Effect of rice husk ash admixed with treated sisal fibre on properties of lateritic soil as a road construction material

Abstract

The effect of rice husk ash admixed with treated sisal fibre on properties of lateritic soil as a road construction material was studied. The natural soil falls under A-7-6(10) classification using the American Association of State Highway and Transportation Officials (AASHTO) classification and CL (Lean Clay) according to Unified Soil Classification System (USCS). Treatment of the soil was done with Rice Husk Ash (RHA) and treated Sisal Fibre (SF) in stepped concentrations of 0, 2, 4, 6, 8% and 0, 0.25, 0.5, 0.75, 1.0% by dry weight of soil, respectively. Preliminary test, compaction test (using British Standard light (BSL) energy) and unconfined compressive strength (UCS) test were carried out. Analysis of variance was carried out using Microsoft Excel Analysis Tool Pak Software Package. Mini-tab R15 Software was used for regression analysis. Laboratory results were used to generate reliability indices using a FORTRAN based first order reliability program. Outcome of the laboratory tests show that MDD decreased from 1.85 mg/m3 for the natural soil to 1.73 mg/m3 at 0% RHA/1% SF content. The OMC increased from 18% for the natural soil to 26.5% at 6% RHA/1% SF content. The UCS increased from 100.57 kN/m2 for the natural soil to 139.38 kN/m2 at 0% RHA/0.25%SF content by dry weight of soil. The increasing trend continued to 696.63 kN/m2 at optimum 6% RHA/0.75%SF content by dry weight of soil, which met the regulatory minimum UCS value of 687–1373 kN/m2 for pavement applications. Reliability indices varied for all the variables considered with MDD and OMC having more significant effect on the UCS. Based on the results obtained, an optimum blend of 6%RHA/0.75% SF content by dry weight of soil is recommended for used as sub-based material for lightly trafficked roads.