EFFECT OF CASHEW NUT SHELL LIQUID ON COIR REINFORCED SOIL – AN EXPERIMENTAL INVESTIGATION

Abstract

Weak soils frequently require stabilization to meet the increased strength and durability demands of their intended applications. Such porous soils are widely distributed across Northern and Southern India. During road construction, enhancing the strength of weak subgrades is crucial, as this directly influences both the required thickness and the overall service life of the pavement. We engineers have to minimize pavement thickness to lower the construction cost and conserve conventional building materials for enhancing the stability of subgrade soil, using coconut fibre for this enhancement is highly an advantage since it offers economical, ecofriendly, efficient and accessible characteristics. Bio-degradable fibres act as a super alternative for soil stabilization but also comes with challenges. One of those challenges is its susceptibility to biodegradation and Hydrophilic nature which restricts its broader application in geotechnical engineering. Nevertheless, this challenge can find a solution in modifying the fibre surface with proper chemical treatment which converges with sustainability. This research studies the effect of treating the coil fibres with cashew nut shell liquid, an affordable agricultural by product. Hence coating these fibres with natural biopolymer that is CNSL renders the surface into hydrophobic thereby reducing moisture and fungal or microbial attack. This iii enhances the durability of the fibre and long-term retention of the subgrade. The study evaluates the engineering properties of the soil (poorly graded sand (SP)) reinforced with coir fibre and CNSL coated coir fibre. Laboratory tests including Proctor, Direct shear and CBR were performed using 3cm long coconut fibre with varying percentages (0.1%, 0.2%, 0.3%). Compaction tests across different fibre contents established the specific characteristics of the compaction curves, while Direct Shear tests analysed the comparative strength profiles. Results indicated that untreated fibres, owing to their lightweight nature and higher water absorption capacity, exhibited a higher optimum moisture content (OMC) and a lower maximum dry density (MDD) than the CNSL treated variants. The shear strength parameters of the reinforced soil samples were quantified through apparent cohesion and the interface friction angle. Experimental findings demonstrated that CNSL-treated coir geotextiles significantly enhanced these interface shear strength parameters. Ultimately, the CNSL coating diminished the interaction between the fibres and water, thereby effectively decelerating the biological degradation process of the coir material.