Hydration mechanism of cement-based composites incorporating ground pond ash: Towards sustainable building and infrastructure solutions

The growing emphasis on sustainability and decarbonization in the building and infrastructure industry has driven demand for alternative cementitious materials, such as pond ash, in cementitious applications. Pond ash, composed of excess coal fly ash (CFA), a sediment of fine coal particles and water, is typically disposed of in ash ponds. While it can potentially enhance pozzolanic activity and reduce the uptake of clinker in cement production, its utilization remains limited due to off-standard classification and lower reactivity. Hence, this study aims to optimize the processing of raw pond ash (RPA) into ground pond ash (GPA) using ball mill grinding and to characterize the hydration mechanism of cement-based composites incorporating GPA. The characterization process involved comprehensive mechanical, chemical, and microstructural analyses. The two most optimized GPA-based composite cementitious binders from different strength classes, OPC80-GPA20 (20% GPA as OPC substitution) and OPC55-GPA45 (45% GPA as OPC substitution) were compared to OPC100-GPA0 (control) binder, offering reduced OPC content and enhanced environmental sustainability. Strength analysis revealed a 33% to 51% increase in compressive strength from RPA to GPA at 2, 7, and 28 days, confirming the enhanced feasibility of GPA-based cementitious binders. XRD results at 28 days revealed higher substitution between portlandite and C-S-H gels in OPC80-GPA20 than in OPC100-GPA0, with reduced C 3 S and C 2 S. TGA results supported this finding, showing portlandite contents of 2.48%, 2.40%, and 1.67% for OPC100-GPA0, OPC80-GPA20, and OPC55-GPA45, respectively, which corresponded to C-S-H gel formations of 3.62%, 4.29%, and 3.45%. Additionally, environmental and economic analyses indicated that OPC80-GPA20 and OPC55-GPA45 reduced CO 2 emissions (in kg.CO 2 /m 3 ) by 18% and 41%, and production costs (in MYR/m 3 ) by 18% and 40%, respectively, compared to OPC100-GPA0. With effective grinding treatment and optimized ratios, pond ash can serve as a viable and sustainable cement alternative, aiding in decarbonization within the building industry. • Hydration mechanism of cement-based composites incorporating ground pond ash (GPA). • Enhancement of raw pond ash’s feasibility through the ball mill grinding process. • Synthesis of GPA-based cement composites conforming to codal requirements. • Experimental findings were validated through chemical characterization.