Comprehensive Engineering Performance of Waste Silt Stabilized with a Cement-Based Geopolymer for Road Subgrade Applications

The high water content, low strength and high compressibility of waste silt limit its direct reuse as road subgrade fill. This study evaluated a cement-based geopolymer comprising cement, ground granulated blast-furnace slag, fly ash and NaOH for stabilizing waste silt. Its engineering performance was assessed through strength, bearing, water stability, consolidation, direct-shear and permeability tests, using cement and geopolymer treatments as references. The 7 day unconfined compressive strength (UCS) of the composite reached 1428 kPa. Its soaked California bearing ratio (CBR) was 215.7% after 7 days of curing followed by 96 h of immersion, the highest among the tested groups. Composite specimens remained intact after early-age immersion, whereas reference specimens fractured or disintegrated. At 14 day, the immersed UCS reached 2155.1 kPa with 97.2% strength retention, and the coefficient of compressibility was 0.0400 MPa−1. The cohesion and internal friction angle exceeded those of the 15% cement and geopolymer treatments. Permeability was lowest among stabilized groups but remained higher than that of untreated silt. These findings support the potential use of cement-based geopolymer for improving the engineering suitability of naturally wet silt as road subgrade fill.