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Coefficient of air permeability of non-homogeneous substrates and drying concrete



Author(s): T. Dobel, L.F. Luco
Paper category: Conference
Book title: 2nd International conference on Microstructural-related Durability of Cementitious Composites
Editor(s): Guang Ye, K. Van Breugel, Wei Sun, Changwen Miao
Print ISBN: 978-2-35158-129-2
e-ISBN: 978-2-35158-123-0
Publisher: RILEM Publications SARL
Pages: 1305- 1314
Total Pages: 9
Language: English


Abstract: 
The air permeability of cover concrete can be used as a durability indicator. Commercially available equipment, the TPT, capable of assessing the coefficient K of air permeability using the double chamber vacuum method (Swiss Standard SIA 262/1-E), was used in this research.
The instrument relies on the assumption that the concrete being evaluated is homogeneous and thus, the K coefficient informed by the instrument is constant through the full depth affected by the measure and estimated by the equipment at the end of each test.
In actual concrete, this assumption may not be valid, especially when the concrete has been submitted to early drying, as outer layers develop a lower hydration degree and therefore a higher porosity.
This paper deals with the measure of the air permeability coefficient K on nonhomogeneous substrates, aiming at determining whether the instrument is capable of identifying such non-homogenous condition.
Two different situations were considered: non-homogeneity due to early drying and due to a non-linear profile of humidity content as a result of the drying process, applied to concretes of w/c from 0.35 to 0.60.
The results obtained show that it is not easy to distinguish a non-homogenous substrate from the information provided by the equipment.
The effect of water content in low-permeability concretes may affect the results in a different direction than the one suggested by the author of the equipment in earlier works, as the measurement of partially humid concrete may result in a permeability coefficient higher than the one obtained on a conditioned corresponding sample.
As a result of this research, a simple procedure to overcome the influence of water for on-site measurements of moderately wet low-permeability concrete is provided.


Online publication: 2013
Publication Type: full_text
Public price (Euros): 0.00