Effect of SCC Mixture Composition on Thixotropy and Formwork Pressure

High lateral pressure exerted on formwork systems by self-consolidating concrete (SCC) is one of the hindrances for using such highly flowable concrete in cast-in-place applications. Self-consolidating concrete is a complex system that can be made using a wide range of mixture proportioning and often incorporated various chemical admixtures and supplementary cementitious materials. The investigation of the effect of each material ingredient independently on lateral pressure of SCC is not a simple task. In this study, thixotropy is rather used to assess the effect of various mixture parameters on formwork pressure. Thixotropy is determined by the evaluation of the structural buildup at rest using a concrete rheometer and two field-oriented test methods (inclined plane and portable vane). Sherbrooke pressure device is employed to evaluate the maximum lateral pressure of SCC. The device receives 0.5 m of fresh concrete and pressurized with air to simulate 13 m of concrete casting at the required casting rate. A parametric study and full-factorial design approaches were employed to evaluate the effect of concrete consistency level, coarse aggregate content, sand-to-total aggregate ratio, paste volume, and nominal maximum size of aggregate on SCC thixotropy and formwork pressure. The investigation resulted in proposing statistical models to determine the effect of each of the modeled mixture parameters and their interaction on thixotropy and lateral pressure. Contour diagrams were established to compare the trade-off between the effects of the different mixture parameters on thixotropy and formwork pressure characteristics. DOI: 10.1061/(ASCE) MT.1943-5533.0000463. © 2012 American Society of Civil Engineers.