The role of residual cracks on alkali silica reactivity of recycled glass aggregates

Despite its environmental and economical advantages, crushed recycled glass has limited application as concrete aggregates due to its deleterious alkali-silica reaction. To offer feasible mitigation strategies, the mechanism of ASR should be well understood. Recent research showed that unlike some natural aggregates, soda-lime glass undergoes ASR within cracks in the interior of glass particles and not at glass-paste interface. These cracks originate during bottle crushing and propagate further by ASR. This paper examines whether glass aggregates could become innocuous if these cracks are healed by annealing or when the crack widths are smaller than a critical size. The results confirm that glass annealed at 650 °C for 40 min or particles containing cracks smaller than approximately 2.5 μm can be considered innocuous based on ASTM C1260. Also larger glass particles contain significantly higher percentages of reactive microcracks which may explain why ASR expansions are lowered by reducing the size of glass aggregates.