Effect of Rice Husk Ash on the Hydraulic Conductivity and Unconfined Compressive Strength of Compacted Bentonite Enhanced Waste Foundry Sand

Abstract

A laboratory study of the hydraulic conductivity, (HC), and unconfined compressive strength, (UCS), of compacted bentonite enhanced waste foundry sand (BEWFS) treated with rice husk ash, (RHA) for possible use as liner material is presented. The bentonite enhanced waste foundry sand, BEWFS, was obtained by blending waste foundry sand (WFS) with 12% bentonite by weight of the WFS and mixing the resulting blend thoroughly to obtain a homogenous mix. RHA was added to the BEWFS in increment of 2, 4, 6, 8 and 10% respectively of the dry weight of the BEWFS. The entire blended material was thoroughly mix together to obtain sample with different content of RHA. Index tests, compaction, UCS and HC tests were carried out on the blended materials to determine the effect of RHA on the behaviour of the BEWFS. HC as well as UCS of the materials were study using three compactive efforts of British standard light, (BSLC), West African standard, (WASC) and British standard heavy, (BSHC) compactive efforts respectively. The results obtained show that addition of RHA to BEWFS affected the index properties of the material marginally where the liquid limit increased to 35 from 32 %, plastic limit reduced from 12 to 11% and plasticity index increased from 20 to 25% respectively. The HC of the material was found to increase slightly from 6.28 x 10-08 to 3.90 x 10-08, 2.64 x 10-09 to 2.07 x 10-08 and 8.55 x 10-11 to 1.83 x 10-10 m/s with addition of up to 10 % RHA content and compacted at BSLC, WASC and BSHC respectively. Similarly, the UCS was found to increase to peak values of 177.22, 288.48 and 454.26 kN/m2 at same RHA content and compactive efforts. The implication of this result is that the addition of RHA up to 10% to BEWFS slightly increase the HC but does not compromise it while the strength gain in term of UCS can be said to compensate for the slight lost in HC. It is recommended that BEWFS treated with between 8 to 10% RHA content and compacted at BSHC compactive effort can be applied as liner in engineered waste containment system.