Underlying mechanisms of the effect of microfines of manufactured sand on non-linear structural build-up of cement paste

Abstract

The rheological properties of cement-based materials made with manufactured sand vary with the content and physio-chemical properties of microfines in the sand. However, the evaluation of rheological properties regarding the structural build-up at early-age hydration remains challenging for the cementitious materials prepared with different manufactured sands, due to complicated underlying structuration mechanisms. This paper studies the effect of disparate microfines of different manufactured sands on the non-linear growth of static yield stress of cement pastes at rest. The paste mixtures were prepared with 0.40 and 0.275 water-to-cement mass ratio (W/C) and had a fixed mini-slump flow of 240 ± 5 mm. Test results show that the additional microfines facilitate the rapid early increase of static yield stress over 10 min rest, due to the intensified flocculation between total solid particles and simultaneously the greater strengthening of the agglomerating network by rapid cement hydration. Besides, the microfines promote the exponential growth of static yield stress over 10 to 120 min rest, given the accelerated particle network densification by the continuous cement hydration. Qualitative approaches describing the enhancement of flocculation by rapid early hydrates and the particle network densification during the succeeding early-age hydration are proposed to evaluate the rapid increase and exponential growth of static yield stress, by taking into account the evolving ratio of solid particles to excess interstitial solutions and the degree of cement hydration.