Effect of mineral admixtures on the structural build-up of cement paste

Structural build-up is of great importance in many concrete applications, such as formwork pressure, multi-layers casting, slip form paving, stability, and 3D printing. In this paper, the growth of static yield stress (τs) and thixotropic area were used to characterize the structural build-up of cement paste. The effects of different mineral admixtures, i.e. silica fume (SF), ground slag (GS), fly ash (FA), attapulgite (AG), nano calcium carbonate (NC), and nano silica (NS) on the structural build-up of cement pastes were studied. Calorimetric curves, zeta potential and conductivity of the pastes were also measured. Results showed that thixotropic behavior characterized by the growth of τs and thixotropic area gave different ranking on cement pastes with various mineral admixtures. NS, AG, NC and SF increased the growth of τs over 120 min, and NS was the most effective one. FA and GS decreased the growth of τs over 120 min. Hydration of cement played a dominant role in the structural build-up of cement paste. However, high hydration rate didn't always lead to high structural build-up rate.