Research On The Protective Performance Of Fast-Curing And Early-Strength Polyurea Coating In Marine Environment

With the development of the marine industry,more and more marine structures are built.The complex marine environment will have a certain impact on the marine structure,especially the seawater immersion,natural exposure,dry-wet cycle,and shorten its service life.The coating has a certain protective effect on the marine concrete structure,and the fast curing and early strength polyurea coating(Fp)also has the characteristics of fast curing,which not only improves the protective ability of the concrete substrate,but also quickly repairs the damage of the substrate due to the marine environment.Therefore,it is of great significance to study the protective performance of coatings in marine environments/the marine environment.In this paper,the change of hardness,glossiness,tensile strength(Tsl),elongation at break(Eb)and tear strength(Tss)of fast curing early strength polyurea coating and pure polyurea coating were investigated using/utilizing ageing resistance test and temperature and humidity resistance test;the chloride ion penetration resistance of pure polyurea and fast curing early strength polyurea XS-7 coating concrete was studied,as well as the chloride ion penetration resistance in the presence of cracks Protection capability.In addition,scanning electron microscopy(SEM)and Fourier transform infrared spectroscopy(FTIR)were used to investigate the changes of surface morphology,chemical bond and coating structure of fast curing early strength polyurea and pure polyurea coatings under simulated seawater immersion,10% sulfuric acid immersion and temperature and humidity.Based on the above experiments,the following conclusions are obtained.1.Curing in normal temperature(23?),high temperature(70?)and low outdoor temperature(-1?-6?)environment,it is found that the mechanical properties of fast curing and early strength polyurea XS-1 increase faster in a short period of time.It has a certain protective performance,which is of great significance for its application in the repair and protection of concrete structures.After soaking in a 3.5% Na Cl solution for 240 days,the coatings' surface properties and mechanical properties decreased as a whole.The contact angle and tensile strength of pure polyurea coating decreased by 33.19% and 29.14%respectively;the contact angle and tensile strength of XS-1 decreased by 38.81% and 8.80%respectively;the contact angle and tensile strength of XS-7 decreased by 37.48% and 18.52%,respectively;the contact angle and tensile strength of XS-8 decreased by 34.10% and 17.35%,respectively.SEM analysis showed that the surface of fast curing early strength polyurea and pure polyurea coating was powdered,white filiform attachments appeared,and some cracks and cracks appeared.The corrosion ions in the coating chloride salt will penetrate into the coating through the bubbles and micropores generated in the process of coating preparation and curing,thus damaging the coating.After 210 days of dry-wet cycle,the contact angle of pure polyurea,XS-1,XS-7 and XS-8 coatings decreased by 31.25%,33.57%,24.21% and 33.60% respectively,and the tensile strength decreased by 23.12%,23.44%,16.60% and 15.31%,respectively.The results show that the surface properties and mechanical properties of the coatings show a downward trend.The chloride ion concentration difference formed in dry-wet cycle accelerates the corrosion of chloride ion on the coatings,thus reducing the performance of the coatings.2.The surface properties and mechanical properties of the coatings under natural exposure were studied.The results showed that after natural exposure for 210 days,the gloss of pure polyurea decreased by 90.06%,almost completely lost light.The tensile strength of pure polyurea,XS-1,XS-7 and XS-8 coatings decreased by 24.93%,25.94%,17.35% and31.29%,respectively.The ultraviolet radiation and coating's swelling lead to the fracture of the molecular bond of the coating,which leads to the degradation of the performance.After soaking in 10% sulfuric acid for 210 days,the light loss rate was 19.49%,62.49%,58.73%and 49.56%,the tensile strength decreased by 23.52%,28.41%,21.56% and 40.14%,and the tear strength decreased by 3.57%,38.70%,28.52% and 39.50%,respectively.Compared with the acidic condition,the surface properties and mechanical properties of the coatings in alkaline solution decreased slightly.At the same time,the FTIR spectra of pure polyurea and XS-1 coating soaked in 10% sulfuric acid solution for 90 days show that the stretching vibration peaks at N-H,C-H,C = O and C-O-C are weakened,and the chemical bond is not obviously damaged.3.There is no crack in the low temperature bending area of the coating after various environmental treatments,which indicates that the pure polyurea and fast curing early strength polyurea coating has good flexibility.The Shao D,glossiness,contact angle,tensile strength and tear of Pp,XS-1,XS-7 and XS-8 were decreased in varying degrees after 210 days of alternating temperature and humidity.The tensile strength of the coatings decreased by 21.52%,27.28%,18.98% and 26.43%,respectively,after 210 days.The FTIR spectra show that the stretching vibration peaks at N-H,C-H,C = O and C-O-C of pure polyurea and XS-1 coating after 90 days of temperature and humidity are weakened,and the chemical bond is not obviously damaged.4.The change of chloride ion content of pure polyurea and XS-7 coated concrete under natural immersion was studied.At 5mm,the chloride ion content of pure polyurea coated concrete after immersion for 30 d,60d,90 d and 120 d decreased by 94.37%,92.96%,93.03%and 93.61% respectively compared with uncoated concrete.The chloride ion content of XS-7 coated concrete after immersion for 30 d,60d,90 d and 120 d decreased by 94.37%,92.96%,93.03% and 93.61% respectively compared with uncoated concrete 36%,92.75%,92.96%,93.61%.In the crack following test,the crack following elongation of the coating increases with load increase,but the curve of pure polyurea decreases faster than that of XS-7,indicating that the flexibility of fast curing early strength polyurea film is greater than that of pure polyurea film.In conclusion,the surface properties and mechanical properties of pure polyurea and fast curing early strength polyurea coatings in various corrosive environments have obvious changes.Their properties gradually decrease with the increase of test age,but they still have certain protective properties.