The pore structure and autogenous shrinkage of high-performance concrete with ternary binders

Most modem high performance concretes contain supplementary cementitious materials such as silica fume, slag or fly ash. However, highly reactive silica fume adversely affects the autogenous shrinkage properties and increases the risk of cracking at early ages. In order to compensate for the adverse effects of silica fume, ultrafine fly ash was also incorporated into the binder phase of the concrete. Part of cement and part of silica fume were replaced by ultrafine fly ash and early age properties of the mixtures with these ternary binders were compared. Strength gain was followed by compression testing and, autogenous shrinkage properties were measured under free conditions. It is seen that ternary binders can decrease the autogenous shrinkage strains, while keeping the early strength gain at a comparable level. Results of the thermogravimetric analysis showed that mixtures with ternary binders had a similar hydration rate compared to the mixture with silica fume only. Mercury intrusion porosimetry proved that the amount of finer pore volume, one of the major reasons of autogenous shrinkage, was decreased with the incorporation of ultrafine fly ash.