Nanosilica particles as structural buildup agents for 3D printing with Portland cement pastes

Abstract

This work presents a comparative study of the effects of nanosilica particles on the fresh state properties of a Portland cement paste designed for 3D printing. Cement pastes were prepared with different solid substitutions of cement by pozzolanic particles and their yield stress was measured after different resting times. Rheological results were used to obtain the rate of thixotropic buildup of each paste, which was used to compute the parameters of an ideal 3D printing process (layer height, time to extrude one layer, and horizontal velocity). Results obtained for nanosilica were compared with results from other three commonly used pozzolanic nano and micro particles (microsilica, metakaolin and nanoclay). All pozzolanic particles studied were capable of increasing both the initial yield stress and the rate of thixotropic buildup of cement paste through different mechanisms; nevertheless, these increases did not translate directly into a more efficient 3D printing process due to the limitations imposed by the need to avoid cold joints between layers. It was concluded that even though nanosilica particles are more efficient thickeners for cement paste than the other particles studied, their effect is constrained by the maximum and minimum printing velocities. Additional chemical accelerators should be considered to reach the full potential of nanosilica as a structural buildup agent.