AN EXTERNAL SURFACE COATING TO PROTECT CONCRETE AND STEEL FROM AGGRESSIVE ENVIRONMENTS

Carbonation and chloride ions are known to be the two major factors re sponsible for the premature corrosion of steel reinforcement in concre te. Surface coatings on concrete can provide an effective and efficien t protection for both concrete and the steel embedded in it, and can e nhance the long-term durability of concrete materials and concrete str uctures exposed to aggressive environments. In practice, concrete is o ften cracked, and the crack-bridging ability of coatings is an importa nt factor to be considered in evaluating their performance characteris tics. Four different surface coatings were evaluated for their crack-b ridging ability by tests of exposure to ozone and ultraviolet light, a nd for their ability to control chloride penetration and steel protect ion by accelerated wet-dry or continuous salt spray tests. From these results, a highly elastic acrylic rubber coating was chosen for furthe r 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 i n 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 hi gh 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 l ong-term serviceability of the concrete structure is to be ensured.