Effect of fine aggregate on the rheology properties of high performance cement-silica systems

This paper deals with the effect of fine aggregate particles on the theological properties of high performance cement-based materials. The effect of narrow fractions of fine aggregate particles on the rheology of silica fume-modified low water cement systems was analysed by means of a mortar rheometer. Yield stress and plastic viscosity were derived for time intervals between 10 and up to 150 min after water addition, and comparison with the slump value taken by the flow table test was done. It is concluded that the fine aggregate particles act as water fixation points in the diameter range of 75-1000 mu m, via surface area, whereas for higher particle diameters the governing factor in terms of the resistance to flow may be related to other physical phenomena, such as the particle dimension and the resultant friction forces. Moreover, the water requirement in order to give each system the same workability is performed by adjusting the water content on each system. Furthermore, a quantitative model is proposed to describe the characteristic initial torque peak and resistance to flow behaviour of high performance concrete, as function of the particle size of aggregate. The combined effect of silica fume and fine aggregate particles on the rheology parameters is discussed. (C) 2009 Elsevier Ltd. All rights reserved.