Evaluation of Hydrophobic Concrete Coatings in Tropical Marine Environments

摘要

This paper reports an eight-year field- and laboratory-based study carried out to compare the performance of two proprietary hydrophobic coating systems (silane- and siloxane-based coatings), designed to reduce chloride ingress and reinforcement corrosion. Their behavior in the laboratory was also compared by using concrete of two different mixes (w/c = 0.40 and 0.65). Tests were carried out on a Portland cement concrete with a w/c ratio of 0.4 and exposed to a very aggressive tropical marine environment (average parameters: T >28°C, RH > 80%, time of wetness > 60%, Cl~- > 160 mgm~(-2)d~(-2)). The following tests were performed to characterize the concrete mix both physically and mechanically: Compressive strength (ASTM Standard C 39); Total Absorption and Porosity (ASTM Standard C 642); Capillary Absorption (Fagerlund Technique); Rapid Chloride Permeability (ASTM C 1202). All tests were performed at 28 days of cure.Six reinforced concrete probes (three per coating), 15×15×30 cm, were placed in the exposure site. The rebars were placed into the probes to obtain concrete covers of 20, 25 and 30 mm. During the test period, evaluation of the climatic and environmental parameters in each of the exposure sites was based on the methodology established by ISO Standard 9233 for classifying atmospheric aggressiveness. The evaluation of half-cell potential (E_(corr)), corrosion rates (i_(corr)), and electrical resistivity of the concrete (p) was determined monthly. Corrosion rate was measured by the Linear Polarization Resistance (LPR) technique. The carbonation front and chloride concentration profiles were determined after an eight-year exposure.The results showed that when Siloxane-based coating is used there is an improvement in the behavior of the concrete with respect to chloride-ion penetration. The behavior of the coatings depends not only on the quality of the concrete, but also on the company who manufactured them.