: Expansivity mitigation of black clay soil using agro-waste based inorganic polymer cement for flexible pavement subgrade

Abstract

The use of cement for deficient black clay soil (BCS) improvement is a long time practice. But given the huge negative contribution of cement to carbon emission and climate change and its high demand by the construction industry that led to its scarcity and expensiveness, there is a need for an alternative binder to cement. The possible use of two biomass based inorganic polymer cements (IPC) was investigated herein. Rice husk ash (RHA) and sawdust ash (SDA) from biomass were used for this study. All experimental tests were carried out in accordance with British Standards. Soil samples were mixed with ash-IPC in steps of 0, 5, 10, 15 and 20% of the dry weight of the natural black clay soil. Results indicated significant improvement in all the geotechnical properties tested. The percentage passing the #200 sieve was reduced from 76.25% to 24.34% and 35.51% by RHA-IPC and SDA-IPC respectively at 20% treatment. Peak UCS values of 1123.56 and 954.28 kN/m2 were respectively recorded for RHA-IPC and SDA-IPC treatments at 20% IPC content and at 28 days curing period. That represents an 813% increment in UCS value at 20% RHA-IPC content and 675% for SDA-IPC. The CBR value increased by 1500 and 1233% respectively for RHA-IPC and SDA-IPC treatments. The Scanning electron microscopy and energy dispersive X-Ray spectrometer EDS results indicated obvious improvement in the particle sizes in the microstructure of the treated BCS. The achieved improvements in all parameters tested are indications that the expansivity of the weak BCS has been reduced to acceptable levels and the effectiveness of using RHA-IPC and SDA-IPC for subgrade soils improvement.