Evaluation Of Sulfate Corrosion Mechanism And Residual Life Of Concrete In Strong Corrosion Area

Salt lakes in China are widely distributed.Salt lakes or underground pore brine lakes are distributed in half of the country and most of them are distributed in western regions.These regions generally contain high concentrations of sulfate ions and the weather is extremely cold and hot.Due to the changes in water level,the concrete structure serving under this environmental condition has been subjected to the combined effects of dry and wet cycles and sulfate corrosion for a long time,resulting in cracks on the concrete surface,exposed steel bars,and reduced bearing capacity of the concrete structure,which accelerates the deterioration of the concrete And seriously affected the structural durability of concrete.In view of this,in this paper,through the combination of theoretical analysis and laboratory accelerated testing,macro analysis and micro analysis,the corrosion degradation mechanism of concrete under dry-wet cycle-strong sulfate corrosion was obtained.It is of great significance to the structural design safety,scientific prediction of the service life and durability of concrete in the wet and dry cycle-strong sulfate corrosion environment.Water-binder ratio and mineral admixture can greatly affect the microstructure of concrete,and then affect the sulfate resistance of concrete.So this paper mainly studies the different water-binder ratios(0.26,0.32,0.38),different mineral admixtures(silica fume,fly ash),and different amounts of silica fume(6%,8%,10%).Effects of dry and wet cycle-6% sodium sulfate solution on the appearance,quality,compressive strength,dynamic modulus of elasticity,pore structure,and sulfate ion distribution.The main findings are as follows:(1)The deterioration process of concrete under the effect of dry-wet cycle-strong sulfate corrosion can be divided into three stages: in the first stage,cement continues to hydrate and due to the action of sulfate,a small amount of expansive erosion products are generated inside the concrete.Filling the pores shows that the compressive strength and dynamic elastic modulus of the concrete have increased to different degrees in terms of macro mechanical properties;in the second stage,the concrete quality,compressive strength,and dynamic elastic modulus have a small decrease: In the third stage,cement hydration products and sulphate produced expanded swell erosion products,and the macroscopic mechanical properties of concrete deteriorated,and the surface cracked,swelled and fell off.(2)As the water-binder ratio decreases,the internal density of concrete materials increases,the porosity decreases,the deterioration process slows down,and the resistance to sulfate attack increases.(3)Reasonable addition of silica fume and fly ash can greatly enhance the sulfate resistance of concrete.The effects of mineral admixtures on the sulfate resistance of concrete from strong to weak are as follows: silica fume> fly ash> no admixture.The addition of fly ash in the early stage of erosion will cause the initial strength of the concrete to decrease.When the amount of silica fume is between 6% and 10%,the resistance to sulfate corrosion of the concrete will increase with the increase of the amount.(4)The indoor accelerated test can greatly shorten the prediction time of concrete service life and provide a large amount of data foundation for it,which is conducive to the prediction of the service life of concrete.This paper is based on mathematical models such as the acceleration coefficient,damage attenuation equation and damage degree of indoor acceleration test.Prediction of the service life of concrete under dry-wet cycle-sulfate corrosion conditions was carried out.