Alkali Silica Reaction Mitigating Properties of Ternary Blended Cement with Calcined Clay and Limestone

Supplementary cementitious materials (SCMs) are widely used in concrete either in blended cements or added separately in the concrete mixer. SCMs such as calcined clays, slags or fly ashes are widely used to partially substitute plain Portland cement (PC). A particurlarly promising blend is a blend with a high level of substitution by widely available SCMs such low grade calcined clay and limestone. The use of such materials, where no additional clinkering process is involved leads to a significant reduction in CO2 emissions per ton of material. Further, blended systems have numerous well established benefits in terms of durability. ASR is the most important such issue not related to reinforcing steel. Prevention of this phenomenon is critical as sources of non-reactive aggregates are increasingly scarce. The most economical path to ASR resistant concrete is through ternary blends. Since the reaction occurs between alkalis in pore solution and reactive silica, most mitigation methods rely on lowering the alkalinity of the solution through Supplementary Cementitious Materials (SCMs). The effectiveness of SCMs in mitigating ASR is attributable to pore refinement, alkali binding by secondary hydration due to replacing part of the Portland cement, but mainly to the inhibition of silica dissolution when Al ions provided by the SCM are present in the solution. Due to yet uncommon usage in the field, the performances and mechanisms which underlie the properties of such blends are still not wholly understood. In this study, we demonstrate the performance of blends with high level of replacement (reaching 50%) of cement with limestone and calcined clay. The use of these two SCMs at such high level of replacement promise improvement of the resistance to expansion compared to PC in environmentally friendly blends. © RILEM 2015.