| Due to the influence of various factors such as sunlight,water,oxygen and corrosive ions,the reinforced concrete structure in the marine atmosphere has premature failure,and the durability problem is becoming increasingly prominent.As one of the main protective means of reinforced concrete structures,organic protective coating plays a vital role in the protection of reinforced concrete structures.In this paper,three protective coatings,QF-162,QF-165 polyurea coating and QF-177 polyurethane coating were studied.The conventional properties of three protective coatings(gloss,tensile properties,hardness,contact angle and surface energy)were discussed.Combined with microscopic scanning electron microscopy(SEM)and infrared spectroscopy(FT-IR),the seawater corrosion resistance,acid corrosion resistance and long-term natural aging properties of protective coatings were studied.The focus is on the comparative study of the aging resistance of the three coatings in the outdoor long-term natural exposure environment.The main conclusions are as follows:(1)The changes of tensile strength,elongation at break,hardness,contact angle and surface energy of QF-162 and QF-165 polyurea coatings were studied during immersion in seawater,and the surface morphology and internal structure of the two polyurea coatings after seawater immersion were analyzed by SEM and FT-IR.The results showed that the tensile strength and elongation at break of the two polyurea coatings all decreased after 120 days of seawater immersion.The tensile strength of the two polyurea coatings decreased by 4.23% and 13.29%,respectively;The elongation at break decreased by 7.10% and 8.66%,respectively;After seawater immersion,the hardness of QF-162 and QF-165 polyurea coatings did not change much.The rate of change was-3.23% and 1.10%,respectively.The contact angles of the two polyurea coatings decreased with the immersion time,while the surface energy increased,which indicated that the wettability of the two polyurea coatings increased with the increase of seawater immersion time.After soaking for 120 days,the contact angles of the two polyurea coatings decreased by 6.08% and 4.46%,respectively;The surface energy increased by 15.83% and 12.20%,respectively;The SEM test results showed that the surface of the two polyurea coatings became rough and uneven after seawater immersion.Many cracks were formed on the surface of the QF-165 polyurea coating,and holes were partially formed on the surface of the QF-162 polyurea coating.The results of FT-IR study showed that the QF-162 and QF-165 polyurea coatings showed slight cracking of N-H chemical bonds on the surface of the coating after soaking for 120 days.The changes of other stretching vibration peaks were not obvious,and position of the peak basically kept the same of the stretching vibration peak as not immersion.(2)The acid corrosion resistance of QF-162 polyurea coating showed that the coating had a light loss rate of 1.45% when immersed in 10% sulfuric acid solution for 30 days,and the loss rate of light was 14.86% when the coating was immersed in 10% hydrochloric acid solution for 30 days.According to the degree of loss of light,the QF-162 polyurea coating did not lose light in the sulfuric acid solution,and slight loss of light occurs in the hydrochloric acid solution.The mechanical properties study found that after immersion in 10% sulfuric acid and hydrochloric acid solution for 30 days,the tensile strength of QF-162 polyurea coating was about 17 MPa,the elongation at break was about 480%,and the hardness was above 90.The higher tensile properties and hardness indicated that the QF-162 polyurea coating has better elastic properties.The surface performance test results showed that the contact angle of QF-162 polyurea coating decreased by 29.41% and 32.36% in 10% sulfuric acid and hydrochloric acid solution respectively,and the surface energy increased by 105.87% and 117.45% respectively.It can be seen that the same concentration of sulfuric acid and hydrochloric acid solution had little influence on the surface properties of QF-162 polyurea coatings.The results of SEM showed that the surface roughness of QF-162 polyurea coating increased with sulfuric acid and hydrochloric acid soaking,and there was no obvious crack on the surface of the coating,indicating that sulfuric acid and hydrochloric acid had little effect on the surface morphology of the coating.The FT-IR test results showed that the intensity of N-H stretching vibration peak on the surface of QF-162 polyurea coating slightly weakened during the soaking process of sulfuric acid and hydrochloric acid.The intensity change of other peaks was not obvious,indicating that acid immersion caused micro-fracture of chemical bonds on the surface of QF-162 polyurea coating.(3)The changes of macroscopical properties(gloss,tensile properties,hardness,surface properties)and microstructure(surface morphology and internal structure)of QF-162,QF-165 polyurea coating and QF-177 polyurethane coating under outdoor natural exposure environment were studied.The results showed that the gloss of QF-162,QF-165 polyurea coating and QF-177 polyurethane coating decreased after 2493 d outdoor exposure,and the loss rate of the coating was 86.84%,94.67% and 96.15%;According to the level of loss of light level,the gloss of the three coatings were completely lost,and the loss level of light is grade 5.After natural exposure for 2493 d,the tensile strengths of the three coatings were 16.02 MPa,15.25 MPa and 1.94 MPa,respectively,and the change rates were-29.37%,-39.12%,-91.52%,respectively;The elongation at break was 436.44% and 381.99%,and 30.78%,respectively.The rate of change was-14.38%,-17.57%,and-94.38%,respectively;The hardness change rate was 5.38%,10.99%,and 12.09%,respectively.The hardness reduction rate of QF-165 polyurea coating was about 2 times that of QF-162 polyurea coating.After 2493 d aging,the contact angle of QF-162 and QF-165 polyurea coating decreased by 53.91% and 60.93%,and the contact angle of QF-177 polyurethane coating could not be tested;SEM results showed that after aging for 2493 d,many fine cracks were formed on the surface of QF-162 polyurea coating,which were dentritic on the surface of the coating.The surface of QF-165 polyurea coating showed obvious defects,covered with different sizes.Meanwhile,some of the coating had peeled off,and the surface was getting rougher.The surface of QF-177 polyurethane coating was uneven,the shape of the coating was obviously wrinkled,and the coating peels off.FT-IR results showed that the chemical bonds of N-H,C=O and C-H on the surface of the three coatings were obviously broken after aging.Compared aging with that before 2493 d,it can be seen from the internal morphology of the three coatings that the internal sample structure of the coating was almost the same as that before aging,which indicated that under the outdoor natural exposure environment,the three coatings only aging on the surface,and the internal structure of the coating did not undergo any chemical bond breakage and redox reaction.Through the above experimental results,it can be found that the polyurea protective coating exhibits good corrosion resistance and aging properties in seawater,10% sulfuric acid,10% hydrochloric acid and outdoor natural exposure environment.Therefore,the polyurea coating is an excellent protective coating. |
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