Measurements of Breakdown and Buildup of Thixotropy in Cement Pastes Containing Diatomaceous Earth

This paper proposes a comprehensive series of protocols that can make quantitative measurements on both breakdown and buildup aspects of thixotropic behaviors of cement pastes. While measuring breakdown and buildup separately, the correlations between these two aspects have also been investigated. Cement pastes with different water-to-binder ratios (w/b=0.4, 0.5 and 0.6) and different replacement levels of Diatomaceous Earth (DE) (0%, 2%, 6% and 10% by weight of cement) were studied. To simulate the real on-site conditions, parameters such as pressure and temperature were also considered during the measurement. The research found that increase in DE replacement dosage can reduce the energy required to breakdown thixotropic structure of cement pastes while no specific trend on buildup aspect was observed. Among the three used w/b ratios, the 0.5 w/b ratio has the most reduction effect in breakdown energy, where using 10% DE can lead to 65% of energy reduction in breakdown compared to the control sample. However, the measured yield stress for these specimens were very similar to each other.  In addition, increase in temperature significantly increases the buildup ratio of cement pastes while increase in pressure as high as 20 MPa has a minimal impact on thixotropic properties of cement pastes.