Degradation of Silicate Glass Used as Fine Aggregate in Concrete

ABSTRACT

A large body of literature has previously reported on the deleterious expansion which occurs if recycled soda lime silica (SLS) bottle glass is used as fine aggregate in concrete cast with ordinary Portland cement (OPC). It is theorized that this expansion is due to a propensity for the formation of a volume‐expanding alkali–silica reaction (ASR) gel within microcracks on the aggregate particles due to interplay between SLS, OPC, and environmental water, which leads to cracking and premature material failure. However, while the mechanisms for ASR gel formation have been extensively studied, there is a lack of understanding on how specific interactions between the reactive silicate glass and the microcrack geometry lead to such reactive enhancement. In this work, we demonstrate that SLS window glass which does not exhibit ASR gel‐induced expansion when used in an accelerated mortar bar test will still preferentially form ASR gel within the constrained geometry of a model crack test (MCT). Fused silica, in contrast, was found to undergo bulk‐scale cracking and significant expansion after a single day of accelerated mortar bar testing, and also exhibited significant ASR gel growth in the MCT. These results suggest that the limited expansion for the sample with SLS glass in the accelerated mortar bar tests is a by‐product of the lack of microcracks, rather than an inherent chemical resistance of the SLS glass used.