Effect of fineness and particle size distribution of granulated blast-furnace slag on the hydraulic reactivity in cement systems

This paper presents the results of an investigation into the influence of fineness and particle size distribution of granulated blast-furnace slag (GBFS) on its hydraulic reactivity in cement systems. The GBFS vas separated into different fineness classes by grinding and/or air separation. The particle size distributions were determined by laser analysis and the specific surface by means of nitrogen adsorption Brunauer, Emmett and Taylor (BET) equation. The fineness affects the hydraulic reactivity of the GBFS considerably. In the case of a grain size > 20 mu m, the reactivity is greatly decreased. The fraction < 5 mu m plays an important role during hydration. For the development of the compressive strength of blast-furnace slag cement the fraction 20-0 mu m is crucial. The contribution of the fraction with a grain size > 20 mu m in increasing the strength up to 7 days is of minor relevance. In order to obtain an effect on strength increasing tip to 28 days the GBFS should be ground to < 40 mu m at least.