Research On Durability Of Concrete With Joints Under Chloride Environment

Bridge engineering is an important part of transportation infrastructure,and its large-scale construction is of great significance to the realization of my country’s "transportation power" strategy.Continuous beam bridges and fabricated simply supported beam bridges occupy a large proportion in bridge engineering due to their wide application range and convenient construction.However,during the construction of beam bridges,joints will inevitably occur(such as segmental casting of continuous beam bridges and the connection between beams of simple beam bridges),resulting in differences in structural performance at the joints.For concrete bridges serving in the coastal environment,the joints may become a fast path for the corrosion of harmful substances such as chloride ions,leading to the premature corrosion of the steel bars here.At present,there is little research on this aspect at home and abroad,and there is a lack of reasonable suggestions in the relevant regulations.To this end,this article has carried out research on chloride ion corrosion in jointed concrete members under different situations.The main contents are as follows:1.Research on the chloride ion transmission law in different joint types of concrete under chloride environment.The chloride ion erosion of jointed concrete specimens through three different types of joints(direct wet joints,shaved joints,and interfacial agent joints)under different erosion ages(90 d,180 d,270 d)In the test,the chloride ion concentration distribution in the concrete at and near the joints was detected.The results show that the impact of joints on the distribution of chloride ions in the concrete is mainly within 20 mm from the joints,and the concentration of chloride ions in the concrete at the direct wet joints is the largest;with the increase of erosion time,the joints are on both sides of the joints.The influence of chloride ion concentration distribution in concrete gradually increases;among the three types of joints,the chloride ion diffusion coefficient at the direct wet joint is the largest,and the chloride ion diffusion coefficient at the interface agent joint is the smallest.2.Study on the chloride ion transmission law of different joint materials in concrete under chloride environment.Through the chloride ion erosion test of three different joint materials(M5 mortar,M10 mortar,grouting)with jointed concrete specimens under different erosion times(90 d,180 d,270 d),the different positions of the Distribution of chloride ion concentration.The results show that the chloride ion concentration of the concrete on both sides of the joint is less than the chloride ion concentration at the joint;within 20 mm from the joint,the closer to the joint,the greater the chloride ion concentration,while the chlorine concentration outside the joint is 20 mm.The ion concentration has no obvious change with the increase of the distance from the joint;the relationship between the chloride ion diffusion coefficients of the three joint materials obtained by regression is: grouting material <M5 mortar <M10 mortar.3.Research on the transmission law of chloride ions in the new and old combined concrete under the chloride environment.By premixing a certain concentration of chloride salt solution in the concrete to represent the old concrete,three new and old combined concretes with different initial chloride ion concentrations(0.5%,0.75%,and 1% sodium chloride solution are used to pour the base concrete)The specimens were immersed in a chloride solution at different times(90 d,180 d,270 d)to detect the free chloride ion concentration in the joint area and the nearby concrete.The results show that the chloride ion concentration in the joints and the concrete on one side of the pre-chlorinated salt solution is significantly greater than that in the concrete mixed with limestone powder on the other side without the chloride salt solution,and with the increase of the initial chloride ion concentration,the joints at the same depth The chloride ion concentration increases,and with the extension of the erosion age,its influence further increases;with the increase of the limestone powder content,the chloride ion concentration at the joints gradually increases.4.Simulation of chloride ion transmission process in concrete with joints and prediction of durability life.Considering factors such as the thickness of the joint area,the diffusion coefficient of chloride ions,and the decay effect of the diffusion coefficient of chloride ions over time,a two-dimensional numerical model of the jointed concrete was established using Comsol software,and the diffusion process of chloride ions in it was carried out in a two-dimensional manner.Numerical simulation and calculation of the durability life of jointed concrete members under different parameters.The results show that the chloride ion concentration distribution obtained by the simulation is in good agreement with the test results;the durability life of jointed concrete components in the chloride salt environment increases with the increase of the thickness of the protective layer,and decreases with the increase of the thickness of the joint area.