Abstract
Carbonation and chloride ions are known to be the two major factors responsible for the premature corrosion of steel reinforcement in concrete. Surface coatings on concrete can provide an effective and efficient protection for both concrete and the steel embedded in it, and can enhance the long-term durability of concrete materials and concrete structures exposed to aggressive environments. In practice, concrete is often cracked, and the crack-bridging ability of coatings is an important factor to be considered in evaluating their performance characteristics. Four different surface coatings were evaluated for their crack-bridging ability by tests of exposure to ozone and ultraviolet light, and for their ability to control chloride penetration and steel protection by accelerated wet-dry or continuous salt spray tests. From these results, a highly elastic acrylic rubber coating was chosen for further long-term stability tests. The data presented show conclusively that the acrylic rubber coating can prevent penetration of water, air and chloride ions, and ensure the long-term durability of steel embedded in concrete both when the concrete is free of chlorides and when it is contaminated with sodium chloride up to 1% of the mortar matrix. At high levels of chloride in the concrete, a high cover is also essential if the benefits of the surface coating are to be fully realized, and long-term serviceability of the concrete structure is to be ensured.
Resume
La carbonatation et les ions chlorures sont connus comme les deux principaux facteurs de corrosion prématurée de l'armature d'acier du béton. Des revêtements de surface peuvent assurer une protection réelle et efficace à la fois du béton et de l'acier noyé dans le béton, et améliorer la durabilité à long terme des matériaux du béton et des ouvrages exposés à des milieux agressifs. Dans la pratique, le béton est souvent fissuré et il convient de considérer la capacité de reprise de fissuration des revêtements comme un élément important de l'évaluation de la performance. Cette capacité a été évalua'ee pour quatre revêtements de surface différents par des expositions à l'ozone et aux ultraviolets. On a aussi déterminé l'aptitude à contrôler la pénétration de chlorure et la protection de l'acier par des essais accélérés secs/humides et l'essai continu au brouillard salin. Sur la base de ces résultats, on a choisi un revêtement de caoutchouc acrylique très élastique pour des essais ultérieurs de stabilité à long terme. En conclusion, les données présentées montrent que le revêtement de caoutchouc acrylique peut empêcher la pénétration d'eau, d'air et d'ions chlorures, et assurer une durabilité à long terme de l'acier noyé dans le béton, à la fois quand le béton est exempt de chlorures et quand il est contaminé par des chlorures de sodium jusqu'à un taux de 1% de la matrice de mortier. Pour des niveaux élevés de chlorure, il est aussi essentiel que l'épaisseur d'enrobage soit élevée si l'on veut que les avantages du revêtement de surface soient pleinement réalisés et la durée de vie à long terme de la structure en béton assurée.
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Swamy, R.N., Tanikawa, S. An external surface coating to protect concrete and steel from aggressive environments. Materials and Structures 26, 465–478 (1993). https://doi.org/10.1007/BF02472806
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DOI: https://doi.org/10.1007/BF02472806