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 interparticle 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.