Early age monitoring and hardened properties of SCC with limestone filler and active mineral additions

Abstract

An experimental program on SCC with limestone filler and three active mineral additions (AMA), microsilica (MS), nanosilica (NS) and Metakaolin (MC), was carried out to evaluate their influence during early ages and in the hardened state. The aim was to characterize SCC further than the usual workability and mechanical parameters, in the understanding that the main microstructural changes in the material occur during the first hours and that early age cracking, porosity, pore size and permeability can compromise SCC durability. In-situ temperature, ultrasonic pulse velocity, mass loss and free drying shrinkage of samples subjected to a wind flow were simultaneously monitored for 24 hours. Profiles of the reaction process, the microstructural evolution and the physical effects of water evaporation were obtained. The early age measured 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 hours. The simultaneous monitoring of those parameters allowed a better understanding of the mechanisms involved during early ages. These parameters were compared to the early age cracking due to drying shrinkage. In the hardened state, a mechanical characterization was conducted and porosity and vapor permeability were measured on paste samples (without aggregates) under two environmental conditions during setting process: subjected to 3 m/s air flow and covered with a plastic film. The use of AMA increased mechanical strength. Although, the early age cracking risks also increased, especially in the case of AMA with smaller particle size (NS and MC). The external conditions applying on the samples during early ages also modify porosity, pore size and permeability of the hardened SCC.