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
ii
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.
iii
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.
iv
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
v
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
vi
Chapter 5 Conclusions and Recommendations ............................................................................. 77
5 Conclusions .............................................................................................................................. 77
5.1 Recommendations ............................................................................................................. 79
References ..................................................................................................................................... 80
Appendices .................................................................................................................................... 86
vii
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
viii
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
ix
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
x
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
1
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
2
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.
3
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
4
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)
5
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
6
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).
7
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
8
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.
9
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).
10
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).
11
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
12
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.
13
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.
14
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).
15
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.
16
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
17
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).
18
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
19
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
20
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).
21
(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
22
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
23
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
24
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).
25
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.
26
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%.
27
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
28
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.
29
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
30
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.
31
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
32
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
33
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.
34
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.
35
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
36
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.
37
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
38
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.
39
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.
40
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.
41
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.
42
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.
43
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
44
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.
45
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:
46
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
47
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.
48
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.
49
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
50
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
51
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.
52
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
53
Figure 17: Initial Rate of Absorption of Trowel-Finished Samples
Figure 18: Initial Rate of Absorption of Formed-Finished Samples
54
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.
55
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
56
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
57
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
58
Figure 20: Initial Rate of Absorption at 5mm below Surface
Figure 21: Initial Rate of Absorption at 10mm below Surface
59
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.
60
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
61
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
62
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
63
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
64
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.
65
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.
66
Figure 29: Distribution of Aggregates in Trowel-Finished Slabs
Figure 30: Distribution of Aggregates in Form-Finished Slabs
67
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
68
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
69
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%
70
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
71
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
72
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
73
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.
74
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
75
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.
76
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%
77
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
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
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.
80
References
American Concrete Institute C301. (2010). ACI 301-10 Specifications for Structural Concrete.
Farmington Hills: ACI.
American Concrete Institute C302. (2004). ACI 302: Guide for Concrete Floor and Slab
Construction. Farmington Hills: ACI.
Ansari, F., Zhang, Z., Szary, P., & Maher, A. (2002). Effects of Synthetic Air Entraining Agents
on Compressive Strength of Portland Cement Concrete Mechanisms of Interaction and
Remediation Strategy. Chicago: New Jersey Department of Transportation.
ASTM International. (2004). Standard Test Method for Measurement of Rate of Absorption of
Water by Hydraulic-Cement Concretes. Pennsylvania: ASTM International.
Basheer, P. A., & Nolan, E. (2001). Near-Surface Moisture Gradients and in-situ Permeation
Tests. Construction and Building Materails, 15, 105-114.
Bentz, D. P., Clifton, J. R., Ferraris, C. F., & Garboczi, E. J. (1999). Transport Properties and
Durability of Concrete: Literature Review and Research Plan. Gaithersburg: NIST.
Canadian Standards Association. (2009). CSA A23.1-09 Concrete materials and methods of
concrete construction/Test methods and standard practices for concrete. Ottawa: CSA.
Cao, H., Bucea, L., Khatri, P., & Siriviva, V. (2001). The Resistance of Mortar with
Supplementary Cementitious Materials to Caustic Attack. Retrieved 3 23, 2012, from
International Concrete Research & Information Portal:
http://www.concrete.org/PUBS/JOURNALS/AbstractDetails.asp?ID=10507
Carlson , J., Sutter , L., Peterson, K., & Van Dam, T. (2005). An Update on Application of a
Flat-Bed Scanner for Performing ASTM C 457. Proceedings, 27th International
Conference on Cement Microscopy. Victoria.
Carlson, J. (2005). Advancement on the Application of a Flat-Bed Scanner forHardened
Portland Cement Concrete Air Void Analysis. Houghton: Michigan Technological
University, PhD Thesis
81
Cerny, R., & Rovnanikova, P. (2002). Transport Processes in Concrete. Spon Press: New York.
Chatterji, S., & Gudmundsson, H. (1977). Characterization of Entrained Air Bubble Systems in
Concrete by Means of an Image Analysing Microscope. Cement and Concrete Research,
7(4), 423-428.
Chidiac, S. E., Panesar, D. K., & Zibara, H. (2012). The effect of short duration NaCl exposure
on the surface pore structure of concrete containing GGBFS. Materials and Structures, 8,
1245-1258.
De Larrard, F. (1999). Concrete Mixture Proportioning. CRC Press: New York City
DeSouza, S. J. (1996). Test methods for the evaluation of the durability of covercrete. University
of Toronto, Civil Engineering. Toronto: University of Toronto, MASc Thesis.
DeSouza, S.J, Hooton, R.D, & Bickley, J. (1997). Evaluation of Labratory Drying Procedures
Relevant to Field Conditions for concrete Sorptivity Measurements. Cement, Concrete
and Aggregates, 19(2). 59-63
Dewar, J.D. (1985). Testing concrete for durability. Concrete Magazine, 19(7), 19-21.
Dhir, R. K., Hewlett, P. C., & Chan, Y. N. (1991). Near-surface characteristics of concrete:
abrasion resistance. Materials and Structures, 24, 122-128.
Fine Homebuilding. (2003). Foundations and Concrete Work. Newton: Taunton Press.
Gerdes, A., Wittmann, F. H., & Lehmann, E. (1999). Characterisation Of Transport Processes
In Surface Near Zones Of Concrete By Means Of Neutron Radiography. ETH. Zurich:
PSI Annual Report Annex VI.
Germann Instruments. (2010). Merlin Brochures. Retrieved 12 5, 2012, from Germann
Instruments: http://www.germann.org/Brochures/Merlin.pdf
Gummerson, R. J., Hall, C., & Hoff, W. D. (1980). Water movement in porous building
materials-II. Building and Environment, 15(2), 101-108.
82
Hall, C. (1989). Water Sorptivity of Mortars and Concretes: A Review. Magazine of Concrete
Research, 41(147), 51-61.
Hanzic, L., Kosec, L., & Anzel, I. (2010). Capillary Absorption in concrete and the Lucas-
Washburn Equation. Cement and Concrete Composites, 32(1), 84-91.
Hearn, N., Hooton, D. R., & Nokken, M. R. (2006). Pore Structure, Permeability, and
Penetration Resistance Characteristics of Concrete. In J. F. Lamond, & P. Klieger (Eds.),
Significance of Tests and Properties of Concrete and Concrete-Making Materials (pp.
244-245). New Jersey: ASTM International Technical Publication.
Ho, D., & Lewis, R. (1984). Concrete Quality as Measured by Concrete Sorptivity. Civil
Engineering Transactions, 4, pp. 306-313.
Hooton, R.D. (2006). Testing and Standards Related to Fluid and Chemical Transport. Toronto,
Canada: University of Toronto: Civ514 Lecture Notes.
Iowa Department of Transportation. (2013). Why Air Entrainment is Important to Concrete.
Retrieved 7 15, 2013, from Iowa Department of Transportation:
http://www.iowadot.gov/construction/pcc/air.pdf
Judd, D. B., & Wyszecki, G. (1975). Color in Business, Science and Industry. New York: Wiley-
Interscience.
Kreijer, P. (1984). The Skin of Concrete: Composition and Properties. Materials and Structures,
17(4), 275-283.
Kucharczyková, B., Misák, P., & Vymazal, T. (2010). Determination and Evaluation of the Air
Permeability Coefficient Using Torrent Permeability Tester. Russian Journal of
Nondestructive Testing, 46(3), 226-233.
Lampacher, B. J., & Blight, G. E. (1998). Permeability and Sorption Properties of Mature Near-
Surface Concrete. Journal of Materials in Civil Engineering, 10, 21-25.
Lane, S. (2012). Concrete Permeability Testing – Part 2. Retrieved 2 24, 2012, from HPC
Bridge Views: http://www.hpcbridgeviews.com/i59/Article4.asp
83
Licheng , W., & Uedab, T. (2011). Mesoscale Modeling of Water Penetration Into Concrete by
Capillary Absorption. Ocean Engineering, 38(4), 519-528.
McCarter, W.J. (1993). Influence of Surface Finish on Sorptivity on Concrete. Journal of
Materials in Civil Engineering, 5(1), 130–136.
McCarter, W.J. (1996). Monitoring the Influence of Water and Ionic Ingress on Cover-Zone
Concrete Subjected to Repeated Absorption. Cement, Concrete and Aggregates, 18(1),
55-63.
McCarter, W. J., Ezirim, H., & Emerson, M. (1992). Absorption of water and chloride into
concrete. Magazine of Concrete Research, 44(158), 31 –37.
Microanalysis Consultants Ltd. (2012). Sulfate attack in concrete and mortar. Retrieved 3 20,
2012, from Understanding Cement : http://www.understanding-cement.com/sulfate.html
Nokken, M., & Hooton, R.D. (2002). Dependence of Rate of Absorption on Degree of Saturation
of Concrete. West Conshohocken, PA: ASTM International.
Pade , C., Jacobsen, H., & Elsen , J. (2002). A New Automatic Analysis System for Analyzing
the Air void system in Hardened Concrete. (pp. 204-213). San Diego: Proceedings of the
International Cement Microscopy Association.
Parrott, L. J. (1992). Variations of Water Absorption Rate and Porosity with Depth from an
Exposed Concrete Surface: Effects of Exposure Conditions and Cement Type. Cement
and Concrete Research, 22(6), 1077–1088.
Parrott, L. J. (1992). Water Absorption in Cover Concrete. Materials and Structures, 25, 284-
292.
Parrott, L. J. (1994). Mositure Conditioning and Transport Properties of Concrete Test
Specimens. Materials and Structures, 27, 460-468.
Peterson, K. (2002). Automated Air-void System Characterization of Hardened Concrete:
Helping Computers to Count Air-voids Like People Count Air-voids---Methods for
84
Flatbed Scanner Calibration. Michigan: Michigan Technology University, Ph.D.
Dissertation.
Pigeon, M., & Pleau, R. (1995). Durability of Concrete in Cold Climates. Abingdon: Taylor and
Francis.
Pleau , R., Pigeon , M., & Laurencot , J. (2001). Some Findings on the Usefulness of Image
Analysis for Determining the Characteristics of the Air-Void System on Hardened
Concrete. Cement and Concrete Composites, 23, pp. 247-254.
Portland Cement Association. (2012). Corrosion of Embedded Metals. Retrieved 3 20, 2012,
from Portland Cement Association: http://www.cement.org/tech/cct_dur_corrosion.asp
Poulsen, E., & Mejlbro, L. (2005). Diffusion of Chloride in Concrete: Theory and Application.
Abingdon: CRC Press.
Powers, T.C. (1939). The Bleeding of Portland Cement Paste. ACI Journal, 35, 465-479.
Powers, T.C. (1968). The Properties of Fresh Concrete. John Wiley & Sons Inc.
Price, W. F., & Widdows, S. J. (1991). The Effects of Permeable Formwork on the Surface
Properties of Concrete. Magazine of Concrete Research, 43(155), 93-104.
Samuelsson, P. (1970). Voids in Concrete Surfaces. American Concrete Institute Journal,
67(11), 868-874.
Senbetta, E. (1981). Development of a Laboratory Technique to Quantify Concrete Curing.
Purdue University: JTRP Technical Report.
Simon, M. J. (2005). An Interlab Evaluation of the Variability in the ASTM C457 Linear
Traverse Method. Missouri Department of Transportation.
Snyder, K., Natesaiyer, K., & Hover, K. (2001). The Stereological and Statistical Properties of
Entrained Air Voids in Concrete: A Mathematical Basis For Air Void System
Characterization. Materials Science of Concrete, 129-214.
85
Stanish, K., Hooton, R., & Thomas, M. (2000). Testing the Chloride Penetration Resistance of
Concrete: A Literature Review. Toronto: University of Toronto, Report to FHWA.
Tumidajski, P. J. (2006). Effect of Slag, Silica Fume, and Finishing on the Sorptivities of Field
Concrete. Canadian Journal of Civil Engineering, 33, 1022-1026.
Tutti, K. (1982). Corrosion of steel in concrete. Stockholm: Swedish Cement and Concrete
Research Institute.
WHD Microanalysis Consultants Ltd. (2013). Carbonation of concrete. Retrieved 7 15, 2013,
from http://www.understanding-cement.com/carbonation.html
Whiting, D., & Nagi, M. (1998). Manual on Control of Air Content in Concrete. Portland
Cement Association.
Wilson, M. A., Taylor, S. C., & Hoff, W. D. (1998). The Initial Surface Absorption Test (ISAT):
an Analytical Approach. Magazine of Concrete Research, 50(2), 179-185.
Wright, P. (1953). Entrained Air in Concrete. 2, pp. 337-358. ICE Proceedings.
Appendix 86
Appendices
Appendix A: Material Properties Tables
Appendix 87
Physical and Chemical Composition GU cement
Appendix 88
Physical and Chemical Composition GranCem (Slag)
Appendix 89
Composition and Properties of Chameleon Liquid Red Iron Oxide A1070
Trace Metal Content in Parts Per Million (ppm)
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
Appendix 91
Appendix B: Detailed Concrete Mixture Design
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
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)
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)
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.
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
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
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.
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.
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
Appendix 101
Appendix C: Initial and Secondary Rates of Absorption Results
Appendix 102
Mix 1: 0.55GU-5%air Initial and Secondary Rates of Absorption Results
Appendix 103
Appendix 104
Appendix 105
Appendix 106
Appendix 107
Appendix 108
Mix 5: 0.45GU-2%air Initial and Secondary Rates of Absorption Results
Appendix 109
Appendix 110
Appendix 111
Appendix 112
Appendix 113
Appendix 114
Mix 6: 0.45GU-3.5%air Initial and Secondary Rates of Absorption Results
Appendix 115
Appendix 116
Appendix 117
Appendix 118
Appendix 119
Appendix 120
Mix 2: 0.45GU-5.6%air Initial and Secondary Rates of Absorption
Appendix 121
Appendix 122
Appendix 123
Appendix 124
Appendix 125
Appendix 126
Mix 2Red: 0.45GU-6.4%air Initial and Secondary Rates of Absorption
Appendix 127
Appendix 128
Appendix 129
Appendix 130
Appendix 131
Appendix 132
Mix 7: 0.45GU-7%air: Initial and Secondary Rates of Absorption Results
Appendix 133
Appendix 134
Appendix 135
Appendix 136
Appendix 137
Appendix 138
Mix 8: 0.45GU-8%airV Initial and Secondary Rates of Absorption
Appendix 139
Appendix 140
Appendix 141
Appendix 142
Appendix 143
Appendix 144
Mix 3: 0.38GU-5.5%air Initial and Secondary Rates of Absorption Results
Appendix 145
Appendix 146
Appendix 147
Appendix 148
Appendix 149
Appendix 150
Mix 4: 0.38HSF-8%air Initial and Secondary Rates of Absorption Results
Appendix 151
Appendix 152
Appendix 153
Appendix 154
Appendix 155
Appendix 156
Appendix D: Scanned Images
Mix 1: 0.55GU-5.2%air
Slump: 90mm Depth (mm)
Trowel-Finished Form-Finished
0
5
10
20
Appendix 157
Mix 1: 0.55GU-5.2%air B&W
Slump: 90mm Depth (mm)
Trowel-Finished Form-Finished
0
5
10
20
Appendix 158
Mix 5: 0.45GU-2%air
Slump: 120mm Depth (mm)
Trowel-Finished Form-Finished
0
5
10
20
Appendix 159
Mix 5: 0.45GU-2%air B&W
Slump: 120 Depth (mm) Trowel-Finished Form-Finished
0
5
10
20
Appendix 160
0.45GU-3.5%air
Slump: 110 mm Depth (mm)
Trowel-Finished Form-Finished
0
5
10
20
Appendix 161
0.45GU-3.5%air B&W
Slump: 110 mm Depth (mm) Trowel-Finished Form-Finished
0
5
10
20
Appendix 162
0.45GU-5.6%air
Slump: 160 mm Depth (mm)
Trowel-Finished Form-Finished
0
5
10
20
Appendix 163
Appendix 164
RED 0.45GU-6.4%air
Slump: 112 mm Depth (mm)
Trowel-Finished Form-Finished
0
5
10
20
Appendix 165
Appendix 166
0.45GU-7%air
Slump: 150 mm Depth (mm)
Trowel-Finished Form-Finished
0
5
10
20
Appendix 167
0.45GU-7%air
Slump: 150 mm Depth (mm) Trowel-Finished Form-Finished
0
5
10
20
Appendix 168
0.45GU-8%airV
Slump: 175mm Depth (mm)
Trowel-Finished Form-Finished
0
5
10
20
Appendix 169
0.45GU-8%airV
Depth (mm)
Trowel-Finished Form-Finished
0
5
10
20
Appendix 170
0.38GU-5.5%air
Slump: mm Depth (mm)
Trowel-Finished Form-Finished
0
5
10
20
Appendix 171
0.38GU-5.5%air
Slump: 65mm
Depth (mm)
Trowel-Finished Form-Finished
0
5
10
20
Appendix 172
0.38HSF-8%air
Slump: 77 mm Depth (mm)
Trowel-Finished Form-Finished
0
5
10
20
Appendix 173
Appendix 174
Appendix 175
Appendix E: Raw Analysis Results from Duplicate Samples
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
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
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
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
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
Top Related