Assessment of blended cements effectiveness against ASR by mortar and concrete expansion tests

The effectiveness of blended cements (three pozzolanic cements - two with natural pozzolana and one with coal fly ash – and one blast-furnace cement) in counteracting alkali-silica reaction (ASR) was assessed by using both the ASTM C1567 accelerated mortar bar expansion test and the accelerated concrete prism expansion test at 38°C and 100% RH. A low-alkali Portland cement was also tested as ASR inhibitor. The results of the mortar and concrete expansion tests were analyzed through a kinetic-based model (KAMJ model) to evaluate the expansion rate constant, k, and the Avrami exponent M. These two kinetic parameters were taken as efficacy parameters for each type of inhibitor. The results of the concrete prism expansion tests were also analyzed through an innovative methodological approach and a third efficacy parameter, such as the potential minimum alkali contribution by the inhibitor to concrete (Lim), was evaluated. It was found that the values of ln(k)mb =-6.0 for mortar bars and ln(k)cp = -7.7 for concrete prisms were appropriate efficacy criteria for discriminating between deleteriously expansive and non-deleteriously expansive mortar or concrete mixes, respectively. In the case of concrete mixes, a good relationship between the efficacy parameter Lim and the kinetic parameter Mcp was found, thus demonstrating the suitability of Mcp as a criterion for ranking not expansive concrete mixes. With respect to the kinetic parameters ln(k)cp and Mcp, the efficacy parameter Lim appears to be of greater technological interest, the last being strictly related to the composition of the concrete mix.