胶州湾跨海大桥箱梁氯离子侵蚀状态及细观结构特征分析

Chloride Ion Erosion State and Microstructural Features of Box Beams of Jiaozhou Bay Bridge

为明确胶州湾跨海大桥箱梁现阶段的氯离子侵蚀状态及箱梁混凝土当前的细观结构特征,依托胶州湾跨海大桥暴露试验站进行了取样测试,测试了总氯离子浓度、自由氯离子浓度,并开展了工业CT扫描。通过暴露试件氯离子浓度曲线拟合,分析了现阶段箱梁的氯离子侵蚀状态;根据历史测试数据,分析了北方高纬度海域自然暴露条件下的表面氯离子浓度以及龄期衰减系数;通过对工业CT扫描数据进行分析,研究了箱梁混凝土当前阶段的细观孔结构特征,包括孔隙分布、孔隙率、孔隙尺寸等。研究结果发现:在当前阶段,胶州湾跨海大桥箱梁的氯离子侵蚀最大深度为14~28 mm,表观氯离子扩散系数与有效氯离子扩散系数的比值为1.24~2.77;大气区与浪溅区氯离子结合性能差异较大,大气区氯离子结合系数随深度的变大而逐渐变大,并趋于稳定;在北方高纬度海洋环境下,大气区与浪溅区表面氯离子浓度演变均可采用对数增长规律描述,胶州湾跨海大桥箱梁氯离子传输的龄期衰减系数为0.6129;当服役13.7 a时,胶州湾跨海大桥箱梁混凝土孔隙率为1.05%,等效孔隙直径服从对数正态分布,孔隙表面积与孔隙体积服从指数分布。

To understand the chloride ion erosion state and the microstructural features of box beams of Jiaozhou Bay Bridge in the current stage,sampling tests were conducted according to the supports of exposure test station of Jiaozhou Bay Bridge.Total chloride ion concentration and free chloride ion concentration were tested,and industrial CT scan was also completed.By fitting the chloride ion concentration curve of the exposed specimens,the chloride ion erosion state of box beams in the current stage was investigated.Based on historical test data,the surface chloride ion concentration and age decay coefficient under natural exposure conditions in high latitude northern sea areas were analyzed.Through the analysis of industrial CT scan data,the microscopic pore structure characteristics of box girder concrete at the current stage were studied,including pore distribution,porosity,pore dimension,etc.The research results find that in the current stage,the maximum chloride erosion depth of box beam of Jiaozhou Bay Bridge is around 14~28mm.The ratio of apparent chloride ion diffusion coefficient to effective chloride ion diffusion coefficient is 1.24~2.77.There is a big difference between the chloride ion binding performances of specimen in atmospheric area and splash area.The binding coefficients of chloride ion in atmospheric area increase gradually with the increase of the depth,and then tend to be stable.In the high latitude marine environment of the north,the evolution of surface chloride ion concentration in atmospheric and splash areas can be both described by logarithmic growth law.The age decay coefficient of chloride ion transport is 0.6129 for the box beams of Jiaozhou Bay Bridge.When in service for 13.7 years,the porosity of the box girder concrete of Jiaozhou Bay Bridge is 1.05%,and the equivalent pore diameter follows a lognormal distribution.The pore surface area and pore volume follow an exponential distribution.