Met a Kaolin

PSZ 19:16 (Pind.1/97)

UNIVERSITI TEKNOLOGI MALAYSIA

BORANG PENGESAHAN STATUS TESIS♦

JUDUL:

_ _____ _

SESI PENGAJIAN: 2006/ 2007 / 01_ Saya: _______________ __________________ ___

(HURUF BESAR)

mengaku membenarkan tesis (PSM / Sarjana / Doktor Falsafah)* ini disimpan di Perpustakaan Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut: 1. Tesis adalah hakmilik Universiti Teknologi Malaysia. 2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi. 4. ** Sila tandakan ( ) (Mengandungi maklumat yang berdarjah keselamatan atau SULIT kepentingan Malaysia seperti yang termaktub di dalam ATKA RAHSIA RASMI 1972) (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan) TIDAK TERHAD Disahkan oleh (TANDATANGAN PENULIS) (TANDATANGAN PENYELIA)

Alamat Tetap:

_____________ _ _ _ ___________________________ Nama Penyelia

Tarikh: ___6 NOVEMBER 2006_____ Tarikh: ____6 NOVEMBER 2006___ __

769, TAMAN KOTAMAS, 70200 SEREMBAN, NEGERI SEMBILAN.

ONG CHEE HUAT

PERFORMANCE OF CONCRETE CONTAINING METAKAOLIN AS CEMENT REPLACEMENT MATERIAL

P.M. DR. ABDUL RAHMAN MOHD. SAM

TERHAD

CATATAN: * Potong yang tidak berkenaan. ** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/ organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu

dikelaskan sebagai SULIT atau TERHAD. ♦ Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana secara

Penyelidikan, atau disertai bagi pengajian secara kerja kursus dan penyelidikan, atau Laporan Projek Sarjana Muda (PSM).

“I/We hereby declare that I/we have read this project report and in my/our opinion this

report is sufficient in terms of scope and quality for the award of the degree of Master of

Engineering (Civil - Structure).”

Signature :

Name of Supervisor : Assoc. Prof. Dr. Abdul Rahman Mohd. Sam

Date : 6 November 2006

PERFORMANCE OF CONCRETE CONTAINGING METAKAOLIN AS

CEMENT REPLACEMENT MATERIAL

ONG CHEE HUAT

A project report submitted in partial fulfillment of

the requirements for the award of the degree of

Master of Engineering (Civil - Structure)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

NOVEMBER, 2006

ii

I declare that this project entitled “Performance of Concrete Containing Metakaolin

As Cement Replacement Material” is the result of my own research except as cited in

the references. The report has not been accepted for any degree and is not

concurrently submitted in candidature of any other degree.

Signature :

Name of Author : Ong Chee Huat

Date : 6/11/2006

iii

To my beloved parents and family

iv

ACKNOWLEDGEMENT

I would like to express my greatest appreciation to my supervisor, Assoc.

Prof. Dr. Abdul Rahman Mohd. Sam, for his generous guidance, advice and

motivation throughout this research.

A special thank dedicated to my beloved parents and family, for their

continuing financial and morale supports throughout my studies. Finally, my sincere

appreciation also extends to all my friends, the structural laboratory personnel, those

who were directly or indirectly involved in the process of producing this research

report, for their generous assistance, useful views and tips.

Without their support and contribution, this research project would not have

been possible.

v

ABSTRACT

Concrete is probably the most extensively used construction material in the

world. However, environmental concerns both in terms of damage caused by the

extraction of raw material and CO2 emission during cement manufacture have

brought pressures to reduce cement consumption by the use of supplementary

materials. The utilization of calcined clay, in the form of metakaolin (MK) in

concrete has received considerable attention in recent years. On this matter, a study

has been conducted to look into the performance of metakaolin as cement

replacement material in concrete. The study focuses on the compressive strength

performance of the blended concrete containing different percentage of metakaolin.

The cement is replaced accordingly with the percentage of 5 %, 10%, 15%, 20% and

30% by weight. Concrete cubes are tested at the age of 1, 3, 7, and 28 days. In

addition, the effect of calcination temperature to the strength performance is included

in the study. Finally, the strength performance of metakaolin-concrete is compared

with the performance of concrete blended with silica fume and slag. The results show

that the strength development of concrete blended with metakaolin is enhanced. It

was found that 10% replacement appears to be the optimum replacement where

concrete exhibits enhanced compressive strength at all ages comparable to the

performance of SF and GGBS. The study also reveals that optimum calcination

temperature of 750°C is important to improve the performance of metakaolin-

concrete.

vi

ABSTRAK

Konkrit merupakan salah satu bahan binaan yang paling banyak digunakan

dalam dunia. Akan tetapi, terdapat masalah pencemeran persekitaran yang

disebabkan oleh penggunaan simen dalam konkrit. Pencemaran berlaku semasa

pengekstrakan bahan mentah dan penghasilan karbon dioksida semasa pemprosesan

simen. Hal ini telah menimbulkan tekanan untuk mengurangkan penggunaan simen

dan diganti oleh bahan gantian. Penggunaan tanah liat terbakar dalam bentuk

metakaolin (MK) dalam konkrit telah mendapat perhatian yang lebih kebelakangan

ini. Dalam hal ini, satu kajian telah dijalankan untuk mengkaji prestasi metakaolin

sebagai bahan gantian simen dalam konkrit. Kajian ditumpukan ke atas kekuatan

mampatan konkrit yang mengandungi metakaolin dalam peratusan yang berbeza.

Simen digantikan dalam peratusan 5 %, 10%, 15%, 20% dan 30% mengikut berat.

Kekuatan konkrit diuji pada hari ke-1, 3, 7 dan 28. Pada masa yang sama, pengaruh

suhu bakaran ke atas kekuatan mampatan turut dikaji. Prestasi kekuatan konkrit-

metakaolin juga dibandingkan dengan prestasi konkrit yang mengandungi wasap

silika dan sanga relau bagas. Keputusan eksperimen menunjukkan gantian

metakaolin dalam konkrit telah meningkatkan perkembangan kekuatan mampatan

konkrit di mana gantian 10% merupakan peratusan gantian yang paling optima.

Kajian juga mendapati metakaolin adalah setara dengan bahan gantian simen yang

lain seperti wasap silika dan sanga relau bagas dalan perkembangan dan peningkatan

kekuatan mampatan konkrit. Suhu bakaran didapati mempunyai pengaruh yang

ketara terhadap kekuatan mampatan konkrit-metakaolin. Kajian menunjukkan Suhu

bakaran setinggi 750°C merupakan suhu yang paling sesuai bagi meningkatkan

prestasi konkrit-metakaolin.

vii

CONTENTS

CHAPTER SUBJECT PAGE

THESIS TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SHORTFORMS xvi

LIST OF APPENDICES xv

CHAPTER I INTRODUCTION 1

1.0 Introduction 1

1.1 Objective of Study 3

1.2 Significant of the Study 3

1.3 Scope of Study 4

viii

CHAPTER II LITERATURE REVIEW 6

2.0 Concrete 6

2.1 Cement 8

2.2 Cement Replacement Material 10

2.2.1 Pozzolanic Behavior 10

2.2.2 Types of Material 11

2.3 Kaolin 14

2.3.1 Classification 15

2.3.2 Mineralogy 16

2.4 Physical and Chemical Properties of Kaolin 16

2.4.1 Particle Size 17

2.4.2 Color and Brightness 18

2.4.3 pH 19

2.4.4 Chemical Composition 19

2.5 Application and Specification 20

2.5.1 Paper 20

2.5.2 Ceramic and Refractory 21

2.5.3 Rubber 22

2.5.4 Paints 22

2.5.5 Others Uses 23

2.6 Calcination 24

2.6.1 Temperature 26

2.6.2 Method of Calcination 28

2.7 Metakaolin 29

2.7.1 Sources for Metakaolin 30

2.7.2 High Reactivity Metakaolin 31

2.8 The Pozzolanic Reaction 33

CHAPTER III RESEARCH METHODOLOGY 35

3.0 Introduction 35

3.1 Materials 36

ix

3.1.1 Cement 36

3.1.2 Kaolin 37

3.1.3 Silica Fume 37

3.1.4 Ground Granulated Blast Furnace Slag 37

3.1.5 Sand and Aggregate 40

3.1.6 Water 40

3.2 Calcining Kaolin 41

3.3 Concrete Mixes 42

3.4 Mixing Procedure 43

3.5 Preparing Test Cubes 44

3.6 Curing 44

3.7 Compression Test 46

CHAPTER IV RESULT AND DISCUSSION 48

4.0 Introduction 48

4.1 Effect of MK to Compressive Strength 49

4.1.1 5% and 15% Replacement 49

4.1.2 10% Replacement 53

4.1.3 20% and 30% Replacement 55

4.2 Effect of Calcination Temperatures to Strength 60

Development

4.2.1 Effect of Calcination 60

4.3 Effect of Calcination Temperature 61

(10% Replacement)

4.4 Effect of Calcination Temperature 67

(20% Replacement)

4.5 Comparison between MK and Others Pozzolans 71

to the Strength Performance of Concrete

4.6 Further Discussion 75

x

CHAPTER V CONCLUSIONS AND RECOMMENDATIONS 80

5.1 Conclusion 80

5.2 Recommendations 81

REFERENCE 83

APPENDIX 86

xi

LIST OF TABLES

TABLE NO. TITLE` PAGE

2.1 Typical Properties of Normal-Strength Portland 7

Cement Concrete.

2.2 Properties of Kaolin. 17

2.3 Chemical Properties of Kaolin 19

3.1 Properties of Cement, Kaolin, SF and GGBS 38

3.2 Mix Proportions 43

4.1 Cube Test Results for Different Mix Ratios 51

4.2 Cube Test Results for Mixes with Different Calcination 62

Temperatures

4.3 Cube Test Results for Mixes with Different Calcination 67

Temperatures

4.4 Strength Comparison between MK, SF and GGBS Concrete 71

4.5 Compression Test Results for Cubes Cured In Water 75

4.6 Compression Test Results for Cubes Cured Using Sacks 76

xii

LIST OF FIGURES

FIGURE NO. TITLE` PAGE

2.1 Fly Ash. 11

2.2 Silica Fume. 13

2.3 Kaolin. 14

2.4 Structure of Kaolinite. 15

2.5 Kaolin Particle Size. 18

2.6 Crystalline of Kaolinite. 24

2.7 DTA Curve. 25

2.8 SEM Photographs of Calcined Kaolin at Temperature 27

(a) 550°C, (b) 650°C, (c) 800°C and (d) 900°C.

2.9 Rotary Kiln. 28

2.10 Metakaolin Particle. 30

3.1 Flow Chart of the Study. 36

3.2 Kaolin. 39

3.3 Silica Fume. 39

3.4 Ground Granulated Blast Furnace Slag. 39

3.5 Oven for Heating the Aggregates. 40

3.6 Calcining Kaolin. 41

3.7 Kaolin Before Calcination and After Calcination. 42

3.8 Curing Using Sacks. 45

3.9 Covering the Sacks with Plastic Sheets. 45

3.10 Concrete Cubes. 46

3.11 Compression Test 47

3.12 The Tested Cubes 47

xiii

4.1 Compressive Strength For 5% And 15% Replacement 52

Compared to Control

4.2 Compressive Strength For 10% Replacement Compared 54

to Control

4.3 Compressive Strength For 20% And 30% Replacement 56

Compared to Control

4.4 Strength Development for Various Mixes 59

4.5 Strength Performance With 10% MK Calcined at Various 63

Temperatures

4.6 XRD Pattern of Kaolin 64

4.7 Strength Performance With 20% MK Calcined at Various 68

Temperatures

4.8 Strength Comparison for MK, SF and GGBS Concrete 72

4.9 Compression Test Results For Cubes Cured In Water and 77

Cured Using Sacks

4.10 White Sediment Forming On The Top of the Cube 78

4.11 Bubbles on the Surface of the Cube 79

xiv

LIST OF SHORTFORMS

% - percentage

°C - Celcius

GGBS - Ground Granulated Blast Furnace Slag

kg - kilograms

m - meter

m3 - meter cubes

MK - Metakaolin

MPa - Mega Pascal

SF - Silica Fume

xv

LIST OF APPENDICES

APPENDIX TITLE` PAGE

A Silica Fume 86

1

CHAPTER 1

INTRODUCTION 1.0 Introduction

Concrete is one of the most common materials used in the construction

industry. In the past few years, many research and modification has been done to

produce concrete which has the desired characteristics. There is always a search for

concrete with higher strength and durability. In this matter, blended cement concrete

has been introduced to suit the current requirements. Cementitious materials known

as pozzolans are used as concrete constituents, in addition to Portland cement.

Originally the term pozzolan was associated with naturally formed volcanic ashes

and calcined earths will react with lime at ambient temperatures in the presence of

water. Recently, the term has been extended to cover all siliceous/aluminous

materials which, in finely divided form and in the presence of water, will react with

calcium hydroxide to form compounds that possess cementitious properties. The

current area of research in the concrete is introducing clay (metakaolin) in the

concrete. Clays have been and continue to be one of the most important industrial

minerals. Clays and clay minerals are widely utilized in our society. They are

important in geology, agriculture, construction, engineering, process industries, and

environmental applications. Traditional applications of clay including ceramics,

2

paper, paint, plastics, drilling fluids, chemical carriers, liquid barriers, and catalysis.

Research and development activities by researchers in higher education and industry

are continually resulting new and innovative clay products.

Metakaolin is one of the innovative clay products developed in recent years.

It is produced by controlled thermal treatment of kaolin. Metakaolin can be used as a

concrete constituent, replacing part of the cement content since it has pozzolanic

properties. The use of metakaolin as a partial cement replacement material in mortar

and concrete has been studied widely in recent years. Despite of the recent studies,

there are still many unknowns with the use of metakaolin. Study is needed to

determine the contribution of metakaolin to the performance of hardened concrete.

There are great concerns on the strength and durability of metakaolin-concrete when

used as construction materials in the construction industries. If it is proven that the

concrete is durable and strong, this will lead to the use of metakaolin to replace part

of the cement.

3

1.1 Objective of Study This study is conducted to accomplish some predefined objectives. These

objectives are:

i) To study the performance of concrete containing different percentages

of metakaolin and to identify the optimum replacement percentage. ii) To investigate the effect of calcination temperatures to the strength

performance of metakaolin-concrete.

iii) To compare the performance of metakaolin with other cement

replacement materials (CRMs).

1.2 Significant of the Study Concrete has been used in the construction industry for centuries. Many

modifications and developments have been made to improve the performance of

concrete, especially in terms of strength and durability. The introduction of pozzolans as cement replacement materials in recent

years seems to be successful. The use of pozzolan has proven to be an effective

solution in enhancing the properties of concrete in terms of strength and durability.

The current pozzolans in use are such as fly ash, silica fume and slag. Development

and investigation of other sources of pozzolan such as kaolin will be able to provide

more alternatives for the engineer to select the most suitable cement replacement

4

material for different environments.

Unlike other pozzolans, metakaolin is not a by-product which means its

engineering values are well-controlled. Therefore, using metakaolin should promise

some advantages compared to other cement replacement materials. In this case,

studies are needed to study the performance of concrete using metakaolin. The

performance of metakaolin-concrete will be compared to the cost of production of

metakaolin to determine whether metakaolin is worthy to be developed as a new

cement replacement material. In addition, the use of metakaolin is not common in the Malaysian

construction sector. This study will be able to enhance the understanding on the

suitability of metakaolin as cement replacement material. 1.4 Scope of Study

This study focuses on the strength performance of concrete with metakaolin.

Strength is the most important property of concrete since the first consideration in

structural design is that the structural elements must be capable of carrying the

imposed loads. Strength characteristic is also important because it is related to

several other important properties which are more difficult to measure directly. With regard to this matter, the development of compression strength of

metakaolin concrete is studied. Cement replacements by 5%, 10%, 15%, 20% and

30% with metakaolin are studied. Concrete tests are conducted on the concrete

samples at the specific ages. All the strength tests are limited to the ages of 28 days.

5

In the study of the effect of calcination temperatures to the strength

performance of metakaolin, the temperatures is set within the range of 600°C-800°C.

The temperatures interval used is 50°C. For the performance comparison study, the cement replacement materials

used are silica fume and ground granulated blast furnace slag. These two cement

replacement materials are chosen as they are the most common replacement

materials nowadays and will be good comparisons to metakaolin. The comparison is

made on the compressive strength performance of metakaolin, silica fume and slag

concrete.

6

CHAPTER 2

LITERATURE REVIEW 2.0 Concrete

Concrete is known to be a simple material in appearance but with a very

complex internal nature. In contrast to its internal complexity, versatility, durability,

and economy of concrete have made it the most frequently used construction

material in the world. Concrete is a mixture of cement, water, and aggregates, with or without

admixtures. The cement and water will form a paste that hardens as a result of a

chemical reaction between the cement and water. The paste acts as glue, binding the

aggregates (sand and gravel or crushed stone) into a solid rock-like mass. The quality

of the paste and the aggregates dictate the engineering properties of this construction

material. During hydration and hardening, concrete will develop certain physical and

chemical properties, among others, mechanical strength, low permeability and

chemical and volume stability. Concrete has relatively high compressive strength,

but significantly lower tensile strength (about 10% of the compressive strength).

Table 2.1 shows the typical properties of normal strength Portland cement concrete

(Hewlett, 1998).

7

Table 2.1: Typical Properties of Normal-Strength Portland Cement Concrete

Characteristic

Compressive strength 20–40 MPa

Flexural strength 3–5 MPa

Tensile strength 2–5 MPa

Modulus of elasticity 14,000–41,000 MPa

Permeability 1x10–10 cm/sec

Coefficient of thermal expansion 10–5/°C

Drying shrinkage 4–8 x 10–4

Drying shrinkage of reinforced concrete 2–3 x 10–4

Poisson’s ratio 0.20–0.21

Shear strain 6000–17,000 MPa

Density 2240–2400 kg/m3

Concrete is used to make pavements, building structures, foundations, roads,

overpasses, parking structures, brick/block walls and bases for gates, fences and

poles. Over six billion tons of concrete are made each year, amounting to the

equivalent of one ton for every person on Earth, and powers a US$35 billion industry

which employs over two million workers in the United States alone (Kosmatka,1999).

Over 55,000 miles of freeways and highways in America are made of concrete.

8

2.1 Cement

Cements may be defined as adhesive substances capable of uniting

fragments or masses of solid mater to a compact whole (Lea, 1970). Portland cement

was invented in 1824 by an English mason, Joseph Aspdin, who named his product

Portland cement because it produced a concrete that was of the same color as natural

stone on the Isle of Portland in the English Channel. Raw materials for manufacturing cement consist of basically calcareous and

siliceous (generally argillaceous) material. The mixture is heated to a high

temperature within a rotating kiln to produce a complex group of chemicals,

collectively called cement clinker (Neville, 1987). Cement is distinct from the

ancient cement. It is termed hydraulic cement for its ability to set and harden under

water. Briefly, the chemicals present in clinker are nominally the four major potential

compounds and several minor compounds. The four major potential compounds are

normally termed as tricalcium silicate (3CaO.SiO2), dicalcium silicate (2CaO.SiO2),

tricalcium aluminate (3CaO.Al2O3) and tetracalcium aluminoferrite (4CaO.

Al2O3.Fe2O3). The American Society for Testing and Materials (ASTM) Standard C 150,

Specification for Portland cement, provides for the following types of Portland

cement:

Type I General Portland cement

Type II Moderate-sulfate-resistant cement

Type III High-early-strength cement

Type IV Low–heat-of-hydration cement

Type V High-sulfate-resistant cement

9

Type I Portland cement is a general cement suitable for all uses where

special properties of other cements are not required. It is commonly used in

pavements, building, bridges, and precast concrete products.

Type II Portland cement is used where precaution against moderate sulfate

attack is important where sulfate concentrations in groundwater or soil are higher

than normal, but not severe. Type II cement can also be specified to generate less

heat than Type I cement. This moderate heat of hydration requirement is helpful

when placing massive structures, such as piers, heavy abutments, and retaining walls.

Type II cement may be specified when water-soluble sulfate in soil is between 0.1

and 0.2%, or when the sulfate content in water is between 150 and 1500 ppm. Types

I and II are the most common cements available. Type III Portland cement provides strength at an early age. It is chemically

similar to Type I cement except that the particles have been ground finer to increase

the rate of hydration. It is commonly used in fast-track paving or when the concrete

structure must be put into service as soon as possible, such as in bridge deck repair. Type IV Portland cement is used where the rate and amount of heat

generated from hydration must be minimized. This low heat of hydration cement is

intended for large, massive structures, such as gravity dams. Type IV cement is

rarely available. Type V Portland cement is used in concrete exposed to very severe sulfate

exposures. Type V cements would be used when concrete is exposed to soil with a

water-soluble sulfate content of 0.2% and higher or to water with over 1500 ppm of

sulfate. The high sulfate resistance of Type V cement is attributed to its low

tricalcium aluminate content.

10

2.2 Cement Replacement Material With the extensively use of cement in concrete, there has been some

environmental concerns in terms of damage caused by the extraction of raw material

and CO2 emission during cement manufacture. This has brought pressures to reduce

the cement consumption in the industry. At the same time, there are getting more

requirements for enhancement in concrete durability to sustain the changing

environment which is apparently different from the old days.

With the development in concrete technology, cement replacement materials

(CRM) have been introduced as substitutes for cement in concrete. Several types of

materials are in common use, some of which are by-products from other industrial

processes, and hence their use may have economic advantages. However, the main

reason for their use is that they can give a variety of useful enhancements or

modifications to the concrete properties. All the materials have two common features

(Malhotra, 1986): i) Their particle size range is similar to or smaller than that of Portland

cement. ii) They are pozzolan material.

2.2.1 Pozzolanic Behavior

A common feature of nearly all CRM is that they exhibit pozzolanic

behaviour. Pozzolanic materials the materials which contains active silica (SiO2) and

11

is not cementitious in itself but will, in a finely divided form and in the presence of

moisture, chemically react with calcium hydroxide at ordinary temperatures to form

cementitious compounds (Malhotra, 1983). 2.2.2 Types of Cement Replacement Material

The main cement replacement materials in use world-wide are:

i) Fly Ash Fly ash (shown in Figure 2.1) is the finely divided mineral residue resulting

from the combustion of powdered coal in electric generating plants. Fly ash

consists of inorganic, incombustible matter present in the coal that has been

fused during combustion into a glassy, amorphous structure. Coal can range

in ash content from 2%-30%, and of this around 85% becomes fly ash. It

can replace up to 50% by mass of Portland cement (Hewlett, 1998), which

can add to the final strength of the concrete and increase chemical resistance

and durability.

Figure 2.1: Fly Ash

12

ii) Ground Granulated Blast Furnace Slag (GGBS)

Ground granulated blast furnace slag or slag is the by-product of smelting

ore to purify metals. They can be considered to be a mixture of metal

oxides. However, they can contain metal sulphides and metal atoms in the

elemental form (Hewlett, 1998). Slags are generally used as a waste

removal mechanism in metal smelting but they can also serve other

purposes such as assisting in smelt temperature control and to minimize

re-oxidation of the final product before casting. Slag has a pozzolanic reaction which allows the increase of concrete

strength. Slag has proven to produce very good and dense concrete allowing

increased durability.

iii) Silica Fume

Silica fume (shown in Figure 2.2) which also known as micro silica, is a

by-product of the reduction of high-purity quartz with coke in electric arc

furnaces in the production of silicon and ferrosilicon alloys. Silica fume is

also collected as a byproduct in the production of other silicon alloys. Because of its extreme fineness and high silica content, silica fume is a

highly effective pozzolanic material. Silica fume is used as an admixture in

Portland cement concretes to improve their qualities. It has been found that

silica fume improves compressive strength, bond strength, and abrasion

resistance (Poon et. al, 2005).

13

Figure 2.2: Silica Fume It may be argued that the most important development in concrete production

in the last century is the utilization of industrial by-products such as fly ash and

ground granulated blast-furnace slag as partial cement replacement materials. This

utilization is now extended to other by-products including silica fume and rice husk

ash. The volume of pozzolanic by-products produced world-wide currently

exceeds that utilized. Many of these by-products contain toxic elements which can be

hazardous if exposed to ground water, when used as land fill or road-bases. Increase

in the utilization of pozzolanic materials in concrete comes from greater awareness

of current and potential uses of alternative recycled materials and wider realization of

the environmental benefits accrued. Such increase in use of waste materials will

contribute to the requirements of environmental protection and sustainable

construction in the future. However, it has been reported that the supply of suitable fly ash and slag for

blending with cements in some countries is becoming more and more limited. There

are compelling reasons to extend the practice of partially replacing cement in

concrete and mortar with waste and other less energy intensive processed materials,

which have pozzolanic properties. One possible source for the production of such a

pozzolan is natural clay (Sabir et al., 2001).

14

The use of kaolin as a partial cement replacement material in mortar and

concrete has been studied widely in recent years (Murat, 1995). The research work

on metakaolin is focused on two main areas. The first one refers to the kaolin

structure, the kaolinite to metakaolinite conversion and the use of analytical

techniques for the thorough examination of kaolin thermal treatment. The second one

concerns the pozzolanic behavior of metakaolin and its effect on cement and

concrete properties. The studies done revealed that calcined kaolin (metakaolin) is a

very effective pozzolan and results in enhanced strength in the concrete.

2.3 Kaolin

The name kaolin is derived from the Chinese term “Kauling” meaning high

ridge, the name for a hill near Jauchau Fu, where this material was mined centuries

ago for ceramics (Hamer, 1977). Figure 2.3 shows the typical view of kaolin. The

main constituent, kaolinite is a hydrous aluminium silicate of the approximate

composition 2H2O.Al2O3.2SiO2. Kaolinite is the clay minerals which provide the

plasticity of the raw material and change during firing to produce a permanent

material.

Figure 2.3: Kaolin

15

Structurally, kaolinite consists of alumina octahedral sheets and silica

tetrahedral sheets stacked alternately with the theoretical composition of 46.54%

SiO2, 39.50% Al2O3 and 13.96% H2O. The arrangement of atoms in the kaolinite

group is shown in Figure 2.4.

Figure 2.4: Structure of Kaolinite Kaolin is one of the most versatile industrial minerals. It is chemically inert

over a relatively wide pH range, is white in color and has good covering power when

used as a pigment or extender. Kaolin is soft and non-abrasive, and has a low

conductivity of heat and electricity. Some uses of kaolin are paper coating, fillers for

paints and plastic require very rigid specifications including particles size, color and

brightness and viscosity whereas other uses require no specifications.

16

2.3.1 Classification Kaolin is generally classified as primary or secondary deposits. Primary

kaolin is formed by the alterations of crystalline rocks such as granite and are found

in the location where they are formed. Secondary kaolin deposits are sedimentary in

nature and are formed by the erosion of primary deposits. As the eroded materials are

washed down stream, separation takes place by gravity and particle size resulting

finer and lighter kaolin 2.3.2 Mineralogy

The term “kaolin” is used as a group name for minerals including kaolinite,

nacrite, deckite and halloysite (Hamer, 1977). Kaolinite normally occurs as crystals

ranging in size from a fraction of a micron up to several hundred microns across.

Halloysite has the same composition as kaolinite with an additional sheet of oriented

water molecules between the layers. In certain ceramic applications, halloysite has

some advantages, but in most other cases its presence is neutral or disadvantageous. 2.4 Physical And Chemical Properties of Kaolin

The physical and chemical properties of kaolin determine its use as an

industrial mineral. These uses are governed by several factors including the

geological conditions under which the kaolin formed the total mineralogical

composition of the kaolin deposit, the physical and chemical properties. Some of the

properties of kaolin are shown in the Table 2.2 (Prasad et al., 1991).

17

Table 2.2: Properties of Kaolin

Properties Description

Color Usually white, colorless, greenish or yellow

Luster Earthy

Transparency: Crystals are translucent

Cleavage Perfect in one direction, basal

Fracture Earthy

Hardness 1.5 - 2 (can leave marks on paper)

Specific gravity 2.6 (average) 2.4.1 Particle Size

Kaolin has the particle size ranging from 0.2-15 microns with the specific

area of 10 000-29 000 m2/kg. The 2 μm point is used as the commercial control point

(Murray, 1991). The coarser kaolin is usually used as filler clays and the finer

materials are normally used as coating products.

The shape and size distribution of kaolin are important factors in controlling

many other properties such as brightness, viscosity, strength and shrinkage. The

particle size is expressed as equivalent spherical diameter (e.s.d.) and is determined

by sedimentation method from a flocculated suspension of clay in water. Cumulative

particle size distribution curves for kaolin of different origin are shown in Figure 2.5

(Murray, 1991).

18

Figure 2.5: Kaolin Particle Size

2.4.2 Color and Brightness

Kaolin is usually white in color but it may also appear in other colors. In

many parts of the world, it is colored red-orange by iron oxide, giving it a distinct

rust hue. Lighter concentrations yield a yellow or light orange color. The optical properties of kaolin are important in most commercial

application. The presence of ancillary minerals such as micas may contribute to the

color impurities. This may be removed using chemical treatment.

19

2.4.3 pH

The pH of kaolin ranges from 2.0 – 7.5. A high pH generally indicates the

presence of soluble salts which can cause severe problems in many applications.

2.4.4 Chemical Composition

According to Malaysian Standard (MS 756), the properties of the kaolin are

shown in Table 2.3.

Table 2.3: Chemical Properties of Kaolin

Characteristic Percent by mass

Alumina (Al2O3)

Silica (SiO2)

Iron Oxide (Fe2O3)

Titanium Dioxide (TiO2)

Potash (K2O)

Sodium (Na2O)

Loss On Ignition

Fineness (Residue on 38 micron

sieve)

Water Of Plasticity

Linear Shrinkage: (Drying)

(Firing at 1000°C)

36.0 – 39.0

45.0 – 47.0

1.0 max

1.0 max

2.0 max

2.0 max

12.5 min

1.0 max

20.0 min

7.0 max

18.0 max

20

The major chemical constituents in kaolin are silica (SiO2) and alumina

(Al2O3) forming over 70% by mass of kaolin. Silica and alumina are the crucial

ingredients in clay and allow for the development of an interlocking crystal matrix

after firing in earthenware, stoneware and porcelain ceramic processes. The presence

of iron and titanium oxide minerals is disadvantageous as they impair whiteness and

reduce brightness. Also, the presence of excess silica in the form of quartz or

cristobalite generally introduces abrasion problems in paper applications. The

presence of micas and feldspar may influence the brightness and abrasion

characteristics.

2.5 Application and Specification

Kaolin is an extremely useful mineral raw material. Its properties of white

color, softness, small particle size and chemical inertness make it suitable for a

number of different industrial applications (Murray, 2000). The physical and

chemical properties of kaolin determine its use as an industrial mineral. These uses

are governed by several factors including the geological conditions under which the

kaolin formed the total mineralogical composition of the kaolin deposit, and the

physical and chemical properties.

2.5.1 Paper

The paper industry is the largest single user of kaolin (Murray, 2000).

Kaolin is used in paper to add a bright, glossy sheen as in magazine, to improve the

ink receptiveness and smoothness of fibrous papers and as a substitute for pulp.

There are two basic types of kaolin used in paper i.e. filler kaolin and coating kaolin.

21

Kaolin’s principal function as a filler is to act as a substitute for the

expensive pulp web to reduce the cost. The actual loading level depends on the pulp

used and the final product requirement. Kaolin also has a principal advantage of its

chemical inertness to other paper making material. In addition to the cost reduction,

kaolin filler also enhances opacity, brightness and printability. In the use as paper coating, kaolin can endow the paper with a

topographically smooth, bright surface, possessing good ink receptive properties.

Besides, kaolin also possesses rheological properties suitable for modern high-speed

paper coating machine. A smooth paper is at prerequisite in producing high gloss

paper with good printability. 2.5.2 Ceramic and Refractory

One of the highest volume non-paper uses for kaolin is in the ceramics and

refractory industries. Clay is an essential raw material in ceramic production,

comprising 25-100% of the ceramic body. Kaolin is only one of a number of clays

used in this industry. Kaolin makes up an average of 25% of earthenware, 60% of

porcelain and wall tiles (Murray, 2000). Refractory uses include linings of

open-hearth and blast furnaces in the steel industry and in cement and ceramic films.

The use of kaolin in the ceramic and refractory industries can be separated

into two groups based on the important of a white firing color to the end-use.

White-firing colors are most important in the production of porcelains and wall or

floor tiles.

22

Important properties for the use of kaolin in ceramic and refectories are

green strength (wet strength), dry strength, drying and firing shrinkage, refractory

grade and fires colors. Kaolin has high green and dry strength but is not very plastic

when wet, which create some problem when molding. 2.5.3 Rubber

The beneficial quality of kaolin for rubber is its low cost since it is much

cheaper than either natural or synthetic rubber. Kaolin stiffens the compound and

reinforces it when cured. It is used as a low cost pigment. Kaolin is normally used in

non-black rubber goods such as toys and floor mats. Kaolin used in the rubber

industry must have low amount of coarse materials, very fine grain size, low amouns

of impurities, pH value of 4.5 to 5.5 and a constant specific gravity so that it can be

formulated with the other ingredients of the rubber compound.

2.5.4 Paints Kaolin is used in the manufacture of paint as an extender white pigment. It

increases the whiteness of paint but will not add to the covering power of paint on it

own. It can increase the covering power of other pigments because of its flat shape in

which particles arrange themselves in an overlapping pattern. Kaolin is also valued

for its hydrophilic characteristics, which make it a premier extender in latex paint.

23

However, kaolin will reduce the gloss in gloss paint because of its high oil

absorption characteristics. Thus, kaolin is limited to not more than 10% by weight in

paint.

2.5.5 Other uses

Kaolin can be used in plastics, adhesive and fiberglass industries as a filler

to substitute for resin. The advantages of using kaolin in these products are that

kaolin can reduce the material costs and also act as perfect filler in these industries.

The chemical industry consumes significant quantities of kaolin. Production

of aluminium compounds such as aluminium phosphate, sulfate and trichloride

account for major application for kaolin. Aluminium sulfate accounts for about half

of the chemical production using kaolin. A relatively small end-use for kaolin is in the agriculture sector. Kaolin are

used by the agriculture industry in the manufacture of fertilizers pesticides, and

animal feed. Kaolin is used in feed and fertilizers mainly as a filler to bring the

product to the correct consistency, in pesticides as dilutant to dilute the toxic portion

of the pesticide and as dispersants to make the pesticide easy to apply. A minor kaolin use is in the pharmaceutical industry. The highest purity

kaolin is used mainly as an inert filler, and also be an active ingredient such as in

upset stomach remedies and cosmetic mud.

24

2.6 Calcination

The kaolin without further process is not reactive enough to perform as

pozzolan. In normal temperature, kaolinite exists in a stable crystalline form and will

not react chemically with calcium hydroxide to produce cementitious materials.

Figure 2.6 shows the crystalline of kaolinite. To enable kaolin to perform as a

reactive pozzolan, it must be thermally treated. This process is known as calcination

(Sabir et al., 2001).

Figure 2.6: Crystalline of Kaolinite The burning or calcining of kaolin affects the pozzolanic reactivity of the

resulting product. Heating first removes the absorbed water. As the temperature

increase, the interlayer and hydrate water is removed. The effect of heating is

normally monitored using Differential Thermal Analysis (DTA). Figure 2.7 shows

the DTA curve for the common clay (Swamy 1986). The important endothermic

peaks (reaction involving absorption of heat) cause by dehydroxylation or the

expulsion of combined water (Swamy, 1986). From the figure, it can be seen that the

endothermic peaks are generally followed at higher temperatures by exothermic peak

(reaction involving emission of heat) caused by recrystallization of the residual

25

amorphous matrix to form high-temperature silicates and oxides.

Figure 2.7: DTA Curve

The clay is in its most reactive state when the calcining temperature leads to

loss of hydroxyls and results in a collapsed and disarranged crystal lattice structure

forming a transition phase with high reactivity (Kaloumenou, 1999). The pozzolanic

reactivity of calcined is associated with the removal of the structure water from the

crystalline kaolinite layer producing an amorphous or semi-amorphous product of

high surface area and high chemical reactivity. It is known that during calcination, kaolinite loses the OH lattice water and

the kaolinite structure will collapse. The collapsed kaolinite will tend to rearrange

themselves in chains of kaolinite. These chains of kaolinite are known as

metakaolinite, a material with some degree of order. In metakaolinite, the Si–O

network remains largely intact and the Al–O network reorganizes itself (Swamy,

1986). The dehydroxylation of kaolinite and formation of metakaolinite can be

expressed on the following expression:

Al2Si2O5(OH)4→Al2Si2O5(OH)xO2−x+(2−x/2)H2O (2.1)

26

2.6.1 Temperature

The necessary calcining temperature depends upon the nature of the clay

mineral and the thermal energy required to release the hydroxyl ions. Grinding may

also be advantageous in breaking up particle agglomerates and exposing additional

surface for reaction The calcining temperature producing the active state is usually in the range

600–800°C. Ambroise et al. (1985) determined the effect of the calcining

temperature of kaolinite (600–800°C) on the strength development of concrete. The

optimum calcining temperature, to give maximum strength at 3, 7 and 28 days was

700°C. In another work, Ambroise et al. showed that calcination below 700°C results

in less reactive metakaolinite with more residual kaolinite. Above 850°C

crystallization occurs and reactivity declines. Marwan et al. (1992) have shown that

on calcination at 800°C kaolinite and gibbsite present in laterite soils are transformed

into transition phases of metakaolin and amorphous alumina. If clays are heated at

even higher calcining temperatures, liquid phase forms which on cooling solidifies

into an amorphous glass phase. Another study done by Changling (1994) is focused on the pozzolanic

activity of the calcined kaolin. In this study, scanning electron microscopy (SEM)

was used to take photographs of kaolinite after the kaolin had been calcined at

temperatures of 550°C, 650°C, 800°C and 950°C. The SEM photographs are shown

in Figure 2.8. The results show that the kaolinite crystalline form becomes multiple

lobed flakes. At temperature of 550°C, kaolinite crystals with hexagonal outlines

were found occasionally preserved in the sample. As the temperatures increase

(650°C and 800°C), the kaolinite flakes became more deformed and locally

condensed into bundles. After calcination at 950°C, the samples appeared more

massive and flakes had sintered rims.

27

(a) (b)

(c) (d)

Figure 2.8: SEM Photographs of Calcined Kaolin at Temperature (a) 550°C, (b) 650°C, (c) 800°C and (d) 900°C.

28

2.6.2 Method of Calcination

Traditionally, the most common means of calcination has been the rotary

kiln as shown in Figure 2.9. This method has been extensively used in USA, Brazil

and for various dam projects in India. Although there are obvious differences, the

kilns used have varied in length from 6.5 m to 40 m with a diameter from 1 to 3 m

(Swamy, 1986). Natural gas or oil have been the most commonly used fuels. The

length of time for calcination appears to have been around 1 hour. The daily output

varied from 12.5 to 100 ton depending on the size With the development of technology, kaolin are now calcined in rotary kilns

or using fluidised bed processes which allows the reduction of calcining time from

hours to minutes. Salvador (1995) used flash-calcination to reduce the calcining time

to seconds. The process consists of rapid heating, calcining and cooling. Different

qualities of metakaolin are obtained depending on the temperature (500–1000°C) and

time of flash-calcination (0.5–12 s) and that more active metakaolin can be produced

by this method, than by soaking.

Figure 2.9: Rotary Kiln

29

2.7 Metakaolin

Metakaolin, generally called ‘‘calcined clay,’’ is a reactive alumina-silicate

pozzolan produced by heating kaolinite at a specific temperature regime. Metakaolin

is a chemical phase that forms upon thermal treatment of kaolinite. Kaolinite’s

chemical composition is Al2O3:2SiO2. 2H2O and as a result of thermal treatment in

the range of 400-500°C, the water is driven away to form an amorphous alumina

silicate called metakaolin. The temperature range depends on the kaolin (kaolinite

with minor impurities) characteristics such as degree of crystallinity and particle size.

Metakaolin is white in color and acts as a pozzolanic material. It may react

with calcium hydroxide to form calcium silicate and calcium aluminate hydrates. The

reactivity of the metakaolin may also be affected by grinding to a finer particle size.

The purity of the kaolin also affects the overall color and reactivity. For example,

according to ASTM 618 the minimum amount of SiO2, Al2O3 and Fe2O3 that needs to

be present in a class N pozzolan is 70%. Therefore an impure source of kaolin may

be used to result in a pozzolanic material that meets the ASTM C618 requirements.

The lower amount of siliceous and aluminous material will result in a lesser

reactivity, which may be further diminished by a coarse particle size. Also, the color

will not be white and depending on the impurity type and level may vary resulting in

an inconsistent product. Metakaolin as shown in Figure 2.10 typically has an average particle size of

about 1.5 μm in diameter, which is between silica fume (0.1 to 0.12 μm) and

Portland cement (15 to 20 μm).

30

Figure 2.10: Metakaolin Particles

As a new mineral admixture for producing high performance concrete,

metakaolinite can produce concrete of compressive strengths in excess of 110 MPa

through replacing part of the cement in the mixture. Tests have shown that the use of

5 to 10% by mass of metakaolin can produce concrete with performance

characteristics comparable to those of silica fume concretes with respect to strength

development, chloride ion penetration, drying shrinkage, and resistance to

freeze–thaw cycles and scaling.

2.7.1 Sources for Metakaolin

Metakaolin is normally produced by calcining pure clays at appropriate

temperatures. Ambroise et al. (1985) demonstrated that metakaolin can also be

obtained by the calcination of indigenous laterite soils. On calcination of laterites in

the range 750–800°C, kaolinite and gibbsite are transformed into transition phases of

metakaolin and amorphous alumina both of which possess pozzolanic properties.

Pera and Ambroise (1985) showed that blended cements containing 30% calcined

31

laterites produced strengths (between 7 and 28 days) higher than that of plain

concrete pastes. At 180 days the strength of paste containing 50% calcined laterites

was 87% of that developed by plain Portland cement. Another source for the production of metakaolin is that of calcining waste

sludge from the paper recycling industry. Pera and Ambroise (1985) showed that

calcination of waste paper sludge at about 700°C produces highly reactive

metakaolin. Using DTA to evaluate the calcium hydroxide consumption in Portland

cement pastes blended with calcined sludge, it is found that the main parameters

influencing the pozzolanic activity were the quantities of kaolinite in the inorganic

fraction, calcium hydroxide derived from the calcite present in the sludge and

particle sizes smaller than 10 μm. Pera and Amrouz (1998) found that despite smaller

kaolinite content, the DTA analysis showed that burnt paper sludge exhibited more

pozzolanic activity than commercially available metakaolin, particularly at early ages.

This was attributed to the presence of superficial defects that occur during the

calcination of the sludge. 2.7.2 High Reactivity Metakaolin (HRM)

High Reactivity Metakaolin (HRM) is a refined form of an ASTM C 618,

Class N (natural) pozzolan that is produced by calcining purified kaolinite clay at a

specific temperature range. The particle size of HRM is significantly smaller than

cement particles, yet not as fine as silica fume. It has the highest content of siliceous

and aluminous material among the purified kaolin. This is because at least 90% of

the product consists of silica and alumina.

32

The HRM is manufactured under controlled conditions to provide consistent

product in terms of particle size distribution, surface area, and color and chemical

composition. Unlike industrial byproducts, such as silica fume, fly ash, and

blast-furnace slag, HRM is water-processed to lighten its color, remove inert

impurities, and control particle size distribution. The carefully controlled refining

process results in an almost 100% reactive white powder that is consistent in

appearance and performance from lot to lot. The HRM by virtue of its highest purity is white in color, which is critical to

architectural applications. HRM shows promise as a mineral admixture for

high-performance concrete. Because of its white color, HRM does not darken

concrete as silica fume does. This makes it ideal for color matching and other

architectural applications as it produces concrete similar in color to conventional

exposed concrete. HRM is thermally activated such that the heat treatment results in maximum

pozzolanic activity for the product. Typically added to concrete at rates of 5% to 10%

by weight of cement, HRM improves concrete performance by combining

chemically with free lime (by-product Portland-cement hydration) to form additional

cementitious materials. It is proven that the compressive and flexural strength

development of HRM mixes is significantly greater than that of a non pozzolanic

control mixture and similar to that of silica-fume mixtures. Some of the benefits of

the HRM concrete are:

i. Requires 25% to 35% less super plasticizer than silica-fume concrete to

achieve a comparable slump (at water-cementitious materials ratios

above 0.35).

33

ii. Has a very low chloride permeability, similar to that of silica fume

concrete.

iii. Exhibits less drying shrinkage than conventional Portland-cement

concrete, and drying shrinkage similar to that of silica-fume concrete. 2.8 The Pozzolanic Reaction

Portland cement, if fully hydrated, produces calcium hydroxide of about

28% of its own weight, although in practice, in fully mature concrete, this figure

would not normally exceed 20%. The calcium hydroxide reacts with the added

pozzolan resulting in additional calcium silicate hydrates. The calcium hydroxide

liberated by the hydration of PC does not make a significant contribution to strength

and can be harmful to concrete durability. Its elimination or reduction by reaction

with the pozzolan can result in greatly enhanced durability and strength. Because of

these advantages and in some cases economic advantages, there has been increasing

and widespread utilization of FA, SF and natural pozzolans in concrete over the last

few decades. Metakaolinite (AS2) reacts particularly well with lime and forms in the

presence of water hydrate compounds of Ca and Al silicates. Therefore, it is

considered to be a good synthetic pozzolan. The development of pozzolanic

properties in fired clays mainly depends on the nature and abundance of clay

minerals in the raw material, on the calcination conditions and on the fineness of the

final product. While kaolinite is crystalline, metakaolinite has a highly disordered

structure and offers good properties as mineral additive.

34

The principal reaction is that between the metakaolinite and the calcium

hydroxide derived from cement hydration, in the presence of water. This reaction

forms additional, cementitious aluminium containing C-S-H gel, together with

crystalline products, which include calcium aluminate hydrates and alumino-silicate

hydrates). The crystalline products formed depend principally on the

metakaolinite/calcium hydroxide ratio and the reaction temperature. In addition if

carbonate is freely available carbon-aluminates may also be produced. These

chemical reactions may be expressed in the equation (Dunster, 1999) as follow:

AS2 + 6CH + 9H C4AH13 + 2CSH (2.2)

AS2 + 5CH + 3H C3AH6 + 2CSH (2.3)

AS2 + 3CH + 6H C2AH8 + CSH (2.4)

The optimum replacement levels of Portland cement by metakaolin are

associated with changes in the nature and proportion of the different reaction

products (depending on composition) temperature and reaction time, which are

formed in the Portland cement–metakaolin system.

35

CHAPTER 3

METHODOLOGY 3.0 Introduction

This chapter describes the materials used, the preparation of the test

specimens and the test procedures. Also, the properties and chemical compositions

were listed down in this section. In order to achieve the stated objectives, this study was carried out in few

stages. On the initial stage, all the materials and equipments needed must be gathered

or checked for availability. Then, the optimum calcinations temperature was

determined. Calcined kaolin was used in the concrete mixes according to the

predefined proportions. Concrete samples were tested through concrete tests such as

cube test. Finally, the results obtained were analyzed to draw out conclusion. The

flow chart of all the stages was as indicated in Figure 3.1.

36

Calcining Kaolin Using Different Temperature

Preparing Concrete Mixes

Testing Concrete

Result Analysis

Conclusion

Figure 3.1: Flow Chart of the Study

3.1 Materials The materials used in this study were cement, kaolin, silica fume (SF),

ground granulated blast furnace slag (GGBS), sand, aggregates and water. The

description of each of the material is described in the following sections. 3.1.1 Cement

Cement used in this study was the Ordinary Portland Cement of “Seladang”

brand obtained from Tenggara Cement Manufacturing Sdn. Bhd. The cement was

kept in an airtight container and stored in the humidity controlled room to prevent

37

cement from being exposed to moisture. The chemical and physical properties of this

material were shown in Table 3.1. 3.1.2 Kaolin

Kaolin used in the study was a product obtained from the Kaolin Malaysia

Sdn. Bhd, known as Refined Kaolin Akima 15. The sample was in powder form with

yellowish white. The properties of the kaolin (provided by Kaolin Malaysia Sdn.

Bhd.) are listed in Table 3.1.

3.1.3 Silica Fume (SF) The silica fume sample was obtained from Degussa Construction Chemical

Malaysia Sdn Bhd with the brand name as MB-SF. Some extra information about the

sample is given in Appendix A. The chemical compositions of the sample are listed

in Table 3.1.

3.1.4 Ground Granulated Blast Furnace Slag (GGBS) In the present study, the slag was obtained from Slag Cement Sdn. Bhd. at

Pasir Gudang, Johor. The slag was kept in airtight plastic bag and stored in a

humidity-controlled room. The chemical compositions of the sample are shown in

Table 3.1.

38

Table 3.1 Properties of Cement, Kaolin, SF and GGBS

Parameters Cement (%) Kaolin (%) SF (%) GGBS (%)Silica (SiO2) Alumina (Al2O3) Iron Oxide (Fe2O3) Calcium Oxide (CaO) Magnesium Oxide (MgO) Sodium (Na2O) Potash (K2O) Titanium Dioxide (TiO2) Loss On Ignition Fineness (2μm)

20.1 4.9 2.5 65 3.1 0.2 0.4 0.2 -

2.4

55 29 1 -

0.5 0.02 3.1 -

8.8 10 min

85-96 - - - - - - -

3.5 -

28 10 2 50 5

0.1 0.6 -

0.2 -

Figure 3.2, Figure 3.3 and Figure 3.4 show the images of kaolin, silica fume

and slag used in the study. From the figures, it is observed the kaolin is yellowish

white in color while the silica fume and slag has a blue-purple color and white color

respectively.

39

Figure 3.2: Kaolin

Figure 3.3: Silica Fume

Figure 3.4: Ground Granulated Blast Furnace Slag

40

3.1.5 Sand and Aggregate

The aggregates were selected based on the limitation of BS 881 and 882.

The sand used was natural river sand and the aggregate was 10 mm crushed granite.

These materials will be dried at a temperature of 100°C for 24 hours to control the

water content in the concrete. Figure 3.5 shows the oven used to dry up the materials.

Figure 3.5: Oven for Heating the Aggregates

3.1.6 Water

Water is needed for the hydration of cement and to provide workability

during mixing and for placing. There is not much limitation for water except that the

water must not severely contaminated. In this study, normal tap water was used.

41

3.2 Calcining Kaolin

The kaolin was thermally treated at temperatures of 600°C, 650°C, 700°C,

750°C and 800°C using a furnace. The kaolin was put into the furnace and the

temperature reading was set to predefined temperatures. The kaolin was thermally

treated for the duration of 3 hours. After that, it was left to be cooled to room

temperature and stored in plastic bag.

Figure 3.6: Calcining Kaolin

After calcinations, it was observed that the sample becomes harden after

being cooled to room temperature. It seem that the kaolin was some sort of “melting”

that enable it to model the shape of the container after cooling. However, this harden

kaolin can be easily smashed into powder form. Figure 3.7 shows the image of the

harden kaolin.

42

BEFORE AFTER

Figure 3.7: Kaolin Before Calcination and After Calcination

3.3 Concrete Mixes In this study, three series of concrete mixes were developed. These series of

concrete mixes were prepared with the water-cement ratio of 0.56 and the targeted

compressive strength of 40 MPa at 28 days.

The first series was the control mix and concrete with predefined

replacement ratio with metakaolin treated at temperature of 750°C. This series was

used to study the strength development of concrete containing different percentage of

metakaolin. The second series was concrete blended with 10% and 20% metakaolin

using kaolin treated under different temperatures. The purpose of preparing this

series was to look into the effect of calcination on the strength of

metakaolin-concrete. The final set was concrete blended with silica fume and slag

used as comparison of the strength performance of Metakaolin-concrete. All the mix

proportions of the series were shown in Table 3.2.

43

Table 3.2: Mix Proportions

Water Binder(kg/m3) Fine Coarse (kg/m3) CRMs Agg. Agg. Series Mix

Cement

Type Temp.°C Weight (kg/m3) (kg/m3)1 Control 250 446 - 0 794 860 5% 250 424 MK 750 22 794 860 10% 250 401 MK 750 45 794 860 15% 250 379 MK 750 67 794 860 20% 250 357 MK 750 89 794 860 30% 250 312 MK 750 134 794 860 2 10% 250 401 MK 600 45 794 860 10% 250 401 MK 650 45 794 860 10% 250 401 MK 700 45 794 860 10% 250 401 MK 750 45 794 860 10% 250 401 MK 800 45 794 860 20% 250 357 MK 600 89 794 860 20% 250 357 MK 650 89 794 860 20% 250 357 MK 700 89 794 860 20% 250 357 MK 750 89 794 860 20% 250 357 MK 800 89 794 860 3 10% 250 401 SF - 45 794 860 10% 250 401 GGBS - 45 794 860

3.4 Mixing Procedure

The mixing procedures were divided into three stages. In the first stage, all

the binders (cement, metakaolin, silica fume and slag) were weighted accordingly

and mixed by hand until all the constituents mixed uniformly. This was to make sure

all the binders were mixed thoroughly to produce a homogenous mix. The second

stage involves mixing the binders with the aggregates for about 5 minutes. At the

final stage, measured water was added into the concrete mix. This step was crucially

important to make sure that the water was distributed evenly so that the concrete will

44

have similar water-binder ratios for every cube. After that, the concrete was then

poured into the mould. 3.5 Preparing Test Cubes The size of the mould used to produce the cubes was 100 x 100 x 100 mm.

Twelve cubes were used for each concrete mix. The concrete was poured into the

mould in two layers where each layer was compacted using a steel bar. The cubes

were removes from the moulds after 24 hours and cured using sacks in room

temperature. 3.6 Curing

In this study, the cubes were cured using wetted sacks at room temperature.

The cubes were cured until they were ready to be tested at the designated ages. The

sacks were kept wetted by pouring water from time to time to enabled the cubes to be

cured in a high moisture environment. In order to prevent excessive loss of moisture,

the sacks were covered with plastic sheets. Figures 3.8 and 3.9 show the curing

process done in this study.

45

Figure 3.8: Curing Using Sacks

Figure 3.9: Covering the Sacks with Plastic Sheets

46

3.7 Compression Test As stated earlier, this study focuses on the performance of concrete blended

with metakaolin in term of its compressive strength. The compression test is an

important concrete test to determine the strength development of the concrete

specimens. Compressive strength tests (BS 1881: Part 103: 1983) were performed on

the cube specimens at the ages of 1, 3, 7, and 28 days. Figure 3.10 shows the

concrete cubes prepared in this study. Testing was conducted immediately after the specimens were removed

from the curing sacks. The compression load was applied using compression

machine at the rate of 0.3 N/mm2/s. Figure 3.11 shows the compression test while

Figure 3.12 shows the tested cubes. Three specimens were tested at each age to

compute the average strength. Additional specimens were tested if any individual

strength result deviated substantially from the mean. A new average was computed

based on the three closest strength results. The results are recorded for further

analysis.

Figure 3.10: Concrete Cubes

47

Figure 3.11: Compression Test

Figure 3.12: The Tested Cubes

48

CHAPTER 4

RESULT AND DISSCUSSION

4.0 Introduction

In this chapter, all the strength performance of various mixes containing

different percentage of metakaolin will be discussed. All the tests conducted were in

accordance with the methods described in chapter three. The discussion will be divided into three sections according to objectives

stated in the earlier parts. The results are to be discussed and analyzed accordingly to

draw out the conclusion later. The three sections mentioned are: i) Effect of Metakaolin to Compression Strength

ii) Effect of Calcination Temperature to Strength Development

iii) Comparison between Metakaolin and other Cement Replacement

Materials to the Strength Performance of Concrete.

49

1.0 Effect of Metakaolin to Compression Strength

In this section, the main concern is to study the compressive strength of

concrete containing various percentage of metakaolin. Control specimens are

concrete with 100% cement which is compared with the strength performance of

concrete containing 5%, 10%, 15%, 20% and 30% metakaolin. Cubes with the size of 100 x 100 x 100 mm were tested at the ages of 1, 3, 7

and 28 days. The results of the compressive strength test are shown in Table 4.1,

where each value is averaged from the results of three cubes. 4.1.1 5% And 15% Replacement

For 5% and 15 % cement replacement with metakaolin, the strength

development of the concrete is quite similar to the control. This can be clearly shown

in Figure 4.1. Both concrete cubes with 5% and 15% replacements show higher

compressive strength than the control in the first day after casting. Concrete with 5%

metakaolin replacement achieve an early compressive strength of 11.3 MPa while

15% replacement attain 11.3 MPa. However, the strength enhancement by

metakaolin is reduced on the third day when the compressive strength of the blended

concrete was below the control. On the third day, the cubes with 5% and 15%

replacement only achieve the compressive strength of 23.2 MPa and 23.5 MPa,

respectively, compared to 24.7 MPa for the control mix.

50

On the following days, the difference in strength achievement between

blended concrete and control has been extended. However, the results show that the

strength development of the blended concrete is relatively close to the control. This

can be clearly revealed when 5% and 15% achieved compressive strength of 38.8

MPa and 38.2 MPa respectively compared to 41.2 MPa of the control at 28 days. Based on the results, it can be seen that the amount of metakaolinite presents

in 5% replacement is not sufficient enough to enhance the compressive strength over

the control as the replacement ratio is too small. The metakaolinite available only

react with a portion of calcium hydroxide released from the cement hydration which

limits the strength development at the later ages. The secondary CSH produced is

limited to a certain numbers. However, the enhancement of these additional CSH

gels is then overridden by the dilution effect. As the results, the blended concrete

exhibits similar strength development compared with the control beginning from the

third day onwards. The 15% replacement also exhibits similar strength development as the

control. Compared to 5% replacement, the amount of metakaolinite exists in the

blended concrete are probably too high. The quantity of calcium hydroxide produced

from the hydration of cement is not enough to react with all the metakaolinite to

produce extra CSH. The calcium hydroxide has been reduced to the minimum level

while some metakaolinite are left out without any chemical reaction.

51

Table 4.1: Cube Test Results for Different Mix Ratios

Calcination Age Temperature(˚C) (days) Cube 1 Cube 2 Cube 3 Average

Control - 1 8.5 9.0 8.0 8.53 24.5 25.5 24.0 24.77 28.0 29.0 29.5 28.8

28 41.0 42.5 40.0 41.2

5% MK 750 1 12.0 11.0 11.5 11.53 23.5 23.5 22.5 23.27 27.5 26.5 27.0 27.0

28 38.0 39.0 39.5 38.8

10% MK 750 1 11.0 11.5 11.5 11.33 26.5 27.0 26.0 26.57 32.5 32.0 32.0 32.2

28 48.0 44.0 43.5 45.2

15% MK 750 1 11.0 12.0 11.0 11.33 23.0 24.0 23.5 23.57 26.5 27.0 27.0 26.8

28 37.5 38.0 39.0 38.2

20% MK 750 1 11.5 11.5 11.0 11.33 22.5 22.0 24.5 23.07 24.5 25.0 25.0 24.8

28 33.0 32.0 34.5 33.2

30%MK 750 1 8.5 8.0 8.0 8.23 16.5 16.0 17.0 16.57 20.5 21.0 19.0 20.2

28 30.5 29.0 29.5 29.7

MixCompressive Strength (MPa)

52

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Control5%15%

Figure 4.1: Compressive Strength For 5% And 15% Replacement Compared to Control

53

4.1.2 10% Replacement

The concrete cubes with 10% replacement exhibits the best strength

performance in this study. The strength development for concrete with 10%

replacement and the control is shown in Figure 4.2. For 10% replacement of PC with metakaolin, the blended concretes exhibit

higher strength than the PC at all ages. On the first day, the cubes with 10%

replacement have exceeded the compression strength of the control to 11.3 MPa. On

the third day, the strength of the blended concrete has achieved 26.5 MPa compared

to 24.7 MPa of the control. The strength increases over the control continue over the

following ages until concrete with 10% replacement achieves compressive strength

of 45.2 MPa, about 10% higher than the control. From the results, it is clear that

among different replacement levels, the use of metakaolin at the replacement level of

10% performed the best, which resulted in the highest strength increase over the

control concretes at all test ages.

54

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Control10%

Figure 4.2: Compressive Strength For 10% Replacement Compared to Control

55

4.1.3 20% And 30% Replacement

The compressive strength of the cubes with 20% and 30% replacement are

generally lower than the control at all test ages. The comparison of strength

development between the 20% and 30% replacement with the control is shown in

Figure 4.3. At the age of 1 day, concrete cubes with 20% replacement exhibits

compressive strength greater than the control, that is 11.3 MPa compared to 8.5 MPa

of the control. After that, the dilution effect starts to take into action where the

strength of the control has increased over the blended concrete at the age of 3 days.

Since from the third day, the compressive strength of the control is higher than 20%

replacement of 1.7 MPa at the third day, 4 MPa at the 7 days and 8 MPa at 28 days. The strength development for 30% replacement is much slower than the

control. The cubes with 30% replacement only attain compressive strength of 8.2

MPa at the age of 1 day. Among all the replacement ratio, only 30% replacement

shows a lower strength than the control in the first day. The 30% replacement

continues to exhibits weaker strength on the following ages until the cubes reach

strength of 29.7 MPa at 28 days, which is 11.5 MPa lower than the control. The results indicated that the replacement ratio over the optimum ratio will

tend to reduce the compressive strength of the concrete. The strength reduction is

proportional to the replacement level.

56

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0 5 10 15 20 25 30

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Control20%30%

Figure 4.3: Compressive Strength For 20% And 30% Replacement Compared to Control

57

Generally, metakaolin is proven to be a reactive pozzolan especially in the

early ages. This can be seen when all the metakaolin-concrete with different

replacement ratios except for 30% replacement exhibits higher compressive strength

in the first day. The very early strength enhancement is probably due to a

combination of the filler effect and accelerated cement hydration. It is known that kaolin has the particle size ranging from 0.2-15 microns

with the specific area of 10 000-29 000 m2/kg which is much finer than cement.

These finely divided cement replacement materials have a physical effect in that they

behave as fillers. This is particularly significant in the interfacial zone regions where

they produce more efficient packing at the cement paste-aggregate particle interface,

reducing the amount of bleeding and produce a denser, more homogeneous, initial

transition zone microstructure and also a narrower transition zone. Partial

replacement by metakaolin results an increase in the strength of concrete possibly

due to an improved transition zone.

Metakaolin rapidly removes calcium hydroxide from the system and

accelerates the ordinary Portland cement (OPC) hydration. The hydration of cement

is accelerated by the presence of particles of metakaolin which acted as nucleation

sites for the reaction products (calcium hydroxide). However, the results show that the strength development is retarded at the

third day. The compressive strength of all the mixes except 10% replacement is lower

than the control. This is generally caused by the “dilution effect”. As the replacement

rations exceed 10%, the amount of metakaolinite is in excess to react with calcium

hydroxide. These extra metakaolinite produce an immediate dilution effect such that

the water-cement ratio is reduced. Concrete strength is reduced in approximate

proportion to the degree of replacement. As the results, the 30% replacement endures

the most critical strength lost.

58

Subsequently, the concrete’s strength is further enhanced by the pozzolanic

reaction between metakaolin and the calcium hydroxide produced by the hydration of

the cement. However, only concrete with 10% replacement exhibits higher strength

than the control at 28 days, this is predicted that the content of metakaolinite in the

samples is high. The replacements over 10% cause the concrete to have excess of

metakaolinite to react with the hydrated calcium hydroxide and thus reduce the

compressive strength of the concrete. Compared to the findings of other studies, it appears that the results of this

study do not cohere with some of the studies although there are some studies agree

the optimum metakaolin replacement is around 10%. Kostuch et al.'s (2000) results

show that 20% replacement of cement by metakaolin is the optimum replacement at

28 days, whereas Oriol et al. (2002) report that between 30% and 40% metakaolin is

required to achieve highest compressive strength at a water-binder ratio of 0.5 when

cured in lime-saturated water for 28 days. These variations are not surprising as the

products of hydration and pozzolanic activity depend on the Portland cement

composition, the purity of the metakaolin and the water-binder ratio. In this study, the kaolin samples have silica and alumina content of 81%. It

is considered that the kaolin has a high purity and high kaolinite content. As a result,

10% replacement is sufficient to reduce the calcium hydroxide to the minimum level

and attains the highest compressive strength in 28 days.

59

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Control5%10%15%20%30%

Figure 4.4: Strength Development for Various Mixes

60

4.2 Effect of Calcination Temperature To Strength Development

The main concern in this section is to study the effect of calcination

temperature to the strength performance of the metakaolin-concrete. Five different

calcination temperatures were selected, ranging from 600˚C to 800˚C. One additional

set of mix is prepared using kaolin as cement replacement material to act as control.

The results of the compressive strength test are shown in Table 4.2, where each value

is averaged from the results of three cubes.

4.2.1 Effect of Calcination The study reveals the importance of calcination for converting kaolin to

metakaolin. The concrete cubes using kaolin endure excessive loss of strength at all

ages. Referring to Table 4.2, the compression strength for the cubes at the first day is

only 5.2 MPa, 3.3 MPa lower than the plain concrete mix. The strength loss

continues to occur for the remaining ages. At 28 days, the kaolin-concrete attains a

strength of 27.3 MPa compared to 41.2 MPa of the control. If compared to the

best-performed metakaolin @ 750˚C of 45.2 MPa, the difference is even larger. The strength differences between concrete using kaolin and metakaolin can

be clearly seen as the differences are greater. Kaolin without calcination will not act

as pozzolan but will severely reduce the concrete strength. This proves that kaolin by

itself is not a reactive cement replacement material. Calcination is needed to improve

the performance of kaolin, converting it to metakaolin. Through calcination, kaolin

will become reactive to react with calcium hydroxide to enhance the strength of

concrete. The calcination temperatures do have some effects on the performance of

metakaolin-concrete which is discussed in the following section.

61

4.3 Effect of Calcination Temperature (10% Replacement)

The results of compression test for the second series are shown in Table 4.2

and Figure 4.5. Referring to the results, metakaolin @ 750˚C has the best

performance among other samples. At the first day, metakaolin-concrete @ 750˚C

has reached strength of 11.3 MPa, the second highest among the others. After that,

the strength has developed to 26.5 MPa on the third day, 32.2 MPa on the seventh

day and reaches an ultimate strength of 45.2 MPa at 28 days. Contrast to the well-performed metakaolin @ 750˚C, metakaolin @ 600˚C

is the least performed metakaolin. It only manages to attain compressive strength of

8.3 MPa at the first day. The further strength development for metakaolin-concrete

@ 600˚C is 21.2 MPa (3 days), 28.8 MPa (7 days) and 36.5 MPa (28 days). From the results, it can be seen that the calcinations temperatures do affect

the strength performance of the metakaolin-concrete. Starting from 600˚C to 750˚C,

the compressive strength of the concrete increases with the increase in calcinations

temperatures until the optimum temperature of 750˚C. After the calcinations

temperature has increased to 800˚C, the concrete strength is reduced. However, it is

noticed that the reduction is not severe as the performance of metakaolin @ 800˚C is

about the same as metakaolin @ 750˚C.

62

Table 4.2: Cube Test Results for Mixes with Different Calcination Temperatures

Calcination Compressive Strength (MPa) Mix Temp. (˚C)

Age (days) Cube 1 Cube 2 Cube 3 Average

10% Kaolin - 1 5.0 5.5 5.0 5.2 3 16.0 16.5 16.5 16.3 7 23.5 20.0 20.5 21.3 28 27.0 27.5 27.0 27.2

10% MK 600 1 8.0 8.0 9.0 8.3 3 21.0 20.5 22.0 21.2 7 28.0 30.0 28.5 28.8 28 36.5 37.0 36.0 36.5

10% MK 650 1 8.0 7.5 8.0 7.8 3 24.0 22.0 22.5 22.8 7 27.5 29.5 30.0 29.0 28 37.5 36.5 37.0 37.0

10% MK 700 1 8.5 9.0 9.0 8.8 3 25.5 23.0 24.5 24.3 7 31.0 32.0 31.0 31.3 28 38.5 41.0 39.0 39.5

10% MK 750 1 11.0 11.5 11.5 11.3 3 26.5 27.0 26.0 26.5 7 32.5 32.0 32.0 32.2 28 48.0 44.0 43.5 45.2

10% MK 800 1 12.0 11.5 11.5 11.7 3 25.0 25.5 26.0 25.5 7 32.5 32.0 33.0 32.5 28 44.0 43.0 43.0 43.3

63

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600650700750800WC

Figure 4.5: Strength Performance With 10% MK Calcined at Various Temperatures

64

It is known that when kaolin is heated below 100°C, the low temperature

will release the absorbed water in pores and on the surfaces. When the temperature is

increased to 400–650°C, there will be dehydroxylation of kaolinite and formation of

metakaolinite. This statement can be explained using the study done by G. Kakali et

al. (2001).

Figure 4.6: XRD Pattern of Kaolin (1: KAl(SO4)2, 2: Al2(SO4)3, 3: mullite, 4:

γ-Al2O3, 5: kaolinite, 6: quartz, 7: K-Alunite, 8:K2SO4).

Figure 4.6 shows the X-ray Powder Diffraction (XRD) pattern of kaolin at

various temperatures from the study done by G. Kakali (2001). It shows that kaolinite

is still exists at temperature of 550°C in a small amount. When the temperature

increases, the amount of kaolinite is getting lesser and converted to metakaolinite. At

650°C, almost all the kaolinite has been converted to metakaolinite. It can be

predicted that the amount of metakaolinite converted from kaolinite is proportional to

the calcination temperature. The amount of metakaolinite will increased as the

temperature increases and attains a peak number at the optimum temperature.

65

Other than the amount of metakaolinite, the calcination temperature also

affects the reactivity of metakaolinite. Metakaolinite has a highly disordered

structure and reacts particularly well with lime and forms in the presence of water

hydrate compounds of Ca and Al silicates. However, the amorphous metakaolinite of

high surface area is actually the result of the thermal treatment. The calcination

temperatures determine the degree of disorder of metakaolinite and hence affect its

chemical reactivity. The metakaolin calcined under optimum temperature will be

more reactive than the others. Refer to the results, it is predicted that the dehydroxylation of kaolinite

already started at the temperature of 600°C to form metakaolinite. However, the

dehydroxylation process is not complete as parts of the kaolinite remain intact. Also,

the reactivity of the metakaolinite produced is not as high as other samples treated at

higher temperature. Because of its low chemical reactivity, metakaolin-concrete @

600°C only attain strength of 8.3 MPa at the first day (the second lowest) and 21.2

MPa at the third day (the lowest). At the same time, the limited amount of

metakaolinite cause the concrete to achieve the lowest ultimate strength at 28 days

compared to the other samples.

As the calcination temperature increases, the performance of

metakaolin-concrete has been improved. Increased calcination temperature results in

higher content of metakaolinite with higher reactivity. Metakaolin @ 650°C has

higher early and ultimate strength than metakaolin @ 600°C although the difference

is not much. The improved performance of metakaolin continues for temperatures of

700°C and 750°C. The performance improvement is not proportional to the

temperature increment, where little improvement is observed for temperature of

600°C and 650°C but the improvement within temperature 700°C and 750°C is more

obvious. This indicates that the performance of metakaolin is not linearly

proportional to the calcination temperatures.

66

When the calcination temperature reaches 750°C, the peak performance of

metakaolin-concrete is achieved. The experimental data shows that the temperature

of 750°C is the optimum calcination temperature for this study. At this stage, the

metakaolin has a maximum amount of metakaolinite and also the highest chemical

reactivity. This enables it to have the highest early and ultimate strength, about 8.7

MPa or 24% higher than metakaolin @ 600°C at 28 days. As the calcination temperature is increased to 800°C, it is observed that the

performance of the concrete is declining although it is still better than

metakaolin-concrete @ 700°C. This is probably due to when kaolin is heated at the

temperature over the optimum temperature, recrystallization will occur reducing the

amount and reactivity of metakaolinite. This condition causes the metakaolin to

become less-performed. From the study, it is clearly reveals that the strength performance of

metakaolin is influenced by the calcination temperature. The performance of

metakaolin will increases with the increment of temperature until it reach the

optimum thermal treatment. The increment of calcinations temperature over the

optimum level will cause recrystallization in metakaolin, reducing the strength

performance of metakaolin-concrete.

However, another set of testing reveals that the effect of calcination

temperature will be reduced once the replacement ratio has been increased over the

optimum level. This matter is discussed in the next section.

67

4.4 Effect of Calcination Temperature (20% Replacement) Table 4.3: Cube Test Results for Mixes with Different Calcination Temperatures

Calcination Compressive Strength (MPa) Mix Temp. (˚C)

Age (days) Cube 1 Cube 2 Cube 3 Average

20% Kaolin - 1 5.0 4.5 4.5 4.7 3 14.0 14.0 13.5 13.8 7 16.0 16.5 17.5 16.7 28 22.0 22.5 21.0 21.8

20% MK 600 1 9.0 9.0 9.5 9.2 3 20.0 21.0 21.0 20.7 7 26.0 27.5 25.0 26.2 28 35.0 37.5 36.0 36.2

20% MK 650 1 9.5 9.0 8.0 8.8 3 21.0 20.5 19.0 20.2 7 27.0 26.5 27.0 26.8 28 34.0 33.5 35.0 34.2

20% MK 700 1 11.5 10.5 11.0 11.0 3 20.5 21.0 20.5 20.7 7 27.5 28.5 28.0 28.0 28 32.5 38.0 36.0 35.5

20% MK 750 1 11.0 11.5 11.5 11.3 3 22.5 23.0 22.0 22.5 7 24.5 26.0 25.0 25.2 28 33.0 34.0 36.0 34.3

20% MK 800 1 10.0 9.0 10.5 9.8 3 21.0 20.5 19.0 20.2 7 25.0 25.5 26.5 25.7 28 35.0 36.0 36.0 35.7

68

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Pa600 650 700 750 800

Figure 4.7: Strength Performance With 20% MK Calcined at Various Temperatures

69

Table 4.3 and Figure 4.7 show the compression test results for

metakaolin-concrete calcined under temperatures of 600˚C to 800˚C at 20%

replacement. Concrete mixes with 20% kaolin is used as control in the experiment. Referring to Figure 4.7, it shows that the compressive strength development

for all the mixes except the control is actually about the same. At the first day, the

best performed mix is the metakaolin-concrete @ 750˚C, achieving an early strength

of 11.3 MPa. Compared to the least performed metakaolin @ 650˚C with early

strength of 8.8 MPa, the strength difference is 2.5 MPa. At the remaining days, the

maximum strength difference for the third day is 2.3 MPa (between 750˚C and

650˚C), 2.8 MPa at 7 days (between 700˚C and 750˚C) and 2.0 MPa (between 600˚C

and 650˚C). In contrast to 20% replacement, the strength difference of 10% replacement

is more obvious. The strength difference at the first day is already 3.8 MPa and the

differences extended to 8.7 MPa at 28 days. The differences between 10% and 20% replacement are mainly due to the

amount of calcium hydroxide produced from cement hydration is limited. For 20%

replacement, the amount of calcium hydroxide generated is even less than those in

10%. So, it can be predicted that the amount of calcium hydroxide will be limited to

react with metakaolinite. At 20% replacement, the amount of metakaolinite contained in the concrete

mixes is definitely more than the amount in 10% replacement. In this situation,

although the metakaolin is not calcined under the optimum temperature, it still has

the sufficient amount of metakaolinite to react with the limited calcium hydroxide.

Even if metakaolinite is calcined under optimum temperature (750°C) which enable

70

it to have more reactive metakaolinite, these extra metakaolinite are kept intact due

to limited amount of calcium hydroxide. Subsequently, all the metakaolin samples

perform similar strength development. However, the effect of calcination temperatures to the reactivity of

metakaolin can still be seen although it is not obvious as the 10% replacement.

Metakaolin calcined at temperature of 600°C and 650°C is not calcined under the

optimum temperature (750°C). As the results, the metakaolin is not as reactive as the

other samples (metakaolin @ 750°C and 800°C) calcined at temperature closer to the

optimum temperature. This explains why the two metakaolin-concrete are only able

to attain strength around 8 MPa while the others attain strength over 11 MPa at the

first day. These two metakaolin-concrete manage to achieve similar strength as the

other mixes at 28 days only because they have the sufficient metakaolinite to react

with the limited amount of CH. Another matter to be observed is the reactivity of metakaolin @ 750°C.

Although the concrete mix cannot achieve the highest ultimate strength at 28 days,

its strength is the highest at the first and third day. This is because the sample is

calcined under the optimum temperature which enables it to have the highest

reactivity and maximum amount of metakaolinite. Amount of metakaolinite is not

important for the 20% replacement but the high reactivity causes the concrete to

perform the best at early ages. From the results, it can be seen that once the replacement ratios have been

increased over the optimum level, the effect of calcination temperatures to the

concrete’s ultimate strength will be reduced.

71

4.5 Comparison between Metakaolin and Others Pozzolans to the Strength

Performance of Concrete.

The results of compression test for the third series are shown in Table 4.4

and Figure 4.8. At the first day, both silica fume and slag concrete exhibit higher

strength than the metakaolin concrete, achieving strength of 15 MPa and 14.2 MPa,

respectively, while the strength of metakaolin concrete is only 11 MPa. However, the

condition is different at the following days when metakaolin-concrete has the highest

compressive strength at 3, 7 and 28 days compared to silica fume and slag concrete.

Table 4.4: Strength Comparison between MK, SF and GGBS Concrete

Calcination Compressive Strength (MPa) Mix Temp.(˚C)

Age (Days) Cube 1 Cube 2 Cube 3 Average

10% MK 750 1 11.0 11.5 11.5 11.3 3 26.5 27.0 26.0 26.5 7 32.5 32.0 32.0 32.2 28 48.0 44.0 43.5 45.2

10% SF - 1 15.0 16.0 14.0 15.0 3 25.0 25.0 25.0 25.0 7 32.5 33.0 31.0 32.2 28 43.5 46.0 42.5 44.0

10% BBGS - 1 13.5 14.0 15.0 14.2 3 24.5 24.0 24.0 24.2 7 31.5 31.0 31.0 31.2 28 42.5 40.5 43.0 42.0

72

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Pa10% MK 10% SF 10% BBGS Control

Figure 4.8: Strength Comparison for MK, SF and GGBS Concrete

73

The results show that the metakaolin used in this study is superior to silica

fume and slag in terms of the strength enhancement of concrete. At this first day,

both silica fume and slag have higher strength is mainly because the samples used in

this study are processed product where they have been processed to increase their

reactivity. If referred to other studies, silica fume and slag concrete usually manage

to attain strength of equal or lower than the plain concrete at the early ages.

Generally, the results indicate that the performance of metakaolin is

comparable with other types of pozzolans in enhancing the concrete strength. Indeed,

the compressive strength of metakaolin-concrete is superior in the early ages

compared to other pozzolans. It is seen that although the acidic oxides (silica and alumina) contents vary

from metakaolin, silica fume and slag, the common feature of natural and processed

pozzolan is that silica is a major component of their composition. The glassy silica in

natural pozzolans is formed by rapid cooling of molten lava, which normally consists

of porous spherical particles. The glassy amorphous structure of artificial waste

product pozzolans (silica fume and slag) is also formed by rapid cooling. In the case

of metakaolin the crystalline structure is broken down by calcination at temperatures,

which are in general lower than those necessary to generate liquid phase and produce

glass on cooling. It is universally accepted that the principal cementitious reaction is

facilitated by the dissolution of the glassy/amorphous silica, producing silica in

solution in the pore water, which then reacts with the calcium hydroxide to form

CSH gel. Alumina will also dissolve in the high pH environment. A small amount is

incorporated in the CSH gel but the bulk reacts to form (normally crystalline) CAH

and CASH phases, which may also assist in the cementation process and contribute

to strength. The dissolution rate will depend on the specific surface, which is the

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main factor behind the different activities shown by the various pozzolanas with

respect to the time taken to produce strength enhancement in concrete. Compared to slag, the silica fume and metakaolin particles are more finely

graded particle. This explains the rapid enhancement in strength when silica fume or

metakaolin is incorporated in concrete. Also, high surface area of metakaolin particle

enables the amorphous silica to dissolute quicker than silica fume. This explains why

the reactivity of metakaolin is higher than silica fume and slag. The higher rate of strength development at early ages for metakaolin

concrete especially between 1 and 3 days has also been observed by Malhotra (1995).

He attributed this phenomenon to the higher rate of hydration in the

metakaolin-concrete. In metakaolin-concrete, metakaolin contributes to the strength

of concrete at early ages mainly by the fast pozzolanic reaction. Generally, the strength comparison at 10% replacement is not relevant to be

used as indicator for the comparison between metakaolin, silica fume and slag. This

is because each type of cement replacement materials has its own optimum

replacement ratio. For example, if the replacement is increased to 20% replacement,

the metakaolin concrete may not be the best-performed material. However, it is

general agreed that small replacement percentage (like 10%) of CRMs will always

enhance the properties of concrete although it is not the optimum replacement

percentage. In this study, 10% replacement is used and it does bring strength

enhancement to all metakaolin, silica fume and slag concrete. Using 10%

replacement should be able to provide a rough review of the performance

comparison of the CRMs in enhancing the performance of concrete.

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4.6 Further Discussion In this section, the discussion will focus on the extra findings that are not

included in the objectives of the study. During the experiment, the cubes were initially cured in water and not using

sacks. However, it was soon found out that the strength of the cubes were generally

lower than the control. Table 4.5 and Table 4.6 show the compression test result for

the cube cured in water and cured using sacks.

Table 4.5: Compression Test Results for Cubes Cured In Water

Calcination Compressive Strength (MPa) Mix Temp.(˚C)

Age (Days) Cube 1 Cube 2 Cube 3 Average

10% MK 650 1 8.0 7.5 8.0 7.8 3 19.5 19.0 19.0 19.2 7 26.0 26.5 25.0 25.8 28 36.0 35.0 35.5 35.5

10% MK 700 1 8.5 9.0 9.0 8.8 3 22.0 21.5 22.5 22.0 7 27.5 28.0 28.0 27.8 28 37.0 39.0 38.5 38.2

10% MK 750 1 11.0 11.5 11.5 11.3 3 22.0 22.5 23.0 22.5 7 27.0 28.0 29.5 28.2 28 42.5 41.0 42.0 41.8

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Table 4.6: Compression Test Results for Cubes Cured Using Sacks

Calcination Compressive Strength (Mpa) Mix Temp.(˚C)

Age (Days) Cube 1 Cube 2 Cube 3 Averege

10% MK 650 1 8.0 7.5 8.0 7.8 3 24.0 22.0 22.5 22.8 7 27.5 29.5 30.0 29.0 28 37.5 36.5 37.0 37.0

10% MK 700 1 8.5 9.0 9.0 8.8 3 25.5 23.0 24.5 24.3 7 31.0 32.0 31.0 31.3 28 38.5 41.0 39.0 39.5

10% MK 750 1 11.0 11.5 11.5 11.3 3 26.5 27.0 26.0 26.5 7 32.5 32.0 32.0 32.2 28 48.0 44.0 43.5 45.2

For clear and better view of the differences, metakaolin-concrete calcined

under temperature of 750˚C is selected for comparison. Referring to Figure 4.9, it is

observed that metakaolin-concrete cured using sacks actually performed better than

the concrete cured in water. At the ages of 3 and 7 days, cubes cured using sacks had

a higher strength of 4 MPa. At 28 days, the difference remained although the strength

difference was reduced to 3.3 MPa. When the cubes were cured in water, it was observed that there was white

sediment forming on the top of the cubes. Besides, there were also bubbles forming

on the surface of the cubes. When the cubes were let to dry, the bubbles became

harden and were white in colors. The white sediment can be easily scraped into white

powder and seemed to be kaolin. Figure 4.10 and Figure 4.11 show the picture of the

white sediment and bubble around the cubes.

77

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

0 5 10 15 20 25 30

Age (days)

Com

pres

sion

Str

engt

h, M

PaCured In Water Cured Using Sacks

Figure 4.9: Compression Test Results For Cubes Cured In Water and Cured Using Sacks

78

White Sediment

Figure 4.10: White Sediment Forming On The Top of the Cube

Bubbles

Figure 4.11: Bubbles on the Surface of the Cube

The main reason why curing in water will result in lower strength and the

formation of sediment and bubbles are not known. Without the analysis on the

chemical composition of the bubble and sediment, hypothesis is generated without

the support of evidence.

79

It is believed that as the metakaolin is a very fine particle. The fine particles

will tend to stick together forming stacks of metakaolin particles with some air

trapped inside. During the mixing of concrete, the stacks will trapped in the concrete

mixes together with some air. At the age of 1 day, there is some calcium hydroxide

produced from the hydration of cement. As the hydration process is not complete, so

the concrete medium is not dense and contains some capillaries. When cured in water, the water will seep into the concrete medium through

the capillaries. Some of the calcium hydroxide dissolved in the water and increase

the transition of the water. Air trapped within metakaolin particles will tend to seep

out of the concrete as it is lighter than the concrete and water. As a result, air at the

top surface of the cube is seeping through the capillaries along with some metakaolin

particles forming white sediment at the top surface of the cube. For air which was trapped near the side surfaces, it also seeping out from the

side surface and forming bubbles. Some dissolved calcium hydroxide also seeping

through the capillary along with the air, this calcium hydroxide will cover the inner

surface of the bubbles which make the bubbles harden when dried. As the concrete has lost some of the metakaolin and CH which are needed

for forming of CSH gel, the concrete will suffer from the strength reduction as shown

in the experiment. However, this hypothesis relies on many assumptions which need

to be proven. Further study is required to investigate this phenomenon.

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CHAPTER 5

CONCLUSIONS AND RECOMMENDATIONS

5.0 Conclusion From the study, it can be concluded that:

i) Metakaolin is an effective pozzolan and results in enhanced early strength

and ultimate strength of concrete. The compressive strength of young

concrete, say from 1 to 3 days is improved by blending the Portland cement

with 10% of metakaolin by weight. The 10% replacement with metakaolin is

the most optimum replacement, enhancing the concrete’s compressive

strength at all ages. ii) It has been known that the calcination temperature has influence on the

performance of metakaolin in small replacement ratio. The

metakaolin-concrete will perform better if the calcination temperature is

closer to the optimum temperature. The optimum calcination temperature in

this study is 750°C. iii) As the replacement percentages has been increased over the optimum

replacement. The effect of calcination temperatures to the strength

performance will be reduced. However, the reactivity of the metakaolin

81

calcined at the optimum temperature can still be observed. iv) When compared to silica fume and slag, metakaolin appears to be an effective

pozzolan in enhancing concrete strength. From the study, it is clear that

metakaolin is a very reactive pozzolan and results in enhanced early strength

and some improvement in, the long-term strength comparable to others

cement replacement materials.

Presently metakaolin or even kaolin is more expensive than Portland

cement, as is silica fume, even though its processing involves moderately low

temperatures and its overall production cost is significantly less than that of PC.

More studies should be conducted to study the performance of metakaolin-concrete

especially in the durability aspect. Wider realization of the benefits of metakaolin in

mortar and concrete will lead to greater demands and this will inevitably drive the

costs down.

5.1 Recommendation From this study, there are few recommendations for the future study: i) It is observed that the optimum replacement percentage for metakaolin in this

study is only 10% that is comparatively low compared to others CRMs. It is

suggested that additional of lime is needed to increase the replacement

percentages. Additional lime increases the amount of CH to react with

metakaolinite. In this situation, the replacement percentage with metakaolin is

increased. However, the additional lime will bring many impacts to the

properties of concrete especially the durability aspect. On this matter, further

82

study is needed. ii) In this study, there is only one kaolin sample used fro the experiment. Future

study should gather more kaolin samples from various sources. It is important

to study the different behavior of metakaolin-concrete calcined from different

kaolin to look into the performance contingency of the samples. iii) Future study should look into the durability aspect of the metakaolin-concrete

which is not covered in this study. The advantages of metakaolin-concrete in

the durability aspect should be able to widen the application of

metakaolin-concrete.

83

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APPENDIX A