-
Seediscussions,stats,andauthorprofilesforthispublicationat:http://www.researchgate.net/publication/260286772
StrengthActivityIndexandMicrostructuralCharacteristicsofTreatedPalmOilFuelAshDATASETFEBRUARY2014
CITATIONS7
DOWNLOADS65
VIEWS100
5AUTHORS,INCLUDING:
Dr.NurdeenAltwairAl-MerghebUnvirsity21PUBLICATIONS28CITATIONS
SEEPROFILE
MegatAzmiMegatJohariUniversityofScienceMalaysia51PUBLICATIONS387CITATIONS
SEEPROFILE
S.F.s.HashimUniversityofScienceMalaysia20PUBLICATIONS106CITATIONS
SEEPROFILE
Availablefrom:Dr.NurdeenAltwairRetrievedon:02July2015
-
International Journal of Civil & Environmental Engineering
IJCEE-IJENS Vol: 11 No: 05 100
115905-7676 IJCEE-IJENS October 2011 IJENS I J E N S
Strength Activity Index and Microstructural Characteristics of
Treated Palm Oil Fuel Ash
Nurdeen M. Altwair, Megat Azmi Megat Johari and Syed Fuad Saiyid
Hashim
Abstract The strength activity index of mortar and
microstructural characteristics of pastes containing treated palm
oil fuel ash (POFA) have been investigated. POFA obtained from a
palm oil mill was treated via sieving, grinding and heating at
temperature of 450C for 90 minutes in order to improve the
pozzolanic reactivity of the POFA. The pozzolanic reactivity of the
treated POFA was evaluated by conducting strength development tests
according to ASTM C311. The hydration products of hardened pastes
were analyzed by means of thermogravimetric analysis (TGA), x-ray
diffraction (XRD), and scanning electron microscopy (SEM) in order
to quantify the influence of the treated POFA which was used at
different POFA/cement ratio ranging from 0 to 0.8. After 28 days,
the strength activity index of the treated POFA with ordinary
Portland cement exhibited very good performance and was higher than
100%. At 90 days, the strength activity index increased to 101.72
%. Using TGA, XRD, and SEM, a significant reduction in Ca(OH)2
content was observed with increasing amount of treated POFA. The
development of C-S-H gel was higher when POFA/cement ratio was
raised up to 0.3.
Index Terms - Palm oil fuel ash; Strength activity index;
Hydration products.
1. INTRODUCTION
Compounds present in ordinary Portland cement, such as C3S and
C2S, are known to react with water and form calcium silicate
hydrates (C-S-H) and calcium hydroxide (Ca(OH)2) [1]. Approximately
70% C-S-H, 20% Ca(OH)2, 7% sulfoaluminate, and 3% secondary phases
are formed as a result of the aforementioned reaction [2].
Dr. Megat Azmi Megat Johari is currently and Associate Professor
at the School of Civil Engineering, Universiti Sains Malaysia 14300
Nibong Tebal, P. Pinang, Malaysia (E-mail: [email protected]).
Nurdeen M. Altwair is with the School of civil Engineering,
Universiti Sains Malaysia 14300 Nibong Tebal, P. Pinang, Malaysia,
(corresponding author phone: +60174158209; e-mail:
[email protected]). Dr. Syed Fuad Saiyid Hashim is a Senior
Lecturer at the School of School of Materials and Mineral Resources
Engineering, Engineering Campus, Universiti Sains Malaysia, 14300
Nibong Tebal, P. Pinang, Malaysia (E-mail:
[email protected]).
Silica, alumina, and iron oxides are found in agricultural
residues. To directly replace cement, agro-wastes require thermal
treatment and are milled to small particle size to improve their
pozzolanic reactivity. Burning such wastes produces crystalline
phases or crystallization of amorphous material [3]. When an
agro-residue is utilized in concrete, two important factors should
be considered; namely ash content and chemical constituents [4].The
silica content of the ash is another important factor because, when
ash from certain agricultural byproducts (e.g., rice husk and
bagasse) is added to cement, the silica reacts with Ca(OH)2 to form
additional C-S-H in the hydrated cement matrix, which increases the
density of the matrix, and refines the pore structure [5, 6].
Malaysia is one of the largest producer of palm oil with around
41% of the total world supply in years 20092010[7]. After the
extraction of oil from fresh fruit bunches, considerable amount of
solid waste by-products in the form of nutshells, fibers, and empty
bunches, (i.e., more than 70 % of fresh palm oil fruit) are
discharged from the mill [8].This waste is reused by the same
industry as fuel in boilers for the production of steam to generate
electricity and run internal operations, leaving behind 5% ash [9,
10] known as palm oil fuel ash (POFA). However, because of the
deficiency in nutrients required in fertilizers, POFA is thrown
into wastelands surrounding the palm oil mill, causing
environmental problems and health hazards [8, 11]. With the aim of
finding a solution to this issue, various studies have been carried
out to determine the feasibility of using POFA in concrete and
mortar. These studies have revealed that POFA can be used as a
supplementary cementitious material when properly processed [12].
Majority of these studies were conducted on ashes obtained directly
from palm oil mills to establish the pozzolanic activity and
suitability of POFA as binders after grinding [13-15]. The POFA
contains high amounts of unburned matter, silicon, and aluminum. In
general, unground POFA is light gray because of the unburned carbon
content left at a relatively low burning temperature. The colour
becomes dark gray in the case of ground POFA [16]. The unburned
carbon is the most significant factor to consider. The unburned
carbon particles result in an increase in water requirement and
dosage of super plasticizer (SP) because SP is absorbed by carbon
particles [13, 17].
-
International Journal of Civil & Environmental Engineering
IJCEE-IJENS Vol: 11 No: 05 101
115905-7676 IJCEE-IJENS October 2011 IJENS I J E N S
Studies have been conducted on the effect of POFA on the
engineering properties of mortar and concrete, including their
mechanical and durability related properties. However, the
influence of adding different amounts of POFA without unburned
carbon on pozzolanic reaction has not been well established.
Recognizing the potential technical benefit of treated POFA on
pozzolanic activity and microstructure of cement paste, which could
lead to the greater utilization of POFA in concrete and
subsequently could be useful in protecting the environment by
minimizing the volume of waste disposed on the wasteland, has
initiated the current research work. Consequently, the aim of the
present research work is to investigate the pozzolanic reactivity
of treated POFA mortars and to study the microstructure of
POFA-cement pastes through the analysis of hydration products by
thermogravimetric analysis (TGA), x-ray diffraction (XRD), and
scanning electron microscopy (SEM).
2. MATERIALS AND METHODS
2.1 Materials
Ordinary Portland cement (OPC) supplied by Cement Industries of
Malaysia, Berhad was used as the main binder material. This cement
has a specific gravity of 3.15 and a Blaine surface area of 340
m2/kg. Table 1 shows the chemical compositions of the OPC as well
as the treated POFA.
Table1. Chemical Constituents of OPC and treated Palm Oil Fuel
Ash.
Chemical constituents (%) OPC Treated POFA Silicon dioxide
(SiO2) 20.9 66.91 Aluminum oxide (Al2O3) 5.27 6.44 Ferric Oxide
(Fe2O3) 3.1 5.72 Calcium oxide (CaO) 62.8 5.56 Magnesium Oxide
(MgO) 1.52 3.13 Sodium oxide (Na2O) 0.16 0.19 Potassium oxide (K2O)
0.63 5.20 Sulfur oxide (SO3) 2.73 0.33 Phosphorus oxide (P2O2) 0.13
3.72 LOI 0.87 2.3
POFA was collected from a nearby palm-oil mill, United Oil Palm
Industries Sdn. Bhd. located in Nibong Tebal, Penang, Malaysia. The
removal of excess carbon and other unburned organic materials
contained in POFA is important to avoid their potential negative
effect on hydration. Thus, the POFA was dried in an oven at 100C
for 24 h and then sieved using a set of sieves (3 mm, 600 m, and
300 m sieves) to remove the particles coarser than 300 m. The
average particle size of POFA before milling was around 74.29 m
with the specific surface area around 540 cm2/g. The untreated POFA
was then ground in
a ball mill to reduce the particle size to improve reactivity.
The milling time was approximately 6 hours at 45 rpm. To prevent
glassy phase crystallization and particle agglomeration both of
which could affect the pozzolanic properties, untreated POFA was
heated at low temperature of 450C for 1.5 hours in an electric
furnace. After the heat treatment, the colour of treated POFA
turned from light brown to grayish red after the unburned residue
was removed. Under the said method of treatment and temperature
conditions, the agglomeration and crystallization of glassy phase
of POFA particles did not occur during the heating process (Fig.
1).
Fig. 1. XRD patterns of POFA before and after treatment
(Q-Quartz; C-Cristobalite; S-Amorphous silica; K-potassium aluminum
phosphate K3Al2(PO4)3). The specific surface area of the treated
POFA was around 6200 cm2/g. The average particle sizes of untreated
and treated POFA were approximately 2.87 and 2.99 m, respectively.
The treated POFA particles were irregular in shape and having
porous texture. In addition, there was no agglomeration of POFA
particles after the heat treatment as can be seen in Figs. 2 and 3.
The main component of the treated POFA is SiO2, and the total
amount of SiO2, Al2O3, and Fe2O3 is 79.07 (Table 1), which
indicates that the chemical compositions of the treated POFA was
well within the specifications set by ASTM C618-05[18].
Fig. 2. Cumulative particle size distribution curves of POFA
before and after treatment.
0.1 1 10 100
Cum
ula
tive
pass
ing
(%)
Particle size (m)
Ground POFA after treatment
Ground POFA before treatment
-
International Journal of Civil & Environmental Engineering
IJCEE-IJENS Vol: 11 No: 05 102
115905-7676 IJCEE-IJENS October 2011 IJENS I J E N S
Fig. 3. SEM photographs of treated POFA.
2.2 Pozzolanic activity method
The pozzolanic activity of the POFA has been determined based on
compressive strength according to ASTM C311. Mortar containing 20 %
POFA partially replacing the OPC was tested. The control mixture
was prepared with 1500 g of OPC, 4125 g of graded sand and 726 g of
water. The test mixture was prepared with 1200 g of OPC, 300 g of
POFA, 4125 g of graded sand and the required quantity of water to
obtain a flow of 110% of the control mixture. Fifty-millimeter
cubes were cast for the present study. After moulding, the
specimens and moulds were placed in the moist room at maintained 23
2C for 24 hours. Then the cube samples were removed from the moist
room, and demoulded from their respective moulds. The cubes were
then placed and stored in saturated lime water. The compressive
strength was determined from the average of three specimens at the
ages of 3, 7, 14, 28, and 90 days. The cubes were tested using a
universal testing machine (Model UH-F1000kNI) test system with a
1000 kN capacity loading frame. The compressive strength was
measured using a constant loading rate of 21 MPa/min.
2.3 Microstructural characteristics
A total of seven POFA-cement pastes and a control paste were
prepared to study the hydration products (Table 2). The
water/binder ratio was fixed at 0.29.The cement paste and
POFA-cement pastes were tested and analyzed using TGA (LINSEIS
THERMOWAAGE L81, XRD (RIGAKU D/Max 2000), and SEM (KEYENCE,
VE-9800). The tests were conducted after 90days of curing to
estimate the hydration products. Analyses using TGA, XRD and SEM
were performed to assess the reaction with calcium hydroxide. XRD
analysis was carried out in terms of qualitative values. The
analysis was based on the intensity of the peak corresponding to
Ca(OH)2 in the samples.TGA is defined as the technique whereby the
mass of a substance in a heated environment is recorded at a
controlled rate as a function of time or temperature[19]. In
addition, TGA is more suitable for studying the hydration or
pozzolanic
reaction that takes place at later stages [20]. Thermo-grams
after 90-days of curing were obtained at a temperature of 251000C
at a rate of 6C/min. Ca(OH)2 can be measured by the amount of water
loss, which is very close to its water content and hence
proportional to the amount of Ca(OH)2 [21, 22]. The hydration
products were also examined by SEM to understand the paste
morphology.
Table 2. Paste mix proportions.
POFA/C W/B C/C Symbols 0 0.29 1 Mc
0.1 0.29 1 M1 0.2 0.29 1 M2 0.3 0.29 1 M3 0.4 0.29 1 M4 0.5 0.29
1 M5 0.6 0.29 1 M6 0.8 0.29 1 M7
The pastes were cast in 403030 mm cube moulds, compacted using a
tamping rod, and sealed in plastic sheets to prevent water
evaporation. The samples were cured in water at 23 1C for 90 days.
The moulds were then removed and the samples were immediately
immersed in acetone for 24 hours to stop the hydration process. The
testing was performed on powder samples (95% passing 45 m sieve)
obtained by grinding the hardened pastes. The grinding process was
carried out by crushing the hardened pastes into smaller pieces,
followed by milling in a grinding bowl. A small amount of the
sample was used to determine the Ca(OH)2 content by TGA and XRD
analyses. The powder sample was divided into two parts of 10 g
each. An XRD test was conducted on one of the samples, whereas a
TGA test was conducted on the other. Before grinding, small pieces
of hardened paste with an average diameter of approximately 1 cm
were taken to determine paste morphology using SEM.
3. RESULTS AND DISCUSSION 3.1 Strength activity index
Strength activity indices for all mortars are shown in Fig. 4.
The strength activity index is the ratio of the strength of the
POFA-cement mortar to the strength of the reference (cement mortar)
at each specific curing time. The rate of strength development of
cement mortar relies principally on its hydration rate. In
contrast, the said rate relies on the cement hydration and
rehydration caused by the pozzolanic reactivity of POFA in
POFA-cement mortar. Figure 4 shows that the strength activity
indices at 3, 7, 14, 28, and 90 days were higher than the minimum
requirement of 75% as specified in ASTM C 618-05.The POFA cement
presents a strength activity index of 97.3%, 97.6%, 99.3%, 100.7%
and 101.6% of the reference cement strength at 3, 7, 14, 28, and 90
days, respectively. At the early ages of 3
-
International Journal of Civil & Environmental Engineering
IJCEE
and 7 days, replacing OPC with 20% POFA was found reduce the
compressive strength in comparison to the reference mortar. This
could be attributed to dilution effect and delayed onset of
pozzolanic reaction of POFACa(OH)2.
Fig. 4. Strength activity index of POFA mortar at 3, 7, 14, 28,
and 90 days.
Nonetheless, the high fineness of the POFA could have
contributed as fillers, filling the voids between the pates and the
sand and contributing to greater than 97 % strength activity index
[15]. At 14 days, the strength activity index increases to more
than 99 %, which could have contributed by the pozzolanic reaction
of POFA with Ca(OH)producing C-S-H and increasing the strength.
days, the compressive strength of the POFAwas higher than that of
the reference cementcould be attributed to pozzolanic reaction of
POFA. results generally agree with the experimental results
obtained by Sata et al. (2004), who found thatdays of curing time,
the concretes with 20% of lower compressive strength than concretes
POFA. The same results were observed after 7 concretes with 20%
POFA gave higher compressive strength than concretes with 10% and
30% POFA.
At longer curing period of 90 days, the POFAmortar recorded a
strength activity index of greater than 101 %. Hence, at this later
age, the amorphous aluminous and siliceous minerals could have
still actively reacted with Ca(OH)2, producing C-S-H and hydrated
calcium aluminates, improving interfacial bonding between the sand
and pastes. These characteristics have been shown to improve,
thereby the increasing the compressive strength and density of
mortar [1,23,24].
3.2 POFA-cement hydration
Since the POFA contains high amount of amorphous SiOit is
expected to have pozzolanic properties and will chemically react
with Ca(OH)2 produced from the hydration reaction of cement within
the POFApaste. In general, TGA has been widely accepted as a
9596979899
100101102103
3 7 14 28
Stre
ngt
h ac
tivity
in
dex (%
)
Age (days)
Reference Treated POFA
International Journal of Civil & Environmental Engineering
IJCEE-IJENS Vol: 11 No: 0
115905-7676 IJCEE-IJENS October 2011 IJENS
, replacing OPC with 20% POFA was found to in comparison to
the
reference mortar. This could be attributed to dilution effect
and delayed onset of pozzolanic reaction of POFA with
activity index of POFA mortar at 3, 7, 14,
Nonetheless, the high fineness of the POFA could have filling
the voids between the pates
contributing to greater than 97 % strength strength activity
index
increases to more than 99 %, which could have contributed by the
pozzolanic reaction of POFA with Ca(OH)2,
H and increasing the strength. After 28 POFA-cement mortar
the reference cement, which again could be attributed to
pozzolanic reaction of POFA. These
experimental results found that, before 7 20% of POFA gave
essive strength than concretes with 10% of after 7 days. The
concretes with 20% POFA gave higher compressive 30% POFA.
longer curing period of 90 days, the POFA-cement mortar recorded
a strength activity index of greater than 101 %. Hence, at this
later age, the amorphous aluminous and siliceous minerals could
have still actively reacted with
ydrated calcium improving interfacial bonding between the
These characteristics have been shown to compressive
strength
high amount of amorphous SiO2, it is expected to have pozzolanic
properties and will
produced from the hydration reaction of cement within the
POFA-cement
widely accepted as a
suitable technique to assess Ca(OH)hydration products, including
C-Spaste. Figure 5 shows the TGA curves which indicate the changes
in mass of pastes due to heating from room temperature to about
1000C.
Fig. 5. TGA curves of the hydrated powder pastes ratio of 0.29:
(a) POFA/C= 0; (b) POFA/C= 0.8.Three considerable endothermic
shifts slope of each curve; at approximately and 6801000C. These
changes take place mass loss. The first abrupt shift is broad and
attributed to the removal of water molecules and decomposition of
C-S-H, ettringite,second weight loss at approximately attributed to
the Ca(OH)2 corresponding endothermic shift is reaction, which
reveals the presence of Ca(OH)
Ca(OH)2 CaO + 2OH
The third shift at 680 C may be caused bycarbonate
decomposition. The carbonation of the paste may occur during the
preparation or grinding of TGA [26]. The endoshift at 680C is
following reaction:
CaCO3 CaO + CO
As shown in Table 3 and Figure was determined from the changes
in by the decomposition of Ca(OH)between 415515C in TGA
90
No: 05 103
I J E N S
Ca(OH)2 content and other S-H in hydrated cement
shows the TGA curves which indicate the changes in mass of
pastes due to heating from room
hydrated powder pastes at w/b ratio of 0.29: (a) POFA/C= 0; (b)
POFA/C= 0.8.
shifts take place in the approximately 100400, 415515,
take place as a result of shift is broad and can be
removal of water molecules and , and C2ASH8 [25]. The
approximately 415C can be dehydroxilation. The
corresponding endothermic shift is caused by the following
reaction, which reveals the presence of Ca(OH)2:
CaO + 2OH (1)
may be caused by calcium The carbonation of the paste may
or grinding of the paste before The endoshift at 680C is caused
by the
CaO + CO2 (2) 6, the Ca(OH)2 content
from the changes in mass of water caused )2 at temperature
range
curves. TGA allows
-
International Journal of Civil & Environmental Engineering
IJCEE-IJENS Vol: 11 No: 05 104
115905-7676 IJCEE-IJENS October 2011 IJENS I J E N S
estimation of the content of Ca(OH)2 present in the hardened
pastes. The TGA results show a clear relationship between the
reactive SiO2 content of POFA and the amount of Ca(OH)2 consumed by
the pozzalanic reaction at 90 days. The DTG curve peak for Ca(OH)2
of the pastes containing POFA decreases with increasing POFA
content. As shown in Figure 6, Mc (POFA/C= 0) contained the highest
value of Ca(OH)2 loss which is approximately 6.39% in comparison to
all pastes containing POFA. The increase in the Ca(OH)2 of the OPC
paste was caused by the hydration of the cement. Addition of POFA
by 0.1in term of POFA/cement ratio leads to a significant loss of
Ca(OH)2 [i.e., approximately 4%]. The mass loss due to
decomposition of Ca(OH)2 reduces only slightly at POFA/cement
ratios between 0.1 to 0.3. Hence, Ca(OH)2 consumption due to
pozzalanic reaction is nearly at the same level when POFA/cement
ratio is between 0.10.3.
Table 3. Mass loss of calcium hydroxide according to TGA.
Mass loss of Ca(OH)2 by TGA, (% mass/mass) Symbols 6.39 Mc
4.096 M1 4.003 M2
3.8006 M3 3.148 M4 2.196 M5 2.056 M6 1.96 M7
Fig.6. TGA analysis on hydrated POFA/cement paste at 90
days.
POFA content of up to 0.8 (POFA/cement ratio) leads to loss of
Ca(OH)2 of approximately 2%. Hence, the higher the content of POFA,
the higher the consumption of Ca(OH)2 as a result of pozzolanic
reaction, which concurs with the observation from TGA analysis in
Fig. 6. In addition, the low Ca(OH)2 concentrations with increasing
POFA contents may have been also caused by the dilution effect at
higher POFA/cement ratio. With the inclusion of POFA at POFA/cement
ratio of 0.8, the amount of CaO in
the Portland cement is reduced, resulting in low C-S-H and
Ca(OH)2. The reduction of Ca(OH)2 content at 90 days in the TGA
results explains the role of POFA in reducing Ca(OH)2 via the
pozzolanic reaction. The observation is generally in agreement with
previous findings of Chandara [7].
The XRD patterns of hydrated powder pastes with and without POFA
at 90 days are shown in Figure 7. The XRD analysis was performed on
prepared powder pastes. The XRD pattern at Theta angle from 1090
was studied to identify the peak patterns of Ca(OH)2 and C-S-H. The
Ca(OH)2 and C-S-H peaks after 90 days of curing were identified and
presented. The concentrations of hydration products were determined
through the length intensity of Ca(OH)2 and C-S-H collected by
X-ray scans recorded as intensity in unit counts.
Ca(OH)2 could be detected at several locations along the 2
Theta; specifically, at peaks of 2 Theta of 18.6, 34.4, and 47.5. A
comparison of patterns clearly show that the intensity of CH peaks
representing Ca(OH)2 was significantly reduced with the increase in
the POFA/cement ratios, as demonstrated by the TGA results. Thus,
the XRD patterns support the TGA results and provide additional
information about the mineral phases existing in the hydrated
cement pastes.
Fig.7. XRD pattern of hydrated powder pastes containing POFA at
age of 90 days.
The reduction of Ca(OH)2 in the pastes indicates its consumption
in the pozzolanic activity. More Ca(OH)2 is consumed during
hydration as the POFA contents increase (i.e., the higher addition
of POFA), the higher the content of amorphous SiO2 available to
react with Ca(OH)2. This reaction is more effective with the
largest amount of Ca(OH)2, which comes from the hydration of OPC to
produce C-S-H. The POFA reaction can be expressed as
01234567
0 0.2 0.4 0.6 0.8 1
Mas
s lo
ss o
f Ca(O
H)2
(% )
POFA/C
-
International Journal of Civil & Environmental Engineering
IJCEE-IJENS Vol: 11 No: 05 105
115905-7676 IJCEE-IJENS October 2011 IJENS I J E N S
Ca(OH)2 (from the hydration of OPC) + SiO2 (POFA) C-S-H (calcium
silicate hydrate) (3)
The incorporation of POFA at 0.1 to 0.3 (POFA/cement ratio)
resulted in a remarkable increase in C-S-H, detected along the 2
Theta axis between 13.755.5C of 2 Theta. This is confirmed by the
XRD pattern and SEM images. However, the high intensity and broad
peaks of C-S-H at these ratios could be attributed to pozzolanic
reaction between Ca(OH)2 and amorphous SiO2, indicating that the
reaction at these ratios was extremely active due to the presence
of a large amount of Ca(OH)2. This active reaction matches with the
result of mass loss of Ca(OH)2 by TGA [the Ca(OH)2 losses for 0.1,
0.2, and 0.3 POFA/cement ratios were approximately 4.09, 4.0, and
3.8, respectively]. In addition, the fineness of the POFA could
have affected the pozzolanic reaction rate [25] (i.e., the fineness
of POFA affected the increase in production rate of C-S-H). The
C-S-H of pastes with POFA/cement ratio of 0.10.3 increased
significantly than OPC paste which may be attributed to the
particle sizes being smaller than OPC (the average particle size of
POFA was about 2.99 m). Moreover, the fine POFA has a larger
surface area to provide the silica for pozzolanic reaction and
probably also could have some accelerating effect on OPC hydration.
From Figure 8, the intensity of C-S-H in the POFA/cement ratio up
to 0.8 is lower than the others because of the dilution effect. The
degree and the rate of hydration provided by the OPC is reduced
when OPC is fixed at constant weight and POFA is increased in
hardened pastes because of the increase in the amount of POFA in
the total mass of paste. This, in turn reduces the amount of
Ca(OH)2 gradually, resulting in less amount of C-S-H. Besides, from
the C-S-H and Ca(OH)2 formed during the hydration process, the XRD
profiles indicate the presence of a small peak representing calcium
aluminates hydrates (C4AHx). The POFA contains Al2O3 in an
amorphous form (more than 5% of Al2O3 in amorphous form) [27],
which plays a very important role in pozzolanic reaction. Thus, the
pozzolanic reaction of POFA with Ca(OH)2 released from hydration of
cement leads to the production of a greater amount of calcium
aluminate hydrate (C-A-H).
The above results were also confirmed by the SEM images. The
typical microstructures of fractured surface of hardened pastes at
90 days with or without POFA are shown in Fig.9. Pastes with 0,
0.3, and 0.8 of POFA/cement ratios were chosen for SEM because they
were clearer in terms of change in the amount of hydration
products. OPC paste had been hydrated in a wide zone, and cement
particles had been coated by C-S-H. The remaining calcium hydroxide
appears brightest followed by C-S-H and large dark pore sand cracks
revealing particle boundaries (Fig. 9a).
Fig. 8. XRD patterns of calcium silicate hydrate (C.H.S) formed
by adding different POFA/C at age of 90 days.
-
International Journal of Civil & Environmental Engineering
IJCEE-IJENS Vol: 11 No: 05 106
115905-7676 IJCEE-IJENS October 2011 IJENS I J E N S
Fig. 9. SEM photos of hardened pastes at 90 days curing time:
(a) POFA/C= 0; (b) POFA/C= 0.3; (c) POFA/C= 0.8.
The absence of the pozzolanic material (i.e., POFA) causes the
lime to remain as it is since there are no pozzolanic activities
that can improve the structure through formation of additional
C-S-H gel [28]. For the microstructure pattern of POFA paste when
POFA/C is 0.3, the structure contained small pores, and the
fractured surface was almost completely covered by C-S-H. Most
large spaces had been filled with C-S-H gel, forming a dense
structure. The hydration reaction was very active, and a huge
amount of gel was formed (Fig. 9b). Therefore, the microstructure
of the paste became denser. Figure 9c shows the SEM image of a
sample with 0.8 POFA/cement ratio. Residual POFA grains appear
brightest with the products of reaction. Unreacted particles of
POFA could be observed. These particles exist because they contain
POFA on some particles in the form of crystalline phase. The amount
of crystalline particles increases when POFA is increased. In
addition, reducing Ca(OH)2 and increasing POFA leads to dilution
effect. Most voids had been filled by small unreacted POFA
particles made it serving as inert filler.
4. CONCLUSIONS Based on the experimental studies presented in
this paper, the following conclusions can be drawn:
1. Ground POFA obtained by heating at 450C for 1.5 hours
resulted in loss on ignition significantly lower than that of the
untreated POFA (LOI= 2.3). Hence, the treated POFA was free from
carbon and other organic matter. In addition, the treatment process
yielded POFA with high specific surface area, preserving the
amorphous characteristic related to pozzolanic activity of POFA and
free from particle agglomeration.
2. Strength activity index of POFA/cement mortar fulfilled the
requirements of pozzolanic materials as per ASTM C 618-05.
Compressive strength test confirmed that after 28-days of curing
time, the strength of treated POFA was
greater than that of the reference cement. This increase was
larger at 90 days. Hence, strength increased as curing time
progressed because of the consumption of Ca(OH)2 by the POFA via
the pozzolanic reaction.
3. At 90 days curing time, TGA data and interpretations of XRD
diagrams of the POFA/cement pastes confirmed that Ca(OH)2 gradually
decreased with an increase of POFA content. C-S-H compound was
identified as the main product of the reaction between POFA and
Ca(OH)2. This product was higher with the addition of POFA up to
0.3 from the mass of cement. The results of SEM analysis of the
POFA/cement pastes confirmed that there was an increased pozzolanic
reaction when POFA/C ratio was up to 0.3.
ACKNOWLEDGEMENT The authors gratefully acknowledge the
Universiti Sains Malaysia for providing the financial support
through the Research University and Short-Term Grant Schemes for
undertaking the research work. The support provided by the
technical staffs from the School of Civil Engineering as well as
the School of Materials and Mineral Resources Engineering,
Universiti Sains Malaysia is greatly appreciated. Special thanks
are due to United Palm Oil Industries for providing the palm oil
fuel ash.
REFERENCES
[1] A.M. Neville, Properties of concrete, England, Prentice Hall
2002.
[2] B.K. Ngun, H. Mohamad, E. Sakai, Z.A. Ahmad, Effect of rice
husk ash and silica fume in ternary system on the properties of
blended cement paste and concrete, Journal of Ceramic Processing
Research 11(2010) 311-315.
[3] S.A. Rydholm, Pulping Processes, Interscience Publishers,
New York(1965) 1049-1053.
[4] S. Karthick, T. Ravi Kumar, Utilization of Agroresidual
Waste in Effective Blending in Portland Cement, ISRN Civil
Engineering 2011(2011).
[5] K. Ganesan, K. Rajagopal, K. Thangavel, Evaluation of
bagasse ash as supplementary cementitious material, Cement and
Concrete Composites 29(2007) 515-524.
[6] M. Zhang, R. Lastra, V. Malhotra, Rice-husk ash paste and
concrete: some aspects of hydration and the microstructure of the
interfacial zone between the aggregate and paste, Cement and
Concrete Research 26(1996) 963-977.
[7] C. Chandara, Study of Pozzolanic Reaction and Fluidity of
Blended Cement Containing Treated Palm Oil Feul Ash as Mineral
Admixture, Universiti Sains Malaysia, 2011.
[8] D. Tonnayopas, F. Nilrat, K. Putto, J. Tantiwitayawanich,
Effect of oil palm fiber fuel ash on compressive strength of
hardening concrete, , Proceedings of the 4th Thailand Materials
Science and Technology Conference, Pathumthani, Thailand, March
31-April 1, 2006, 1-3., 2006.
[9] V. Sata, C. Jaturapitakkul, C. Rattanashotinunt, Compressive
Strength and Heat Evolution of Concretes Containing Palm Oil Fuel
Ash, Journal of Materials in Civil Engineering 22(2010) 1033.
-
International Journal of Civil & Environmental Engineering
IJCEE-IJENS Vol: 11 No: 05 107
115905-7676 IJCEE-IJENS October 2011 IJENS I J E N S
[10] M. Safiuddin, M.A. Salam, M.Z. Jumaat, Utilization of palm
oil fuel ash in concrete: a review, Journal of Civil Engineering
and Management 17(2011) 234-247.
[11] S.R. Sumadi, M.W. Hussin, Palm oil fuel Ash (POFA) as a
future partial cement replacement material in housing construction,
Journal of ferrocement 25(1995) 25-34.
[12] V. Sata, C. Jaturapitakkul, K. Kiattikomol, Utilization of
palm oil fuel ash in high-strength concrete, Journal of Materials
in Civil Engineering 16(2004) 623.
[13] V. Sata, C. Jaturapitakkul, K. Kiattikomol, Influence of
pozzolan from various by-product materials on mechanical properties
of high-strength concrete, Construction and Building Materials
21(2007) 1589-1598.
[14] W. Tangchirapat, T. Saeting, C. Jaturapitakkul, K.
Kiattikomol, A. Siripanichgorn, Use of waste ash from palm oil
industry in concrete, Waste Management 27(2007) 81-88.
[15] W. Tangchirapat, C. Jaturapitakkul, P. Chindaprasirt, Use
of palm oil fuel ash as a supplementary cementitious material for
producing high-strength concrete, Construction and Building
Materials 23(2009) 2641-2646.
[16] K. Abdullah, M. Hussin, F. Zakaria, R. Muhamad, Z. Abdul
Hamid, POFA: A potential partial cement replacement material in
aerated concrete, (2006).
[17] C. Chandara, E. Sakai, K.A.M. Azizli, Z.A. Ahmad, S.F.S.
Hashim, The effect of unburned carbon in palm oil fuel ash on
fluidity of cement pastes containing superplasticizer, Construction
and Building Materials 24(2010) 1590-1593.
[18] ASTM, Standard specification for coal fly ash and raw or
calcined natural pozzolan for use in concrete (ASTM C618), West
Conshohocken, PA, USA., 2005.
[19] C.J. Keattch, D. Dollimore, An introduction to
thermogravimetry, Heyden, 1975.
[20] I. Pane, W. Hansen, Investigation of blended cement
hydration by isothermal calorimetry and thermal analysis, Cement
and Concrete Research 35(2005) 1155-1164.
[21] H. Midgley, The determination of calcium hydroxide in set
Portland cements, Cement and Concrete Research 9(1979) 77-82.
[22] A. Goyal, A.M. Anwar, Propertier of Sugar Cane Bagasse Ash
And Its Potential As Cement - Pozzolana Binder, 12th International
Colloquium on Structural and Geotechnical Engineering., 10-12 Dec.
Cairo - Egypt, 2007.
[23] M.H. Zhang, V.M. Malhotra, High-performance concrete
incorporating rice husk ash as a supplementary cementing material,
ACI materials journal 93(1996).
[24] G. Isaia, A. Gastaldini, R. Moraes, Physical and pozzolanic
action of mineral additions on the mechanical strength of
high-performance concrete, Cement and Concrete Composites 25(2003)
69-76.
[25] W. Kroehong, T. Sinsiri, C. Jaturapitakkul, P.
Chindaprasirt, Effect of palm oil fuel ash fineness on the
microstructure of blended cement paste, Construction and Building
Materials 25(2011) 4095-4104.
[26] T. Perraki, G. Kakali, E. Kontori, Characterization and
pozzolanic activity of thermally treated zeolite, Journal of
thermal analysis and calorimetry 82(2005) 109-113.
[27] C. Chandara, K.A.M. Azizli, Z.A. Ahmad, S.F.S. Hashim, E.
Sakai, Analysis of Mineralogical Component of Palm Oil Fuel Ash
with or without Unburned Carbon, Advanced Materials Research
173(2011) 7-11.
[28] M.W. Hussin, K. Muthusamy, F. Zakaria, Effect of Mixing
Constituent toward Engineering Properties of POFA Cement-Based
Aerated Concrete, Journal of Materials in Civil Engineering
22(2010) 287.