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SELF HEALING CONCRETE
BY INCORPORATING PAL': OIL FUEL ASH .(POFA)
AS CEMENT REPLACEMENT MAIERIAL
MUHD AZZUHIF Y B ZAFRI
A thesis submitted in fulfillment of the requirement for
the award of -the 'degree in I achelor of Civil Engineering
Faculty of Civil Engineering and Environment Resources
Universiti :Malaysia Pahang
DISEMEER 2010
ABSTRACT
Malaysia as The world largest exporter of palm oil has been facing problem in
disposing palm oil fuel -ash -(POFA), a -by-product -of palm oil mill. Previous researchers
were revealing the potential of this finely ground waste as a partial cement replacement in
reacted as pozzolans to produce a self healing concrete. In this study, the effectiveness
using POFA as -cement replacement -material towards self -healing of -concrete were
investigated. Four series of mix formulation in producing IOFA concrete with different
percentage of cement replacement namely 0%, 10%, 20% -and 30% were designed. All
specimens were subjected -to -compressive strength due to 7, 28, -60 -and0 days cured in
water. In addition, the UPV test was conducted in order to -monitor self healing progress
of POFA -concrete specimens -due -to hairline -crack. The specimens were tested at
different curing types subjected to UPV test. It was found that, the concrete with 20% of
POFA recorded highest compressive strength co pare to those mixes. It also revealed
that, the UPV values were increases correspondingly to curing ages when POFA concrete
immersed in water curing type. it shows the water curing were the effective mechanism
towards self healing process.
V
ABSTRAK
Malaysia sebagai salah satu pengeksport kelapa sawft lerbesar di dunia
menghadapi rnasaiah pelupusan abu terbang kelapa sawit :POFA), salah satu produk
sampingandari. kilang kelapa sawit. Para penyelidik telahnienemuiiahwa •ábu terbang
yang dildsar halus untuk menggantikan sebahagian simen dapat mengaktifkan
tindakbalas pozzolana untuk penghasiian konkrit putih sendlri. KajIan mi merninjukkan
.keberkesanan POFA untUk .menggantikan sirnen dalam :koikrit pulih sendiri:. Terdapat
empat -siri formula carnpuran untuk menghasiikan konkrit POFA yang menggantikan
simen dengan peratusan yang berbezaiaitu 0%,10%, 20 1/o dan 30% dikendalikan. Sernua
sampel diuji d iganujiarrrnampatanpadahari ke 7, 28, 60 dan 90 yang telah direndarn di
dalam air. Selain itu, ujian UPV turut -dijalankan untuk memantau proses pemulihan
sendiri :koñkit yang rnempunyai retakan halus tersebut. :Sampel yang diuji adalah
mengikut proses kuring yang telah di tentukan. Hasil ujian menunjukkanbahawa konicrit
yang mempunyli 20% kandungan POFA merekodkan iceputusan ujian mampatan yang
palintinggi brbaning dngan pratusan lain. &lain itu, nilai UiV methigkat dai han
ke han semasa pemantauan dibuat dan -k-uring air adalah yang terbaik di antara tiga jenis
kuring yang lain mi menunjükkan bahawa kuning air adalah lkur.ing yang paling terbaik
untuk proses pemulihan kcnkrit.
vi
1. vi'
TABLE -OF CONTENTS
CHAPTER TITLE PAGE
TITLE
DECLARATION
DEDICATION
AOWLEDGEMENT iv
ABSTRACT v
TABLE OF CONTENT vii
-LIST OF TABLES xi
LIST OF FIGURES xiii
CHAPTER 1 INTRODUCTION
Li Background of Study 1
1.2 Rational of Study 2
1.3 Problem Statement 3
-1.4 Objectives 'of Study 4
'Scope of Study 5
CHAPTER 2 LITERATURE REVIEW
2.1 Introduction -6
2;2 Cementitious Reaction of Portland Cement 7
2.3 Cement 'Replacement Materials 8
2:4 Pozzolanic Materials 9
2.5 Pozzolanic Behaviours 11
2.6 Types of Pozzolanic Materials 12
2.7 Origin of Palm Oil Fuel Ash 13
2.8 Pozzolanicity of Palm Oil Fuel Ash 13
2:9 Effect of Fineness of the POFA 14
2.10 Effect of Ash Contents 16
2.1'l Strength Development 17
2.12 Length of .Cuiing •ig
2.1.3 Concrete Durability: Role ccfiozzoian 19
2.14 Chemical Attack 20
2.15 Chloride Penetration 20
2.16 Sulphate Attak 22
2.17 Acid Attack '24
2.18 Summary 25
CHAPTER .3 METHODOLOGY
3.1 Introduction 26
3.2 Experimental Program 27
3.3 Selection of Materials :28
3.3. -1 Ordinary Portland Cement (OPC) 28
3.3.2 Palm Oil Fuel Asli :(POFA) 29
3.3.3 Coarse Aggregate 30
3.14 Fine Aggregate 31
3.3.5 Water 32
14 Mix Design 32
3.4. .1 Concrete Grade 30 32
3.5 Preparation ofSarnples 33
VIII
ix
3.5.1 Specimen Dimension and Quantity 34
3.52 Batching, Mixing and Casting 36
3.5.3 Curing Ages 37
33.4 Curing Types 37
3.6• Testing Method 39
Córnpresion Test 40
3.5:1 Ultrasonic Pulse Wiocity(UVV) 41
3.5:2 Pre-crackon Spehnens 42
CRAPTER.4 iUSIJLTS AND DISCUSSIONS
4.1 Introduction 45
4.2 Physical Properties of Palm Oil Fuel Ash 46
4.2.1 Chemical Composition of POFA 46
4.2.2 Particle Size Analysis of POFA 48 4.3 investigation of Compressive Strength 50
4.4 Investigation in Mechanism of Curing 55
4;4. 1 Ulltrasoiiic Pulse Vàlocity(UPV)Resiilts 56
444.2 Air Curing 57
4.4.3 Control Room Curing 58
4.4.4 Wet & Dry Curing 60
4:.45 Water Curing 61 4.5 Optimum Percentage oIPOFA Partial 63 Replacement
4:6 Finest Mechanism for self-healing 63
CHAPTERS CONCLUSIONS AND RECOMMENDATIONS
5.1 Introduction 66
5.2 Condusions 67
5.3 Recommendations 68
REFERENCES
APPENDIX
xi
LIST OF TABLES
TABLE NO. TITLE PAGE
3.1 Chemical Composition of POFA and 4OPC 30
3.2 Quantities ofthe Constituents Per Meter Cubic 33
3.3 Quantityof Specimen (cube) for Each Replacement 35
3.4 Total Specimen for Each Curing Types 38
3.5 Concrete Quality Grading for UPV 41
4.1 Chemical Composition of the OPC and POFA 47
•4.2 Compressive Strength for 7 Days Curing Period 50
4.3 Compressive Strength for 28 Days Curing Period 51
4.4 Compressive Strength for 60 Days Curing Period 52
4.5 Compressive Strength for 90 Days Curing Period 53
46 Compressive Strength Result 54
4.7 tfltrasonic Pulse Velocity Classification 56
4.8 Results for UPV Test Exposed to Air Curing 58
4;9 Results fOr UPV Test of Exposed to Control Room Curing 59
4.10 Results for UPV Test 4 Exposed to Wet & Dry Curing 60
xl'
4.11 Results for UFV Test of Exposed to Water Curing 62
4.12 Type ofCurin.g for POFA-20
ZI
4.13 Type of Curing for POFA-30 65
xli'
LIST 'OF 'FIGITRIS
TABLE NO. TITLE PAGE
2.1 Example of White 'Pozzolanic 10
2.2 Pozzolanic Material under Microscope 10
2.3 Fineness of Ash Effect 16
2.4 The Effect of Ash Content Replacement 'Level Towards 17 The Strength
2.5 Diversity ' 'fOPC rand POFA 'Con'crete'Strength '18
3.1 Experimental 'flow Process 27
3.2 "Ordinary Portland Cement (OPC) 29
3.3 Raw Pi1rnOi'FFuei. Ah 29
3.4 'Coarse Aggregate 31
3.5 Fifl Aggregate 31
3.6 Mixer Used -to Mixing Concrete 33
3.7 Dimension of -Concrete Cube 34
3.8 Standard Càst iron Mould 36
19 After Casting Concrete into Mould 36
3.10 Water Curing for Early Strength 37
3.11 Water Curing .318
3.12 Air-Curing 38
3.13 Wet andDryCuring 39
3.14 'Control Room 'Curing 39
3.15 'Cornpression.Test 40
xiv
3.16 Ultrasonic Pulse Wlocity(UPV) 42
3.17 Hairline Crack on .Speimen 43
3.18 Hairline crack on Concrete Specimen under Microscope 44
4.1 Percentages Chemical Composition of .POFA 47
4.2 POFA and OPC Particle Size Distribution 49
4.3 Compressive Strength of 7 Days Curing Period 50
4.4 Compressive Strength for 28 Days -Curing Period 51
4.5 Compressive Strength for 60 Days Curing Period 52
4.6 Compressive Strength for -90 DaysCuring Period 53
4.7 jCompresgiveStrength for all Percentage. 54
4.8 UPV Value 'Exposed to Air Curing 58
4.9 IJPV Value Exposed to Control Room Curing 59
4.10 UPV Value Exposed to Wet & Dry Curing 61
4.11 U:V Value Exposed-to Water Curing 62
4.12 131W Value for Each Type of Curing for POFA-20 64
4.13 TJPV Value for Each 'Type of Curing for POFA .30 65
CHAPTER I
INTRODUCTION
1.1 Background of Study
Palm oil industry in Malaysia is one of the sectors famously chosen to be
developed commercially in several tropical countries located in Asian region. The
development on agriculturalbaed industry in Maiaysia 'since 4revious century has able
to generate and become the largest producer focusing on palm <il industry. Basiron and
Simeh (2005) reported that Malaysia has become the cunnl niunber one palm oil arcand
Asian which the development must be maintain its lead position over the next one and the
half decades producing 18 million tones or 42% of the world palm oil in 2020.
It is predicted that the quantity of palm oil fuel ash (POFA), a profitless by-
product 'generated by palm oil 'mill will increase as the production 'of :palrn o11 continue to
grow over the year,. Therefore, it is anticipated that the success in discovering the
utilization of this material in any type of-material making process would be able to reduce
quantity of waste thrown 'and assist palm oil industry to be more eclogical friendly
sector. Glancing through the :history of this material introduced in construction area, it
2
has been Malaysian researcher who managed to prove that this material possesses
pozzolanic properties (Abu, 1990). Abdul Awal and Hussin (1997) have proved that this
waste could be used as partial cement replacement in concrete for production of stronger
and more durable construction material. Succeeding the findings, more researchers have
integrated POFA as one of mixing ingredient in the mix to produce new type of -concrete
such as high-strength concrete (Sata ct 'al., 2004) and lightweight concrete
(Mat Yahaya, 2003).
Palm oil -fuel ash .(POFA) is -a by-product -from burning process in thermal power
plant, which paimnut and. fiber 'of palm 'are burnt 'at temperature about 3004000 -Celcius.
Each year more than 100,000 -tons. -of POFA has been disposed and tended to 'increase
annually. From the study of the ,chemical composition, it was 'found that The POFA could-
be used as a .pozzolana. In this 'study, the quality of POFA was improved by grinding
until the -median particle sizes were 19.9 and 10.1 microns. The POFA were used to
replace Portland cement (OPC) 'up to 30% by weight of cement. After that, water curing
process and compressive strength test -of specimens at -the age -of 7, 28, -60 and 90 days
will be monitored and recorded.
1.2 Rational-of-the Study
The -accelerated -devlopments 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 -orjustified because
of the economical gains in producing stronger structures that are smaller in -component
dimensions while 'larger in resulting -space 'availability.
3
In recent years, studies have been carried out by various researchers in using
waste generated from the agricultural and industrial activities as partial replacement of
cement in making concrete Cray 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).
The consideration -usage of the Palm Oil Fuel Ash (POFA) which possesses
Pozzolanic material in selThealing concrete is to reduce the -excessive wastage of the
100,000 tons of POFA 'has b'en disposed and 'tended 'to increase 'annually '(Tangchirapat
and Saeting, 2007). Rather than exposed as wasted -materials -or fill embankment
materials, hence The wastage of the POFA apparently use in concrete as replacement of
partial cement quantity. One 'other of the 'main concern is the 'emission of CO2 during 'the
hardening process from the chemically -caldnations of the limestone can :be reduce -and
apparently the positive 'significance is the 'greenhouse effect tan be 'reduced worldwide.
Besides that, quantity-of-the-cement 'for-concrete -can be 'reduced about 20% 'untI .30%.
13 Problem ,Sttement
Concrete 'is the most widely used man-made construction 'materials. It is 'obtained
by mixing cement, water, aggregate -and -admixture -Csmiti -quantity). The prát'iem with
concrete is crack normally happened at the concrete' structure such as beam, column,
foundation and others 'structure element which 'can causing 'concrete failure 'occurred by
the shrinkage, overload., rapid changing temperature -and settlement above ground level.
.4
ft can be outlined where 'self-healing concrete incorporating palm oil fuel ash
(POFA) as an alternative to avoid creeping on hardening Concrete. The hairline creep
usually occurs during the maturing periods of concrete. Hence, the self-healing concrete'
is expect to be able repairing it own creep within the curing process. Since the engineers
and expertise always faced this problem for everyday during producing the high financial
system loss to prevent this problem occurred, it is best to study the effectiveness of this
POFA to perform in concrete replacing the cement within the suitable percentage of
replaced by POFA up to .30%. Beside: the main problem of hairline creep, the emission of
the CO2 expected to reduce andavoiding the :greenhouse effect from rapidly 'happens
nowadays.
1.4 Objectives of Study
The objectives of this study are:-
i. To study the effectiveness 'using 'POFA inseifheaiing concrete process
ii. To study mechanism of self-healing concrete incorporating POFA
iii. To obtain optimum percentage of POFA in concrete mixture
5
1.5 Scope of Study
This study were focused on the investigation of the concrete containing palm oil
fuel ash (POFA) substituted as ordinary Portland cement (OPC) replacement. The
limitation on this study are to determine the effectiveness of self-healing concrete
incorporating POFA (POFA -concretes) as pozz6ianhc material with different percentage
of POFA subjected 'to different curing types. The different percentages of POFA used
were calculated 'based on 'total weight of the OPC which is '0%, 10%, 20% and 30%. All
the specimens were labeled -as POFA-0, POFA-lO, POFA-2'() -and POFA-3'0 respectively.
After designation of the mix proportion, the ton'crete were 'cast into the 'standard steel
mould with dimensions 'of -150 mm x 150 mm x 150 mm. The POFA-concretes where
cured in water will be :test due to compressive strength. The compressive strength test
was accordance to ASTM £39 / £39M 09a. 'On the 'other hand, the POFA-concretes
specimens were subjected to ultrasonic pulse velocity (IJPV) were -cured at 7, 2'8, 60 and
90 days with different type of curing.
There 'are 'four (4) 'tyç es of curing namely water curing, 'air 'curing, wet 'and 'dry
curing and control room curing. Each type of curing has its own possession in term of
humidity, dryness, temperature and environment condition. Concrete -with grade 30 were
designed and poured into standard -cast iron mould. After 'concrete were 'hardened at 24
hours, the concrete specimens were test under The compressive load to create pre-crack
(hairline crack) on the 'sui ace of The 'sample for 'UPV test. This test will be monitored
cautiously to avoid the concrete cube -over-crake& After' the 'precrack process, the
sample were cured into four different 'types of curing process which is air curing, water
curing, wet and dry curing and -control room 'curing correspondingly far self-healing Concrete.
'CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
Large number of researches '(Mëhta, 1983; Maihotra et al., 1992; Massazza, 1993
and Nagataki, 1994) conducted since last century has provided a wealth of information on
composition and characteristics ofpozzolans and their effects on properties of concrete.
However, pübiihed literatures on the performance of concrete containing piIm oil fuel
ash which started last two decades are not many. The Objective of this thesis is to present
a durability of 'high 'strength 'conciete in particular, from the viewpoint on providing
scientific expla ations for some of the phenomenologicái observations. This is needed to
encourage the:çroper use of-new cement substitutes in 'cement and concreteindustry.
7
Firstly, a •sh 'review ofchemical reactions, considered responsible for setting
and hardening of Portland cement, will be given. This will be followed by thedescription
of pozzolans and poZZolaflic reactions. The rest of chapter includes the performance
characteristics of concrete 'containing the pozzolanic materials on different aspects of
durability in terms of chloride penetration, Sulphate attack and acid attack.
2.2 Cernentitious Reaction'of Portland Cement
Calcium combination with silica, alumina and iron oxide is essentially of
crystalline compounds of the Portland cement's consists. These compounds are usually
regarded as the major 'constituents of cement. The actual quantities 'of 'the various
compounds vary con derably from cement to cement, and in practice different types of
cements are obtained by suitable proporti-oning of the 'materials. Along 'with the 'rain
compounds, there 'exist minor 'compounds such as S03, MgO, K20 and Na2O, which
usually amount to nOt more than ,a few percent of the weight of cement.
The compounds of Portlatid cement clinker are anhydrous, 'hut when 'water is
added the minerals begin to ionize, and the ionic species 'form hydrated products of'Iow
solubility that precipitate out ofthe solution. The .main product of hydration of silicate
mineral is a 'calcium silicate hydrate'(C-S-44) of colloidal dimensiOn that, 'at early -age,
under a scaiming electron 'mIcroscope, usually shows up as an aggrega1ion of very' fine
grains partly inter-grown together.. The structure of 'C-SH is not constant in space and time.
-8
It adopts a variety -of morphologies, some based on thin sheets to give fibrous or
honeycomb structures at early ages, others with a more compact structure (Reinhardt,
1995). It is highly cementitious and constitutes about 60 to 65 percent of the total solids
in a filly hydrated Portland cement. The other product of hydration of the silicate
minerals is about 20 percent calcium 'hydroxide (CM), which usually occurs as large
hexagonal crystals, and contributes little to the cementitious properties of the system.
Also, being relatively most sokbie and alkaline than the other hydration products, it is
easily subjected to attack by water or , acidic solutions, thus reducing durability of
Portland cement systems to such environments (Mehta, 1983). Indeed, the hydration of
Portland cement and The reactions involved in it-are vast.and quite complex in nature.
2.3 Cement Replacement Materials
Cement replacement -materials (illston and Domon; 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 -cementhious
materials, cement extenders, mineral admixtures, tnitieral additives, iatnt hydraulic
materials or, simply, cementitious materials.
Several types of materials are common in 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 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.
I,'
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 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'niaterials, i.e. the Portland 'cement :plus the
Cement Replacement Materials.
2.4 Pozzolanic Materials
A pozzolana is 'a 'siliceo'us 'or 'siliceous 'and 'aluminous 'material 'which in itself
possesses little or no 'cernentitious value but ii1l, :in fin1y 'divided 'Form and :in the
Presence of moisture, chemically react with calcium 'hydroxide at ordinary temperatures
to form compounds possessing cementitious properties Neville, 2005). 'Figure 2.1 and
2.2 will show the example of pozzoianic material and its condition under microscope.
Figure 2.1: Exarple of White Tozzolanic
(Source: www.bombayharbor.com)
Figure 2.2: Pozzolanic Material under Microscp
(Source: www.hepco;co.jp )
Ia
ii
2.5 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 (iliston 'and Domone, 2001). A pozzolanic material is
one which contains active silica (SIO2) and is not cementftious 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 disordere'd: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 :pozzo'ianic Te'action is that produced from the cement hydration.
Further quantities of-calcium silicate hydrate are produced in Equation 23
2S± 3d 4'C3S2 E13 [Equation 2.1]
The reaction is 'clearly secondary to 'the -i ydration of the 'Portland"••ment, 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 contbution to the strength and other
Properties of the hardened cement paste and concrete.
12
2.6 Types of Pozzolanic Materials
The performance 'of:pozzolanic material when added as a mixing ingredient in a
concrete differ base on Their Origin, nature and characteristics. It may be interesting here
to speculate why rice 'husk ash (RHA) is the most reactive of all the supplementary
cementing materials, in spite 'of the fact that condensed silica fume and many fly ashes
and granulated blast-furnace slag also contain large amounts of non-crystalline reactive
minerals. Mehta '(1992) 'has the 'explanation for the above. 'speculation. According to
Mehta, these materials are obtained from, rapid cooling or condensation of droplets of
high-temperature melts. The surface of products formed by condensation of a melt is not
micro-porous, therefore, an induction period 1 needed to activate the surface in the
alkaline environment provided by the hydration of Portland cement. The same researcher
added that in the case of RHA particles with highly 'microporous surface, a long
induction period is not necessary for the surface reactions involving the fomation of C-
S-H and hydrous silica.
There are many types nf the pozzolanic material (lllston 'and Dcmone, 2001). The main cement replacement materials in use world-wide are:-
i. Pulverized fuel ash (PFA); calied 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 parkle iize range for'use In concrete
ii. 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;
Condensed silica fume (CSF); often called micro silica, extremely fine particles of
silica condensed from the waste gases given 'off in the production of silicon metal;
iv. Calcined clay or shale; .a clay or shale heated, rapidly cooled and ground;
13
V. Rice husk ash; 'ash from the controlled burning of rice husks after the rice grains
have been separated;
vi. Natural pozz4lafls; some volcanic ashes and diatomaceous earth.
2.7 Origin of Palm Oil Fuel Ash
Palm oil fu1 ash is a by-pro&ict produced in-palm oil mill. After palm oil is
extracted from the pain 'oil "fruit, 'both :palm'o'il 'husk and palm oil-shell-are burned as fuel
in the boiler ofpalm oil mill . ,Generally, after -combustion About S % palm oil fuel ash by
weight of solid wastes is produced (Abdullah.and Hussin, 2006).
The ash :produce'd 'sometinies varies in 'tone of colour from whitish grey to darker
shade based on 'the carbon 'content in it. In other words, the physical 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 (Abdulláh and ilusin, 2:006).
2.8 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 pozzolanic 'activity 'index •which
determines the totals 'acth4ty 'of .pozzolana'(Neville, 2005).
