PALM KERNEL SHELL AS A SUBSTITUTE FOR COARSE AGGREGATE IN CONCRETE WORKS

This research gives an account of the study conducted on the substitution of palm kernel shell for coarse aggregate in concrete works. It is aimed at determining the properties of palm kernel shells (PKS) that makes it suitable for concrete works in place of natural aggregate and the effects of mixing ratios on the strength characteristics of palm kernel shell concrete. A number of tests were conducted on the Palm Kernel Shells and concrete produced with palm kernel shells (PKSC). Tests conducted on PKS are; sieve analysis, fineness modulus, specific gravity, water absorption capacity and moisture content, Aggregate Crushing Value and Aggregate Impact Value tests respectively. While the tests conducted on palm kernel shell concrete (PKSC) include slump test, density, compressive strength test, modulus of rupture, splitting tensile strength test and modulus of elasticity test. Concrete mixes of 1: 2: 4, 1:1½:3, 1:2:4 were used to produce cubes, beams and cylinders which were cured for 28 days before testing. Slump test was carried out as concrete cubes; beams and cylinder were being casted. The results obtained gave the specific gravity of palm kernel shell as 1.29, thickness ranging from 0.7mm to 4.0mm, fineness modulus of 5.09 and Aggregate crushing value of 5.02% which are less than that of normal weight aggregate but within the specified range of values for light weight aggregates classifying palm kernel shell concrete as a lightweight aggregate. The palm kernel shell has bulk density of 580kg/m³ and aggregate impact value of 16.19% which is an indication that PKS can conveniently be used for structural light weight constructions as light weight aggregate. The Average moisture content of 6.12% obtained for the PKS which also falls within the specification for light weight aggregates but greater than that of the Normal weight aggregates is an indication that light weight aggregates retains moisture than normal weight aggregates.   The particle size distribution shows that palm kernel shell has a maximum grain size within the range 16.0mm and 17.0mm, although, this is less than that of normal weight aggregate being replaced, it is light enough to be used as a coarse aggregate. The highest slump value of 30cm was obtained for the nominal mix 1:1:2 which make it the most workable mix. The results show that concrete mix of 1:1:2 with compressive strength of 9.86N/mm² at 28 days hydration period is similar to previous research findings that the compressive strength of palm kernel shell concrete (PKSC) ranges from 5N/mm² to 25N/mm² based on mix design by Okafor; (1988). The density of the PKSC is lower than 2050 kg/m³ but greater than 1700kg/m³ which characterize PKSC as a lightweight concrete; higher strength can be achieved by better mix. Result of test on modulus of rupture and splitting tensile strength exhibited similar trend to that of compressive strength test in the nominal mix 1:1:2 gave the highest values of modulus of rupture, splitting tensile strength and modulus of elasticity respectively. The results show that increase in the ratio of sand to cement relative to increase in PKS contents, leads to decrease compressive strength. Hence, to produce a high strength value of PKSC will require low ratio of sand to cement.