Effect of mixture consistency on formwork pressure exerted by highly flowable concrete

An experimental program was undertaken to evaluate the effect of a mixture's consistency on the lateral pressure that can be developed by highly flowable concrete. Six mixtures, with various contents of high-range water-reducing admixtures, were tested and had consistency levels varying between a slump of 220 mm and a slump flow of 750 mm. The mixtures had similar water-to-cementitious materials and sand-to-total aggregate ratios of 0.40 and 0.46, respectively. Depending on the mixture consistency, the maximum initial pressures varied between 75 and 98% of hydrostatic. Concretes with lower consistency were shown to exert lower initial lateral pressure and had faster rates of pressure drop with time. This can be attributed to the increased degree of shear strengths that enables the fresh concrete to further resist vertical stresses, hence precluding the development of high lateral pressure. Self-consolidating concrete mixtures made with standard CSA Type 10 cement exhibited higher initial pressure and lower rates of pressure drop compared to those of equal consistency prepared with ternary cement. At the end of the dormant period of cement hydration, the acceleration of formation of hydrates is shown to enable the concrete to be self-bearing-resulting in the cancellation of lateral pressure.