The effect of adding fly ash on the shear strength of clay soil considering the age of fly ash

Abstract The Clay soils present specific challenges in civil engineering due to their inherent weaknesses. Therefore, it is crucial to enhance bearing capacity of clay soil through stabilization methods such as chemical stabilization using fly ash. This research investigates the effect of fly ash at varying ages as stabilizing agent for clay soil on shear strength. In this research fly ash was added in proportions of 8%, 16%, and 24% by weight of dry soil, using both fly ash aged less than 1 year and fly ash aged more than 1 year. The clay soil used in this research was classified using Unified Soil Classification System (USCS). Shear strength tests were conducted in accordance with Indonesian National Standard (SNI) procedures. The results showed that fly ash aged more than 1 year consistently improves shear strength of the clay soil with increasing fly ash content, with the highest shear strength on 53.089 kN/m 2 observed in the mixture of clay soil and 24% fly ash aged more than 1 year. While, for fly ash aged less than 1 year the maximum shear strength on 34.962 kN/m 2 was achieved with 16% fly ash, then the strength decreased to 32.372 kN/m 2 with 24% fly ash.