Influence of synthetic aggregates on expansion due to alkali–silica reaction

Alkalis that are present naturally in cement react expansively with some siliceous aggregates, causing cracking in concrete. This paper investigates the effects of replacing a small amount (5%) of reactive aggregate in mortar with a synthetic aggregate on expansion under accelerated testing conditions for alkali–silica reaction (modified ASTM C 1260). It was found that 5% replacement of sand with an inert aggregate (sintered alumina) had no effect on expansion; replacement with a lightweight aggregate (sintered, pulverised fly ash) decreased expansion by 30%; and replacement with a sintered microcrystalline silica aggregate reduced expansion by 80% during the 14-day period monitored by the test.