Abstract
An experimental investigation is reported of drying and conditioning concrete at 50°C to obtain a uniform moisture distribution, prior to testing for air permeability and water absorption rate. The use of 100 mm cubes of concrete with a cast-in cylindrical cavity facilitated assessment of moisture distribution and measurement of air permeation through the surface layers of concrete: the moisture distribution was assessed by comparing the relative humidities measured within the cavity and at the surface of the test specimen. Partial drying followed by sealed storage at 50°C for a few days provided a rapid and convenient method of obtaining a uniform moisture distribution. The test results for a range of concretes indicated that air permeability and water absorption rate were very sensitive to the moisture content of the concrete, particularly at relative humidities above 60% and which were common for field exposure. The transport properties of the empty capillary pore system could be assessed using test specimens preconditioned at 60% relative humidity, but preconditioning at 85% relative humidity might be more appropriate for assessing field performance if there is a risk of carbonation induced corrosion.
Resume
On décrit une étude expérimentale de séchage et de conservation du béton à 50°C pour obtenir une distribution uniforme de l'humidité avant l'essai du taux de perméabilité à l'air et de la vitesse d'absorption de l'eau. L'utilisation de cubes de 100 mm de côté comportant une cavité cylindrique a facilité l'évaluation de la répartition de l'humidité et la mesure de la perméabilité à l'air au travers des couches superficielles du béton: la répartition de l'humidité a été évaluée en comparant les humidités relatives mesurées à l'intérieur de la cavité et à la surface de l'éprouvette. Un séchage partiel suivi d'un stockage étanche à 50°C pendant quelques jours apparaît comme une méthode rapide et commode pour l'obtention d'une répartition uniforme de l'humidité. Les résultats d'essais sur un éventail de bétons ont montré que la perméabilité à l'air et la vitesse d'absorption de l'eau étaient très liées à la teneur en humidité du béton, en particulier pour des humidités relatives dépassant 60%, qui sont courantes pour l'exposition in situ. On a pu évaluer les propriétés de transfert du système de capillarité des pores vides à l'aide d'éprouvettes préconservées à 60% d'humidité relative; cependant, la préconservation à 85% d'humidité relative pourrait convenir mieux à l'évaluation de la performance in situ s'il existe un risque de corrosion due à la carbonatation.
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Parrott, L.J. Moisture conditioning and transport properties of concrete test specimens. Materials and Structures 27, 460–468 (1994). https://doi.org/10.1007/BF02473450
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DOI: https://doi.org/10.1007/BF02473450