Properties and optimisation of SLUBRITE: a sustainable laterite replacement for subgrade applications

The depletion of natural laterite and the growing volume of industrial byproducts such as Waste Paper Sludge Ash, Water Treatment Sludge, and Bottom Ash highlight the need for sustainable subgrade alternatives. This study presents SLUBRITE, a synthetic laterite replacement developed by blending these waste materials with Ordinary Portland Cement. Physicochemical and microstructural analyses confirmed the pozzolanic potential of the materials, resulting in improved strength development and long-term durability through the formation of a stable solid matrix. SLUBRITE exhibited favourable geotechnical properties, including good plasticity, compaction behaviour, and an alkaline pH range of 8.5 to 12.8, effectively neutralizing the acidity of natural laterite. Mechanical testing demonstrated superior performance, with an unconfined compressive strength of 7077 kilopascals and a California Bearing Ratio of 98.20 percent, significantly outperforming natural laterite. Response Surface Methodology optimized the mix design, identifying 20 percent Waste Paper Sludge Ash, 20 percent Water Treatment Sludge, and 60 percent Bottom Ash as the most effective blend. This composition achieved 100 percent waste substitution, satisfied subgrade performance criteria, and produced a desirability score above 0.9. The findings establish SLUBRITE as a high-performance, cost-effective, and environmentally sustainable alternative, supporting circular economy practices, reducing landfill dependency, and contributing to national waste valorisation goals.