Influence of flocculation structure on time-dependent fluidity and rheological property of cement paste: Analytical models based on fractal theory

Abstract

The time-varying evolution of the flocculation structure of cement paste is the fundamental cause of fluidity loss and rheological property degradation. To quantitatively analyze these time-dependent behaviors, the flocculation structure, fluidity, rheological property, and hydration heat of cement paste affected by different factors were tested and analyzed in this study. In addition, the correlations between the mesoscopic flocculation structure and the macroscopic fluidity, rheological property of cement paste were quantitatively analyzed based on fractal theory. Results reveal that a larger fractal dimension corresponds to a smaller size and greater dispersion of the flocculation structure, while a smaller fractal dimension corresponds to a larger size and higher compactness of the flocculation structure. As time progresses, the fractal dimension decreases, indicating a larger flocculation structure size and reduced self-similarity. The fractal dimension curve and the fluidity curve show similar trends, with a positive correlation between fluidity and the fractal dimension of the flocculation structure. In contrast, the fractal dimension curve and the rheological parameter curve exhibit opposite trends, indicating a negative correlation between rheological parameters and the fractal dimension of the flocculation structure. The water-cement ratio and PCE content significantly affect the initial flocculation structure size, while the addition of a retarder brings no impact. A higher water-cement ratio and PCE content result in a larger fractal dimension. Based on the hydration degree of cement and the dispersing mechanism of PCE, and considering the relation between fluidity and fractal dimension, an analytical model was established for the time-dependent fluidity of cement paste. Additionally, using the YODEL model and the Krieger-Dougherty model, and considering the relation between yield stress, plastic viscosity of cement paste and fractal dimension of flocculation structure, analytical models were developed for the rheological property of cement paste. The study established functional analytical models between the mesoscopic flocculation structure and the macroscopic fluidity, rheological property of cement paste, providing essential guidance for controlling the fluidity and rheological property of cement-based materials.