Influence of ultrafine powder on the fluidity and strength of cement paste

The influence of several kinds of ultrafine powders (UFPs) of mineral admixtures on the fluidity and strength of cement paste have been studied. Experiments show that silica fume and UFPs of natural zeolite have a filling effect and little dispersing effect on the fluidity of cement paste; UFPs of phosphorous slag and blastfurnace slag have both a filling effect and a dispersing effect. Both kinds of UFP have a strengthening effect. Adding UFP and superplasticizer simultaneously leads to better filling and dispersing effects in cement paste, because the particles of UFP cannot fill in the cement floc effectively unless the self-coagulation of the UFP is destroyed by adsorbing superplasticizer. The strengthening effect of UFP is due to its densifying effect and chemical activity, as well as its capacity to modify the pore structure.