Effect of Silica Sol on Rheological Behavior of the Cement Paste

Effect of nano-silica powder and silica sol addition on rheological behavior of the fresh cement paste with low water-cement ratio (w/c=0.3) and the mechanism were investigated. The viscosity showed a slight decrease with increasing the nano-silica content while incorporating nano-silica powder and silica sol in the cement paste with the addition below 0.6%. The viscosity showed a slight increase with further increasing the nano-silica content while adding nano-silica powder. However, the viscosity showed a sharp increase with further increasing the nano-silica content while incorporating silica sol in the cement paste, and the paste showed an obvious shear-thinning behavior. The apparent viscosity reached as high as 10 and 18 Pas at the shear rate of 2.509 s(-1) for the paste with incorporation of 0.8% and 1.0% silica sol, respectively. With increasing the shear rate, the viscosity dropped sharply and were about 1.2 and 1.8 Pas at the shear rate of 163.1 s(-1). Through sedimentation test and microstructure observation by optical microscopy, it is found that there were more obvious agglomerations of the silica nanoparticle together with the cement particles, which was resulted from the aggregation or gelation of the colloidal silica sol, due to rapid increasing of the ionic strength in the paste once the cement particles were added to the water.