The Preparation Of Organic And Inorganic Corrosion-resistant Coating And Its Protective Effect On The Durability Of Concrete

Concrete is prone to be corroded by corrosion media in marine environment and hence seriously affecting the service life of infrastructure.The steel corrosion in concrete structures in severe environment has been an interesting aspect in fields of corrosion and civil engineering materials.Surface coating has become an effective protection against steel bar corrosion of reinforced concrete structure.There are mainly divided into organic coating and inorganic coating.The organic coating possesses excellent water proof and corrosion resistant properties whereas poor aging resistance,insufficient adhesion and environmental pollution.The inorganic coating exerts outstanding aging resistance and high adhesion,but it fails in poor waterproof performance.The organic-inorganic hybrid composite coating offsets the traditional singe material’s defects and combines the two advantages of organic and inorganic materials.This paper aims to synthesis a SiO₂-PDMS composite coating with inorganic precursor TEOS,organic precursor PDMS in presence of coupling agent KH560.Firstly,the effect of addition level of KH560 on the composite sol-gel formation,structure,performance is explored.Secondly,the performance of SiO₂ as a modification agent of the composite coating to improve aging resistance and corrosion resistance has been monitored.Finally,the practical protective performance in ocean environment and protection mechanism of the synthesized composite coating is studied,providing theoretical basis for its practical application.Results in this study are summarized as follows:（1）The PDMS and KH560 content on SiO₂-PDMS had notable influence in coating performance of the resulting composite on cement surface.In the sol system,when PDMS and KH560 content is less than 100%,the resulting composite sol had appropriate viscosity,excellent stability and the satisfied gel time.However,when the PDMS and KH560 content were more than 100%,the PDMS and KH560 reacted to form a Si-O-Si network composite structure,which showed relatively low volume shrinkage and swelling degree.When the content was 100%,the composite coating presented the lowest bibulous rate,good hydrophobicity and film-forming on the cement surface,and the coating hardness and adhesion achieved high value 3H and 5A,respectively.However,composite coating with 100%PDMS and KH560 had poor resistance performance against heat,corrosion and aging.（2）The modification effect and mechanism of SiO₂ on KH550,structure and properties of SiO₂-PDMS as well as the coating performance of SiO₂-PDMS on the cement surface were studied.Results revealed that with addition of various SiO₂,the basic ultraviolet aging resistance were all significantly improved,while the hardness,adhesion level and hydrophobic properties of the synthesized composite coating remained the same.It is noteworthy that colloidal silica with particle size of about 100 nm in the reaction system had good dispersion and the shortest gel time.With assistance to the SiO₂ modification,the heat resistance of composite coating was improved,and exothermic peak temperature of composite gel appeared at 420^oC.Compared with the commonly used acrylic coating,inorganic coating and silicone coating,silica sol modified SiO₂-PDMS coating excreted best hydrophobic performance,the highest pencil hardness and adhesion level,and the highest bond strength.In addition,silica sol modified SiO₂-PDMS coating had no significant weight loss after soaking in acid and alkali corrosion situation for 48 h,only with little change in contact angle and chemical composition before and after ultraviolet aging and gloss.SiO₂-PDMS coating with lowest 7 d bibulous rate performed the best protection on cement.（3）The SiO₂-PDMS composite coating,acrylic coating,inorganic coating and organic silicon coating on the protective effect of concrete with exposure to the various corrosive environment（CO₂ corrosion,salt fog corrosion,sea water corrosion）were studied.Results showed that in CO₂ corrosion environment,the carbonation depth of SiO₂-PDMS composite coating were only 1.4 cm and 2 cm after 14 d and 28 d,respectively,and the calcium carbonate percentage were 4.77%.The quality of the carbide 1420 cm^-1 wave was narrow,indicating a sound corrosion resistance performance.Under the corrosion condition of salt fogging for 1000 h,quality rate of SiO₂-PDMS composite coating increased at the least rate with only 0.24%,and the chloride ion content were only 0.02%.This indicated an excellent resistance performance of SiO₂-PDMS against fog corrosion.Under the condition of seawater immersion corrosion for 240 d,quality rate of SiO₂-PDMS composite coating was 0.24%.The chloride ion penetration depth was 0.13 mm,and the chloride ion content of specimen with surface depth of 0-0.5 cm and 0.5-1 cm were 1.17 mg/L and 0.49 mg/L,respectively,which were lower than the other three kinds of coatings.