Study On The Effect Of Sulfate Corrosion On The Mechanical Properties And Durability Of Concrete Beams

There are a large number of salt lakes and saline soils in northwestern my country.Salt corrosion problems caused by these special geographical environments are very common.Due to salt corrosion,many reinforced concrete structures have suffered premature diseases and even structural failures,which have seriously affected The service life of the structure.Among the salt corrosion problems,sulfate corrosion is particularly prominent and needs to be paid attention to.Common sulfate corrosion mainly occurs in industrial buildings（such as chemical plants）,underground buildings,buildings on the coast,road and railway facilities in saline soil environments,and hydraulic structures in inland salt lakes.For concrete bridges,not only the foundation piers,but also the upper beam bodies have suffered serious sulfate corrosion problems.There are many sources of these sulfate ions,such as the evaporation of water in the saline soil,the erosion of the saline soil by rain water,and the effect of acid rain.With the rapid development of the world today,various roads,railways and other infrastructures in our country are under vigorous construction,and higher requirements are put forward on the safety and durability of concrete structures.Therefore,it is necessary to conduct research on sulfate corrosion of concrete structures.This paper takes the concrete box beam as the research object to analyze the influence of sulfate on the mechanical properties and durability of the concrete beam.In this paper,the flexural mechanical properties of two test beams corroded at 0d and60d are studied through experiments,and an ABAQUS finite element analysis is established.The plastic damage model is used to reflect the sulfate corrosion.Combined with the experiment,the concrete beams under long-term sulfate corrosion are further analyzed.Changes in mechanical properties and deterioration of durability,the main research contents of this article are as follows:（1）Design the size and reinforcement of the test beam,prepare a 10%Na₂SO₄solution,and conduct a static failure test on the test beams that have been corroded for 0d and 60d by means of dry and wet cycles.It is found that the compressive strength of the concrete in the60-day-corroded test beam has been improved to a certain extent compared with that before the corrosion,and the mechanical properties of the concrete under bending have also been partially improved.It shows that in the early stage of corrosion,sulfate will improve the strength,stiffness and mechanical properties of concrete beams.（2）The calculated values of the bending mechanical properties of corrosion 0d and 60d obtained by the ABAQUS finite element model are in good agreement with the test results,indicating that the test results are reliable and the ABAQUS nonlinear analysis is also feasible.The model is used to study the stress conditions that have not been analyzed in the test,and the crack propagation conditions of different corrosion days are compared and analyzed.（3）Use the ABAQUS finite element model to further analyze the changes in the mechanical properties of the test beam under long-term sulfate corrosion.Under the effect of long-term sulfate corrosion,the overall bending mechanical properties of the test beam are gradually degraded,and the degradation rate is getting faster and faster.Secondly,by fitting the calculation results of the model,the flexural bearing capacity degradation model of the test beam and the degradation of its effective flexural cross-sectional area are deduced.It shows that under the condition of long-term sulfate corrosion,due to the peeling of concrete,the flexural resistance The reduction of the effective cross-sectional area degrades the rigidity of the beam body and causes the continuous degradation of the flexural load-bearing capacity.（4）Finally,considering the resistance degradation caused by sulfate corrosion of the beam,based on the reliability theory,a life prediction model for the bearing capacity of the concrete structure is established,and the corresponding function function is established.Substituting the deduced flexural bearing capacity degradation model of the test beam into it,and combining the calculation examples to obtain the service life of the test beam under a specific load environment.And through another calculation example,the service life of an actual bridge under the condition of sulfate corrosion is obtained.In summary,the basic ideas and recommended steps for the life prediction of concrete bridges whose upper beam structure is corroded by sulfate are further given.