Resistivity Results .......................................................................................................... 49

Table 4: Initial Rate of Absorption Results Summary .................................................................. 52

Table 5: General Comparison in Sorptivity Results ..................................................................... 55

Table 6: Effect of Air Entrainment on Initial Rate of Absorption ................................................ 55

Table 7: Comparison Several Parameters in the Initial Rate of Absorption Results .................... 56

Table 8: Initial Rate of Absorption % Change Each Depth vs. Surface ....................................... 60

Table 9: Aggregate Fraction Results ............................................................................................. 64

Table 10: Hardened Air Content Results Summary ..................................................................... 68

Table 11: Difference of Air Content between Trowel and Formed-Finished Samples ................ 69

Table 12: Paste Content Results ................................................................................................... 73

Table 13: Paste Content Results Summary ................................................................................... 74

Table 14: Range of Aggregate Contents in Concrete Cylinders ................................................... 76

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List of Figures

Figure 1: Idealized Depiction of Concrete Surface Properties ..................................................... 21

Figure 2: Slab and Core Extraction Layout .................................................................................. 35

Figure 3: Core Slice Layout .......................................................................................................... 36

Figure 4: Rate of Absorption Test Setup ...................................................................................... 37

Figure 5: Sample Coloured Scan ……………………………………………………….……….39

Figure 6:Section of Actual Pixel Size Sample ………………………………………………….39

Figure 7: Phenolphthalein Sprayed Surface 100 mm Concrete Samples ..................................... 40

Figure 9: Example Progression Image Analysis ........................................................................... 41

Figure 3: Automated Hardened Air Content Analysis Breakdown .............................................. 44

Figure 4: Compressive Strength Test Results ............................................................................... 46

Figure 5: Effect of w/cm on 28 Day Compressive Strength ......................................................... 46

Figure 6: Influence of Air Entrainment on Compressive Strength ............................................... 47

Figure 7: Merlin and RCON Resistivity Results .......................................................................... 48

Figure 8: Merlin and RCON 56 Day Resistivity Results .............................................................. 49

Figure 9: RCPT Results ................................................................................................................ 50

Figure 10: RCPT Results with Varying Air Contents .................................................................. 51

Figure 11: Initial Rate of Absorption of Trowel-Finished Samples ............................................. 53

Figure 12: Initial Rate of Absorption of Formed-Finished Samples ............................................ 53

Figure 13: Initial Rate of Absorption of Different Finishing Techniques at Surface ................... 57

Figure 14: Initial Rate of Absorption at 5mm below Surface ....................................................... 58

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Figure 15: Initial Rate of Absorption at 10mm below Surface ..................................................... 58

Figure 16: Initial Rate of Absorption at 20mm below Surface ..................................................... 59

Figure 17: Depiction Coarse Aggregate Distribution at Formed Surface Boundary .................... 60

Figure 18: Initial Rate of Absorption Comparison Polished and Saw-Cut Surface ..................... 61

Figure 19: Aggregate Fraction vs. Depth of Trowel-Finished Specimen ..................................... 62

Figure 20: Aggregate Fraction vs. Depth of Formed-Finished Specimens .................................. 62

Figure 21: Effect of Air Content on Aggregate Fraction for Trowel-Finished 0.45 w/cm Samples

....................................................................................................................................................... 63

Figure 22: Effect of Air Content on Aggregate Fraction for Form-Finished 0.45 w/cm Samples 63

Figure 23: Distribution of Aggregates in Trowel-Finished Slabs ................................................. 66

Figure 24: Distribution of Aggregates in Form-Finished Slabs .................................................... 66

Figure 25: Hardened Air Content of Surface-Finished Concrete Slabs ........................................ 67

Figure 26: Hardened Air Content of Formed-Finish Concrete Slabs ........................................... 67

Figure 27: Hardened Air Content of Trowel-Finished Samples at Constant w/cm ...................... 70

Figure 28: Hardened Air Content of Form-Finished Samples at Constant w/cm ......................... 70

Figure 29: Paste Content of Trowel-finished Slabs at Various Depths from Surface .................. 71

Figure 30: Paste Content of Form-Finished Slabs at Various Depths from Surface .................... 71

Figure 31: Paste Content of Trowel-finished Slabs at Various Depths from Surface .................. 72

Figure 32: Paste Content of Form-Finished Slabs at Various Depths from Surface .................... 72

Figure 33: Aggregate Distribution over Depth in Concrete Cylinders Mix 2 Red: 0.45GU-

6.4%air .......................................................................................................................................... 76

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List of Appendices

Appendix A: Material Properties …………………...……………………………………….…..86

Appendix B: Concrete Mixture Designs…………………………………………………………91

Appendix C: Initial and Secondary Rates of Absorption Results ……………………….……..101

Appendix D: Scanned Images ………...…………………………………………………..……156

Appendix E: Raw Analysis Results Duplicate Samples ………………..………………….…..175

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Chapter 1 Introduction

1 Background

The near-surface zone or cover is one of the most important areas in any concrete structure. This

area provides the first line of defense against the ingress of fluids in concrete. The importance of

this area is highlighted since the protection of reinforcement bars is also dependent on the depth

and physical properties of the concrete in the cover zone. Given the importance of this region, it

is of paramount importance to become familiar with how the physical properties of the near

surface zone affect the performance of concrete. What makes the surface of concrete even more

interesting is the overall sensitivity of this area to not only casting and compaction procedures,

but also with regards to the type of finish used along with curing procedures. The quality of the

surface zone is a major factor of its penetration resistance which greatly influences the durability

of the concrete structure. The recognition of the nature and weaknesses of this zone will help

with a better understanding of the range of phenomena at work near the surface and would also

benefit practitioners to use more suitable techniques that can result in more durable concrete

surfaces.

1.1 Objective

The goal of this study was to evaluate the effect of each finish on the paste content at different

depths and how the paste and aggregates are positioned throughout the cover. Furthermore, the

influence of the finishing techniques on the entrained air content of the near surface zone was

studied. In addition to this, the effects of surface finish on the sorptivity of concrete were

examined.

1.2 Description of Experimental Work

The primary objective of this research was to look at two types of concrete finishes: a form-

finished surface cast against plywood moulds and surface finished using a magnesium trowel and

evaluate the effect of each finish on surface properties of concrete. For the purposes of this study,

a number of concrete mixtures were made in order to examine the effect of surface finish on a

wide range of concrete mixtures. For each mixture, duplicates of formed and trowel-finished

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slabs were made in order to test the effect of the surface finish on concrete properties. A wide

range of entrained air contents were also targeted in each mixture in order to explore the effect of

air in the covercrete with the different finishing techniques. The slabs were later cored and slices

were cut at different depths below surface and conditioned. Samples were obtained from the

surface and 5mm, 10mm, and, 20 mm below the surface. In this study, the scope of analysis was

designed to test the surface of the concrete only up to a depth of 20mm under the surface. This

depth was established based on findings from previous studies as noted in the literature review.

These samples were then tested to determine the rate of absorption in a 3% chloride solution.

The surface of each sample was later analyzed in order to determine the aggregate fraction, air

and paste contents of the suction face. Overall, more than 160 samples were tested in this study.

Before outlining a detailed description of experimental procedures, a brief literature review is

presented to explain the phenomena behind each test and also in order to help explain the

planning and decision criteria which shaped the scope of this project.

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Chapter 2 Literature Review

2 Background

This chapter covers the basic concepts and theories related to this research in addition of

reviewing some of relevant previous research. The purpose of this section is to discuss the basic

concepts and previous studies related to this research. First, a brief and elementary background

on concrete components and nature of hydrates is provided. Next, an outline of air entrainment in

concrete along with various air entraining agents and methods of measuring the volume of air in

fresh concrete are described. Afterwards, a series of techniques to measure and analyze the

hardened air, paste and aggregate content in concrete are described. This is followed by

describing some of the more common placement, finishing and curing techniques used to cast

concrete structures. Finally, a few studies presented by other researchers related to the scope of

this research are mentioned.

2.1 Concrete Components and Hydration

Concrete can be thought of as a composite material consisting of several ingredients. In the most

basic terms, concrete is made up of aggregates incorporated in a hardened matrix compound of

cement and water. The cement reacts with water in the paste results in set and strength develops

and this reaction is called hydration. To describe this complex reaction in the simplest terms, the

alite, belite, aluminate and ferrite phases present in Portland cement each react with water and

this reaction results in formation of new hydrated compounds. As a result of this, concrete

hardens and gains strength. The primary products of this reaction are calcium hydroxide and

calcium-silica-hydrates.

In a properly proportioned concrete mixture, the paste coats the surface of all the fine and coarse

aggregates and, as it hydrates, it forms a solid composite material. For this reason, the

proportions of each ingredient in the concrete mix are very important. Typical mixes often

contain about 10-15% cement, 60-75% aggregate, and 15-20% water (De Larrard, 1999). Other

components like supplementary cementing materials such as silica fume, blast-furnace slag, and

flyash are also often added into concrete. Various chemical admixtures are usually added into

concrete in order to change the properties of the concrete. For instance, air entraining

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admixtures are used to increase the air content of concrete and water-reducers or

superplasticizers are added in order to increase the workability of fresh. The ratio between water

and cementitious material, also known as the water to cementitious ratio (w/cm) is one of the key

factors in the final strength and properties of the concrete. Although concrete gains most of its

strength early on, the hydration does not stop as long as there is sufficient moisture available for

this reaction to continue. However, it is important to emphasize the fact that proper

proportioning of each ingredient affects every aspect of concrete from workability and

finishibility properties of the fresh concrete to strength and long term durability afterwards.

2.2 Transport Mechanisms in Concrete

The long term durability of concrete is an important factor in structures and most degradation

mechanisms in concrete depend on the transport of fluids and ions into concrete. Concrete

structures may be exposed to a variety of solutions which can potentially decrease the life of the

structure. NaCl and Na2SO4 are examples of such solutions and, if not designed accordingly,

these ions can threaten the durability and service life of any structure. For instance, chlorides

from de-icer salts can lead to the corrosion of rebar in concrete (Portland Cement Association,

2012). Sulphate from ground water has the potential to result in sulphate attack and causing

deterioration of concrete (Microanalysis Consultants Ltd, 2012). Equally important, the exposure

of concrete to alkali solutions has been shown to cause cracking, crystallization of salts in the

crack and expansion of concrete (Cao, Bucea, Khatri, & Siriviva, 2001). Furthermore, water is a

common medium in each solution in addition to contributing to freeze-thaw damage in concrete.

There are a number of factors which contribute to the transport of fluids in concrete. Diffusion,

permeability, sorption, and wick action are the primary mechanisms of fluid transfer. These are

time-dependent mechanisms and the rate of ingress of fluids is mainly based on the quality of

concrete, binding reactions, defects present, and curing regime (Hooton, 2006). The movement

of moisture and ions in concrete is particularly interesting compared to other materials due to the

complex pore structure of concrete. The rate and amount of fluid ingress in concrete is dependent

on the pore structure which is affected by such factors as w/cm ratio, use of supplementary

cementing materials and degree of hydration (Stanish, Hooton, & Thomas, 2000). Sorptivity in

unsaturated or partly saturated concrete is very important given that it can occur over a much

shorter time span compared to other transport mechanisms (hours compared to days or months)

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and water can penetrate 5 to 15mm into even high performance concrete in a matter of hours by

absorption (Hooton, 2006). Diffusion is another important mechanism which many concrete

structures may experience. Diffusion refers to the movement of fluids in concrete as a result of a

concentration gradient and is described by Fick‟s laws. Ions can therefore pass through saturated

concrete without the movement of water. For example, during winter months in cold climates,

the surface of roads and parking structures are often in contact with chloride de-icing salts. The

chloride ions near the surface move through the saturated concrete towards the core in order for

the concentration gradient to balance out (Poulsen & Mejlbro, 2005). Usually, water and ionic

fluids advance into unsaturated concrete by absorption and once the surface of concrete becomes

fully saturated, the forces of diffusion assist with the advancement of the solution front. Rarer

than these two is the process of permeation since it requires a pressure gradient which rarely

exists in a typical concrete structure. Understanding the nature and actions of fluid transport

mechanisms in concrete is important for designing more durable concrete structures. The

primary focus of this section will be on the rate of absorption or sorptivity of concrete since

capillary absorption is the dominant initial force behind the ingress of water and, dissolved ions

into the concrete surface.

2.2.1 Sorptivity

The flow rate of fluids in unsaturated concrete is defined as sorptivity. Fluid and ion transport in

concrete has been studied extensively over the years and has formed the basis for ASTM C1585

Standard Test Method for Measurement of Rate of Absorption of Water by Hydraulic-Cement

Concretes. The principle theories behind calculating the rate of absorption of concrete specimen

were originally intended for calculating the unsaturated flow of water into other porous building

materials such as bricks (Gummerson, Hall, & Hoff, 1980) and through a series of experiments a

relationship was observed between the cumulative absorbed volume per unit area of the inflow

surface and the square root of the elapsed time, most often expressed as:

(Equation 1)

Where S is the sorptivity of the material and t is time in seconds (Hall, 1989). For unsaturated or

partly saturated concrete specimen, the sorptivity of the material is higher in the initial 6 hour

phase compared to later on and thus the rate of absorption is often expressed as initial and

secondary absorption. Similarly, according to ASTM C1585, the absorption, I, is the change in

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mass divided by the product of the cross-sectional area of the test specimen and the density of

solution:

I = (Equation 2)

I = absorption (mm),

mt = change in specimen mass in grams, at the time t,

a = exposed area of the specimen, in mm2, and

d = density of the water in g/mm3.

Studies done by Hooton and Bickley (2006) showed that the penetration and absorption of fluids

depends on the continuity of capillary and size of the pores and for unsaturated concrete the

capillary tension will draw the solution into a depth of between 5-15mm inwards from the top

surface in a matter of hours until the surface becomes saturated.

There are a number of standardized absorption tests including BS1881 “Test for Determining the

Initial Surface Absorption of Concrete”, ASTM C1585 “Test Method for Measurement of Rate

of Absorption of Water by Hydraulic Cement Concrete” in North America or its equivalent in

Australia, known as AS1342. One major problem with these standards is that the pre-

conditioning of the samples and differences in the test procedures creates a large variance in the

final sorptivity measurement (Hearn, Hooton, & Nokken, 2006). There have been a number of

studies done with regards to the sorptivity of concrete but there lacks a comparative analysis with

regards to different test methods.

Previous studies have shown that in-situ concrete is not fully dry but is rarely fully saturated

(DeSouza, Hooton, & Bickley, 1997). This creates a problem when it comes to conditioning

samples in the lab to simulate the internal moisture content of in-situ concrete. The reason why

the initial moisture content of the sample is so important is because of the fact that sorptivity is

directly related to the initial water content (Hall, 1989). The drier the sample is, the higher the

rate of sorption will be and vice versa. Such a phenomenon also complicates the matter when it

comes to model the flow of fluids in concrete. As a result, an extended version of Darcy‟s

equation is most often used to describe the flow of fluids in unsaturated media (Licheng &

Uedab, 2011).

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In studies by Parrott (1994) it was found that the relative humidities of most structural concretes

in service are in the range of 40 to 100%. Other studies showed that drying the concrete sample

for a fixed period of seven days at 50 degrees Celsius would not cause any damage but the

internal moisture content of the sample will not be uniform through its depth (Nokken & Hooton,

2002). Experiments showed that after an initial 3 days in the oven at 50 degrees Celsius, the

samples should be placed in a sealed container at 50 degrees for 4 additional days to allow the

residual moisture gradient to equilibrate in the pore system (DeSouza, Hooton, & Bickley, 1997).

This was tested and resulted in sorptivity values that appeared to be unrelated to the quality of

concrete being tested and is believed to be a fast way of achieving moisture contents which

simulate in-situ concrete (DeSouza, Hooton, & Bickley, 1997).

A number of other experimental studies have been published which examined the sorptivity of

concrete. In some of these studies, certain factors were neglected which leaves the findings of

these experiments questionable. For instance, the preconditioning of concrete specimens is an

important issue and the moisture content at the time of testing is very important since it

significantly alters the results. In a number of studies, the preconditioning regime was designed

to condition the sample at 105 degrees Celsius for 6 days before starting the test (Kelham, 1988).

However, such a conditioning regime will lead to micro cracks which will alter the final results

significantly and display very high values of sorptivity.

The pore size distribution of concrete also affects the rate of absorption. In this process, the fluid

selects a pathway in this porous media and larger pores remain empty and are often filled at a

later stage in the sorption process. This is because of the fact that the liquid supply inside the

concrete pores is finite and the liquid advances through smaller pores first since the capillary

force is larger in comparison to counteracting forces. Over time, the diameter of the pores that

are filled with the fluid increases. Equally important, in larger pores, the liquid propagates as a

thin layer on the walls of the pore while the central parts of the pore can remain empty (Hanzic,

Kosec, & Anzel, 2010). It should be noted that no capillary absorption occurs in pores that are

larger than 1mm in diameter since the surface tension of the water is much smaller than the force

of suction and very little absorption occurs in pores that are under 1µm in diameter since

counteracting forces arising from the surface tension of the fluid are similar to the gravitational

forces acting on the solution (Hanzic, Kosec, & Anzel, 2010). Comparative studies conducted on

the sorptivity of water and a silane solution in concrete using neutron radiography found that

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silane uptake was significantly higher compared to water. This was associated with the lower

surface tension of silane (Gerdes, Wittmann, & Lehmann, 1999). For this reason, the surface

tension and type of solution being studied must be taken into account when performing sorptivity

tests.

Equally important are the effects of admixtures on the porosity and sorptivity of concrete. Air-

entraining agents shift the size of the pores to a larger size class and studies have shown that the

majority of the pores will be larger than 0.1µm (Hanzic, Kosec, & Anzel, 2010). As a result it is

expected that air entrained mixes to have a lower absorption rate since the pores are larger and

even though the total porosity increases with these mixes, the pore size increase does not favor

absorption (Hanzic, Kosec, & Anzel, 2010). Superplasticizers also shift the size distribution of

the pores and the majority of the pore sizes will be concentrated in the micro-capillary pores

which are between 30nm to 1µm. High doses of superplasticizer may also lead to an increase in

the rate of absorption (Hanzic, Kosec, & Anzel, 2010).

Another factor which has the potential of altering the rate of absorption has to do with the nature

of salt transport in concrete. More specifically, salts are easily detached from water and this

could lead to the adsorption of the salt ions on the pore walls. As a result of this sorption, an

electrical double layer could form on the surface of the capillary pores with the amount of

potential being directly related to the type of ions in the salt. Naturally, this potential is stronger

on the outer edges of the pores compared to the interior of the pore. As a result, this electrical

double layer may interfere with the ionic clouds in the solution and affect the movement of the

salt ions and water. This effect is more pronounced in smaller pores since the size of the double

layer is closer to the size of the pores (Cerny & Rovnanikova, 2002).

It should be mentioned that it is hard to distinguish a certain flow pattern based on sorptivity

alone but the fact remains that sorptivity is an important fluid transfer mechanism and the effects

of which could affect the durability of the concrete. The ingress of water and ionic fluids by

sorption is a mechanism often only experienced by the covercrete, further emphasizing the

importance of the properties of the near surface zone and type of concrete finish.

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2.3 Air Entrainment

Air entrainment refers to the practice of adding air into the concrete by stabilizing small and

stable air bubbles in the concrete matrix which are generated during the mixing action. Air

bubbles are dispersed throughout the paste but are not considered to be part of the paste itself.

The primary purpose of air-entraining concrete is to protect the concrete matrix against frost

action. Air entrainment also has other benefits such as increasing the workability of fresh

concrete. Additionally, in air entrained concrete pavements, the bleeding of water on the surface

tends to decrease and the amount of segregation also decreases (Pigeon & Pleau, 1995).

In terms of improved workability, for every percent increase in air, on average the slump

increases by about 50mm (Iowa Department of Transportation, 2013). The mechanism which is

believed to be behind this improved workability is that the air bubbles act as fine aggregate

particles that are elastic with negligible surface friction (Wright, 1953).

The decrease in the bleeding of concrete which has been air entrained is due to the modification

of the pore structure. Bleeding refers to the upward movement of water in the plastic concrete

which results in a formation of a layer of water on the concrete surface after compaction. This

phenomenon occurs as a result of the sedimentation of solid particles in concrete which were

originally separated by a layer of water. As these particles settle due to gravity, some water is

pushed to the surface. In air entrained concrete, the air bubbles decrease the amount of

sedimentation due to their spherical shape and surface tension which makes it difficult for

particles to settle. As a result, very little water gets pushed up to the surface. Furthermore, the

reduction in bleeding also reduces the extent of capillary pores in the cover zone since less water

travels upwards to the surface and hence the pore size structure of concrete near the surface

would be similar to that of the rest of the concrete (Wright, 1953).

One of the drawbacks of air entrained concrete is the loss of compressive strength as a result of

replacing part of concrete with air. For each percent of added air, a loss of 2 to 5 percent in

compressive strength can be expected. This issue can be dealt with by reducing the water content

since the entrained air in the concrete improves the workability and a slight addition in cement

content should not significantly alter the workability of the concrete mixture (Whiting & Nagi,

1998).

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There are a number of theories as to how frost action affects concrete but it is primarily believed

that since water expands by nine percent when frozen and if the concrete pores are saturated

above 90%, repeated freeze-thaw cycles will damage the concrete due to the expansion of water

in the capillary pores, unless it can find room to expand.

2.3.1 Air Entraining Agents

Air entraining agents are admixtures used in order to intentionally increase the air content of

concrete. There are two primary ways of air entraining concrete. ASTM C233 is the Standard

Specification for Entraining-Air Admixtures for Concrete which tests air entraining admixtures

in order to check that the admixture meets the appropriate uniformity and performance

requirements.

Air entraining admixtures are either derived from by-products of various industries such as pulp,

petroleum, animal processing, or through synthetic means. Regardless of the origin, these

admixtures are often categorized as surfactants. Surfactants are chemicals in which their

molecules are easily adsorbed. The primary nature of these molecules is that they are hydrophilic

at one end and are attracted to water while the other end is hydrophobic and repels water. When

used correctly, these molecules rearrange themselves in a manner which allows the hydrophilic

end to get attached to the water molecules and the hydrophobic end to air (Whiting & Nagi,

1998).

By-products of various resins and solvents from pine are used as air entraining agents. These

solvents are neutralized with sodium hydroxide in order to convert them into a soluble compound

and enable the admixture to form a film layer around the air bubble once it is mixed. They are

often categorized under the trade name Neutralized Vinsol resin, “originally marketed as V-insol,

shorthand for „very insoluble‟, and later were trademarked as Vinsol resin” (Whiting & Nagi,

1998). This type of resin is composed of a number of compounds, the majority of which are

phenolic compounds mixed with waxes and resin acids. Wood derived based admixtures are able

to quickly generate midsized air bubble when compared to other types of admixtures and result

in very little air gain with continuous mixing. Prolonged mixing, however, decreases the volume

of entrained air (Whiting & Nagi, 1998).

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Synthetic detergents used as admixtures are derived from the byproducts of industrial processes.

These compounds are modified to reduce any water solubility so that the primary sulfonate

compound would remain. Synthetic detergents produce air quickly and most often larger sized

air bubbles are generated compared to wood-derived detergents (Whiting & Nagi, 1998; Ansari,

Zhang, Szary, & Maher, 2002).

2.3.2 Measuring Fresh Air Content

There are a number of standardized methods for measuring the fresh air content of concrete. It is

worth noting that a representative sample of concrete should be used in order to do determine the

air content. ASTM C172 Standard Practice for Sampling Fresh Mixed Concrete, as well as ACI

301 offers some guidelines regarding this matter.

The testing techniques used to measure the air content of fresh concrete were developed in the

1950s while many of the testing practices have been standardized over the years (Whiting &

Nagi, 1998). There are a number of ways to determine the fresh air content of concrete and such

methods include the Gravimetric method, pressure method and volumetric method. The pressure

method was used for the purposes of this research. The ASTM C231 Standard Test Method for

Air Content of Freshly Mixed Concrete by the Pressure Method was used as a guidline and the

principles behind this test are discussed next.

The Pressure method relies on the assumption that air is the only component in concrete which

can be compressed and Boyle‟s law is used to calculate the volume of air based on the applied

pressure. There are two types of equipment which can be used for the pressure method test: Type

A or Type B meters. A Type B meter was used for this research. In this test, concrete is placed

and consolidated in a standardized container. A cap is placed on top of the container and water

added into the meter to remove fill any remaining voids after which the valves are closed and the

entire sample is then pressurized. Once the valve is opened, the air inside the concrete moves out

of the chamber and since it is assumed that air is the only compressible ingredient, any decrease

in pressure is assumed to be proportional to the air contained in the sample. The advantage of

this meter is the lack of influence from atmospheric pressure but calibration issues and issues

with the pressure gauge may pose some problems and decrease the accuracy of the

measurements (Powers , 1968). For accurate air result readings, the aggregate correction factor

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also needs to be determined in order to discount the bias in results caused by the porous nature of

some aggregates.

2.4 Methods for Measuring Air Content in Hardened Concrete

It is important to mention that a minimum level of air entrainment is required in order to protect

the concrete against freeze-thaw damage. The air-void system in concrete is determined by

obtaining concrete samples and examining them in accordance with ASTM C457, Standard Test

for Determination of Parameters of the Air-Void System in Hardened Concrete. In order for

concrete to be durable under freezing conditions, a minimum level of air entrainment, which is

the total volume of air in concrete as well as the maximum spacing factor, which is the maximum

distance water needs to travel before it gets to an air void must be achieved. These two

parameters are very important for the performance and durability of concrete since they ensure

that the volume of entrained air is sufficient and the bubbles are uniformly distributed in the

system. Both ACI (C201, C301) and CSA A23.1 have developed charts specifying the minimum

volume of air and maximum spacing factor required for a variety of aggregate sizes in different

exposure conditions. For most concrete structures in cold climates, a maximum spacing factor of

0.2mm (0.008 inches), specific surface area greater than 24mm2/mm

3 and around 6% volume of

air is often specified (Whiting & Nagi, 1998) (American Concrete Institute C301, 2010). The

Canadian Standards Association recommends a less conservative maximum spacing factor of

0.023mm (0.009 inches) (Canadian Standards Association, 2009).

Once the concrete has hardened it is beneficial to analyze the air-void parameters in order to

ensure adequate distribution and volume of entrained air. Air bubbles in hardened concrete are a

three dimensional entity having a finite volume but in order to determine the air content of any

given sample, the surface of the concrete is most often analyzed two dimensionally due to

various technical issues regarding three dimensional analysis and this analysis is used to estimate

the three dimensional air parameters

There are a number of techniques available to analyze the air content of hardened concrete.

ASTM C457 and EU 480 are two standards which outline the proper procedures of going about

this process.

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ASTM C457 outlines the procedures required for the determination of the air content in hardened

concrete using a microscope and the air content, spacing factor, void frequency and specific

surface area of a concrete sample can be measured using this standard. This analysis is conducted

by either using the linear- traverse method (method A) or modified point count method (method

B) in order to calculate the air parameters in hardened concrete.

Regardless of method used to analyze the concrete sample, all specimens must be prepared in

accordance to ASTM C856 Standard Practice of Petrographic Analysis of Concrete and ASTM

C457. The standard also specifies the minimum area required for a complete analysis and this

area is dependent on the maximum nominal aggregate size. For instance, for a concrete sample

containing a 19mm nominal maximum sized aggregates, the minimum area required to be

traversed is 71 cm2. It is also stated that for performance requirement testing, three concrete

samples must be obtained over the area of the concrete surface in order to determine the air

content of concrete.

In the linear traverse method, the air content of concrete is calculated by examining the sample

under a microscope and tracing a series of envisioned parallel lines on the polished concrete

surface and measuring the chord length of the line which intersects an air void or paste. The air

content is calculated by taking into account the total length of the chords with the total length of

the traverse lines. A minimum length of traverse line is required for more accurate results and

this is dependent on the coarse aggregate size as specified in ASTM C457. For instance, when

using a 19mm maximum coarse nominal size aggregate, the minimum length of traverse should

be 2286mm. There are a series of other equations which can be used with the collected data

estimate the specific surface area and minimum spacing factor of the air voids and a version of

that information, as outlined in ASTM C457 and summarized by Simon (2005) , is shown in

Table 1.

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Table 1: ASTM C457 Air Void Parameter Equations

(Simon, 2005)

In the modified count method, a grid system is visualized on the concrete surface and the

encountered phase of the material observed under the microscope‟s cross hairs is determined at

regularly spaced intervals. Counters are used to track the number of instances where the

crosshair lands on an aggregate, paste or air. The air content is calculated based on the ratio of air

void counter and paste counter and other parameters such as spacing factor, specific surface area

and void frequency can be calculated using the equations provided in ASTM C457. Once again,

the minimum traverse length and number of stops required to estimate the air content within

certain accuracy is dependent on the size of the coarse aggregate. For instance, when analyzing a

sample with a 19mm maximum coarse aggregate nominal size, a traverse line of 2286mm with

1350 counter points are required by ASTM C457.

One of the biggest disadvantages of ASTM C457 is the time consuming nature of the test. In

fact, the analysis of each sample takes about 5 to 7 hours. In addition to this, operator experience

and error in distinguishing each phase makes a significant difference. Another problem with this

process is the low repeatability and accuracy between several test runs (Simon, 2005).

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For these reasons, automated test methods for performing this test are very beneficial both in

terms of efficiency as well as reducing the potential of user error. Various automated techniques

have been presented by a number of researchers (Chatterji and Gudmundsson 1977; Pleau ,

Pigeon and Laurencot 2001; Pade , Jacobsen and Elsen 2002; Peterson 2002) and some of the

existing standards have adopted the newer automated techniques including EN 480. With these

automated techniques, the polishing process remains similar to that as before; however, a

computer is used to run the final analysis. Different forms of hardware from cameras connected

to microscopes, scanning electron microscopes, to flatbed scanners can be used to obtain an

image of the sample and perform the necessary analysis by computer. The primary objective of

doing so is to reduce the amount of time required to perform the analysis while minimizing

human error.

A new technique was developed at Michigan Technical University for analyzing air voids in

hardened concrete using a flatbed scanner (Peterson 2002; Carlson , Sutter, Peterson and Van

Dam 2005). In this system, a scanner is used to scan a polished concrete sample with the contrast

between its voids and paste enhanced, and a computer software script is used to analyze the

image and output the air void parameters. More specifically, the sample is scanned at a

resolution of about 3175dpi in 24bit colour RGB in order to detect an air void larger than 8µm.

The sample is polished and initially scanned in its natural form without any contrast

enhancement. Then, the sample is sprayed with a phenolphthalein indicator in order to enhance

the contrast between the paste and coarse aggregate and scanned once again. Finally, the sample

is coloured black, the voids filled with white powder and the porous coarse aggregates or any

cracks are re-blackened. The sample is scanned once more but this time in gray scale. The

images are then aligned in order to distinguish each phase more easily and computer software is

used to analyze the surface and output the air content of the sample. The software works by

removing strips of the black and white image much like traverse lines and analyzes the pixels in

the image strip. Each pixel in this gray scale image has a value between 0 to 255 assigned to it to

represent its colour and shade of gray with 0 representing absolute white and 255 absolute black.

The pixels are assigned a numerical value based on the colour contrast between the two phases in

order to categorize it as paste or void. These data are analyzed in the computer and the air

parameters are calculated based on modified point count analysis techniques.

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Use of automated methods is an efficient and cost effective way of analyzing the air content of

concrete. Such techniques enable researchers to obtain more information about the physical

properties of hardened concrete samples.

2.5 Concrete Placement and Finishing

Given that a major aspect of this research has to do with different finishing techniques, it is

essential to have a basic understanding of concrete placement and finishing procedures. The

purpose of this section is to provide a very brief view on placement and finishing techniques

used for concrete floor slabs and surfaces in accordance to ACI 302.1R Construction of Floor

Slabs and ACI 301 Guide to Structural Concrete. It should be noted that there are a number of

ways to finish concrete surfaces; however, only a brief and basic background is provided here for

finishing concrete slabs.

Concrete placement is a vital part of any construction job and proper placement of concrete

greatly influences the durability of the structure. In most cases, formwork or molds are set up in

order to hold the concrete in its fresh state until it gains enough strength and hardens (Fine

Homebuilding, 2003).

Once the concrete is placed, it should be consolidated in order to ensure the entire form is filled

with concrete and also to remove any large entrapped air voids. This is often done by vibrating

the concrete (either internally or externally) or through rodding (for smaller samples cast in the

laboratory). Vibration enables the concrete to behave as a liquid so that it would flow easier. As

a result, any large entrapped air voids are forced to the surface and the internal forces in the

concrete are restored as soon as vibration stops. Care must be taken not to over vibrate the

concrete since it may result in a depletion of entrained air voids.

The type of finishing procedure required for concrete surfaces depends on the desired surface

requirements. Anything from level of flatness to the desired final texture determines the number

and type of finishing procedures. Regardless of the type of finished specified, there is only a

relatively short window in which the concrete should be finished after placement and this time

frame is referred to as the “window of finishability”. It is important not to start the finishing

procedure too early, since closing the concrete surface before the end of bleeding may reduce the

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durability of the surface and cause surface defects. Equally important, if finishing is delayed,

concrete would harden and the possibility of flattening or adding the desire texture is diminished.

2.5.1 Screeding

Once the concrete is consolidated in place, it is time to screed the top surface in order to remove

any excess concrete and to level the top surface. In small concrete pours such as sidewalks, the

edges of the formwork can be used as a guide for screeding the concrete surface. This is often

accomplished by dragging a 2x4” wooden board across the surface in a saw cut motion. For

larger pours such as concrete slabs, chalk lines and screed lines must be set up near the perimeter

and used afterwards as a guide to in order to level the concrete (Fine Homebuilding, 2003). In

such cases, a screed rail may be used to level the surface. Screeding is often at minimum a two to

three person job with two workers working the screed rail back and forth in a saw cut motion

while ensuring that there are no low spots on the surface and a third person removes excess

concrete that accumulates in front of the screed rail once the screeding process is completed.

2.5.2 Floating

Floating refers to the process of compacting the surface of concrete without closing the surface

pores in order to prepare the surface for subsequent finishing procedures while letting the

concrete bleed naturally. Bull floats are often used right after screeding and such floats are often

made up of wood or magnesium. Magnesium floats are recommended for concrete mixtures that

are more “sticky”. After the evaporation of bleed water, additional floating can be performed to

prepare the sample for final troweling steps. Although no exact time can be specified for

predicting the evaporation of bleed water, it is usually identified as the time when the water

sheen disappears on the surface and the concrete has started to stiffen and can withstand the

weight of a person with minor indentation onto the surface. Power floats are sometimes used as

well to remove slight bumps or voids on the surface and further consolidate the surface of the

concrete by using an engine which either revolves a disk or float shoes (American Concrete

Institute C301, 2010).

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2.5.3 Troweling

For the final stages of finishing, trowels are sometimes used to further harden and densify the

surface and to provide a much smoother trowel-finished. Adequate lag time between floating and

the start of troweling is needed to ensure that the bleed water has evaporated from the surface

and concrete has started to stiffen. Extensive troweling passes will result in a concrete surface

that looks highly polished and shines but could become slippery when wet. Air entrained

concrete containing more than 3% air should not be hard troweled since the action of troweling

may decrease the air at the near the surface. Concrete is often specified to be hard enough to

sustain foot pressure with a maximum indentation of 6mm before it can be troweled (American

Concrete Institute C302, 2004). In most cases larger trowels are used in the beginning of the

trowelling operation and smaller trowels are used for subsequent passes. Power trowels are also

available much like power floats and they operate in a similar manner. If the surface is specified

to be hand troweled then each successive trowel pass should use a smaller trowel or the angle at

which the trowel is being used should be increased in order to apply the necessary pressure for

an acceptable final finish. Troweling will compact the surface of the concrete and a decrease in

w/cm ratio at the surface is seen due to the fact that the troweling action will increase the

evaporation of water from the paste since the top surface is being move around. Excessive

troweling, however, could lead to colour variations on the surface and early or improper

troweling techniques may cause surface defects.

Regardless of finishing techniques specified, it is important to follow the correct finishing

procedures in order to avoid problems in the near surface zone. Premature finishing should be

avoided since it may lead to surface defects and the addition of water on the concrete surface

during in order to make the finishing procedures easier could also decrease the durability of the

surface as a result of addition of water in the surface zone. Adequate moisture and curing

practices also need to be followed to ensure high quality surface zone and is discussed next.

2.5.4 Curing

Curing refers to any practice that helps maintain saturation and temperature at the surface of the

concrete. By doing so, there is enough moisture available for the hydration of cement particles in

the near the surface (American Concrete Institute C302, 2004). This process can be achieved in

various ways depending on the type and nature of the concrete structure. Wet curing, wet

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covering, or various moisture retaining techniques can be employed in addition of using curing

admixtures to control the loss of moisture in the surface zone. Proper curing can be achieved by

misting or covering the surface of concrete with a wet membrane to protect the surface against

moisture loss. This process often involves using saturated burlap to cover the surface right after

finishing. Moisture retaining techniques are also used and involve covering the surface of the

concrete with plastic sheets. Curing compounds are also available on the market and can be

sprayed over the surface of finished concrete to protect and ensure adequate curing without

continuous monitoring of the surface. Liquid membrane curing compounds are most widely used

due to their low cost and ease of application.

Regardless of the curing technique used, adequate curing is necessary in cases where the weather

conditions are unfavorable and high water loss from the surface of concrete is expected. For this

reason, after the concrete has been finished, the surface must be protected from ambient

conditions and any delay or lack of protection may lead to such issues as crazing, dusting, loss of

strength in the cover zone, and plastic-shrinkage cracks. Such issues not only affect the aesthetic

look of concrete, they can also decrease the life of the structure.

2.6 Related Studies

The importance of the concrete surface has been noted by a number of researchers and this

surface region has even been referred to as “Achilles heel of concrete” (Dewar, 1985). It is

therefore very important to understand the nature of concrete cover and how it affects the

performance of the structure since the durability of concrete is dependent on the concrete cover.

As previously mentioned, this topic has been researched in a number of studies several of which

are discussed in this section. The focus of this section is to provide a brief summary of the type

and scope of research already present in this area, as well as shed some light on factors that are

worth considering for this particular study.

Some work has been done to distinguish and categorize the near surface zone of concrete. The

area described as concrete cover can be divided into three different layers. The first and top most

layer from the surface is known as cement skin. This layer is about 0.1mm thick. The next layer

below the cement skin is referred to as mortar skin and it is about 5mm thick. The last layer is

called concrete skin and it is about 30mm thick (Kreijer, 1984). These layers are affected by

many factors and the composition of each layer is a result of various phenomena such as

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segregation, wall effects, bleeding and evaporation of water. Aggregate size, casting and

compaction procedures, and type of concrete finish may have an effect on the depth and quality

of each zone. Proper curing is one of the most important and most neglected areas when it comes

to covercrete due to the bleeding of concrete and the exposure of the surface with the elements

(Ho & Lewis, 1984). Each of these factors will affect the physical properties of the covercrete.

The rate of absorption and depth of penetration are two major issues when looking at the

deterioration of concrete. This is due to the fact that harmful fluids and ions such as chlorides

from de-icer salts are absorbed in the cover zone and once the chloride threshold surpasses the

limit of the rebar, potential of rebar deterioration is very high (Tutti, 1982).

As a result of the issues mentioned above, the skin of concrete may have different properties

when compared to the bulk of concrete in the structure. For instance, as a result of segregation

and bleeding, the w/cm ratio of the concrete skin may be higher than the rest of the concrete

structure which is problematic given that this layer is the first line of defense against many issues

the concrete structure will face. In some instances, cement hydration is limited at the surface due

to lack of adequate curing and as a result the porosity of concrete in this area is higher (Parrott,

1992). Figure 1 shows an idealized profile of the sorptivity and permeability of a concrete

sample at various depths (Lampacher & Blight, 1998). A similar porosity gradient has been

presented by other researchers with the porosity at the surface at close to 20% while the porosity

of the heartcrete was close 6% (Basheer & Nolan, 2001).

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(Lampacher & Blight, 1998)

Figure 1: Idealized Depiction of Concrete Surface Properties

On a related note, one study found that a 17% decrease in modulus of elasticity and about a 20%

increase in sorptivity was exhibited when comparing concrete at the surface with the inner

“heartcrete” (Kreijer, 1984). Such a difference will have negative consequences if not taken into

account when it comes to the life of the structure.

Another relevant study looked at the effect of supplementary cementing materials and finishing

techniques on sorptivity of concrete (Tumidajski, 2006). In this test, slabs were cast on site using

commercial techniques. Some slabs were floated and others were troweled finished using a steel

trowel. Slabs were left outside, exposed to the elements and traffic for a period of one year.

Cores were extracted from the slabs, the cores were left to air dry in the laboratory for one day

and the rate of absorption of the samples was determined by placing the top finished surface in

water. Samples were not conditioned since the researchers were interested in simulating in-situ

like conditions. Much like previous studies, it was found that as the degree of saturation of the

cement matrix increases, the capillary suction potential decreases. More importantly, it was

observed that when 8% silica fume or 40% GGBFS was used in a concrete mixture, a decrease of

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20 to 30% was observed in the sorptivity results. It was also found that the surfaces which were

only hand floated and not troweled had a 9% decrease in sorptivity compared to that of trowelled

surfaces. A 14% decrease was seen in sorptivity results of the concrete surfaces formed in steel

formwork compared to that of trowelled finish surfaces (Tumidajski, 2006). Given that the cores

were likely at different levels of saturation, as a result of the coring process, the sorptivity values

reported may be biased due to the moisture contents of the tested specimens.

Variations in sorptivity of concrete with depth from an exposed surface have also been tested by

researchers (Parrott, 1992). Studies using mortar bars showed that the average water sorptivity

of the surface zone down to about 20mm below the surface is greater than in the rest of the

concrete. This deviation was attributed to changes in transport properties as a result of the drying

near the surface zone, resulting in limited cement hydration. An increase in porosity at a

moulded surface was also observed and attributed to wall effects and aggregate particle packing.

Additionally, carbonation was found to decrease the sorptivity of mortars with portland cement

due to the densification of the surface zone but led to an increase in the surface porosity of

mortar samples where granulated blast furnace slag was partially substituted. In the same study,

carbonation depths were found to be less than 30mm after 4 years of normal environmental

exposure. A sharp reduction in sorptivity was observed at a depth of around 20mm under the

surface followed by a gradual plateau after this depth (Parrott, 1992).

Other studies examined the effect of suction surface on the sorptivity results. It has been

observed that with concrete cylinders cast in steel moulds, the upper trowel-finished section has

higher sorptivity values compared to the bottom form-finished section (McCarter, 1993). This

study shows the importance of surface face on sorptivity values. One point worth mentioning

with regard to these results is that samples were conditioned naturally in the lab setting with no

additional conditioning regime.

This work also included abrasion resistance testing of concrete with different trowel-finished to

test the properties of the surface and coverzone. In one study, cores were extracted from concrete

samples where 20mm coarse aggregate was used and each core was cut into smaller slices. Hand

finishing and power finishing techniques were used as the primary finishing methods and the

abrasion resistance and hardness of the samples was tested. It was observed that hand finishing

produces a harder finish but regardless of the finishing technique used, almost no changes in

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sorptivity were observed after 20mm from the surface. No trends were found in terms of

hardness of the hand finished samples at various depths. Similarly, no strong correlation was

seen in the hardness of samples which were power floated at various depths but it is worth noting

that the deviation of results was lower with the power float compared to the hand finish. More

studies have been conducted in this area, relating the abrasion resistance of the surface with

sorptivity of the surface (Dhir, Hewlett, & Chan, 1991), however, proper conditioning regimes

were not used and samples were oven dried at 105 degrees Celsius, causing micro cracks in the

paste.

In another study, it was attempted to categorize the quality of the covercrete by testing the

sorptivity and abrasion resistance of the surface (Senbetta, 1981). Mortar and paste samples were

tested in order to find a way to categorize and comment on the quality of curing procedures used.

A number of test methods were used and it was found that sorptivity and abrasion resistance

were the two best indicators of the quality of the mortar as these two tests are reproducible and

sensitive enough in terms of precision and accuracy. For this reason, the categorization between

adequate and inadequate curing was made based on the results of sorptivity tests since the results

would reflect deviations in the pore structure at the surface. In this study it was found that if the

difference in initial sorptivity values at a depth of 10mm and 60mm under the surface was

greater than 5.5x10-6

cm2/sec, the mortar samples were poorly cured. One issue in this study was

that the top 10mm surface region of all samples were ignored because of bleeding of concrete

and subsequent changes caused by the resulting formation of water channels. Much like other

studies, a decrease in sorptivity was observed at different depths and the changes were much

more gradual beyond 10mm from the surface with almost no changes at 20mm or more. The

difference in sorptivity of the samples covered with wet burlap and plastic at different depths

was not as significant (Senbetta, 1981).

Another study on the effect of bleeding and compaction in the near surface zone found that there

exists a zone of maximum compaction with the lowest water content near the bottom of the

concrete slab due to bleeding. This is followed by a transition zone of variable water content

above this zone and a zone of constant water content after that (Powers, 1939).

McCarter (1996) studied the movement of water and ionic fluids in the cover zone and this was

accomplished in one study by embedding conductivity probes within the surface of concrete

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slabs. It was observed that the ingress of water and ionic fluids into the covercrete increases the

conductivity of the concrete at the surface compared to the past cover zone. A difference of

300% was observed in some cases between the surface and at depth although the change in

conductivity from the surface to beyond the covercrete was not linear. The conductivity values

were observed to be high at the surface and down to 30mm under the surface of the concrete.

The difference between the two zones can be explained by the fact the concrete at the surface

zone was saturated as a result of the advancing fluid front and this saturated zone diminished at

around 30mm under the surface. In terms of the accuracy and spread of conductivity results, it

was also observed that near surface conductivity values were within 10% of the mean whereas

this spread increased to about 20% of the mean at a depth of 30-50mm below the surface. The

increase in the range of results at the deeper region was caused by the uneven penetration depth

of the advancing fluid front (McCarter, 1996). The use of supplementary cementing materials

such as slag caused a decrease in conductivity values associated with the infilling of pores due to

the pozzolanic nature of the materials and also the increase in chemical binding of chloride ions.

On a similar note, other researchers have pointed out that the penetration and binding of

chlorides in concrete may alter the pore size distribution of the cement paste possibly due to the

constriction of pores given that the concentration of chloride ions correlated with the size of the

pores (Chidiac, Panesar, & Zibara, 2012).

There are a number of tests available in order to test the in-situ permeability of the concrete

cover. A majority of these practices however are dependent on various factors and therefore have

serious limitations. Examples of such techniques include: Initial surface absorption test (ISAT

test), TORRENT permeability tester, Figg method test, Covercrete absorption test (CAT), Air

permeability of near surface test (APNS), and the CLAM water permeability test. An important

shortcoming of these tests is the variability of the results which are dependent on the moisture

content of the in-situ concrete, making it difficult to compare the results of this test between two

structures (Wilson, Taylor, & Hoff, 1998); (Kucharczyková, Misák, & Vymazal, 2010). An

additional problem with some of these techniques is their intrusive nature where, in some cases,

a hole has to be drilled onto the concrete surface. A further issue with some of these techniques

is that the effect of the cement and mortar skin layers are also ignored given that the test

measures the sorptivity of the concrete inside a hole a few millimeters under the surface

(DeSouza, 1996).

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The finishing method used is not the only parameter which affects surface characteristics. In one

study it was also found that the type and amount of form release agent used in the formwork will

affect the impermeability and sorptivity of the concrete surface (Samuelsson, 1970). For this

particular study, several form release agents were tested and although no clear correlation was

found on which type of release agent performs the best, it was observed that the formed surface

became more impermeable as the amount of release agent applied to the surface increased. For

the limited set of samples tested, increasing the amount of release agent at the surface led to an

increased void formation on the surface of the concrete (Samuelsson, 1970). The permeability of

the formwork is also believed to affect the properties of the covercrete and its overall

performance against the ingress of fluids into the surface (Price & Widdows, 1991).

The goal of this study is to evaluate the effect of finish on the sorptivity of concrete and how the

paste and aggregates are positioned throughout the cover. In many of the studies mentioned in

this section, the influence of the surface zone on the sorptivity or hardness of the concrete

diminished at around 20mm under the surface even when 20mm nominal coarse aggregates were

used. As a result of these findings, the samples in this study were only examined up to this depth.

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Chapter 3 Experimental Procedures

3 Background

This chapter outlines the types of material, concrete mixtures and testing procedures used in this

study in order to perform the desired tests. The physical and chemical properties of the

cementitious materials and some of the admixtures as well as the sieve analyses for both fine and

coarse aggregates can be found in Appendix A.

3.1 Materials

3.1.1 Cementitious and Supplementary Cementing Materials

Two types of cement were used in this project. A CSA A3000 General Use (GU) Portland

cement and a blended cement with 8% silica fume (GUb). In addition to this, ground granulated

blast furnace slag (GGBFS) was also used in all mixtures. All three materials were supplied by

Holcim from their Mississauga cement plant in Ontario.

3.1.2 Fine Aggregate

Natural sand was used as the fine aggregate in this study. The fine aggregate was obtained from

Sunderland Pit and was supplied by St. Mary‟s Cement Group, Canadian Building Materials

division (St. Mary‟s CBM) plant at Scarborough, Ontario. The fine aggregate‟s relative density

was 2680 kg/m3 and the absorption was 0.69%.

3.1.3 Coarse Aggregate

Nineteen millimetre crushed dolomitic limestone coarse aggregate was used for all the concrete

mixtures batched in this study. The coarse aggregate was from Dufferin Aggregates‟ Milton

quarry and was supplied by Holcim Canada. All of the coarse aggregates used were from the

same stockpile and one delivery. The coarse aggregate‟s relative density was 2700 kg/m3 and its

absorption was 1.42%.

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3.1.4 Chemical Admixtures

A number of chemical admixtures were used in this study in order to modify the properties of the

concrete mixtures. Mid-range and high range water reducing admixtures were used to increase

the workability of the concrete mixtures and air-entraining admixtures were also used. Glenium

7700 superplasticizer, PolyHeed 1725 Mid-range water reducing admixture, and MicroAir air

entraining agent were the three primary chemical admixture used for this project. All three

admixtures were supplied by BASF chemical group. An additional neutralized Vinsol resin air-

entraining admixture was also used for one of the concrete mixtures. For uniformity purposes, all

admixtures were carefully agitated before use.

For one of the concrete mixtures, red liquid pigment intended for concrete was added in order to

colour the concrete red. Red pigment was added to this mixture in order to make the distinction

between paste and aggregates easier for calculating the aggregate fraction and paste content.

Chameleon Liquid Red A1070 liquid pigment (color index number 77491) was used and this

product was supplied from Davis Colors (See appendix A for chemical composition).

3.2 Concrete Mixture Design

A number of concrete mixtures were designed and cast for this study in order to evaluate the

effect of different surface finish on concrete properties. Nine concrete mixtures were designed

ranging in cement, water, and air content. All mixes were cast in the laboratory. The concrete

mixtures were designed to meet a number of CSA A23.1 class exposures for concretes structures

exposed to various conditions. For this reason, concrete mixtures ranging from 0.55 to 0.38 w/cm

were made with cement contents ranging from 290 to 420 kg/m3. The target volume of entrained

air for the concrete mixtures was categorized into three groups ranging from no air entrainment

(1+2%), mid-range air entrainment (4+2%), and high air entrainment (6+2%).

The target slump for the concrete mixtures in this study was 120+20mm but a few of concrete

mixtures were designed to either have a higher slump of about 150mm and others a low slump

of about 70mm in order to evaluate the effect of segregation. Twenty five percent of the

cementitious content was replaced with granulated ground blast furnace slag (GGBFS) in all

mixtures. This replacement level was chosen since it was allowed by the Ontario Ministry of

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Transportation. The complete concrete mixture designs are provided in Appendix B and a

summary of concrete mixtures used is also provided in Table 2:

Table 2: Summary of Concrete Mixtures

Mix

ID w/cm

Fresh

Air

Content

(%)*

Slump

(mm)

Cement

Type

Cement

Content

(kg/m3)

GGBFS

Content

(kg/m3)

Water

Content

(L/m3)

Coarse

Aggregate

Content

(kg/m3)

Fine

Aggregate

Content

(kg/m3)

Air

Entraining

Admixture

(mL/100kg

cement)**

Mid-Range

Water

Reducer

PolyHeed-

1725

(mL/100kg

cement)

Super

plasticizer

Glenium

7700

(mL/100kg

cement)

Mix 1 0.55 5.2 90 GU 218 73 160 1060 723 62 0 0

Mix 5 0.45 2.0 120 GU 316 105 189 1060 607 0 293 0

Mix 6 0.45 3.5 10 GU 316 105 189 1060 556 20 0 0

Mix 2 0.45 5.6 160 GU 316 105 189 1060 555 42 210 0

Mix

2RED

***

0.45 6.4 110 GU 316 105 189 1060 555 42 195 0

Mix 7 0.45 7.0 150 GU 316 105 189 1060 448 80 199 0

Mix 8 0.45 8.0 175 GU 316 105 189 1060 448 133 ** 173 0

Mix 3 0.38 5.5 65 GU 316 105 160 1060 579 73 400 730

Mix 4 0.38 8.0 80 HSF 316 105 160 1060 507 220 350 390

*Fresh Air Content not adjusted for Aggregate correction factor

** Vinsol resin used as Air-Entraining Admixture in Mix 8; MicroAir was used in all other mixtures

***Red Liquid Pigment dosage: 60mL/100kg cement

3.2.1 Mix Proportioning

Concrete mixtures were designed and proportioned using the volumetric method. Trial batches

were cast for some of the concrete mixtures in order to determine the necessary dosage of

chemical admixtures needed to achieve the desired properties. As mentioned previously, the

complete concrete mixture designs are provided in Appendix B. It is important to mention that

the air-entraining admixture as well as the mid-range water reducer were accounted for as part of

the total volume of concrete but were not added to the water content for calculating the w/cm.

For this reason, the w/cm values reported in Table 1, the values are calculated based on the

amount of cementitious material and water content. Equally important, the superplasticizer and

red liquid pigment used for some of the mixtures were not included in the mix design volume

calculations or the w/cm and were treated as separate entities.

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3.2.2 Casting Procedures

One day prior to casting concrete, the required materials were batched and prepared. To do so,

coarse aggregate was taken out of the bin and placed in perforated buckets and thoroughly

washed in order to remove any dust and debris from the surface. Afterwards the aggregates were

left to drain in the perforated buckets for about five hours in order for the excess water to drain

out. Next, the aggregate was placed in sealed plastic buckets to protect against moisture changes

and contamination. The fine aggregate was placed directly from the bin into sealed plastic

buckets. One point worth mentioning is that the top surface of the fine aggregate in the bin was

found to be much drier compared to the particles a few centimetres below the surface. For this

reason, the fine aggregate in the bin was mixed thoroughly in order to collect aggregate of

uniform moisture content before placing the material in the sealed buckets.

For both types of aggregates, moisture content of the material had to be calculated in order to

adjust the water and amount of aggregates in the batch to the correct proportions outlined in the

mixture design. Therefore, prior to placing the aggregates into sealed buckets, a small sample of

each was collected and placed in an oven at 110 degrees Celsius. In most cases, about 3kg of

coarse aggregate and 2kg of fine aggregate was collected and placed in the oven overnight. The

moisture content was determined in accordance to ASTM C566, Standard Test Method for Total

Evaporable Moisture Content of Aggregate by Drying, and the concrete mixture proportions

were adjusted in order to obtain the desired design. Cement and supplementary cementing

materials were also weighed and placed in sealed plastic container one day prior to mixing in

order to ensure everything was ready for the next day of casting. All materials were stored in the

laboratory setting at room temperature.

The next day, the aggregate pans were taken out of the oven and cooled to room temperature

before measuring the change in mass and to determine the moisture content of the two

aggregates. Meanwhile, 100x200mm plastic cylinder moulds as well as 200x300x90mm

plywood moulds used for the casting of cylinders and slabs were lubricated. Next, once the

moisture content of the aggregates was determined, the concrete mixture proportions were

adjusted and the exact amount of aggregate and water required was determined and batched.

Water was divided into two containers so that the chemical admixtures could be mixed with the

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initial water. The required doses of chemical admixtures were also measured prior to starting the

mixer.

The concrete mixer used for this study has a capacity of about 70L and a rotation paddle speed of

119 rotations per minute. Prior to the commencement of each mix, the mixing pan as well as the

paddles were moistened with a wet rag to minimize any moisture loss from the concrete mixture.

It should be noted that a “butter mix” using the same mixture design proportioning to lubricate

the pan would have been more ideal but was not followed in this project.

Before starting the mixer, coarse aggregate and about half of the fine aggregate was placed inside

the mixer. The mixer was then started and air entraining admixture was mixed with one of the

two water containers and added into the mixer. The mixer was then started. After about 30

seconds, the cementitious, fine aggregate, and the rest of the water with the mid-range water

reducer mixed into it were slowly added into the mixer in small portions until everything was

added in. Once all of the materials were in the mixer, the concrete was mixed for three minutes

followed by a three minute rest and a final two minutes of mixing at the end in accordance with

ASTM C109, Standard Practice for Making and Curing Concrete Test Specimens in the

Laboratory. In some cases, superplacticizer was also added into the mixer. Most often,

superplasticizer was drizzled over the concrete mixture in 10mL increments either in the first two

minutes of mixing or the first minute of remixing.

After the first eight minutes of mixing, slump and air content (using pressure method) were

measured. If the fresh concrete mixture achieved the targeted properties, placement of concrete

into the moulds would begin. If the air or slump did not reach the desired target level, the

concrete was remixed and additional chemical admixtures were added into the mixer. In most

cases, concrete mixtures were remixed for an additional two minutes after which both the slump

and air were measured once more.

The slump test was carried out in accordance with ASTM C143, Standard Test Method for

Slump of Hydraulic-Cement Concrete as a measure of the consistency of fresh concrete and to

provide a basis for the workability of the concrete mixture. Air content was measured using the

pressure meter (method B) in accordance with ASTM C231 Standard Test Method for Air

Content of Freshly Mixed Concrete by the Pressure Method. If the air content and slump met the

target requirements, the placement of concrete into the moulds followed.

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Fresh concrete was then placed into the 100x200 mm plastic cylinder moulds and the

200x300x90 mm plywood slab moulds. Four concrete slabs and over twelve cylinders were

placed for each mixture. The cylinder moulds were filled in three layers and each layer was

rodded 25 times and the sides of the cylinders were tapped to get rid of any large entrapped air

voids in accordance to ASTM C192 Standard Practice for Making and curing Concrete Test

Specimens in the Laboratory. The top of the cylinders were levelled using a metal rod in a

sawing action to level the top surface and plastic lids were placed on top of the cylinder to

minimize moisture loss.

Concrete slabs were filled in one layer and each slab was rodded 72 times. Afterwards, the sides

of the moulds were lightly tapped using a mallet to get rid of any large entrapped air voids and a

wooden float was used to screed the top surface of the concrete by levelling the surface in a

sawing action. In most cases, a pass in each direction was made in order to achieve a relatively

level surface. It should be mentioned that in some cases, the trowel-finished surface was not

perfect due to imperfections in the moulds especially when the sides of the moulds did not

perfectly match on another. Part of this difficulty was due to the size of the finishing tools with

respect to the moulds and the fact that the wooden screeder and magnesium float used for

finishing the slabs were approximately 300mm in length and the size of the moulds were

200x300mm. For this reason, when screeding the surface in the lengthwise direction, the screed

could not be rested on the edges of the moulds easily because of its small size. In addition to this,

when floating the surface at the end of the finishing process, it was found that the magnesium

float was too large for the size of the moulds used and a smooth and uniform floating motion on

the top surface was difficult to achieve with this type of float. In such cases, the slabs were

finished as best as possible but in most cases, the texture of the surface at the corners was more

distinct as a result.

Afterwards, the slabs were covered with wet burlap but care was taken to ensure that the burlap

did not touch the surface of the concrete slab and altered the texture or water content on top. This

was done in order to ensure that the surface did not dry too quickly and to provide enough

moisture around the slab.

Subsequently, the slabs were monitored for the next several hours to check the bleeding rate

while observing for signs of initial setting. Once the water sheen on top of the concrete surface

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started to disappear and the concrete had gained enough strength to resist the force of a thumb

being pressed into it, the final finishing procedures were done.

ASTM C232, Standard Test Method for Bleeding of Concrete was followed as a guideline in

order to determine the rate of bleeding. Fresh concrete was sieved using a 3.75mm sized sieve

and was placed in a 150x150mm cylinder. A piece of plexi-glass was placed on top of the

cylinder to minimize moisture loss from the top surface. After about one hour from the initial

contact between water and cement, the cylinder was placed on a 35 degree angle for ten minutes

and the water on top of the surface was collected using a syringe and weighed. This was done

every half an hour until noticeable decrease in amount of bleeding water was observed in which

point it was believed that the concrete was near initial set. Originally a penetration resistance

probe was to be used in accordance to ASTM C403, Standard Practice for Time of Setting of

Concrete Mixtures by Penetration Resistance to determine the time of initial and final set,

however, due to equipment malfunction and calibration issues this test method was not

successfully implemented. This test requires a series of probes decreasing in size to be pushed

into a mortar sample and the pressure required to push the probes is measured. Probes are

pressed into the mortar and when the pressure has reached 3.5MPa (500psi), it is considered that

the mortar has reached initial set. This test is continued until a pressure of 30MPa (4000psi) is

reached in which case the mortar has reached final set. Unfortunately, due to equipment

malfunction, even after the concrete was fully set, the device was only measuring very low

pressures and the results were therefore ignored.

A magnesium float was used for the final finish. The top surface was floated with as few passes

as possible to achieve a flat and smooth surface. This was found to be achievable with two passes

with each pass perpendicular to the last. For each pass, the float was passed over the surface with

constant pressure and in a continuous motion from one corner of the slab to the opposite corner.

All four concrete slabs were finished and the two more ideal finished slabs were considered for

testing the finished surface and the other two slabs, the form-finished side was used for the

purposes of testing.

3.2.3 Curing Procedures

Once the surface was finished, the slabs and cylinders were covered overnight with wet burlap

and plastic wraps to provide adequate curing conditions. The day after casting, the samples were

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de-moulded, labelled and placed in the moist room at 100% relative humidity and 23 degrees

Celsius for the rest of their curing regime.

Samples undergoing resistivity and RCPT (Rapid Chloride Penetration Test) were also placed in

the moist room until the day before test. The samples were then vacuum saturated for four hours

one day prior to the test to make certain that the sample was fully saturated.

3.3 Testing Hardened Concrete Properties

3.3.1 Compressive Strength

The compressive strength of 100x200mm concrete cylinders was measured in accordance with

ASTM C39, Standard Test method for Compressive Strength of Cylindrical Concrete Specimens.

For each concrete mixture, two cylinders were tested at 28 and 56 days of age.

Cylinders were ground flat at both ends using a cylinder end grinder and were tested at saturated,

surface-dry conditions in a compressive strength machine having a capacity of 2000kN. The

average of two cylinders for each concrete mixture was used to determine the compressive

strength. It should be mentioned that some of the samples were not tested at exactly 28 or 56

days of age due to delays and issues encountered in the laboratory. In such cases, the exact age of

the sample is mentioned in the results section of the next chapter.

3.3.2 Resistivity and Permeability Tests

3.3.2.1 Background

Three tests were used in order to assess the resistivity and the permeability of the concrete

samples through indirect means. The Merlin, RCON, and Rapid Chloride Permeability Test

(RCPT) were used.

Duplicate samples were tested and the average was reported. The same specimen was used for all

three test methods in order to minimize bias in the results and to allow for comparative

evaluation of the different tests. For these tests, the 100x200 mm concrete cylinders were cut in

the middle using a water-cooled 355 mm (14”) diamond blade saw and a 50mm slice was taken

from the top and bottom the middle section. The samples were then vacuum saturated one day

prior to testing.

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3.3.2.2 RCON Resistivity Test

The RCON test is a resistivity test developed by Giatec Inc. and measures the uniaxial electrical

resistivity of concrete samples. This was the fastest test compared to other techniques used in this

study and the results were obtained in a few seconds. In this test, the concrete samples were

sandwiched between two brass electrode plates and wet sponge. This setup was hooked up to a

resistivity meter. A 500 gram block was also placed on top of the plates to apply additional

pressure and ensure that full contact was made between the electrodes and the concrete sample.

A frequency of 1 kHz was applied through the sample and the electrical resistance of the sample

was output on the display of the meter.

3.3.2.3 Merlin Resistivity Test

The Merlin Test developed by Germann Instruments is another resistivity test which measures

the bulk resistivity of concrete specimen. In this test, a clamp like device is used hold the

concrete sample in between two electrodes which are hooked up to a computer. Alternating

current is applied to the saturated sample and a voltmeter and ammeter are used to measure the

voltage and current drop across the sample and the conductivity and resistivity of the sample is

then calculated by considering the size of the specimen (Germann Instruments, 2010).

3.3.2.4 ASTM C1202

The ASTM C1202, Standard Test Method for Electrical Indication of Concrete’s Ability to

Resist Chloride Ion Penetration was used for performing RCPT. After testing the resistivity

using the RCON and Merlin tests, the same specimen was used for conducting RCPT. In this

test, the sides of the concrete samples were taped using electrical tape to ensure uniaxial testing

conditions and the sample was sandwiched between two electrodes and submerged in a 3%

sodium chloride and sodium hydroxide solution on either side with a charge of 60 volts being

applied to the sample for six hours. The amount of coulombs passed through the sample is

measured and the durability of the sample is categorized based on this value. Much like the

compressive strength measurement, some of the samples were tested at a later age due to

unforeseen issues and the exact age of those samples is mentioned in the results section of the

next chapter.

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3.3.3 Rate of Absorption Test

Determining the initial rate of absorption of concrete was one of the most important tests in this

study. The ASTM C1585, Standard Test Method for Measurement of Rate of Absorption of

Water by Hydraulic Cement Concretes is a simple and inexpensive way of to measure the rate of

absorption of water in concrete. For the purposes of this study, a modified version of ASTM

C1585 was used. The major modifications were with regards to the texture of the surface, pre-

conditioning of the samples and the type of solution used as discussed next. These changes were

made in order to analyze other desired properties later on.

Duplicate samples were tested and the average of the two samples was reported. For each

concrete mixture, 18 samples were tested, 16 of which were obtained from the cores and two

additional samples were obtained from a cylinder cut in half with two 50mm slices extracted

from the top and bottom of the middle cut.

Prior to starting the absorption test, the samples had to be preconditioned in order to reach

suitable moisture content. Thus, concrete slabs were taken out of the moist room after 28 days

and four 100mm cores were extracted from each slab (see Figure 2). The cores were then cut

using a 14” water cooled diamond blade saw in order to obtain 50+3mm slices of concrete. From

each slab, four cores were extracted and each core was cut at either end in order to obtain

samples at various depths from the top surface (see Figure 3). Overall, more than 150 concrete

slices were obtained and tested.

Figure 2: Slab and Core Extraction Layout

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Figure 3: Core Slice Layout

Once the cores were cut down to the appropriate size they were immediately washed with water

and dried with compressed air in order to keep the surface clean and free of any residual paste

built-up in the pores. Concrete samples were then polished using a hand polisher. The polishing

started with a 120 grit polishing plate. Samples were polished on this plate with water until the

texture of the surface looked smooth and uniform and light was reflected off of the sample when

viewed at a low angle into the distance. Afterwards, a LapMaster polisher was used to further

polish the sample using 600 grit carbon silicate powder for about 15 minutes. This device rotates

a cast aluminum polishing plate onto which three samples were placed and polished against

using the 600 grit carbon silicate and water. Afterwards the sample was once again checked for

smoothness and later cleaned with water and high pressure air. The top portion of the polished

surface was then submerged in water and placed in an ultrasonic bath for five minutes in order to

ensure that none of the fine carbon silicate powder had clogged any of the pores.

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After the ultrasonic bath, the samples were placed in the oven at 50 degrees Celsius for three

days. After three days, samples were placed in a sealed container and once again placed back in

the oven for four additional days. This conditioning regime should produce samples that have a

surface relative humidity of above 40% and moisture content above 1.0% which is comparable

of in-situ concrete (DeSouza, Hooton, & Bickley, 1997). On the day of testing, samples were

taken out of the oven and left outside in their sealed containers until the samples cooled down to

room temperature before initiating the absorption test. This was done since temperatures will

have an effect on the surface tension and the dynamic viscosity of the advancing fluid which may

also cause variations on the water-cement paste interaction given the solubility of calcium

hydroxide at higher temperatures (Bentz, Clifton, Ferraris, & Garboczi, 1999).

Each sample was taken out of its individual container, weighed, its size measured with a caliper

and the sides were sealed with electrical tape in order to ensure one dimensional flow with

virtually no evaporation occurring from the sides. Plastic shower caps were placed on top of the

samples in order to control evaporation from the top surface. The bottoms of the samples were

then placed in a 3% chloride solution and the test was started. This setup is shown in Figure 4:

(ASTM International, 2004)

Figure 4: Rate of Absorption Test Setup

The absorption test, 2-3mm of the top surface was immersed in the chloride solution and the

change in mass was measured over a specific time period. The mass of the samples were

measured at 5, 10, 20, 30 minutes and 1 hour intervals for the first 6 hours and once a day for at

least 7 days in accordance with ASTM C1585. The change in mass of each specimen was

measured and the area of the sample and density of the chloride solution were taken into account

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in order to calculate the initial and secondary rate of absorption for each specimen. Linear

regression analysis was used in order to determine the rates of absorption. The initial and

secondary rates of absorption results obtained from all samples are presented in Appendix C.

3.3.4 Hardened Air, Aggregate and Paste Content Analysis

Once the rate of absorption test was finished, the surface of the sample was washed with water

and pressurized air in order to wash and clean the top polished surface. The samples were then

placed in an oven at 50 degrees Celsius for about 15 minutes to dry the surface and a 5:1

acetone-nail hardener polish mixture was brushed on the top surface. This acetone-nail polish

layer was applied in order to densify the top surface and make it easier to distinguish air bubbles

later on. The samples were once again placed in the oven at 50 degrees Celsius for 10 minutes

for the polish to dry and were taken out and hand polished on a polishing table using water and

600 grit carbide sand paper. This step was added in order to remove any streak lines left behind

from the brushing step. The samples were polished just enough so that streak lines left behind

from the acetone-nail hardener polish would be removed. Samples were once again washed with

water and pressurized air and placed in the oven at 50 degrees Celsius to dry.

Once the concrete sample had dried in the oven, the polished surface was placed on a flatbed

scanner and scanned at a resolution of 3175dpi in 24 bit colour and saved as .TIFF format. An

example of one of the scans is shown in Figures 5 and 6. At this resolution, any voids larger than

8 microns are visible which surpasses ASTM C457 specification that voids larger than 10

microns in size are should be distinctly visible. With respect to the scanned images, for every

linear inch, there will be 3175 pixels of data present and each pixel has 256 shades of red, green,

or blue in which close to 17 million colour variations are available while in realistic terms the

human eye can only distinguish up to a limit of about 10 million (Judd & Wyszecki, 1975). An

Epson Perfection V500 flatbed scanner was used to scan all of the samples. This scanner has a

maximum optical resolution of 6400 dots per inch (dpi) and each scan took about 15 minutes to

complete.

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Figure 5: Sample Coloured Scan (Actual image size of 6.6x5mm)

Figure 6: Section of Actual Pixel Size Sample

After this initial scan, the goal was to spray the sample with a 1% phenolphthalein solution in

order to more easily distinguish between paste and aggregate particles. Phenolphthalein is used

as an indicator in concrete to distinguish between paste and aggregate and in certain situations, to

visualize the extent of carbonation. This indicator turns purplish-pink if the pH of the concrete is

above 8.6. If the indicator remains colourless after being applied, the surface of concrete has a

pH of below 8.4 which will be the case if the surface has carbonated (WHD Microanalysis

Consultants Ltd, 2013). Samples from one of the trial concrete mixtures were sprayed with a

1% phenolphthalein solution. It is important to note that the samples from this trial batch were

not brushed with acetone and nail hardener. However, only a minor change in colour was

observed around the coarse aggregate. The surface of the samples were thought to have been

carbonated and for this reason the specimen were hand polished once more in order to expose a

fresh new surface. Samples were sprayed with phenolphthalein indicator once more and without

much success (see Figure 7). It is believed that the carbonation depth was deep enough that

polishing a few micro millimeters from the surface did not fully remove the carbonated zone. As

a result of this outcome, this step was removed from the research outline. Eliminating this step

was not deemed crucial since distinguishing the aggregates using the scanned images was not

made much more difficult and therefore its effect on the results should be minimal.

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Figure 7: Phenolphthalein Sprayed Surface 100 mm Concrete Samples

After the samples were originally scanned, the surfaces of the samples were painted in order to

enhance the contrast between air voids, paste, and aggregate. This was done by blackening the

top polished surface. In order to do this, a flat tip felt marker was used and parallel lines were

drawn on the surface until the entire surface was black. This was done once more at a

perpendicular direction in order to fully darken the top surface. Samples were then placed back

in the oven at 50 degrees Celsius for a few minutes for the ink to fully dry. Afterwards, white

calcium silicate powder (Wollastonite CaSiO3) having an average particle size of 2µm was used

and pressed onto the top surface in order to fill all the voids with white powder and to enhance

the contrast between voids (white) and the rest of the concrete (black). Calcium silicate powder

was chosen since it is white, inert, chemically stable and relatively cheap. Other types of

powders have also been used such as barium sulfate but were not considered in this study.

Calcium silicate powder was poured over the surface of the concrete sample and a large flat

plastic disk was used to push the powder into all of the voids. Next, a razor blade was used to

remove the excess powder on the top surface. After that, the surface was wiped to remove any

leftover powder on the surface. An example of the progression from initial polish to contrast

enhance image is shown in Figure 8.

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Figure 8: Example Progression Image Analysis

The samples were then scanned once again at a resolution of 3175 dpi but this time in 8 bit gray

scale and each scan took about four minutes to complete. Once the samples were scanned, all of

the images were used to determine the aggregate fraction, air and thus paste content.

To determine the aggregate fraction in each sample, the initial coloured scan image was used.

The image was opened using Adobe Photoshop and an additional software script imported into

Photoshop was used to determine the aggregate fraction. This script enables the user to conduct a

modified point count analysis. The software creates a traverse grid on the sample in which a

crosshair moves across and lands on the grid. At each point, the user has to determine if the

crosshair is placed on top of an aggregate or not. A small screen magnifies the point where the

crosshair is placed by about 100% in order to make the distinction between the different phases

easier. Despite this, distinguishing aggregates that are the same colour as paste was sometimes

difficult and guesses had to be made. A red liquid pigment was used in one of the mixtures in

order to color the paste red and to distinguish the aggregates from the paste more easily;

however, it was found that this process did not greatly improve the process of determining

aggregate fraction.

For a sample having a surface area of about 8000mm2, about 700 points could be established. For

the purpose of this research, between 500 to 600 points were looked at for each sample in order

to determine the aggregate fraction. As mentioned before, red liquid pigment was added in one

of the concrete mixtures in order to evaluate if the distinction between paste and aggregates

would be easier for this analysis.

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Overall, five-hundred points was chosen as a minimum since the coefficient of variation for the

type of concrete mixtures being studied here would be under 7% for samples with a paste content

of around 30%. This value was calculated using Equation 3:

(Equation 3) (Snyder, Natesaiyer, & Hover, 2001) Equation 3

Where, Cp is the coefficient of variation of paste content, Sp is the number of stops over paste and

St is the total number of stops.

Once the sample is analyzed, the script outputs a results summary of the mean aggregate fraction

and the relative standard deviation. This analysis was done on all the samples being considered

in this study.

After the aggregate fraction was determined, the original colour was used to mask out all the

coarse aggregates since entrapped and entrained air were the two parameters of interest and not

the voids in the aggregates. Adobe Photoshop was used to mask out all of the aggregates and a

new layer was created to mark and using a black coloured brush to blacken all of the aggregates

so that they would not be considered. A circular brush 200 pixels in diameter which translates to

about 2mm2 was used initially to blacken all of the larger coarse aggregates and a finer 75 pixel

diameter brush which translates to a brush of about 0.3mm2 in size was used to blacken the

smaller aggregates and the edges of the larger aggregates. Once all of the coarse aggregates were

blackened, this masked layer was saved and transposed on top of the black and white scanned

image.

Some difficulty was encountered in lining up the blackened masked layer and the full black and

white image scan. This was due to the fact that the computers could not handle the large image

sizes and as a result, two images had to be aligned by the user in Adobe Photoshop. Therefore,

the masked aggregate layer was transposed on top of the black and white image and the masked

layer was rotated until the edges of the masked layer and the coarse aggregate were lined up as

best as possible. Since the alignment is not perfect, there is the possibility of the masked scan

going over some of the other phases at the edges but the effects of such minor layer effects was

considered to be trivial given the small area over which such an error might be occurring.

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Once the two layers were aligned and all of the coarse aggregates blackened, the two layers were

merged into one layer. Afterwards, another script also added into Photoshop was used to

determine the air content. This script was set to determine the air content of the specimen in

accordance to ASTM C457 using the modified point count technique. The script requires a

number of inputs by the user before it can perform the necessary analysis. Such information

include things like the paste to aggregate ratio of the mix, number of traverse lines required for

analysis and, type of thresholding method to be applied for analysis. Void frequency and air

content threshold values were used and these numbers were set based on round robin testing

comparing manual air content analysis with the scanner in order to calibrate the software. The

goal of using these two factors is for the results to have the least deviation when compared to

manual air content analysis techniques. Thus, the program was set to apply both void frequency

and air content threshold for more accurate results.

The paste to aggregate ratio of all samples in each mixture was assumed to be the same and was

calculated from the mixture design. Fifty traverse lines were selected for the analysis of the

script. This was set since assuming that the average traverse line would be around 50mm on each

sample since only a square area in the middle of each sample is selected for analysis and by

having fifty traverses which are 50mm or more in length would surpass the 2286 mm minimum

traverse length requirement in ASTM C457. The program also requires the use to determine the

white balance of each scan in order to set limits for absolute shades of “black” and “white”. To

do this, a black and white block made using electrical tape was scanned with every image. This

black and white sticker represents the absolute limits of the colour black and white in every

image. Thus, to set the white balance for every image, a portion of the black and white sticker

was selected and input into the program. The program converts then analyzes the pixels and the

rest of the analysis is based on these two values. In other words, the shade of black present on the

black sticker is given the value of 255 and the shade of white on the white sticker is assigned the

value of 0 in a 256 gray-scale analysis.

After all the variables were input into the program the image analysis part could commence. In

order to speed up the process, the program takes the traverse lines and removes each one as a

strip in order to perform the point count analysis on each line rather than on the whole image.

The pixels in each of those lines are then converted to binary values with zero representing the

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colour white or an air void and 1 representing black or other phases in concrete (see Figure 9).

The scanned images are provided in Appendix D.

(Carlson , Sutter , & Van Dam, 2005)

Figure 9: Automated Hardened Air Content Analysis Breakdown

Therefore, each pixel represents an eight by eight micron sized block and for an air void that is

48 microns in diameter and perfectly aligned on the traverse line, six pixels would be assigned

the value of zero or white. This analysis takes place on all 50 traverse lines and the data is

collected in a spreadsheet. The air content of the sample is calculated by dividing the total

number of cells classified as air voids by the total number of cells analyzed. The program also

calculates the spacing factor, specific surface and other parameters.

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Chapter 4 Results and Discussion

4 Background

The results of the tests conducted as well as a discussion of the results are presented in this

chapter. The figures shown in this chapter are organized in a way that the data is primarily

presented from the highest w/cm to lowest w/cm. In addition to this, for concrete mixtures where

w/cm was kept constant, the data is presented from lowest to highest air content (from left to

right). First a summary of the compressive strength results is presented and discussed, followed

by resistivity and permeability results. Afterwards, the initial rate of absorption with respect to

different finishing techniques and at various depths below the surface are presented and

examined. This is followed by an examination of the hardened concrete properties of the samples

in terms of aggregate fraction, air content, and, paste content. The average of duplicate samples

was calculated and used for the results presented in this chapter and the raw data obtained from

each samples tested for this study is also provided in Appendix E. For the parameters above,

trends and correlations observed in the results are discussed as well as any anomalies. An in-

depth examination of the results is essential in order to reach conclusions with regards to the

effects of finishing techniques on concrete properties.

4.1 Compressive Strength Results

The compressive strength results of all nine concrete mixtures are presented in Figure 10. As

previously noted, concrete samples were to be tested at 28 and 56 days of maturity, however,

some of the samples in the 28 day age category were tested at a later age (28-42 days) as noted in

Figure 10:

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Figure 10: Compressive Strength Test Results

An average increase of 10% was seen between the 28 day and 56 compressive strength results

for the concrete samples that were tested at exactly 28 and 56 days. As expected, samples with a

lower w/cm had a higher compressive strength, as shown in Figure 11, when comparing three

concrete mixtures of varying w/cm and about 5% air. The concrete with the lowest w/cm (Mix

3:0.38GU5.5%air) had the highest compressive strength at both ages.

Figure 11: Effect of w/cm on 28 Day Compressive Strength for Mixtures with 5% air

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In terms of the influence of air entrainment, as the air content of the concrete mixtures

increased, the compressive strength decreased as shown in Figure 12 comparing four concrete

mixtures at w/cm of 0.45 and a range of air contents. For instance, the compressive strength of

Mix 6: 0.45-3.5%air was about 20% higher compared to Mix 7: 0.45-7%air at 36-42 days. For

concrete samples in the mid to high levels of air entrainment (4-8%), on average, every 1%

increase in air led to a decrease of about 10% in compressive strength. The Vinsol resin air-

entraining admixture displayed similar compressive strength values to MicroAir when used in a

similarly proportioned concrete mixture.

Figure 12: Influence of Air Entrainment on Compressive Strength of 0.45 w/cm Concrete

Two minor anomalies were observed in this data set. One such case occurs when comparing

Mix5 and Mix6. Both mixtures were proportioned at a w/cm of 0.45 with Mix 6 having an air

content of 3.5% and Mix 5 of 2%. It was expected that the higher air entrained mixture would

exhibit lower compressive strengths but there was a slight increase instead. Another issue was

again observed with regards to Mix 6 when comparing the 42 and 56 day compressive strength

results. It appears that the two results are very similar with the 42 days results even being slightly

higher than the 56 day results.

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4.2 Resistivity and Permeability Results

The results of resistivity and permeability tests for the concrete samples tested in this study are

divided into two sections. The first section outlines the resistivity results obtained from the

Merlin and RCON tests and the second part of the section focuses on the RCPT results.

The resistivity results obtained using the Merlin and RCON tests are shown in Figure 13.

Figure 13: Merlin and RCON Resistivity Results

As previously noted, concrete samples were to be tested at 28 and 56 days, however, some of the

samples were tested at a later age as was specified in the compressive strength results. The

Merlin test resulted in much lower values compared to RCON at both ages as shown in Table 3.

On average, the 28-42 day resistivity results obtained from the Merlin test were about 40% lower

than that of RCON. Similarly, the 56 day resistivity results were about 30% lower when

comparing the Merlin test with RCON.

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Table 3: Resistivity Results

Mix Design

28-42 Day

Merlin

Bulk

Resistance

(kΩ)

28-42 Day

Rcon Bulk

Resistance

(kΩ)

Difference

% Rcon vs.

Merlin 28-

42 Day

56 Day

Merlin

Bulk

Resistan

ce (kΩ)

56 Day

Rcon Bulk

Resistance

(kΩ)

Difference

% Rcon vs.

Merlin 56

Day

Mix 1: 0.55GU-5.2%air 0.69 1.11 38% 0.76 1.15 34%

Mix 5: 0.45GU-2%air 0.61 0.88 31% 0.65 1.06 39%

Mix 6: 0.45GU-3.5%air 0.59 1.12 47% 0.69 0.99 30%

Mix 2: 0.45GU-5.6%air 0.66 1.18 44% 0.62 1.06 42% Mix 2RED: 0.45GU-

6.4%air 0.68 0.93 27% 0.89 1.33 33%

Mix 8: 0.45GU-8%airV 0.63 1.09 42% 0.75 1.02 26%

Mix 7: 0.45GU-7%air 0.63 1.22 48% 0.62 1.09 43%

Mix 3: 0.38GU-5.5%air 0.69 1.25 45% 0.95 1.47 35%

Mix 4: 0.38HSF-8%air 1.92 2.54 24% 2.22 2.66 16%

Average 38% Average 33%

Both RCON and Merlin exhibited similar changes in terms of resistivity values between

different concrete mixtures. This relationship is clearer when examining the results of the

samples tested at 56 days as shown in Figure 14, since the results at 28-42 days are biased by the

differential in the actual test ages.

Figure 14: Merlin and RCON 56 Day Resistivity Results

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As expected, the highest resistivity values were observed in concrete mixtures with the lowest

w/cm. The additions of silica fume increased the resistivity of concrete. In this case, an increase

of about 50% was observed in both RCON and Merlin results with the addition of silica fume

when comparing the resistivity results between Mix 4 and Mix 3, both mixes are at w/cm of 0.38

while a silica fume blended cement was used in Mix 4. Varying the air content appears to have a

little effect on the resistivity values.

Some irregularities were also observed in these results. First, Mix 2 and Mix 2 Red which have

very similar composition (0.45 w/cm and around 6% air) with the only major difference between

the two being the addition of red pigment to Mix 2 Red. However, an increase of about 20% in

the resistivity results was observed in the red mix compared to the other. This may be caused by

the chemical composition of the pigment since most red pigments contain iron oxides which may

have altered the chemical composition of the fluid inside the concrete pores. Another anomaly

seen in the results is with regards to Mix 1 and despite it having a w/cm of 0.55; it has shown

slightly higher resistivity values compared to 0.45 w/cm ratio mixtures in both Merlin and

RCON tests. Once again, the difference in testing age was the cause of this.

The RCPT results are summarized in Figure 15. The same samples used in Merlin and RCON

tests were also used for RCPT afterwards.

Figure 15: RCPT Results

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The RCPT results were adjusted in order to take into account slight size variations (in terms of

thickness) of the concrete samples tested. As anticipated, at 56 days, less charge was passed

through the samples compared to 28-42 day test results. The lowest charge was passed through

Mix 4 containing silica fume. A decrease of about 150% is observed comparing Mix 4 and Mix 3

which are similar mixtures with the only exception being the use of a silica fume blended cement

in Mix 4 compared to GU Portland cement used in Mix 3.

A weak correlation was observed with regards to increasing the air content of the sample which

appears to increase the amount of charge passed although the variability in the results (low

coefficient of determination from the trend line) does not allow making this conclusion certain as

shown in Figure 16.

Figure 16: RCPT Results of 0.45 w/cm Concrete with Varying Air Contents

Once again it appears that Mix 1 having a w/cm of 0.55 has similar permeability characteristics

to concrete mixtures having a w/cm of 0.45 as a result of the difference in the age of the samples

at the time of testing. No changes in permeability were observed in Mix 8 (0.45w/cm-8%airV)

when comparing the 35 and 56 day results.

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4.3 Sorptivity Results

A major aspect of this research was focused on the initial rate of absorption of concrete samples

tested at various depths below the surface. The results obtained from both formed and trowel-

finished slabs are shown in Table 4 and Figures 17 and 18. As previously mentioned, duplicate

samples were tested for each test and the results presented are the average of duplicate samples

(see appendix E for full results). The concrete samples were moist cured for 28 days and later

polished and preconditioned. The samples were between 35-49 days old when the initial rate of

absorption test was conducted.

Table 4: Initial Rate of Absorption Results Summary

Initial Rate of Abs (mm/sqrt(sec))

Sample

Age

(Days)

Trowel-

Finished

Form-

Finished

Trowel-

Finished

Form-

Finished

Trowel-

Finished

Form-

Finished

Trowel-

Finished

Form-

Finished

Depth Below Surface (mm) 0 0 5 5 10 10 20 20

Mix 1: 0.55GU-5.2%air 46 0.0045 0.0044 0.0049 0.0043 0.0054 0.005 0.0047 0.005

Mix 5: 0.45GU-2%air 42 0.0042 0.0035 0.0042 0.0041 0.0045 0.0035 0.0047 0.0041

Mix 6: 0.45GU-3.5%air 48 0.0041 0.0042 0.004 0.0041 0.0043 0.0037 0.0045 0.0041

Mix 2: 0.45GU-5.6%air 45 0.0063 0.0055 0.007 0.0051 0.007 0.0049 0.0067 0.0061

Mix 2RED: 0.45GU-

6.4%air 35 0.0043 0.0048 0.0041 0.0044 0.0044 0.0048 0.0045 0.0041

Mix 7: 0.45GU-7%air 49 0.0063 0.005 0.0055 0.0045 0.0055 0.0048 0.0049 0.0045

Mix 8: 0.45GU-8%airV 41 0.0057 0.005 0.0059 0.0048 0.006 0.0054 0.0059 0.0054

Mix 3: 0.38GU-5.5%air 37 0.0024 0.0031 0.0029 0.0029 0.0029 0.0028 0.0033 0.0031

Mix 4: 0.38HSF-8%air 41 0.0026 0.0023 0.0025 0.0024 0.0028 0.0023 0.0029 0.0025

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Figure 17: Initial Rate of Absorption of Trowel-Finished Samples

Figure 18: Initial Rate of Absorption of Formed-Finished Samples

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The concrete samples with a lower w/cm exhibit the lowest initial rate of absorption values

across all depths. Some of the comparisons between different concrete mixtures at surface and

20mm below surface have been summarized in Table 5. On average, the sorptivity values were

lower by about 65% when comparing the results between 0.38 w/cm and the 0.45 w/cm concrete

mixtures at the surface. Similarly, at 20mm below the surface, the results were still lower than

but not as extensive as the surface and on average a decrease of about 50% was observed with

the lower w/cm concrete. The addition of silica fume also decreased the initial rate of absorption

by about 15% at surface and at 20mm below surface when compared to a similar concrete

mixture (0.38w/cm-7%air) where GU cement was used.

The initial rate of absorption appears to increase with air content as shown in Table 6. The

increase appears to be around 10% when comparing non air entrained mixtures with mid-range

air entrainment levels and an increase of about 15% was observed between mid-range and high-

range air entrainment levels.

The Mix 2 sorptivity results are unusually high for both types of finishes. These results should be

ignored due to problems encountered during the conditioning phase. The problem was that the

oven stopped working overnight while the samples were in it. The problem was noticed the next

day and the oven was replaced; however, the samples were left in the oven for an extra half day

to compensate for this incident which in retrospect appears to have been unnecessary. As a result

of this, it appears that the samples in this mixture were less saturated compared to the other

mixtures during the sorptivity test.

Vinsol resin air-entraining agent appears to have a greater influence and an increase in the initial

rate of absorption of about 5 to 15% was recorded at 5, 10, and 20mm below the surface when

comparing concrete mixtures containing Vinsol resin instead of MicroAir in Mixes 7 and 8.

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Table 5: General Comparison in Sorptivity Results

At Surface 20 mm Below Surface

Trowel-Finished

Form-Finished

Average From

and Trowel-

Finished

Trowel-Finished

Form-Finished

Average From

and Trowel-

Finished

Difference Mix 3 and Mix 1 (w/cm 0.38 vs. 0.55) -84% -44% -64% -43% -62% -53%

Difference Mix 4 and Mix 3 (w/cm 0.38: HSF vs. GU) 5% -32% -14% -12% -24% -18%

Difference Mix 5 and Mix 7 (w/cm 0.45: air 2% vs. 7%) -48% -43% -46% -4% -9% -6%

Difference Mix 7 and Mix 8 (w/cm 0.45: Vinsol vs.

MicroAir) -10% -1% -5% 16% 17% 16%

Table 6: Effect of Air Entrainment on Initial Rate of Absorption

Average Initial Rate of Abs. Form and Trowel-Finished (mm/sqrt(sec))

Depth Below Surface 0-5mm 10-20mm

%diff b/t Mixes %diff b/t Mixes

Mix 5: 0.45GU-2%air 0.004 -10%

0.0042 -6%

Mix 2RED: 0.45GU-6.4%air 0.0044 0.0045

Mix 7: 0.45GU-7%air 0.0053 -21% 0.0049 -10%

It is interesting to note that Mix 7 and Mix 8 were expected to have lower sorptivity values in

comparison to Mix 1 due to their higher cement content, but this was not the case. One reason for

this discrepancy may be may be related to the high air contents of Mixes 7 and 8. As previously

mentioned in the literature review, adding air entraining agents can shift the pore size

distribution of concrete (Hanzic, Kosec, & Anzel, 2010). Although larger pores are associated

with lower sorptivity values due to a decrease in capillary suction force, with the case of chloride

solutions, an increase in the sorptivity may be seen due to the fact that the double layer charge

effect on the sides of the pores would not be as pronounced for larger pores and therefore more

solution is absorbed as a result.

An increase of about 20% was observed in Mix 7 and when comparing the initial rate of

absorption results obtained at the surface versus at lower depths as shown in Table 7. This case

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was the largest difference in the results obtained from all concrete mixtures. Such an increase in

terms of sorptivity at the surface is attributed to the possibility of the surface being overfinished.

The results at the surface are almost doubled in Mix 7 compared to Mix 8 when examining the

surface sorptivity results between form and trowel-finished (13% for Mix 7 compared to 20% for

Mix 8) even though the two concrete mixtures are very similar in composition.

Table 7: Comparison Several Parameters in the Initial Rate of Absorption Results

Diff Sorptivity at Top

Surface: Trowelled vs.

Form-finished

Diff Sorptivity Trowel-

Finished: Top surface vs.

20mm Below

Diff Sorptivity Form-

Finished: Top surface vs.

20mm Below

Mix 1: 0.55GU-5.2%air 2% -4% -14%

Mix 5: 0.45GU-2%air 18% -12% -19%

Mix 6: 0.45GU-3.5%air -1% -10% 1%

Mix 2: 0.45GU-5.6%air 14% -5% -11%

Mix 2RED: 0.45GU-6.4%air -12% -5% 14%

Mix 7: 0.45GU-7%air 20% 21% 10%

Mix 8: 0.45GU-8%airV 13% -3% -9%

Mix 3: 0.38GU-5.5%air -26% -34% -2%

Mix 4: 0.38HSF-8%air 10% -13% -9%

Average* 5% -8% -4%

*Mix 2 results as well as Mix 3 and 7 Trowel-Finished results were not used in the average calculations

This hypothesis is further established by the difference seen in the results of the sorptivity of the

trowel-finished slabs with the form-finished ones as shown in Figure 19. In this figure, for the

majority of the concrete samples, the trowel-finished surface does exhibit a higher initial rate of

absorption. However, in Mix 7, the difference between the surface and form-finished results is

more drastic and a difference of about 20% increase is seen in the trowel-finished surface while

for other concrete mixtures this difference is not as pronounced. Equally important, in Table 7,

results obtained from Mix 2 and the results of the trowel-finished specimen in Mix 3 were not

used for calculating the average or the variance since Mix 2 samples were over dried and Mix 3

samples were finished late and the top surface was “force-finished”.

A breakdown of sorptivity results at each depth is also provided in Figures 19 to 22. As shown

in Figure 19, at the top surface, trowel-finished samples appear to have higher sorptivity rates

compared to form-finished samples and this increase on average is about 5% as shown in Table

7. The effect of the type of specified finish appears to diminish at 20mm below the surface and

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the results of both formed and finished surfaces were very similar to one another as shown in

Figure 22.

At first, the higher initial rate of absorption of trowel-finished samples at the surface was

associated with the increase in surface area available and exposed to the solution front. In other

words, the finished texture on trowel-finished samples are not as smooth as form-finished slabs

and for this reason when looking at the topography of the surface on a macroscopic level, there

are more troughs and peaks with the trowel-finished sample which would contribute to the

increased sorptivity values. But such a hypothesis would only affect the first few readings taken

at 5 to 10 minutes and not the rest of the data set. Another factor may be due to the bleeding of

concrete and the pore structure in this region becoming weaker as a result of it. It is important to

note that the difference observed in the sorptivity of form-finished samples compared to trowel-

finished ones at the surface may be caused by the bleeding at the surface of trowel-finished

specimen and effect of gravity in the form-finished samples. As previously mentioned in the

literature review, similar correlations were also reported in other studies (McCarter, 1993).

Figure 19: Initial Rate of Absorption of Different Finishing Techniques at Surface

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Figure 20: Initial Rate of Absorption at 5mm below Surface

Figure 21: Initial Rate of Absorption at 10mm below Surface

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Figure 22: Initial Rate of Absorption at 20mm below Surface

Another parameter examined was the change in the initial rate of absorption at 5, 10, and 20 mm

below the surface compared to the top surface as shown in Table 8. It should be noted that the

results of trowel-finished slabs from Mix 7 were not used to calculate the average due to the fact

that the top surface was overfinished and the average would have been biased. When comparing

the results of the top surface with respect to other depths, among the trowel-finished samples, the

top surface has the lowest sorptivity rates and an increase in the initial rate of absorption is

observed beyond 10mm below the surface. On average, an increase of about 10% was observed

comparing the surface results with samples at 20mm below the surface.

On the other hand, the change of sorptivity rate with depth is not as pronounced with form-

finished samples. In this case, on average, a slight decrease of about 5% is observed at 20mm

below the surface compared to the top surface based on analysis shown in Table 8. The biggest

variation in results occurs beyond 10mm below the surface and is attributed to the particle

packing and wall effects of the form work interaction with the aggregates and its resulting effect

of the aggregate distribution throughout the depth of the sample as shown in Figure 23.

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Figure 23: Depiction Coarse Aggregate Distribution at Formed Surface Boundary

Overall, for trowel-finished samples, on average the sorptivity increases by about 7% when

comparing the surface to concrete below 10mm or more. In finished samples, almost no change

is observed when comparing the results at the formed surface with depth.

Examining the deviation between the sorptivity results at various depths shows that the largest

variation occurs between the top surface and 10mm under the surface as shown in Table 8 based

on analysis using sum of least squares. Since 19mm coarse aggregate was used in the concrete, it

is expected that the largest surface area of aggregates are present at 10mm under the surface of

form-finished slabs and the variation in terms of sorptivity experienced at this depth may be

caused by this increase in aggregate fraction as shown in Figure 23. To check this hypothesis, all

samples were analyzed for aggregate fraction, hardened air content and paste content as

discussed later on in the chapter.

Table 8: Initial Rate of Absorption % Change Each Depth vs. Surface

Trowel-Finished: %change

from surface

Formed-Finished: %change from

surface

Depth Below Surface (mm) 5 vs. 0 10 vs. 0 20 vs. 0 5 vs. 0 10 vs. 0 20 vs. 0

Mix 1: 0.55GU-5.2%air 8% 17% 4% -2% 11% 13%

Mix 5: 0.45GU-2%air -1% 6% 11% 16% 1% 16%

Mix 6: 0.45GU-3.5%air -3% 4% 9% -2% -11% -1%

Mix 2: 0.45GU-5.6%air 10% 10% 5% -7% -13% 10%

Mix 2RED: 0.45GU-6.4%air -5% 3% 5% -8% 0% -16%

Mix 7: 0.45GU-7%air -13 -14 -27 -11% -4% -11%

Mix 8: 0.45GU-8%airV 3% 5% 3% -4% 8% 8%

Mix 3: 0.38GU-5.5%air 18% 16% 26% -4% -8% 2%

Mix 4: 0.38HSF-8%air -1% 7% 12% 3% -1% 8%

Average * 3% 9% 9% -2% -2% 3%

Variance (Sum of least Squares) 7% 2% 6% 5% 9% 10%

Mix 7 trowel-finished results were not used for calculating the average

The sorptivity results in this study were obtained from samples whose surface were polished to a

high degree and not just saw cut as in ASTM C1585. For this reason, several concrete

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specimens were used to evaluate the difference in sorptivity results when comparing a polished

surface to a saw cut surface. This was accomplished by cutting several 100x200mm concrete

cylinders in half and taking two 50mm slices from the top and bottom of the middle face. The

same sample surface (i.e. surface at 100mm depth) was tested for absorption with the exception

that one of the two surfaces was polished and the other left as is. The results obtained from this

analysis are shown in Figure 24. The analysis shows that there is an increase of about 5% in the

initial rate of absorption of a saw-cut surface over a polished face.

Figure 24: Initial Rate of Absorption Comparison between Polished and Saw-Cut Surfaces

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4.4 Aggregate Distribution Results

As stated earlier, the same concrete surfaces used in the rate of absorption test were later

analyzed in order to determine the aggregate fraction at various depths under the surface. The

results of this analysis are shown in Figures 25 to 28.

Figure 25: Aggregate Fraction vs. Depth of Trowel-Finished Specimen

Figure 26: Aggregate Fraction vs. Depth of Formed-Finished Specimens

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Once again, these results are obtained by averaging the calculated aggregate fraction of

duplicate samples (see Appendix E for all raw results). As mentioned in the testing procedures,

given that about 500 to 600 points were used in the point count analysis, the variation of test

results for each sample is about 7%.

The air content of concrete does not appear to have a direct influence on the distribution of

aggregates at various depths as shown in Figures 27 and 28 which display the aggregate fraction

of four concrete mixtures with a w/cm of 0.45 and increasing air content from left to right.

Figure 27: Effect of Air Content on Aggregate Fraction for Trowel-Finished 0.45 w/cm

Samples

Figure 28: Effect of Air Content on Aggregate Fraction for Form-Finished 0.45 w/cm

Samples

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Overall, the highest aggregate fraction at all depths under the surface was observed with Mix 1

having w/cm of 0.55 and 5.5%air. On average, Mix 1 had an aggregate fraction of about 70%

throughout its depth which was expected given the high theoretical aggregate content calculated

from the mix design. Equally important, the aggregate fraction of Mix 4 containing silica fume

was very uniform throughout the depth of the slab and the spread of data (max-min range) was

the lowest with this mixtures as shown in Table 9.

Table 9: Aggregate Fraction Results

Aggregate Fraction (%) Mix

Design

Trowel-

Finished

Form-

Finished

Trowel-

Finished

Form-

Finished

Trowel-

Finished

Form-

Finished

Min-

Max

Range

Trowel-

Finish

Min-

Max

Range

Form-

Finish

Slump

(mm)

Depth below Surface 5 5 10 10 20 20

Mix 1: 0.55GU-5.2%air 69% 70% 69% 68% 73% 65% 67% 5% 6% 90

Mix 5: 0.45GU-2%air 65% 67% 67% 64% 69% 61% 65% 6% 4% 120

Mix 6: 0.45GU-3.5%air 63% 62% 67% 61% 70% 62% 62% 1% 8% 110

Mix 2: 0.45GU-5.6%air 63% 63% 70% 58% 72% 59% 63% 5% 9% 160

Mix 2RED: 0.45GU-

6.4%air 60% 58% 63% 58% 63% 63% 60% 5% 3% 110

Mix 7: 0.45GU-7%air 59% 57% 66% 64% 63% 61% 62% 7% 4% 175

Mix 8: 0.45GU-8%airV 59% 61% 70% 62% 64% 60% 59% 2% 11% 150

Mix 3: 0.38GU-5.5%air 64% 66% 72% 64% 67% 61% 66% 5% 6% 65

Mix 4: 0.38HSF-8%air 62% 65% 66% 64% 64% 65% 63% 1% 3% 80

Average 63% 68% 63% 67% 62% 63% 4% 6%

Difference Form vs.

Trowel-Finished (%) 7% 7% 2%

Several correlations are seen when comparing the results of the trowel-finished and form-

finished samples in Table 9. Overall, formed-finish specimens were found to contain slightly

higher aggregate contents near the surface. This difference was typically about 7% between the

two finishing techniques up to about 10mm below the surface after which almost no change was

observed between the two finishing techniques. This once again shows that beyond 20mm below

the surface, the concrete properties are unaffected by the method of finishing used.

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More specific patterns were also observed for each individual finish. For instance, as shown in

Table 9, the general trend is that the aggregate content remains constant or decreases from the

surface to 20mm below the surface. This distribution is a positive sign which shows that

segregation was not a factor in this case. This trend was not observed in Mix 7 where there

appears to be a slight spike in aggregate content at a depth of 10mm and once again the high

slump of this mix may have led to this minor segregation effect as shown in Figures 29 and 30.

Further analysis was made in order to quantify the observed variation in the data set. The average

spread of the results (in terms of the maximum and minimum aggregate contents at different

depths) was higher for the form-finished samples compared to the trowel-finished ones. Overall,

the average spread (min-max range) of results for form-finished samples between 5, 10, and

20mm below the surface was 6% while for the trowel-finished specimen this range was about

4%. It was also observed that the range and spread of results between the aggregate fractions at

various depths increased as the slump of the concrete mixture increased. As shown in Table 9,

and Figures 29 and 30, the mixtures with a high slump typically show more of a spread between

the maximum and minimum aggregate fractions compared to those with a low slump. In other

words, when comparing the aggregate fraction of a particular mixture, the range between the

maximum aggregate fraction and minimum aggregate fraction between 5 to 20mm below the

surface increases as the slump of the mixture increases. This may be due to the fact that the

aggregates are not able to shift around as much after placement in low slump mixtures that are

less workable and as a result, the spread of aggregate content at various depths with respect to

the mean is smaller.

The data depicted in Figures 25 to 28 are also displayed in Figures 29 and 30 in a different

format in order to show the trend of all the concrete mixtures at the three testing depths and with

respect to slump. A theoretical aggregate fraction is also shown for each of the concrete

mixtures in these two figures. It is important to note that the density of the fresh concrete was not

measured during mixing and only a theoretical aggregate content was calculated using the

concrete mixture proportions. Upon closer examination of Figures 29 and 30, it is apparent that

on average, the aggregate fractions of the form-finished slabs are lowest at 20mm below the

surface while for the surface-finished slabs such a trend was not seen in the distribution of

aggregates at different depths in which case the average aggregate fraction was at about 60%

throughout the depth as shown in Table 9.

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Figure 29: Distribution of Aggregates in Trowel-Finished Slabs

Figure 30: Distribution of Aggregates in Form-Finished Slabs

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4.5 Hardened Air Content Analysis

The results of the hardened air content in the samples are shown in Figures 31 and 32 as well as

Table 10. A difference of about 1.5% was observed in the air contents of the fresh concrete

versus the hardened air contents for each mixture. This decrease of 1.5% was caused by the

aggregate correction factor since it was not taken into account for the fresh air content.

Subsequently, tests were conducted in order to analyze the aggregate correction factor which was

determined to be just over 1%.

Figure 31: Hardened Air Content of Surface-Finished Concrete Slabs

Figure 32: Hardened Air Content of Formed-Finish Concrete Slabs

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Table 10: Hardened Air Content Results Summary

Air Content (%) Trowel-

Finished

Form-

Finished

Trowel-

Finished

Form-

Finished

Trowel-

Finished

Form-

Finished

Min-

Max

Range

Trowel-

Finish

Min-

Max

Range

Form-

Finish Depth below Surface (mm) 5 5 10 10 20 20

Mix 1: 0.55GU-5.2%air 3 4 4 3 4 3 0.8 0.6

Mix 5: 0.45GU-2%air 1 1 1 1 1 1 0.4 0.3

Mix 6: 0.45GU-3.5%air 2 2 2 2 3 2 1.4 0.0

Mix 2: 0.45GU-5.6%air 5 4 5 4 5 4 0.7 0.4

Mix 2RED: 0.45GU-

6.4%air 4 5 4 4 4 5 0.6 0.8

Mix 7: 0.45GU-7%air 5 5 5 5 5 5 0.5 0.7

Mix 8: 0.45GU-8%airV 8 6 9 8 7 8 2.0 1.7

Mix 3: 0.38GU-5.5%air 4 4 5 4 6 4 2.2 0.7

Mix 4: 0.38HSF-8%air 6 6 6 7 6 6 0.6 0.8

Average 1.0 0.7

Trowel-finished samples had lower air contents near the top surface compared to form-finished

samples and on average a decrease of about 4% was observed between the two. This trend was

altered at a depth of 10mm and beyond however, where the trowel-finished samples contained

more air on average by about 4% at 10mm below the surface and 9% at 20mm below the surface

as shown in Table 11.

Overall, the average spread of results (max-min range) was smaller for form-finished samples

compared to trowel-finished ones. This shows that surface finishing techniques increases the

variability and properties of the near surface. This relationship is also shown in Figures 33 and

34, when comparing concrete mixtures with the same w/cm and various air contents between

form and trowel-finished samples. As shown in the figures, air content of form-finished samples

at various depths is close to one another compared to trowel-finished samples.

Overall, the hardened air content of the trowel-finished samples appears to be higher than their

form-finished counterparts at deeper depths as shown in Table 11. For the most part, the lowest

air content was observed near the surface at a depth of 5mm below the surface in the trowel-

finished slabs while the highest air contents were at 20mm below the surface. The slightly lower

values at the surface compared to the rest of concrete were attributed to the process of screeding

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and floating the top surface which may have had effected the volume of entrained air in the

surface zone.

Table 11: Difference of Air Content between Trowel and Formed-Finished Samples

Air Content (%)

% Diff Trowel

vs. Form-

Finished

% Diff Trowel

vs. Form-

Finished

% Diff Trowel

vs. Form-

Finished

Depth below Surface (mm) 5 10 20

Mix 1: 0.55GU-5.2%air -9% 17% 27%

Mix 5: 0.45GU-2%air -5% -18% 18%

Mix 6: 0.45GU-3.5%air -18% 2% 31%

Mix 2: 0.45GU-5.6%air 1% 15% 22%

Mix 2RED: 0.45GU-6.4%air -16% -11% -19%

Mix 7: 0.45GU-7%air -11% 10% -10%

Mix 8: 0.45GU-8%airV 21% 15% -8%

Mix 3: 0.38GU-5.5%air -5% 28% 23%

Mix 4: 0.38HSF-8%air 2% -20% 0%

Average -4% 4% 9%

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Figure 33: Hardened Air Content of Trowel-Finished Samples at 0.45 w/cm

Figure 34: Hardened Air Content of Form-Finished Samples at 0.45 w/cm

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4.6 Paste Content Analysis

In order to calculate the paste content, the aggregate fraction and air content was

subtracted from the whole since the entrained air voids were not considered part of the paste (i.e.

1-aggregate fraction-air content = paste content). The results of the paste content for all concrete

mixtures at various depths are presented in Figures 35 and 36. The same data is also shown in

Figures 37 and 38 in a different manner in order to show the deviation and change in paste

content at various depths more clearly. Theoretical paste contents were also calculated using the

concrete mixture proportions. It should be noted that the fresh concrete density was not measured

and therefore only a theoretical paste content value was calculated and is presented in Figures 37

and 38 as well as Tables 12 and 13.

Figure 35: Paste Content of Trowel-finished Slabs at Various Depths from Surface

Figure 36: Paste Content of Form-Finished Slabs at Various Depths from Surface

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Figure 37: Paste Content of Trowel-finished Slabs at Various Depths from Surface

Figure 38: Paste Content of Form-Finished Slabs at Various Depths from Surface

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Table 12: Paste Content Results

Paste Content Trowel-Finish

Form-Finish

Trowel-Finish

Form-Finish

Trowel-Finish

Form-Finish Mix

Design Slump (mm) Depth Below Surface

(mm) 5 5 10 10 20 20

Mix 1: 0.55GU-5.2%air 25% 27% 28% 24% 31% 30% 25% 90

Mix 5: 0.45GU-2%air 32% 32% 34% 30% 38% 34% 33% 120

Mix 6: 0.45GU-3.5%air 36% 31% 37% 27% 35% 36% 33% 110

Mix 2: 0.45GU-5.6%air 33% 26% 37% 24% 36% 33% 33% 160

Mix 2RED: 0.45GU-6.4%air

33% 37% 33% 37% 36% 33% 36% 110

Mix 7: 0.45GU-7%air 39% 29% 31% 32% 34% 33% 33% 175

Mix 8: 0.45GU-8%airV 31% 24% 28% 29% 33% 33% 33% 150

Mix 3: 0.38GU-5.5%air 30% 25% 30% 29% 33% 29% 30% 65

Mix 4: 0.38HSF-8%air 29% 28% 31% 29% 29% 31% 30% 80

The concrete mixtures which were not air entrained or in the low air category have higher paste

contents compared to mid-range air entrained mixtures especially at deeper depths. This was

anticipated given that air voids were not treated as part of the paste and thus were subtracted in

order to calculate the paste content. However, as the air content of the mixture increased to above

6%, this relationship was no longer valid.

An abnormality was seen in the results with Mix Red 2 where the formed-finish specimens had

very similar paste contents at all three depths as shown in Figure 38.

A number of conclusions can be made based on these figures. First, with regards to the trowel-

finished slabs, Mix 1 has the lowest paste content just below the surface and one of the lowest

paste contents at all other depths when compared to all other concrete mixtures as expected given

its lower theoretical paste content. The results of the paste contents at various depths are also

shown in Tables 13 along with the spread of results between the various depths.

Overall, form-finished concrete samples typically had lower paste content compared to trowel-

finished samples. This difference was about 10% near the surface and decreased to about 5% at

20mm under the surface as shown in Table 13.

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Table 13: Paste Content Results Summary

Paste Content (%) Trowel-

Finished

Form-

Finished

Trowel-

Finished

Form-

Finished

Trowel-

Finished

Form-

Finished

Max-

Min

Range

Trowel-

Finish

Max-

Min

Range

Form-

Finish

Slump

(mm)

Depth below Surface

(mm) 5 5 10 10 20 20

Mix 1: 0.55GU-5.2%air 25% 27% 28% 24% 31% 30% 6% 6% 90

Mix 5: 0.45GU-2%air 32% 32% 34% 30% 38% 34% 6% 4% 120

Mix 6: 0.45GU-3.5%air 36% 31% 37% 27% 35% 36% 2% 9% 110

Mix 2: 0.45GU-5.6%air 33% 26% 37% 24% 36% 33% 4% 9% 160

Mix 2RED: 0.45GU-

6.4%air 33% 37% 33% 37% 36% 33% 3% 4% 110

Mix 7: 0.45GU-7%air 39% 29% 31% 32% 34% 33% 8% 4% 175

Mix 8: 0.45GU-8%airV 31% 24% 28% 29% 33% 33% 5% 9% 150

Mix 3: 0.38GU-5.5%air 30% 25% 30% 29% 33% 29% 3% 4% 65

Mix 4: 0.38HSF-8%air 29% 28% 31% 29% 29% 31% 2% 3% 80

Average 32% 29% 32% 29% 34% 32% 4% 6%

Difference Form vs.

Trowel-Finished (%) -11% -11% -4%

It is also observed that the spread of results in terms of the difference between the maximum and

minimum paste content at various depths is slightly lower with the trowel-finished samples

compared to form-finished ones (4% compared to 6% on average) as shown in Table 13. From

this table, it also appears that the paste content is relatively uniform near the surface and slightly

increases by about 5-10% at a depth of 20mm below the surface for trowel and form-finished

samples respectively. As shown in Table 13, for the majority of samples, the paste content

increases with depth and the highest paste contents at about 20mm under the surface for both

finishing techniques. It is important to note that the paste content of Mix 3 and Mix 4 where a

w/cm of 0.38 was used and about 6% entrained air is not significantly higher than the other

concrete mixtures with a higher w/cm since for these two mixtures the water content was

decreased while the cement content was not altered.

The addition of silica fume, as well as lowering the w/cm of concrete mixtures, also decreases

the spread of results in terms of the maximum and minimum range of paste contents at different

depths. This is shown in Mix 4 where w/cm of 0.38 and addition of silica fume help to keep the

paste content at a relatively constant level with minimal change across the depth of the slab. This

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is also represented by the “Max-Min range” in Table 13 in which Mix 4 has one of the lowest

values (under 3%) throughout its depth when compared to other mixtures. It is worth noting that

although Mix 3 and 4 are almost identical, slightly higher paste values are observed in Mix 4

where blended silica fume cement was used and this is due to the fact that the density of this

cement is slightly lower compared to GU cement and thus slightly more cement was used in Mix

4.

Overall, for majority of the mixtures the calculated theoretical paste content (from the mix

designs) fell somewhere in between the analyzed paste content at various depths below the

surface. For form-finished samples, theoretical values were closer to the paste contents analyzed

at 20mm below the surface while for trowel-finished samples no clear relationship between

theoretical values and analyzed values was observed.

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4.7 Cylinder Aggregate and Paste Distribution

Additional samples were tested in order to examine the aggregate and paste distribution at depths

beyond 20mm and to study the role and extent of segregation. To do this, two 100x200mm

concrete cylinders from Mix 2 Red were sliced from the top to the bottom at 10, 30, 70, 100, 130,

and 160mm from the top surface. Each slice was then examined and the aggregate fraction, paste

and air content of each slice were measured as summarized in Figure 39.

Figure 39: Aggregate Distribution over Depth in Concrete Cylinders Mix 2 Red: 0.45GU-

6.4%air

The average aggregate fraction of Cylinder #12 (C12) was about 55% and for cylinder #15 (C15)

was close to 59%. The average range of values is about 11% as shown in Table 14. As shown in

Figure 39, the aggregate content appears to be increasing depth increases. Although this increase

is under 10% and the methods of testing are not sensitive enough to fully determine the extent of

this issue, it can be argued that segregation of fresh concrete may be a factor.

Table 14: Range of Aggregate Contents in Concrete Cylinders

Average Max-Min

Range Depth below

surface 10 40 70 100 130 160

Mean Aggregate

Fraction Red Mix

C12

57% 47% 57% 49% 60% 51% 54% 13%

Mean Aggregate

Fraction Red Mix

C15

54% 55% 60% 60% 62% 60% 59% 8%

Average 56% 51% 59% 55% 61% 56% 56% 11%

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Chapter 5 Conclusions and Recommendations

The concrete cover over reinforcement, also known as covercrete, is one of the most important

areas in any concrete structure as it provides the first line of defense against the ingress of fluids

in concrete. Understanding the physical properties of the near surface zone as well as the factors

which influence such properties are important for designing more durable concrete structures.

This study was conducted in order to evaluate the effect of two trowel-finished on the near-

surface properties of concrete. Different types of concrete mixtures were designed and samples

were tested for sorptivity. To do this, concrete slabs were cast and the surfaces tested were either

trowel finished or the formed surface cast against plywood moulds.

Concrete slabs were cored, sliced, and conditioned in order to test the sorptivity at various depths

underneath the surface in a chloride solution. This test was conducted on the surface of the slab,

as well at depths of 5, 10, and 20mm below the surface. In order to have a better understanding

of the factors which influence the quality of the cover, the sorptivity specimens were analyzed

and the aggregate, air and paste contents at each depth were also determined.

5 Conclusions

The following conclusions summarize the key findings of this study:

1. Decreasing the w/cm of concrete will decrease the initial rate of absorption at all

depths under the surface. The sorptivity results of concrete samples with 0.38

w/cm where almost half of concrete samples with 0.45 w/cm

2. Silica fume blended cement (8% silica fume at 0.38 w/cm 8% air) decreased the

initial rate of absorption by about 15% compared to GU cement (at 0.38 w/cm and

6% air). The addition of silica fume was also beneficial for obtaining concrete

samples of uniform paste and aggregate distributions since the spread of values at

various depths below the surface is smaller compared to comparable mixtures

where silica fume was not used.

3. Air entrainment increases the initial rate of absorption. A 10% increase was

observed in sorptivity results of non-air entrained concrete compared to mid-range

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78

air entrained samples (2%-5% air). The sorptivity results continued to increase

comparing mid-to-high range air entrained samples (5-8% air) by about 15%.

Vinsol air entraining admixture increased the rate of absorption by 5 to 15% at

various depths below the surface when compared to similar concrete with

MicroAir air entraining agent.

4. Higher initial rates of absorption were observed at the surface; the results at the

surface were about 10% higher for both finishing techniques. A 5% increase in

sorptivity was observed with trowel-finished samples compared to form-finished

samples at the top surface. This effect disappears at 20mm below the surface. The

effect of surface finish appears to diminish at 20mm below the surface. The

bleeding of concrete and resulting extend of capillaries in the coverzone for the

trowel-finished sample compared to the effect of segregation in the form-finished

is believed to be responsible for this observed pattern.

5. With regards to trowel-finished slabs, the lowest sorptivity values were observed

at the top surface. The sorptivity values below the surface increased by about 10%

at 20mm below the surface compared to the top surface.

6. Overfinishing concrete surfaces doubled the initial rate of absorption at the

surface for concrete mixtures at 0.45w/cm 6% air.

7. A 5% decrease in initial rate of absorption was observed between highly polished

and saw-cut face of the same concrete specimen

8. Form-finished samples on average had higher aggregate contents of about 7%

compared to trowel-finished samples. Aggregate fraction decreased with depth

regardless of the type of finishing method. For form-finished samples, the

aggregate fraction was lowest at 20mm below the surface. With respect to trowel-

finished samples, the distribution of aggregates was uniform and constant

throughout the depth compared to form-finished samples.

9. When comparing the aggregate fraction results at the three studies surfaces below

the surface, it appears that the spread of results between the three depths is

dependent on the slump and as the slump of concrete increased to above 150mm,

the spread between the three depths also increased compared to other concrete

mixtures at a slump of 110+ 20mm

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79

10. Trowel-finished samples contained less air near the top surface compared to form-

finished samples and a decrease of about 5% was observed between the two

finishing techniques. Beyond 10 mm below the surface however, the trowel-

finished samples contained more air on average by about 10%.

11. Lower paste contents were observed with form-finished samples and on average,

a 10% decrease was observed at the surface and a 5% decrease at 20mm below

the surface when compared to trowel-finished samples.

5.1 Recommendations

Several recommendations can be provided for future research in order to improve certain aspects

of this study:

1. Larger concrete slabs cast on site by professional concrete casting and finishing crew

may be beneficial in order to ensure that the slabs are finished in an appropriate manner.

The small plywood moulds used in this study proved to be troublesome when it came to

finishing the samples due to their small size and uneven height at each side of the moulds

and the size of finishing tools used

2. Although the purpose of this study was to compare the effect of trowel-finish surface to

that of a form-finish surface, a true comparison cannot be made due to the orientation of

the surfaces where the trowel-finish surface was positioned on top of the mould and the

form-finished surface was at the bottom face of the mould. For this reason, the effect of

bleeding and segregation may be the primary factors for the patterns observed in this

study. For future studies it may be beneficial to test the form-finished surface by placing

a mould surface on top of the fresh concrete instead of using the bottom face in order to

avoid the effect of segregation

3. In this study, the results are based on duplicate samples being tested. More accurate

observations could be made if more samples were tested especially given the variability

of each test method.

4. The parameters examined in this project were too broad and the testing methods were not

sensitive enough to provide precise and accurate results given the variability observed in

some of the test results. Additional test methods such as CT-Xray scanning may be

beneficial especially with regards to analysis of the distribution of aggregates.

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80

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85

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Appendix 86

Appendices

Appendix A: Material Properties Tables

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Appendix 87

Physical and Chemical Composition GU cement

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Appendix 88

Physical and Chemical Composition GranCem (Slag)

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Appendix 89

Composition and Properties of Chameleon Liquid Red Iron Oxide A1070

Trace Metal Content in Parts Per Million (ppm)

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Appendix 90

Fine Aggregate Sieve Analysis

Sunderland Quarry Fine Aggregate

Sieve Size Percent Retained

9.5 100.0

6.7 99.9

4.75 97.1

2.36 83.8

1.18 68.6

0.6 50.6

0.3 23.6

0.15 5.4

0.075 1.4

Pan 0.0

Coarse Aggregate Sieve Analysis

Sieve Size (mm)

Percent Passing (%)

OPSS Requirement for 19 mm Aggregate 19 mm

37.5 mm - 100

26.5 mm 100 100

19 mm 85 - 100 90

16 mm 65 - 90 67

12.5 mm - 42

9.5 mm 20 - 55 18

6.7 mm - 4

4.75 mm 0 - 10 1

2.362 mm - 1

1.18 mm - 1

600 μm - 0

300 μm - 0

150 μm - 0

Pan - 0

Note: The results shown are rounded to the nearest integer and are average values based on two tests

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Appendix 91

Appendix B: Detailed Concrete Mixture Design

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Appendix 92

MIX 1

Mixed on: Jan.28.2013

MIX 1: 0.55GU 0.25S 6%

S.G. kg/m3

design Mass

per m^3 (kg) Volume

m3

70 L

batch Adj. Mass

Type GU 3150 218 0.069 15.3 kg 15.3 kg

Slag (Holcim) 2890 73 0.025 5.1 kg 5.1 kg

Coarse Agg. 2700 1060 0.393 74.20 kg 74.4 kg

Fine Agg, 2680 785 0.293 54.94 kg 56.5 kg

H2O 1000 160 0.160 11.20 L 9.4 L

Air Entrainment 1200 72.00 0.060 9.5 ml* ml*

water reducer 1100 0 0.0000 0.0

ml*

* ml**

W/C ratio 0.55

ABSfineagg 0.69%

ABScoarseagg 1.42%

MCfineagg 3.5%

MCcoarseagg 1.8%

paste content 0.25

*MicroAir air-entrainer 62 ml/100kg

**PolyHeed1725 mid-range water reducer 0 ml/100kg

Glenium 7700 Superplasticizer 0 ml

AIR CONTENT 5.2% at 10min

SLUMP 90 mm

Notes:

Slabs placed and troweled in 35 min

Bleeding Rate (cumulative)

3mL at 2hr

5.7mL at 3hr

7.2mL at 3.5hr

slabs finished at

4hr

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Appendix 93

MIX 5

Mixed on: January.9.2013

MIX 5: 0.45GU 0.25S 2%

S.G. kg/m3

design

Mass per

m^3 (kg)

Volume

m3

65 L

batch

Adj.

Mass

Type GU 3150 316 0.100 20.53 kg 20.53 kg

Slag (Holcim) 2890 105 0.036 6.83 6.83

Coarse Agg. 2700 1060 0.393 68.90 kg 69.3 kg

Fine Agg, 2680 698 0.260 45.37 kg 46.0 kg

H2O 1000 189 0.189 12.31 L 11.32 L

Air Entrainment 1200 24 0.020 0.0 ml* ml*

water reducer 1100 1.0 0.0009 60.1

ml*

* ml**

W/C ratio 0.45

ABSfineagg 0.69%

ABScoarseagg 1.42%

MCfineagg 2.0%

MCcoarseagg 2.0%

paste content 0.33

*MicroAir air entrainer 0 ml/100kg

**PolyHeed1725 mid-range water reducer 293 ml/100kg

Glenium 7700 Superplasticizer 0 ml

Air 2.0% at 10 min

Slump 120mm

Notes:

Mix Started at 12:00pm

Cast was finished and all specimen were placed by 12:40pm

calorimeter inserted and initialized at 12:40 inside the specimen

slabs were covered and waiting for initial set to

finish

bleeding rate

at 2hr: 4.2mL

at 3hr: 4mL

at 4hr: 1.2mL

slabs were finished at 4:00pm (4 hr. after initial contact)

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Appendix 94

MIX 6

Mixed on: Jan.29.2012

MIX 6: 0.45GU 0.25S 4%

S.G. kg/m3

design

Mass per

m^3 (kg)

Volume

m3

70 L

batch Adj. Mass

Type GU 3150 316 0.100 22.11 kg

22.

11

Slag (Holcim) 2890 105 0.036 7.35

7.3

5 kg

Coarse Agg. 2700 1060 0.393 74.20 kg

74.

63 kg

Fine Agg, 2680 647 0.241 45.28 kg

46.

33 L

H2O 1000 189 0.189 13.26 L

11.

79 ml*

Air Entrainment 1200 48 0.040 4.4 ml* ml**

water reducer 1100 0.0 0.0000 0.0

ml*

*

W/C ratio 0.45

ABSfineagg 0.69%

ABScoarseagg 1.42%

MCfineagg 3.0%

MCcoarseagg 2.0%

paste content 0.33

*MicroAir air entrainer 20 ml/100kg

**PolyHeed1725 mid-range water reducer 0 ml/100kg

Glenium 7700 Superplasticizer 0 ml

AIR CONTENT 3.5% at 10 min

SLUMP 110

Notes:

Mix Started at 11:30am

slabs placed and troweled by 12:10

pm

Bleeding Rate (cumulative)

2.5mL at 2hr

5 mL at 2.5hr

6 mL at 3hr

slabs finished at 2:45pm (3hr 15min from start)

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Appendix 95

MIX 2

Mixed on: Jan.14.2012

MIX 2: 0.45GU 0.25S 6%

S.G. kg/m3

design

Mass per

m^3 (kg)

Volume

m3

76 L

batch

Adj.

Mass

Type GU 3150 316 0.100 24.00 kg 24.00 kg

Slag (Holcim) 2890 105 0.036 7.98 kg 7.98 kg

Coarse Agg. 2700 1060 0.393 80.56 kg 81.23 kg

Fine Agg, 2680 645 0.241 49.03 kg 49.67 kg

H2O 1000 189 0.189 14.40 L 13.09 L

Air Entrainment 1200 48 0.040 10.1 ml*

water reducer 1100 0.7 0.0007 50.4

ml*

*

W/C ratio 0.45

ABSfineagg 0.69%

ABScoarseagg 1.42%

MCfineagg 2.0%

MCcoarseagg 2.3%

paste content 0.33

*MicroAir air entrainer 42 ml/100kg

**PolyHeed1725 mid-range water reducer 210 ml/100kg

Glenium 7700 Superplasticizer 0 ml

AIR CONTENT 5.6% at 10 min

SLUMP 160mm

Notes:

Mix Started at 10:30am

All specimen cast and placed by

11:30

Penetration resistance device broken: low values reported even after set

Bleeding Rate (Cumulative)

6.1mL at 2.5 hr.

9.2mL at 3hr

11.2mL at 4hr

11.8mL at 4.5 hr.

slabs finished at 4.5 hr.

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Appendix 96

Mix 2 Red

Mixed on: May.7.2013

MIX 2RED: 0.45GU 0.25S 6%

S.G. kg/m3

design

Mass per

m^3 (kg)

Volume

m3

60 L

batch

L

Batc

h Adj. Mass

Type GU 3150 421 0.134 18.95 kg 18.95 kg

Slag (Holcim) 2890 105 0.036 6.32 kg 6.316 kg

Coarse Agg. 2700 1060 0.393 63.60 kg 64.36 kg

Fine Agg, 2680 555 0.207 33.29 kg 33.35 kg

H2O 1000 189 0.189 10.23 L 9.417 L

Air Entrainment 1200 48 0.040 8.0 ml*

water reducer 1100 0.9 0.0008 36.9 ml**

W/C ratio 0.45

Volume Check 1.0

ABSfineagg 0.69%

ABScoarseagg 1.42%

MCfineagg 0.9%

MCcoarseagg 2.6%

paste content 0.36

*MicroAir air entrainer 42 ml/100kg

**PolyHeed1725 mid-range water reducer 195 ml/100kg

Glenium 7700 Superplasticizer 0 ml

Red Paint

1.14 L

AIR CONTENT 6.4%

at 10 min SLUMP 110 mm

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Appendix 97

MIX 7

Mixed on: Jan.15.2013

MIX 7: 0.45GU 0.25S 8%

S.G. kg/m3

design

Mass per

m^3 (kg)

Volume

m3

78 L

batch

L

Batc

h Adj. Mass

Type GU 3150 316 0.100 24.6 kg 24.63

k

g

Slag (Holcim) 2890 105 0.036 8.2 8.19

k

g

Coarse Agg. 2700 1060 0.393 82.68 kg 83.41

k

g

Fine Agg, 2680 538 0.201 41.96 kg 42.51

k

g

H2O 1000 189 0.189 14.78 L 13.5 L

Air Entrainment 1200 96 0.080 19.7 ml*

water reducer 1100 0.7 0.0006 49.0 ml**

W/C ratio 0.45

ABSfineagg 0.69%

ABScoarseagg 1.42%

MCfineagg 2.0%

MCcoarseagg 2.3%

paste content 0.33

*MicroAir air entrainer 80 ml/100kg

**PolyHeed1725 mid-range water reducer 199 ml/100kg

Glenium 7700 Superplasticizer 0 ml

AIR CONTENT 7.0% at 25 min

SLUMP 150mm

Notes:

Mix started at 10:30am

Air and Slump tested at 10min: air=5.4%, slump 180mm

5mL additional MicroAir added and remixed for

2min

slump and air measured once more: 7%, 150mm

casting started

slabs finished after 4hr

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Appendix 98

MIX 8: 0.45GU 0.25S 6%V

Mixed on: 23.Jan.2013

MIX 8: 0.45GU 0.25S 6%V

S.G. kg/m3

design

Mass per

m^3 (kg)

Volume

m3

78 L

batch

L

Batc

h Adj. Mass

Type GU 3150 316 0.100 24.6 kg

24.6

3 kg

Slag (Holcim) 2890 105 0.036 8.2 8.19 kg

Coarse Agg. 2700 1060 0.393 82.68 kg

82.9

5 kg

Fine Agg, 2680 538 0.201 41.98 kg

43.1

6 kg

H2O 1000 189 0.189 14.78 L

13.3

2 L

Air Entrainment 1200 96 0.080 32.8 ml*

water reducer 1100 0.6 0.0005 42.6 ml**

W/C ratio 0.45

ABSfineagg 0.69%

ABScoarseagg 1.42%

MCfineagg 3.5%

MCcoarseagg 1.8%

paste content 0.33

*MicroAir air entrainer 133 ml/100kg

**PolyHeed1725 mid-range water reducer 173 ml/100kg

Glenium 7700 Superplasticizer 0 ml

AIR CONTENT 8.0%

at 20min

SLUMP 175mm

Notes:

Mix started at 10:30 am

Slump and Air measured at 10min: 8%air, 190mm slump

Mix was remixed for 4 additional minutes to decrease slump

Slump measured at 20min: 175mm

Bleeding Rate (cumulative)

4mL at 2hr

7mL at 2.5hr

14mL at 3hr

19mL at 3.5 hr.

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Appendix 99

slabs finished at 2:20 pm (3hr 50min after start)

MIX 3

Mixed on: Dec/19/2012

MIX 3: 0.38GU 0.25S 6%

S.G. kg/m3

design Mass

per m^3

(kg) Volume m3

65 L

batch

L

Batch Adj. Mass

Type GU 3150 316 0.100 20.5 kg 20.53 kg

Slag (Holcim) 2890 105 0.036 6.8 6.825 kg

Coarse Agg. 2700 1060 0.393 68.90 kg 69.99 kg

Fine Agg, 2680 669 0.250 43.47 kg 43.61 kg

H2O 1000 160 0.160 10.40 L 9.177 L

Air Entrainment 1200 72 0.060 15.0 ml*

water reducer 1100 1.4 0.0013 82.1 ml**

W/C ratio 0.38

Volume Check 1.0

ABSfineagg 0.69%

ABScoarseagg 1.42%

MCfineagg 1.0%

MCcoarseagg 3.0%

paste content 0.30

*MicroAir air entrainer 73 ml/100kg

**PolyHeed1725 mid-range water reducer 400 ml/100kg

Glenium 7700 Superplasticizer 730 ml/100kg 150 ml

AIR CONTENT 5.5% at 25 min

SLUMP 65 mm

Time Initial Set

3 hours 45 min

Cast started, air content/ slump too low

20 ml of additional w/r added at 2min

superp added 3 min after rest, 100ml from 6-9min

slump and air tested at 10-15min, air 4.9%, slump 55mm

2ml extra air entrainer added, 50 ml superp

Slabs finished at 3 hr. 40 min (a little too late, surface had harden and past initial finish (should calibrate pressure

resistance instrument) and thus very hard to finish, possibility overfinishing.

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Appendix 100

MIX 4

Mixed on: 24.Jan.2013

MIX 4: 0.38HSF25%Slag6%air

S.G. kg/m3

design Mass

per m^3 (kg) Volume m3

65 L

batch Adj. Mass

Type HSF 3000 316 0.105 20.53 kg 20.53 kg

Slag (Holcim) 2890 105 0.036 6.83 6.83 kg

Coarse Agg. 2700 1060 0.393 68.90 kg 69.47 kg

Fine Agg, 2680 602 0.225 39.14 kg 40.24 kg

H2O 1000 160 0.160 10.40 L 8.73 L

Air Entrainment 1200 96 0.080 45.2

m

l*

water reducer 1100 1.2 0.0011 71.8

m

l*

*

W/C ratio 0.38

ABSfineagg 0.69%

ABScoarseagg 1.42%

MCfineagg 3.5%

MCcoarseagg 2.3%

paste content 0.30

*MicroAir air entrainer 220 ml/100kg

**PolyHeed1725 mid-range water reducer 350 ml/100kg

Glenium 7700 Superplasticizer 390 ml/100kg

AIR CONTENT 9.5%

SLUMP 77mm

Notes:

Mix Started at 10:30am

during initial 3 minutes of mixing 50mL of additional WR added

at 10 min: slump 50mm, air 8%

30mL extra SP added and remixed for 2 minutes

at 18min: 77mm slump, 9.5% air

Casting started at 25 minutes

Casting finished at 1hr 20 min

Slabs covered at 1hr 30min

unable to collect any bleed water (tested every hour for first 5 hours after initial contact cement with water)

Slabs were finished after around 3 hours from initial mixing

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Appendix 101

Appendix C: Initial and Secondary Rates of Absorption Results

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Appendix 102

Mix 1: 0.55GU-5%air Initial and Secondary Rates of Absorption Results

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Appendix 103

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Appendix 104

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Appendix 105

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Appendix 106

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Appendix 107

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Appendix 108

Mix 5: 0.45GU-2%air Initial and Secondary Rates of Absorption Results

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Appendix 109

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Appendix 110

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Appendix 111

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Appendix 112

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Appendix 113

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Appendix 114

Mix 6: 0.45GU-3.5%air Initial and Secondary Rates of Absorption Results

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Appendix 115

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Appendix 116

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Appendix 117

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Appendix 118

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Appendix 119

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Appendix 120

Mix 2: 0.45GU-5.6%air Initial and Secondary Rates of Absorption

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Appendix 121

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Appendix 122

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Appendix 123

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Appendix 124

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Appendix 125

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Appendix 126

Mix 2Red: 0.45GU-6.4%air Initial and Secondary Rates of Absorption

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Appendix 127

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Appendix 128

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Appendix 129

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Appendix 130

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Appendix 131

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Appendix 132

Mix 7: 0.45GU-7%air: Initial and Secondary Rates of Absorption Results

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Appendix 133

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Appendix 134

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Appendix 135

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Appendix 136

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Appendix 137

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Appendix 138

Mix 8: 0.45GU-8%airV Initial and Secondary Rates of Absorption

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Appendix 139

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Appendix 140

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Appendix 141

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Appendix 142

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Appendix 143

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Appendix 144

Mix 3: 0.38GU-5.5%air Initial and Secondary Rates of Absorption Results

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Appendix 145

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Appendix 146

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Appendix 147

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Appendix 148

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Appendix 149

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Appendix 150

Mix 4: 0.38HSF-8%air Initial and Secondary Rates of Absorption Results

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Appendix 151

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Appendix 152

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Appendix 153

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Appendix 154

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Appendix 155

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Appendix 156

Appendix D: Scanned Images

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Mix 1: 0.55GU-5.2%air

Slump: 90mm Depth (mm)

Trowel-Finished Form-Finished

0

5

10

20

Appendix 157

Ardavan
Typewritten Text
Ardavan
Typewritten Text
Ardavan
Typewritten Text
Ardavan
Typewritten Text
Ardavan
Typewritten Text
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Mix 1: 0.55GU-5.2%air B&W

Slump: 90mm Depth (mm)

Trowel-Finished Form-Finished

0

5

10

20

Appendix 158

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Mix 5: 0.45GU-2%air

Slump: 120mm Depth (mm)

Trowel-Finished Form-Finished

0

5

10

20

Appendix 159

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Mix 5: 0.45GU-2%air B&W

Slump: 120 Depth (mm) Trowel-Finished Form-Finished

0

5

10

20

Appendix 160

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0.45GU-3.5%air

Slump: 110 mm Depth (mm)

Trowel-Finished Form-Finished

0

5

10

20

Appendix 161

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0.45GU-3.5%air B&W

Slump: 110 mm Depth (mm) Trowel-Finished Form-Finished

0

5

10

20

Appendix 162

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0.45GU-5.6%air

Slump: 160 mm Depth (mm)

Trowel-Finished Form-Finished

0

5

10

20

Appendix 163

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Appendix 164

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RED 0.45GU-6.4%air

Slump: 112 mm Depth (mm)

Trowel-Finished Form-Finished

0

5

10

20

Appendix 165

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Appendix 166

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0.45GU-7%air

Slump: 150 mm Depth (mm)

Trowel-Finished Form-Finished

0

5

10

20

Appendix 167

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0.45GU-7%air

Slump: 150 mm Depth (mm) Trowel-Finished Form-Finished

0

5

10

20

Appendix 168

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0.45GU-8%airV

Slump: 175mm Depth (mm)

Trowel-Finished Form-Finished

0

5

10

20

Appendix 169

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0.45GU-8%airV

Depth (mm)

Trowel-Finished Form-Finished

0

5

10

20

Appendix 170

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0.38GU-5.5%air

Slump: mm Depth (mm)

Trowel-Finished Form-Finished

0

5

10

20

Appendix 171

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0.38GU-5.5%air

Slump: 65mm

Depth (mm)

Trowel-Finished Form-Finished

0

5

10

20

Appendix 172

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0.38HSF-8%air

Slump: 77 mm Depth (mm)

Trowel-Finished Form-Finished

0

5

10

20

Appendix 173

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Appendix 174

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Appendix 175

Appendix E: Raw Analysis Results from Duplicate Samples

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Raw Results Duplicate Samples

Mix 1: 0.55GU‐5.2%air

File NameDepth Under Surface (mm)

Initial Rate of Abs (mm/sec1/2)

Difference Initial Rate of Abs. (%) b/t Duplicates

Mean Aggregate Fraction

Difference Aggregate Fraction (%) b/t 

Duplicates

Hardedend Air content (%)

Difference Air Content  (%) b/t 

DuplicatesPaste Content

Difference Paste Content   (%) b/t 

Duplicates

10Mix1SF11 0.0049 0 0 14Mix1SF21 0.0040 0 0 18Mix1SF12 0.0046 0.7126 4.35 0.243915Mix1SF22 0.0051 0.6853 2.28 0.264614MiX1SF13 0.0054 0.6747 3.96 0.285716Mix1SF23 0.0054 0.6912 3.3 0.27586Mix1SF14 0.0045 0.6687 4.55 0.285813Mix1SF24 0.0048 0.6335 3.73 0.3292

2Mix1FF11 0.0045 0 0 112Mix1FF21 0.0043 0 0 11Mix1FF12 0.0044 0.67 3.07 0.29937Mix1FF22 0.0042 0.7146 4.14 0.2449Mix1FF13 0.0049 0.7425 3.45 0.22311Mix1FF23 0.0050 0.7237 2.54 0.25095Mix1FF14 0.0051 0.6788 3.11 0.29013Mix1FF24 0.0050 0.654 2.97 0.3163Average 3% 1% 9% 4%Max 19% 5% 48% 18%Min ‐9% ‐7% ‐35% ‐15%

 Mix 5: 0.45GU‐2%air

File NameDepth Under Surface (mm)

Initial Rate of Abs (mm/sec1/2)

Difference Initial Rate of Abs. (%) b/t Duplicates

Mean Aggregate Fraction

Difference Aggregate Fraction (%) b/t 

Duplicates

Hardedend Air content (%)

Difference Air Content  (%) b/t 

DuplicatesPaste Content

Difference Paste Content   (%) b/t 

Duplicates

15Mix5SF11 0.0041 0 0 18Mix5SF21 0.0043 0 0 12Mix5SF12 0.0043 0.694 1.1 0.29514Mix5SF22 0.0041 0.6376 0.95 0.352911Mix5SF13 0.0044 0.6449 1.19 0.34321Mix5SF23 0.0046 0.642 1.14 0.34665Mix5SF14 0.0048 0.5978 1.83 0.38396Mix5SF24 0.0047 0.6236 0.97 0.3667

13Mix5FF11 0.0036 0 0 116Mix5FF21 0.0034 0 0 112Mix5FF12 0.0042 0.6371 1.06 0.35234Mix5FF22 0.0040 0.7012 1.09 0.28799Mix5FF13 0.0036 0.683 1.24 0.304610Mix5FF23 0.0034 0.6879 1.51 0.2977Mix5FF14 0.0040 0.7706 1.29 0.21653Mix5FF24 0.0042 0.6497 1 0.3403Average 2% 2% 7% 6%Max 6% 16% 47% 18%Min ‐5% ‐10% ‐22% ‐57%

0%

‐8%

3%

‐15%

0%

18%

‐13%

‐9%

0%

‐20%

‐1%

4%

18%

2%

‐57%22%

0%

48%

17%

18%

0%

‐35%

26%

5%

0%

14%

4%

47%

‐3%

‐22%

8%

0%

‐4%

‐10%

‐1%

16%

0%

4%

‐2%

5%

0%

‐7%

3%

4%

0%

3%

4%

4%

6%

‐5%

19%

‐9%

1%

‐8%

4%

3%

‐1%

2%

‐5%

5%

‐4%10

20

0

5

10

20

Trowel‐ Finished

Form‐Finished

10

20

0

5

10

20

0

5

0

5Trowel‐ Finished

Form‐Finished

Appendix 176

Page 187: Effect of Surface Finish on Concrete Properties · 2013-12-05 · 2.3.2 Measuring Fresh Air Content ... slabs were made in order to test the effect of the surface finish on concrete

 Mix 6: 0.45GU‐3.5%air

File NameDepth Under Surface (mm)

Initial Rate of Abs (mm/sec1/2)

Difference Initial Rate of Abs. (%) b/t Duplicates

Mean Aggregate Fraction

Difference Aggregate Fraction (%) b/t 

Duplicates

Hardedend Air content (%)

Difference Air Content  (%) b/t 

DuplicatesPaste Content

Difference Paste Content   (%) b/t 

DuplicatesMix 6SF11 0.0043 0 0 1Mix6SF21 0.0039 0 0 1Mix6SF12 0.0039 0.0499 2.08 0.3796Mix6SF22 0.0040 0.0376 1.88 0.34Mix6SF13 0.0043 0.0453 2.2 0.3574Mix6SF23 0.0042 0.0533 2.6 0.3744Mix6SF14 0.0046 0.0791 2.25 0.3154Mix6SF24 0.0044 0.0688 4.53 0.376

Mix6FF11 0.0042 0 0 1Mix6FF21 0.0041 0 0 1Mix6FF12 0.0047 0.637 2.69 0.3338Mix6FF22 0.0034 0.0726 2 0.2762Mix6FF13 0.0039 0.0441 2.61 0.2842Mix6FF23 0.0036 0.0847 2.09 0.2617Mix6FF15 0.0037 0.0512 2.15 0.3822Mix6FF24 0.0045 0.0621 2.54 0.3375

Average 4% 15% 11% 4%Max 26% 89% 26% 17%Min ‐20% ‐92% ‐101% ‐19%

 Mix 2: 0.45GU‐5.6%air

File NameDepth Under Surface (mm)

Initial Rate of Abs (mm/sec1/2)

Difference Initial Rate of Abs. (%) b/t Duplicates

Mean Aggregate Fraction

Difference Aggregate Fraction (%) b/t 

Duplicates

Hardedend Air content (%)

Difference Air Content  (%) b/t 

DuplicatesPaste Content

Difference Paste Content   (%) b/t 

Duplicates

9Mix6SF11 0.0063 0 0 115Mix6SF21 0.0064 0 0 111Mix6SF12 0.0074 0.5848 4.45 0.37077Mix6SF22 0.0066 0.6742 4.56 0.28022Mix6SF13 0.0068 0.6451 4.87 0.306216Mix6SF23 0.0073 0.5237 5.24 0.42394Mix62SF14 0.0073 0.5784 6.17 0.359912Mix6SF24 0.0061 0.6031 4.26 0.3543

8Mix6FF11 0.0048 0 0 113Mix6FF21 0.0061 0 0 16Mix6FF12 0.0051 0.6771 4.39 0.2791Mix6FF22 0.0052 0.7135 4.52 0.241310Mix6FF13 0.0047 0.7234 4.01 0.23653Mix6FF23 0.0050 0.7079 4.57 0.24645Mix6FF14 0.0056 0.6316 3.75 0.330914Mix6FF24 0.0065 0.6267 4.39 0.3294Average 5% 3% 4% 5%Max 16% 19% 31% 24%Min ‐28% ‐15% ‐17% ‐38%

2%

0%

14%

‐4%

0%

‐19%

0%

17%

8%

12%

0%

24%

‐38%

10%

‐5%

‐17%

‐18%

0%

‐2%

‐8%

31%

0%

‐3%

‐14%

10%

‐18%

‐101%

0%

26%

20%

19%

‐4%

0%

‐5%

2%

1%

‐18%

13%

0%

89%

‐92%

‐21%

0%

‐15%

25%

‐2%

10%

‐8%

16%

‐28%

‐3%

‐7%

‐16%

8%

‐2%

3%

4%

1%

26%

8%

‐20%

10

20

0

5

10

20

5

0

5

Form‐Finished

Trowel‐ Finished

Form‐Finished

Trowel‐ Finished

10

20

0

5

10

20

0

Appendix 177

Page 188: Effect of Surface Finish on Concrete Properties · 2013-12-05 · 2.3.2 Measuring Fresh Air Content ... slabs were made in order to test the effect of the surface finish on concrete

 Mix Red 2: 0.45GU‐6.4%air

File NameDepth Under Surface (mm)

Initial Rate of Abs (mm/sec1/2)

Difference Initial Rate of Abs. (%) b/t Duplicates

Mean Aggregate Fraction

Difference Aggregate Fraction (%) b/t 

Duplicates

Hardedend Air content (%)

Difference Air Content  (%) b/t 

DuplicatesPaste Content

Difference Paste Content   (%) b/t 

Duplicates2Mix3RedFF11 0.0043 0.0000 0 13Mix3RedFF21 0.0043 0.0000 0 18Mix3RedFF12 0.0040 0.6510 4.62 0.3011Mix3RedFF22 0.0042 0.6011 3.92 0.365Mix3RedFF13 0.0047 0.6148 3.74 0.359Mix3RedFF23 0.0041 0.6501 3.67 0.316Mix3RedFF14 0.0047 0.5611 3.75 0.4010Mix3RedFF24 0.0043 0.6445 4.05 0.326Mix3RedFF15 0.5996 4.29 0.3610Mix3RedFF25 0.5811 4.56 0.37

Surface Finish 4Mix3RedSF11 0.0051 0.0000 0 11Mix3RedSF21 0.0044 0.0000 0 112Mix3RedSF12 0.0045 0.5603 5.22 0.3915Mix3RedSF22 0.0044 0.6038 4.66 0.357Mix3RedSF13 0.0049 0.5514 4.02 0.4114Mix3RedSF23 0.0047 0.6164 4.22 0.3416Mix3RedSF14 0.0040 0.6453 4.55 0.3113Mix3RedSF24 0.0042 0.6093 4.7 0.3416Mix3RedSF15 0.6203 3.66 0.3413Mix3RedSF25 0.5508 5.08 0.40

Average 2% 3% 4% 5%Max 13% 11% 15% 22%Min ‐5% ‐15% ‐39% ‐19%

 Mix 7: 0.45GU‐7%air

File NameDepth Under Surface (mm)

Initial Rate of Abs (mm/sec1/2)

Difference Initial Rate of Abs. (%) b/t Duplicates

Mean Aggregate Fraction

Difference Aggregate Fraction (%) b/t 

Duplicates

Hardedend Air content (%)

Difference Air Content  (%) b/t 

DuplicatesPaste Content

Difference Paste Content   (%) b/t 

Duplicates3Mix7SF11 0.0062 0 0 114Mix7SF21 0.0063 0 0 115Mix7SF12 0.0054 0.5486 4.42 0.407212Mix7SF22 0.0057 0.5881 4.67 0.365210Mix7SF13 0.0051 0.6031 4.34 0.35356Mix7SF23 0.0058 0.6673 5.82 0.274518Mix7SF14 0.0050 0.6041 4.9 0.346913Mix7SF24 0.0049 0.6255 4.56 0.3289

9Mix7FF1 0.0053 0 0 17Mix7FF21 0.0047 0 0 15Mix7FF12 0.0044 0.6981 4.11 0.260811Mix7FF22 0.0046 0.6157 6.02 0.32411Mix7FF13 0.0054 0.6227 5.4 0.32338Mix7FF23 0.0042 0.6469 3.7 0.316117Mix7FF14 0.0048 0.6096 5.45 0.335916Mix7FF24 0.0042 0.6267 4.99 0.3234Average 4% 2% 8% 4%Max 21% 12% 31% 22%Min ‐14% ‐11% ‐46% ‐24%

10%

22%

5%

0%

‐24%

2%

4%

22%

0%

10%

16%

‐11%

‐16%

0%

0%

‐19%

10%

‐46%

31%

8%

‐5%

‐3%

‐39%

0%

‐6%

‐34%

7%

0%

0%

15%

2%

‐8%

0%

11%

0%

12%

‐4%

‐3%

‐6%

‐15%

0%

‐8%

‐12%

6%

11%

0%

8%

‐1%

‐5%

13%

10%

13%

2%

3%

‐5%

0

5

10

20

30

10

20

0

5

10

20

0

5

0

5

10

20

30

Form‐Finished

Trowel‐ Finished

Form‐Finished

‐1%

‐4%

‐14%

1%

12%

‐5%

21%

13%

‐7%

‐11%

‐4%

0%

Appendix 178

Page 189: Effect of Surface Finish on Concrete Properties · 2013-12-05 · 2.3.2 Measuring Fresh Air Content ... slabs were made in order to test the effect of the surface finish on concrete

 Mix 8:0.45GU‐8%airV

File NameDepth Under Surface (mm)

Initial Rate of Abs (mm/sec1/2)

Difference Initial Rate of Abs. (%) b/t Duplicates

Mean Aggregate Fraction

Difference Aggregate Fraction (%) b/t 

Duplicates

Hardedend Air content (%)

Difference Air Content  (%) b/t 

DuplicatesPaste Content

Difference Paste Content   (%) b/t 

Duplicates19Mix8SF11 0.0057 0 0 125Mix8SF21 0.0057 0 0 122Mix8SF12 0.0053 0.6514 6.96 0.27930Mix8SF22 0.0065 0.568 8.21 0.349920Mix8SF13 0.0060 0.641 7.01 0.288929Mix8SF23 0.0060 0.608 11.13 0.280732Mix8SF14 0.0054 0.5915 6.5 0.343531Mix8SF24 0.0063 0.6134 7.63 0.3092

26Mix8FF11 0.0051 0 0 128Mix8FF21 0.0048 0 0 118Mix8FF12 0.0043 0.6912 5.93 0.249521Mix8FF22 0.0052 0.7041 6.1 0.234923Mix8FF13 0.0059 0.6591 8.47 0.256224Mix8FF23 0.0049 0.6154 6.87 0.315927Mix8FF14 0.0055 0.5781 8.29 0.33917Mix8FF24 0.0053 0.6019 7.03 0.3278Average 5% 2% 8% 4%Max 16% 13% 19% 10%Min ‐23% ‐4% ‐59% ‐25%

File NameDepth Under Surface (mm)

Initial Rate of Abs (mm/sec1/2)

Difference Initial Rate of Abs. (%) b/t Duplicates

Mean Aggregate Fraction

Difference Aggregate Fraction (%) b/t 

Duplicates

Hardedend Air content (%)

Difference Air Content  (%) b/t 

DuplicatesPaste Content

Difference Paste Content   (%) b/t 

Duplicates4Mix3SF11 0.0025 0 0 11Mix3SF21 0.0024 0 0 113Mix3SF12 0.0031 0.6629 3.52 0.3010Mix3SF22 0.0031 0.6660 3.71 0.3011Mix3SF13 0.0030 0.6097 4.55 0.345Mix3SF23 0.0029 0.6749 6.18 0.2612Mix3SF14 0.0030 0.5669 6.97 0.366Mix3SF24 0.0029 0.6558 4.73 0.30

2Mix3FF11 0.0028 0 0 13Mix3FF21 0.0030 0 0 18Mix3FF12 0.0026 0.7030 2.82 0.279Mix3FF22 0.0030 0.7288 4.79 0.2216Mix3FF13 0.0031 0.6338 3.26 0.337Mix3FF23 0.0034 0.7085 4.48 0.2514Mix3FF14 0.0030 0.6522 4.7 0.3015Mix3FF24 0.0032 0.6743 4.27 0.28Average 3% 3% 11% 5%Max 5% 0% 32% 26%Min ‐17% ‐16% ‐70% 0%

2%

24%

18%

0%

17%

26%

6%

‐25%

3%

10%

0%

6%

‐23%

3%

0%

0%

‐3%

19%

15%

0%

‐5%

‐36%

32%

0%

‐70%

‐37%

9%

0%

‐18%

‐59%

‐17%

0%

‐16%

0%

‐4%

‐12%

‐3%

0%

13%

5%

‐4%

0%

‐2%

7%

‐4%

0%

0%

‐11%

4%

0%

5%

5%

‐9%

‐17%

‐11%

‐5%

1%

‐23%

0%

‐17%

6%

‐22%

16%

4%

10

20

0

5

10

20

10

20

0

5

10

0

5

0

5Trowel‐ Finished

Form‐Finished

20

Form‐Finished

Trowel‐ Finished

Appendix 179

Page 190: Effect of Surface Finish on Concrete Properties · 2013-12-05 · 2.3.2 Measuring Fresh Air Content ... slabs were made in order to test the effect of the surface finish on concrete

 Mix 4:0.38HSF‐8%air

File NameDepth Under Surface (mm)

Initial Rate of Abs (mm/sec1/2)

Difference Initial Rate of Abs. (%) b/t Duplicates

Mean Aggregate Fraction

Difference Aggregate Fraction (%) b/t 

Duplicates

Hardedend Air content (%)

Difference Air Content  (%) b/t 

DuplicatesPaste Content

Difference Paste Content   (%) b/t 

Duplicates1Mix4SF11 0.0028 0 0 16Mix4SF21 0.0023 0 0 112Mix4SF12 0.0029 0.6179 7.57 0.306413Mix4SF22 0.0021 0.6788 4.47 0.27653Mix4SF13 0.0032 0.6087 5.69 0.334416Mix4SF23 0.0023 0.6648 5.43 0.28094Mix4SF24 0.0033 0.64273 4.89 0.29558Mix4SF14 0.0025 0.6556 7.53 0.282

10Mix4FF11 0.0022 0 0 15Mix4FF21 0.0024 0 0 12Mix4FF12 0.0026 0.6597 6.47 0.275611Mix4FF22 0.0022 0.6579 5.27 0.28949Mix4FF13 0.0023 0.6084 7.88 0.312814Mix4FF23 0.0022 0.6709 5.45 0.274615Mix4FF14 0.0025 0.5946 6.76 0.33787Mix4FF24 0.0025 0.6642 5.6 0.2798Average 8% 3% 10% 4%Max 28% 0% 41% 17%Min ‐11% ‐12% ‐54% ‐5%

16%

5%

0%

‐5%

12%

17%

0%

10%

31%

41%

5%

‐54%

0%

19%

17%

0%

‐10%

0%

‐9%

‐2%

0%

0%

‐10%

‐12%

26%

28%

23%

‐11%

17%

4%

3%

18%

10

20

0

5

10

20

0

5Trowel‐ Finished

Form‐Finished

Appendix 180