Performance evaluation and multi-criteria optimisation of FA–GGBS–cement stabilised pond ash for sustainable geotechnical applications

Pond ash (PA), a by-product of coal-fired power generation, presents environmental and geotechnical challenges because of its low strength, high compressibility, and weak particle bonding. This study investigates the stabilisation of PA using fly ash (FA), ground granulated blast furnace slag (GGBS), and cement to enhance its engineering performance and durability. Six stabilised mixtures (M1–M6) with different stabiliser contents were examined through compaction, California Bearing Ratio (CBR), unconfined compressive strength (UCS), and durability tests. Increasing the stabiliser content improved the overall engineering behaviour of PA. The optimum moisture content decreased from 22.14% to 18.08%, whereas the maximum dry density increased to 15.81 kN/m3. The 28-day UCS reached 1250 kPa for M5, demonstrating a marked improvement over untreated PA. Similarly, the CBR increased from 2.11% to 12.23%, indicating improved load-bearing capacity. Exposure to sulphate and acidic environments resulted in satisfactory strength retention and limited mass loss. Microstructural observations confirmed the formation of compact cementitious products and a denser internal structure. Although higher stabiliser contents increased the treatment cost, M5 provided the most favourable strength–cost balance. Entropy-based TOPSIS and EDAS analyses independently identified M5 as the best-performing mixture.