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Yield stress measurement of mortar using geotechnical techniques



Author(s): R. Hendrickx, K. Van Balen, D. Van Gemert
Paper category: Symposium
Book title: 3rd International RILEM Symposium on Rheology of Cement Suspensions such as Fresh Concrete
Editor(s): O.H. Wallevik, S. Kubens, S. Oesterheld
ISBN: 978-2-35158-091-2
e-ISBN: 978-2-35158-092-9
Pages: 273- 282
Total Pages: 10
Language: English


Abstract: 
The rheological characteristics of masonry mortar are hard to measure with traditional rheometric techniques. The problems encountered are shear localisation, structural build-up or break-down, dilation upon shearing and local inhomogeneity. Some of these problems are typical for granular pastes at high solid fraction and low shear rates, which are subjected to a frictional flow regime. This means that shear stress is dependent on normal force: a feature usually not included in rheological models. We propose to explore the possibilities of geotechnical methods to quantify the shear strength of mortars. The setups used are the direct shear apparatus and an adapted laboratory vane apparatus. The results demonstrate that the maximum stress in an undrained mortar is not a material constant, but shows important variations depending on the rate of stress increase and the normal stress applied. A simple Coulomb relation can be found between normal stress and shear strength, but knowledge of pore water pressure is lacking to perform effective stress analysis. The phenomenon of dilation is measured and its dependence on normal stress demonstrated. Dilating behaviour and shear strength of mortar are compared to the characteristics of the sand. It appears that pore water pressure and dilation are interrelated and play an important role.


Online publication: 2009
Publication Type: full_text
Public price (Euros): 0.00