Research On Carbonization Performance For Concrete Box Girder

Because the long-term use of concrete structures is closely related with our safety,the durability of concrete has got more and more attention from all walks of life.Carbonation is also an important aspect of the durability of concrete.The most significant impact is to change the acidity and alkalinity of concrete interior,caused corrosion,expansion and serious damage,and even the protective layer of concrete to be cracked.Ultimately,it brings significant risks to use and safety of structures.(1)This work expounds the mechanism of carbonization,and derives the diffusion control equation,and the similarity between heat transfer problem and carbonization problem in finite element software is also compared.Some existing research was to take a certain method to simplify and approach the carbonization process,and obtained a variety of theoretical models.There are also many studies that aimed at various factors influencing carbonization,and studied the degree of influence.In particular,when the carbonization problem is studied by using computer technology,the main factors are directly coupled into a major factor,which is more intuitive and has significant effects and results.Based on existing carbonation models and research conclusions,this paper focuses on the characteristics of concrete box girder in the construction,especially the mechanical characteristics,from the theory of concrete carbonation.(2)The rapid carbonation test of concrete box girder model his carried out to explore the influence of special structure of box girder on carbonation.And numerical simulations for box girder model are undertaken by using finite element software and the APDL program.At the same time,combined with the results of carbonization test and numerical simulation,it calibrates the numerical model and proves that it is reliable and effective to study the concrete carbonization problem in this way.The statistical results show that the carbonization depth of concrete in the outer corner area is 1.56 times of that of the non-corner concrete,which is about twice that of the inner corner concrete.The carbonation of the flange end region is a simple one-dimensional carbonation at an early stage.As the reaction progresses to the late stage,the carbonation reaction is accelerated at the end of the concrete due to the increase in the depth of carbonization of the upper and lower edges.(3)The carbonation performance of concrete box girder under natural conditions is analyzed numerically under stress condition.In the natural environment,because of the low CO2 concentration,the carbonation of concrete takes a long time,and the long-term exposure test has a great deal of limitation for the premise that it is necessary to lead the study conclusion in a relatively short period of time,So the advantages of numerical analysis method for carbonation problem is obvious.By the analysis,the distribution law of carbonization depth in the section of box girder is obtained,and the time required to reach the thickness of protective layer of concrete box girder is also predicted.The results show that the outer corner of the concrete box girder under the stress state and the non-stress state is the region most affected by carbonization,and the carbonation rate is higher than that of other parts.