Hardened properties and microstructure of SCC with mineral additions

The paper investigates the effects of three active mineral additions (AMA): microsilica (MS), nanosilica (NS) and metakaolin (MC), on the hardened properties, microstructure and mechanical performance of self compacting concretes (SCC) with limestone filler (LF). Compressive strength, P- and S-waves Ultrasonic Pulse Velocity (P- S-UPV) of hardened SCC were jointly studied with porosity and water vapor permeability (WVP) of paste samples covered and uncovered with plastic film during setting time, simulating two environmental conditions during early ages (EA). The interfacial transition zone (ITZ) was also examined using scanning electron microscopy (SEM). Substitution of 50% of cement by LF significantly reduced density, stiffness and compressive strength while slightly increased paste porosity and WVP in comparison with reference SCC. The use of AMA significantly increased compressive strength and reduced the presence and size of large Portlandite crystals in the ITZ of concrete, but that did not significantly improve the stiffness (ultrasonic modulus of elasticity). AMA also moderately reduced porosity and WVP of the paste phase, which would expect to improve durability of concrete. It was deduced that WVP was correlated to porosity rather than pore size or pore tortuosity. Compressive strength of pastes followed a different pattern regarding porosity. Depending on the presence of LF, the strength increased with porosity on pastes without filler while it decreased in its absence, depending on AMA's pozzolanic activity. The curing conditions at EA also affected hardened properties and paste's microstructure as larger evaporation for uncovered samples significantly reduced porosity, tortuosity and WVP, although increased average pore diameter.