Effect of Mixing Speed on Rheology of Superplasticized Portland Cement and Limestone Powder Pastes

This paper examines the effect of mixing intensity on superplasticized cement pastes and reference limestone pastes; specifically, the effects of high mixing intensity on the rheological properties were examined. Increasing the mixing intensity applied to a paste does not always cause a reduction in the rheological properties of the paste, especially when the pastes contain a high-range water reducing admixture (HRWRA). Mechanisms underlying this effect were examined. The physical effects due to cement being a powder material cannot solely explain the behavior seen; rather, the chemical effects from cement being hydraulic, as well as the amount of foaming of the incorporated admixture, play a role. Pastes prepared with an HRWRA that had a high degree of foaming exhibited greater increases in their rheological response than pastes prepared with HRWRAs containing low foaming potential, which suggests that the air bubbles in the foam network act as rigid inclusions instead of soft, deformable inclusions. Keywords: cement paste; chemical admixture; foaming; limestone powder; mixing intensity; rheology.