Mechanical and microstructural evaluation of lime-wheat husk ash blend for clay subgrade stabilization

Abstract

Introduction Clay soils often exhibit poor geotechnical properties, limiting their suitability for road construction. Stabilizing agents such as lime and agricultural waste provide cost-effective and environmentally friendly solutions. This study investigates the stabilization of clay subgrade soil using wheat husk ash (WHA) and lime. Methods X-ray fluorescence (XRF) analysis was conducted on WHA and clay soil to determine their oxide composition. Soil stabilization was performed with varying combinations of lime (5–7%) and WHA (1–3%). Engineering properties were assessed through Atterberg limits, compaction tests, unconfined compressive strength (UCS), and microstructural analysis using SEM-EDS. Results The natural soil exhibited a plasticity index (PI) of 25.34%, indicating the need for improvement. The soil’s oxide composition classified it as laterite, with a silica/sesquioxides ratio between 1.33 and 2.00. WHA acted as an additive, with Fe 2 O 3 + Al 2 O 3 + SiO 2 content below 70%. Stabilized soils achieved maximum dry densities (MDD) ranging from 1603 to 1798 kg/m 3 and optimum moisture contents (OMC) between 13.7% and 20.2%. Significant improvements in MDD were observed at 7% Lime + 1% WHA, 6% Lime + 2% WHA, and 5% Lime + 3% WHA, all exceeding 1700 kg/m 3 . UCS values improved across all mixes, with the highest strength of 291.71 kN/m 2 recorded for 7% Lime + 1% WHA. Microstructural analysis confirmed enhanced bonding and strength development. Discussion The combined use of lime and WHA significantly improved the geotechnical properties of clay soil, particularly in terms of plasticity, compaction, and UCS. The optimized mix design (7% Lime + 1% WHA) demonstrates the potential of agricultural waste-based stabilization for sustainable highway subgrade and subbase applications.