Mix design factors of self-consolidating cement paste affecting the magnitude of variations in rheological properties induced by the addition time of PCE-superplasticizer

Robustness, which is defined as the capacity of a mixture to tolerate changes and variations in materials and procedures that are inevitable with production at any significant scale, is a key property to expand the use of self-consolidating concrete (SCC). Typically for robustness studies, the most investigated parameter is a variation in the water content. This paper evaluates the effect of the adding time of superplastizer (SP), which was either incorporated in the mixing water or delayed for 2.5 min, on the rheological properties of cement pastes with SCC consistency. Two different SCC mix design concepts, the powder-type (mixture 1) and VMA-type (mixture 2), were selected for this research. The results show that the selected powder-type mix design is more robust than the VMA-type to a change in addition time of SP. In the next step, different mix design parameters have been evaluated by varying the binder combination, the type of PCE-SP and the addition of viscosity-modifying agent (VMA) to determine which particular parameters cause the largest difference in rheological behavior due to a change in adding time of SP. The results have revealed that the limestone filler appears to have the most beneficial effect on the robustness of the cement pastes.