Valorization of Waste Pond Ash Replacing River Sand in Sustainable Mortar: Assessing Engineering Properties and Sustainability Aspects Using Life-Cycle Assessment and Analytic Hierarchy Process

In this study, river sand in cement mortar was systematically replaced with pond ash to promote circular economy principles. Two experimental series were conducted using cement–sand volumetric mix ratios of 1∶3 and 1∶6. In Series-1, river sand was replaced with pond ash in the range of 20–100%, and the resulting engineering properties were evaluated. For the 1∶3 mix, the maximum enhancement in compressive strength (29.9%), tensile bond strength (21%), and adhesive strength (24%) was observed at 30% replacement and remained comparable up to 60% pond ash content. However, higher pond ash contents led to a significant increase in drying shrinkage. To mitigate shrinkage, Series-2 involved partial replacement of cement with lime (1–7.5%) while limiting pond ash content to 20–40%. The incorporation of lime further improved strength properties by 13–62%, where the maximum enhancement in strength was observed at 2.5% lime and 30% pond ash contents. In addition, drying shrinkage was reduced by up to 4% in the mix with 7.5% lime and 20% pond ash. A life-cycle assessment (LCA) revealed a 13–16% reduction in land use for the 1∶3 mix with 40% pond ash. The analytic hierarchy process (AHP) was used to identify the most optimal mix by evaluating engineering properties, sustainability, and cost parameters. Results showed that the mix containing 30% pond ash and 7.5% lime performed best overall. This study demonstrates that the integration of pond ash in mortar not only enhances engineering properties but also reduces the cost and environmental footprint and supports sustainable construction through circular resource utilization.