PENGARUH PENAMBAHAN ABU SEKAM PADI TERHADAP INDEKS PLASTISITAS PADA TANAH LEMPUNG

Abstract

Clay soil is classified as a cohesive soil with relatively low bearing capacity, as well as exhibiting significant shrink-swell behavior and high deformability, particularly in response to changes in moisture content. These properties make clay soil less suitable for direct use as a subgrade material in road construction. To address these challenges, this study was conducted using a stabilization method involving the addition of an alternative additive material in the form of rice husk ash, a biomass waste rich in silica content with potential application as a soil stabilizer. The research was carried out in two main stages: physical characterization tests and consistency limit (Atterberg limits) tests, aimed at evaluating changes in plasticity properties due to rice husk ash addition. The test results indicate that the addition of rice husk ash contributes to a reduction in the liquid limit of the clay soil, from 59.62% in its natural state to 56.65% at a 3% mixture, and further down to 45.28% at a 9% mixture. This reduction is attributed to microstructural densification of the soil, influenced by pore-filling effects and the binding of clay particles by ash particles. Concurrently, the plastic limit increased from 29.73% to 31.47% at a 3% mixture and to 38.08% at a 9% mixture. This phenomenon reflects ionic reactions between calcium in the ash and clay minerals, which initiate flocculation and aggregation of soil particles. As a result of the reduced liquid limit and increased plastic limit, the plasticity index decreases, indicating a reduction in soil cohesion and an improvement in plastic stability. Overall, the utilization of rice husk ash has been proven effective in enhancing the plasticity characteristics of clay soil and demonstrates the potential for reusing agricultural waste materials as alternative soil stabilizers in civil engineering applications.