Effect of Curing Regime on Compressive Strength of Aerated Concrete Containing Palm Oil Fuel Ash as Partial Sand Replacement

Abstract

Issues on preservation of natural river sand from being used excessively in concrete industry has led to the efforts of utilizing palm oil fuel ash, a by-product from palm oil industry as partial sand replacement in production of aerated concrete. This paper reports the effect of curing regime on compressive strength development of aerated concrete containing palm oil fuel ash as partial cement replacement. Two types of mixes were used in this experimental work namely plain aerated concrete acting as control specimen and aerated concrete containing 30% palm oil fuel ash as partial sand replacement. Concrete cubes were subjected to different types of curing namely initial water curing for 7 days followed by air curing, water curing and air curing until the testing date. The compressive strength test was conducted in accordance to BS EN 12390-3 at 7, 14, 28 and 90 days. Application of water curing is the most suitable method to be applied to ensure better strength development in aerated concrete containing POFA as partial sand replacement. Continuous presence of moisture promotes better hydration and pozzolanic reaction leading to formation of extra C-S-H gel and that subsequently make the concrete denser and compressive strength higher.

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Mat Yahaya et al. Concrete Research Letters Vol. 6(2) 2015
54
www.crl.issres.net
Vol. 6 (2) – June 2015
Effect of Curing Regime on Compressive Strength
of Aerated Concrete Containing Palm Oil Fuel Ash
as Partial Sand Replacement
Fadzil Mat Yahaya1, Khairunisa Muthusamy2 and Mohd Warid Hussin3
1,2 Faculty of Civil Engineering and Earth Resources, Universiti Malaysia Pahang,
MALAYSIA
3 Faculty of Civil Engineering, Universiti Teknologi Malaysia, MALAYSIA
Received: 15/03/2015 – Revised 30/04/2015 – Accepted 30/05/2015
Abstract
Issues on preservation of natural river sand from being used excessively in concrete
industry has led to the efforts of utilizing palm oil fuel ash, a by-product from palm oil
industry as partial sand replacement in production of aerated concrete. This paper reports
the effect of curing regime on compressive strength development of aerated concrete
containing palm oil fuel ash as partial cement replacement. Two types of mixes were used
in this experimental work namely plain aerated concrete acting as control specimen and
aerated concrete containing 30% palm oil fuel ash as partial sand replacement. Concrete
cubes were subjected to different types of curing namely initial water curing for 7 days
followed by air curing, water curing and air curing until the testing date. The compressive
strength test was conducted in accordance to BS EN 12390-3 at 7, 14, 28 and 90 days.
Application of water curing is the most suitable method to be applied to ensure better
strength development in aerated concrete containing POFA as partial sand replacement.
Continuous presence of moisture promotes better hydration and pozzolanic reaction leading
to formation of extra C-S-H gel and that subsequently make the concrete denser and
compressive strength higher.
Keywords: aerated concrete; palm oil fuel ash; partial sand replacement; curing regime;
compressive strength.
1. Introduction
The present research stems out from two factors presented by two different industries in
Malaysia that is solid waste disposal by palm oil industry and the increasing demand for natural
sand for concrete production. The growing Malaysian palm oil industry has led to generation of the
palm oil mill by-product known as palm oil fuel ash (POFA) which dumped in the landfill. The
palm oil mill has been facing difficulties in disposing this abundantly generated waste [1]. In future,
more dumping site needs to be allocated for this waste disposal and large sum of money is to be
spent for the management of this waste unless this material is processed for other applications. So
far, researches conducted since the end of 20th century have proposed this solid waste after

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processed to be used as partial cement replacement in various types of concrete [2-6]. Discovering
other potential of this by-product would widen the application of this material and would reduce
amount disposed as environmental polluting waste.
At the same time, the developing local construction industry demands for concrete material has
become higher which indirectly increases the need for larger quantity of sand supply. Continuous
sand mining from the natural environment would pose negative impact to the environment in terms
of water pollution, ecological imbalance at river bed environment and also the possibility of this
material to deplete in future. The negative impact of excessive sand mining was elaborated by
Asyraf et al., [7]. This issue has motivated researchers [8 - 10] to investigate the potential of using
waste materials as partial sand replacement material in concrete production. Success in integrating
waste material as partial sand replacement in concrete would result in a more sustainable concrete
product and cleaner environment. In view of environmental sustainability, Mat Yahaya [11]
successfully incorporate 30% palm oil fuel ash as partial sand replacement in aerated concrete
production. The positive contribution of palm oil fuel ash which manifested through the increment
in aerated concrete strength performance has encouraged for more investigation in other aspects for
determining the suitable application of modified lightweight concrete. Thus, this paper discusses the
strength performance of this modified lightweight concrete upon exposure to different types of
curing regimes.
2. Experimental Programme
2.1. Materials
Among the mixing ingredient used in the production of aerated concrete are ordinary Portland
cement (OPC), river sand, potable water, aluminium powder, superplasticizer and palm oil fuel ash
(POFA). POFA used in this research was obtained from a palm oil mill in the state of Johor, West
Malaysia. The ashes were sieved passing 300 μm sieve to remove debris. Then it was oven dried
before ground in a Los Angeles Abrasion Machine in order to reduce the particle size. Based on the
chemical composition in Table 1, the processed ash is classified as pozzolanic material belonging to
Class F as per ASTM C618-05 [12].
TABLE1: CHEMICAL COMPOSITION OF PALM OIL FUEL ASH
Chemical Composition
POFA
Silicon dioxide (SiO2)
82.07
Aluminium oxide (AL2O3)
6.04
Ferric oxide (Fe2O3)
2.70
Calcium oxide (CaO)
5.11
Magnesium oxide(MgO)
2.28
Sodium oxide (Na2O)
1.34
Pottasium oxide (K2O)
2.90
Sulphur oxide (SO3)
2.20
Loss of ignition (LOI)
5.30
2.2. Mix Proportion and Testing
Specimens were prepared in two sets, a control specimen consisting 100% OPC known as plain
aerated concrete and another mix of OPC/POFA consisting the processed ash of 30%. The ash was
mixed as a weight-for-weight replacement of sand in a constant quantity. Specimens were produced
by adding constant quantity of sand, cement, aluminium powder and adequate water dry mix ratio.
The mix proportion used to produce aerated concrete containing palm oil fuel ash as partial sand
replacement is tabulated in Table 2.
The specimens were prepared by pouring the slurry aerated concrete mix into mould cubes (100
x 100 x 100 mm). The mixture was left to expand like a cake before trimming the excess of

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concrete. After that, the specimens were covered with wet gunny sack before demoulded after 24
hours. Then, specimens were placed in different curing environment namely water curing and initial
water curing for 7 days followed by air curing, continuous water curing and air curing until the
testing date. The compressive strength test was carried out in accordance to BS EN 12390-3 [13] at
7, 28 and 90 days.
TABLE 2: MIX PROPORTION OF AERATED CONCRETE CONTAINING PALM OIL FUEL ASH
Binder Sand Ratio
Ordinary Portland cement (%)
30 : 70
82.07
Palm oil fuel ash replacement (%)
6.04
River sand (%)
2.70
Water dry mix ratio
0.45
Aluminium powder (%)
0.2
3. Results and Discussions
The curing methods applied do influence the strength development of this lightweight
concrete as illustrated in Figs. 1 and 2. Inclusion of palm oil fuel ash as partial sand replacement
enhances the strength of aerated concrete. This probably owing to the palm oil fuel ash filling effect
which increases the concrete packing density and pozzolanic reaction that contributes towards
densification of concrete microstructure. Specimens subjected to water curing exhibit the highest
compressive strength and continuous air cured aerated concrete possess lowest strength value. On
overall, all specimens exhibit continuous strength development throughout the curing age which
indicates the increment in the amount of C-S-H gel.
It is interesting to note, aerated concrete with palm oil fuel ash as partial sand replacement
which has been placed in water curing condition for 7 days exhibit higher strength compared with
control specimen even at the early age of curing. Integration of palm oil fuel ash as mixing
ingredient in aerated concrete and at the same time maintaining the quantity of cement used has
resulted in producing concrete with added value in terms of strength. Adding palm oil fuel ash has
open the door for occurrence of reaction between silica from the ash and calcium hydroxide, a by-
product of cement hydration in the continuous presence of moisture leading to formation of
secondary C-S-H gel. The occurrence of hydration and pozzolanic reaction in aerated concrete
containing POFA causes the total amount of C-S-H gel to become higher and thus the concrete
strength to be better than plain specimen. Furthermore, the fine ash also functions as filler by filling
in the existing voids which makes the concrete internal structure more packed and that leads to
strength enhancement. Previous researcher, Isaia et al. [14] has highlighted that filler effect that
takes place as the proper arrangement of small particles fill the voids and contribute to the
increment of compressive strength without any chemical reaction. Both the filling effect and
pozzolanic reaction initiated by palm oil fuel ash has contributed to positive strength achievement
of aerated concrete.
Looking at the effect of curing regime on the concrete strength, it is evident that the strength
development of concrete becomes varied when placed in different curing regime depending on the
duration of water supplied to the specimens. Continuous supply of moisture allows undisturbed
pozzolanic reaction to take place thus generating larger amount of C-S-H gel filling in the concrete
pores. This helps the water cured concrete possess the most dense internal structure and thus being
able to exhibit the highest strength compared to other specimens. Aerated concrete subjected to
initial water curing for 7 days and then air curing for the rest of curing age, has provided conducive
environment for formation of C-S-H gel during early stage whereby the specimens were immersed
in water. After 7 days, when left in the open air, the reactions in the concrete were disrupted due to
absence of water causing it to exhibit lower strength value compared to water cured specimen. The
non-availability of water for air cured specimen retards the hydration and pozzolanic reaction

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leading to the least amount of total C-S-H gel and this caused the concrete to possess the lowest
strength value.
Realizing that calcium silicate hydrate is a major strength-providing reaction product of
cement hydration, which also acts as a porosity reducer resulting in a dense microstructure in
concrete [15], it is justified that continuous water curing which able to produce largest amount of C-
S-H gel is the most suitable curing method. Similarly, previous researchers [16, 17] has highlighted
the suitability of continuous water curing for better strength performance of concrete containing
palm oil fuel ash. On overall, all the three curing regimes applied in this experimental work can be
applied to produce aerated concrete specimens containing palm oil fuel ash as partial sand
replacement having adequate strength enabling it to be used for non-structural purpose.
Figure 1. Effect of curing regime on compressive strength of plain aerated concrete without palm oil
fuel ash as partial sand replacement up to 90 days.
Figure 2. Effect of curing regime on compressive strength of aerated concrete containing palm oil fuel
ash as partial sand replacement up to 90 days.

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4. Conclusions
On overall, curing methods influence the strength performance of aerated concrete containing palm
oil fuel ash. Continuous presence of moisture through water curing enables aerated concrete with POFA
to exhibit higher strength through the generation of larger amount of C-S-H gel from hydration and
pozzolanic reactions. Being added as partial sand replacement material, palm oil fuel ash contributes
towards strength enhancement of lightweight concrete, offers solution to palm oil mills to manage their
waste and reduce the dependency of concrete industry on natural sand supply. Success in identifying
alternative material derived from locally generated waste to be used as mixing ingredient is
expected to encourage production of aerated concrete by local manufacturer which would be more
economic.
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