Rheological Characterization of Self-compacting Concrete Pastes with Polymeric Admixtures

Multipurpose admixtures such as superplasticizers (SP), viscosity modifying agents (VMA) and superabsorbent polymers (SAP) are polymers commonly used in self-compacting concrete (SCC). Their main effect is positive for SCC fresh properties, minimizing some technical barriers of SCC production and cast in-place technology. However, they also affect fresh SCC rheological properties. This study addresses the rheological behaviour of fluid SCC pastes, modified with SP, VMA, SAP and their combined effects and interactions. A cement-limestone filler blended paste and two water-to-binder ratio (w/b) were designed as a reference mixture. Three dosages of VMA and SAP, 0.2%, 0.4% and 1.0% of cement weight, were investigated. The kinetics of water uptake of VMA and SAP admixtures were compared using the tea bag test in neutral pH and alkaline pH solutions. Additionally, SP was added to achieve a similar slump flow with final spread diameters of 300 mm and 400 mm, on pastes with and without VMA and SAP. The rheological parameters of the fresh pastes were tested with the mini-cone slump test. Final spread diameter, final height and time to final spread were measured after the mixing. It was found that the effectiveness of SP on the final spread diameter depended on the w/b ratio of reference paste. On the other hand, VMA increased the time to final spread, while slightly reducing the final spread diameter. SAP affected the maximum diameter due to water absorption kinetics and an increase of w/b ratio was needed to achieve similar spread diameters. It was observed that the combined use of SP and VMA or SAP affected the measured parameters. The particular effects of SP, VMA and SAP admixtures on the rheological parameters depended on w/b ratio, the amount of polymer and the combination of components.