A Review of Soil Stabilization Using Brick Kiln Dust and Pond Ash for Sustainable Pavement Subgrades

The growing demand for sustainable ground improvement has encouraged the use of industrial by-products as alternatives to conventional soil stabilizers. This review examines brick kiln dust and pond ash as materials for improving problematic subgrade soils. Studies concerning their physical, chemical, mineralogical, microstructural and environmental characteristics are synthesized, together with their effects on plasticity, compaction, California Bearing Ratio, unconfined compressive strength and permeability. Brick kiln dust is generally a non-plastic, sand- and silt-sized material containing mainly silica, alumina and iron oxides. Its addition commonly reduces liquid limit, plastic limit, plasticity index, free swell and maximum dry density, while increasing optimum moisture content and bearing capacity. Pond ash consists predominantly of sand- and silt-sized particles, has low specific gravity and negligible plasticity, and generally lowers soil plasticity and maximum dry density while increasing optimum moisture content. Most studies report improved CBR with increasing pond ash content; however, UCS behaviour varies with soil type and the presence of cement, fibres or rice husk ash. Environmental studies identify potential leaching of toxic elements from both wastes. Overall, the reviewed evidence supports use of brick kiln dust and pond ash in pavement subgrades, subject to source characterization, optimum proportioning, durability evaluation and environmental assessment.