Title:
Effect of Geometry, Gap, and Surface Friction of Test Accessory on Measured Rheological Properties of Cement Paste
Author(s):
Mohamed Ataur Rahman and Moncef Nehdi
Publication:
Materials Journal
Volume:
100
Issue:
4
Appears on pages(s):
331-339
Keywords:
admixture; cement; plate; rheology; viscosity; yield.
DOI:
10.14359/12672
Date:
7/1/2003
Abstract:
The rheology of portland cement paste should be well characterized so that it can be adequately simulated in the concrete particulate suspension. The relationship between cement paste rheology and fresh concrete rheology is, however, very complex. Cement paste is sheared through the coarse and fine aggregates in the fresh concrete. Its flow path inside the fresh concrete is not easily predictable. To simulate various flow paths in cement paste rheological tests, various test geometries, sample thicknesses, and friction levels of shearing walls were considered in this work. Four major groups of cement pastes with different mineral additions, chemical admixtures, and water-binder ratios (w/b) were tested using four different test geometries including coaxial cylinders, a vane rotor, and smooth and serrated parallel plates. For parallel plates, different gaps between the plates were also used to simulate the range of aggregate spacing in fresh concrete. Bingham’s linear model was used to calculate the rheological properties. For the same cement paste and sample thickness, test geometries with higher friction capability such as the serrated plate and vane rotor showed higher yield stress and lower viscosity compared with results of other test geometries with lower friction capability. The effect of the variation of the gap between parallel plates on yield stress and viscosity depended on the friction of the shearing wall and cement paste composition. The measured rheological properties were significantly affected not only by the cement paste composition but also by the test geometry used and the friction of and gap between its shearing surfaces.