Desulphurisation ash recycling in soil modification for roadbed materials: a case study

A large amount of desulphurisation ash (DA) lacks effective utilisation, resulting in land occupation and environmental pollution. This study investigates DA as a lime substitute for subgrade soil modification. Laboratory tests (Atterberg limits, compaction, CBR, UCS, SEM-EDS) were conducted with 2–8% DA content, followed by a pilot project to compare the performance of DA- and lime-treated roadbeds. The results show DA reduces soil plasticity, increases optimal moisture content and decreases maximum dry density. CBR increases by 135% (8% DA) and UCS improves by 167% (6% DA, 7 days curing). Field tests confirm comparable performance between DA- and lime-treated sections. Mechanistically, DA modifies soil via cation exchange, pozzolanic reactions and hydration, forming AFt and AFm, enhancing micro–macro integrity. Excessive DA (>6%) risks expansion and performance loss. DA recycling as a soil modifier in roadbed applications can effectively save engineering costs and reduce CO2 emissions.