Showing the role of weakly-bound particles flocculation in the reversibility of thixotropic behavior for fresh cement paste

The thixotropic behavior of fresh cement-based materials has been found to be derived from the reversible breakage and agglomeration of flocculated cement grains. The existence of thixotropy can lead to significant variations in shear stress and apparent viscosity under the same shear rate, which brings great challenges for measuring rheological performance. This paper highlights the difference between strong and weak particles flocculation for the first time, and then reveals the intrinsic interactions of various thixotropic and rheological parameters. The thixotropic behavior and dynamic yield stress were evaluated for cement paste samples with different resting time and temperature conditions. It was found that the longer resting time, the higher temperature, and the larger solid volume fraction increased the difficulties for both the structural breakdown and the subsequent structural re-buildup processes, indicating the lower reversibility of thixotropic behavior; These factors also led to higher dynamic yield stress, more amount of strongly-bound flocs, but less weakly bound flocs. After removal of shear force, the microstructure reconstruction ability of fresh cement paste was highly correlated to the recovery of dispersed weak flocs, but with little regard to strong flocs. The dynamic yield stress value could be dependent on the breakage degree of flocculation, while the prolonged duration of last several steps in the descending portion of the rheometric procedure enhanced the dynamic yield stress due to structural re-buildup. The results will provide new in-depth insights into the roles of strong and weak flocs in the reversible thixotropic behavior of fresh cement-based materials.