Investigation On The Durability Of Surface Permeable Silicone Coatings In Marine Concrete

The concrete material is the one of the largest amount of materials in marine engineering. However, due to the complexity and diversity of marine environment, the marine structure corrosion occurs gravely, which diminish the safety and durability of marine concrete structure fearfully. Silicone protective coating which is widely used in marine engineering protection has excellent performance of heat resistance, stability to extremes of temperature, weathering resistance, and so on. But, the research on the durability of silicone protective coating is neglectful.Isobutyl triethoxysilane coating was selected from different manufactures. The silicone coating was brushed to the mortar specimens. To evaluate the durability performance of the silicone coating, the specimens were aged by single factor (light aging, heat aging, chemical corrosion and freeze-thaw cycle) and multiple corrosion factors circulation role. The main results are as follows:(1) After light and heat aging, water absorption of mortar specimens with the silicone coating was significantly greater than the water absorption of unaged mortar specimens, which was indicated that the protection of silicone coating to specimens was diminished. The result of thermal aging shows that with the increasing of temperature, the differences of water absorption in specimens with different silicone coating gradually decreased due to the increased damager of the silicone coating with the increment of aging temperature. Because of the silicone coating damaged by the combined effect of light and heat, water absorption of specimens after ultraviolet aging is larger than that after thermal aging.(2) According to calculate the peak area ratio of the silicon-oxygen-silicon bonds found that after specimens aging, the peak area ratio decreased, which because the adhesion performance of silicone and mortar degradation caused by aging. And the decrement of ultraviolet aging was larger than that of thermal aging, which means that silicone coating showed better performance under thermal aging.(3) With the help of Arrhenius equation to predict the service life of three silicone coatings found that:when the using temperature is low, the life of three kinds of silicone coating has a significant difference. The differences decreased with the increasing temperature. Within15℃to40℃, the life of silicone coating would accordingly reduce twice for every increase of5℃.(4) The mechanical properties of specimens that coated with silicone coating decreased with the extension of corrosion time. In the condition of alkali corrosion, the decrement of mechanical properties is least that means silicone coating has excellent performance in the alkali corrosion condition.(5) The compressive strength of specimens coated with silicone coating after100freeze-thaw cycle lost20%, and the flexural strength lost40%, that was much better than that of uncoated specimens. That shows that the silicone coating can reduce damage of freeze-thaw cycle to specimen. The mechanical properties were not very different after50freeze-thaw cycle and100freeze-thaw cycle, which means freeze-thaw cycle has less influence on the performance of the silicone coating.(6) The mechanism may be that silicone coating which applied to concrete surface could penetrate into a porous wall of the silicate material to form a thin repellent film that can provide protections to concrete. Therefore, it evidently debased the freeze-thaw injury caused by the water of capillary porosity.(7) In the condition of multiple corrosion factors circulation function, with the increase of the cycle number, the water absorption would increase, and the mechanical properties would decline rapidly. The damage of multiple corrosion factors to the silicone coating is much larger than the destruction of single corrosion factor on the silicone. After the first cycle, although the specimen was aged1d by ultraviolet radiation, because of the corrosion factors cycle role, the water absorption is much larger than that of the single light aging12d. After five times cycle, the specimen experienced50times freeze-thaw cycle, the mechanical properties of specimen is worse than that of single100times freeze-thaw cycle.