Experimental Investigations and a New Numerical Model for Evolution of Formwork Pressure in SCC

摘要

A new FEM-based numerical model is proposed for simulating the evolution of formwork pressure exerted by fresh self-compacting concrete (SCC). The proposed model considers SCC as an isotropic linear elastic homogeneous material confined in a rigid body, with the boundary layer behavior being simulated as viscoplastic. The values of the boundary shearing stress at wall vary with height depending on the resting time between castings of a specific portion of the SCC to the moment the pressure measurement is taken. Experimental investigations were conducted on a full-scale formwork to obtain the evolution of formwork pressure exerted by SCC mixes made with different mineral admixtures. Concrete was poured in a steel formwork of thickness of 200 mm, length of 3.0 m and overall height of 3.1 m. The variation of pressure across the height was measured using pressure transducers placed at different heights along the wall for a total period of 12 h. Four SCC mixes with different mineral admixtures, fly ash, silica fume, ground granulated blast furnace slag and the control mix with a w/c ratio of 0.35 were used in the experimental program. Rheological parameters including the yield stress, relative viscosity and thixotropy were obtained for each mix and determined simultaneously. The experimentally obtained pressure-time evolution curves correlated reasonably well with those obtained from the proposed numerical model. The results indicate that the decay of formwork pressure after an initial period becomes sensitive to the time evolution of the Poisson ratio of the blended concretes.