Physical Properties and Behaviour of High-Performance Concrete at High Temperature by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783319954325
Publisher: Springer International Publishing

When heating, free water is released between each step of temperature (and particularly, a lot between 100 and 200 ℃), and it is essential to wait until this liquid water has evaporated before carrying out the permeability test. If any liquid water remains inside the specimen, under gas pressure, a moisture clog effect appears, so that the gas becomes temporarily unable to pass through the specimen, making any gas permeability test impossible. From the analysis of (Chen et al. 2009), free water inside the macro-pores, as well as bound water released from the C–S–H, dilate or vaporise, and obstruct the interconnected porous network. Due to moisture clogging, no more gas is allowed through the material pore network: a so-called gas retention phenomenon occurs. It is also concluded that cement-based material composition, i.e. bound water release ability, is influential in gas transport phenomena under temperature. This liquid water also arises in concrete exposed to fire where it joins the cracks before turning to vapour. If the path to the crack is too long a fluid pressure can appear because this liquid phase does not move easily in the porous concrete, as shown before.

The ratio between residual permeability and permeability obtained at elevated temperature, is shown in Fig. 3.19 (Haniche 2011). The observed scatter of the results might be an indication that all of the parameters that influence the permeability were not sufficiently controlled.

Fig. 3.19Ratio between residual permeability and permeability obtained at temperature (Haniche 2011)

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