Effects of Shape and Packing Density of Powder Particles on the Fluidity of Cement Pastes with Limestone Powder

Abstract

The fluidity and flow mechanism of suspensions containing low-heat Portland cement, limestone powders with different characteristics, and a polycarboxylate-based superplasticizer have been studied. Limestone powders with six different degrees of grinding were prepared using a ball mill and a jet mill. The circularity of the limestone powder particles was determined by analyzing scanning electron microscope (SEM) photographs of the particles using an image analyzer and the point counting method. A computer program for determining the packing fraction of powder particles directly from the particle size distribution was written and the packing fraction was calculated. It was made clear quantitatively that the packing fraction and circularity of limestone powder particles significantly affected the fluidity of the suspensions. The addition of finely ground limestone powders prepared by jet mill increased the fluidity of suspensions. The fluidity of low-heat Portland cement paste with finely ground limestone powders prepared by jet mill at a water-to-powder ratio of 0.225 is as same as the fluidity of low-heat Portland cement paste at a water-to-powder ratio of 0.30. The fluidity of a suspension could be approximated with accuracy using the packing fraction and the circularity of powders. Particles with a circular shape and a high packing fraction result in increased fluidity. The ratio of the contribution made by the packing fraction to this improvement in fluidity to that of shape ranged from 1:1 to about 1:2.