Action Mechanism And Nano-modification Of Penetrative Protective Agent Of Reinforced Concrete In Marine Construction

In the marine environment, the vast economic losses due to marine corrosion of reinforced concrete have become one of the most difficult problems for the world’s marine economic development, which drives governments and enterprises make great effort on the study of durability and protection of marine reinforced concrete. As one of the durability enhancing technologies for reinforced concrete, penetrative protective agent penetrates into concrete to form a hydrophobic protective film, which has attracted great attention. Up to now, researches about penetrative protective agent mainly focus on macro-protective properties of concretes with surface treatment, but the action mechanism of carbonation, freezing-thawing and durability on concrete remains unclear. Silane type products take a larger proportion of penetrative protective agent market, but have defects such as large quantity of volatile, long film-forming time and son on. Therefore, it needs more further studies on the action mechanism of penetrative protective agent of reinforced concrete and new type of agent.In this paper, we began with the review of marine engineering material durability enhancing technology and the research status of penetrative protective agent. Then the film-forming mechanism of penetrative protective agent on the concrete was studied by concrete moisture test, accelerated carbonation test, rapid freezing and thawing test, outdoor service test. After studying the protective performance of different types of penetrative protective agent, we prepared the nano-modified silane penetrative protective agent in the concrete anti-corrosion field by sol gel acid/base two-step process for the first time, which is rapid film-forming and effectively protective for concrete. The main work and conclusions are as follows:(1) Changing rule of penetration ability and protective properties of penetrative protective agent on concretes with different moisture was studied. The increasing drying time of concrete before surface treatment would lower the moisture of concrete, and also result in agent’s deeper penetration depth, shorter film-forming time and lower chloride charge passed. When drying time changed from 6 to 48h, penetration depth of concrete specimens increased 1.8mm, film-forming time decreased 36h and chloride charge passed of concrete with sreface treatment decreased by 80%.(2) Changing rule of carbonation depth of different compactness concretes with penetrative protective agent was investigated by accelerated carbonation test. The results showed that during the accelerated carbonation process, penetrative protective agent improved carbonation resistance on the higher compactness concretes, and carbonation depth of concrete with surface treatment was smaller than untreated specimen; on the contrary, penetrative protective agent accelerated the carbonation process on the lower compactness concretes, and the carbonation depth of concrete with surface treatment was larger than untreated specimen.(3) Changing rules of mass loss and dynamic modulus of elasticity decrease of concrete with penetrative protective agent were investigated by rapid freezing and thawing test. The results showed that the concrete specimens with surface treatment showed an obvious water-absorption weight compared with untreated specimens at the early 25 freezing-thawing cycles, then lost mass rapidly with proceeding freezing-thawing cycles, reaching 2.7% loss after 125 freezing-thawing cycles. During freezing-thawing cycles test, the decrease of dynamic modulus of elasticity of concrete specimen was accelerated by penetrative protective agent, decreasing 51.3% at most after 125 freezing-thawing cycles.(4) Changing rules of penetration depth and protective properties of penetrative protective agent on early-age concretes were studied by outdoor service test. The results showed that penetration depth of penetrative protective agent decreased gradually with a diminishing decrease extent, reaching a steady depth finally. Although penetration depth decreased, all surface-treated mortars kept excellent hydrophobic property, of which 24h water absorption reduced more than 90% throughout the outdoor service test.(5) The preparation and properties of nano-modified penetrative protective agent were studied. The nano-modified penetrative protective agent was prepared by solvent silane wrapping silica sol, showing fast film-forming and effectively protective properties on concrete. The nano-modified penetrative protective agent of only 4h film-forming time and optimal protective property was prepared with alkaline silica sol of 30nm particle size,20:1 composite proportion at reaction temperature of 20℃.