CAPE COAST POLYTECHNIC

SCHOOL OF ENGINEERING

CIVIL ENGINEERING DEPARTMENT

COMPARING THE COMPRESSIVE STRENGTH OF CONCRETE

UTILIZING NATURAL POZZOLANA AS A PARTIAL

REPLACEMENT OF ORDINARY PORTLAND CEMENT IN

CONCRETE PRODUCTION

BY

ASARE OSEI SAMUEL

(02/07/0012/D/CVE)

ODOOM ANTHONY

(02/07/0029/D/CVE)

A PROJECT WORK SUBMITTED IN PARTIAL FULFILLMENT OF THE AWARD

OF CERTIFICATE IN HIGHER NATIONAL DIPLOMA (HND) IN CIVIL

ENGINEERING.

JUNE, 2010.

TABLE OF CONTENT

CONTENT PAGE

Declaration i

Certification ii

Dedication iii

Acknowledgement iv

List of Tables v

List of Figures vi

Abstract vii

CHAPTER ONE

1.0 introduction 1

1.1 Purpose of the study 1

1.2 statement of the problem 3

1.3 aim of the study 4

1.4 project objectives 4

1.5 significance 4

1.6 scope of the study 5

CHAPTER TWO

2.0 literature review 6

2.1 introduction 6

2.2 background 8

2.3 materials 12

2.3.1 Cement 12

2.3.2 Aggregate 14

2.4 concrete production 15

2.4.1 Proportioning and mixing concrete 16

2.4.2 Conveying 16

2.4.3 Placing 17

2.4.4 Curing 18

2.4.4.1 Curing methods 19

2.4.4.1.1 water cure 19

2.4.4.1.2 Water retaining method 19

2.4.4.1.3 Waterproof paper or plastic film seal 19

2.4.4.1.4 Chemical membranes 19

2.5 quality control 20

2.5.1 Slump test 21

2.5.2 Compaction factor test 22

2.6 pozzolana 23

2.6.1 Engineering properties of pozzolana 28

2.6.1.1 Fineness 28

2.6.1.2 Pozzolanic activity (chemical composition and mineralogy) 28

2.6.1.3 Loss on ignition 28

2.6.1.4 Moisture content 29

2.6.1.5 Workability 29

2.6.1.6 Time of setting 29

2.6.1.7 Bleeding 29

2.6.1.8 Pumpability 29

2.6.1.9 Strength development 29

2.6.1.10 Heat of hydration 30

2.6.1.11 Permeability 30

2.6.1.12 Resistance to freeze-thaw 30

2.6.1.13 Sulphate resistance 31

2.6.1.14 Alkali-silica reactivity 31

2.6.2 Advantages of the natural pozzolan 32

2.6.2.1 Litification 32

2.6.2.2 Autogenously healing 32

2.6.2.3 Reduced permeability and voids 32

2.6.2.4 Reduces expansion and heat of hydration 32

2.6.2.5 Reduces creep and cracks 33

2.6.2.6 Reduces microcracking 33

2.6.2.7 Increases compressive strength 33

2.6.2.8 Increases resistance to chloride attack 33

2.6.2.9 Increases resistance to sulphate attack 33

2.6.2.10 reduces alkali-aggregate reaction 34

2.6.2.11 protects steel reinforcement from corrosion 34

2.6.2.12 increases abrasion resistance 34

2.6.2.13 lowers water requirement with high fluidity, 34

Self-levelling and compression

2.6.2.14 improves durability 34

2.7 design considerations 35

2.7.1mix design 35

CHAPTER THREE

3.0 methodology 37

3.1 introduction 37

3.2 data collection 37

3.3 desk study 37

3.4 mix proportion 37

3.5 casting and curing 38

3.6 test procedures 38

3.6.1 Slump test 38

3.6.2 Setting times 38

3.6.3 Compressive strength 38

CHAPTER FOUR

4.0 Data Presentation and Analysis 39

4.1 Silt Test Results and Analysis 39

4.2 Properties of Fresh Concrete 44

4.2.1 Slump Test 44

4.2.2 Compaction Factor Test 47

4.3 Compressive Strength 56

CHAPTER FIVE

5.0 Conclusion and Recommendations 63

5.1 Conclusion 63

5.2 Recommendations 64

References 65

Appendices 66

i

DECLARATION

We the undersigned declare that this project work is the result of our own investigation

carried out on assessing the properties of concrete cubes utilizing natural pozzolana as a

partial replacement under the supervision of Mr Emmanuel Nana Jackson of Cape Coast

Polytechnic.

Name Signature Date

SAMUEL OSEI ASARE 2nd

July, 2010

ANTHONY ODOOM 2nd

July, 2010

nanakwame

anthony odoom

ii

CERTIFICATION

The appendix signature certifies that this project is an original work undertaken and presented

in accordance with the regulation governing the preparation and presentation of a project

work in cape coast polytechnic for acceptance of dissertation entitle study to assess the

properties of concrete cubes utilizing natural pozzolana as a partial replacement

This report is submitted by SAMUEL OSEI ASARE (02/07/0012/D/CVE) and ANTHONY

ODOOM (02/07/0029/D/CVE) to the department of civil engineering in partial fulfilment of

the requirement for the award of higher national diploma (HND) in Civil Engineering.

nana kackson 2nd

July, 2010

Mr Emmanuel Nana Jackson date

(Supervisor)

iii

DEDICATION

This project work is dedicated to the almighty God and the department of Civil Engineering,

Cape Coast Polytechnic.

iv

ACKNOWLEDGEMENT

Acknowledgement is due to the department of Civil Engineering, Cape Coast Polytechnic for

the use of the laboratory for the purpose of this work.

The investigators would also like to thank Mr Emmanuel Nana Jackson for his dedication and

assistance with the entire work as well to our families for their financial and morale support

and to all those who contributed immensely to the success of this work especially to Mr

Nathan Kofi Kakra Asare, (Sonitra Ghana), Mr Daniel Kofi Panyin Asare (MTN Ghana Ltd),

madam Felicia Adu, Evelyn Essel and to Madam Cecielia Mensah, Madam Veronica Odum,

and Michael Odoom.

The investigators are thankful to all staff of The Civil Engineering Department, Cape Coast

Polytechnic for their assistance in diverse ways for the successful completion of this project.

v

LIST OF TABLES

Table 2.1: chemical and physical analysis of cement 13

Table 4.1: Results of obtained from silt test conducted sand sample 39

Table 4.2: Mix proportion details 40

Table 4.3: Results of grading test for coarse aggregate 41

Table 4.4: Results of grading test for fine aggregate 42

Table 4.5: Slump properties of fresh concrete 45

Table 4.6: Results of Compaction factor test of concrete incorporating pozzolan 46

Table 4.7: Detail results of Compressive strength of concrete grade 20 at all ages 48

Table 4.8: compressive strength incorporating pozzolan at all ages of test 56

Table 4.9: A one sampe statistics standard deviation and standard error 61

mean for various concrete from 7 -28 days

Table 4.10: 95% Confidence Interval of the Difference for Various Concrete 61

From 7 -28 Days

Table 4.11: A Correlation Matrix for Various Concrete From 7 -28 Days 63

Table 4.12: An Explanation of the Total Variance of Concrete From 7 -28 Days 64

vi

LIST OF FIGURES

Fig. 4.1: Grading curve for coarse aggregate 41

Fig. 4.2: Grading curve for fine aggregate 43

Fig. 4.3 Effect of pozzolanic material on the slump of concrete 45

Fig. 4.4: Effect of pozzolanic material on the compaction factor of 46 concrete

Fig. 4.5: Effect of pozzolanic replacement on the compressive 58

strength of concrete at 7days Fig. 4.6: Effect of pozzolanic replacement on the compressive 58

strength of concrete at 14 days Fig. 4.7: Effect of pozzolanic replacement on the compressive 59

strength of concrete at 21 days Fig. 4.8: Effect of pozzolanic replacement on the compressive 59 strength of concrete at 28 days

Fig. 4.9: Effect of pozzolanic replacement on the compressive 60 strength of concrete at all ages

Fig. 4.10: line diagram illustrating the effect of pozzolanic replacement 60

on the compressive Strength of concrete at all ages

vii

RÉSUMÉ

Naturelles matériau pouzzolanique est disponible en sacs de 50kg de la construction et

l'institut de recherche routière (BRRI) au Ghana. Ce projet de recherche avait pour but l'étude

préliminaire de la performance du béton en utilisant le matériau naturel pouzzolanique.

Le matériau de la pouzzolane BRRI a été constituée dans le béton pour remplacer le ciment

partielle d'étudier les effets du niveau de remplacement sur le développement de la résistance

à la compression du béton à différents âges. Facteur Slump et le compactage du béton frais

ont également été mesurées.

Les résultats montrent que l'inclusion de pouzzolanes naturelles dans le béton pour remplacer

le ciment partielle ne nuit pas à des propriétés du béton frais. Son incorporation dans le béton

a augmenté de manière significative la résistance à la compression à tous les âges pour le

mélange de remplacement de pouzzolane 30% par rapport à d'autres mélanges. Une

augmentation de la force moyenne de 1,1 MPa a été enregistré à partir du test

Cependant remplacement partiel des mélanges de 70%, 60% et 80% de pouzzolane n'a pas

atteint la résistance de calcul de 20 N/mm2. Résistance à la compression et les essais

maniabilité suggéré que la pouzzolane, pourrait être remplacé par du ciment Portland jusqu'à

30% dans la fabrication de béton sans perte de maniabilité ou de force.

Afin d'améliorer le développement de la résistance, la réactivité pouzzolanique des

pouzzolanes pourrait être sensiblement améliorée / modifiée en utilisant un ou une

combinaison de plusieurs méthodes de traitement. Cependant, toutes les méthodes peut être

possible d'atteindre le niveau optimal. Par conséquent, il est fortement recommandé que,

outre employant diverses méthodes de traitement, l'applicabilité de faisabilité et pratiques de

chaque méthode doit être étudié en détail.

viii

ABSTRACT

Natural pozzolanic material is available in bags of 50kg from the building and road research

institute (BRRI) in Ghana. This research project was aimed preliminary study of the

performance of concrete utilizing the natural pozzolanic material.

The pozzolan material from the BRRI was incorporated in concrete as partial cement

replacement to study the effects of replacement level on the compressive strength

development of concrete at various ages. Slump and compaction factor of fresh concrete were

also measured.

The results show that the inclusion of natural pozzolana in the concrete as partial cement

replacement was not detrimental to for the properties of fresh concrete. Its incorporation in

the concrete increased the compressive strength significantly at all ages for the replacement

mix of 30% pozzolana as compared to other mixes. An average strength increase of 1.1 Mpa

was recorded from the test

However Partial replacement mixes of 70%, 60% and 80% pozzolana did not attain the

design strength of 20 N/mm2

. Compressive strength and workability tests suggested that

pozzolan, could be substituted for Portland cement at up to 30% in the manufacture of

concrete with no loss in workability or strength.

In order to enhance the strength development, the pozzolanic reactivity of pozzolans could be

significantly improved/modified by using one or a combination of several treatment methods.

However, not all methods may be feasible to achieve the optimum level. Therefore, it is

strongly recommended that, besides employing various treatment methods, the feasibility and

practical applicability of each method needs to be investigated in details.

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CHAPTER ONE

1.0 INTRODUCTION

1.1 PURPOSE OF THE STUDY

Manufacturing of Portland cement requires high energy and releases a very large amount of

green-house gases to the atmosphere; approximately 13,500 million tonnes is produced from

this process worldwide, which accounts for 7% of the green house gas produced annually

[Sumrerng Rukzon, 2009].

The use of pozzolana, especially waste pozzolana, to replace part of Portland cement is

therefore receiving a lot of attention. Historically, Pozzolans are named after the volcanic

additives used in mortar by the Romans.

Pozzolans are fine materials containing silica and/or alumina and while they do not have any

cementing properties of their own, in the presence of calcium oxide (CaO) or Calcium

Hydroxide (Ca(OH2), silica and alumina in the pozzolana reacts and form cementitious

material.

Ash from some agricultural by-products such as rice husk ash, bagasse ash and palm oil fuel

ash have been shown to be good Pozzolan.

Their uses are receiving more attention now since the properties of the blended cement

concrete using them are generally improved. In addition, they can also save the cost of

construction materials and reduce the negative environmental effects.

Palm oil fuel ash is one promising Pozzolans and is available in many parts of the world. It is

a by-product obtained from a small power plant, which uses the palm fibre, shells and empty

fruit bunches as fuels which are burnt at 800-1000°C. The main chemical composition of

palm oil fuel ash is silica, which is the main ingredient of pozzolanic material.

At present, palm oil fuel ash is sent to landfill which is a problem for all power plants

because it has not been proven useful yet and treated as a waste.

The use of pozzolana to replace part of Portland cement improves durability of concrete

through the pore refinement and the reduction of calcium hydroxide in the cement paste

- 2 -

matrix. Resistance to chloride penetration, acid solution attack, and sulphate attack of the

concrete containing Pozzolan is generally enhanced. The other important property, which

also influences the performance of concrete, is carbonation in steel reinforcement. The

ingress of carbon dioxide into the cement matrix results in a reduction in the ability of the

cement matrix to protect the steel reinforcement as the passive layer at the surface of the

reinforcing bars is destroyed. The carbonation is usually severe in the high carbon dioxide

environment and in the relatively dry or indoor environment of 50-60% relative humility

(RH). In particular when thin concrete sections, such as slabs and thin walls, are involved, the

concrete covering of steel reinforcements is small and protection of the steel reinforcement

by the cement matrix against penetration of carbon dioxide is much reduced. Although paint

and other surface covering of concrete surface can help reduce the carbonation, the modern

designs using dare concrete surfaces are often preferred.

The use of these agricultural by-products ashes as Pozzolan usually requires grinding to

produce relatively fine Pozzolana. Their use reduces the bulk density of the concrete

products, as their specific gravity is usually around 2.0-2.3, which is much lower than the

overall 3.15 of Portland cement. Other advantages are that the product is less stiff, which

gives better performance in terms of noise absorption and fire resistance [Sumrerng Rukzon,

2009]. The application of these materials in concrete for indoor use is therefore very

attractive. The fineness of the Pozzolan is known to have a large influence on the properties

of concrete through increase in the packaging effect and pozzolanic activity thus ultimately

improves the durability of the matrix through pore refinement and reduced Ca (OH) 2. The

parameter used to quantify this is the Blaine number, a surface area measurement that has

been used since the 1940s to determine cement quality.

Cement is responsible for 7% of the world’s total emission of CO2, which is a major green

house gas implicated in global warming. The addition of industrial waste and natural

resources such as slag, fly ash, silica fume or natural pozzolana to cement during

manufacturing contributes to a decrease in energy consumption and the amount of CO2

released into the air. Hence, low cost environmental friendly cement is obtained. Also, when

used as a concrete admixture, the amorphous silica present in these additives combined with

the calcium hydroxide liberated during the hydration of cement in concrete to form additional

cementitious compound, namely calcium silicate hydrate (CSH). The resultant binder matrix

is more chemically resistant by virtue of its denser microscopic pore structure.

- 3 -

A large number of studies have shown that different additions, when used as partial cement

replacement materials in mortar and concrete have many advantages but also some

disadvantages. [Nehdi, 2001].

It should be possible, by the systematic adjustment of the proportions to produce ternary

blended cement (OPC-NP-SF) which utilizes the desirable characteristics of one addition

which compensating for the undesirable characteristic of the other. For example, SF increase

the low early strength caused by the inclusion of NPJ and the NP decrease the high water

demand of SF. On the other hand, the best combined of these mineral additions, can lead to

excellent durability [Sumrerng Rukzon, 2009].

The objective of this research work is to access the strengths and durability of concrete using

a mixture of ordinary Portland cement and natural pozzolana. The result could be beneficial

to the understanding of the mechanism involve as well as future applications of these

materials in the construction industry based on the strengths and durability of concrete.

1.2 STATEMENT OF THE PROBLEM

The requirement for high durability concrete structures exposed to harsh environment such as

seafloors, offshore structures, tunnels, highway bridges, sewage pipes etc. cannot be easily

achieved using Ordinary Portland Cement. The phenomenon of the widespread deterioration

of concrete structures during the past two decades has become a matter of global concern.

The issue of ensuring long-term durability of concrete structures has therefore assumed great

importance.

As a result, new materials and composites are being investigated and improved cements are

produced. The present state of the art in concrete research has demonstrated the benefits of

pozzolanic materials as partial replacement. In addition, the use of pozzolanic materials

conserves energy and has environmental benefits as a result of the reduced use of cement (the

production of which is associated with high carbon dioxide emission).

Pozzolanic materials are divided into natural and by-product materials. By-product materials

are fly ash, slag and silica fumes whereas natural pozzolanic material is obtained from

volcanic rocks.

- 4 -

Since the past decade the use of pozzolanic materials in concrete is gaining impetus because

of its benefits. Most of the research has been concentrated on by-product pozzolanic materials

and little effort was dedicated to natural pozzolanic materials,

Regarding Ghana’s natural pozzolanic material, no information pertaining to engineering and

durability related properties is available. Therefore, there is a need to investigate and explore

the potential of this material for the use in concrete [Khan and Alhozaimy, 2005].

1.3 AIM OF THE STUDY

The aim of the study was to compare the strength of concrete using a mixture of pozzolana

and Ordinary Portland Cement (OPC) as a binder to that of OPC only in concrete production.

1.4 PROJECT OBJECTIVES

1. This project was intended to investigate the performance of locally available natural

pozzolanic material in the republic of Ghana.

2. To investigate the influence of the pozzolan on the properties of fresh concrete and

compressive strength development.

1.5 SIGNIFICANCE

The high economy associated with concrete works with the use of cement as a binder has

necessitated the study into the benefits of partial replacement of concrete with natural

pozzolanic material, which will reduce the effect of carbon-dioxide emission, increase

durability and reduce cost of production of concrete.

- 5 -

1.6 SCOPE OF THE STUDY

The area under study was Cape Coast Metropolitan Assembly and its environs in the Central

Region of Ghana. The materials for the study were all found in Cape Coast and its environs.

The laboratory tests were done in the Cape Coast Polytechnic Civil Engineering laboratory.

This research was strictly based on testing of concrete cubes with the mixture of pozzolana

and ordinary Portland cement and ordinary Portland cement only as binders. The research

was limited to testing of concrete cubes and the factors affecting the compressive strength of

concrete were accessed.

- 6 -

CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 INTRODUCTION

It is now well established that in order to produce a durable concrete, a dense homogeneous

concrete microstructure, especially in the interface region between hydrated paste and

aggregate, is required [Aitcin and Neville 1994]. The densification and homogeneity of the

interfacial region are achieved through the incorporation of natural and by-products

pozzolanic material. In addition, the incorporation of natural and by-product material in

concrete can significantly enhance its basic properties in both the fresh and hardened states.

Blended cements with mineral admixtures offer improved performance over that of ordinary

Portland cement with respect to microstructure and durability of concrete [Malhotra and

Mehta, 1996], [Gjorv, 1994].

The incorporation of pozzolanic materials in concrete reduces bleeding and segregation and

enhances cohesiveness of concrete, reduces heat evolution during hydration leading to lower

tendency for crack formation during hardening which is beneficial in mass concrete

application. The inclusion of natural pozzolana or slag or silica fume results in concrete with

reduced or similar permeability to that of plain concrete; such concrete increases the

resistance against chloride attack [Malhotra and Mehta, 1996] and performs satisfactorily

against Sulphate attack [Alhoziamy; Soroushian and Mirza, 1996].

The research on by-products material namely, natural pozzolana, slag and silica fume is well

documented while research on natural pozzolana is hardly available. Natural pozzolanic

material behaves in similar manner to that of by-product pozzolanic admixtures. It is reported

that natural pozzolanic material tends to increase the water demand. However, this excess

water is consumed by pozzolanic reaction at the later stages [Malhotra and Mehta, 1996].

Setting time of natural pozzolanic material is retarded as compared to ordinary Portland

cement concrete, as is the case in the by-product pozzolanic material. Due to the inference

provided by finely divided particles and the absorption by microporous, natural pozzolan

reduces the bleeding of concrete. This reduction in the internal bleeding improves the

interfacial zone of the concrete hence the strength of the concrete. [Mehta and Monteiro,

1995], [Neville, 1996].

- 7 -

The incorporation of natural pozzolanic materials delays the rate of strength development like

natural pozzolana and slag. It reported that the concrete mixes containing 10, 20 and 30%

natural pozzolanic material (Santorin earth) demonstrated less strength at 7 days as compared

to that of control mix. At 28 days, concrete with 10% replacement showed higher strength

than that of control mix. Further, the inclusion of natural pozzolanic material in concrete did

not demonstrate the significant change in drying shrinkage as compared to the control mix

[Mehta, 1981].

The addition of natural pozzolan enhances the hydration products of Portland cement;

however, the rate of enhancement depends on its characteristics. [Cook, 1986].

Pozzolanic material efficiently decreases the permeability, thereby increasing the resistance

of concrete to deterioration by aggressive chemicals such as chlorides [Malhotra and Mehta,

1996)]. Therefore, the incorporation of pozzolanic material in the concrete has become an

increasingly accepted practice in the construction of structures exposed to harsh

environments. Natural pozzolana is reported to have similar influence on the permeability of

concrete as that of natural pozzolana and slag. Concrete containing natural pozzolana

improves permeability and pore size distribution of the concrete [Mehta, 1981].

The scientific information on by-product pozzolanic materials such as natural pozzolana, slag

and silica fume are well documented and little effort has been dedicated to the natural

pozzolanic materials. The technical information on locally available natural pozzolanic

material is not available. Therefore, there is a need to investigate and explore the potential of

this material for use in concrete as partial cement replacement.

- 8 -

2.2 BACKGROUND

Concrete is a stone-like material obtained by permitting carefully proportioned mixture of

cement, sand and gravel or other aggregate, and water to harden in forms of the shape and

dimensions of the desired structure. The bulk of the material consists of fine and coarse

aggregate. Cement and water interact chemically to bind the aggregate particles into a solid

mass. Additional water, over and above that needed for this chemical reaction, is necessary to

give the mixture the workability that enables it to fill the forms and surrounds the embedded

reinforcing steel prior to hardening. Concrete with a wide range of properties can be obtained

by appropriate adjustment of the proportions of the constituent materials. Special cements

(such as high early strength cements), special aggregate (such as various lightweight or heavy

weight aggregate), admixtures such as plasticizers, air-entraining agents, silica fume, and

natural pozzolana), and special curing methods (such as steam curing) permit an even wider

variety of properties to be obtained.

These properties depend to a very substantial degree on the proportions of the mix, on the

thoroughness with which the various constituents are intermixed, and on the conditions of

humidity and temperature in which the mix is maintained from the moment it is placed in the

forms until it is fully hardened. Curing is done to control the conditions after placement. To

protect against the unintentional production of substandard concrete, a high degree of skillful

control and supervision is necessary throughout the process, from the proportioning by

weight of the individual components, through mixing and placing, until the completion of

curing.

The factors that make concrete a universal building material are so pronounced that it has

been used, in more primitive kinds and ways than at present, for thousands of years starting

with lime mortars from 12,000 to 6000 B.C. in Crete, Cyprus, Greece and the Middle East.

The facility with which, while plastic, it can be deposited and made to fill forms or moulds of

almost any practical shape is one of these factors. Its high fire and weather resistance are

evident advantages. Most of the constituent materials, with the exception of cement and

additives, are usually available at low cost locally. Its compressive strength, like that of

natural stones, is high, which makes it suitable for members primarily subject to compression,

such as columns and arches. On the other hand, again as in natural stones, it is relatively

brittle material whose tensile strength is small compared with its compressive strength. This

prevents its economical use in structural members that are subject to tension either entirely

- 9 -

(such as in tie rods) or over part of their cross sections (such as in beams or other flexural

members). Concrete (construction), artificial engineering material made from a mixture of

Portland cement, water, fine and coarse aggregates, and a small amount of air. It is the most

widely used construction material in the world.

Concrete is the only major building material that can be delivered to the job site in a plastic

state. This unique quality makes concrete desirable as a building material because it can be

moulded to virtually any form or shape. Concrete provides a wide latitude in surface textures

and colours and can be used to construct a wide variety of structures, such as highways and

streets, bridges, dams, large buildings, airport runways, irrigation structures, breakwaters,

piers and docks, sidewalks, silos and farm buildings, homes, and even barges and ships.

Other desirable qualities of concrete as a building material are its strength, economy, and

durability. Depending on the mixture of materials used, concrete will support, in

compression, 700 or more kg/sq. cm (10,000 or more lb. /sq. in). The tensile strength of

concrete is much lower, but by using properly designed steel reinforcing, structural members

can be made that are as strong in tension as they are in compression. The durability of

concrete is evidenced by the fact that concrete columns built by the Egyptians more than

3600 years ago are still standing.

The two major components of concrete are a cement paste and inert materials. The cement

paste consists of Portland cement, water, and some air either in the form of naturally

entrapped air voids or minute, intentionally entrained air bubbles. The inert materials are

usually composed of fine aggregate, which is a material such as sand, and coarse aggregate,

which is a material such as gravel, crushed stone, or slag. In general, fine aggregate particles

are smaller than 6.4 mm (.25 in) in size, and coarse aggregate particles are larger than 6.4 mm

(.25 in). Depending on the thickness of the structure to be built, the size of coarse aggregate

particles used can vary widely. In building relatively thin sections, a small size of coarse

aggregate, with particles about 6.4 mm (.25 in) in size, is used. At the other extreme,

aggregates up to 15 cm (6 in) or more in diameter are used in large dams. In general, the

maximum size of coarse aggregates should not be larger than one-fifth of the narrowest

dimensions of the concrete member in which it is used.

When Portland cement is mixed with water, the compounds of the cement react to form a

cementing medium. In properly mixed concrete, each particle of sand and coarse aggregate is

- 10 -

completely surrounded and coated by this paste, and all spaces between the particles are filled

with it. As the cement paste sets and hardens, it binds the aggregates into a solid mass.

Under normal conditions, concrete grows stronger as it grows older. The chemical reactions

between cement and water that cause the paste to harden and bind the aggregates together

require time. The reactions take place very rapidly at first and then more slowly over a long

period of time. In the presence of moisture, concrete continues to gain strength for years. For

instance, the strength of just-poured concrete may be about 70,307 g/sq. cm (1000 lb./sq. in)

after drying for a day, 316,382 g/sq.cm (4500 lb./sq. in) in 7 days, 421,842 g/sq. cm (6000

lb./sq. in) in 28 days, and 597,610 q/sq. cm (8500 lb./sq. in) after 5 years.

Concrete mixtures are usually specified in terms of the dry-volume ratios of cement, sand,

and coarse aggregates used. A 1:2:3 mixtures, for instance, consists of one part by volume of

cement, two parts of sand, and three parts of coarse aggregate. Depending on the applications,

the proportions of the ingredients in the concrete can be altered to produce specific changes

in its properties, particularly strength and durability. The ratios can vary from 1:2:3 to 1:2:4

and 1:3:5. The amount of water added to these mixtures is about 1 to 1.5 times the volume of

the cement. For high-strength concrete, the water content is kept low, with just enough water

added to wet the entire mixture. In general, the more water in a concrete mix, the easier it is

to work with, but the weaker the hardened concrete becomes.

Concrete can be made to have any degree of water tightness. It can be made to hold water and

resist the penetration of wind-driven rains. On the other hand, for purposes such as

constructing filter beds, concrete can be made porous and highly permeable. Concrete can

also be given a polished surface that is as smooth as glass. By using heavy aggregates,

including steel fragments, dense concrete mixtures can be made that weigh 4005 or more

kg/cu m (250 or more lb. /cu ft.). Concrete that weighs only 481 kg/cu m (30 lb. /cu ft.) can

be made by using special lightweight aggregates and foaming techniques. Forms consisting

of such lightweight aggregates can be floated on water, sawed into pieces, or nailed to

another surface.

For small jobs and minor repairs, concrete can be mixed by hand, but machine mixing

ensures more uniform batches and, therefore, superior performance. For most home repairs

and improvements—for example, floors, walks, driveways, patios, and garden pools—the

recommended proportion is a 1:2:3 mix.

- 11 -

After exposed surfaces of concrete have hardened sufficiently to resist marring, they should

be cured by sprinkling or ponding (covering) with water or by using moisture-retaining

materials such as waterproof paper, plastic sheets, wet burlap, or sand. Special curing sprays

are available. The longer concrete is kept moist, the stronger and more durable it will

become. In hot weather, it should be kept moist for at least three days. In cold weather,

drying concrete must not be allowed to freeze. This can be accomplished by covering the

cement with a tarpaulin or some other material that helps trap the heat generated by the

chemical reactions within the concrete that cause it to harden [Microsoft ® Encarta ® 2009]

- 12 -

2.3 MATERIALS

2.3.1 CEMENT

Cementitious material is one that has the adhesive and cohesive properties necessary to bond

inert aggregate into a solid mass of adequate strength and durability. This technologically

important category of materials includes not only cements proper but also limes, asphalts, and

tars as they are used in roads building, and others. For making structural concrete, so-called

hydraulic cements are used excessively. Water is needed for the chemical process (hydration)

in which the cements powder sets and hardens into one solid mass. Of the various hydraulic

cements that have been developed, Portland cement, which was first patented in England in

1824, is by far the most common.

Portland cement is finely powdered, grayish material that consists chiefly of calcium

Aluminium silicates. The common raw materials from which it is made are limestone, which

provide CaO, and clays or shale, which furnish SiO2 and Al2O3. These are ground, blended,

fused to clinkers in a kiln, and cooled. Gypsum is added and the mixture is ground to required

fineness.

Over the years, five standard types of Portland cement have been developed. When cement is

mixed with water to form a soft paste, it gradually stiffens until it becomes solid. This process

is known as setting and hardening. The cement is said to have set when it gains sufficient

rigidity to support an arbitrarily defined pressure, after which it continues for a long time to

harden i.e., to gain further strength. The water in the paste dissolves material at the surfaces

of the cement grains and forms a gel that gradually increases in volume and stiffness. This

leads to a rapid stiffening and hardening of the mass. The principal products of hydration are

calcium silicate hydrate, which is insoluble, and calcium hydroxide, which is soluble.

In ordinary concrete, the cement is probably never completely hydrated. The get structure of

the hardened paste seems to be the chief reason for the volume changes that are caused in

concrete by variations in moisture, such as the shrinkage of concrete as it dries.

For complete hydration of a given amount of cement, an amount of water equal to about 25

percent of that of cement, by weight – i.e. a water-cement ratio of 0.25 is needed chemically.

An additional amount must be present, however, to provide mobility for the water in the

cement paste during the hydration process so that it can reach the cement particles and to

provide the necessary workability of the concrete mix. For normal concretes, the water-

- 13 -

cement ratio is generally in the range of 0.40 to 0.60, although for high-strength concretes,

ratios as low as 0.21 have been used. In this case the needed workability is obtained through

the use of admixtures. Any amount of water above that consumed in the chemical reaction

produces pores in the cement paste. The strength of hardened paste decreases in inverse

proportion to the fraction of the total volume occupied by pores. Put differently, since only

the solids, and not the voids, resist stress, strength increases directly as the fraction of the

total volume occupied by the solids. That is why the strength of the cement paste depends

primarily on, and decreases directly with an increasing water-cement ratio. The chemical

process involved in the setting and hardening liberates heat, known as heat of hydration. In

large concrete masses, such as dams, this heat is dissipated very slowly and results in

temperature rise and volume expansion of the concrete during hydration, with subsequent

cooling and contraction. To avoid the serious cracking and weakening that may result from

this process; special measures must be taken for its control.

The source of cement, manufactured by GHACEM in Ghana was used in this investigation.

The chemical and physical properties of cement are given in table 2.1. It complies with

ASTM C150.

Table 2.1: Chemical and physical analysis of cement

Properties Source

SiO2 (%) 19.90

Al2O3 (%) 5.13

Fe2O3 (%) 3.75

CaO (%) 63.59

MgO (%) 1.50

SO3 (%) 2.75

Loss on ignition (%) 2.21

Fineness- Blaine (cm2/g) 3282

Source: Dr. Muhammad and Dr. Alhozaimy (2005).

- 14 -

2.3.2 AGGREGATE

In ordinary structural concretes the aggregates occupy about 70 to 75 percent of the volume

of the hardened mass. The remainder consist of hardened cement paste, uncombined water

(i.e. water not involved in the hydration of the cement), and air voids. The latter two

evidently do not contribute to the strength of the concrete. In general, the densely the

aggregate can be packed, the better the durability and economy of the concrete. It is there

considerably important that particle size in the aggregate is properly graded. It is also

important that the aggregate has good strength, durability, and weather resistance; that its

surface is free from impurities such as loam, silt, clay and organic matter that may weaken

the bond with cement paste; and that no unfavourable chemical reaction takes place between

it and the cement.

Natural aggregates are generally classified as fine and coarse. Fine aggregate (typically

natural sand) is any material that will pass a No. 4 or 0.150mm.

Materials which are coarser than 0.150mm are classified as coarse aggregate. When

favourable gradation is desired, aggregate are separated by sieving into two or three size

groups of sand and several size groups of coarse aggregate. These can then be combined

according to grading charts to result in densely packed aggregate.

- 15 -

2.4 CONCRETE PRODUCTION

Concrete is a mixture of two components: aggregates and paste. The paste, comprised of

cement and water, binds the aggregates (usually sand and gravel or crushed stone) into a

rocklike mass as the paste hardens because of the chemical reaction of the cement and water.

Supplementary cementitious materials and chemical admixtures may also be included in the

paste. The processes used vary dramatically, from hand tools to heavy industry, but result in

the concrete being placed where it cures into a final form.

When initially mixed together, Portland cement and water rapidly form a gel, formed of

tangled chains of interlocking crystals. These continue to react over time, with the initially

fluid gel often aiding in placement by improving workability. As the concrete sets, the chains

of crystals join up, and form a rigid structure, gluing the aggregate particles in place. During

curing, more of the cement reacts with the residual water (Hydration).

This curing process develops physical and chemical properties. Among other qualities

mechanical strength, low moisture permeability, and chemical and volumetric stability.

[http://en.wikipedia.org]

- 16 -

2.4.1 PROPORTIONING AND MIXING CONCRETE

The various components of a mix are proportioned so that the resulting concrete has adequate

strength, proper workability for placing, and low cost. To achieve low cost in concrete

production requires the use of minimum amount of cement (which is the most costly

component) that will achieve adequate properties. The better the gradation of aggregate, i.e.

the smaller the volume of voids, the less cement paste is needed to fill these voids. In addition

to the water required for hydration, water is needed for wetting the surface of the aggregate.

As water is added, the plasticity and fluidity of the mix increases (i.e. its workability

improves), but the strength decreases because of the larger volume of voids created by the

free water. To reduce the free water while retaining the workability, cement must be added.

Therefore, as for the cement paste, the water-cement ratio is the chief factor that controls the

strength of the concrete. For a given water-cement ratio, the minimum amount of cement that

will secure the desired workability is selected.

2.4.2 CONVEYING

Conveying of most building concretes from the mixer or truck to form is done in bottom-

dump trucks or by pumping through steel pipelines. The chief danger during conveying is

that of segregation. The individual components of concrete tend to segregate because of their

dissimilarity. In overly wet concrete standing in containers or forms, the heavier gravel

components tend to settle, and the lighter materials, particularly water, tend to rise. Lateral

movement, such as flow within the forms, tends to separate the coarse gravel from the finer

components of the mix

- 17 -

2.4.3 PLACING

Placing is done by transferring the fresh concrete from the conveying device to its final place

in the forms. Prior to placing, loose rust must be removed from the reinforcement, forms must

be cleaned, and hardened surface of previous concrete lifts must be cleaned and treated

appropriately. Placing and consolidation are critical in their effect on the final quality of the

concrete. Proper placement must avoid segregation, displacement of forms or of

reinforcement in the forms, and poor bond between successive layers of concrete.

Immediately upon placing, the concrete should be consolidated, usually by means of

vibrators. This prevents honeycombing, ensures close contact with forms and reinforcements,

and serves as a partial remedy to possible prior segregation. Consolidation is achieved by

high-frequency, power-driven vibrators.

Fresh concrete gains strength most rapidly during the first few days and weeks. Structural

design is generally based on the 28-day strength, about 70 percent of which is reached at the

end of the first week after placing. The final concrete strength depends greatly on the

conditions of moisture and temperature during this initial period. Curing is then done to

maintain the proper conditions. Thirty percent of the strength or more can be lost by

premature drying of the concrete; similar amounts may be lost by permitting the concrete

temperature to drop to 40⁰F (4.4⁰C) during the first few days unless the concrete is kept

continuously moist for a long time thereafter. Freezing of fresh concrete may reduce its

strength by 50 percent or more. To prevent such damage, concrete should be protected from

loss of moisture for at least 7 days and in. more sensitive work, up to 14 days. When high

early strength cements are used, curing periods can be cut in half. Curing can be achieved by

keeping exposed surfaces continually wet through sprinkling, ponding, or covering with

plastic film or by use of sealing compounds, which, when properly used, form evaporation-

retarding membranes. In addition to improving strength, proper moist curing provides better

shrinkage control. To protect the concrete against low temperature during cold weather, the

mixing water, and occasionally the aggregates, is heated; temperature insulation is used

where possible; and special admixtures are employed. When air temperatures are very low

external heat may have to be supplied in addition to insulation [ACI Manual of Concrete

Practice, Part 2, 2003]

- 18 -

2.4.4 CURING

Curing is the process of controlling the rate and extent of moisture loss from concrete during

cement hydration. It may be either after it has been placed in position (or during the

manufacture of concrete products), thereby providing time for the hydration of the cement to

occur. Since the hydration of cement does take time – days, and even weeks rather than hours

– curing must be undertaken for a reasonable period of time if the concrete is to achieve its

potential strength and durability. Curing may also encompass the control of temperature since

this affects the rate at which cement hydrates. The curing period may depend on the

properties required of the concrete, the purpose for which it is to be used, and the ambient

conditions, i.e. the temperature and relative humidity of the surrounding atmosphere. Curing

is designed primarily to keep the concrete moist, by preventing the loss of moisture from the

concrete during the period in which it is gaining strength. Curing may be applied in a number

of ways and the most appropriate means of curing may be dictated by the site or the

construction method.

In all but the least critical applications, care needs to be taken to properly cure concrete, and

achieve best strength and hardness. This happens after the concrete has been placed.

Cement requires a moist, controlled environment to gain strength and harden fully. The

cement paste hardens over time, initially setting and becoming rigid though very weak, and

gaining in strength in the days and weeks following. In around 3 weeks, over 90% of the final

strength is typically reached though it may continue to strengthen for decades. [ACI Manual

of Concrete Practice, Part 2, 2003]

Hydration and hardening of concrete during the first three days is critical. Abnormally fast

drying and shrinkage due to factors such as evaporation from wind during placement may

lead to increased tensile stresses at a time when it has not yet gained significant strength,

resulting in greater shrinkage cracking. The early strength of the concrete can be increased by

keeping it damp for a longer period during the curing process. Minimizing stress prior to

curing minimizes cracking. High early-strength concrete is designed to hydrate faster, often

by increased use of cement which increases shrinkage and cracking.

During this period concrete needs to be in conditions with a controlled temperature and

humid atmosphere. In practice, this is achieved by spraying or ponding the concrete surface

with water, thereby protecting concrete mass from ill effects of ambient conditions. The

- 19 -

pictures to the right show two of many ways to achieve this, ponding – submerging setting

concrete in water, and wrapping in plastic to contain the water in the mix.

Properly curing concrete leads to increased strength and lower permeability, and avoids

cracking where the surface dries out prematurely. Care must also be taken to avoid freezing,

or overheating due to the exothermic setting of cement (the Hoover Dam used pipes carrying

coolant during setting to avoid damaging overheating). Improper curing can cause scaling,

reduced strength, poor abrasion resistance and cracking.

2.4.4.1 CURING METHODS

2.4.4.1.1 Water cure: The concrete is flooded, ponded, or mist sprayed. This is the most

effective curing method for preventing mix water evaporation.

2.4.4.1.2 Water retaining methods: Use coverings such as sand, canvas, burlap, or straw

that is kept continuously wet. The material used must be kept damp during the curing period.

2.4.4.1.3 Waterproof paper or plastic film seal: Are applied as soon as the concrete is hard

enough to resist surface damage. Plastic films may cause discoloration of the concrete-do not

apply to concrete where appearance is important.

2.4.4.1.4 Chemical Membranes: The chemical application should be made as soon as the

concrete is finished. Note that curing compounds can effect adherence of resilient flooring,

your flooring contractor and/or chemical membrane manufacturer should be consulted.

- 20 -

2.5 QUALITY CONTROL

The quality concrete is assured by the producer, who must exercise systematic quality

controls, usually specified pertinent standards. Concrete is produced at or close to the site,

and its final quality is affected by a number of factors. Thus, the systematic quality control

must be instituted at the construction site.

The main measure of the structural quality of concrete is its compressive strength. Test for

this property are made on cylindrical specimen of height equal to twice the diameter, usually

150 ×300 mm. impervious molds of this shape are filled with concrete during the operation of

placement as specified by ASTM C 172 ―Standard Method of Sampling Freshly Mixed

Concrete,‖ and ASTM C 31, ―Standard Practice for Making and Curing Concrete Test

Specimens in the Field‖. The cylinders are moist-cured at about 70⁰F (21.1⁰C), generally for

28 days, and then tested in the laboratory at a specified rate of loading. The compressive

strength obtained from such tests is known as the cylinder strength ƒ’c and is the main

property specified for design purposes. To provide structural safety, continuous control is

necessary to ensure that the strength of concrete is furnished is in satisfactory agreement with

the value called for by the designer.

It is evident that, if concrete were proportioned so that its mean strength were just equal to the

required strength ƒ’c it would not pass these quality requirements because about half of its

strength test results would fall below the required ƒ’c. It is therefore necessary to proportion

the concrete so that it’s mean strength ƒ’cr used as the basis for selection of suitable

proportions, exceeds the required design strength ƒ’c by an amount sufficient to ensure that

the two quoted requirements are met.

- 21 -

2.5.1 SLUMP TEST

The slump test is the most well-known and widely used test method to characterize the

workability of fresh concrete. The inexpensive test, which measures consistency, is used on

job sites to determine rapidly, whether a concrete batch should be accepted or rejected. The

test method is widely standardized throughout the world, including in ASTM C 143 in the

United States and EN 12350-2 in Europe.

The slump test is however, not considered applicable for concrete with a maximum coarse

aggregate size greater than 1.5 inches. For concrete with aggregate greater than 1.5 inches in

size, such larger particles can be removed by wet sieving.

Additional qualitative information on the mobility of fresh concrete can be obtained after

reading the slump measurement. Concretes with the same slump can exhibit different

behavior when tapped with a tamping rod. A harsh concrete with few fines will tend to fall

apart when tapped and be appropriate only for applications such as pavements or mass

concrete. Alternatively, the concrete may be very cohesive when tapped, and thus be suitable

for difficult placement conditions.

- 22 -

2.5.2 COMPACTION FACTOR TEST

The compaction factor test [Powers 1968; Neville 1981; Bartos 1992, Sonebi, and Tamimi

2002] measures the degree of compaction resulting from the application of a standard amount

of work. The test was developed in Britain in the late 1940s and has been standardized as a

British Standard 1881-103.

The compaction factor is defined as a ratio of the mass of concrete compacted in the

compaction factor apparatus to the mass of the fully compacted concrete. The standard test is

appropriate for maximum aggregate sizes of up to 20mm. a larger apparatus is available for

concretes with maximum aggregate sizes of up to 40mm. [ICAR]

- 23 -

2.6 POZZOLANA

A pozzolan is a material which, when combined with calcium hydroxide, exhibits

cementitious properties. Pozzolans are commonly used as an addition (the technical term is

"cement extender") to Portland cement concrete mixtures to increase the long-term strength

and other material properties of Portland cement concrete and in some cases reduce the

material cost of concrete. Pozzolans are primarily vitreous siliceous materials which react

with calcium hydroxide to form calcium silicates; other cementitious materials may also be

formed depending on the constituents of the pozzolan.

The pozzolanic reaction may be slower than the rest of the reactions that occur during cement

hydration, and thus the short-term strength of concrete made with pozzolans may not be as

high as concrete made with purely cementitious materials; conversely, highly reactive

pozzolans, such as silica fume and high reactivity metakaolin can produce "high early

strength" concrete that increase the rate at which concrete gains strength.

The first known pozzolan was pozzolana, a volcanic ash, for which the category of materials

was named. The most commonly used pozzolan today is fly ash, though silica fume, high-

reactivity metakaolin, ground granulated blast furnace slag, and other materials are also used

as pozzolans.

A pozzolan is a siliceous or aluminosiliceous material, which is highly vitreous. This material

independently has few/fewer cementitious properties, but in the presence of a lime-rich

medium like calcium hydroxide, shows better cementitious properties towards the later day

strength (> 28 days). The mechanism for this display of strength is the reaction of silicates

with lime to form secondary cementitious phases (calcium silicate hydrates with a lower C/S

ratio) which display gradual strengthening properties usually after 7 days.

The extent of the strength development depends upon the chemical composition of the

pozzolan: the greater the composition of alumina and silica along with the vitreous phase in

the material, the better the pozzolanic reaction and strength display.

Many pozzolans available for use in construction today were previously seen as waste

products, often ending up in landfills. Use of pozzolans can permit a decrease in the use of

Portland cement when producing concrete; this is more environmentally friendly than

limiting cementitious materials to Portland cement. As experience with using pozzolans has

increased over the past 15 years, current practice may permit up to a 40 percent reduction of

- 24 -

Portland cement used in the concrete mix when replaced with a carefully designed

combination of approved pozzolans. When the mix is designed properly, concrete can utilize

pozzolans without significantly reducing the final compressive strength or other performance

characteristics.

It’s rare to find in nature natural stones with exceptional resistance to every chemical and

mechanical corrosion; many silicates have these features and, among these, the natural

Pozzolana is the only natural material that can be used as such with lime to form cement able

to harden and resist indefinitely in water. The natural pozzolana is a natural fine volcanic ash,

typical of the volcanic region of Pozzuoli (from here, its name) near Naples, Italy, but present

in other volcanic zones of Italy and other Countries.

It was used for the first time by the ancient Romans who started using just the pozzolana

extracted at Pozzuoli. Just the buildings of the ancient Pozzuoli (Puteoli, in Latin) were built

using the pozzolana as cement as well as the early days Forts and castles in the then Gold

Coast, and they resisted for many centuries till today to the action of sea waters that

submerged their imposing ruins because of the bradyseism, typical of that area.

The pozzolana is formed by volcanic ashes cemented by the heat of deep magmas and then,

after their eruption, exposed to a long action of the atmospheric agents, H2O and CO2, so that

the original complex silicates were transformed in a fine dust of simple silicates and oxides

(SiO2, Al2O3, Fe2O3).

When these oxides react with lime, Ca(OH)2, they harden relatively quickly, also under

water, forming complex and insoluble calcium silicates and aluminates, more and more

resistant with the passing time and not needing to react also with CO2 to form CaCO3

(limestone) as it happens in the cement, like that used by the Romans before they discovered

the pozzolana.

The Romans were able to build exceptional monuments and palaces, like the Pantheon dome

in Rome and the foundations of their harbours just with this volcanic cement, the "opus

coementicium".

The Roman architect Vitruvium already distinguished 4 types of pozzolana; white, yellow,

gray and red.

- 25 -

After the fall of the Roman Empire, the use of this cement was lost and forgotten; buildings

like the Pantheon become impossible during the middle Ages, for the absence of equally

resistant cement to water.

Only Filippo Brunelleschi, the genial Florence architect of the first half of the XV century,

started to use again the pozzolana and, since the late Renaissance, this cement has been used

frequently for some specific works, reaching again the building quality of the ancient Romans

and it's still in use.

Very used is also the artificial pozzolana, prepared heating at about 700C a clay mixture

formed by SiO2, Al2O3, MgO and CaO. The natural pozzolana is still extracted today in

many volcanic zones but it's replaced, in most of cases, by the hydraulic cement, discovered

in England about 1750 and made of lime and the much more common clay, with the same

function of pozzolana.

Various mixtures of this new cement were improved during the XIX century, until reaching

the formula of the Portland cement (1924), formed by limestone and 40% of clay that hardens

with higher speed than pozzolana.

Then, mixtures of the Portland cement with natural or artificial pozzolana started to be

available, in the last century, to improve cement resistance to water.

So, pozzolana is again more and more frequent in some cement used for modern restoring

works and for building bio-compatible houses.

Concrete is a compound material made from sand, gravel and cement. The cement is a

mixture of various minerals which when mixed with water, hydrate and rapidly become hard

binding the sand and gravel into a solid mass. The oldest known surviving concrete is to be

found in the former Yugoslavia and was thought to have been laid in 5,600 BC using red lime

as the cement.

The first major concrete users were the Egyptians in around 2,500BC and the Romans from

300 BC The Romans found that by mixing a pink sand-like material which they obtained

from Pozzuoli with the informal lime-based concretes they obtained a far stronger material.

The pink sand turned out to be fine volcanic ash and they had inadvertently produced the first

'pozzolanic' cement. Pozzolana is any siliceous or siliceous and aluminous material which

possesses little or no cementitious value in itself but will, if finely divided and mixed with

- 26 -

water, chemically react with calcium hydroxide to form compounds with cementitious

properties.

The Romans made many developments in concrete technology including the use of

lightweight aggregates as in the roof of the Pantheon, and embedded reinforcement in the

form of bronze bars, although the difference in thermal expansion between the two materials

produced problems of spalling. It is from the Roman words ―caementum‖ meaning rough

stone or chipping and 'concretus' meaning grown together or compounded, that we have

obtained the names for these two now common materials.

Lime and Pozzolana concretes continued to be used intermittently for nearly two millennia

before the next major development occurred in 1824 Cement was, made from a mixture of

clay and limestone, which had been crushed and fired in a kiln, was an immediate success.

Although many developments have since been made, the basic ingredients and processes of

manufacture are the same today

The oldest known form of concrete is to be found in the Middle East and it dates back to

5600 BC; the Egyptians (XXVI Century BC) used mixed with straw to bind dried bricks,

gypsum and lime mortars in stone masonry (in particular for the construction of pyramids).

The Greeks living in Crete and Cyprus used lime mortars as well (Eight Century BC),

whereas Babylonians and Syrians used bitumen to construct stone and brick masonries.

The Ancient Greeks, similarly, used calcined limestone, while the Romans made the first

concrete: mixed lime putty with brick dust or volcanic ash. They used it with stone to

construct roadways, buildings and aqueducts.

The Romans used pozzolana, a particular type of sand from Pozzuoli, near the volcano

Vesuvio (Southern Italy), to construct buildings of crucial importance, such as the Pantheon

or the Colosseo.

Pozzolana is an uncommon kind of sand which reacts chemically with lime and water,

becoming a rocklike mass; furthermore, it is siliceous and aluminous and it reacts with

calcium hydroxide to form compounds with cementation properties.

The domed Pantheon, constructed in the Second Century AD, is one of the structural

masterpieces of Roman time: it has a sophisticated structure with a large number of voids,

niches and small vaulted spaces aimed at reducing its weight; in particular the dome shows a

- 27 -

thicker structure at its base, whereas its thickness tends to diminish gradually, according to

the increased height of the dome (in other words, the dome thickness is inversely proportional

to its height). Pliny reported a mortar of lime and sand (one part of lime to four parts of sand),

and Marco Vitruvio Pollione (First Century BC) reported a mixture of pozzolana and lime

(two parts of pozzolana to one part of lime) and we have also an essay of him as regards the

properties of concrete.

The cementitious composition comprises pozzolanic material. Pozzolanic materials are

inorganic materials, either naturally occurring or industrial by- products typically comprising

siliceous compounds or siliceous and aluminous compounds. Examples of suitable pozzolans

include, but not necessarily limited to one or a combination of commercially available

pozzolanic including coal natural pozzolana, silica fume, diatomaceous earth, calcined or

uncalcined volcanic ash, bagasse ash, rice hull ash, natural and synthetic zerolites,

metakaolin, slag and other sources of amorphous silica. Preferred pozzolanic materials are

selected from the group consisting of natural pozzolana, calcined or uncalcined volcanic ash,

rice hull ash, and combinations thereof. Examples of suitable natural pozzolana include, but

are not necessarily limited to, class F, class C or class N as defined in ASTM C-618,

―Specifications for coal Natural pozzolana and Raw or Calcined Natural Pozzolan for use as a

Mineral Admixture in Portland Cement Concrete

All of the alkaline earth metal (preferably calcium-containing material) may be replaced by

the pozzolanic material; however, effective curing conditions for cementitious compositions

that do not include calcium-containing material generally include higher temperatures,

especially autoclaving at about 80⁰ C. In one embodiment, the cementitious composition is

composed of up to about 95% by weight pozzolanic material g suitably from about 10% to

95% by weight pozzolanic material, preferably from about 40% to about 90% by weight

pozzolanic material. In a preferred embodiment, the pozzolanic material makes up

approximately 80% or more by weight, based on the total weight of the cementitious

composition. Preferably the cementitious composition comprises from about 80% to about

95% by weight, more preferably from about 80 wt. % to about 90 wt. % of the cementitious

composition, based on the total weight of the cementitious composition. Suitable pozzolanic

material comprise from about 10% to about 50% by weight amorphous silica or vitreous

silica (hereafter ―silica‖), preferably from about 20% to about 40% by weight silica, even

more preferably about 35% silica.

- 28 -

2.6.1 ENGINEERING PROPERTIES OF POZZOLANA

Some of the engineering properties of natural pozzolana that are of particular interest when

natural pozzolana is used as and admixture or a cement addition to PCC mixes include

fineness, LOI, chemical composition, moisture content and pozzolanic activity. Most

specifying agencies refer to ASTM C618 when citing acceptance criteria for the use of

natural pozzolana in concrete.

2.6.1.1 Fineness: fineness is the primary physical characteristics of natural pozzolana that

relates to pozzolanic activity. As the finess increases, the pozzolanic activity can be expected

to increase. Current specifications include a requirement for the maximum allowable

percentage retained on a 0.045 mm (No. 325) sieve when wet sieved. ASTM C618 specifies a

maximum of 34 percent retained on a 0.045mm (No 325). Fineness can also be assessed by

methods that estimate specific surface area, such as the Blaine air permeability test

commonly used for Portland cement.

2.6.1.2 Pozzolanic Activity (chemical composition and Mineralogy): pozzolanic activity

refers to the ability of the silica and alumina component of natural pozzolana to react with

available calcium and/ or magnesium from the hydration products of Portland cement. ASTM

C618 requires that the pozzolanic activity index with Portland cement, as determined in

accordance with ASTM C311 be a minimum of 75 percent of the average 28-day

compressive strength of control mixes made with Portland cement.

2.6.1.3 Loss on Ignition: many state transportation departments specify a maximum LOI

value that does not exceed 3 or 4 percent, even though the ASTM criteria are a maximum

LOI content of 6 percent (2of 11). This is because carbon contents (reflected by LOI) higher

than 3 to 4 percent have an adverse effect on air entrainment.

Natural pozzolana must have a low enough LOI (usually less than 3.0 percent) to satisfy

ready –mix concrete producers, who t are concerned about product quality and the control of

air-entraining admixtures. Furthermore, consistent LOI values are almost as important as low

LOI values to ready –mix producers, who are most concerned with consistent and predictable

quality.

- 29 -

2.6.1.4 Moisture Content: ASTM C618 specifies a maximum allowable moisture content of

3.0 percent.

Some of the properties of fly ash-concrete mixes that are of particular interest include mix

workability, time of setting, bleeding, pumpability, strength development, heat of hydration,

permeability, resistance to freeze-thaw, sulfate resistance, and alkali-silica reactivity.

2.6.1.5 Workability: At a given water-cement ratio, the spherical shape of most fly ash

particles permits greater workability than with conventional concrete mixes. When fly ash is

used, the absolute volume of cement plus fly ash usually exceeds that of cement in

conventional concrete mixes. The increased ratio of solids volume to water volume produces

a paste with improved plasticity and more cohesiveness.

2.6.1.6 Time of Setting: When replacing up to 25 percent of the Portland cement in concrete,

all Class F fly ashes and most Class C fly ashes increase the time of setting. However, some

Class C fly ashes may have little effect on, or possibly even decrease, the time of setting.

Delays in setting time will probably be more pronounced, compared with conventional

concrete mixes, during the cooler or colder months.

2.6.1.7 Bleeding: Bleeding is usually reduced because of the greater volume of fines and

lower required water content for a given degree of workability.

2.6.1.8 Pumpability: Pumpability is increased by the same characteristics affecting

workability, specifically, the lubricating effect of the spherical fly ash particles and the

increased ratio of solids to liquid that makes the concrete less prone to segregation.

2.6.1.9 Strength Development: Previous studies of fly ash concrete mixes have generally

confirmed that most mixes that contain Class F fly ash that replaces Portland cement at a 1:1

(equal weight) ratio gain compressive strength, as well as tensile strength, more slowly than

conventional concrete mixes for up to as long as 60 to 90 days. Beyond 60 to 90 days, Class

F fly ash concrete mixes will ultimately exceed the strength of conventional PCC mixes. For

mixes with replacement ratios from 1.1 to 1.5:1 by weight of Class F fly ash to the Portland

cement that is being replaced, 28-day strength development is approximately equal to that of

conventional concrete.

Class C fly ashes often exhibit a higher rate of reaction at early ages than Class F fly ashes.

Some Class C fly ashes are as effective as Portland cement in developing 28-day strength.

Both Class F and Class C fly ashes are beneficial in the production of high-strength concrete.

- 30 -

However, the American Concrete Institute (ACI) recommends that Class F fly ash replace

from 15 to 25 percent of the Portland cement and Class C fly ash replace from 20 to 35

percent.

2.6.1.10 Heat of Hydration: The initial impetus for using fly ash in concrete stemmed from

the fact that the more slowly reacting fly ash generates less heat per unit of time than the

hydration of the faster reacting Portland cement. Thus, the temperature rise in large masses of

concrete (such as dams) can be significantly reduced if fly ash is substituted for cement, since

more of the heat can be dissipated as it develops. Not only is the risk of thermal cracking

reduced, but greater ultimate strength is attained in concrete with fly ash because of the

pozzolanic reaction. Class F fly ashes are generally more effective than Class C fly ashes in

reducing the heat of hydration.

2.6.1.11 Permeability: Fly ash reacting with available lime and alkalies generates additional

cementitious compounds that act to block bleed channels, filling pore space and reducing the

permeability of the hardened concrete. The pozzolanic reaction consumes calcium hydroxide

(Ca(OH)2), which is leachable, replacing it with insoluble calcium silicate hydrates (CSH).

The increased volume of fines and reduced water content also play a role.

2.6.1.12 Resistance to Freeze-Thaw: As with all concretes, the resistance of fly ash concrete

to damage from freezing and thawing depends on the adequacy of the air void system, as well

as other factors, such as strength development, climate, and the use of deicer salts. Special

attention must be given to attaining the proper amount of entrained air and air void

distribution. Once fly ash concrete has developed adequate strength, no significant

differences in concrete durability have usually been observed. There should be no more

tendency for fly ash concrete to scale in freezing and thawing exposures than conventional

concrete, provided the fly ash concrete has achieved its design strength and has the proper air

void system.

2.6.1.13 Sulphate Resistance: Class F fly ash will generally improve the sulfate resistance of

any concrete mixture in which it is included. Some Class C fly ashes may improve sulfate

resistance, while others may actually reduce sulfate resistance and accelerate deterioration.

Class C fly ashes should be individually tested before use in a sulfate environment. The

relative resistance of fly ash to sulfate deterioration is reportedly a function of the ratio of

calcium oxide to iron oxide.

- 31 -

2.6.1.14 Alkali-Silica Reactivity: Class F fly ash has been effective in inhibiting or reducing

expansive reactions resulting from the alkali-silica reaction. In theory, the reaction between

the very small particles of amorphous silica glass in the fly ash and the alkalis in the Portland

cement, as well as the fly ash, ties up the alkalis in a nonexpansive calcium-alkali-silica gel,

preventing them from reacting with silica in aggregates, which can result in expansive

reactions. However, because some fly ashes (including some Class C fly ashes) may have

appreciable amounts of soluble alkalis, it is necessary to test materials to be used in the field

to ensure that expansion due to alkali-silica reactivity will be reduced to safe levels.

Fly ash, especially Class F fly ash, is effective in three ways in substantially reducing alkali-

silica expansion:

1) It produces a denser, less permeable concrete;

2) When used as a cement replacement it reduces total alkali content by reducing the Portland

cement; and

3) Alkalis react with fly ash instead of reactive silica aggregates. Class F fly ashes are

probably more effective than Class C fly ashes because of their higher silica content, which

can react with alkalis. Users of Class C fly ash are cautioned to carefully evaluate the long-

term volume stability of concrete mixes in the laboratory prior to field use, with ASTM C441

as a suggested method of test. [Coal Fly Ash journal, 2009]

- 32 -

2.6.2 ADVANTAGES OF THE NATURAL POZZOLAN

2.6.2.1 Lithification: Once the Natural pozzolan-lime mixture is hydrated, the pozzolanic

reaction begins immediately and continues for many years. Eventually, the mass will reach

complete lithification, forming a rocky material similar to plagioclase with some content of

magnetite. The compressive strength as well as the flexural strength will continue to increase

for a long time. This unique characteristic is one of the main reasons many great ancient

structures have lasted for over two thousand years.

2.6.2.2 Autogenous Healing: A unique characteristic of Natural pozzolan is its inherent

ability to actually heal or re-cement cracks within the concrete by means of the continuation

of pozzolanic reaction with the calcium hydroxide freed from the cement hydration reaction.

This results in the filling up of most of the gaps inside the hardened concrete matrix

2.6.2.3 Reduced Permeability and Voids: The leaching of water-soluble calcium hydroxide

produced by the hydration of Portland cement can be a significant contributor to the

formation of voids. The amount of "water of convenience" used to make the concrete

workable during the placing process creates permeable voids in the hardened mass. Natural

pozzolan can increase the fluidity of concrete without "water of convenience," so that the size

and number of capillary pores created by the use of too much water can be minimized.

2.6.2.4 Reduces Expansion and Heat of Hydration: Experiments show that replacing 30%

Portland cement with Natural pozzolan can reduce the expansion and heat of hydration to as

low as 40% of normal. This may be because there is no heat produced when Natural pozzolan

reacts with calcium hydroxide and that the free calcium oxide in the cement can hydrate

with natural pozzolan to form C-S-H. Natural pozzolan decreases the heat generated by

cement hydration and delays the time of peak temperature. The graphic pattern of Natural

pozzolan - Portland cement mixture is extended longer and lower, to form a much more

moderate curve than the heat of hydration curve of Portland cement itself.

2.6.2.5 Reduces Creep and Cracks: While concrete is hardening, the "water of

convenience" dries away. The surface of the hardening mass then begins to shrink as the

temperature goes down from outside. This results in the formation of creep and cracks.

Natural pozzolan moderates the expansion and shrinkage of concrete. It also helps to lower

- 33 -

the water content of the fresh concrete. Therefore, the creep and cracks can be significantly

reduced without the process of water cooling.

2.6.2.6 Reduces Microcracking: The expansion and shrinkage mentioned above also create

microcracks inside the hardened C-S-H paste and in-between the aggregate and the C-S-H

paste. These microcracks significantly contribute to concrete permeability as well as other

concrete defects. The Natural pozzolan- Portland cement mixture expands these shrinks so

moderately that there is no microcracking inside the C-S-H paste after drying.

2.6.2.7 Increases Compressive Strength: The pozzolanic reaction between natural pozzolan

and calcium hydroxide happens after the C3S and C2S in the cement begins to hydrate. At

the early stage of curing, 30% Natural pozzolan substituting Portland cement mixture is

slightly lower than reference OPC [Ordinary Portland Cement} in regard to compressive

strength. As time goes by, natural pozzolan continues to react with the calcium hydroxide

produced by cement hydration and increases the compressive strength by producing

additional C-S-H. After 21 curing days, the 30% Natural pozzolan 70% Portland cement

mixture begins to exceed reference OPC in compressive strength. After 28 days, it exceeds

reference OPC by about 15%. The pozzolanic reaction continues until there is no free

calcium hydroxide available in the mass and the compressive strength exceeds the reference

OPC by 30-40%.

2.6.2.8 Increases Resistance to chloride Attack: Concrete deterioration caused by the

penetration of chloride occurs quickly when chloride ions react with calcium. The expansion

of hydrated calcium oxy-chloride enlarges the microcracks and increases the permeability

that causes quicker chloride penetration and more damage from freezing and thawing action.

The 30% Natural pozzolan added into cement can react with almost all the free calcium

hydroxide and form a much denser past. Thus, the penetration of chloride can be minimized

and the few penetrated chloride ions cannot find free calcium hydroxide with which to react.

2.6.2.9 Increases resistance to sulfate attack: There are three chemical reactions involved

in sulfate attack on concrete:

1) Combination of free calcium hydroxide and sulfate to form gypsum (CaSO4-2H2O).

2) Combination of gypsum and calcium aluminate hydrate (C-A-H) to form ettringite (C3A-

3CaSO-32H2O).

- 34 -

3) Combination of gypsum and calcium carbonate with C-S-H to form thaumasite (CaCO3-

CaSiO3-CaSO4-15H2O).

All these reactions result in the expansion and disruption of concrete. Thaumasite in

particular is accompanied by a very severe damaging effect which is able to transform

hardened concrete into a pulpy mass.

2.6.2.10 Reduces alkali-aggregate reaction: Because Natural pozzolan is shattered into such

a fine particle size resulting in dramatically increased reactive surface area, it can react

quickly with calcium hydroxide and can trap the alkali inside the cement paste. Thus, it helps

to form a denser paste with almost no alkali aggregate reaction at all.

2.6.2.11 Protects steel reinforcement from corrosion: The preceding discussions make it

very clear that concrete made from 30% Natural pozzolan/ 70% Portland cement mixture can

protect steel reinforcement because it creates an environment so densely packed that no

liquids or gases can penetrate through it to cause corrosion to the steel.

2.6.2.12 Increases abrasion resistance: Natural pozzolan increases the compressive strength

of concrete and makes the concrete matrix stronger and denser. It also prevents the formation

of pulpy, crispy, or water-soluble materials created by chemical attack. Therefore, it helps the

concrete to durably resist abrasion

2.6.2.13 Lowers water requirement with high fluidity, self-leveling, and compression: In

normal operations, the bulk volume of concrete in the constructions are placed and

compacted by use of high frequency poke vibrators. The rapid vibration induces segregation

phenomena of all orders of magnitude in the fresh concrete, e.g., stone segregation, internal

bleeding giving bonding failures, and inhomogeneous cement paste and air-void systems.

Under proper use of vibratory compaction, Natural Pozzolan minimizes or eliminates these

problems due to the amorphous structure of the pozzolan particles.

2.6.2.14 Improves Durability: The benefits and characteristics of Natural Pozzolan

mentioned above clearly explain why the ancient structures built by the Greeks have survived

over 2000 years of weathering. [Lawluvi and Odei, 2009 unpublished project work]

- 35 -

2.7 DESIGN CONSIDERATIONS

2.7.1Mix Design

Concrete mixes are designed by selecting the proportions of the mix components that will

develop the required strength, produce a workable consistency concrete that can be handled

and placed easily, attain sufficient durability under exposure to in-service environmental

conditions, and be economical. Procedures for proportioning fly ash concrete mixes differ

slightly from those for conventional concrete mixes. Basic mix design guidelines for normal

concrete [Coal Fly Ash journal, 2009]

One mix design approach commonly used in proportioning fly ash concrete mixes is to use a

mix design with all Portland cement, remove some of the Portland cement, and then add fly

ash to compensate for the cement that is removed. Class C fly ash is usually substituted at a

1:1 ratio. Class F fly ash may also be substituted at a 1:1 ratio, but is sometimes specified at a

1.25:1 ratio, and in some cases may even be substituted at a 1.5:1 ratio. [Coal Fly Ash

journal, 2009]

There are some states that require that fly ash be added in certain mixes with no reduction in

cement content

The percentage of Class F fly ash used as a percent of total cementitious material in typical

highway pavement or structural concrete mixes usually ranges from 15 to 25 percent by

weight. This percentage usually ranges from 20 to 35 percent when Class C fly ash is used.

Mix design procedures for normal, as well as high-strength, concrete involve a determination

of the total weight of cementitious materials (cement plus fly ash) for each trial mixture that

is being investigated in the laboratory. The ACI mix proportioning guidelines recommend a

separate trial mix for each 5-percent increment in the replacement of Portland cement by fly

ash. If fly ash is to replace Portland cement on an equal weight (1:1) basis, the total weight of

cementitious material in each trial mix will remain the same. However, because of

differences in the specific gravity values of Portland cement and fly ash, the volume of

cementitious material will vary with each trial mixture.

When a Type IP (Portland-pozzolan) or Type I-PM blended cement is used in a concrete mix,

fly ash is already a part of the cementing material. There is no need to add more fly ash to a

concrete mix in which blended cement is being used, and it is recommended that no fly ash

- 36 -

be added in such cases. The blended cement can be used in the mix design process in

essentially the same way as Type I Portland cement.

To select a mix proportion that satisfies the design requirements for a particular project, trial

mixes must be made. In a concrete mix design, the water-cement (w/c) ratio is a key design

parameter, with a typical range being from 0.37 to 0.50

When using a blended cement, the water demand will probably be somewhat reduced because

of the presence of the fly ash in the blended cement. When fly ash is used as a separately

batched material, trial mixes should be made using a water-cement plus fly ash (w/c+f) ratio,

sometimes referred to as the water-cementitious ratio, instead of the conventional w/c ratio.

[Coal Fly Ash journal, 2009]

The design of any concrete mix, including fly ash concrete mixes, is based on proportioning

the mix at varying water-cementitious ratios to meet or exceed requirements for compressive

strength (at various ages), entrained air content, and slump or workability needs. The mix

design procedures stipulated in ACI 211.1 provide detailed, step-by-step directions regarding

trial mix proportioning of the water, cement (or cement plus fly ash), and aggregate materials.

Fly ash has a lower specific gravity than Portland cement, which must be taken into

consideration in the mix proportioning process.

- 37 -

CHAPTER THREE

3.0 METHODOLOGY

3.1 INTRODUCTION

Review of data for the study comprised of conduction of test, desk study and review of the

reports to achieve the objectives of this study, which is ―Comparing the compressive strength

of concrete utilizing natural pozzolana as a partial replacement of Ordinary Portland Cement‖

in concrete production.

3.2 DATA COLLECTION

The under listed methods of data collection were used to obtain the necessary data;

Desk study and review of reports

Laboratory test methods

3.3 DESK STUDY

In order to accomplish information on this study, a comprehensive review of previous data

gathered about the study by other researchers were used.

3.4 MIX PROPORTION

The concrete was designed and water/cement ratio was found to be 0.55 for all mixes. Mixing

was done in revolving drum mixer in accordance with ASTM C 192. The pozzolana

replacements were selected at ratios of 50:50, 60:40, 70:30, and 80:20 as a partial cement

replacement by weight of cement content.

- 38 -

3.5 CASTING AND CURING

Ninety (96) concrete cubes were cast and compacted in three layers by tamping. After

casting, the samples were leveled and kept in the mould for 24 hours. The samples were then

demoulded the following day and cured in a curing tank at temperature of 20±2ºC.

3.6 TEST PROCEDURES

Tests were conducted to help prove the study.

3.6.1 SLUMP TEST

Slump tests were performed according to ASTM C 143. The reductions in slump in time were

measured. During the standing time, the concrete were covered to minimize water loss

through evaporation.

3.6.2 COMPRESSIVE STRENGTH

The compressive strengths of concrete were determined, using 150mm cubes prepared and

tested according to BS1881. Three cubes per measurement were cast to determine the

compressive strengths at various ages (7days, 14days, 21days and 28days). The compressive

strengths were taken on the three samples and the average was reported as a result.

- 39 -

CHAPTER FOUR

4.0 DATA PRESENTATION AND ANALYSIS

4.1 SILT TEST RESULTS AND ANALYSIS

SAMPLE 1 SAMPLE 2 SAMPLE 3

Level of Content

150 150 150

Depth of Sand without silt

(ml) 70 70 70

thickness of visible silt

(ml) 20 15 10

Volume of Water (ml)

60 65 70

Percentage by volume of silt depth to sand thickness (%)

29 21 14

Table 4.1: Results of obtained from silt test conducted sand sample. (Source: Laboratory

test 2010)

The average silt content from the results is given as =29+21+14

3

= 21.333%

This is 17.333% above the standard provided by BS 812. The effect of high silt content on

concrete is excessive drying shrinkage thereby decreasing the compressive strength. Since

results obtained from the silt test was 17.333% above the standard and the shrinkage test on

the cubes were immeasurable, the sand used could not have negative influence on the results

of the compressive strength.

40

Table 4.2: Details of Mix proportion

(Source: Laboratory Test, 2010)

MIX WEIGHT OF CEMENT (kg) WEIGHT OF

POZZOLANA (kg) WEIGHT OF SAND (kg)

WEIGHT OF STONES (kg)

WEIGHT OF WATER (kg)

W/C RATIO

CONTROL 14000 0 28000 56000 7700 0.55

POZO 30% 9800 4200 28000 56000 7700 0.55

POZO 70% 4200 9800 28000 56000 7700 0.55

POZO 40% 5600 8400 28000 56000 7700 0.55

POZO 60% 8400 5600 28000 56000 7700 0.55

POZO 20% 2800 11200 28000 56000 7700 0.55

POZO 80% 11200 2800 28000 56000 7700 0.55

POZO 50% 7000 7000 28000 56000 7700 0.55

41

Table 4.3: Results of Grading Test for Coarse Aggregates

Sieve size Weight retained

(g) Weight passed(g) % retained % passing Lower limit Upper limit

38 0.000 8.900 0.000 100.0 100.0 100.0

19 0.916 7.984 11.070 88.9 80.0 100.0

10 5.200 2.784 62.870 26.1 0.0 20.0

5 2.155 0.629 26.050 0.0 0.0 5.0

(Source: laboratory test, 2010)

Fig. 4.1: Grading Curve for Coarse Aggregates

-20.0

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0.1 1 10

% p

assi

ng

Sieve Size, mm

upper limit lower limit grading curve for coarse aggregate

42

Table 4.4: Results of Grading Test for Fine Aggregates

Sieve size (mm) Weight retained

(g) Weight passed(g) % retained % passing

BS Recommended Nominal Size Passing (%)

Lower limit Upper limit

10 0.000 0.400 0.000 100.0 100.0 100.0

5 0.000 0.400 0.000 100.0 90.0 100.0

2.8(No. 7) 0.009 0.391 2.860 97.1 75.0 100.0

1.4(No. 14) 0.067 0.324 2.270 75.9 55.0 90.0

600 µ(No. 25) 0.07 0.254 22.22 53.65 35 60

300µ(No. 52) 0.068 0.186 21.5 32.06 10 30

150µ(No. 100) 0.101 0.085 32.06 0 0 10

(Source: laboratory test, 2010)

43

Fig. 4.2: Grading Curve for Fine Aggregates

0

20

40

60

80

100

120

0.01 0.1 1 10

lower limit upper limit grading curve for fine aggregate

44

A mechanical analysis of the inert material was conducted for the purpose of this work. Dry

sieving was used. After passing the sample through BS sieves, the percentages passing each

sieve were plotted on sand and gravel fraction of a semi-logarithmic chart as shown in Fig.

4.1 for coarse sample and Fig. 4.2 for fine sample.

Comparing the results of the percent passing BS sieves from the test analysis with the BS

Recommended Nominal Size Passing (%) it is shown from the grading curves that the

particle size distribution curves is satisfied.

4.2 PROPERTIES OF FRESH CONCRETE

This section reports on workability using slump test and compaction factor test for concrete

containing natural pozzolana as partial replacement.

4.2.1 Slump Test

The initial slump of all mixes was within the range of 12±1 mm (Table 4.5).

The slump of pozzolanic concrete as compared to the control is shown in Fig. 4.3. This figure

demonstrates that there is little or no significant variation in slump of pozzolanic concrete

mix (30%, 70%, 40%, 60%, 20%, 80% and 50%) and the control mix. However, it was also

observed in other research work on slump loss of pozzolanic mixes that pozzolanic concrete

mixture starts with a slightly higher slump and drops slightly steeper with time as compared

to the control mix.

45

Table 4.5: Slump properties of fresh concrete.

Mix Height of Slump

Control 12

Pozo 30% 13

Pozo 70% 20

Pozo 40% 5

Pozo 60% 6

Pozo 20% 12

Pozo 80% 13

Pozo 50% 12 (Source: Laboratory test 2010)

Fig. 4.3 Effect of pozzolanic material on the slump of concrete

According to Neville, the slump ranging from 15 to 30 is low. The 70% pozzolana mix is of a

low slump while the control and all other mixes are of very low slump.

0

5

10

15

20

25

Control Pozo 30%

Pozo 70%

Pozo 40%

Pozo 60%

Pozo 20%

Pozo 80%

Pozo 50%

Slu

mp

. Mm

Mix

Height of slump

46

4.2.2 Compaction Factor

Table 4.6: Results Of Compacting Factor Tests Of Test Specimen

Mix Weight of Partially

Compacted Conc.

Weight of Fully

Compacted Conc. Compaction Factor

Control 9599 11818 0.81

Pozo 30% 9259 11721.5 0.79

Pozo 70% 8382 11318 0.74

Pozo 40% 8875 11620 0.76

Pozo 60% 8159 11434 0.71

Pozo 20% 9525 10820 0.88

Pozo 80% 7760 10903 0.71

Pozo 50% 9415 11479 0.82

(Source: Laboratory Test, 2010)

Fig. 4.4: Effect of pozzolanic material on the compaction factor of concrete

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

ControlPozo 30%Pozo 70%Pozo 40%Pozo 60%Pozo 20%Pozo 80%Pozo 50%

Co

mp

acti

on

Fac

tor

Mix

compaction factor

47

The compacting factor test conducted on concrete grade 20 indicates an adequate workability

of the concrete using a water/cement ratio of 0.55. From the results obtained, the compacting

factor for the control mix and Pozo 50% and Pozo 20% are of good workability as compared

to the remaining mix ratios.

- 48 -

4.3 COMPRESSIVE STRENGTH

Table 4.7: Detail results of Compressive strength of concrete grade 20 at all ages

CONTROL CONCRETE COMPRESSIVE STRENGHT TEST RESULTS FOR

CONTROL MIX

DESCRIPTION: CONTROL DUARATION: 7DAYS SLUMP: 12mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8170 2.421 367.401 16.329

8144 2.413 380.273 16.901 16.4

8079 2.394 359.351 15.971

DESCRIPTION: CONTROL DUARATION: 14DAYS SLUMP: 12mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8103 2.401 451.615 20.072

8186 2.425 444.870 19.772 20.1

8259 2.447 458.583 20.381

DESCRIPTION: CONTROL DUARATION: 21DAYS SLUMP: 12mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8153 2.415 451.191 20.053

8310 2.462 454.522 20.201 20.2

8068 2.391 457.615 20.338

DESCRIPTION: CONTROL DUARATION: 28DAYS SLUMP: 12mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8153 2.397 591.281 26.279

8101 2.422 564.752 25.100 25.7

8242 2442.000 578.017 25.090

- 49 -

POZZOLANA 30%

CONCRETE COMPRESIVE STRENGHT TEST RESULTS POZO 30%

DESCRIPTION: POZO 30% DUARATION: 7DAYS SLUMP: 13mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8049 2.385 372.032 16.535

8023 2.377 365.689 16.253 16.9

8026 2.378 405.501 18.022

DESCRIPTION: POZO 30% DUARATION: 14DAYS SLUMP: 13mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7977 2.364 479.815 21.325

8008 2.373 445.976 19.821 20.2

8088 2.396 440.256 19.567

DESCRIPTION: POZO 30% DUARATION: 21DAYS SLUMP: 13mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8070 2.391 520.476 23.132

8113 2.404 536.217 23.832 23.7

8014 2.375 543.036 24.135

DESCRIPTION: POZO 30% DUARATION: 28DAYS SLUMP: 13mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8038 2.382 605.381 26.906

7997 2.369 564.123 25.072 25.9

8012 2.374 581.282 25.835

- 50 -

POZZOLANA 70%

CONCRETE COMPRESSIVE STRENGHT TEST RESULTS FOR

POZO 70%

DESCRIPTION: POZO 70% DUARATION: 7DAYS SLUMP: 20mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7826 2.319 117.331 4.671

7822 2.318 110.220 4.899 4.4

7592 2.249 113.244 3.180

DESCRIPTION: POZO 70% DUARATION: 14DAYS SLUMP: 20mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7752 2.297 105.107 4.671

7800 2.311 135.857 6.038 5.2

7705 2.283 113.244 5.033

DESCRIPTION: POZO 70% DUARATION: 21DAYS SLUMP: 20mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7767 2.301 165.311 7.347

7782 2.306 161.422 7.174 6.8

7650 2.267 134.921 5.996

DESCRIPTION: POZO 70% DUARATION: 28DAYS SLUMP: 20mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7799 2.311 160.270 7.123

7778 2.305 184.370 8.194 7.6

7845 2.324 170.280 7.568

- 51 -

POZZOLANA 40%

CONCRETE COMPRESSIVE STRENGHT TEST RESULTS FOR

POZO 40 %

DESCRIPTION: POZO 40% DUARATION: 7DAYS SLUMP: 5mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8109 2.403 274.269 12.190

8050 2.385 295.946 13.153 13.1

8056 2.387 311.789 13.857

DESCRIPTION: POZO 40% DUARATION: 14DAYS SLUMP: 5mm

WEIGHT (kg) DENSITY

(kg/dm3) MAX LOAD (kN)

STRENGTH

(Mpa) AVERAGE

8008 2.373 292.489 13.000

8055 2.387 319.350 14.193 13.8

8017 2.375 317.478 14.110

DESCRIPTION: POZO 40% DUARATION: 21DAYS SLUMP: 5mm

WEIGHT (kg) DENSITY

(kg/dm3) MAX LOAD (kN)

STRENGTH

(Mpa) AVERAGE

8043 2.383 358.454 15.931

8040 2.382 353.485 15.710 15.8

8133 2.410 357.230 15.877

DESCRIPTION: POZO 40% DUARATION: 28DAYS SLUMP: 5mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7951 2.356 368.392 16.373

8052 2.386 370.806 16.480 16.1

8148 2.414 344.844 15.326

- 52 -

POZZOLANA 6O%

CONCRETE COMPRESSIVE STRENGHT TEST RESULTS FOR

POZO 60%

DESCRIPTION: POZO 60% DUARATION: 7DAYS SLUMP: 6mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7663 2.271 132.400 5.884

7890 2.338 177.913 7.907 6.9

7831 2.320 155.733 6.921

DESCRIPTION: POZO 60% DUARATION: 14DAYS SLUMP: 6mm

WEIGHT (kg) DENSITY

(kg/dm3) MAX LOAD (kN)

STRENGTH

(Mpa) AVERAGE

7924 2.348 196.061 8.714

7711 2.285 209.024 9.290 7.6

2369 2.369 106.043 4.713

DESCRIPTION: POZO 60% DUARATION: 21DAYS SLUMP: 6mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7908 2.343 257.130 11.428

2353 2.353 112.308 4.991 8.8

7551 2.237 227.316 10.103

DESCRIPTION: POZO 60% DUARATION: 28DAYS SLUMP: 6mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7802 2.312 276.213 12.276

7736 2.292 274.845 12.215 11.9

7731 2.291 253.745 11.278

- 53 -

POZZOLANA 20%

CONCRETE COMPRESSIVE STRENGHT TEST RESULTS FOR

POZO 20%

DESCRIPTION: POZO 20% DUARATION: 7DAYS SLUMP: 12mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8115 2.404 338.074 15.026

8104 2.401 353.269 15.701 15.6

8063 2.389 361.119 16.050

DESCRIPTION: POZO 20% DUARATION: 14DAYS SLUMP: 12mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8090 2.397 365.080 16.226

8142 2.412 397.486 17.666 17.3

8188 2.426 408.503 18.156

DESCRIPTION: POZO 20% DUARATION: 21DAYS SLUMP: 12mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8100 2.400 441.199 19.609

8003 2.371 366.880 16.306 17.5

8134 2.410 372.353 16.549

DESCRIPTION: POZO 20% DUARATION: 28DAYS SLUMP: 12mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8010 2.373 374.153 16.629

8119 2.406 465.036 20.668 17.9

8074 2.392 372.065 16.536

- 54 -

POZZOLANA 80%

CONCRETE COMPRESSIVE STRENGHT TEST RESULTS FOR POZO

80%

DESCRIPTION: POZO 80% DUARATION: 7DAYS SLUMP: 13mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7823 2.318 63.122 2.805

7691 2.279 63.410 2.818 2.7

7690 2.279 56.785 2.524

DESCRIPTION: POZO 80% DUARATION: 14DAYS SLUMP: 13mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7559 2.240 67.443 2.997

7678 2.275 69.891 3.106 3.1

7725 2.289 69.748 3.100

DESCRIPTION: POZO 80% DUARATION: 21DAYS SLUMP: 13mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7808 2.313 78.461 3.487

7686 2.277 61.178 2.719 3.1

7808 2.313 70.828 3.148

DESCRIPTION: POZO 80% DUARATION: 28DAYS SLUMP: 13mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7683 2.276 80.808 3.591

7735 2.292 93.728 4.166 3.7

7623 2.259 72.988 3.244

- 55 -

POZZOLANA 50%

CONCRETE COMPRESSIVE STRENGHT TEST RESULTS FOR POZO

50%

DESCRIPTION: POZO 50% DUARATION: 7DAYS SLUMP: 12mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7873 2.333 211.328 9.392

7919 2.346 265.627 11.806 10.6

7990 2.367 240.998 10.711

DESCRIPTION: POZO 50% DUARATION: 14DAYS SLUMP: 12mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

8006 2.372 262.315 11.658

7905 2.342 251.188 11.164 11.4

8014 2.375 256.913 11.418

DESCRIPTION: POZO 50% DUARATION: 21DAYS SLUMP: 12mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7932 2.350 279.238 12.411

7938 2.352 328.136 14.584 12.9

7812 2.315 262.675 11.674

DESCRIPTION: POZO 50% DUARATION: 28DAYS SLUMP: 12mm

WEIGHT (kg) DENSITY (kg/dm3)

MAX LOAD (kN) STRENGTH

(Mpa) AVERAGE

7928 2.349 262.891 11.684

8031 2.380 296.882 13.195 13.6

8093 2.398 359.822 15.992

(Source: laboratory test 2010)

- 56 -

Table 4.8: Average Compressive Strengths Incorporating Pozzolan at all Ages of Test.

Mix

Compressive Strength, Mpa

7-days 14-days 21-days 28-days

Control 16.4 20.1 20.2 25.7

Pozo 30% 16.9 20.2 23.7 25.9

Pozo 70% 4.4 5.2 6.8 7.6

Pozo 40% 13.1 13.8 15.8 16.1

Pozo 60% 6.9 7.6 8.8 11.9

Pozo 20% 15.6 17.3 17.5 17.9

Pozo 80% 2.7 3.1 3.1 3.7

Pozo 50% 10.6 11.4 12.9 13.6

(Sources: Laboratory Test, 2010)

Compressive strength was measured on concrete containing various combinations of

pozzolanic material. As presented in Tables 4.7 and 4.8.

All the mixes prepared with pozzolanic materials demonstrated lower compressive strength at

all ages as compared to that of corresponding control mix. However, partial replacement mix

of 30% pozzolana showed an early strength gain compared to the control and a significant

strength gain in later ages too.

The effect of pozzolanic replacement on the compressive strength can be seen in fig. 4.4, 4.5,

4.6, 4.7, 4.8, 4.9, and 4.10

These figures shows the compressive strengths of concrete prepared with 30%, 70%, 40%,

60%, 20%, 80%, and 50% pozzolanic material as cement replacement. The selection of these

ratios was on the basis of information from earlier research work conducted in the Civil

Engineering Department of Cape Coast polytechnic in 2009 that 30% pozzolan replacement

of cement recorded higher compressive strength and could be used as alternative to control.

[Hope and Nasir Odei, 2009. Unpublished project work].

Initially it was expected that pozzolanic concrete might show enhancement in strength at later

ages. As expected, mix with 30% replacement showed higher strengths as compared to the

control at all ages as well as higher strength compared to the other mix ratios at all ages.

- 57 -

Fig. 4.5: Effect Of Pozzolanic Replacement On The Compressive Strength Of Concrete At 7

Days

Fig. 4.6: Effect of pozzolanic replacement on the compressive strength of concrete at 14days

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

Control Pozo 30% Pozo 70% Pozo 40% Pozo 60% Pozo 20% Pozo 80% Pozo 50%

Co

mp

ress

ive

str

en

gth

, Mp

a

Mix

7 days

0.0

5.0

10.0

15.0

20.0

25.0

Control Pozo 30%Pozo 70%Pozo 40%Pozo 60%Pozo 20%Pozo 80%Pozo 50%

Co

mp

ress

ive

stre

ngt

h, M

pa

Mix

14 days

- 58 -

Fig. 4.7: Effect of pozzolanic replacement on the compressive strength of concrete at 21 days

Fig. 4.8: Effect of pozzolanic replacement on the compressive strength of concrete at 28 days

0.0

5.0

10.0

15.0

20.0

25.0

Control Pozo 30% Pozo 70% Pozo 40% Pozo 60% Pozo 20% Pozo 80% Pozo 50%

Co

mp

ress

ive

str

en

gth

, Mp

a

Mix

21 days

0.0

5.0

10.0

15.0

20.0

25.0

30.0

Control Pozo 30% Pozo 70% Pozo 40% Pozo 60% Pozo 20% Pozo 80% Pozo 50%

Co

mp

ress

ive

stre

ngt

h, M

pa

Mix

28 days

- 59 -

Fig. 4.9: Effect of pozzolanic replacement on the compressive strength of concrete at all ages

Fig. 4.10: line diagram illustrating the effect of pozzolanic replacement on the compressive

strength of concrete at all age

0.0

5.0

10.0

15.0

20.0

25.0

30.0

Control Pozo 30% Pozo 70% Pozo 40% Pozo 60% Pozo 20% Pozo 80% Pozo 50%

Co

mp

ress

ive

str

en

gth

, Mp

a

Mix

7 days

14 days

21 days

28 days

0.0

10.0

20.0

30.0

0 7 14 21 28

Co

mp

ress

ive

Stre

ngt

h, M

Pa

Age, days

Control

Pozo 30%

Pozo 70%

Pozo 40%

Pozo 60%

Pozo 20%

- 60 -

Table 4.9: A One -Sample Statistics for Various Concrete From 7 -28 Days

N Mean Std. Deviation Std. Error Mean

Control 3 25.6897 .58950 .34035

Pozo 30% 3 25.9377 .92130 .53191

Pozo 70% 3 7.6283 .53804 .31064

Pozo 40% 3 16.0597 .63762 .36813

Pozo 60% 3 11.9230 .55942 .32298

Pozo 20% 3 17.9443 2.35922 1.36210

Pozo 80% 3 3.6670 .46567 .26886

Pozo 50% 3 13.6237 2.18576 1.26195

Table 4.10: 95% Confidence Interval of the Difference for Various Concrete From 7 -28 Days

Test Value = 0

t df

Sig. (2-

tailed)

Mean

Difference

95% Confidence Interval

of the Difference

Lower Upper

Control 75.481 2 .000 25.68967 24.2253 27.1541

Pozo 30% 48.763 2 .000 25.93767 23.6490 28.2263

Pozo 70% 24.557 2 .002 7.62833 6.2918 8.9649

Pozo 40% 43.625 2 .001 16.05967 14.4757 17.6436

Pozo 60% 36.916 2 .001 11.92300 10.5333 13.3127

Pozo 20% 13.174 2 .006 17.94433 12.0837 23.8050

Pozo 80% 13.639 2 .005 3.66700 2.5102 4.8238

Pozo 50% 10.796 2 .008 13.62367 8.1939 19.0534

- 61 -

Confidence interval (interval estimator) is a formula that tells how to use sample data to

calculate an interval that estimates a population parameter. The chosen confidence level of

95% implies that the method used to construct each of the intervals has 5% long-run error

rate.

In the correct interpretation, the level of 95% refers to the success rate of the process being

used to estimate the proportions and does not refer to the population proportion itself.

Based on the information provided by the various mix proportions, we can be 95% confident

that the mean total of the samples are between their corresponding 95% confidence interval

of the differences. The intervals are relatively wide indicating that the values of the

population mean have not been estimated more precisely in either case. This is not surprising

given the reported sample size. Also it is noted that most of the intervals are relatively

overlapping and this may cause a sceptical statement that a particular sample has a higher

95% confidence level in terms of average 28 day compressive strength compared to others,

―however we are 95% confident that the intervals for the various mixes actually does contain

the true value p” this means that if we were to select many different samples of the same

mixes and construct the corresponding intervals, 95% of them would actually contain the

value of the population proportion.

- 62 -

Table 4.11: A Correlation Matrix for Various Concrete From 7 -28 Days

Contro

l

Pozo

30%

Pozo

70%

Pozo

40%

Pozo

60%

Pozo

20%

Pozo

80%

Pozo

50%

Sig. (1-

tailed)

Control .031 .031 .473 .483 .173 .288 .388

Pozo

30% .031

.062 .496 .452 .204 .319 .357

Pozo

70% .031 .062

.442 .486 .142 .257 .419

Pozo

40% .473 .496 .442

.044 .300 .185 .139

Pozo

60% .483 .452 .486 .044

.344 .229 .095

Pozo

20% .173 .204 .142 .300 .344

.115 .439

Pozo

80% .288 .319 .257 .185 .229 .115

.324

Pozo

50% .388 .357 .419 .139 .095 .439 .324

Table 4.12: An Explanation of the Total Variance of Concrete From 7 -28 Days

Compon

ent

Initial Eigenvalues Extraction Sums of Squared Loadings

Total % of Variance Cumulative % Total % of Variance Cumulative %

1 4.673 58.409 58.409 4.673 58.409 58.409

2 3.327 41.591 100.000 3.327 41.591 100.000

3 4.054E-16 5.067E-15 100.000

4 1.252E-16 1.565E-15 100.000

5 6.385E-17 7.981E-16 100.000

6 -7.461E-18 -9.326E-17 100.000

7 -1.245E-16 -1.557E-15 100.000

8 -1.931E-16 -2.414E-15 100.000

Extraction Method: Principal Component Analysis.

- 63 -

CHAPTER FIVE

CONCLUSION AND RECOMMENDATION

5.1 CONCLUSION

This study was conducted to assess the performance of concrete cubes utilizing natural

pozzolanic material as a partial replacement to ordinary Portland cement. The following

conclusions were drawn from the present study.

The partial replacement mix of 30% pozzolana attained the highest compressive

strength after 28 days as proved by other researchers in earlier works.

Pozzolana concrete could be used in project when early age strength is required

without having detrimental effect on the early age or later age strength development.

The early age compressive strength in this research was found to be higher than that

of Portland Cement concrete (Control)

The inclusion of natural pozzolana in the concrete as a partial replacement was not

detrimental to the properties of concrete. Slump loss, compaction factor and

compressive strength were similar to that of corresponding control mix.

Partial replacement mixes of 20%. 40%, 50%, 60%, 70% and 80% Pozzolana did not

attain the design strength of 20 N/mm2 after 28 days.

- 64 -

5.2 RECOMMENDATIONS

Generally the use of pozzolana has the advantage of lower costs and better durability.

After appraising the results and conclusion from the study the following recommendations

were made:

Compressive strength and workability tests suggested that pozzolan, could be

substituted for Portland cement at up to 30% in the production of concrete with no

loss in workability or strength.

The pozzolanic reactivity could be significantly improved by using one or a

combination of several treatment methods. However, all methods may not be feasible

to achieve the optimum level. Therefore, it is strongly recommended that, besides

employing various treatment methods, the feasibility and practical applicability of

each method needs to be investigated in greater details.

- 65 -

REFERENCES

1. Aitcin P.C and Neville A. ―High-Performance Concrete Demystified,‖ Concrete

International, Vol. 15, No. 1 pp. 21-26, 1993][O.E. Gjorv, ―High Strenght Concrete,‖

Advances in Concrete Technology,. Malhotra V. M, Ed., CANMET, Energy, Mines

sand Resources, Canada, 1994, pp. 19-82.

2. Alhoziamy A.; Soroushian P. and F. Mirza, ―Effects of Curing Conditions and Age

on Chloride Permeability of Fly Ash Mortar‖, ACI Material Journal, Vol. 93 No. 1,

pp. 87-95, Jan-Feb 1996.

3. Coal Fly Ash journal. (2009), pp.2

4. Cook D.J., ― Natural Pozzolana,‖ Cement Replacement Material Vol. 3, Editor,

Swamy R.N., Surry Press, UK, 1986

5. Dr. Muhammad Iqbal khan (PI) Dr. Abdurrahman M. Alhozaimy (2005). King Saud

University College of engineering research center. Final research report no. 423 / 33.

6. Gjorv O.E ―High Strenght Concrete,‖ Advances in Concrete Technology,V. M.

Malhotra, Ed., CANMET, Energy, Mines sand Resources, Canada, 1994, pp. 19-82

7. Guide for MEASURING, Transporting, and Placing Concrete.‖ ACI Committee 304,

ACI Manual of Concrete Practice, Part 2, 2003.

8. http://en.wikipedia.org/wiki/Concrete#Concrete_production, 21/12/09

9. ICAR, Summary of Concrete Workability Test Method, 2001

10. Malhotra V.M. and. Mehta P.K, ―Pozzolanic and Cementitious Materials-Advances in

Concrete Technology,‖ Vol. I, Gordon ND Breach Publishers, Amsterdam,

Netherlands, 1996

11. Mehta P. K. and Monteiro P.J.M, ―Concrete Structure, Properties and Materials,‖

Prentice Hall, USA. 1995

12. Mehta P.K., ―Studies on Blended Portland Cement Containing Santorin Earth,‖

Cement and Concrete Research, Vol. 11 pp. 507-518, 1981

13. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation

14. Nehdi, M. (2001) Tenary and quaternary cement for sustainable development.

Concrete International, 23 (4), PP.35-42.

15. Neville A.M, ―Properties of Concrete,‖ Fourth Edition, Longman, UK, 1996.

16. Sumrerng Rukzon,‖Construction Building and Design‖, SAGE publication,

London,2009.

- 66 -

APPENDIX A

- 67 -

- 68 -

- 69 -

APPENDIX B

DESIGN MIX CALCULATION

It was supposed that the concrete is required for use on roadwork, that it is to be

compacted by power-operated machines, that OPC is to be used, that the aggregate will be

supplied in two sizes and that the concrete is to have a minimum strength of 20 C at 28

days. Reference to Table 1, shows that under such conditions the minimum strength may be

expected to be about 60 percent of the average strength.

The average strength to be aimed at in this design procedure would, therefore, be

𝟐𝟎

𝟔𝟎 × 𝟏𝟎𝟎 = 𝟑𝟑.𝟑𝟑 ≈ 𝟑𝟒 𝑵/𝒎𝒎𝟐

Water cement ratio = 0.55

Workability required = medium

Aggregate size and shape = 19mm Angular

Total Aggregate weight after sieve analysis test= 8.930g

(See Tables 4.3 and 4.4 for sieve analysis test results)

Percentage error = 𝟗 𝒌𝒈−𝟖.𝟗𝟑 𝒌𝒈 ×𝟏𝟎𝟎

𝟖.𝟗𝟑 𝒌𝒈

= 𝟎.𝟕𝟖%

Appendix B. Table 1a

1 2 3 4

19 100 92.0 100 92 100 93 100 93

10 45 48.4 55 52 65 57 75 62

5 30 30.0 35 35 42 42 48 48

No 7 23 30.4 28 34 35 41 42 46

No 14 16 22.3 21 26 28 29 34 36

No 25 8 16.0 14 18 21 23 27 26

No 52 2 10.0 3 11 5 14 12 16

No 100 0 0.0 0 0 0 0 1.5 0

Source: Laboratory test, 2010

Grading curve selected from sieve analysis = curve 4 (Appendix B. Table 1a)

- 70 -

Aggregate cement Ratio (for medium size aggregate) from table 3 = 1:6.4

Percentage of fine to course aggregate = 48%

RATIOS

W/C : CEMENT : AGGREGATE

𝟎.𝟓𝟓 ∶ 𝟏 ∶ 𝟔.𝟒

𝟎.𝟓𝟓 ∶ 𝟏 ∶ 𝟒𝟖

𝟏𝟎𝟎 × 𝟔.𝟒 ∶ 𝟔.𝟒 −

𝟒𝟖

𝟏𝟎𝟎 × 𝟔.𝟒

𝟎.𝟓𝟓 ∶ 𝟏 ∶ 𝟑.𝟎𝟕 ∶ 𝟑.𝟑𝟑

Comparing the design ratio, 1:3.07:3.33 to the natural ratios, then the mix ratio of 1:2:4 for

the design.