Effect of Geometry and Surface Friction of Test Accessory on Oscillatory Rheological Properties of Cement Pastes

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Title: Effect of Geometry and Surface Friction of Test Accessory on Oscillatory Rheological Properties of Cement Pastes

Author(s): M. Nehdi and M.-A. Rahman

Publication: Materials Journal

Volume: 101

Issue: 5

Appears on pages(s): 416-424

Keywords: cement paste; rheology; stress

DOI: 10.14359/13428

Date: 9/1/2004

Abstract:
There is growing interest in investigating the oscillatory rheology of cement paste. The oscillatory flow path of cement paste inside fresh concrete, however, is not easily predictable. To simulate various oscillatory flow paths in cement paste rheological tests, various test geometries and friction levels of shearing surfaces were considered in this work. Four groups of cement pastes with different mineral additions, chemical admixtures, and water-binder ratios (w/ b) were tested using oscillatory rheology with different test geometries including coaxial cylinders (smooth and vaned) and parallel plates (smooth and serrated). The storage modulus and critical stress for the various cement pastes were investigated using a stress sweep test at a constant frequency of 1 Hz. Generally, for the same cement paste and sample thickness, the parallel plates measured significantly lower storage modulus and critical stress values compared with results of the smooth coaxial cylinders and vane rotor. The serrated plate, with relatively higher friction capability, measured higher results of storage modulus and critical stress values compared with those of the smooth plate, indicating a significant effect of slippage on results of the smooth plate. For all cement pastes, coaxial cylinders measured higher values of storage modulus compared with those of the vaned rotor at a low w/ b . At a higher w/ b, however, as slippage became more significant for smooth coaxial cylinders, an opposite trend was observed. Results indicate that the geometry of the test accessory and friction level of its shearing surface must be carefully taken into consideration in critically analyzing oscillatory rheology test results on cement pastes.


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