弯拉应力和硝酸作用下混凝土涂层抗碳化

Carbonation resistance of concrete coating under flexural tensile stress and nitric acid erosion

为研究涂层对承受弯拉应力和硝酸侵蚀作用下混凝土结构抗碳化防护效果,选用混合环氧树脂底漆、公路专用重防腐底漆、1103环氧通用底漆3种混凝土涂层体系,并考虑3种涂层体系和涂层厚度对混凝土抗碳化水平影响,进行100 mm(长)×100 mm(宽)×400 mm(高)标准棱柱体混凝土试块在硝酸侵蚀和弯拉应力共同作用下的室内快速碳化试验,采用酚酞指示剂法和分层取粉配制溶液测pH法对比分析弯拉应力、硝酸侵蚀、碳化时间和涂层种类及厚度等因素对混凝土结构的碳化影响。得到实验室标准碳化条件下单一弯拉应力等级和硝酸溶液浓度影响因素下混凝土结构碳化深度计算公式;提出考虑硝酸溶液浓度、弯拉应力等级和CO_(2)浓度的综合碳化模型;基于分层取粉配制溶液测pH法,结合涂层等效混凝土厚度理论,提出一种估算涂层抗碳化寿命预测模型。研究结果表明:随着侵蚀时间的推移,硝酸侵蚀和弯拉应力均提高混凝土碳化效率,较低浓度硝酸溶液、较高等级弯拉应力影响显著,混凝土试块在3种防护涂层保护下仍会受到CO_(2)和硝酸的侵蚀,但侵蚀程度大幅削弱;在涂层厚度相同时,1103环氧通用底漆的抗碳化防护效果最佳,混合环氧树脂底漆防护效果次之,公路专用重防腐底漆防护效果最差;涂层的防碳化效果主要由其包裹作用提供,但受涂层裂缝封闭性、附着度和耐酸性等差异造成防护效果不同;研究结果对大气环境下混凝土结构防护涂层选用具有指导意义,可为定量分析涂层抗碳化防护性能提供理论基础。

To study the carbonation-resisting protection effect of the coating on the concrete structure under flexural tensile stress and nitric acid erosion,three kinds of concrete coatings including mixed epoxy resin primer,heavy anticorrosive primer for highway,and 1103 epoxy general primer were selected,and the influence of three coating systems and coating thickness on the carbonation resistance level of concrete was considered.The rapid carbonation test of 100 mm(length)×100 mm(width)×400 mm(height)standard prismatic concrete specimens under the coupling effects of nitric acid erosion and flexural tensile stress in the laboratory was carried out.The phenolic phthalein indicator method and the pH measured by simulated pore solution made of layered powder were used to analyze the influences of flexural tensile stress,nitric acid erosion,and carbonation time on the carbonation of uncoated concrete structures and concrete structures with different coating types and thickness.The formula for calculating carbonation depth of concrete structure under bending tensile stress grade and nitric acid solution concentration under standard carbonation conditions in laboratory was obtained respectively.Based on the pH measured by simulated pore solution made of layered powder combined with the theory of equivalent concrete thickness of coating,a prediction model of coating carbonation life was proposed.The results show that with the increase of erosion time,both nitric acid erosion and flexural stress increase the carbonation efficiency,and the effect of lower concentration nitric acid solution and higher grade flexural stress are more obvious,and the effect of higher grade flexural stress is more significant.A comprehensive carbonation model considering the concentration of nitric acid solution,flexural stress level and concentration of CO_(2) is proposed.Under the protection of the three coatings,the concrete test blocks are still eroded by CO_(2) and nitric acid,but the degree of erosion is greatly reduced.When the coating thickness is the same,1103 epoxy general primer has the best anti-carbonation protection effect,followed by mixed epoxy resin primer,and highway special heavy anti-corrosion primer has the worst anti-carbonation effect.The anti-carbonation effects of the coatings are primarily provided by its sealing functions,which are different due to the differences of the crack-sealing property,adhesion and acid resistance.The research results are of significance to the selection of protective coatings for concrete structures in atmospheric environment and provide a theoretical basis for quantitative analysis of anti-carbonation protective properties of coatings.5 tabs,9 figs,32 refs.