Engineering properties of expansive soil stabilized with barley husk ash and lime: case study of Jimma town subgrade soils.

Expansive soils are a prevalent issue in road construction, particularly in regions like Ethiopia. They pose significant challenges due to drastic shrink-swell behavior. Traditional stabilizers such as cement and lime are effective but costly and raise environmental concerns. This necessitates exploring more sustainable, locally-sourced alternatives. This research explores using Barley Husk Ash (BHA), an agricultural byproduct, as a pozzolanic additive to stabilize expansive soil from Jimma, Ethiopia. The untreated soil had an initial PI of 39% and a CBR of 0.8%. The study had two phases. First, optimal lime content was determined by treating the soil with varying lime percentages (0-20%) in 5% increments. Second, this lime content was combined with BHA in similar 5% increments (0-20%). Adding 10% lime reduced the PI to 22%, increased the CBR to 9.72%, and raised the Unconfined Compressive Strength (UCS) to 137 kPa. This met the Ethiopian Roads Authority (ERA) S4 subgrade standard (CBR>5%). Adding 10% BHA to the 10% lime-stabilized soil further improved performance. The PI dropped to 18% and the CBR increased to 18.42%, qualifying the soil for the higher S5 subgrade classification (CBR 15%-30%). Microstructural analysis using SEM confirmed these findings. The BHA-lime blend created a denser, more cohesive soil matrix with enhanced inter-particle cementitious bonding. This explains the improved strength and reduced swell potential. The mean porosity also decreased from 17.33% to 6.74%. This research validates a 10% lime plus 10% BHA blend as a highly effective, sustainable, and locally available solution for modern road construction.