Determining the optimum percentage of natural pozzolan to reduce the alkali–silica reaction in concrete

The use of natural pozzolans as partial replacements for cement or fine aggregate offers a sustainable pathway to enhance the environmental performance of concrete. However, their effectiveness depends on controlling the alkali–silica reaction (ASR), a major durability concern arising from the interaction between reactive silica in aggregates and the alkaline pore solution of cement paste. This study evaluates the potential of a natural pozzolan obtained from the Raviz region of Kerman province, Iran, as a supplementary cementitious material (SCM) for mitigating ASR in mortar. Mortar mixtures were prepared with 0%, 2%, 4%, 6%, 8%, and 10% pozzolan replacements by weight of cement and tested in accordance with ASTM C1567 after immersion in 1 N NaOH solution. Expansion measurements were recorded at 4, 7, 10, and 16 days to assess ASR-induced deformation. Results showed a progressive reduction in expansion with increasing pozzolan content up to 8%, beyond which no further improvement occurred. The optimum replacement level of 8% significantly reduced ASR expansion by about 27% while maintaining material performance, demonstrating the feasibility of using Raviz pozzolan as a sustainable local SCM for durable concrete production.