The influence of filler characteristics on the workability of self-compacting concrete

Self-compacting concrete (SCC) is considered more and more as the “concrete of the future”. Its high workability not only improves the labour conditions and the speed of working, also the uniformity and quality of the end product is increased. To reach this high workability, the amount of coarse aggregates has to be reduced and replaced by fine material. Since cement is quite expensive and a too high amount of cement causes a strong hydration reaction, with possible problems of shrinkage cracks, fillers (i.e. mineral additions) are added. This paper presents the results of an investigation on the suitability of different fillers to be used for SCC. An experimental test program has been executed with 12 different SCC mixtures, each mix with another type of filler. The other mix parameters (water-to-cement ratio, fine and coarse aggregates content) were the same for all mixes. The different mixes were investigated with respect to workability (slump-flow, V-funnel and U-test), compressive strength, shrinkage and freeze-thaw resistance. These properties were sometimes very different if only another type of filler was used. Each filler has been characterised with different tests: water demand (beta_p), Blaine, activity index, particle size distribution (by means of laser diffraction) as well as the roundness, sphericality and surface structure of the filler particles which were observed through a scanning electron microscope (SEM). An effort has been made to link the measured properties of the SCC mixtures with the characterising parameters of the fillers. It was found that the microscopic filler particle properties (roundness, sphericality and surface structure) play a determining role.status: publishe