Effect of Mixing Time on Flowability and Slump Retention of Self-Compacting Paste System Incorporating Various Secondary Raw Materials

Abstract

Good workability at construction site is most important aspect of self-compacting concrete. But long delivery times can cause slump loss, which is more pronounced when mineral additives are incorporated into the concrete system. The aim of this paper is to study the effects of prolonged mixing on the flowability and slump retention under action of a high-performance polycarboxylic (PEC)-based superplasticizer used in self-compacting paste systems (SCPs) incorporating various secondary raw materials (SRMs). Experimentation for this research paper was focused on mixing times and slump retention of SCPs incorporating ASTM Class F fly ash (FA), silica fume (SF) and locally available marble powder (MP). While experimenting with SCPs, total mixing time was first restricted to 3 min of mixing to achieve the target flow of 30±1 cm, which was then prolonged to total mixing time of 10 and 20 min keeping the superplasticizer content constant, which showed a more enhanced flow with reduced timing due to better activation of superplasticizer, or enhanced workability but showed some traces of bleeding in the formulations containing MP. The samples were thereafter prepared for strength measurement as per EN-196. Parameters like flow response, strength and microstructures were studied by varying two basic factors in progression: shear time and hold time. Hydration kinetics were also affected by prolonged mixing, and it also decreased the initial and final setting time. FA showed better rheological behaviour upon extended mixing regimes as compared to SF or any other SRMs.