Particle size distribution of GGBS and bleeding characteristics of slag cement mortars

This paper reports an investigation into the influence of particle size distribution (PSD) of ground granulated blast furnace slag (GGBS) on the bleeding characteristics of slag cement mortars. Samples of slag powder with different PSDs (as represented by the parameters of the Rosin-Rammler distribution function, namely, position parameter, x(0), and slope, n, which describe the fineness and the size range of the PSD, respectively) were prepared using a method whereby a commercially available slag sample was first separated into different size fractions and later recombined in some pre-determined proportions. Bleeding rate and bleeding capacity of mortar mixes containing 0, 30, and 70% slag were investigated. The results showed that when varying the PSD of slag by altering n at constant x(0), no specific relationship between bleeding characteristics and psd could be established. However, the highest values of the bleeding rate and capacity were exhibited by the mixes in which the slag with the intermediate value of slope (i.e., having the medium range of PSD) was included. Furthermore, the results showed that for the slag samples with similar size range distribution (i.e., having a constant slope, n), the bleeding capacity increased with increases in x(0), except the 30% slag mixes, which were made to 0.35 w/c. (C) 1998 Elsevier Science Ltd.