Alkali Threshold and its Correlation with Alkali–Silica Reactivity of Coarse Aggregates

This study explores, for the first time, the use of the novel AASHTO T 416 alkali threshold test (ATT) standard to systematically evaluate the alkali threshold (AT) of 156 coarse aggregates of diverse mineralogy from the northeastern region of the United States. Combining the AT results with the reactivity classifications obtained from AASHTO TP 144-21 (T-FAST) revealed a precise portrayal of the alkali–silica reaction (ASR) susceptibility of this sample population. T-FAST detected alkali–silica reactive phases in most of the aggregates used in the study, classifying them as slow or moderately reactive. Compared to the commonly used mortar or concrete-based accelerated methods, T-FAST stood out as the most sensitive test for detecting the alkali–silica susceptibility of aggregates. The T-FAST classification and AT values of aggregates were combined to design prescriptive approaches. This study presents an example illustrating how the information from T-FAST and ATT can be used to minimize the ASR risk of concrete in the field and optimize mitigation strategies.