Abstract
Oxygen permeability tests were carried out on plain ordinary Portland cement (OPC) and fly ash concretes at three nominal strength grades. Prior to testing the concretes were subjected to a wide range of curing and exposure conditions. The results emphasize the importance of adequate curing to achieve concrete of low permeability, especially when the ambient relative humidity is low. In addition, the results demonstrate the considerable benefit that can be achieved by the use of fly ash in concrete. Even under conditions of poor curing, fly ash concrete is significantly less permeable than equal-grade OPC concrete, the differences being more marked for higher-grade concretes. Attempts were made to correlate strength parameters with permeability but it is concluded that neither the strength at the end of curing nor the 28-day strength provides a reliable indicator of concrete permeability. A reliable correlation was established between the water to total cementitious material ratio [w/(c+f)] and the permeability of concretes subjected to a given curing and exposure regime.
Resume
On a effectué des essais de perméabilité sur des bétons de ciment Portland ordinaire non armé (OPC) et sur des bétons aux cendres volantes de trois classes de résistance nominale. Auparavant, on a soumis les bétons à toute une gamme de conditions de conservation et d’exposition. Les résultats font ressortir l’importance d’une conservation adéquate pour obtenir un béton de faible perméabilité, surtout quand l’humidité relative ambiante est basse, et démontre, de plus, l’avantage considérable que procure l’utilisation de cendres volantes dans le béton.
Même dans des conditions médiocres de conservation, le béton aux cendres volantes est beaucoup moins perméable que le béton OPC de classe équivalente, les différences étant plus marquées pour des bétons de haute classe. On s’est efforcé d’établir une corrélation entre les paramètres de la résistance et la perméabilité, mais on a conclu que ni la résistance en fin de conservation, ni la résistance à 28 jours, ne sont des témoins fiables de la perméabilité du béton. On a établi une corrélation sûre entre le rapport eau/matériau cimenteux total (w/(c+f)) et la perméabilité des bétons soumis à une conservation donnée et à un régime d’exposition.
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Thomas, M.D.A., Matthews, J.D. The permeability of fly ash concrete. Materials and Structures 25, 388–396 (1992). https://doi.org/10.1007/BF02472254
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DOI: https://doi.org/10.1007/BF02472254