Research And Application Of Maintenance Methods And Durability Assessment For Coastal Environmental Concrete Bridges

For a long time in the past,concrete bridge construction has always been concerned with safety over durability,which leads to the failure of many bridges due to durability problems before reaching the designed service life,especially in the harsh environment such as the coastal area.Chloride erosion is a key factor affecting the durability evaluation and residual life prediction of concrete bridges in coastal environments.Therefore,it is particularly important to study the invasion law of chloride in concrete and seek for effective durability maintenance methods.Based on the reconstruction and expansion project of Huiyan Expressway in Shenzhen section,the chloride diffusion model and effects of two durability maintenance methods,namely amino carboxylic acid rust inhibitor and zinc sacrificial anode protection system,were studied.The main research work and achievements include:1.A long-term（540 days）simulateing the coastal environment durability experiment was designed and carried out.The chloride diffusion rule and effects of two durability maintenance methods,namely amino carboxylic acid rust inhibitor and zinc sacrificial anode protection system,were tested and studied.Specimens of ordinary concrete,mixed rust inhibitor,migration rust inhibitor and sacrificial anode system were designed and made.NaCl solution,（NH₄）₂SO₄and nitric acid mixed solution and periodic atomization spray were used to simulate the action of chloride erosion,acid rain and dry-wet circulation in the coastal environment.2.Based on the analysis of basic chloride diffusion model,the influencing factors of chloride diffusion coefficient and the existing diffusion model are collected.The results of long-term simulation experiment are used to compare and analyze the existing diffusion model.The results show that some of the models have some reliability,but they do not fully consider the influence factors of diffusion coefficient and are not suitable for wet and dry alternate environments.Considering the influences of water-cement ratio,service time,temperature,relative humidity,chloride binding capacity,concrete degradation and load on diffusion coefficient,and combining with the time-varying of chloride concentration on concrete surface,a chloride diffusion model based on water-cement ratio in dry and wet alternate environment was established.The model is in good agreement with the experiment data and broadens the applicable scope of the diffusion model.3.Based on the characteristics of information collection of existing concrete structures and considering the practicality,a chloride diffusion coefficient model with concrete strength as the main parameter,which is easily obtained in engineering practice,is tentatively constructed.On the basis of collecting and sorting out chloride diffusion coefficient and concrete strength test results of 11 concrete structures in coastal environments,a practical model of chloride diffusion based on concrete strength was proposed,and its feasibility was verified by comparison with the lone-term simulation experiment results.At the same time,a durability evaluation method for existing concrete bridges is proposed.4.Based on the action mechanism of amino carboxylic acid rust inhibitor and zinc sacrificial anode protection system,combined with the long-term simulation experiment data,the long-term protection effects of the two durability maintenance methods were studied and compared.The results show that both the amino carboxylic acid mixed and migration rust inhibitor can effectively improve the durability of concrete,among which the chloride invasion resistance is increased by 16%～20%,the carbonization resistance is slightly improved,and the compressive strength changes little.The two maintenance methods can effectively protect the rebar and slow down the corrosion rate at different chloride concentrations.Among them,the rust resistance efficiency of sacrificial anode system can reach 60%when the material is sufficient,and that of rust inhibitor is about 30%-50%.Order of rust resistance effect:zinc sacrificial anode protection system>amino carboxylic acid mixed rust inhibitor>amino carboxylic acid migration rust inhibitor.