Use of a natural pozzolan to control alkali–silica reactivity inpolylithological fluvial gravels from the province of Tucumán,Argentina

This study evaluates the effectiveness of a natural zeolite-bearing vitreous breccia from southern Mendoza (Argentina) as an active mineral addition (AMA) for mitigating the alkali–silica reaction (ASR) in a reactive coarse aggregate sourced from a fluvial basin in northwestern Argentina. Accelerated mortar bar tests (IRAM 1674) with 10%, 20%, and 30% cement replacement indicate that only the 30% substitution effectively suppresses expansion below the 0.10% limit and prevents microcracking. Petrographic observations and SEM-EDS analyses reveal the dissolution of Si and Al from the pozzolan, Ca diffusion from the cement matrix, and the formation of early C-(A)-S-H phases, confirming its pozzolanic activity. The results demonstrate that this natural pozzolan provides an effective strategy for mitigating ASR in reactive fluvial aggregates from the region.