Study On Protective Performance Of Coated Concrete Under The Action Of Marine Environment And Bending Load

The marine environment is complex and changeable.The deterioration of the concrete structure and the corrosion of the internal reinforcement caused by the erosion of chloride ions is an important factor affecting the service life.Dry and wet alternately,load and other factors combined with chloride ions and other corrosive media has a more adverse impact on the durability of concrete structure.Coating protection of concrete structures is one of the most simple and effective methods.In this paper,the conventional properties of Qtech T501-Ⅲand t54 protective coatings and the protective effect on the mortar matrix under 3.5%NaCl solution were studied by electrochemical impedance spectroscopy（EIS）and chemical analysis,and the effect of dry and wet alternation and load on chloride ion erosion was further studied.Based on the above research,the following main conclusions are obtained:1.The results show that Qtech T501-Ⅲis a high gloss material and t54 is a low gloss material.In the outdoor exposure,chloride salt immersion,dry and wet alternating environment,loss of light of Qtech T501-Ⅲis greater than t54.Adhesion experiments show that the adhesion of Qtech T501-Ⅲhas a certain degree of decline in different aging environments and the adhesion of t54 decreased slightly,basically stable.The water absorption of the mortar without coating is 3.41%.The water absorption of the mortar coated Qtech T501-Ⅲand t54 are 0.66%and 0.48%,which indicates that the coating effectively blocks moisture intrusion.The solid contents of Qtech T501-Ⅲand t54 were 95.49%and 96.35%,respectively.The drying time of Qtech T501-Ⅲwas shorter than that of t54.After 120 days of outdoor exposure,the tensile strength of Qtech T501-Ⅲdecreased by 30.27%.The value of elongation at break and the tear strength show the characteristics of increasing first and then decreasing.The results of ATR-FTIR show that the peak intensity of some characteristic peaks is weakened to a certain extent.2.The EIS experiments show that the coated concrete reinforcement system is similar to the concrete reinforcement system,and the equivalent circuit is fitted with two time constants.The high frequency zone responds to the properties of the mortar（concrete）around the rebar,and the low frequency zone responds to the characteristics of the interface between the bar and the mortar（concrete）.In the early stage of the corrosion reaction,the equivalent data R（QR）（QR）can be used to fit the experimental data well and at the end of the corrosion reaction,the Warburg impedance is required to fit equivalent circuit.The concrete material has the characteristics of heterogeneity and inhomogeneity and the internal reinforcement has a certain roughness so that the electric field on the electrode surface exhibits nonuniformity,which is called the dispersion effect.So we need to use CPE to analyze electrochemical impedance.3.The charge transfer resistance R_ct of the mortar without protective coating after immersion in 3.5%NaCl solution for 15 days was 129.2Ω·cm²,which is less than the evaluation criteria of 250Ω·cm².After 90 days,the values of R_ct of the mortar coated t54 and Qtech T501-Ⅲwere 7937Ω·cm² and 1500Ω·cm² respectively,which shows that there is almost no corrosion in the internal reinforcement.After 15 times of wet and dry experiment,the value of R_ct of mortar coated t54 was 3552Ω·cm² and the value of R_ct of mortar coated Qtech T501-Ⅲwas 155Ω·cm²,which shows that in the drying-wetting cycle environment,the protective performance of t54 is better than that of Qtech T501-Ⅲ.4.The chloride ion concentration of the uncoated and coated mortar decreases with increasing depth under the condition that the mortar is completely immersed in the chloride solution.After 120 days,the chloride ion content at the depth of 4mm to6mm of uncoated,coated Qtech T501-Ⅲ,coated t54 mortar was 0.2591%,0.0344%and 0.0202%,respectively.The results of the chloride diffusion coefficient show that the mortar coated Qtech T501-Ⅲand t54 are reduced by 73.98%and 77.03%,respectively,compared with the uncoated mortar.It shows that the two coatings can effectively reduce the erosion effect of chloride ions on mortar.In the drying-wetting cycle environment,the chloride ion concentration of the mortar specimen shows the characteristics of the first increase and then decrease,which is related to the mechanism of drying-wetting cycles.There is a certain depth of convection in the surface of the mortar.After 60 times of drying-wetting cycles,the content of chloride ions at the depth of 4mm to 6mm was 0.2806%,0.0426%and 0.0278%,respectively,in mortar without coating,coated Qtech T501-Ⅲ,and coated t54.The chloride ion content is improved compared to the fully immersed environment.This indicates that drying-wetting cycles accelerate the aging of the coating and the deterioration of the mortar matrix,which in turn leads to an accelerated rate of chloride ion erosion.Experiments on the interaction between the load and the chloride ion show that the tensile stress can promote the development of microcracks and voids in the mortar,and accelerate the intrusion and penetration of chloride ions.The experimental results also show that a certain size of the compressive stress will make the channels of moisture and ion narrow in mortar and reduce the pores,which is beneficial to the protection of the coating.