Colloidal nanosilica promotes high-density calcium-silicate-hydrates in fine recycled concrete aggregate mortar

The use of recycled concrete aggregates for new concrete production is an important avenue to increase the sustainability of concrete. While numerous studies have demonstrated the benefit of nanosilica on recycled aggregate concrete, a connection between the enhanced properties and the properties of the calcium -silicatehydrates is unproven. Thus, we investigate how nanosilica modifies the distribution of calcium -silicate -hydrates in fine recycled concrete aggregate mortar. Using an interdisciplinary approach of nanomechanical testing, data science, and advanced chemical, microstructural and pore structure characterization, we find that 12 wt.% nanosilica results in a 30.8% increase in the combined relative amount of high -density and ultra -high -density C -S -H, 16.7% reduction in C -S -H gel porosity, 24.4% reduction in total porosity, and 3.9% increase in fracture toughness.