Early age monitoring of self-compacting concrete with mineral additions

An experimental program on SCC at early age (EA), combining limestone filler with several active mineral additions (AMA), metakaolin (MC), microsilica (MS) and nanosilica (NS), was carried out to assess the temporal relations among hydration, microstructure changes and drying shrinkage and their influence on early age cracking risks. The relationships between cement reaction and microstructural changes were investigated by monitoring temperature and ultrasonic pulse velocity (UPV). The risk of early age cracking due to drying shrinkage was evaluated, monitoring water evaporation, capillary pressure and shrinkage and measuring cracking on double restrained slabs subjected to an air flow of 3 m/s during the first 6 h. The reaction process, the microstructural evolution and the physical effects of water displacement and evaporation could be followed. For a better comparison among the different compositions, the measured early age parameters were related to a reaction index (Ir,24), defined as the fraction of heat produced (accumulated plus released) with regard to the total heat at 24 h. Several relationships among the EA parameters were identified. Cracking risk due to drying shrinkage at EA increased when some events related to the early age parameters occurred simultaneously.