A novel insight into the physical implication of percolation threshold of cement suspensions from microscopic and macroscopic perspectives

The percolation threshold plays a significant role in influencing the yield stress of cement-based materials. However, this crucial parameter has not been well understood given the absence of robust and reliable experimental methods and computing models. This study estimates the percolation threshold through regression analysis of yield stress and reveals its physical implications from the microscopic and macroscopic perspectives. The results indicate that the regression approach does not capture the theoretical percolation threshold, but rather a rigidity percolation threshold. The rigidity percolation threshold, reflecting the formation of a mechanically stable interaction network, is governed by the balance between colloidal forces and dominant separating force, either gravity or Brownian force. In cement pastes where gravity dominates over Brownian motion, the rigidity percolation threshold is significantly higher than the theoretical percolation threshold. A power-law relationship has been established between rigidity and theoretical percolation thresholds where the exponent is dependent on the gravitational Péclet number. In pastes containing large amounts of finer particles, where Brownian motion exceeds gravity, the rigidity percolation threshold aligns with the theoretical percolation threshold. From a macroscopic perspective, the rigidity percolation threshold is directly linked to the bleeding of cement pastes. A reduction in the solid volume fraction below the rigidity percolation threshold can result in bleeding, since the insufficient cement grains cannot form an internal particle network to resist gravity.