GAS PERMEABILITY OF CONCRETE: DEFINITION OF A PRECONDITIONING PROCEDURE FOR MEASUREMENTS AND CROSSOVER TRIALS

This paper describes the main results obtained jointly by a number of French laboratories within the framework of a group under AFREM (Association Francaise de Recherches et Essais sur les Materiaux et les Constructions). The objectives of this group were to define a preconditionin g process which would result in a better distinction between the various types of concrete with an acceptable test length, and to draft a recommendation for measuring the gas permeability of concrete. The procedure for measuring the gas permeability of concrete provides good reproducibility. However, the equipment used does not allow the measurement of permeability values greater than 10 -19 m². A conditioning procedure for predrying a test sample before measurement was defined. This conditioning procedure is the result of a compromise among the necessary attributes of a test, which should be easy to apply and as rapid as possible, while not degrading the test sample excessively. A drying temperature of 80°C was selected, with two permeability measurements (at seven and 28 days). It was noted during the tests that the moisture content of the material had a considerable impact on gas transfer, and consequently that measuring permeability alone was not sufficient to distinguish between concrete types. It is absolutely essential that this test be accompanied by a measurement of mass loss, and a graph representation of permeability as a function of mass loss seems to be the only effective way of distinguishing between types of concrete.