In the palm oil mill, the boiler ash (from PPF, PKS and EFB) creates a lot of envi­ronmental problems as their disposal methods are unsafe. The ash is normally dumped at landfills without any sustainable means of utilising it. Recent studies have reported many different ways of transforming the palm ash to value-added products such as concrete materials which are used in buildings. Moreover, the quantity of OPW which is not utilised by the boiler as fuel can also be combusted into ash and used for as concrete material. One important benefit of using OPW as concrete materials is that they are organic and therefore do not contaminate or leach out to produce toxic substances once they are bound in concrete matrix.

Ground palm ash would make an excellent pozzolanic material which can be used as a cement replacement in concrete (Chandara et al. 2010; Yin et al. 2008). The replacement of Portland cement type I by 30% palm fuel ash (from EFB, PPF and PKS) gave the compressive strengths of concrete at 90 days higher than that of concrete made from Portland cement type I alone (Tangchirapat et al. 2007). Ismail et al. (2011) have investigated into the residual compressive strength of concrete containing OPW ash after exposure to elevated temperatures and subsequent cool­ing. The residual performance was found to be higher in OPW concrete than in the normal concrete. Concrete containing OPW as aggregate materials therefore serves as potential building concrete for constructing pavements, floorings and walls.

PKS is used as coarse aggregate in road binder course in order to add more strength to the asphalt concrete (Yusoff 2006; Teo et al. 2007). Concrete with PKS as coarse aggregates has been proven to exhibit good properties in terms of com­pressive strengths, workability and density (Basri et al. 1999; Shafigh et al. 2012). Recently, a new method has been investigated into by Shafigh et al. (2011) who showed that it is possible to produce grade 30 PKS concrete without the addition of any cementitious materials. Tay and Show (1995) have concluded that the work­ability, setting times and soundness test results of concrete containing ash from EFB are satisfactory with no segregation. Their results also indicated the high possibility of blending the ash with small amounts of ordinary Portland cement for concrete making without detrimental effects on long-term strength property. Blended cement paste with high fineness OPW ash possesses a higher compressive strength than that with coarse OPW ash (Kroehong et al. 2011).