Research On The Sulfate Corrosion Performance Of Concrete Under The Effect Of Multi-factor Coupling

The degradation failure of the actual concrete structures exposed to sulfate complex en-vironment was caused by additional materials, physics, chemistry, stress and many otherfactors that lead to mutual coupling. The underground concrete structures full-buried orfull-immersed under the sulfate environment will be subjected to the full-immersion corro-sion sulfate. And the underground concrete structures half-buried or semi-immersed underthe sulfate environment will be suffered from the dry-wet circulation corrosion. Meanwhile,One side of the concrete under the sulfate corrosion is in contact with the corrosive envi-ronment, and the other side is exposed to the air corrosion, which is called the one-sidedsulfate corrosion.In this paper, the full-immersion corrosion, dry-wet circulation corrosion and one-sidedcorrosion were experimented studied respectively. Select factors and levels affecting the sul-fate corrosion to analyze the sulfate corrosion performance degradation rule of the mul-ti-factor coupling concrete and interpret the corrosion process in theory. The factors and le-vels are Na2SO4solution concentration (2%,5%and10%), water-cement ratio (0.4,0.5and0.6) and fly ash (0%,10%and20%).In the full-immersion corrosion experiment, compressive strength and sound velocityfirstly increase and then decrease with the increase of the corrosion time; strength loss rateand corrosion damage degree are negative at the early corrosion stage and positive but in-creasing later. The concrete sulfate corrosion is the process of the corrosion transition layerfurther degradation to the corrosion damage layer and constantly advancing from the outside.Calculate the corrosion damage layer thickness, and analyze the time variation of sound ve-locity of the corrosion damage layer and the ratio of the sound velocity of the no corrosiondamage layer. The orthogonal experiment analysis shows that the combination of the strong-est corrosion is A3B3C1, A1B1C2is the most weak corrosion combination; Na2SO4solutionconcentration is the biggest influence factors, followed by water-binder ratio and fly ashcontent; establish the calculation model about the corrosion damage layer thickness and thecorrosion time and the factor.In the dry-wet circulation corrosion experiment, corrosion damage degree and corrosiondamage layer thickness are positive and increase with the corrosion time. Each cycle corro-sion process is "corrosion–fill–damage-damage accumulation-degradation and craze".Compared with the full-immersion corrosion, the dry-wet circulation corrosion is more se-vere and gives priority to the sulfate physical crystallization corrosion. The moisture trans- mission and Na2SO4solution concentration play a key role in the process of the dry-wetcirculation sulfate corrosion.The one-sided corrosion experiment results demonstrate that in the concrete adsorptionzone there are three areas: water film, crystalline flake area and adsorption crystalline region.Concrete corrosion damage layer thickness in the adsorption zone is greater than that in thesoaking zone. And the fly ash concrete sulfate corrosion in the adsorption zone is more se-rious. Water and SO42-in the soak zone diffuse from the outside along the thickness directionof the specimen box wall and bottom under the action of moisture gradient and concentrationgradient. Water and SO42-in the adsorption zone transfer from the bottom up along theheight direction of the specimen box wall under the effect of capillary pressure. At the sametime, water is lost from evaporation, and SO42-gather in the concrete surface.