Abstract – Palm oil fuel ash (POFA) is a waste material produced from the combustion of biomass in palm oil industry. The potential biomass as alternative fuel increases the palm oil production, leaving a pile of POFA which continues increase without any commercial return. Moreover, most of it is disposed of in landfills with uncontrolled disposal method, causing environmental impact. This study investigated the potential of POFA as a partial cement replacement in foamed concrete which having a density of 900kg/m3 and cement to sand ratio of 1:1.5. Cement is replaced by POFA at replacement levels up to 60% by the weight of the binder. Mechanical properties including compressive, flexural strength and ultrasonic pulse velocity have been investigated at the ages of 7, 14, 28 and 56 days. The results exhibited the advantages of POFA as cement replacement material and also revealed that foamed concrete with 20% POFA produced the superior 28-day strength of 3.21MPa than those obtained by the control mix of 1.33MPa. Utilization POFA in foamed concrete production promising is not only contributes to reducing cement demand but also in saving the environment. Keywords – Foamed concrete, palm oil fuel ash, cement replacement 1. IntroductionThe extreme reliance on the use of cement as a primary binder in concrete production gave a major challenge to the construction industry in a past few decades. Cement manufacturing process requires a huge energy from the fossil fuels, makes the cement industry become the most intense energy consumer of all manufacturing industries (EIA, 2013). Apart from intensively consuming the energy, cement manufacturing process also responsible for ~5% of the worldwide anthropogenic carbon dioxide (CO2) emission (Zhu, 2011), with the rate of 900kg CO2 per ton of cement produced (Benhelal et al. 2012), hence, it is significantly become contributors to climate change (Mishra and Siddiqui, 2014). In the realization of the adverse environmental effect due to the utilization of cement, the construction industries had commenced of approaches to minimize the cement use with the supplementary binder material, such as pozzolanic material. In the current knowledge development in this field, pozzolanic materials are usually produced from industrial and agricultural waste ashes. One of the preferential pozzolanic materials is a waste ash from palm oil industry.Aside from producing food commodity, palm oil industry produces a large amount of waste material such as empty fruit bunch, fiber and kernel shell. Initially, the waste materials were used as the raw material in the fertilizer industry, animal feeds industry, paper industry, composite wood industry and pharmaceutical industry (Tan, 2006). However, it is realized that the fiber and kernel shell has a good potential to be used as biomass, the alternative fuel source in palm oil steam boiler, known as “bio-diesel” fuels (Munir et al., 2015). The world global crude palm oil production increased almost threefold in the past three decades, dominates by Indonesia and Malaysia which produced around 55% and 30%, respectively, of the total 58.31 million tons in 2016 (Din, 2017). In Malaysia alone, the palm oil industry becomes an important agriculture-based industry over the last few decades. Palm oil plantation area has been growing up from 400 hectares in 1920 (Abdullah et al., 2009) to 5.74 million hectares in 2016 (Malaysian Palm Oil Board, 2016).However, regardless of the profitable potential of biomass as alternative fuel, there are problems arising from the by-product resulted from the incineration of biomass itself. The incineration process of biomass produces 5% POFA by the weight of solid waste (Sata et al., 2004). Approximately 2.6 million tons of biomass in the ash form has produced in Malaysia annually and increases every year (Usman et al., 2014). This kind of ash is simply disposed of in landfills without any commercial return which poses enormous environmental pollution (Deepak et al., 2014). A common practice for disposing of this by-product was by dumping the POFA over the premises of the mill. The uncontrolled disposal method was conducted without consideration to the surrounding environment, affecting to environmental deterioration (Khankhaje et al., 2016). POFA is usually left open and not prevented from spreading into the groundwater levels. Moreover, due to its fine particle, it can be easily carried away by wind on a hot and humid day hence causing smog (Tay and Show, 1995). To overcome the environmental problem caused by the waste, efforts have been made on the potential utilization of POFA as the building material. It has been identified that POFA has good pozzolanic properties that can be used as supplementary cementing material in the mortar and concrete mixes (Tay, 1990; Awal and Hussin 1997; Sata, et al., 2010).Physically, POFA is greyish in colour that becoming darker with the increasing the proportion of unburned carbon (Altwair et al., 2011) but can be lighter when the temperature of burning process is increased. The chemical composition indicates that silicon dioxide (SiO2) is the main chemical constituent of POFA, hence it potential to be used as an alternative binder to replace cement (Tay, 1990).The usage of POFA as a supplementary cementing material for concrete in Malaysia was started by Tay in 1990, who found that the unground POFA had a low pozzolanic property when it is used to partially replace ordinary Portland cement (OPC) due to its large particle size and porous structure. Therefore, the utilization of the unground POFA as partial cement replacement is limited until 10% by the weight of cement. Later on, many researchers revealed that the pozzolanic reaction of the POFA can be improved by grinding. Tangchirapat et al. (2007) demonstrate that ground POFA has good pozzolanic reaction as cement replacement in concrete at levels up to 30% by weight of binder, Sata et al., (2004) recommend to utilize 20% ground POFA to achieve a high strength concrete, Megat Johari et al., (2012) used the heat treatment and regrinding POFA at levels of 40%, higher than the OPC concrete, while Abdullah et al., (2006) recommend to replace cement with ground POFA at level up to 30% in aerated concrete. The potential POFA as supplementary binder material becomes an improvement of knowledge on building technology and environmental safety, since it is not only reducing the amount of POFA that is disposed into landfills but also reducing the amount of energy used and the emitted greenhouse gases released from cement production. Instead, integrating POFA in concrete enable to improve the strength and durability of concrete and also reduces the cost and energy consumed due to the less use of cement.