APPLICATION OF SCHEFFE’S MODEL IN COMPRESSIVE STRENGTH OPTIMISATION OF CONCRETE USING RICE HUSK ASH AS PARTIAL REPLACEMENT OF CEMENT

ABSTRACT

This study investigates the economic application of scheffe’s model in compressive strength optimisation of rice husk ash-cement concrete. Physical properties of the aggregates such as specific gravity, bulk density and sieve analysis were determined. Specific gravities of fine and coarse aggregates were 2.64 and 2.66 respectively. The bulk densities were 1745kg/m3 and 1660kg/m3 respectively. From the sieve analysis test, the sand belonged to zone 2 and well graded with coefficient of gradation of 1.04. Ninety 150mm x150mm x 150mm cube specimens were produced for the compressive strength test. Model was fitted to data obtained on the compressive strength and mathematical model was developed based on Scheffe’s model. The formulated model was tested for adequacy at 95% level of confidence using t-statistic and was found to be adequate. The compressive strength of concrete was observed to decrease with increase in the percentage replacement of cement with rice husk ash. The reduced value of the compressive strength may be due to lower specific gravity value of rice husk ash compared to that of cement. The blending of the two materials caused a reduction in strength value of the end product since specific gravity is strength related. The reduced compressive strength value may also be due to the fact that rice husk ash has less binding properties compared to cement. After 28 days of water curing, the concrete gave an average optimum compressive strength value of 22.84N/mm2 corresponding to a mix proportion of 0.95, 0.05, 1, 2 (cement, rice husk ash, sand, granite) at a water-cement ratio of 0.4.This compressive strength value obtained at 5% replacement is within the recommended value required for plain concrete works, lean concrete, simple foundations, masonry walls and other simple construction works in low-cost housing constructions.