Effects of temperature and bleeding on rheology of cement paste

Abstract

The bleeding and rheology of a cement paste affect the grouting reinforcement effect in a high-temperature stratum. However, the effect of the slurry bleeding on the rheology at high temperatures is not clear. This research examined the bleeding characteristics of slurries in a high-temperature environment and changes in the density and flow pattern during bleeding. The material was ordinary Portland cement with a strength grade of 42.5. The water-cement ratio (W/C) ranged from 0.6 to 2.0. An environment of 20 °C–90 °C was simulated in a laboratory. The bleeding process was divided into six stages according to the total bleeding rate and rheological tests were conducted at each stage. The results showed that the total bleeding rate of the slurry increased with the increase of the W/C and decreased approximately linearly with the increase of temperature. The density change rate before and after bleeding decreased with the increase of temperature and increased with the increase of the W/C. The final density change rate of the cement paste at different temperatures was determined by the W/C. Newtonian and power law models were used to describe the rheological characteristics of slurries with W/Cs ranging from 1.5 to 2.0 and 0.8 to 1.2, respectively, during the bleeding period. As the bleeding rate increased, the R2 of the Newtonian model decreased from 0.98 to 0.9. A constitutive equation considering the temperature and bleeding characteristics was proposed. The relationship between the flow characteristic and consistency indexes at different bleeding stages changed from non-linear to linear with increasing temperature.