ECO-FRIENDLY STABILIZATION OF BABOLSAR COASTAL SAND USING CEMENT, AGRICULTURAL WASTE ASH AND CARBON FIBERS

Abstract

Sandy soils in coastal regions often exhibit low strength and instability, posing challenges for ge-otechnical applications. This study examines the combined influence of cement, carbon fibers, and rice husk ash (RHA) on the shear strength of sand from the Babolsar coastline. Specimens were pre-pared with varying cement contents (1–2%), RHA proportions (3–7%), and fixed carbon fiber dosag-es (0.1% and 0.15%), then tested under direct shear after different curing periods. The mixture con-taining 2% cement, 7% RHA, and 0.15% carbon fiber displayed the highest strength, with an internal friction angle of 30.81° and cohesion of 0.17 kg/cm² after 7 days. Strength gains persisted over time, with friction angle increases of 3.45–13.25% and cohesion gains of up to 9.52% compared to day 1. Microstructural analyses using XRD and SEM revealed the formation of C–S–H, calcite, and crystal-line silica, alongside dense packing, uniform fiber dispersion, and reduced porosity. These findings confirm that incorporating cement, RHA, and carbon fibers can synergistically enhance coastal sand stability, offering a sustainable and cost-effective improvement method for short-term engineering applications