Performance of Expansive Soil blended with Waste Marble Dust and Natural Pozzolana for Road Subgrade

This research examined the effects of Natural Pozzolana (NP) on expansive soil blended with Waste Marble Dust (WMD), focusing on improving its engineering properties. The NP was sourced from Kanzenze, Rubavu, Rwanda, oven-dried, ground into powder, and sieved to 0.452 mm. WMD was added to the soil in 5% increments (5%-30%), with the optimal dosage found at 25%. The California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) tests showed that untreated soil had a CBR of 1.1%, UCS of 93.213 kN/m², a Plasticity Index (PI) of 39.5%, and linear shrinkage of 15.21%. Adding 25% WMD increased the CBR to 4.82% and UCS to 163 kN/m² after 7 days of curing, reaching 190 kN/m² and 219.5 kN/m² after 14 and 28 days, respectively. PI decreased to 25.38%, and linear shrinkage reduced to 13.93%. However, these values were below the standards of Kenya's Pavement Guidelines. Incorporating 20% NP also enhanced soil properties, with CBR increasing to 10.4%, UCS reaching 184.76 kN/m² after 7 days, 223.38 kN/m² after 14 days, and 371.819 kN/m² after 28 days. PI decreased to 13.93%, and linear shrinkage dropped to 11.5%. These results met the requirements of 15% PI and 5% CBR. The study results suggest that the combined use of WMD and NP significantly enhances the strength of expansive soils.