ACI 225.1T-20 PDF Download

The ACI 225.1T-20 standard addresses the issue of alkali-silica reactivity (ASR) in concrete. ASR is a reaction between alkalies in the concrete and certain aggregates that can cause expansion and damage to structures.

In the past, it was believed that limiting the alkali content of cement to below 0.60 percent by mass could reduce the risk of ASR. However, further research has shown that this limit may not effectively control ASR in all situations. The new standard acknowledges that factors such as the reactivity of the aggregate and the amount of alkalies present in the concrete play a more significant role in predicting ASR than the cement alkali content alone.

The removal of the optional alkali limit in the standard specifications for Portland cement reflects this updated understanding. It recognizes that additional measures, such as using low-alkali cement, selecting non-reactive aggregates, or employing supplementary cementitious materials, may be necessary to mitigate the risk of ASR. By removing the specific alkali limit, the standard allows for more flexibility in choosing appropriate strategies to address ASR based on the specific characteristics of the concrete mixture and the aggregates being used.