Formwork Pressure of Self-Consolidating Concrete Made with Various Binder Types and Contents

Self-consolidating concrete (SCC) is a high-performance concrete that flows readily under its own weight and achieves good consolidation with a minimum degree of segregation. This article reports on a study undertaken to determine the effect of binder type and content on variations in the lateral pressure of SCC. The mixtures were prepared with five binder types incorporated at various contents varying from 400 to 550 kg/m3. The influence of thixotropy, determined from concrete and concrete-equivalent-mortar (CEM) mixtures, on the variations of lateral pressure development was also investigated. Results showed that, for a given binder content, the initial lateral pressure and rate of pressure drop with time are significantly affected by the binder type in use. Self-consolidating concrete made with 450 kg/m3 of Type 10 CSA cement (GU) and no supplementary cementitious materials exhibited the highest initial pressure, corresponding to 98% of hydrostatic pressure. Test results also indicate that the rate of pressure drop following casting is dependent on the degree of increase in cohesion. The increase in the degree of thixotropy of SCC and CEM can lead to lower initial pressure. The increase in thixotropy determined from concrete mixtures is highly affected by internal friction resulting from the presence of coarse aggregate. This can overshadow the development of cohesion resulting from the binder phase that controls the rate of pressure drop with time. Thixotropy evaluated using CEM mixtures is more adequate to assess the decrease in lateral pressure development with time than thixotropy determined from SCC mixtures.