Engineering and mineralogical properties of stabilized expansive soil compositing lime and natural pozzolans

Black cotton soils (BCSs) were stabilized with various percentage of lime, natural volcanic ash (VA) and their combinations. The laboratory tests were performed to evaluate the influence of the stabilizers on the physical-mechanical properties of BCS. These laboratory tests included Atterberg limits, California bearing ratio (CBR), swell percent and unconfined compressive strength (UCS). The changes of minerals were also derived by performing X-ray diffraction, Infrared spectroscopy and scanning electron microscope, which were employed to explain the stability mechanism of BCS together with pH test. Results revealed that the added stabilizers improved greatly the physical-mechanical properties of BCS. The use of combinations of lime and VA showed superior results when compared with the single stabilizer. BCS can meet the performance requirements of roadbed materials referring to JTG D30-2015 just by mixing with 3% lime and 15% VA. The increased pH of the stabilized BCS indicated that solubility of the silicate and the aluminate increased, which accelerated the pozzolanic reaction between clay soils and stabilizers. The intrinsic lamellar structures of clay mineral were destructed in the reaction process. Moreover, several new minerals were produced to stabilize the soil fabric. Overall, the use of VA can reduce the consumption of lime in BCS stabilization and actualize the utilization of vast resources BCS as a low-cost roadbed material.