Strength and microstructural behaviour of soil stabilised with sewage sludge ash

Abstract

Marginal silty soils often exhibit poor engineering properties, such as low strength and high compressibility, making them unsuitable for construction applications. This study explores the potential of sewage sludge ash (SSA) as an eco-friendly stabiliser to improve the geotechnical characteristics of marginal silty soil. SSA, a byproduct of wastewater treatment plants, contains pozzolanic compounds that can enhance soil strength through cementitious reactions. The stabilisation potential of sewage sludge ash (SSA) was evaluated for marginal silty soil at dosages of 0, 5, 10, 15, and 20%. The results indicate a systematic reduction in plasticity and significant improvement in strength characteristics with increasing SSA content. The optimum performance was achieved at 15% SSA, where the unconfined compressive strength increased from 0.95 MPa (untreated soil) to 1.85 MPa, representing an enhancement of approximately 95%. Cohesion also increased substantially from 2 to 25 kPa. Compaction characteristics showed improved density response, indicating better particle packing and reduced void ratio. Microstructural and chemical analyses (SEM, FESEM-EDAX, and FTIR) confirmed the formation of a dense, cemented matrix due to pozzolanic reactions. The findings demonstrate that SSA is an effective stabilising agent for enhancing the mechanical performance of marginal silty soil, with optimum behaviour observed at 15% inclusion.