Repair of aging structures is one of the major problems facing those responsible for maintaining our infrastructure economically. This is especially important for steel reinforced concrete structures that are beginning to fail due to corrosion of the steel from repeated exposure to chloride deicing salts or carbonation. To a large extent the choices have been the implementation of a cathodic protection system or extensive concrete repairs. In this paper, it is shown that a cost effective alternative based upon an organofunctional silane corrosion inhibitor surface post-treatment is a viable alternative.
One of the approaches used to impart corrosion resistance for new construction is the use of silane with or without inhibitors as a surface treatment or as an admixture. Friedel et al showed that a dry powder oligomeric silane corrosion inhibitor (Protectosil® DRY CIT(1)) was effective as an admixture at 2% and 4% by mass of cement.1 In addition, they showed good performance of a liquid organofunctional silane inhibitor (Protectosil® CIT(2)) surface treatment, when used before exposure to chloride, at 500 g/m2 (0.1 lb/ft2). The concrete had a 0.6 w/c with 10, 28 and 48 mm (0.39, 1.1, and 1.9 in) cover over the steel. Water absorption tests showed that the above silane products significantly reduced water ingress, with the organofunctional silane surface treatment being the most effective followed by the 4% admixed powder. Chloride ingress followed the same pattern. However, these numbers are influenced by the concrete resistance which increases over time and would lower macrocell currents. Other studies with water repelling admixtures have shown this,2-4 so additional work is needed to more accurately determine the threshold levels for chloride induced corrosion when drying is occurring under less severe conditions that will often be the case in the field.
