Effect of silica-based nano and micro additions on SCC at early age and on hardened porosity and permeability

A comparative study assessed the effect of silica-based micro and nano additions on Self Compacting Concretes at early age (EA) and on hardened porosity and permeability. Several parameters were monitored during 24 h: water evaporation, capillary pressure, free drying shrinkage, temperature and ultrasonic pulse velocity (UPV). All the silica-based additions modified the material at EA regarding water displacements, the chemical reaction and the development of the hardened structure. Some effects of the silica-based additions depended on the particle size. Nanosilica accelerated SCC early stiffening and had larger EA water evaporation, which leaded to larger porosity at 7 days. However, leaded a lower hardened porosity and water vapor permeability was measured at 28 days due to the pozzolanic effect along with the particle size effect.