Traditionally fly ash (FA) has been used to replace cement as binder in the geopolymer concrete. The utilization of palm oil industrial waste materials known as palm oil fuel ash (POFA) and oil palm shell (OPS) that are abundantly available in South East Asia as binder and coarse aggregate in geopolymer concrete would give an added advantage in both the environmental and economic aspects. The mechanical properties of the OPS geopolymer concrete (OPSGC) through the use of POFA, FA, and OPS are investigated and reported. A total of ten OPSGC mixtures were prepared with varying percentages of POFA and FA such as 0, 10, 20, 40, and 100%. The specimens prepared with two alkaline solution to binder (AK/B) ratios of 0.35 and 0.55 were oven cured at 65°C for 48 hours. The experimental results showed that the highest compressive strength of 30？MPa was obtained for the mix with 20% replacement of FA by POFA and AK/B ratio of 0.55, which underwent oven curing. Further, the mix of up to 20% POFA (with AK/B ratio of 0.55) can be categorized as structural lightweight concrete. An increase of the POFA content beyond 20% decreases the mechanical properties, and hence this mix is recommended to be used. 1. Introduction Cement is an indispensable material in the development of concrete even though the conventional concrete is made of composite materials such as fly ash, ground granulated blast furnace slag, and silica fume. The use of ordinary Portland cement (OPC) was not environmental friendly and caused adverse effect, resulting from the energy intensive and greenhouse effects [1]. Davidovits [2] was the pioneer in introducing binders other than cement that could be produced by the reaction between alkaline solution (AK) and source materials that are rich in silica (SiO2) and alumina (Al2O3), commonly known as geopolymerization. In comparison with the normal concrete, the geopolymer concrete has more factors that affect its properties due to the use of AK. Sathonsaowaphak et al. [3] reported that the geopolymer mortar with AK/B ratios of 0.43–0.71 achieved compressive strength of 42–52？MPa by using FA and bottom ash as binders. Furthermore, geopolymer concrete could achieve high early compressive strength when oven cured, instead of undergoing ambient curing [4]. Since Malaysia is the second largest palm oil producer, the leftover agricultural wastes have been cumulative and caused land and air pollution in the vicinity of the palm oil factories. Many researchers have taken the initiative to utilize the palm oil industrial wastes, such as OPS and POFA, to develop
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