Impact of rice husk ash on swelling and durability of expansive soils

This study evaluates the impact of rice husk ash (RHA) on the strength, durability, swelling potential, and microstructure of expansive soils with varying liquid limits. Four types of natural soils (S1, S2, S3, and S4) were treated with optimum RHA contents: 7 %, 10 %, 12 %, and 15 %, respectively. Several laboratory tests were conducted on both natural and treated soils for each soil type, including unconfined compressive strength (UCS) at 0 and 28-day curing, wet-dry, and freeze-thaw cycles (mass loss, UCS, durability index), free swell (FS), swelling pressure (SP), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis. The results indicated that the addition of RHA to Soil 1 and Soil 4 significantly increased UCS, with improvements of 74 % and 192 %, respectively, after 28 days of curing. Additionally, under wet-dry and freeze-thaw cycles, RHA-treated soils showed reduction in mass loss, DI, and more cycles compared to natural soils, with the best performance at optimum RHA contents. Moreover, FS and SP for Soil 4 with 15 % RHA decreased significantly to 6.6 % from 15 % and to 99.9 from 187.4 kPa, respectively. Whereas, SEM, FTIR, EDS, and XRD indicated a transformation from porous, weakly bonded structures in natural soils to dense, cohesive in RHA-treated soils, highlighting the microstructural improvement. Based on the results, the study reveals that RHA is an effective, sustainable stabilizer, improving strength, durability, and swelling resistance. Also, the research contributes new insights by correlating RHA optimum ratios with the liquid limit (LL) comparison and by correlating these microstructural changes with durability and swelling reductions.