An Investigation on the Influence of Bagasse Ash and Zycobond on Improving the Strength Characteristics of Expansive Soil as Subgrade for Flexible Pavements Under Cyclic Pressures

Abstract

Expansive soils pose a serious threat to transportation infrastructure when used as pavement subgrade material. Because of their pronounced tendency to swell and shrink with changing moisture conditions, these soils give rise to differential settlement, surface cracking, heaving, rutting and premature deterioration of pavements. Such problems lower ride comfort, raise vehicle-operating costs, demand more frequent maintenance, disrupt traffic flow and shorten pavement service life, ultimately affecting both the economics and safety of road networks, particularly in regions that experience marked seasonal changes in moisture. In the present work, a highly expansive soil was stabilized using sugarcane bagasse ash (SBA) together with Zycobond, and the resulting improvement was assessed through geotechnical and microstructural testing. Untreated soil and soil treated with different proportions of SBA and Zycobond were examined in the laboratory to identify the optimum blend. The best performance was obtained with a combination of 20% SBA and 1.5% Zycobond. Under this treatment, the differential free swell fell from 110% to 20%, the liquid limit dropped from 66.51% to 52.00%, and the plasticity index reduced from 29.17% to 11.95%, shifting the soil classification from CH to CI. Maximum dry density rose from 1.588 to 1.780 g/cm³ while optimum moisture content fell from 27.88% to 16.82%. Soaked CBR values increased from 2.0% to 7.56%, pointing to a marked gain in bearing capacity. Results from cyclic plate load tests reinforced this trend, with the failure load rising from 900 kPa for the untreated soil to 2600 kPa for the stabilized blend, achieved at a lower settlement. X-ray diffraction (XRD) patterns showed a decline in expansive clay minerals and the appearance of stable cementitious phases, confirming that pozzolanic reactions were responsible for the observed gains in engineering behaviour. Overall, the combined use of SBA and Zycobond offers a sustainable, economical and environmentally sound approach for stabilizing expansive subgrade soils in pavement and foundation applications.