The Effect Of Water/cement Ratio On Compressive Strength Of Palm Kernel Shell Concrete At 1:2:4 Nominal Mix

2.4    PHYSICAL PROPERTIES OF PALM KERNEL SHELL (PKS)
Palm kernel shells are organic waste materials obtained from crude palm oil producing factories in Asia and Africa (Alengaram et al; 2010). In recent years, many research works on use of PKS are lightweight aggregate (LWA) to produce lightweight aggregate concrete (LWAC) have been carried out by Abdullah, (1984), Okafor, (1988), Mannan and Ganapathy, (2002), mannan et al; (2004), Olanipekun et al; (2006) Alengaram et al; (2008), Mahmud et al; (2009) and jumaat et al; (2009). Past research work carried out on PKS focused on using the shells of different sizes above 3mm after removing smaller particle less 3mm. the use of PKS as lightweight aggregate, structural grade concrete of compressive strength of about 15 to 25mpa could be produced (Mannan et al; 2002).
Generally, PKS possesses hard characteristics as coarse aggregates and there have been attempts by Abdullah (2003), Okafor (1988), Okpala (1990) and Basri et al., (1999) to use PKS as coarse aggregates replacing normal granite aggregates traditionally used for concrete production. When density of concrete is lower than 2000kg/m3, it is categorized as lightweight concrete. Thus the palm kernel shell concrete with density which varies from 1700 to 2050 kg/m3depending on factors such as type of sand and palm kernel shell content (Mahmud et al; 2008) is categorized as lightweight concrete (Okpala, 1998, 1990). Lightweight aggregate has unit weight less than 1120kg/m3 palm kernel shells consist of 60-90% of the particles in the range of 5-12.5mm Okafor, (1988) and Okpala, (1990). The specific gravity of PKS varies between 1.17 and 1.37 while the maximum thickness of the shell was found to be about 4mm.
According to Neville A.M. (1995), the specific gravity of the palm kernel shells does not place it in category of common rock groups whose gravities range from 2.62-3.00. however, it showed same porosity as granite, quartzite, far above limestone. The arrangement of the shells as they touched each other would have accounted for this. Dry density values place the palm kernel shells in the same category as light weight aggregate especially pumice, scoria or vermiculate for natural and fly ash and clinker for processed aggregates.
Aragbaiye, (2007) conducted a project on the use of palm kernel shell as a composite material. The report shows that the average specific gravity of the PKS is 1.169 which is lighter compared to the specific gravity of the granite which is 2.62 this makes it suitable for the production of lightweight concrete. The particle size distribution of PKS according to him has a maximum grain size of 14mm. it is smaller compared to the granite which is to be replaced but still large enough to be used as a coarse aggregate. The compressive strength test result shows that the average compressive strength obtained decreases as the percentage of PKS increases. PKS would not give a stronger concrete than granite but would produce concrete of considerable strength depending on the specific required (Joe, 2008).