| The marine economy is currently in an important period of rapid development.A large number of marine reinforced concrete structures are under construction or planning,and their protection is still a key concern.Concrete coating protection technology is currently a relatively simple and effective way.In this paper,polyurethane?urea?and polyurea were studied.The effects of isocyanate group?NCO?content and resin structure on the basic properties and hydrogen bonding of polyurethane?urea?were investigated.The macro-microscopic properties of the three coatings and the macro-microscopic changes at the interface of the coating mortar under the conditions of outdoor exposure,chloride salt immersion and bending load coupled with chloride salt immersion were studied by Fourier transform infrared spectroscopy?FTIR?,scanning electron microscopy?SEM?,and interface strain gauge method.It showed that all three coatings had good protection performance.The main conclusions were as follows:?1?The results of the study on the structure and properties of polyurethane?urea?coatings showed that with the increase of NCO content from 8%to 12%,the gel time and surface drying time of polyurethane?urea??referred to as QT420 polyurethane?urea??coating prepared from F420 polyaspartate resin decreased from 203 s and 576 s to 166s and 289 s;while the mechanical properties of the coating increased,the contact angle decreased gradually,the surface energy increased,and the hydrogen bonding degree of the carbonyl region increased from 52.71%to 56.50%.For the NCO content of 10%,polyurethane?urea?prepared by F524 polyaspartate resin?referred to as QT524polyurethane?urea??had longer gel time and flexibility,while QT420 polyurethane?urea?had greater tensile strength,tear strength,hardness,contact angle and hydrogen bonding.?2?After 210d outdoor exposure,the tensile strength change rate of QT420polyurethane?urea?and polyurea coatings was about-17%,and the maximum change rate of tensile strength of QT524 polyurethane?urea?coating was-18.74%,the gloss and contact angle of the two polyurethane?urea?coatings showed samller changes than the polyurea coating.FTIR analysis of the surface of the coating revealed that the chemical bonds appeared to varying degrees of fragmentation,and SEM analysis of the surface of the polyurea coating revealed cracks on the surface of the coating.The hydrogen bonding degree of the carbonyl region of the QT524 polyurethane?urea?coating increased after 210 days of outdoor exposure.After the coating mortar block was exposed for 210 days,the adhesion of QT420 polyurethane?urea?,QT524polyurethane?urea?and polyurea coatings were more than 2 MPa,and the adhesion was still maintained.The SEM cross-section showed that there were no obvious crack at the interface between the coating and the mortar.The static strain at the interface of the coating mortar showed that the interfacial strain of QT420 polyurethane?urea?coating mortar was at a stable state under room temperature conditions.After 30 days of outdoor exposure,the strain change trend firstly rose and then stabilized,and the strain changes at the corner points were larger than the center point,indicating that outdoor exposure had a certain degree of influence on the interface performance of the coating mortar.?3?After the chloride salt immersion for 210d,the polyurea coating showed a minimal decrease performance,followed by QT420 polyurethane?urea?coating and QT524 polyurethane?urea?coating.Through the surface FTIR analysis of the coating,it was found that the surface of the coating was hydrolyzed and a certain degree of chemical bond cleavage occurred.The hydrogen bonding degree of QT524polyurethane?urea?decreased slightly after 210 days of chloride salt soaking.Under the conditions of chloride salt immersion and bending load coupled with chloride salt immersion,the adhesion of the loaded coating decreased more.It could be seen from the SEM cross-section that the interface was closely attached,which indicating that the excellent adhesion properties between the three coatings and the interface.Through the static strain study at the interface of the coating mortar,it was found that the strain of QT420 polyurethane?urea?coated mortar tends to be slightly increased after immersion in a single chloride salt,and the strain applied with the bending load first decreased and then rose slightly and stabilized,and the change in strain indicated a change in interfacial adhesion properties.?4?The corrosion resistance of the coating mortar against chloride ion showed that the chloride ion content of the load applied mortar was slightly higher during the same corrosion time;the chloride ion content QT524 polyurethane?urea?coated mortar,QT420 polyurethane?urea?coated mortar,polyurea coated mortar at the same depth showed a declining trending.After the coupling of bending load and chloride salt immersion for 210 days,the chloride diffusion coefficients of the three coatings were4.29×10-13m2/s,4.40×10-13m2/s and 3.38×10-13m2/s,and the chloride ion diffusion coefficient of the coating mortar was much lower than that of the uncoated mortar,indicating that the coating had good resistance to chloride ion penetration. |
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