Gas permeability is commonly used to evaluate durability characteristics of concrete. However, these values are often achieved using never stressed or damaged specimens. The objective of this study is to examine experimentally the effect of axial compressive loading on the permeability of three different types of concrete: ordinary concrete (OC), high-performance concrete (HPC), and high-performance steel fiber-reinforced concrete (HPFC). Monotonic and cyclic loads are applied on 220 Â 110-mm diameter specimens. Stress levels vary between 60% and 90% of the ultimate strength. At the end of the loading phase, a disc is extracted from the middle part of the cylinders and is dried in a ventilated oven. Four different gas permeability tests are conducted during the drying procedure. The results show that, for each drying stage, the gas permeability of the discs increases with the load-induced strain. A correlation is worked out between the increase in permeability and the applied-strain/yield-strain ratio. Finally, a relationship between mechanical damage indicators and the increase in permeability is also discussed.

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2014 La méthode de mesure de la conductivité thermique d'une substance par chauffage impulsionnel à l'aide d'une sonde cylindrique plongée dans cette substance et par observation de l'évolution consécutive de température du milieu a été souvent mise en application. La variante de cette méthode, décrite ici, et particulièrement adaptée à l'étude de matériaux de construction tels que mortiers, bétons, plâtres, etc..., présente la particularité suivante : la même sonde sert à l'émission de chaleur et à la détection de l'évolution de la température qui est celle de la sonde elle-même. Deux types de sonde ont été mis au point : 2014 fils de thermocouple soudés bout à bout aux extrémités libres desquels on mesure une f.é.m., 2014 fil d'acier dont on mesure la variation de résistance électrique. Ce procédé de mesure de la conductivité thermique locale d'un matériau de construction doit permettre l'étude des transferts simultanés de chaleur et d'humidité au sein d'une paroi soumise à un régime hygrothermique variable.Abstract. 2014 The method of measurement of thermal conductivity of a stuff by mean of the pulse heating of a cylindrical probe dived into this stuff and by observation of the temperature following evolution was often applied.Here we describe a variant of this method, which fits specially the study of building materials such as mortars, concretes, plasters and so on, for it presents a typical feature : the same probe serves simultaneously as a heat transmitter and a detector of the evolutive temperature of this very probe. Two différent probes were achieved : 2014 end to end brazed thermocouple wires, whose disconnected ends are used for the measurement of an e.m.f., -steel wire, whose electrical résistance variation is measured. This measuring process of the local thermal conductivity of building materials is likely to study simultaneous heat and moisture transfers inside a wall forced by a variable hygrothermal rate.

International audienceA new technical approach of a traditional method for the rapid (and therefore, non interfering) determination of the thermophysical properties of porous materials likely, a priori, to undergo coupled heat and moisture transfers is described. The improvements discussed here consist in the use of a heater film suiting the “method of the hot plane film” especially well. A comparison with former works by one of the method's author is made. Finally, the updated method is applied to a variety of particularly significant materials

Thermal stresses due to hydration heat release within concrete structures can lead to early age cracking particularly in cases of massive structures. In order to prevent, minimise and avoid this, a good knowledge of the evolution of cement-based material heat transfer properties at early stages of hydration is essential. In order to address the problem of the evolution of the thermal conductivity of fresh cement paste, two models developed by the authors are discussed: first, the 'apparent' thermal conductivity is calculated, assuming the fresh cement paste to be a multiphase material, which makes it possible to consider the material chemical evolution. The second modelling approach is based on the theory of heat and mass transfer within non-saturated porous media. The second modelling results appear to fit the experimental results better. Notation