PERFORMANCE OF COMPRESSED EARTH BLOCKS STABILISED WITH CEMENT AND PALM KERNEL SHELL ASH COMPOSITIONS

Abstract

Cement is the conventional stabiliser used for Compressed Stabilised Earth Blocks (CSEB), which has been in use as a building material over the ages. However, its production causes environmental pollution. Hence, efforts have been directed at finding partial replacements for it with domestic, industrial and agricultural wastes such as Palm Kernel Shell Ash (PKSA). The PKSA has been used to partially replace cement in concrete blocks but information on its use in CSEB is sparse. Therefore, the potential of using PKSA as a supplementary cementitious material in CSEB was investigated. The physical properties (specific gravity, moisture content, liquid limit, plastic limit and plasticity index) of lateritic soil used for the production of the CSEB were determined, as well as the chemical composition of PKSA. The CSEB (100x100x100mm) cubes were produced from lateritic soil, cement, PKSA and water at 11.5% water to mixture of soil and binder. The cement-PKSA mixes were stabilised at 8:2, 6:4, 4:6, 2:8, while the control mix was stabilised at 10.0% cement. The mixes were compacted with a pressure of 6 MPa for the production of 66 Control Mix Blocks (CMB) and 528 Cement-PKSA Blocks (CPB). The blocks were cured at 100% humidity followed by 28 days secondary curing. Wet and Dry Compressive Strengths (WCS and DCS), Block Dry Density (BDD) and Total Water Absorption (TWA) of the blocks were determined according to standards. Data were analysed using a t-test at α0.05. Specific gravity, moisture content, liquid limit, plastic limit and plasticity index values were 3.3, 17.7, 53.4, 59.5 and 6.1%, respectively. The average chemical compositions of PKSA were 46.6 SiO2, 13.5 Al2O3, 11.8 Fe2O3, 0.5 SO3, 1.0 MgO, 1.5 K2O, 1.4 Na2O and 9.8% CaO, while specific gravity was 2.0. The WCS for CMB was 8.99 MPa, while CPB were 9.84, 7.51, 5.29, 3.21 MPa for 8:2, 6:4, 4:6, 2:8 mix proportions, respectively. The DCS for CMB was 9.84 MPa and at 8:2, 6:4, 4:6, 2:8 mix proportions, CPB were 11.79, 9.66, 7.33, 4.61 MPa, respectively. These values fare better than the 3.00 and 4.12 MPa recommended standards for WCS and DCS, respectively. The BDD for CMB was 2128±0.33 kg/m3, while CPB ranged from 2102 to 2132 kg/m3 for 8:2, 6:4, 4:6, and 2:8 mix proportions, respectively, all within the required minimum standard of 2000 kg/m3. The TWA for CMB was 7.5% and ranged from 6.8 to 9.8% for CPB. These values were lower than the 12% maximum standard. A 44% decrease in TWA with variation in cement content from 2 to 8% was attained; with a 2.3% increase in density. An increase in BDD led to an increase in WCS for both CMB and CPB (100% positive correlation). An increase in BDD led to a 44% decrease in TWA for both CMB and CPB (strong negative correlation). Palm kernel shell ash is a suitable partial cement replacement in the production of compressed stabilised earth blocks, with the best performance obtained at 4% PKSA and 6% Cement.