دانلود رایگان مقاله جریان شروع ملات تازه در روانه سنج و سهم لخته خمیر

Abstract

Shear-induced particle migration is widely recognized to be a challenge in characterizing the rheological properties of fresh cement-based mortars. In this study, we aim to quantify shear-induced particle migration by characterizing the stress decay process during constant shear flow with the aid of a modified thixotropy/migration model. It is found that a conventionally used single exponential model is not sufficient to fit the stress decay and describe the destructuration and sand migration of mortar under shear. Instead, a two exponential model is needed to capture the interaction of sand particles and the suspending cement paste phase. Model parameters are used to quantify the effect of sand volume fraction, clay addition, and applied shear rate on the kinetics and intensity of colloidal deflocculation and sand migration. Results provide evidence that the colloidal and granular contributions to the overall stress decay of mortars can be represented by each of the two exponentials.

4. Conclusions

In this study, a modified two exponential thixotropy/migration model is proposed to quantify the stress decay of fresh mortar under constant shear rate. Results support that destructuration and sand migration are represented by the two exponentials. α and characteristic time 1=ðαγ_Þ are related to the rate of these two stress decay mechanisms, and torque M and normalized M indicate the intensity of each phase. Test results indicate the following: • Increase of sand volume fraction increases all five parameters, along with normalized M1 and M2, indicating faster kinetics and increased intensity of both colloidal deflocculation and sand migration. This is Fig. 7. Effect of angular velocity on parameters α in agreement with observations of other studies.