Nanosilica in-situ produced with sodium silicate as a performance enhancing additive for concretes

This study proposes to use an in-situ produced nanosilica to enhance the performance of cement mortar. To this end, a two-step mixing method is developed. In Step I, low-cost sodium silicate and tannic acid (TA) solutions are mixed with the mixing water, in which TA can trigger the condensation of sodium silicate to produce porous silica nanoparticles and disperse the produced nanoparticles in the mixing water. The resulting mixing water with nanosilica is then directly used to mix cement mortar. Experimental results show that the compressive strength at 28d of the cement mortar produced by the proposed method is 35% higher than the one produced using the existing method. This strength improvement far exceeds what can be achieved by the ex-situ addition of nanosilica, which can be attributed to the fact that the in-situ produced nanosilica can significantly reduce the porosity of the cement paste, as revealed by the mercury intrusion porosimetry test. For the same reason, the produced cement mortar's resistance to sulfate attack is also enhanced by the proposed method. The proposed method is ready for large-scale field application in concrete since it overcomes all challenges facing the utilization of nanoparticles in concretes, such as high cost and difficult dispersion.