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The present state of the use of palm oil fuel ash (POFA) in concreteHussein M. Hamada a, Gul Ahmed Jokhio a,⇑, Fadzil Mat Yahaya a, Ali M. Humada b,Yasmeen Gul ca Faculty of Civil Engineering & Earth Resources, University Malaysia Pahang, 26300 Gambang, Pahang, Malaysiab Electricity Production Directorate of Salahaldeen, Ministry of Electricity, 34007 Baiji, Iraqc School of Civil and Environmental Engineering, National University of Science and Technology, Pakistan
h i g h l i g h t s
Palm oil fuel ash (POFA), a waste by-product, can be used to partially replace cement in concrete production. POFA is rich in SiO2, therefore, is a good pozzolanic material. Ultrafine and Nano POFA increase the compressive strength of concrete. POFA reduces drying shrinkage as well as workability of concrete. The use of POFA in concrete is favourable to the environment.
a r t i c l e i n f o a b s t r a c t
Article history: Concrete industry consumes considerably large quantities of natural resources in addition to generatingReceived 26 September 2017 toxic gases, such as CO2, in the atmosphere. In order to achieve more sustainability in the concrete sector,Received in revised form 20 March 2018 research should focus on using alternative renewable resources such as palm oil waste for concrete pro-Accepted 23 March 2018 duction purpose. Palm oil fuel ash (POFA) is a by-product obtained during the burning of waste materials such as palm kernel shell, palm oil fiber, and palm oil husk; it can be utilized to partially replace cement in a concrete mix. This paper presents a review of the applications and effects of POFA on concrete prop-Keywords: erties as reported by previous studies that have been conducted to find out POFA properties and its effectsPalm oil fuel ashChemical and physical properties of under various conditions. Chemical and physical properties of the resulting concrete have been illus-concrete trated depending on the POFA characteristics in several sources. Many studies have shown that concreteCompressive strength and durability containing POFA has better compressive strength, durability and other properties than concrete contain-CO2 emissions ing Ordinary Portland Cement (OPC) only. Other researchers have shown more advantages of POFAEnvironment friendly materials replacement in concrete in specific proportions, especially minimizing CO2 gas emissions and thus improving environmental conditions. Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 1.1. Preparation of POFA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 1.2. Environmental benefits of POFA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 1.3. Nano POFA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 1.4. Nano silica with POFA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2. Utilization of POFA in concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3. Utilization of POFA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 3.1. POFA as SCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 3.2. POFA in self-compacting concrete (SCC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 4. POFA properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4.1. Chemical composition of POFA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4.2. Physical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
⇑ Corresponding author. E-mail address: firstname.lastname@example.com (G.A. Jokhio).
https://doi.org/10.1016/j.conbuildmat.2018.03.2270950-0618/Ó 2018 Elsevier Ltd. All rights reserved. H.M. Hamada et al. / Construction and Building Materials 175 (2018) 26–40 27
1. Introduction POFA is also one of the ash family of materials resulting from the burning of waste materials such as palm kernel shell and palm Concrete industry presents a challenge to the global environ- oil husk [7]. POFA is usually disposed in landfills, which results inment as it consumes significantly large quantities of natural the increased amount of ash deposits every year and now hasresources in addition to generating toxic gases, such as CO2. In become a burden [16]. Therefore, it is needed to devise new waysorder to achieve more sustainability in the building construction to benefit from these waste materials and avoid the potential risks.sector, researchers in this field need to focus on using alternative In the 1990s, Tay [17] started studying the properties of palm oilrenewable resources, such as palm oil waste. Malaysian Palm Oil fuel ash as a concrete material. The study was conducted by replac-Board (MPOB) in 2012 reported that the plantation area of palm ing Portland cement with POFA ranging between 10 and 50%. Itoil covers about 5.07 million hectares in Malaysia [1]. The United was noted that the compressive strength of the specimensStates Department of Agriculture reported that the production of decreased when between 20 and 50% of cement was replaced bypalm oil in years 2016 and 2017 was estimated to be 64.5 million POFA. Since then, many studies have been conducted to enhancemetric tons [2]. Southeast Asian countries are the main palm oil the concrete properties, for example, Awal and Hussin [15] discov-producers. Palm oil fuel ash (POFA) is one of the significant mate- ered that POFA has a significant impact to prevent and reduce therials produced as a byproduct of the palm oil industry [3,4], which sulfate attack. In 2011, Kroehong et al. [18] conducted a study tois obtained by burning the waste materials such as palm oil fiber, find out the effects of POFA fineness on pozzolanic reaction ofkernels, empty fruit bunches, and shells in the power plants to gen- cement paste. The Ground Palm Oil Fuel Ash (GPOFA) and Grounderate energy [4]. POFA can be utilized to partially replace cement in River Sand (GRS) were used to replace the Portland cement byconcrete production [5]. The quantity of POFA being produced is GPOFA or GRS at 10%, 20%, 30% and 40% by weight of cementitiousincreasing with time due to the increase in the production of palm materials, whereas the water to binder ratio (W/B) was 0.35 for theoil. Leaving this waste material without any further utilization is in mixes of cement pastes. It was concluded that the effects of POFAitself an environmental challenge. Malaysia is one of the largest on the cement paste and concrete mixtures increase when POFA isexporters and producers of palm oil all over the world [6]. Produc- of higher fineness.tion of POFA in Malaysia alone is approximately 10 Million tons/ In 2015, Rajak et al. [19] conducted research to determine theyear [7,8]. Whereas, just 104 tons/year of POFA are being produced morphological characteristics of hardened cement pastes whichin Thailand, which continue to increase with time [4]. contain Nano-POFA with particle sizes ranging between 20 nm Recently, there has been an increasing interest in the use of and 90 nm. It was discovered that Nano-POFA particles have a sig-industrial and agricultural waste materials in the construction nificant effect on pozzolanic reactions in the pastes because of theindustry, especially during the concrete preparation [9]. There is filling effect. In Thailand, P. Chindaprasirt et al. [18] used the POFAan urgent need for disposal of harmful residual agricultural and and Rice-husk Bark Ash (RBA) to determine the water permeabilityindustrial products which has become a threat for human life. In and strength of concrete replacing the cement in the concrete byrecent years, many studies have emerged that indicate to use the various percentages ranging between 20%, 40%, and 55% by weight.agricultural residues in the concrete industry [5,10–12]. From envi- It was concluded that replacing 20% of ordinary Portland cementronmental perspective, agricultural waste materials have been by POFA and RBA leads to increasing the compressive strengthinvestigated by many researchers and have been shown to have and workability, while the value of compressive strength decreasesbetter properties in concrete than the cement materials, whereas when the replacement quantity increases up to 40% due to thethe latter also generates a high amount of CO2, which is harmful increased requirement of water [16].for environment [9]. Due to the fact that POFA is a geopolymer, it The above discussion leads to the objectives of the presentis environmentally friendly and consumes less amount of energy paper to review the state of the use of POFA in the production ofthan traditional materials during production [13,14]. In Malaysia, concrete. In this regard, the process of the preparation of groundmore than 1000 tons of POFA have been dumped into lagoons and nano POFA has been reviewed first. This has been followedand landfills without exploiting the use of this material in other by a review of the chemical and physical properties of POFA itself.industries [15]. In terms of cost saving, using POFA as partial The effects of the use of POFA in concrete on the properties of freshcement replacement will reduce the cost of cement production concrete and hardened concrete have been discussed in the latteras well as transportation of the same from cement plants to the half of the paper. Finally, at the end, a section of discussion andstores. Moreover, this will improve the environment by mitigating conclusions has been provided that includes a few directions forand reducing waste materials in landfills. the future research in this field.28 H.M. Hamada et al. / Construction and Building Materials 175 (2018) 26–40
Palm Kernel Shell Empty Palm Fruit Bunches Palm oil fiber Fig. 1. Waste materials from palm oil tree to produce POFA [22].
1.1. Preparation of POFA remove moisture in the oven at 105 ± 5 °C, then passing dry POFA through number 300 sieve in order to remove foreign and coarse Production of POFA is due to heating of significant amounts of particles and also to dispose of kernels and fibers which failed topalm oil fiber, shell, and empty palm fruit bunches as shown in burn. The second step was grinding POFA particles to get a suffi-Fig. 1; these wastes are employed at the palm oil mills as a main cient fineness followed by combustion in gas furnace at high tem-source of energy. The byproduct which constitutes about 5% of perature of up to 500 ± 50 °C to remove unburned carbon andtotal waste weight is called POFA [20]. In the palm oil mills, the obtain POFA with high fineness. The third step was conducting fur-waste materials are burnt at high temperature, which reaches up ther grinding of POFA similar to the previous step to get UPOFA.to 1000 °C [19], and thus used as fuel to generate electricity [21].In Malaysia, more than 3 million tons of POFA is produced everyyear [20], while in Thailand, production of POFA is more than 1.2. Environmental benefits of POFA100,000 tons annually [5]. Instead of using electricity from familiarenergy sources that causes many environmental issues and In a study, Ali et al. [30] claimed that the cement industry alonerequires high cost, waste materials produced from palm oil mills consumes almost 12–15% of the energy allocated for industrialcan be used to generate electricity by heating up the boilers in purposes [28]. Cement manufacturing process requires burningthe palm oil factories [4]. of fossil fuels, coal, petroleum coke, and fuel oils in order to main- POFA constitutes about 5% of the total waste materials after tain the temperature at 1450 °C in the oven [29]. Therefore, it gen-burning shells and fibers to generate electricity in palm oil mills erates approximately 0.97 ton of CO2 for each ton of clinker[3,17]. Out of 4 kg of raw palm oil, only 1 kg is palm oil and the rest produced [30]. Around 7% of CO2 gas emissions are caused byis production residues which represent dry biomass [4,23–25]. cement production processes in factories, which increases green-Palm oil fronds and palm oil trunks are about 75% of the total house gases and causes environmental problems [30,31]. It waswaste; this waste is left to be recycled and used as plant fertilizer predicted in 2008 that the cement manufacturing may increasefor future plant strengthening, while the remaining proportion, by 100% in 2020 [32]. Another study predicted the increase inwhich is 25% and includes empty fruit bunches, mesocarp fiber, the cement production due to increase in demand to reach 200%and palm kernel shells can be used to generate electricity in palm by 2050 in relation to the production rate in 2010 [33]. Besides,oil mills by combustion of these wastes under high temperature the energy consumed to produce 1 ton of cement is a significantranging between 800 and 1000 °C [26,27]. Preparation of POFA amount; more than 1700 MJ/ton clinker [34,35], and about 1.5can be achieved in different ways depending upon the burning pro- ton of raw materials are required. Moreover, it has also beencess and raw materials used. Noorvand et al. [20] studied initial reported that the cement industry alone consumes about 5% ofPOFA preparation by putting dried samples in an oven at the tem- total energy [36]. Production of cement has been considered asperature of 105 ± 5 °C for 24 h. While another study by Tangchira- the second biggest contributor of CO2 gas emissions worldwidepat et al. [5] obtained POFA through combustion of waste materials [37].at the temperatures of up to 1000 °C, followed by using sieve (1.18 In recent years, there has been an increased concern regardingmm opening) in order to remove the large foreign particles. In a the environmental issues and their effects on various aspects ofnew study by Zeyad et al. [2] to prepare ultrafine POFA, three steps life. The global warming is partially due to widespread solid wastewere adopted as shown in Fig. 2. The first step was to dry POFA to materials resulting from agricultural and industrial products, which has become the most significant environmental issue world- wide [38]. According a study by Tay and Show [39], the transporta- Step 1 tion and disposal of POFA into the landfills and open fields without • Oven Dry at 105oC treatment may cause various diseases and be uncomfortable for Wet Palm Oil Fuel Ash • Pass through number 300 sieve human life. Also, the production of huge quantities of concrete (W-POFA) due to the increased demand for the construction of new buildings will result in significant damages to the atmosphere through the generation of CO2 emissions [40]. Many researchers emphasize the need to mitigate the risk to the environment, especially result- ing from the agriculture wastes, and to develop methods to use Step 2 Step 3 these materials in cement mortar [20,41,42]. In addition, disposal • Grind in Ball Mill to obtain • Grind in Ball Mill to obtain of POFA in the landfills resulting into significant environmental Ground POFA (G-POFA) ultrafine POFA (U-POFA) risks cannot be ignored. Recently, studies have been conducted • Treat in Gas Furnace at 500oC to obtain heat treated POFA (T- replacing Portland cement by POFA rich silica as cementitious POFA) material aimed at creating sustainable construction materials [13]. In Malaysia alone, around 3 million tons of POFA was pro- Fig. 2. Production process for ultrafine POFA [2]. duced in 2007 as waste material [38]. These materials can cause H.M. Hamada et al. / Construction and Building Materials 175 (2018) 26–40 29
damages to the environment if not utilized by other industries 1.3. Nano POFAsuch as construction industry [16,43]. Therefore, Tangchirapatet al. [3] utilized POFA in their study as a pozzolanic material in Nanotechnology has been applied in many scientific disciplines.concrete in order to reduce the environmental problems by con- It is also relevant here due to the unique chemical and physicalsuming POFA resulting from the palm oil industry in concrete characteristics of concrete composites [19]. Nano-particles arepreparation, thus reducing the burden on landfills and decreasing the particles that have sizes less than 100 nm (100 109 m)the environmental risk by lowering CO2 emissions. [51]. The integration of cement with Nano-additive replacements Due to the increasing demand for energy resources, researchers such as nano-SiO2, silica fume, Nano-clay, Nano-fly ash and carbonhave started searching for new renewable resources instead of the nanotubes in cement pastes has significantly improved the cementnon-renewable resources such as natural gases and petro- paste properties, especially, increasing the compressive strengthchemicals, which contribute to global warming and cause signifi- and durability of concrete mixtures [52–55]. Many studies havecant harm [44]. The concrete made from agricultural wastes such been conducted to find out the potentials of Nano POFA to improveas POFA has been termed as Green concrete and is considered envi- properties of concrete and cement paste, such as [18,56]. They con-ronmental friendly. In this case, the concrete production consumes cluded that addition of Nano POFA can enhance the concrete prop-less energy than the traditional concrete made of cement; it also erties by decreasing the amount of calcium hydroxide. Rajak et al.reduces the carbon dioxide emissions in the air. Besides, it helps [19] used Nano POFA as pozzolanic material in concrete mixtures.control the 5–8% of CO2 emissions produced by the cement indus- The purpose of using Nano-POFA was to understand the effects oftry which leads to potential environmental risks in the future Nano- POFA on cement hydration, especially on the microstructure[45,46]. The waste resulting from palm oil industry constitutes properties of cement paste. POFA is a pozzolanic material due toabout 80% of materials such as palm oil shells and fruit bunches, the fact that it has a significant quantity of SiO2 in its particleswhich can cause serious environmental issues if not treated [47]. [57]. Abutaha et al. [58] conducted a study to find out the impactIn studies by Tay, and Tay and Show [17,39], it was said that with of adding high volume Nano POFA on the cement mortar; they con-increased demand of the palm oil products, the waste materials cluded that incorporating high volume of Nano POFA can produceproduced also increase dramatically. These waste materials can concrete with the qualities of being more sustainable and withpotentially cause dangerous environmental problems, financial higher compressive strength. Many studies such as [3,17,39] havelosses, and health hazards if left without any utilization in various shown that the original size of POFA is not strong in themanufacturing processes. Incorporation of POFA in concrete as microstructure because of its porosity with large particle size inpartial replacement of cement is increasing with time due to the natural condition. On the other hand, [59–61] suggest to grindenhancement of concrete in terms of physical and chemical prop- POFA to get finer particles and thus improve the reactions witherties. It also decreases the cost and improves the environmental other particles in the concrete mixtures. Tangchirapat et al. [3]situation [1]. showed that the fineness of POFA has significant effects on the The concrete ingredients resulting from biomass products can compressive strength.be more beneficial than traditional materials especially if those Due to the large particles of POFA in its original size, itsdo not contribute to the environmental damages. In order to man- microstructure composition is weak and highly porous [3,17,39].age the solid waste materials resulting from the production of Therefore, reducing its particle sizes to micro or Nano by grindingpalm oil, many researchers have exploited this waste as partial process to improve its reactivity with other materials and enhancereplacement of cement in concrete manufacturing [48]. Incorporat- its properties has been recommended [59–61]. Many studies haveing waste materials such as POFA in concrete manufacturing will incorporated different fineness of POFA as cement replacement, forresult in minimizing the impact of CO2 emissions due to decreased example, Tangchirapat et al. [3] concluded that POFA with the par-quantity of wastes landfilled and thus improving the environment ticle size of 7.4 mm and the replacement quantity of cement up to[49]. In the long term, with increasing pressure to minimize CO2 10% has the same values of compressive strength as the controlemissions resulting from cement production, the need to use green samples. Sobolev and Gutierrez [62] concluded that incorporationconcrete by incorporating palm oil fuel ash as pozzolanic material of nanoparticles with cementitious composites has the ability toand partial replacement of cement will increase significantly [38]. improve the chemical and physical properties for composites.In other words, using the waste materials in concrete production Kroehong et al. [18] noted that Portland cement Type I can beassists to reduce the volume of the solid waste materials in land- replaced by high fineness particles of POFA to use it as pozzolanicfills and thus reduces harmful gases in the atmosphere [50]. The material with proportion up 30% of binder by weight. In a recentsuccessful use of POFA and other agricultural waste materials will study by Lim et al. [63], it was claimed that using high volume ofcontribute by reduction in the dumping of these wastes in landfills, Nano POFA with particle size less than 1 mm and with the percent-and thus reducing CO2 gas emissions. This will also result in age up to 80% as replacement of cement can achieve high compres-improving concrete properties such as compressive strength, dura- sive strength with high quality of concrete, and thus mitigatebility, and resistance to attack of chloride and sulfate. Generally, carbon dioxide gasses emission from cement production process.concrete consists of cement, water, fine and coarse aggregate. Con- In a study by Johari et al. [64], it was shown that ultrafine POFAsumption of these traditional materials can generate harmful gas leads to increasing the concrete workability and delay in the set-emissions. Therefore, most of the researchers in this field who ting time especially when higher content of POFA instead ofare also interested in the environmental aspects have begun to cement is used. Ultrafine POFA (UPOFA) contains more silica thanuse new materials that have less impact on the environment and, OPC and Ground POFA (GPOFA), and thus, it can produce extraat the same time, do not negatively impact the concrete properties. calcium-silicate-hydroxide (C-S-H) gels to make cement mortarAlthough many studies have been conducted aimed at reducing the much denser and durable. Therefore, UPOFA can be classified as Fair pollution by using POFA to reduce CO2 emissions, to date no pozzolan class, while GPOFA can be classified as C pozzolan classstudies have mentioned the effects of POFA on the water and soil [65]. However, to date there have been few studies conducted topollution. Therefore, there is an urgent need to encourage combine Nano POFA and other waste materials in nano size suchresearchers to make additional efforts towards minimizing water as nano Fly ash and nano lime. Therefore, there is a research gapand soil pollution in this regard. in this area where it is needed to study mixing of Nano POFA with30 H.M. Hamada et al. / Construction and Building Materials 175 (2018) 26–40
any other Nano composite or geopolymer to enhance the concrete expansion due to magnesium sulfate attack. They discovered thatproperties. concrete containing POFA leads to delay in setting time depending upon the proportions of POFA replacing cement and its degree of fineness. In terms of compressive strength, the concrete samples1.4. Nano silica with POFA made from cement and the POFA with original size have less com- pressive strength than conventional concrete samples, but the con- Nano silica consists of small particles sized (1–50 nm); it has crete samples made from cement and POFA with fine particlesspherical particles and can enhance the concrete properties in have compressive strength higher than traditional concrete sam-fresh and hardened states [66]. Nano silica has been added as ples. To produce lightweight foamed concrete (LFC) that has lowercement replacement with POFA in order to enhance the concrete density than normal concrete, Lim et al. [87] used POFA as replace-properties, such as dry shrinkage and compressive strength. ment of cement to get low concrete density 1300 ± 50 kg/m3 withFarzadnia et al. [66] conducted a study by adding Nano silica to improved properties such as compressive strength, thermal con-POFA replacing 30% of cement. It was noted by the authors that ductivity, and flexural strengths. To find out the mechanical prop-the compressive strength increased by 15% compared to the con- erties of concrete containing fiber, Islam et al. [88] also used POFAtrol sample, the shrinkage decreased while lowering free water, with ground granulated blast-furnace slag (GGBS) as binder and oiland the hydration volume in cement matrix increased. POFA can palm shell as coarse aggregate in preparing geopolymer concrete.be utilized as a pozzolanic material in concrete mix because it In order to exploit palm oil waste in the construction industry,has a significant content of SiO2 [66]. Incorporation of Nano silica POFA has been adopted as cement replacement up to 25% and oilwith unground POFA was studied by Noorvand at al. [20] in order palm shell as a coarse aggregate. A study concluded that POFAto improve mechanical properties of concrete mix. The reduction of within 10–15% of cement replacement gives better results in termswater absorption and the increase in the compressive strength of of compressive strength; in contrast, increased POFA proportionsconcrete resulted from adding Nano silica to the POFA-cement lead to decrease in the splitting and flexural tensile strengthsmortars. Tobon et al. [67] found that after adding Nano silica to [89]. Liu et al. [90] utilized POFA and fly ash as concrete binderthe cement pastes, especially in the first days of curing process, to prepare lightweight-foamed concrete containing oil palm shellthe compressive strength increases due to the good distribution (OPS) as lightweight coarse aggregate. The main purpose of theof C-S-H and thus causes a larger quantity of hydration compared study was to evaluate the mineralogy and the morphology of oilto plain cement paste. Sanchez and Sobolev [68] reported that palm shell foamed geopolymer concrete.Nano silica is the most common among nanomaterials, which are Chindaprasirt et al. [16] examined the amount of water perme-used to enhance and improve the chemical and mechanical proper- ability and concrete strength containing POFA. They found that theties of cementitious materials and has been widely examined. Add- compressive strengths of concretes containing 20% of GPOFA wereing Nano silica to the cementitious materials ranges from small to higher than compressive strength of OPC concrete. But, they alsolarge quantities [69–77]. After adding small amount ranging from found that the permeability of water was still lower than that in1% to 3% of Nano silica, it was noted that the compressive strength, OPC state. It was concluded that POFA can be used as a pozzolanicdurability, and microstructure of cementitious composites are material in concrete and thus achieve an acceptable permeabilitymodified and improved. From chemical aspect, Nano silica acceler- and strength for concrete samples. In terms of using other wastesates the C3S dissolution because of its high surface area [78]. In fact with POFA as cement replacement, Ranjbar et al. [13] replacedNano silica also affects the physical properties through the con- the Fly Ash (FA) by POFA as a pozzolanic material and measuredsumption of calcium hydroxide (CH) and formation of C–S–H clus- the volume change, the density, microstructural characteristics,ters to improve pozzolanic properties in cementitious materials and compressive strength of concrete samples. They replaced the[70]. Many studies have reported that POFA has high silica content FA contents by 0%, 25%, 50%, 75% and 100% of POFA to preparewhich ranges between 50% and 70% of total weight and makes it a the geopolymer mortar. All the samples were exposed to a varietygood pozzolanic material in the concrete mixtures, therefore, there of temperatures starting at room temperature as a reference tois no need to add more silica to cement containing POFA [1]. 300 °C, 500 °C, 800 °C and 1000 °C. The researchers found that, Previous studies such as [69,76,79–83] have focused on the after exposing the concrete sample with POFA and FA to higherenhancement of properties of mortar, paste, and concrete mixtures temperatures, the compressive strength starts decreasing whento fast CH consumption, particularly at early ages of concrete sam- the temperature becomes more than 500 °C. In another study,ples to discover the high reactivity of Nano particles that includes POFA was utilized as a pozzolanic material in concrete. The POFASiO2. In a recent study by Farzadnia et al. [66], it was reported that particle sizes in the study were between 7.4 and 15.9 mm, the Port-adding Nano silica to POFA advantageously affected the land cement was replaced by POFA at 10%, 20%, 30%, and 40% bymicrostructure and the shrinkage of concrete. However, there is weight of binder [3]. Some researchers [64,91] have used high vol-still need to conduct further experimental works by adding Nano ume of ultrafine POFA as replacement of cement reaching up tosilica under different conditions to cement containing POFA. 60% of total cement mass to produce concrete. POFA has a signifi- cant content of silica and thus it has the ability to replace cement2. Utilization of POFA in concrete in the concrete mixtures [57]. There are significant concerns related to the durability of concrete buildings as a result of erosion POFA has many benefits to be utilized in concrete manufactur- and reduction of the age of concrete structures as well as the gen-ing such as enhancing the concrete properties to resist chloride eration of harmful gases into the surrounding environment. There-attack [84], assisting to increase the drying shrinkage of concrete fore, a significant number of researchers have begun to exploit new[85], decreasing heat development, resisting concrete sulfate materials that have high durability and resistance to corrosion,attack [3,86], and reducing the effect of acidic environment on con- such as FA and POFA [92]. Some researchers have reported thatcrete [17]. In 2011, Awal and Hussin [7] studied the effects of POFA the thermal properties of concrete improve if POFA is used as par-on the heat control of concrete during chemical reactions. They tial cement replacement in concrete [38]. The production of C-S-Hfound that the hydration heat depends mainly on the type of gels results from the interaction between Al2O3 and SiO2 with Cachemical interactions of the materials. In Thailand, Tangchirapat (OH)2 in a cement paste to produce pozzolanic material [93], andet al. [3] used POFA to find out its effect on the concrete properties increasing fineness of pozzolanic materials will result in increasingsuch as compressive strength, initial and final setting time, and the resistance to sulfate in concrete and reduction in the content of H.M. Hamada et al. / Construction and Building Materials 175 (2018) 26–40 31
Ca(OH)2. In addition to that, concrete with high pozzolanic reaction related to using POFA in the concrete mixtures has been applied inis better in terms of enhanced concrete compressive strength along very warm climates. Due to the increasing demand of cementwith being more homogeneous and dense. POFA satisfies the ASTM materials all over the world, and because of the decrease of coalC618 chemical requirements in terms of using a binder pozzolanic fly ash as a supplementary cementitious material, there is anmaterial having (LOI) value less than 10%, which makes it suitable urgent need to use new supplementary cementitious materialsto be used in the concrete production. such as POFA to replace PC fully or partially even in colder climates Many studies have been conducted to benefit from Palm oil [49]. In Thailand, Tangchirapat et al. [5] used the POFA as supple-waste applications in concrete manufacturing and it has been mentary cementitious materials to produce new concrete withreported that these wastes have beneficial value [59,94,95]. In high strength. In 2017, Thomas et al. [44] reviewed many studies2011, Jaturapitakkul et al. [38] claimed that pozzolanic reaction related to using POFA as a supplementary cementitious materialof POFA in early age of concrete sample is low and increases with and the chemical and physical properties of resulting concrete intime. A study on the compressive strength of concrete for 10–40% the fresh and hardened states. The authors reported that POFAof cement replacement was reported where the researchers found gives high strength to concrete in sulfate and acidic environments,the compressive strength of concrete ranging from 0.1 MPa to 4.5 high resistance to chloride and carbonation, in addition to loweringMPa at 7 days and 2.5 MPa to 22.5 MPa at 90 days [60]. POFA can of permeability and shrinkage. Due to the POFA advantages as abe mixed with other waste materials such as fly ash FA in certain supplementary cementitious material in the long-term, it has beenproportions [1] to give high concrete quality in terms of improved more extensively used in concrete preparation, whereas, manyworkability and lowering the quantity of super plasticizer (SP). Due studies have focused on the determination of fresh and hardenedto the considerably large advantages acquired from the utilization state properties. Palm oil industry is one of the most importantof POFA and FA in concrete as partial replacement of cement, it has agro industries in South-East Asian region [102]. POFA is the new-started gaining popularity in concrete manufacturing, especially est addition to the cement paste as a SCM, which can be obtainedtowards minimizing cost and ecological issues. In addition, to pro- as a by-product from the palm oil mills and is considered a signif-duce foamed concrete, good quality is obtained by partially replac- icant pozzolanic material [7].ing cement with POFA. Even when the compressive strength value Many studies have been conducted to benefit from the agrois lower than the control samples, the concrete with POFA can be waste materials such as POFA, FA, and rice husk ash (RHA) asused in non-structural building elements such as producing con- SCM or as pozzolanic materials [103]. Minimizing the permeabilitycrete blocks that do no need to be of high compressive strength in concrete mixes is one of the advantages resulting from using[96]. Also, POFA can be combined with waste plastic resulting from SCMs such as POFA. This alters the pore structure and thusplastic factories and daily use by the people to produce concrete increases resistance to the sulfate and acid attacks. In terms of con-with new properties, such as incorporating POFA with thermoset- crete durability properties, POFA and other SCMs enhance concreteting plastic, whereas thermosetting plastic has been used by durability and reduce environmental damages, which leads to thePanyakap and Panyakapo [97] with fly ash to produce lightweight reduction of concrete cost. However, adding an excessive amountconcrete, which has acceptable compressive strength for non- of SCM in cement paste may result in lowering compressivestructural elements in buildings. In addition, POFA can be used strength because of reduced portlandite concentration in thesealong with egg shells, because the latter is rich in calcium oxide materials [104,105]. Tangchirapat et al. [5] examined water perme-and enhances hydration heat during reaction of materials. Egg ability, drying shrinkage, and sulfate resistance in concrete con-shells were used in concrete by [97,98]. taining POFA, and noted compressive strength up to 70 MPa at One of the disadvantages of POFA is the high content of non- 90 days. The researchers reported that concrete thus producedburning carbon which is considered to be higher than FA and GGBS has lower drying shrinkage than concrete produced from OPC,[21]. Therefore addition of high quantity of POFA will result in the and that the concrete water permeability decreases when GPOFAdecrease of workability when the replacement reaches up to 30%, proportion is increased. Concrete with POFA replacing cementthus necessitating the addition of a superplasticizer [99]. Accumu- shows resistance to sulfate better than conventional concrete.lation of palm oil waste in huge amounts results in the generation Due to the limited availability of concrete materials in most ofof biomass such as mesocarp fiber, empty fruit bunches, palm oil the countries and the high cost of cement, POFA can be used asleaves, palm oil trunks, palm oil kernel shell, and palm oil mill SCM in concrete manufacturing in order to be more economicaleffluent, which cause an environmental risk if not treated directly and environment friendly. The differences in POFA particles[44]. In a study by Hassan et al. [100], it was reported that biomass because of incomplete burning in the boilers for some quantitiesgeneration over the world was 80 million tons and this quantity is can cause higher carbon content and make it darker potentiallyexpected to reach up to 110 million tons in 2020. Therefore, aca- reducing its utilization as SCMs [106].demicians and researchers should play a significant role to encour-age the government and non-government agencies to use these 3.2. POFA in self-compacting concrete (SCC)waste by demonstrating the benefits resulting from utilization inconcrete production and other industries. There are many advantages due to the utilization of waste materials in concrete, one of these advantages is self-compacting concrete (SCC) when it is required to be poured into a narrow area3. Utilization of POFA [107], especially when the concrete reinforcement is congested and it is difficult to conduct compaction process to the concrete3.1. POFA as SCM during casting. Self-compacting concrete requires reduction in the aggregate materials and increase in the bonding materials, There has developed an increasing interest in the recent years which results in additional cost; in order to overcome this problem,towards adopting new supplementary cementitious materials the alternative solution is using a SCM to replace cement partially(SCM) that result in better chemical and physicals characteristics [108]. The SCM improves concrete properties such as workability,than traditional concrete [56,101]. Many studies have used POFA decreases cost due to decrease in the cement amount, andas SCM, for example, Paris et al. [49] conducted a study to find enhances SCC characteristics thus achieving energy saving, whichout the effects of POFA on the physical and mechanical properties can be considered a sustainable construction method [109]. POFAas well as the durability of cement paste. Almost all of the research is one of these SCMs that can be used as a replacement of cement32 H.M. Hamada et al. / Construction and Building Materials 175 (2018) 26–40
because it contains a large quantity of silica that reaches up to 66%, between 43% and 71%, and makes POFA particles with good poz-which enables it to produce a variety of concrete types [110]. zolanic properties to produce high quality concrete.
4.1. Chemical composition of POFA The physical properties of POFA are affected by the burning temperature and other conditions [50,115], for instance, POFA The chemical composition of POFA has been examined by many color is grey in normal state but it becomes darker if it containsresearchers as shown in Table 1. A large variety has been reported high amount of unburned carbon; and after burning further, thein the experimental works, the notable variations are due to differ- carbon is removed and the color changes back to grey [119]. Theent conditions such as burning temperature, burning quantity of physical properties of POFA have been shown in Table 2. Specificpalm oil parts to produce POFA from different factories and other gravity of POFA ranges between 2.6 and 1.89; these values are lessfactors. These factors were identified in detail by [64,91], who than the specific gravity of cement.focused on the higher quantity of silica due to burning some partsof palm oil tree. The chemical properties of constituent materials 4.2.1. Specific gravityaffect the heat of hydration of concrete [102], its compressive A study by Tay in 1990 [17] showed that the specific gravity ofstrength and workability. Using waste materials as a replacement unground POFA is approximately 40% lower than the specific grav-of cement has seen a tremendous advancement due to their chem- ity of OPC, which ranges from 1.78 to 1.97. Sata et al. [59] reportedical composition being suitable to produce high quality concrete in that the specific gravity increases when the POFA particle size isline with increasingly stringent environmental legislation [111]. finer, to reach up to 2.78 because the reduction in particle sizesThe main composition of POFA is silicon dioxide which ranges decreases porosity. There are many factors that affect the POFA
Table 1Chemical compositions of POFA as reported in literature.
References Silicon Aluminum Iron oxide Calcium Magnesium Sodium oxide Potassium Sulfur Loss on dioxide (SiO2) oxide (Al2O3) (Fe2O3) oxide (CaO) oxide (MgO) (Na2O) oxide (K2O) trioxide ignition (LOI) (SO3) [18] 54.0 0.9 2.0 12.9 4.9 1.0 13.5 4.0 3.7 [112] 64.2 3.7 6.3 5.8 4.8 0.18 5.18 0.72 16.3 [56] 65.01 4.68 3.2 8.19 4.58 0.07 6.48 0.33 2.53 [113] 53.5 1.9 1.1 8.3 4.1 1.3 6.5 – 18.0 [15] 43.6 11.4 4.7 8.4 4.8 0.39 3.5 2.8 18.0 [102] 59.62 2.54 5.02 4.92 4.52 0.76 7.52 1.28 8.25 [5] 65.3 2.5 1.9 6.4 3.0 0.3 5.7 0.4 10.0 [59] 65.2 2.6 2.0 6.4 3.1 0.3 5.7 0.5 10.1 [99] 71.67 0.94 2.77 5.61 4.91 0.12 7.89 1.05 – [90] 63.4 5.5 4.2 4.3 3.7 – 6.3 0.9 6.0 [66] 47.37 3.53 6.19 11.83 4.19 – – 1.22 1.84 [20] 48.9 2.71 6.54 13.89 2.74 0.05 7.13 1.54 11.3 [85] 65.3 2.5 1.9 6.4 3.0 0.3 5.7 0.4 10.0 [16] 57.8 4.6 3.3 6.6 4.2 0.5 8.3 0.3 10.1 [43] 60.42 4.26 3.34 11 5.31 0.18 5.03 0.45 2.55 [19] 54.80 7.40 4.47 14.0 4.14 – – 0.71 9.3 [14] 64.17 3.73 6.3 5.8 4.87 0.18 8.25 0.72 16.3 [63] 69.3 5.30 5.1 9.15 4.1 – 11.1 1.59 1.3 [114] 51.55 4.64 8.64 5.91 2.44 0.07 5.50 0.61 5.00 [7] 43.60 11.40 4.70 8.40 4.80 0.39 3.50 2.80 18.00 [1] 52.63 8.991 1.059 3.211 1.459 0.564 3.133 – 27.7 [115] 64.20 4.25 3.13 10.20 5.90 0.10 8.64 0.09 1.73 [50] 62.6 4.65 8.12 5.7 3.52 – 9.05 1.16 6.25 [116] 47.37 3.53 6.19 11.83 4.19 – – – 1.84 [117] 47.22 2.24 2.65 6.48 5.86 1.22 11.86 9.19 5.42 [118] 63.41 5.55 4.19 4.34 3.74 0.16 6.33 0.91 6.20 [119] 62.60 4.65 8.12 5.70 3.52 – 9.05 1.16 6.25 [30] 59.17 3.73 6.33 5.80 4.87 0.18 8.25 0.72 16.1 [120] 65.30 2.60 2.00 6.40 3.10 0.30 5.70 0.50 10.10 [3] 57.71 4.56 3.30 6.55 4.23 0.50 8.27 0.25 10.52 [84] 63.6 1.60 1.40 7.60 3.90 0.10 6.90 0.20 9.60 [121] 66.91 6.44 5.72 5.56 3.13 0.19 5.20 0.33 2.30 [64] 65.01 5.72 4.41 8.19 4.58 0.07 6.48 0.33 2.53 [86] 57.7 4.5 3.3 6.5 4.2 0.5 8.2 0.2 10.5 [111] 65.01 5.72 4.41 8.19 4.58 0.07 6.48 0.33 2.53 [122] 67.72 3.71 4.71 5.57 4.04 0.16 7.67 1.07 6.20 [123] 62.6 4.65 8.12 5.7 3.52 – 9.05 1.16 6.25 [89] 63.4 5.51 4.2 4.35 3.78 0.15 6.35 0.93 6.19 [16] 57.8 4.6 3.3 6.6 4.2 0.5 8.3 0.3 10.1 [61] 55.7 0.9 2.0 12.5 5.1 1.0 11.9 2.9 4.7 [124] 63.41 5.55 4.19 4.34 3.74 0.16 6.33 0.91 6.20 [125] 64.17 3.73 6.33 5.80 4.87 0.18 8.25 0.72 [126] 53.3 1.9 1.9 9.2 4.1 1.3 6.1 [127] 60.42 4.26 3.34 11.00 5.31 0.18 5.03 0.45 2.55 H.M. Hamada et al. / Construction and Building Materials 175 (2018) 26–40 33
properties [130] such as treatment processes [64] and the burning perature for POFA leads to decrease in the unburnt carbon contenttemperature [15]. Therefore, it can be said that the specific gravity proportion, and thus leads to change in its color [8]. In general, theof POFA varies depending on the factors mentioned above but does color of POFA powder is gray and becomes dark when quantity ofnot exceeded 3.0. Other researchers [5,120] have also reported that unburned carbon increases [102]. The decarbonation of POFA isthe specific gravity of POFA increases after the grinding process because of the decomposition of calcium carbonate at tempera-due to the minimization of porosity. The specific gravity of POFA tures ranging between 400 and 600 °C, therefore, the color of POFAranges between 2 and 2.5 and thus is less than the specific gravity changes from dark black to grey [63]. Zeyad et al. [111] concludedof ordinary Portland cement. The specific gravity of POFA particles that the color of POFA particles changes due to the heat treatmentwas reported as 2.16 by a study conducted to find out properties of which causes reduction in carbon content responsible for blacklightweight concrete made from POFA, lime treated sewage sludge color in POFA particles.and sodium silicate [131]. While in a study by Mohammadhusseiniet al. [129] the specific gravity of POFA was reported as 2.42; Islam 4.2.3. Size and shapeet al. [99] reported it to be 2.15. Generally, the particle size of unground POFA is larger than ground POFA. In terms of the geometry, particle shape of unground4.2.2. Color POFA is spherical and porous, whereas the particle shape of ground The color of ground POFA is dark gray, while the color is light POFA is an irregular and angular shape because it consists ofgray for unground POFA because of the exposure to low burning crushed particles [16]. The particle size of ground POFA is smallertemperature of the unburnt carbon content. The high burning tem- than cement particle size which ranges between 7.2 and 10.1 mm,
Table 2Physical properties of POFA as reported in literature.
References Specific gravity Surface area (m2/g) Blaine fineness, m2/g Median particle size, d50 (mm) Retained on sieve No. 325 (%) [117] 2.31 4582 [102] 2.42 4930 10.5 [63] 2.56 7205 1.10 0.13 [20] 1.97 82 75 [85] 2.17 19.9 17.1 [43] 2.6 13.40 1.07 [19] 145.35 20–90 nm [14] 1.89 12.92 22.78 [5] 2.33 10.1 1.5 [18] 2.36 2340 15.6 [128] 2.42 493 14.58 4.98 [60] 2.39 1228 12.30 4.30 [7] 2.22 520 [50] 2.42 4930 [117] 2.16 1977 57.13 [118] 2.2 0.172 88.4 [119] 2.42 4930 33 [86] 2.43 7.4 1.0 [3] 2.36 15.9 19.5 [129] 2.42 4930 33 [99] 2.15 17.10 [111] 2.59 7.670 1.136 2.06 [122] 2.2 1.72 [123] 2.42 4930 [88] 2.14 1.720 [16] 2.43 8.0 1.0 [61] 2.48 1.49 2.1 [124] 2.14 1.72 [125] 1.81 10 96 [127] 2.6 13.40 1.069
while the cement particle size is 10–20 mm [59]. In order to find outshape and size of POFA particles, a scanning electron microscopy(SEM) as one of the analysis tools has been used by many research-ers [19,20,43,113,132–141], most of whom concluded that GPOFAparticles are smaller in size and less porous compared to UPOFAparticles. SEM analysis for GPOFA and UPOFA can be seen in Fig. 3. Although POFA particles have different size and most of thePOFA particles have spherical shape, these still have specific grav-ity less than the cement particles [25]. Regarding the shape ofPOFA, Lim at el. [63] conducted tests on the UPOFA particles to findout morphological structure by Field Emission Scanning ElectronMicroscope (FESEM). They noted that UPOFA particles have irregu-lar, thinner, and crushed particles as shown in Fig. 4. Otherresearchers such as [128,135] reported that POFA has thinner,irregular, crushed particles together with spherical particles, with Fig. 5. Distribution curve of particle size for POFA and OPC [125].some air gaps present.
4.2.4. Fineness The fineness of POFA can be measured through the mass percent- Fineness is one of the significant physical properties of POFA. age passed or retained on sieve No. 325. Due to the fact that parti-The pozzolanic nature of the material and the hydration rate cle size of GPOFA is smaller than that of OPC, the specific surfacedepend on the fineness of POFA particles. With the finer particle area of OPC is smaller than that of GPOFA as listed in Table 3.size, the compressive strength of concrete increases directly The physical and chemical properties of the waste materials result-[20,86,126]. The UPOFA particles are larger than OPC, on the other ing from agricultural combustion residue are affected by the mate-hand, the GPOFA particles are finer than OPC as can be seen in rial treatments inside palm oil mills [49]. Some of these treatmentsTable 3. Finer POFA particle size can be obtained in ball mills are calcination temperature, acidic or alkaline pretreatments, andthrough grinding process [3,5,59]. The porosity of POFA can also the Blaine fineness of POFA which may differ from 300 to 1800be reduced by decreasing particle size through the grinding pro- m2/kg depending on the treatment method [4]. The Particle sizecess [143]. Besides, Paya et al. [144] showed that the grinding pro- of POFA and OPC influence the pozzolanic activity in these materi-cess of POFA particles leads to smaller particles with less porosity. als directly. Khalid et al. [126] claimed that grinding process by rod bar for POFA particles is the best method to get further fineness of particles with high surface area. The distribution curve of POFA particles size in Fig. 5 shows that POFA particles have smaller size than that of OPC particles. In addition to that, there is large quan- tity of unburned carbon which may affect the concrete workability by absorption of a huge amount of super plasticizer. The carbon particles in the unburnt residues can be mitigated or disposed through heating these particles at a high temperature of up to 500 °C for one hour [64,134]. Awal and Shehu [102] used various particle sizes of POFA after grinding process for half an hour, where the specific surface area was 4930 cm2/g, while the ash retained on 45 mm sieve was 10.5% only. As shown in Fig. 5, POFA particle size in normal state is larger than OPC particles. While POFA particles have size 2.99 mm, UPOFA particles have size 2.06 mm, which is considered finer than OPC particles [44]. Another study divided POFA particles into 3 sections, small, medium, and large particle sizes, which have median sizes ofFig. 4. UPOFA shape by Field Emission Scanning Electron Micrograph (FESEM) [63]. 7.4, 15.9, and 183 mm, respectively. The POFA particle fineness and
Table 3Effects of the particle size POFA on concrete properties.
the specific gravity increases whenever the grinding process is was utilized with concrete containing POFA in order to reduceused to get smaller particles. Jaturapitakkul et al. [86] discovered the quantity of super plasticizer in concrete mortar [20]. Aldah-that increasing POFA fineness leads to decrease in the compressive dooh et al. concluded that the workability of concrete increasesstrength in addition to improving resistance against sulfate attack. when using ultra fine POFA particles instead of OPC. The workabil-Lim at al. [63] used UPOFA with particle size 146% less than OPC to ity increases because of the lower carbon content and the lowerfind out impact of Nano POFA on the hydration heat and loss of ignition (LOI) of the ultra-fine POFA [56]. Concrete contain-microstructure properties of cement mortar. UPOFA particles have ing unburned carbon leads to decrease in the workability of con-high surface area than that of GPOFA and OPC particles. crete. Islam et al. studied the behavior of concrete containing POFA. They noted that the concrete workability will be reduced when replacement level of POFA is more than 30% [99]. Also, the4.2.5. Absorption of water slump is not influenced if the POFA content is less than 20%, com- One of the physical properties of cement mortar and concrete pared with Palm oil shell to produce lightweight aggregate con-paste is the ability to absorb water. A few studies have been con- crete (LWAC) without POFA [99]. Other studies, such as [4] haveducted to examine the water absorption of concrete containing concluded that increasing the amount of POFA replacement willPOFA as a replacement of cement material. One of these studies result in decreasing the concrete workability level due to thein 1990 showed that absorption of water increased whenever the increase in water demand. Yusuf et al. [43] investigated impactquantity of POFA content increased in concrete mixture [17,39]. of H2O/Na2O molar ratios on the UPOFA and ground blast furnaceIslam et al. showed that absorption of water in concrete containing slag GBFS. They noted that using Na2O in UPOFA and GBFS has pos-POFA as a replacement of cement with proportion range between itive impact on the workability of concrete, while it has negative10 and 70% increases because of the delayed hydration and ten- impact on the compressive strength of the concrete sample.dency of POFA to absorb water [99]. In a recent study to determine Another study by Ariffin et al. [113] used sodium hydroxide andwater absorption for concrete containing POFA, tests were con- sodium silicate, NaOH and Na2So3, as alkaline solution that haveducted at two ages of 28 and 90 days. Firstly, the disc specimens been mixed together for 5 min; in addition, super plasticizer waswere dried at 105 ± 5C for 2 days and left at room temperature used to achieve required workability ranging between 80 andbefore being immersed in water for curing purpose [99]. Absorp- 100 mm. They noted that the concrete paste had low workabilitytion of water was determined through observing the weight of making it not suitable to be cast in molds. Salami et al. [136]the samples at 30 min and 72 h. Lau et al. [131] noted that increase reported that to achieve the required workability, water shouldof temperature of sintering leads to decrease in the water absorp- be added to fresh concrete containing POFA. Muthusamy et al.tion of light weight concrete containing POFA and lime treated [146] used POFA as cement replacement in various percentagessewage sludge. Mixing waste polypropylene (PP) with POFA was with oil palm shell OPS as a coarse aggregate in order to benefitdone by Mohammadhusseini et al. [129], who investigated the from the waste materials generated from palm oil industry, anddurability properties of sustainable concrete compound, which mitigate the hazardous impacts to the environment. They notedconsisted of POFA and PP (carpet fiber). They noted that mixing that using POFA with 20% to 30% achieved the best results in termsPOFA and PP in concrete assists to decrease the slump value, the of workability and compressive strength. Slump tests were con-water absorption and chloride penetration. In a study by Yahaya ducted by Bashar et al. [122] to investigate the concrete workabil-[145], it was claimed that POFA with pulverized fuel ash PFA used ity; the slump value was recorded zero due to the use of highas replacement of concrete by 10%, 20%, and 30% has ability to quantity of POFA, which caused absorption of high quantity ofenhance concrete porosity due to minimizing voids within con- water resulting in decreasing the concrete workability. Awal andcrete microstructure and thus producing concrete with high den- Mohammadhusseini [123] used 20% POFA as replacement ofsity. It is known that some of the materials have good absorption cement and various proportions of waste carpet fiber (WCF) rang-of water due to the microstructure properties of their composites, ing between 0.25% and 1%. They noted that the slump valueand it is generally agreed upon that materials containing finer par- decreases from 210 mm for the mix without fiber to reach 25ticle have improved resistance to water transportation through mm with the addition of only 1% fiber into the concrete mix. Thethem. Therefore, further studies should be conducted using nano- addition of 20% of POFA also improved the workability by reducingmaterials as cement replacement such as Nano POFA, Nano FA, slump value. Islam et al. [88] conducted a study to examine theand Nano GRBA [59]. extent of concrete incorporating oil palm shell as coarse aggregate and POFA with GGBS as binder replaced in concrete. They con-5. Effects of POFA on the concrete properties cluded that the addition of fibers to concrete results in reducing the concrete workability due to large surface area and the ability5.1. Effects of POFA on fresh concrete properties to absorb high quantity of water. It is noted that there is a lack of studies in literature that focus on evaluating the workability of5.1.1. Workability concrete made by combining POFA and other plastic materials Workability is a significant characteristic to determine the con- [147] in order to fully benefit from the effects of plastic propertiescrete quality. Decrease of concrete workability occurs due to higher on the workability.amount of unburned carbon in POFA, especially when the replace-ment level of cement is high [21]. Slump test is generally used to 5.1.2. Heat of hydrationidentify the workability; Awal and Shehu studied the slump of con- Awal and Shehu noted an increase in the concrete temperaturecrete which contains different percentages of POFA in various con- value containing 50%, 60% and 70% of POFA compared to 100% OPCcrete mixtures; they found that whenever the percentage of POFA in the beginning. However, the total temperature increase reducedis increased in concrete mix, the workability also increases and the in concrete containing POFA and thus the occurrence of peak tem-slump value decreases [102]. On the other hand, Tay and Show [85] perature was delayed [102]. On the other hand, Lim at el. [63] con-noted that workability of concrete decreases with increased ducted a study on the impact of high volume Nano POFA on theamount of POFA percentages in the concrete mortar. They con- hydration temperature and microstructure properties of cementcluded that no segregation in concrete sample occurs when the mortar. They concluded that a high volume of Nano POFA reducescompacting factor value is more than 0.93 [39]. In a recent study the heat of hydration of cement mortar; it can also be used to treatby Noorvand et al. to assess the desired workability, nanosilica thermal cracking resulting from large temperature increase in36 H.M. Hamada et al. / Construction and Building Materials 175 (2018) 26–40
Table 4Compressive strength for concrete containing the POFA as replacement of cement.
mass mortar. However, there are few studies that illustrate the of concrete mixtures containing different percentages of POFA asimpact of Nano POFA along with other Nano composites of waste cement replacement as reported in the literature are shown inmaterials on the heat of hydration of cement. Therefore it is needed Table 4. It may be disadvantageous to use POFA in excessive pro-to study the use of high volume mixing Nano POFA and Nano fly portions if the structure is expected to face adverse conditions suchash and find out how it affects the heat of hydration. In addition as earthquakes [96]. In a recent study by Zeyad et al. [2], it wasto the potential utilization of POFA as cement replacement in cold shown that ultrafine POFA replacing cement can achieve compres-climates, it will also help understand its effects on the heat of sive strength higher than control samples, which may reach morehydration of cement in climate change conditions. than 90 MPa at 28 days. In 2007, Tangchirapat et al. [3] used three types of POFA in concrete; the first type was original POFA called5.2. Effect of POFA on hardened concrete properties OP, the second type was median particles (15.9 m) called MP, and the third type was small particles (7.4 m) called SP. They reported5.2.1. Drying shrinkage that the compressive strength of concrete containing OP was much Drying shrinkage is responsible for cracks occurring because of lower than in case of OPC, while compressive strength of concretethe loss of water from concrete paste, and it occurs particularly in containing 10% MP, and concrete containing 20% SP was betterdry and hot weather [85]. Many studies have been conducted to than normal concrete at 90 days. Application of Nano POFA withfind out the impact of POFA as cement replacement on drying particle size less than 100 nm has better characteristics than nor-shrinkage in concrete. Farzadnia et al. [66] investigated the effects mal cement mortar as filler and binder in cement mortar, in addi-of adding various dosages of Nano silica on short-term drying tion more than 80% cement replacement by Nano POFA in concreteshrinkage of cement mortars containing POFA as partial replace- mix can be used to achieve compressive strength more than nor-ment of cement during the first 28 days. They noted that the con- mal concrete [63]. Another study investigated the potential ofcrete samples with 30% POFA as cement replacement showed using high volume of POFA and OPC in sustainable concrete withincreased compressive strength by 15% during 7 to 28 days of various proportions in addition to the effects of these quantitiestreatment, while drying shrinkage decreased by 7.5%. At the same on the chemical and physical properties [99]. Incorporation oftime, the hydration volume of concrete mix increased. A significant 10–20% of POFA as filler in lightweight foamed concrete improvesresult from a study by Lau et al. [131] is the shrinkage index. They the compressive, flexural, and tensile strength if compared withused POFA, lime treated sewage sludge, and sodium silicate to pro- lightweight foamed concrete containing 100% sand [87]. On theduce lightweight aggregate; all these materials had been sintering other hand, Awal and Mohammadhusseini [123] conducting theirunder three temperatures of 1160, 1180 and 1200 °C. The research- research by incorporating POFA and waste carpet fiber (WCF) asers noted that the fire condition and adding more binder affects the replacement of cement in various proportions of WCF and 20%shrinkage index and water absorption. The shrinkage index can be POFA. The compressive strength was reported to range betweendefined as the percentage for changing in pellets' diameter before 38.1 and 49.1 MPa at the age of 91 days. Some researchers haveand after burning as illustrated in equation below [148]. conducted their studies by adding Nano silica to the unground POFA, for example Noorvand et al. [20], to improve the mechanical d2 d1 properties of concrete, such as increasing the compressive strengthShrinkage index ¼ 100 ð1Þ d1 and decreasing water absorption of cement mortar. More researchwhere d1 is pellets diameter before burning and d2 is pellets diam- is required in this regard to improve mechanical properties of con-eter after burning. crete using waste materials, which are freely available and cost However, adding some materials to the concrete mix is less, such as combination of Nano POFA as cement replacementexpected to change the drying shrinkage value. Other materials with egg shells [152].can be used instead of Nano silica, such as Nano clay [149,150]and Nano alumina [151] to control the drying shrinkage of 6. Discussion and conclusionsconcrete. A review of the literature on the use of POFA as cement replace-5.2.2. Compressive strength ment in the concrete production emphasizes the importance of this Most of the researchers have conducted their studies to practice towards sustainability. On the one hand, cement and con-improve the compressive strength of concrete containing POFA. crete industry has been reported to consume large amounts ofFor example, Muthusamy and Zamri [114] concluded that 20% of energy, utilize great quantities of natural resources and generatePOFA as cement replacement is the optimum level for compressive significant proportion of the CO2 in the atmosphere. Any technol-strength of concrete at 28 days. In another study by Islam et al. ogy aimed at reducing the use of cement in the preparation of con-[89], it was found that 10% of POFA is the optimum level to replace crete is going to be beneficial on all these three fronts i.e. energycement in the concrete mix. The values of the compressive strength economy, resources sustainability, and environmental friendliness. H.M. Hamada et al. / Construction and Building Materials 175 (2018) 26–40 37
On the other hand, large quantities of agricultural/industrial waste Based on the above review of the literature on the use of POFAbyproducts are being dumped in the landfill sites without treat- as partial cement replacement in concrete production, the follow-ment or re-use. The management of these wastes is a significant ing directions are suggested for the future research.environmental challenge. The use of these waste materials in theproduction of concrete can not only result in the efficient solid 1. A comparative study can be carried out between concrete con-waste management of the same but it will also help reduce the taining POFA with micro particles and concrete containinguse of cement realizing all the benefits mentioned above. POFA with Nano particles, in terms of resistance for marine Many researchers have studied the potential of using POFA as environmental conditions.partial cement replacement in concrete. The significant informa- 2. Compressive strength of concrete samples prepared with thetion gathered from reviewing the present state of this practice POFA obtained from various sources such as different factoriescan be summarized as: should be compared in order to determine if the source from where the POFA has been obtained is significant for concrete Palm oil fuel ash (POFA) is obtained as a byproduct when waste properties. materials are burnt in palm oil mills to produce electricity. 3. The use of Nano POFA along with Nano-Alumina in various pro- Grinding procedures can be applied to obtain finer varieties of portions needs to be studied in order to find out the physical POFA such as Ground POFA (GPOFA), Ultrafine POFA (UPOFA), and chemical properties of the resulting concrete. and Nano POFA. In its original size, the microstructure composition of POFA is weak and highly porous. Reducing the particle size to micro Conflict of interest and nano, however, significantly improves the performance of POFA. 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