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Use of palm oil fuel ash (POFA)-stabilized Sarawak peat composite for road subbase Ali A. Mahmood a,⇑, Mohammed Khazal Hussain b, Syazie Nordzaima Ali Mohamad c a
Independent Researcher, Brossard, Quebec J4W 2E6, Canada Technical Engineering College, Middle Technical University, Al-Za’franiya, Baghdad, Iraq c Dept. of Civil Engineering, University College of Technology Sarawak, 868 Persiaran Brooke, 96000 Sibu, Sarawak, Malaysia b
a r t i c l e
i n f o
Article history: Received 1 July 2019 Received in revised form 25 September 2019 Accepted 29 September 2019 Available online xxxx Keywords: Peat CBR Palm oil fuel ash Standard Proctor test Subbase
a b s t r a c t Peat land covers a large portion of the total land area in Malaysia and several other countries throughout the world. The Malaysian state of Sarawak has the most peat land area nationally. Peat is considered a problematic type of soil due to its high compressibility, high moisture content, high organic matter and low shear strength. As a form of stabilization, it is suggested to combine palm oil fuel ash (POFA) with peat. This study investigated the engineering properties of these composite matrices in terms of the California Bearing Ratio (CBR) and Standard Proctor test values. Results showed that the dry density of the peat samples increased with the increase in POFA content. The POFA-peat composites showed an increase of 4 times the untreated peat value. Also, CBR values for these composites increased from 31 to 42 fold, in comparison with untreated peat. The peat-POFA CBR values are rated as good materials for the purpose of road base or subbase construction. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Materials Engineering & Science.
1. Introduction 1.1. Peat Peat is a soft soil characterized by its high organic content, high compressibility, high moisture content and low shear strength [1]. Organic and peaty soils generally have high liquid limit, low density, relatively low plasticity, and different particle size distributions compared to inorganic soils. Peat subgrades are usually avoided when construction work is considered [2]. Peat can be found in many countries. In Malaysia peat land can be found in several states including Sarawak. Most of Sarawak’s peat lands are found in the central region of the State, specifically in Sibu, which covers 70% of the division [3]. ASTM [4] states that peat is classified according to fibre content, ash content and acidity. Under fibre content classification, peat separated into three groups. The first group is fibric. This is the least decomposed and contains fibre content greater than 67%. The Second group is hemic (semi-fibrous) and is in intermediate decomposition. The third group is sapric (amorphous). It is the ⇑ Corresponding author. E-mail address:
[email protected] (A.A. Mahmood).
most decomposed and its fibre content is less than 33%. Fiber, temperature and humidity of peat differ and vary spatially [5]. The Von Post is another peat classification system that is widely used [6]. It consists of 10 different classification levels for peat (H1–H10), depending on its humidification state [6]. Humidification influences the colour, texture and consistency of peat. The index property tests typically performed for peat include water content, loss on ignition, organic content, fibre content, grain size distribution, density, specific gravity and Atterberg Limits [2]. 1.2. Palm oil fuel ash (POFA) Palm oil fuel ash (POFA) is a secondary product produced by burning the palm oil tree husk and palm oil fruit shell as fuel in the boiler inside the palm oil factory [7]. Generally, POFA can vary in appearance from whitish grey to a darker colour depending on its carbon content. The operating process in the palm oil factory largely affects the physical properties of POFA [7]. POFA is one of the wastes largely produced in Malaysia. In the year 2009–2010, Malaysia had produced about 41% of the total world supply of palm oil [8]. These huge amounts cause landfill disposal issues that are plagued with environmental and financial problems. Therefore, and in order to offset this, using POFA in
https://doi.org/10.1016/j.matpr.2019.09.178 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Materials Engineering & Science.
Please cite this article as: A. A. Mahmood, M. K. Hussain and S. N. A. Mohamad, Use of palm oil fuel ash (POFA)-stabilized Sarawak peat composite for road subbase, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.178
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sustainable applications has recently increased in the engineering sector [9–13]. This has the potential to reduce groundwater contamination and public health issues that are characteristic of POFA land filling [14]. There are several advantages of using POFA to stabilize peat. The main advantage is that POFA fills the peat inter-particle voids and undergoes pozzolanic reactions with the organic matter, thus increasing shear strength and contact friction. Furthermore there is an economic advantage of using a byproduct with a low procurement cost as a soil stabilizing agent [15]. In the town of Sibu located in the Malaysian state of Sarawak, severe ground settlement due to peat is a common occurrence. This has caused water stagnation problems in several areas making them prone to flooding [16]. In Malaysia, construction on peat land has witnessed an increase in recent years [17,18]. Hence improving the engineering properties of peat is inevitable for better and more economic infrastructure initiatives. In conclusion, it can be seen from the above that no researcher had attempted to investigate the effect POFA has on the compaction characteristics of local Sarawak peat in the Sibu region. Therefore, this study will focus on the compaction characteristics of peat soil through the conduction of the CBR and Standard Proctor tests. The purpose of this investigation is to assess the applicability of using the POFA-peat composites as road subbase materials in Sibu, Sarawak. 2. Materials and methods
2.3.1. Moisture content The oven-drying method was used in which all 3 samples were over-dried at 105 °C for 24 h, after which the dry weight was determined.
2.3.2. Organic content The oven dry peat samples were then put inside the furnace at temperature of 550 °C for 3 h [20]. After which the organic content was determined based on the loss in weight after combustion.
2.3.3. Specific gravity The pycnometer method was used on 3 samples to determine the specific gravity of the POFA-peat mixtures. Each sample was water submerged in a glass pycnometer and an air pump was used to extract the air bubbles. For about ten minutes, gentle shaking of the pycnometer was performed until all air bubbles have been removed. The average of the 3 samples was used as the peat specific gravity.
2.3.4. Sieve analysis Mechanical sieve analysis was applied on three dry peat samples to determine their particle size analysis. About 500 gm of dry peat was placed, each time, on a stack of sieves that changed from bigger to smaller diameter openings as we move downwards. Mechanical shaking was performed for about 15 min. Afterwards, the weight accumulated on each sieve was measured to determine the particle size distribution of the peat samples.
2.1. Peat The peat used in this study was obtained from a jungle area near the Tun Zaidi stadium in Sibu, Sarawak. All peat samples were extracted from a depth of 3 m below ground level and then placed in plastic bags and properly sealed before being sent to the laboratory. 2.2. Palm oil fuel ash (POFA) Palm oil fuel ash (POFA) passing 300 mm sieve was used in this study. Its reported specific gravity is 1.65 [19]. Table 1 shows its chemical analysis [19]. 2.3. Methods Before the start of the experimentation stage, all peat samples were oven dried to ensure complete dryness. This was done to remove any ambiguity in the test results as a consequence of the presence of water. Also, all plant roots and wood fibres were removed to reduce any testing inaccuracies. Subsequently, index and engineering tests were conducted as follows:
Table 1 Chemical composition of POFA [19]. Chemical Composition
% in POFA
Silica Aluminium Iron Calcium Magnesium Potassium Sodium Phosphorus Chlorine Sulphur LOI
21.81 2.76 3.20 5.70 3.978 3.23 0.76 3.58 0.34 1.28 2.99
2.3.5. Standard Proctor POFA was mixed with dry peat in 5%, 10%, 15%, and 20% combinations to determine their maximum dry density and optimum moisture contents using the Standard Proctor test [21]. The test was performed on 3 similar samples for each mixing combination. The POFA-peat sample, each time, was compacted in a standard mould using a standard hammer that falls from a standard distance onto the sample. Afterwards, the sample-mould was weighed and moisture content specimens were taken for analysis. The whole procedure was repeated at least two more times until a curve with a bell-shaped peak was obtained [21]. This procedure was employed to determine the maximum dry density and the optimum moisture content of the composite mixtures.
2.3.6. California Bearing Ratio (CBR) The same POFA-peat combinations were tested to determine their CBR values [22]. The CBR test is the standard test used to measures the subgrade strength in roads and pavements. For this test, the POFA-peat composite matrices were fabricated by mixing POFA in percentages of: 5, 10, 15 and 20 with the peat to form the composite material. Each matrix combination was compacted in a standard CBR mould then placed in CBR testing machine. Penetration was measured as a function of load. The CBR values were measured based on the load at 5 mm penetration for each composite mixture.
Table 2 Index values for the peat samples. Peat sample
Moisture content (%)
Organic content (%)
Specific gravity
1 2 3
2464 2683 2193
56.41 58.33 56.10
1.14 1.15 1.16
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from 24 to 33 as the POFA percentage increased from 5% to 20%. Water contents for the three samples of each peat-POFA composite mixture was varied as follows: 5%, 7%, 9%.
3. Results 3.1. Index tests Table 2 shows the index test values for the Peat samples. Moisture content of the Peat samples obtained varied between 2193% and 2683%. Organic content varied between 56.1% and 58.33%. Specific gravity values averaged at 1.15. Fig. 1 shows the particle size distribution curve for 3 peat samples. It was observed after the test that the top sieve contained a large amount of coarse materials such as leaves and branches. 3.2. Standard Proctor test The values of the dry density (cd) were plotted against their corresponding moisture contents to find the maximum dry unit weight and the optimum moisture content for the Peat-POFA composite samples. Figs. 2–5 show the results of the Standard Proctor Compaction test on the peat-POFA samples. It is shown in these figures that the optimum moisture content ranges between 6.35% and 7.6% for the range of POFA content from 5 to 20%. Maximum dry density of these samples varied from 2.08 g/cm3 to 2.16 g/cm3, for the same mixtures. 3.3. California bearing ratio test Fig. 6 shows the breakdown of the CBR with mixture values. It is shown here that California Bearing Ratio (CBR) test results varied
4. Discussion Specific gravity values determined are within the range found from previous studies on peat in Sarawak and elsewhere [3,23]. However, organic matter content determined is less than what has been previously reported [3], while natural moisture content is relatively higher for this area [24]. This peat is considered Hemic (H4-H5) according to the Von Post classification system [6]. Most materials retained on the 3.35 sieve (Fig. 1) are leaves and branches in various stages of decomposition. It is well known that soils in general and Peat in particular have properties that substantially vary temporally and spatially. Hence the variation in the peat properties, from previously reported values, for this area of Sarawak is not uncommon. The figures and tables show that the increase in POFA content has lead to an increase in the maximum dry density and optimum moisture content. The increase in POFA content, also, lead to a corresponding increase in the CBR values. This can be explained by the fact that POFA particles have higher density than peat particles and tend to resist more loads. Also since POFA is a highly pozzolanic material, its addition to Peat caused an increase in cohesion. This might have improved the packing of the POFA-Peat matrix composite at the interfaces with the peat particles resulting in a
Fig. 1. Particle size analysis of the peat samples.
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Fig. 2. Standard Proctor Compaction test on the peat-POFA with 5% POFA.
Fig. 3. Standard Proctor Compaction test on the peat-POFA with 10% POFA.
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Fig. 4. Standard Proctor Compaction test on the peat-POFA with 15% POFA.
Fig. 5. Standard Proctor Compaction test on the peat-POFA with 20% POFA.
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Fig. 6. CBR values versus peat-POFA mixtures.
denser stabilized matrix. Neville and Aitcin [25] and Yarbasi et al. [26] reported similar improved packing of soil particles leading to denser stabilized soil sample when using silica fume as an additive. Another reason for the increase in the CBR values when adding POFA is an increase in the maximum unit weight of stabilized samples and a decrease in the void ratio due to the addition of additive mixtures with fine particle size distribution [26]. Therefore this confirms the applicability of using POFA as a stabilizing agent in peat land. Maximum dry density for untreated peat is reported to be about 0.5 g/cm3. The stabilization of peat using POFA has increased the MDD to a range of 2.08–2.16 g/cm3, which is an increase of more than 4 times the untreated value. CBR values for untreated peat are reported to be 0.782% [27]. Therefore the increase in CBR, after treatment with POFA, is estimated at 31–42 fold. Since all CBR values for the tested samples fall between 24 and 33, they are rated as good materials for the purpose of road base or subbase construction [28]. 5. Conclusions The main goal of this research was to investigate the potential use of POFA-peat composite mixtures as road subbase materials. Based on the results of the Standard Proctor and CBR compaction tests, the following conclusions can be drawn: The results of standard proctor test showed that the dry density of peat-POFA composite mixtures increased with the increase in POFA content. The values of the maximum dry density of the POFA-peat composites ranged from 2.08 g/cm3 to 2.16 g/cm3. This is an increase of 4 times the untreated peat value. The increase in POFA content lead to a corresponding increase in the CBR values from 31 to 42 fold, in comparison with untreated peat. The peat-POFA CBR values are rated as good materials for the purpose of road base or subbase construction.
Acknowledgement The authors would like to acknowledge with gratitude the contribution to this research by Mr. Lai Chien Bui.
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Please cite this article as: A. A. Mahmood, M. K. Hussain and S. N. A. Mohamad, Use of palm oil fuel ash (POFA)-stabilized Sarawak peat composite for road subbase, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.178