Relation between the Shape of Silica Fume and the Fluidity of Cement Paste at Low Water to Powder Ratio

The effect of the properties of silica fume on the fluidity of ultra high strength cement paste (UHCP) using a polycarboxylate based superplasticizer, silica fume, and low heat Portland cement was investigated. As the dosage of superplasticizer was increased, the flow curve of UHCP changed from Bingham flow to pseudo-plastic flow to Newtonian flow. Also, the effect of silica fume on the fluidity of UHCP was large, in particular the effect on the shape of powder particles smaller than 0.3μm. It is suggested that this is due to the agglomeration structure, the packing state, and the ball bearing effect of the paste due to the shape of the silica fume.