Improved mechanical models for self-compacting concrete in the paste rheological thresholds theory considering the pressure between particles

Abstract

Based on the mix design method for self-compacting concrete (SCC) established from the rheological threshold theory, SCC's flowability can be predicted through a simple paste rheological test. But this method may have poor prediction accuracy when materials changed. The original theoretical mechanical models of paste threshold theory were set up from the behavior of SCC in slump flow test, more testing situations should be considered. V-funnel test was a classical test method that can reflect both yield stress and plastic viscosity of SCC. This work studied the improvement of the rheological threshold theory by new mechanical models set up from the V-funnel test, considering the flowing state of mortar under the pressure of gravel particles. To verify the models, we conducted 36 paste tests and 36 SCC tests with different powders including cement, fly ash, and limestone powder. The self-compacting zone of paste and SCC, which can reveal the prediction of workability, were obtained by a bilinear interpolation method. We also designed a new assessment method for prediction accuracy. The evaluation of the overlap area and relative position was achieved by two parameters, including the relative accuracy ε and the accuracy index ε’. According to the results, ε of the modified model ranges from 0.84 to 0.96, while that of the original method was between 0.28 and 0.78. ε′ was increased from 0.14–0.89 to 0.54–0.99. This modified method can handle powder changes.