Flow onset of fresh mortars in rheometers: Contribution of paste deflocculation and sand particle migration

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...

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Bibliographic Details
Published in:Cement and concrete research 2016-12, Vol.90, p.97-103
Main Authors: Qian, Ye, Kawashima, Shiho
Format: Article
Language:English
Subjects:
Aggregate (D)
Cement
Cements
Clay
Colloids
Concentration (composition)
Deflocculating
Modelling (E)
Mortar (E)
Mortars (material)
Particle decay
Rheological properties
Rheology (A)
Rheometers
Sand
Sand & gravel
Sand migration
Shear flow
Shear rate
Stresses
Thixotropy
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Summary: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.
ISSN:0008-8846
1873-3948
DOI:10.1016/j.cemconres.2016.09.006