Omar El Mukhtar m Fka 2008

5/24/2018 Omar El Mukhtar m Fka 2008

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STUDY ON THE BEHAVIOUR OF HIGH STRENGTH PALM OIL FUEL

ASH (POFA) CONCRETE

OMAR ELMUKHTAR AHMED ELDAGAL

UNIVERSITI TEKNOLOGI MALAYSIA


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STUDY ON THE BEHAVIOUR OF HIGH STRENGTH PALM OIL FUEL

ASH (POFA) CONCRETE

OMAR ELMUKHTAR AHMED ELDAGAL

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 2008


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To my beloved mother


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ACKNOWLEDGEMENT

First and foremost, praise belongs to Allah, the Most Gracious and Most

Merciful Who has created the mankind with knowledge, wisdom and power. Being

the best creation of Allah, one still has to depend on others for many aspects directly

or in directly.

The author would like to take this opportunity to express profound gratitude

to his research supervisors; Associate Prof. Dr. Mohamed Abdelkader El-Gelany

Ismail and Professor Dr. Mohd Warid Hussin for the noble guidance and valuable

advice throughout the period of study. Their patience, time, and understanding are

highly appreciated. The author is also grateful to Dr. Zaiton Abdul Majid for her

consultation in the chemical and thermogravemetric analysis in this study.

The author is thankful to the Yayasan Pembangunan Johor in Ladang Alaf for

the supplying of the palm oil fuel ash. A word of Gratitude is extended to the

technical staff of the several laboratories of the university.

Last but not the least; the author remembers his parents and relatives for their

countless blessing which have always been source of inspiration in achieving success

to this level.


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ABSTRACT

Many researchers have studied the use of agro-waste ashes as constituents in

concrete. These agro-waste ashes contained an amount of silica which could be used

as a pozzolanic material. Palm Oil Fuel Ash (POFA) is a by-product produced in

palm oil mills. This ash has pozzolanic properties that not only enables the

replacement of cement but also plays an important role in making strong and durable

concrete. Collected POFA was dried and then sieved through a 300 m sieve. Ashes

passing through 300 m sieve were ground in a modified Los Angeles abrasion test

machine. The fineness of the POFA was checked by sieving through 45m sieve at

every half an hour grinding. For this research, total of five mixes were made of OPC

as a control mix, OPC replaced with 20% and 30 % of POFA 10 m and OPC

replaced with 20 and 30 % of POFA 45 m respectively. For compressive strength,

six cubes of 100 mm tested at 7, 28, and 90 days. For flexural strength, three prisms

of 100 x 100 x 500 mm were tested at 28 days. Five cylinders of 100 x 200 mm were

tested for indirect tensile strength at 28 days for each mix. The slump test and

compacting factor test were employed in measuring the fresh concrete. POFA

concrete exhibit lower value of slump compared to slump of OPC concrete. Among

POFA results, the finer the POFA, the lower the slump and hence lower degree of

compaction. Although strength of POFA concrete did not exceed that of OPC, 58

MPa was achieved when using 20 % of POFA 10 m. The flexural strength of POFA

concrete is slightly lower than that of OPC. The higher was the replacement of OPC;

the lower the flexural strength. Like that of flexural strength, indirect tensile strength

of concrete containing POFA developed in a similar way. TG Analysis lead to the

fact that the amount of Ca(OH)2increased with curing age indicating the progress of

cement hydration reaction. And reduction in weight loss attributed to

dehydroxylation of calcium hydroxide, and subsequent increase in compression is

indicative of pozzolanic reaction. From the microstructural analysis (FESEM),

radiating clusters of C-S-H gel have lead to a densification of the structure, and an

increase in strength. Hexagonal platelets of Ca(OH)2 could be observed in some

samples.


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ABSTRAK

Banyak penyelidik telah mengkaji penggunaan abu yang merupakan sisa

industri sebagai bahan dalam pembuatan konkrit. Abu ini mengandungi silica yang

membolehkan ia digunakan sebagai bahan pozolana. Abu kelapa sawit (POFA)

adalah bahan buangan yang dijana oleh kilang memproses kelapa sawit. Abu ini

memiliki sifat-sifat pozolana yang bukan sahaja membolehkan ia berfungsi sebagai

bahan pengganti simen tetapi turut memainkan peranan penting dalam menghasilkan

konkrit yang kuat dan tahan lasak. POFA yang diambil dari kilang telah dikeringkan

dan diayak melepasi ayak 300 m seterusnya dikisar menggunakan mesin pengisar

Los Angeles. Kehalusan POFA kemudian dikenalpasti dangan mengayak abu

tersebut menerusi ayak 45 m pada setiap setengah jam sepanjang pengisaran

dijalankan. Dalam kajian ini, sebanyak lima bancuhan telah dihasilkan iaitu yang

mengandungi simen Portland biasa (OPC) sebagai bancuhan kawalan, OPC yang

diganti dengan 20 % dan 30 % POFA 10 m dan OPC yang diganti dengan 20 % dan

30 % POFA 45 m. Kekuatan mampatan diperolehi dengan menguji enam kiub

bersaiz 100 mm pada 7, 28, dan 90 hari. Kekuatan lenturan pula ditentukan dengan

menguji tiga prisma bersaiz 100 x 100 x 500 mm pada 28 hari. Lima silinder (100 x

200 mm) telah diuji untuk menentukan kekuatan tegangan pada 28 hari bagi setiap

bancuhan. Ujian runtuhan dan ujian faktor pemadatan telah digunakan untuk

menentukan sifat konkrit segar. Konkrit POFA menunjukkan nilai runtuhan yang

rendah berbanding konkrit OPC. Daripada keputusan POFA, semakin halus POFA

maka semakin rendah nilai runtuhan dan nilai pemadatan yang diperolehi. Walaupun

kekuatan POFA tidak mengatasi OPC, kekuatan 58 MPa dapat dicapai apabila

menggunakan 20 % POFA 10 m. Nilai kekuatan lenturan bagi konkrit POFA

adalah sedikit rendah daripada OPC. Semakin tinggi nilai penggatian OPC; semakinrendah kekuatan lenturan. Kekuatan tegangan konkrit POFA menunjukkan corak

sama seperti yang didapati dalam kekuatan lenturan. Analisis TG yang menunjukkan

kandungan Ca(OH)2 meningkat dengan umur pengawetan membuktikan

penghidratan simen terus berlaku. Pengurangan dalam kehilangan berat adalah

disebabkan dehydroxylation kalsium hidroksida manakala peningkatan kekuatan

mampatan membuktikan berlakuanya tindak balas pozolana. Berdasarkan analisis

mikrostruktur (FESEM), perkembangan dalam kelompok C-S-H gel telah membawa

kepada pemadatan struktur dan meningkatkan kekuatan.


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CONTENT

CHAPTER SUBJECT PAGE

CERTIFICATION OF THESIS ii

CERTIFICATION BY SUPERVISOR iii

TITLE PAGE iv

AUTHORS DECLARATION v

DEDICATION vi

ACKNOWLEDGEMENTS vii

ABSTRACT viii

ABSTRAK ix

CONTENTS xLIST OF TABLES xiii

LIST OF FIGURES xiv

LIST OF ABBREVIATIONS SYMBOLS AND xvi

I INTRODUCTION

1.1 Introduction 1

1.2 Background of Research 2

1.3 Objectives of Research 4

1.4 Scope and Limitation 4

1.5 Importance of Research 4

1.5.1 Advantages of High Strength Concrete 5


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II LITERATURE REVIEW

2.1 Cement Replacement Materials 7

2.2 Pozzolanic Materials 8

2.3 Pozzolanic Behavior 9

2.4 Types of Pozzolanic Materials 10

2.5 Origin of Palm Oil Fuel Ash 10

2.6 Pozzolanicity of Palm Oil Fuel Ash 11

2.7 Effect of Fineness of the POFA 11

2.8 Effect of Ash Content 12

2.9 Strength Development 13

III EXPERIMENTAL PROGRAMME AND MATERIAL

PROPERTIES

3.1 Introduction 15

3.2 Selection of Materials 15

3.2.1 Cement 16

3.2.2 Palm Oil Fuel Ash (POFA) 17

3.2.2.1 Preparation of the POFA 18

3.2.2.2 Fineness of the POFA 19

3.2.3 Aggregate 21

3.2.3.1 The Coarse Aggregate 22

3.2.3.2 The fine Aggregate 22

3.2.4 Water 23

3.3 Mix Proportions 24

3.3.1 Number of Specimens for Each Mix 24

3.4 Superplasticizer 26

3.5 Measurement of Workability 27

3.5.1 Slump Test 27

3.5.2 Compacting Factor Test 29

3.6 Curing 30

3.7 Tests on Hardened Concrete 31

3.7.1 Compressive Strength 31


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3.7.2 Flexural Strength Test 32

3.7.3 Splitting Tensile Test 33

3.8 Thermogravimetric (TG) Analysis 34

3.9 Microstructural Analysis 35

IV RESULTS AND DISCUSSION

4.1 Introduction 364.2 Slump Test Result 36

4.3 Compacting Factor Results 38

4.4 Compressive Strength 38

4.5 Flexural Strength Results 41

4.6 Splitting Tensile Test Results 42

4.7 Chemical Analysis of POFA and OPC 43

4.8 Thermogravimetric Analysis 44

4.9 Microstructural Analysis (FESEM) 46

4.10 Summary 52

V CONCLUSIONS AND RECOMMENDATIONS

5.1 Introduction 53

5.2 Behavior of POFA Concrete in the Fresh State 53

5.3 Behavior of POFA Concrete in the Hardened State 54

5.4 Thermogravimetric analysis (TGA) 54

5.5 Microstructural Analysis (FESEM) 54

5.6 Recommendations for Future Investigation 55

REFERENCES 56


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LIST OF TABLES PAGE

Table 3.1: Chemical composition of OPC and Palm Oil Fuel Ash 14

Table 3.2: Grinding time vs. the mean diameter of POFA 18

Table 3.3: Quantities of the constituents per cubic meter 22

Table 3.4: The tests, number of specimens and ages for each test 23

Table 3.5: Correlation of compaction factor test results to slump test results 28

Table 4.1: Compressive strength results 36

Table 4.2: Chemical composition of OPC and POFA 44

Table 4.3: The percent weight loss for P1, P2, P3, and P4 45

Table 4.4: Thermogravimetry data for Po, P1, P2, P3 and P4 at 90-dayscuring age 45


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LIST OF FIGURES PAGE

Figure 1.1: Palm oil shell ad fiber

Figure 2.1: Effect of fineness of ash on compressive strength of concrete 10

Figure 2.2: Effect of ash content on compressive strength of concrete at

28 days 11

Figure 2.3: Strength development of OPC and POFA concretes 12

Figure 3.1: The palm oil mill 15

Figure 3.2: Ash where trapped at the flue of tower 16

Figure3.3: Flow-chart for the manufacture of POFA 17

Figure 3.4: Effect of grinding time on fineness of POFA 18

Figure 3.5: CILAS 1180 Liquid instrument 19

Figure 3.6: The coarse aggregate 20

Figure 3.7: The fine Aggregate 21

Figure 3.8: Slump test apparatus 26

Figure 3.9: Compacting factor apparatus 27

Figure 3.10: Curing of samples in water 28

Figure 3.11: Compression test machine 29

Figure 3.12: Flexural test machine 30

Figure 3.13: Concrete cylinder after testing for tension 31

Figure 4.1: Slump test results 34

Figure 4.2: Compacting factor results 35

Figure 4.3: Relationship between compressive strength results 37

Figure 4.4: Flexural strength results 38

Figure 4.5: Splitting tensile strength results 39


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Figure 4.6: FESEM of P4at 3 days using 1000X magnification showing

porous morphology. 43

Figure 4.7: Granules of POFA when using 1000 X magnification of

P3at 3 days 44

Figure 4.8: FESEM of P3at 7 days using 2000X magnification 45

Figure 4.9: FESEM, P2at 7 days, hexagonal platelets of Ca(OH)2 45

Figure 4.10: Microstructure of P3at 3 days at 500, 1000, and 2000 X

magnification 46

Figure 4.11: Microstructure of P3at 7 days at 500, 1000, and 2000 X

magnification 47


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LIST OF ABBREVIATIONS AND SYMBOLS

Abbreviations:

ACI = American Concrete Institute

ASTM = American Society for Testing and Materials

BS = British Standards

CSF = Condensed Silica Fume

DOE = Department of Environment

FESEM = Field Emission Scanning Electron Microscopy

GGBS = Ground Granulated Blast furnace Slag

LOI = Loss on IgnitionOPC = Ordinary Portland Cement

PFA = Pulverised Fuel Ash

TGA = Thermogravimetric Analysis

Symbols:

Al2O3 = Aluminium Oxide

C2S = Dicalcium Silicate

C3A = Tricalcium Aluminate

C3S = Tricalcium Silicate

CaCO3 = Calcium Carbonate

CaO = Calcium Oxide


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Ca(OH)2 = Calcium Hydroxide

CaO = Calcium Oxide

CO2 = Carbon Dioxide

CH = Calcium Hydrate

C-S-H = Calcium Silicate Hydrate

Fe2O3 = Ferric Oxide

SiO2 = Silicon Oxide

K2O = Potassium Oxide

MgO = Magnesium Oxide

MnO3 = Magnesium Trioxide

Na2O = Sodium Oxide

SMF = Sulfonated Melamine Formaldehyde

SNF = Sulfonated Naphthalene Formaldehyde


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CHAPTER I

INTRODUCTION

1.1 Introduction

Concrete is one of the oldest manufactured construction material used in

construction of various structures around the world. However, continuous research in

the area of concrete material has resulted in production of many types of concrete

known in various names each having a unique characteristic to fulfill the current

construction industry demand. One of the concrete that become famous nowadays is

high strength concrete due to its strength and durability (Abdullah and Hussin, 2006).

Although high strength concrete is often considered a relatively new material,

its development has been gradual over many years. As the development has

continued, the definition of high-strength concrete has changed. In the 1950s,

concrete with a compressive strength of 34 MPa was considered high strength. For

many years, concrete with compressive strength in excess of 41 MPa was available at

only a few locations. However, in recent years, the applications of high-strength

concrete have increased, and high strength concrete has now been used in many parts

of the world (ACI, 1992).


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In order to achieve high strength concretes, several methods can be applied.

In general, high strength concrete contains strong aggregates, a higher Portland

cement content and low water cement or water cementitious ratio. The addition of

water reducing admixtures, superplasicizers, blast furnace slag, or silica fume is

common today (Nawy, 1996).

Savings in overall cost of concrete structural systems are achieved by the use

of higher strength concretes. Components of structure become smaller, thereby

reducing the weight of the system with the resulting reduction in size and then cost of

all components. The use of cement replacement materials in producing high strength

concrete also encouraged sustainable development as it reduces the cement usage. As

some cement replacement materials are obtained from agricultural wastes, it also

helps recycling the by-products (Nawy, 1996).

1.2 Background of Research

Palm oil has been gaining increasing importance as cash crop in several

tropical countries among which Malaysia is the largest producer of palm oil products.

To date there are more than two hundred mills operating in this country (Hussin and

Awal, 1997).

The palm oil industry is one of the major agro-industries in Malaysia. The

commercial palm oil production is mainly located in Peninsular Malaysia and date

back to the 1960s. During the period between 1990 and 2002, palm oil production

was nearly doubled from 6,094,622 to 11,880,000 ton per year, making Malaysia the

biggest palm oil producer worldwide (Vijayaraghavan, 2007).


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It has been reported that the production of palm oil per month is over 435000

tons, 10 % of which is waste by-product of milling process in the form of palm oil

fibre and palm oil shell as shown in Figure (1.1). These by-products are commonly

known as palm oil fuel ash (POFA), are disposed without any commercial return. It

has been identified that this ash has pozzolanic properties that not only enables the

replacement of cement but also plays an active role in making strong and durable

concrete (Hussin and Awal, 1997).

b) Palm oil fibre

a) Palm oil shell

Figure 1.1: Palm oil shell and fibre


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1.3 Objectives of Research

The main objective of this present research is to study the behavior of high

strength concrete by using palm oil fuel ash (POFA) in different fineness as partial

replacement of ordinary Portland cement. In addition to this, study the effect of

POFA on the workability of concrete.

1.4 Scope and Limitation

All test specimens are made up of concrete where Ordinary Portland cement

is replaced with 20 % and 30 % of POFA 10 m, and 20 % and 30 % of POFA 45

m. Compressive, flexural, and tensile strengths are the major tests considered for

determining the strength of concrete. Slump and compacting factor, on the other

hand, are the tests to measure the workability of the concrete.

1.5 Importance of Research

The accelerated developments in concrete research over the past 20 years

have opened new and more proficient utilization of components available in nature,

including industrial waste. The thrust in this accelerated activity has been made or

justified because of the economical gains in producing stronger structures that are

smaller in component dimensions while larger in resulting space availability. Cost

analysis of the use of high strength concrete as compared to normal strength concrete

justifies its viability and utility (Nawy, 1996).


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In recent years, studies have been carried out by various researchers in using

wastes generated from the agricultural and industrial activities as concrete making

materials (Tay and Show, 1994).

Many researchers have studied the use of agro-waste ashes as constituents in

concrete. Their results have revealed that these agro-waste ashes contain high

amount of silica in amorphous form and could be used as a pozzolanic material

(Tangchirapat and Saeting, 2007). Utilization of palm oil fuel ash (POFA) is minimal

and unmanageable, while its quantity increases annually and most of the POFA are

disposed of as waste in landfills causing environmental and other problems

(Tangchirapat and Saeting, 2007). To solve the energy problems, solid wastes from

palm oil residue are used as fuel to produce steam for electricity generation. After

burning, an ash by-product is produced. As a solution to the disposal problem of the

ash derived from palm oil, research studies have been carried out to examine the

feasibility of using the ash as cement replacement materials (Tay and Show, 1994).

1.5.1 Advantages of High Strength Concrete

The advantages of using high strength concrete often balance the increase in

material cost. The following are some advantages that can be accomplished (Nawy,

1996):

1. Reduction in member size, resulting in an increase in rentable space

and reduction in the volume of produced concrete with the

accompanying saving in construction time.

2. Superior long-term service performance under static, dynamic, and

fatigue loading.

3. Low creep and shrinkage.


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4. Greater stiffness as a result of a higher modulus of elasticity.

5. Higher resistances to freezing and thawing, chemical attack, and

significantly improve long-term durability and crack propagation.


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CHAPTER II

LITERATURE REVIEW

2.1 Cement Replacement Materials

Cement replacement materials (Illston and Domone, 2001) are those which

used as a substitute for some of the Portland cement in a concrete; partial cement

replacement materials are therefore a more accurate but less convenient name. There

are also a number of other names for this group of materials, including

supplementary cementitious materials, cement extenders, mineral admixtures,

mineral additives, latent hydraulic materials or, simply, cementitious materials.

Several types of materials are common in use, some of which are by-productsfrom 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 of or modifications to the concrete properties. All the materials have

two common features; their particle size range is similar to or smaller than that of

Portland cement, also they become involved in the hydration reactions.They can be

supplied either as individual materials and added to the concrete at mixing, or as pre-

blended mixtures with the Portland cement. The former case allows choice of the rate

of addition, but means that an extra material must be handled at the batching plant; a


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pre-blended mixture overcomes the handling problem but the addition rate is fixed.

Pre-blended mixtures have the alternative names of extended cements, Portland

composite cements or blended Portland cements. Generally, only one material is used

in conjunction with the Portland cement, but there are an increasing number of

examples of the combined use of two or even three materials for particular

applications.

The incorporation of Cement Replacement Materials leads to a rethink about

the definition and use of the water/cement ratio, which is an important controlling

factor for many properties of hardened cement paste and concrete. It is generally

accepted that this should remain as the ratio of the amount of mix water to that of the

Portland cement, and the term water/binder ratio should be used for the ratio of the

amount of mix water to the sum of the amounts of all of the cementitious materials,

i.e. the Portland cement plus the Cement Replacement Materials.

2.2 Pozzolanic Materials

A pozzolana (Neville, 2005) is a siliceous or siliceous and aluminous

material which in itself possesses little or no cementitious value but will, in finely

divided form and in the presence of moisture, chemically react with calcium

hydroxide at ordinary temperatures to form compounds possessing cementitious

properties.


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2.3 Pozzolanic Behaviour

A common feature of nearly all Cement Replacement Materials is that they

exhibit pozzolanic behavior to a greater or lesser extent, and so we will define this

before discussing the individual materials (Illston and Domone, 2001). A pozzolanic

material is one which contains active silica (SiO2) and is not cementitious by itself,

but will, in a finely divided form, and in the presence of moisture, chemically reacts

with calcium hydroxide at ordinary temperatures to form cementitious compounds.

The key to the pozzolanic behavior is the structure of the silica; this must be in a

glassy or amorphous form with a disordered structure, which is formed in rapid

cooling from a molten state. A uniform crystalline structure which is formed in

slower cooling, such as is found in silica sand, is not chemically active. Naturally

occurring pozzolanic materials were used in early concretes, as mentioned in the

Introduction to this part of the book, but when a pozzolanic material is used in

conjunction with a Portland cement, the calcium hydroxide that takes part in the

pozzolanic reaction is that produced from the cement hydration. Further quantities of

calcium silicate hydrate are produced:

2S + 3CH C3S2H3 (2.1)

The reaction is clearly secondary to the hydration of the Portland cement,

which has lead to the name latent hydraulic material in the list of alternatives

above. The products of the pozzolanic reaction cannot be distinguished from those of

the primary cement hydration, and therefore make their own contribution to the

strength and other properties of the hardened cement paste and concrete.


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2.4 Types of Pozzolanic Materials

There are many types of the pozzolanic material (Illston and Domone, 2001).

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

1. Pulverized fuel ash (PFA); called fly ash in several countries; the ash

from pulverized coal used to fire power stations, collected from the

exhaust gases before discharge to the atmosphere; only selected ashes

have a suitable composition and particle size range for use in concrete;

2. Ground granulated blast furnace slag (GGBS); slag from the scum formed

in iron smelting in a blast furnace, which is rapidly cooled in water and

ground to a similar fineness to Portland cement;

3. Condensed silica fume (CSF); often called microsilica, extremely fine

particles of silica condensed from the waste gases given off in the

production of silicon metal;

4. Calcined clay or shale; a clay or shale heated, rapidly cooled and ground;

5. Rice husk ash; ash from the controlled burning of rice husks after the rice

grains have been separated;

6. Natural pozzolans; some volcanic ashes and diatomaceous earth.

2.5 Origin of Palm Oil Fuel Ash

Palm oil fuel ash is a by-product produced in palm oil mill. After palm oil is

extracted from the palm oil fruit, both palm oil husk and palm oil shell are burned as

fuel in the boiler of palm oil mill. Generally, after combustion about 5 % palm oil

fuel ash by weight of solid wastes is produced (Abdullah and Hussin, 2006).

The ash produced sometimes varies in tone of colour from whitish grey to

darker shade based on the carbon content in it. In other words, the physical


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characteristic of POFA is very much influenced by the operating system in palm oil

factory. In practice, POFA produced in Malaysian palm oil mill is dumped as waste

without any profitable return (Abdullah and Hussin, 2006).

2.6 Pozzolanicity of Palm Oil Fuel Ash

The pozzolanicity of any material is closely related to the ability of silica to

react with calcium hydroxide to produce calcium silicate hydrate. For an assessment

of pozzolanic activity with cement, the method of pzzolanic activity index which

determines the totals activity of pozzolana (Neville, 2005). The pozzolanic activity

indices of palm oil fuel ash was obtained by (Abu, 1990) and (Sumadi and Hussin

1993) are 78.6 and 87.6 % respectively. However, for all classes of ash; the

pozzolanic activity is 75 % (ASTM C 618-94 a).

2.7 Effect of Fineness of the POFA

In order to achieve better strength of concrete consisting POFA, Awal and

Hussin (1996) have been suggested that finer POFA is to be used. By increasing the

fineness of POFA would lead to greater strength development than the coarser one.

In Fig 2.1, it can be seen that lower development in strength with coarse ash. And

that was due its lower surface area of the particle that affect the pozzolanic activity

and hence the strength.


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26.5

35.5

49

0

10

20

3040

50

60

100% Passing 600m , Unground

(Coarse)

100% Passing 300m , Unground

(Medium)

85% Passing 45 m, Ground (Fine)

28-DaysCompressiv

eStrength

(MPa)

Ty e of Ashp

Figure 2.1: Effect of fineness of ash on compressive strength of concrete (Awal,

1998)

2.8 Effect of Ash Content

Beside the effect of particle size of POFA, the material replacement level also

confirmed as one of the factors that could influence the strength of this concrete.

Using ground POFA of 45 m, Awal and Hussin (1997) proved that maximum

strength can be obtained at replacement level of 30 % which is about 10 % higher

than control one. It also has been found that this material could be added as partial

cement replacement material up to 40 % without any adverse effect on strength of

concrete. However, further increase in the ash content would reduce the strength of

concrete gradually (Awal and Hussin, 1996). The effect of POFA replacement level

towards the strength is presented in Figure 2.2.


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0

10

20

30

40

50

60

70

0 20 40 60 80

28-DayCompressive

Strength

(Mpa)

Ash Content (%)

Figure 2.2: Effect of ash content on compressive strength of concrete at 28

days (Awal, 1998)

2.9 Strength Development

POFA concrete is weaker at early age, but at later ages the compressive

strength is found to be higher than that of OPC concrete (Awal and Hussin, 1997) as

shown in figure 2.3. In general, specimens consisting POFA exhibit lesser strength at

early age but compressive continue to increase as curing age become higher. This is

because pozzolana starts reacting somewhat belatedly with the calcium hydroxide

produced by clinker hydration and therefore it behaves like an inert diluting agent

towards the Portland cement with which it has been mixed (Massaza, 1993).


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0

10

20

30

40

50

60

70

0 10 20 30 40 50

Fig 2.3: Strength development of OPC and POFA concretes (Awal and Hussin, 1997)

60 70 80 90 100

CompressiveStrength(MPa)

Curing Period ( days)

OPC

POFA


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CHAPTER III

EXPERIMENTAL PROGRAMME AND MATERIALPROPERTIES

3.1 Introduction

This chapter explains the research that has been carried out. All of the

calculation and equation details are explained in this part. Few lab tests were done to

achieve the objective of this research as discussed in chapter one. Consequently, this

chapter has drawn a clear picture and shows how to achieve the research objective.

3.2 Selection of Materials

High strength concrete has been produced using a wide range of quality

materials based on the result of trial mixes. The production of high strength concretethat consistently meet the requirements for workability and strength development


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places more stringent requirements on material selection than for normal strength

concretes. Quality materials are needed and specifications require enforcement.

3.2.1 Cement

Ordinary Portland cement was used in this study. It is highly durable and

produces high compressive strengths in mortars and concretes. Portland cement is

hydraulic cement that hardens by interacting with water and forms a water-resisting

compound when it receives its final set.

Portland cement (Nawy 1996) is made of finely powdered crystalline

minerals composed primarily of calcium and aluminum silicates. The addition of

water to these minerals produces a paste which, when hardened, becomes of

stonelike strength. Portland cement is made to meet the specification requirements of

ASTM C 150 for types I, II, III, IV, and V. Table 3.1 shows the chemical

composition of palm oil fuel ash and OPC.

Table 3.1: Chemical Composition of OPC and Palm Oil Fuel Ash

Chemical Composition POFA OPC

Silica (SiO2) 48.99 21.45

Aluminium Oxide (Al2O3) 3.78 3.62

Ferric Oxide (Fe2O3) 4.89 3.50

Calcium Oxide (CaO) 11.69 60.98

Magnesium Oxide (MgO) 1.22 0.59

Sodium Oxide (Na2O) 0.73 0.25

Potassium Oxide (K2O) 4.01 0.51

Magnesium Oxide (MnO3) 0.01 0.25

Loss on Ignition (LOI) 10.51 1.37


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3.2.2 Palm Oil Fuel Ash (POFA)

Palm oil fuel ash is a waste product obtained in the form of ash when burning

palm oil husk or fiber and palm kernel shell as fuel in palm oil mill boilers. POFA

which used in this study was collected from a factory processing palm oil owned by

Yayasan Pembangunan Johor in Ladang Alaf at the area of Bukit Lawang, Johor

Darul Takzim as can be seen in Figure 3.1. The ash was found at the flue of tower

where all the fine ashes that were trapped while escaping from the burning chamber

of the boiler. Figure 3.2 shows the ash trapped at the flue of tower of the mill.

Among the available ashes there, only the one looks grayish were sorted out and

collected.

Figure 3.1: The palm oil mill


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Figure 3.2: Ash where trapped at the flue of tower

3.2.2.1 Preparation of the POFA

Firstly, collected POFA was dried in the oven at temperature of 110 C 5

for 24 hours in order to remove moisture from it. Secondly, the dried POFA was

sieved through a 300 m in order to remove any foreign material and bigger size ash

particles. After that, only the fine ashes which pass through 300 m sieve is collected

and ground in a modified Los Angeles abrasion test machine having 10 stainless steel

bars which each of them is 12 mm diameter and 800 mm long in order to acquire

finer particles. Figure 3.3 shows flow-chart for the manufacture of POFA.


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DRYING IN OVEN

SIEVE THROUGH 300 m SIEVE

GRIND IN MACHINE

POFA

ASH FROM THE MILL

Figure 3.3: Flow-chart for the manufacture of POFA

3.2.2.2 Fineness of the POFA

The fineness of the POFA was checked by sieving through 45 m sieve at

every half an hour grinding of 4 Kg ash. Figure 3.4 shows that, by continuing

grinding, the fineness of the ash was obviously found to be increased. The ASTM C

618-94a stated that the maximum amount of all classes of mineral admixtures that

can be retained when using wet sieving on 45 m is 34 %. In other words, 66 % of

the total ash should pass through that sieve. In this project, the time of grinding was

maintained at 3.5 hours for all the grinding operations for 45 m throughout the

project.


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0

20

40

60

80

100

120

0 2 4 6 8

PercentagePassing

%

GrindingTime(hrs)

10

Figure 3.4: Effect of grinding time on fineness of POFA

For ashes finer than 45 m the fineness was checked by using the particle-

size analyzer called CILAS 1180 Liquid as can be seen in figure 3.5. The CILAS

1180 uses a new patented technology. The table below shows the mean diameter for

the grinding hours beyond 7 hours. The time of grinding maintained at 11 hours to

get 10 m throughout the project.

Table 3.2: Grinding time vs. the mean diameter of POFA

Grinding Time (hrs) Mean Diameter ( m)

7 16.749 11.09

11 8.46

13 8.41

15 8.34

17 7.65


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Figure 3.5: CILAS 1180 Liquid instrument

3.2.3 Aggregate

Aggregates (Nawy, 1996) are those parts of the concrete that constitute the

bulk of the finished product. They comprise about 60 to 80 % of the volume of the

concrete and have to be so graded that the entire mass of concrete acts as a relatively

solid, homogeneous, dense combination, with the smaller sizes acting as an inert

filler of the voids that exist between the larger particles.

For optimum compressive strength with high cement content and low water

cement ratio the maximum size of coarse aggregate should be kept to a minimum.

(Al-Oraimi et al., 2005) observed that the compressive strength increased as the

maximum aggregate size decreased.


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3.2.3.1 The Coarse Aggregate

The coarse aggregate was air dried to obtain saturated surface dry condition

to ensure that water cement ratio was not affected. Few characteristics of aggregate

that affect the workability and bond between concrete matrix are shape, texture,

gradation and moisture content. In this study crushed aggregates from quarry with

the nominal size 10 mm in accordance to BS 882, 1992 were used. Figure 3.6 shows

the coarse aggregate used.

Figure 3.6: The Coarse Aggregate

3.2.3.2 The Fine Aggregate

Fine aggregate is commonly known as sand should comply with coarse,medium, or fine grading requirements. The fine aggregate was saturated surface dry


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condition to ensure the water cement ratio is not affected. In this study, sand was

used and sieve analysis was done prior to using it to determine the fine aggregate

passing 600 m sieve. This was the percentage needed for the mix design

calculation. Figure 3.7 shows the fine aggregate used.

Figure 3.7: The Fine Aggregate

3.2.4 Water

In the production of concrete, water plays very important role. The water

used should not contain any substance that might affect the hydration of cement and

affect the durability of concrete. Generally, supplied tap water will be used

throughout the study in mixing, curing and other purposes.


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3.3 Mix Proportions

Mixture proportioning of high strength concrete is more significant process

than in normal strength concrete. In order to achieve high strength concrete, a higher

Portland cement content, a low water/cement or water/cementitious ratio,

incorporating pozzolanic admixtures, and an addition of water reducing admixtures

are considered essential. Method of design used in designing the mix is according to

Department of Environment ( DOE) United Kingdom. According to this method, the

mix design used in this research is shown in figure 3.3.

Table 3.3: Quantities of the constituents per cubic metre.

Constituents Weight (Kg / m3)

Cement 450

Water 195

Fine aggregate 800

Coarse aggregate 900

3.3.1 Number of Specimens for Each Mix

For this research, total of five mixes were caste of ordinary Portland cement

OPC as a control mix, OPC replaced with 20 % and 30 % of POFA 10 m, and OPC

replaced with 20 % and 30 % of POFA 45 m. For compressive strength, 100 mm

cubes were cast and a minimum of five specimens were tested for each age in a

particular mix. For flexural strength, concrete prisms of 100 x 100 x 500 mm

dimensions were prepared and number of specimens for each age in a particular mix

was three. Cylinder specimens of 100 x 200 mm size were made for testing splitting


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tensile strength and number of specimens was five. For both compressive and

flexural tests were conducted at the ages of 7, 28 and 90 days. Table 3.4 shows the

ages of the different test conducted in the project, the specimen used and the number

of the specimen for each mix.

All freshly cast specimens were left in the molds for 24 hours before being

demolded and then submerged into water for curing until it is time to be tested. All

methods of sampling, making and testing of specimens will be in accordance with

BS1881: Part 116 and Part 118.

Table 3.4: The tests, number of specimens and ages for each test.

Test specimen Number of specimens

P0 P1 P2 P3 P4

compressive

strength

7 days Cube

100x100x100

mm

5 5 5 5 5

28days

5 5 5 5 5

90

days

5 5 5 5 5

Splitting tensile test at

28 days

Cylinder

100x200 mm

5 5 5 5 5

Flexural at 28 days Prism 500

x100x100

mm

3 3 3 3 3

Where:

Which: P0= OPC only, P1= OPC + 20 % of 10 m POFA, P2= OPC + 30 % of 10

m POFA, P3= OPC + 20 % of 45 m POFA, and P4= OPC + 30 5 of 45 m POFA.


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3.4 Superplasticizer

The superplasticizers (Roger and Noel, 2002), are a special category of water-

reducing agents in that they are formulated from materials that allow much greater

water reductions, or alternatively extreme workability of concrete in which they are

incorporated. This is achieved without undesirable side effects such as excessive air

entrainment or set retardation. The materials originally developed as the basis for

superplasticizers in the 1960s were sulfonated naphthalene formaldehyde (SNF) and

sulfonated melamine formaldehyde (SMF) in Japan and Germany respectively,

which have found increasing application world-wide over the intervening years. In

the early 1980s, work began on designing polyacrylate-based polymers for

superplasticizer formulations and after some difficulties with severe retardation, and

in some cases excessive air entrainment, products began to appear in the

marketplace, initially in Germany, and then in Japan and the United States. The

polyacrylate-based products are based on three different types of polymer and are

being heralded as the next generation of superplasticizers.

The interaction of superplasticizers with Portland cement is the most

complicated situation of all because of reactions between the various components of

the cement and the competition, for example between the superplasticizer and

gypsum for reaction with C3A. However, in general, the hydration is retarded in a

similar manner to the individual components. The C3S phase is not as strongly

retarded as for the individual material because the C3A strongly adsorbs a large

proportion of the superplasticizer preferentially. And as a result, the formation of

ettringite is accelerated and the higher the molecular weight of SNF, the greater the

retardation of cement hydration (Roger and Noel, 2002).

In this present study, a high-range water reducing chemical admixture known

as Sulfonated Naphthalene Formaldehyde condensate in the form of dry powder was

integrated during the preparation of concrete mix throughout this research. It was


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type F high-range water reducing admixture complying with ASTM C494-05a. The

percentage of superplasticizer used in this research is 0.35 % of (cement + POFA).

3.5 Measurement of Workability

There is no acceptable test which will measure directly the workability of

concrete. Numerous attempts have been made, however, to correlate workability with

some easily measurement, but none of fully satisfactory although they may provide a

useful information within a range of Variation in workability (Neville, 2005).

It is important that the specimens of concrete that is tested to be

representative specimens. If it is not, then the results obtained by testing will not

represent the concrete placed. ASTM makes provision for sampling fresh concrete in

C172. It spells out procedures for sampling various production systems and specifies

a sample size of 1 cubic ft except for routine Slump and Compacting factor tests. The

specimen must be tested within 15 minutes and during testing must be protected from

the weather.

3.5.1 Slump Test

ASTM C143 test for slump of Portland cement concrete details the procedure

for performing Slump tests on fresh concrete. A slump cone is filled in three layers

of equal volume so the first layer is about 4 in. (76 mm) high, and the second layer is

6 in. (155 mm) high. Each layer is rodded 25 times with a tamping rod 24 in. (600

mm) long and 0.63 in. (16 mm) diameter, with a hemispherical tip with 16mm


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diameter. The rodding is uniformly distributed and full depth for the first layer and

just penetrating previous layers for the second and third layers. If the level of

concrete falls below the top of the cone during the last rodding, additional concrete is

required to keep an excess above the top of the mold. Strike off the surface of

concrete by a screeding motion and rolling the rod across the top of the cone. In 5 2

seconds, raise the cone straight up. Set the slump cone next to the concrete, and

measure the difference in height between the slump cone and the original center of

the specimen. With the rod set on the cone, this slump measurement can be read to

the nearest 0.23 in. (6mm). The test from filling of the slump cone to measuring the

slump should take no longer than 2 minutes. If two consecutive tests on a sample

show a falling away of a portion of the sample, the concrete probably lacks the

cohesiveness for the Slump test to be applicable. Figure 3.8 shows the slump test

apparatus.

Figure 3.8: Slump test apparatus


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3.5.2 Compacting Factor Test

The compaction factor test (Neville, 2005) measures the degree of

compaction resulting from the application of a standard amount of work. The test

was developed in Britain in the late 1940s and has been standardized as British

Standard 1881-103, 1993. The apparatus, which is commercially available, consist of

a rigid frame that supports two conical hoppers vertically aligned above each other

and mounted above a cylinder, as shown in Figure 3.9, the top hopper is slightly

larger than the bottom hopper, while the cylinder is smaller in volume than both

hoppers. To perform the test, the top hopper is filled with concrete but not

compacted. The door on the bottom of the top hopper is opened and the concrete is

allowed to drop into the lower hopper. Once all of the concrete has fallen from the

top hopper, the door on the lower hopper is opened to allow the concrete to fall to the

bottom cylinder. A tamping rod can be used to force especially cohesive concretes

through the hoppers. The excess concrete is carefully struck off the top of the

cylinder and the mass of the concrete in the cylinder is recorded. This mass is

compared to the mass of fully compacted concrete in the same cylinder achieved

with hand rodding or vibration.

Figure 3.9: Compacting Factor Apparatus


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The compaction factor is defined as the ratio of the mass of the concrete

compacted in the compaction factor apparatus to the mass of the fully compacted

concrete. The standard test apparatus, described above, is appropriate for maximum

aggregate sizes of up to 20 mm. A larger apparatus is available for concretes with

maximum aggregate sizes of up to 40 mm.

The results of the compaction factor test can be correlated to slump. Table 3.5

relates the results of the compaction factor test to slump and the samples degree of

workability.

Table 3.5: Correlation of compaction factor test results to slump test results

Description of

workability

Compacting factor Corresponding slump

(mm)

Very low 0.78 0-25

Low 0.85 25-50

Medium 0.92 50-100

High 0.95 100-175

3.6 Curing

Water curing of high strength concrete is highly recommended due to low

water / cement ratio. For this research, water curing will be done on specimens by

fully submerging in water after demolding until testing need to be done. Figure 3.10

shows the curing of the concrete specimens in the water.


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Figure 3.10: Curing of samples in water

3.7 Tests on Hardened Concrete

In this present research, the investigation of various aspects of strength

behavior of concrete containing palm oil fuel ash. Except for determination of

flexural and tensile strengths, the investigation of strength was mainly to test for

compression.

3.7.1 Compressive Strength

The compression test was conducted by using compressive test machine at

the material lab of Civil Engineering Faculty of the university as specified in the test

method BS 1881-Part 116,1983. An increasing compressive load was applied to the

specimen until failure occurred to obtain the maximum compressive load. The


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specimen dimension was taken before the testing. The testing was carried out 7, 28,

and 90 days curing as shown in Table 3.4. Figure 3.11 shows the compression test

machine.

Figure 3.11: Compression test machine

3.7.2 Flexural Strength Test

Flexural strength test (Neville, 2005) gives two important parameters. The

first is known as first crack strength, which is primarily controlled by the matrix. The

second is known as the ultimate flexural strength or the modulus of rapture, which is

determined by the maximum load that can be attained. Rectangular beams were used

for this test using the two point loading arrangement specified in the Test method BS

1881-Part 118, 1983. While the test was conducted, the development of first crack

and the cracking up to the failure was closely observed. Record the maximum

reading showed at the display before the specimen failed and measure the distance

from the crack to the nearest support. Figure 3.12 shows the flexural test machine.


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Figure 3.12: Flexural test machine

3.7.3 Splitting Tensile Test

In this test concrete (Neville, 2005) cylinder is placed with its axis horizontal

between the platens of a testing machine as shown in Figure 3.13. And the load is

increased until failure by indirect tension in the form of splitting along the vertical

diameter takes place. During a splitting test, the platens of testing machine should not

be allowed to rotate in a plane perpendicular to the axis of cylinder, but a slight

movement in the vertical plane containing the axis should be permitted in order to

accommodate a possible non-parallelism of the generatrices of the cylinder. This can

be achieved by means of a simple roller arrangement interposed between one platen

and the cylinder. The rate of loading is prescribed by BS 1881: Part 117: 1983.


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Figure 3.13: Concrete cylinder after testing for tension

3.8 Thermogravimetric (TG) Analysis

Thermogravimetric analysis (TGA) is a technique which examines the mass

change of a sample as a function of temperature. TGA data were analyzed by

obtaining the first derivative of the resulting pattern. The first derivative provides a

better tool for defining and attributing the weight loss to different phases. It is

expected that ettringite, monosulfate, and the corresponding carbonated phases

(carboaluminate, hemicarboaluminate, and monocarboaluminate) could all exist

within the paste of investigated specimens. Quantification of AFt and AFm phases

was not done individually, but as a whole in the temperature range from 50C to 260

C. TG analysis allows the estimation of the content of Ca(OH)2 from the weight

losses in the range of temperatures from 400 550oC and quantified based on the

limits of the first derivative of the resulting peaks. The analysis was carried out on

powdered samples using Mettler TG50 system. Samples were heated over the range

of 40 900o C at a constant rate of 20oC/min in N2 atmosphere. TG analysis was

carried out to determine the relative amount of Ca(OH)2 in the concrete samples

prepared.


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3.9 Microstructural Analysis

The structural development of cement is a result of complex hydration

reactions that stiffens, densify and impart structural integrity on the product (Conner,

1990). The main hydration phases under normal conditions are C-S-H gel of

variable stoichiometry and calcium hydroxide which together form about 90 % (w/w)

of the solid hydration products in an OPC paste. The other solid hydration products

are hexacalcium aluminoferrite trisulfate or ettringite type phases and tetracalcium

aluminate monosulfate or monosulfate.

Field emission scanning electron microscopy (FESEM) was used to observe

the morphology of the POFA and concrete samples. Samples that were tested for

strength were soaked in acetone and stored in desiccators until examined. Samples

were manually fractured mounted onto aluminum stubs using conductive carbon

coated cement double sided tape. Samples were coated with gold-palladium for

microstructural scanning. All samples were kept in desiccator prior to analysis.

In the presence of POFA, pozzolanic reaction occurs , involving the reaction

between calcium hydroxide with SiO2 or Al2O3-SiO2 framework to form calcium

silicate hydrate, calcium aluminate hydrate and calcium aluminate ferrite hydrate.

The main reaction product of pozzolanic reaction is C-S-H gel that enhanced the

strength of cement (James and Rao, 1986). Hydration processes that result in

densification of the cement matrix can improve the ability of the product to combat

aggressive condition.


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CHAPTER IV

RESULTS AND DISCUSSION

4.1 Introduction

In this chapter, various tests conducted on the specimens will be looked into.

The present study aims to investigate the workability, compressive strength, and

flexural strength, and indirect tensile strength of palm oil fuel ash concrete. Thespecimens were cured and tested at ages that explained in the previous chapter. Palm

oil fuel ash is added based on the percentage of cement content. Also, the

information may be very useful for future study and future development of building

materials. All the test methods were done as described in chapter III of this thesis.

4.2 Slump Test Results

Figure 4.1 shows the results of slump test. It can be seen that the slump value

for the control mix P0 is not within the design range which is 30 mm-60 mm because

of the effect of using superplasticizer. It can be seen that POFA concrete exhibit


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lower value of slump compared to slump of OPC concrete. It was also observed that

among POFA results, the finer the POFA, the lower the slump.

When using POFA 10 m, concrete in both replacement percentages 20 %

and 30 % exhibit lower workability. In contrast, by using POFA 45 m concrete

exhibits higher workability. For the same fineness of POFA, it is evident that by

replacing OPC by 30 % of POFA it will result in higher workability than using 20 %

replacement.

80

4035

75

65

0

10

20

30

40

50

60

70

80

90

P0 P1 P2 P3 P4

Mix

Slump(mm)

Figure 4.1: Slump test results

The high demand for water as the ash content increases is due to increasedamount of silica in the mixture. This is typical of pozzolan cement concrete as the

silica-lime reaction requires more water in addition to water required during

hydration of cement (Adesanya and Raheem, 2009). As the natural pozzolan addition

ratio increased, water demand to obtain the same consistency and workability

increases. The reason for this is that the rate of increase of water demand is not as

high as the natural pozzolan addition ratio can be, so that natural pozzolan is finely

divided and has a lubricant effect on concrete (Yetgin and Ahmet, 2006).


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4.3 Compacting Factor Results

The results of the compaction factor test can be correlated to slump. Figure

4.2 shows higher degree of compaction for the control mix P0 compared to POFA

concrete. Not only that, but also among mixes with POFA results i.e. P1, P2, P3, and

P4; at the higher percentage of replacement concrete exhibit lower slump and

consequently, lower degree of compaction.

Figure 4.2: compacting factor results

0.95

0.93

0.96

0.95

0.97

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

P0 P1 P2 P3 P4

Mix

Compactingfactor

Figure 4.2: Compacting Factor Results

4.4 Compressive Strength

As described in chapter III, total of 75 cube specimens with the size of 100

x100 x 100 mm were tested for compressive strength for P0, P1, P2, P3, and P4. The

specimens were tested at 7, 28, and 90 days after curing in water. Table 4.1 shows

the compressive strength results for these mixes. Specimens were tested for


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compressive strength by applying increasing compressive load until failure occurs.

Thus, reading of the maximum load for failure can be obtained. The calculation for

compressive strength is obtained from the following equation:

Compressive Strength = P/A

Where:

P: Ultimate compressive load of concrete (N)

A: Surface area in contact with the platens (mm2)

Figure 4.3 shows the relationship between compressive strength results. It can

be seen that, among POFA concrete compressive strength results, the higher

compressive strength was achieved when using OPC replaced with 20 % of 10 m

POFA. Although the higher compressive strength achieved is 58.05 MPa when using

POFA, but it can be seen that this strength did not exceed the compressive strength

for the control mix P0when using OPC only. This is because of the lower percentage

of superplasticizer used. The low percentage of superplasticizer will result in lower

compressive strength at early ages. And as a result, the quantity of calcium hydroxide

Ca(OH)2 will be less, and as a consequence, less C-S-H gel which plays an

important role in making more dense concrete when reacting with the silica

contained in the POFA. (Mahmud, 1996) and (Awal, 1998) observed that by

incorporating superplasticizer, remarkable achievements in the development of

strength have been shown to occur in POFA concrete. And the superplasticizer

increases not only the early-age strength but also increases the long-term

development of concrete strength.


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Table 4.1: Compressive strength results

Mix 7-days compressive

strength (MPa)

28-days compressive

strength (MPa)

90-days compressive

strength (MPa)

P048.73 59.8 66.3

P1 39.70 46.45 58.05

P2 34.55 46.06 46.65

P3 34.89 45.41 50.52

P4 29.45 41.37 45.10

48.

73

39.

70

34.

55

34.

89

29.

45

59.

8

46.

45

46.

06

45.

41

41.

37

66.

3

58.

05

46.

65

50.

52

45.

1

0

10

20

30

40

50

60

70

80

P0 P1 P2 P3 P4

CompresionStrength(MPa)

Mix

7 days

28 days

90 days

Figure 4.3: Relationship between compressive strength results


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4.5 Flexural Strength Results

As described in chapter III, total of 15 specimens of rectangular beams with

the size of 500 mm in length, 100 mm in width and 100 mm in thickness were tested

for observing POFA concrete in flexural behavior, see Table 3.2. The specimens

were tested at 28 days after curing in water. Specimens were tested for flexural

strength by applying increasing load until failure occurs. Thus, reading of the

maximum load for failure can be obtained. The calculation for flexural strength or

the modulus of rapture, which is determined by the maximum load, is obtained from

the following equation (Neville, 2005):

Modulus of rapture (MoR), fb(N/mm2) =

3bd

PL if

3

La > (4.1)

Where,

P = maximum load

L = span of beam (400 mm)

b = width of beam

d = depth of beam

a = position of fracture from near support

The results at 28-day of flexural strength for all specimens tested are shown

in Figure 4.4. It can be observed that the flexural strength of POFA is slightly lower

than that of OPC. By comparing results among POFA concrete, it is found that by

using 30 % of 45 m POFA gave a higher flexural strength. At the same time, it is

much closer to that of OPC concrete. It also can be seen that by using higher

percentage of POFA which is 30 %, a higher flexural strength was achieved.


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7.95

7.57

7.68

7.5

7.83

7

7.2

7.4

7.6

7.8

8

8.2

P0 P1 P2 P3 P4

Flexuralstrength(M

Pa)

Mix

Figure 4.4: Flexural Strength Results

4.6 Splitting Tensile Test Results

Total of 25 cylinders were tested for tensile at 28 days for mixes where

shown in Table 3.2. Figure 4.5 shows splitting tensile strength results for these

mixes. It can be seen that the behavior of concrete in tension is nearly the same to the

behavior in flexure. Except for P2and P4show convergent strength results. Although

the results of POFA concrete in tension are different but alike. The higher percentageof replacement of P2 and P4 when using 30 % POFA gave results of tensile quite the

same. In general, POFA concrete is lesser than OPC concrete in tension.


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9.04

6.72

8.087.77

8.14

0

2

4

6

8

10

12

P0 P1 P2 P3 P4

TensileStrength(M

Pa)

Mix

Figure 4.5: Splitting tensile strength results

4.7 Chemical Analysis of POFA and OPC

The single point BET surface area for POFA10 m and POFA 45 m is 47

and 28 m2/g, respectively. POFA of 10 m showed a higher surface area as expected

due to its smaller particle size compared to POFA 45. The higher surface area for

POFA 10 m could result in a higher rate of reaction, hence higher compressive

strength. Samples containing 20 % of POFA 10 m and 30 % of POFA 10 m,

showed higher compression strength compared to the samples containing POFA 45

m at 90 days curing age.

Both physical properties and chemical analysis indicated that POFA is a

pozzolanic material (Awal and Hussin, 1997; Sumadi and Hussin, 1993). This

pozzolanic material is grouped in between Class C and Class F as specified in

ASTMC618-92a (Awal and Hussin, 1997). POFA is moderately rich in silica content

meanwhile lime content is very low as compared to OPC (Awal and Hussin, 1997).

However, the chemical composition of POFA can be varied due to operating system

in palm oil mill. Table (4.2) shows the chemical composition of the OPC and POFA.


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Table 4.2: Chemical composition of OPC and POFA

Chemical Composition POFA OPC

Silica (SiO2) 48.99 21.45

Aluminium Oxide (Al2O

3) 3.78 3.62

Ferric Oxide (Fe2O3) 4.89 3.50

Calcium Oxide (CaO) 11.69 60.98

Magnesium Oxide (MgO) 1.22 0.59

Sodium Oxide (Na2O) 0.73 0.25

Potassium Oxide (K2O) 4.01 0.51

Magnesium Oxide (MnO3) 0.01 0.25

Loss on Ignition (LOI) 10.51 1.37

4.8 Thermogravimetric Analysis ( TGA)

Thermogravimetry and differential thermogravimetry analysis of the concrete

samples containing POFA 10 m, (P1and P2), and the other one containing POFA 45m; (P3and P4) at 90 days curing age, and which were cured in water showed that

the weight loss due to dehydroxylation of Ca(OH)2 occurred between 410oC to

470oC. Significant weight loss between 550oC and 750oC is also was observed. At

temperatures above 550oC weight loss is attributed partially to CO2 from

decomposition of CaCO3and partially due to the final stages of dehydration of C-S-

H and the hydrated aluminate phases (Taylor, 1990). Some researches attributed

weight losses between 650oC and 850oC as being due to the decomposition of CaCO3

to CO2and CaO (Pacewska, et al., 2002). Table 4.3 shows the percent weight losses

for P1, P2, P3and P4at 7, 28 and 90- day curing ages.


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Table 4.3: The percent weight loss for P1, P2, P3, and P4

Sample Percentage of weight loss %

7 Days 28 Days 90 Days

P1 0.46 0.71 0.87P2 0.70 0.73 0.77

P3 1.125 0.92 0.43

P4 1.11 0.91 0.50

Based on the percent weight loss attributed to dehydroxylation of calcium

hydroxide, Ca(OH)2or portlandite, the amount of Ca(OH)2increases with curing age

for P1 indicating the progress of cement hydration reaction. For P2samples there is

no increase in strength for 28-day and 90-day samples. The percent weight loss

attributed to dehydroxylation of calcium hydroxide remained unchanged for this

sample at the said curing ages. For P3and P4, a reduction in weight loss attributed to

dehydroxylation of calcium hydroxide, or portlandite and subsequent increase in

compression is indicative of pozzolanic reaction. This higher strength can be

attributed to the pozzolanic reaction which occurred between the silica in POFA and

calcium hydroxide which results from the cement hydration reaction. Table 4.4

showed the percent weight loss and temperature ranges for P0, P1, P2, P3, and P4at

90- day curing ages.

Table 4.4: Thermogravimetry data for Po, P1, P2, P3 and P4 at 90 days curing age

Sample

Temperature ranges for weight loss and percent

weight loss (%)

50 - 250CoC 410 470

oC

P0 5.8 1.85

P1 7.5 0.87

P2 6.7 0.77

P3 8.2 0.43

P4 10 0.5


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AFt and AFm phases in the temperature range from 50C to 260C shows

that all samples exhibit weight loss in this temperature range with P4 having the

highest weight loss (10%).

4.9 Microstructural Analysis (FESEM)

The structural development of cement is a result of complex hydration

reactions that stiffens, densify and impart structural integrity on the product (Conner,

1990). The main hydration phases under normal conditions are C-S-H gel of

variable stoichiometry and calcium hydroxide which together form about 90 % (w/w)

of the solid hydration products in an OPC paste. The other solid hydration products

are hexacalcium aluminoferrite trisulfate or ettringite type phases and tetracalcium

aluminate monosulfate or monosulfate.

In the presence of POFA, pozzolanic reaction occurs , involving the reaction

between calcium hydroxide with SiO2 or Al2O3-SiO2 framework to form calcium

silicate hydrate, calcium aluminate hydrate and calcium aluminate ferrite hydrate.

The main reaction product of pozzolanic reaction is C-S-H gel that enhanced the

strength of cement (James and Rao, 1986). Hydration processes that result in

densification of the cement matrix can improve the ability of the product to combat

aggressive condition.

In this study the microstructure of P0, P1, P2, P3 and P4were studied using

Field Emission Scanning Electron Microscope (FESEM) at 3 and 7-day curing ages.

A porous morphology is observed at 1000X magnfication at 3-day curing age as can

be seen in Figure 4.6. At higher magnification, granules of POFA were observed and

also the occurrence of typical hydration reaction products is observable in the

samples that are shown in Figure 4.7.


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Figure 4.6: FESEM of P4at 3 days using 1000X magnification showing

porous morphology.

Figure 4.7: Granules of POFA when using 1000 X magnification of P3at 3

days


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Radiating clusters of Type I C-S-H gel could be observed distributed in all

the samples. Radiating clusters of C-S-H will eventually lead to a densification the

structure, and an increase in strength. Figure 4.8 show higher magnification of

sample P3, it can be seen the presence of fine needle like structures of ettringite

crystals. Studies have shown that the superplasticizer accelerate early ettringite

formation as well as producing ettringite crystals which are smaller. Hexagonal

platelets of Ca(OH)2 could be observed in some samples as shown in Figure 4.9.

Hexagonal platelets of Ca(OH)2are less evidence. Figure 4.10 and Figure 4.11 show

the FESEM of P3 at 3 and 7 days at three different magnifications which is 500,

1000, and 2000 X.

Figure 4.8: FESEM of P3at 7 days using 2000X magnification


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Figure 4.9: FESEM, P2at 7 days, hexagonal platelets of Ca(OH)2.


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Figure 4.10: Microstructure of P3at 3 days at 500, 1000, and 2000 X magnification


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Figure 4.11: Microstructure of P3at 7 days at 500, 1000, and 2000 X magnification


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4.10 Summary

This chapter represents the characteristics features of palm oil fuel ash used

and its influence on some properties of fresh and hardened concrete. Properties of

ash obtained in this present research suggest that POFA is a good pozzolanic material

due to its higher content of silica compared to that of OPC.

Test on workability behavior of concrete containing POFA did not show any

satisfactory result. It has observed that by inclusion the POFA in concrete, the

workability was reduced.

The factors that are responsible for the development of strength of concrete

with common pozzolanic materials have shown to influence the strength of concrete

containing palm oil fuel ash. Study on the effect of using more fine ash with different

contents on compressive strength revealed that, because of pozzolanic activity and

higher surface area, it is better to replace 20 % of cement by POFA of 10 m rather

than using POFA of 30 m with both 20 % and 30 % replacement that is because of

the higher surface area when using POFA of 10 m. Although the results of strength

in flexure and tensile are different but alike. The replacement of OPC with POFA has

result in lower tensile strength. On the other hand, among POFA concrete results, the

higher the replacement the higher the tensile strength. Tests on flexural strength have

revealed to the same of flexural strength.

Studies on samples using Field Emission Scanning Electron Microscope

(FESEM) at 3 and 7-days curing ages revealed that, occurrence of typical hydration

reaction products is observable.


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CHAPTER V

CONCLUSIONS AND RECOMMENDATIONS

FOR FUTURE STUDY

5.1 Introduction

Although conclusions in the form of summary have been mentioned at the

ends of the previous chapters, a short account of important research findings making

up resolutions is presented here for the sake of clarity.

5.2 Behavior of POFA Concrete in the Fresh State

POFA concrete exhibit lower value of slump compared to slump of OPC

concrete. It was also observed that among POFA results, the finer the POFA the

lower the slump. The results of the compaction factor test can be correlated to the

slump. The higher the percentage of replacement concrete exhibit lower slump and

consequently, lower the degree of compaction.


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5.3 Behavior of POFA Concrete in the Hardened State

Study on the effect of using more fine ash with different contents on

compressive strength revealed that, because of pozzolanic activity and higher surface

area, it is better to replace 20 % of cement by POFA of 10 m rather than using

POFA of 30 m with both 20 % and 30 % replacement that is because of the higher

surface area when using POFA of 10 m. The flexural strength of POFA is slightly

lower than that of OPC. Like that of flexural strength, tensile strength of concrete

containing POFA developed in the similar way.

5.4 Thermogravimetric analysis (TGA)

Thermogravimetry analysis of the concrete samples containing POFA

revealed that, the amount of Ca(OH)2 increases with curing age indicating the

progress of cement hydration reaction. Reduction in weight loss attributed to

dehydroxylation of calcium hydroxide, or portlandite and subsequent increase in

compression is indicative of pozzolanic reaction.

5.5 Microstructural Analysis (FESEM)

A porous morphology is observed in some samples at 1000X magnification

and radiating clusters of C-S-H will lead to a densification the structure, and an

increase in strength. Hexagonal platelets of Ca(OH)2 could be observed in some

samples and they are less evidence in relation to the strength.


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5.6 Recommendations for Future Investigation

a. If concepts were developed, it would not be necessarily mean that this

will remain true for all the time. The properties of the ash may vary

from source of supply to another depending on the type of the raw

material and efficiency of burning.

b. Manufacture and testing of concrete with various mix proportions are

recommended not only to satisfy the individual need but also to find a

broader perspective on behavior of this new pozzolanic material.

c. The effect of superplasticizer was observed to be very significant not

only on the early-age strength but also on the development of late-age

strength. Consequently trial mix on different content of

superplasticizer is strongly recommended.

d. Previous researches have revealed that incorporation of POFA in

concrete is advantageous for the durability of concrete in: the rise of

heat, carbonation, penetration of chloride ions, and sulphate

environment. At the same time, using POFA in concrete as

replacement materials, limited compressive strength of 60 MPa was

achieved. Contribution of POFA with high cementitious material such

as GGBFS to get high strength high performance concrete is mainly

recommended.


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