Multi-scale effects of FA and GGBS on rheological properties of cementitious systems: from paste to self-compacting concrete

Abstract In this study, multiscale rheometers and rheological models were used to investigate the effects of mineral admixture types (fly ash (FA) and ground granulated blast-furnace slag (GGBS) and dosages (0%, 10%, 20%, and 30%) on the fluidity and rheological properties of different mixes at three scales: paste, mortar, and self-compacting concrete (SCC). A mini slump cone and an RST-CC rheometer were used to test the fluidity and rheological parameters of the paste and mortar. The slump flow, slump-flow time (T500), yield stress, and plastic viscosity of the SCC were tested using a slump cone and ICAR concrete rheometer. The results indicated a consistent effect of FA and GGBS on the fluidity and rheological properties of the three mixes. FA enhanced the fluidity and rheological properties of the mixes, whereas GGBS had the opposite effect. The yield stresses of paste, mortar, and SCC containing 30% FA were reduced by 51.2%, 6.5%, and 77.6%, respectively, and their plastic viscosities were reduced by 16.7%, 6.3%, and 7.6%, respectively. In contrast, the yield stresses of the paste, mortar, and SCC containing 30% GGBS increased by 16.7%, 6.3%, and 7.6%, respectively, and their plastic viscosity increased by 50.1%, 10.2%, and 32.2%, respectively. In addition, the results of the correlation analyses of the rheological parameters of the three mixes confirmed the two-phase assumption of the SCC. Multiscale correlation analyses demonstrated that the rheological properties of SCC were closely related to those of the paste and mortar. As the yield stress and plastic viscosity of the paste/mortar increased, the yield stress and plastic viscosity of the configured SCC also increased significantly. These results provide a reference for SCC mix design and construction quality control.