Abstract
In South Africa the fineness of Ground Granulated Blastfurnace Slag (GGBS) has remained the same for nearly forty years. In 1999, producers of GGBS were considering the use of relatively finer ground GGBS with a view to improving the strength performance of concrete. The concomitant increase in compressive strength of concrete with an increase in GGBS fineness was confirmed in an extensive investigation carried out by Slagment (Pty) Ltd (Slagment, 1999). However, the effect of relative fineness of South African GGBS on the workability of concrete mixes had not been assessed. This paper discusses the results of an investigation that was aimed at quantifying the influence of finer ground GGBS on the workability of concrete, based on the work of Page (2001). Traditionally, GGBS was ground to a fineness of 3 600 cm2/g, GGBS (3600), and it was proposed to increase its fineness to 5000 cm2/g, GGBS (5 000). The experimental programme included four binder types, namely, CEM I 42,5 alone or in combination with either GGBS (3 600) or GGBS (5 000) or Fly Ash (FA). To eliminate the effects of aggregates on workability, only binder pastes were tested. The results revealed that, as expected, the binder containing the Fly Ash was the most workable. In general, the finer slag, GGBS (5 000), exhibited a higher viscosity and hence lower workability than the GGBS (3 600), due to its relatively higher surface area.