Impact of nanosilica size and surface area on concrete properties

In this work, the impact of nanosilica particles in grouts and concrete samples were measured to identify the change to temperature of cement hydration, strength, and permeability. The compressive strength and modulus of elasticity were also evaluated as a means to understand the impact that the nanosilica size and surface area had on the macroscopic properties traditionally used in the concrete industry. Finally, electrical resistivity was measured as a means to understand how the pore connectivity and permeability of the concrete specimens were manipulated by nanosilica addition. Three types of nanosilica dispersions were added to cement composites and examined over short and long curing times. All three different-sized nanoparticles were added to have an equal surface area of silica. The larger particles exhibited higher levels of enhancement on the cement composite, showing increased compressive strength and modulus of elasticity by more than 20% over the reference mixtures. The smallest nanosilica particle exhibited a 20% increase in compressive strength at its lowest dosages and a 14% reduction in compressive strength at its highest dosage. These results illustrate a limitation when using the smallest nanosilica particle. Finally, the addition of all nanosilica particles proved to increase the electrical resistivity of the concrete by 30% for the smallest nanosilica particles and 700% for the largest nanosilica particle. This increase could be attributed to a reduction in permeability from a denser concrete specimen.