Influence of nano-sized highly purified magnesium alumino silicate clay on thixotropic behavior of fresh cement pastes

Thixotropic behavior of cementitious materials is attracting much attention due to its important applications in concrete practice, such as formwork pressure, multi-lift casting, slip form paving, pumping and segregation. This study investigates the influences of nano-sized highly purified magnesium alumino silicate clay (3 nm in diameter, called nanoclay) on thixotropic behavior, particularly, the structural rebuilding of fresh cement pastes. In this study, rheological properties (yield stress, viscosity and thixotropy) of cementitious pastes, with and without nanoclay, were measured at every 15 min after the pastes were mixed. Flow table tests were conducted, and the results were compared with those measured from the rheology tests. Statistical methods were utilized to determine the rates of changes in thixotropy with time. The results indicate that a small amount of nanoclay addition (0.5-1% by mass of cement) significantly facilitates particle re-flocculation or structural rebuilding, and effectively enhances the thixotropy of cement pastes.