Study On The Performance Of Concrete Resistance To Sulfate Attack Under Combined Cyclic Environments And Flexural Loading

The research of concrete resistance to sulfate attack has become an importantpart of the durability of concrete. In the thesis, many factors were selected for thedurability test of concrete under multi-factors coupling actions, including5%and10%concentration of sodium sulfate erosion solution, bending stress of0and50%, asteel fiber volume content of0and1%and2%, fly ash content of0and20%,concrete strength ranged from C30to C70and dry-wet cycle, etc. Meanwhile, atwo-dimensional numerical simulation was carried out to analyze the distribution ofsulfate ions in the concrete.The research results show that the failure process of concrete subject to sulfateattack can be divided into two stages. The first stage is, in the early days of erosion,the sulfate attack products gypsum and ettringite filling up the pores of the concrete,which makes the concrete denser. Evaluation index, such as relative weight anddynamic elastic modulus of the concrete etc., were growing with erosion time; thesecond stage is, after pores of the concrete were completely filled, gypsum andettringite still continue producing, which lead to concrete expansion cracks andspalling. While the evaluation index would declining continuously after reached thepeak. Finally, the concrete damaged due to cracking off serious or evaluation indexdropped too much.The study found that the steel fiber can enhance the performance of concreteresistance to sulfate attack effectively, especially for the concrete under bending stress.Compared with the concrete without steel fiber, the concrete with1%volume contentsteel fiber can enhance concrete anti-erosion ability to a large extent. Although theconcrete with2%volume content steel fiber has a stronger anti-erosion ability thanthe concrete with1%volume content steel fiber, the effect is not significant. Fly ashcan also improve the ability of concrete resistance to erosion. As for the factor ofconcrete strength, it has a certain influence to anti-erosion ability. Bending stressapplied to sulfate attack of concrete favorable channel to accelerate the destruction ofthe concrete. The applied bending stress provides a favorable channel for sulfateattack to the concrete, which accelerate the destruction of the concrete. Base onimpact factors as steel fiber, concrete strength, bending stress, combined withsubstances decay law, a concrete damage decay model, which selects the relativedynamic elastic modulus, the relative weight, and the flexural strength corrosioncoefficient, was given. It can forecast the preliminary sulfate resistance ability of the concrete.Based on the variation of sulfate ion with the concrete erosion depth obtainedfrom the experiment, a two-dimensional diffusion model of sulfate ion free diffusionand chemical reaction, which use Fick’s second law as the basic diffusion model,combined with the basic chemical reaction of concrete suffer to sulfate attack, wasestablished in this thesis. The model can simulate the sulfate ion concentration ofconcrete at any time and anywhere.