Comparative properties of sodium sulfate-activated lime–pozzolan cements incorporating rice husk ash or corn cob ash

Growing environmental concerns associated with ordinary Portland cement (OPC) production have intensified the search for sustainable, low-carbon cementitious materials. Rice husk ash (RHA) and corn cob ash (CCA) are promising agricultural-waste-derived pozzolans for lime-based binders because of their potential to partially replace conventional cementitious materials and utilize locally available biomass residues. However, their comparative performance in separate lime-RHA and lime-CCA systems, particularly under chemical activation and sulfuric acid exposure, remains insufficiently understood. This gap limits a clear understanding of how the distinct chemical and mineralogical characteristics of these ashes influence strength development and durability in activated lime–pozzolan binders. This study examined the physicochemical characteristics, mechanical behavior, and sulfuric acid resistance of two sodium sulfate-activated lime binder systems incorporating RHA and CCA separately. In the mixtures, 50% of hydrated lime was replaced with either RHA or CCA, while sodium sulfate solution served as the chemical activator. The raw materials and hydration products were characterized using XRF, XRD, FTIR, and electrical conductivity analyses. Compressive strength, porosity, and acid resistance were assessed after 28 days of curing. The findings revealed that RHA showed greater pozzolanic reactivity than CCA, with electrical conductivity reductions of about 63% and 28%, respectively. Sodium sulfate activation markedly improved strength development, increasing compressive strength from 2.91 to 6.75 MPa for LC50 and from 3.70 to 7.91 MPa for LR50. Porosity also decreased from 12.47 to 9.23% in LC50 and from 12.32 to 7.95% in LR50, contributing to enhanced sulfuric acid resistance. The XRD and FTIR results suggest changes in portlandite-related phases and the formation of additional reaction products in the activated binders. These findings demonstrate that sodium sulfate activation effectively improves the performance and durability of agricultural ash-based lime binders for masonry and other non-structural applications.