Effect Of Recycled Aggregate With Sulfate Corrosion Medium On Performance Of Concrete

During the long-term service,the concrete structure is subjected to sulfate attack.When it is mixed into recycled aggregate,it will carry sulfate corrosion medium.When such aggregate is mixed into new concrete,the corrosive medium will form internal corrosion in concrete under certain conditions,and affect its long-term performance.Durability can be considered as a criterion for the long-term safe use of concrete structures,and sulfate erosion is a key component of durability of concrete.Nowadays,it only pays attention to the external sulfate attack.However,lack of the mechanism of concrete degradation caused by the recycled aggregates carrying corrosion medium.Based on this,the dissolution characteristics and diffusion mechanism of recycled aggregates carrying sulfate corrosion medium in cement hydration environment were studied.The effects of recycled aggregates on long-term mechanical properties,damping properties shrinkage and frost resistance performance of concrete were investigated.And the Interface transition zone,composition and distribution of corrosion products in concrete were analyzed in this paper.The main results of this paper are as follows:Firstly,the recycled aggregate and the self-made mortar stick are soaked in a sodium sulfate solution to simulate aggregates of varying degrees of corrosion,and the dissolution characteristics and diffusion mechanism of sulfate-containing corrosive medium in the form of sulfate ion,such as distilled water,saturated solution of calcium hydroxide and cement slurry,were investigated.Results indicated that the higher the corrosion degree of the recycled aggregate,the more sulfate ion elution in solution environment.The mortar stick is placed in the middle of the mold,and the pulsed electric field is used to accelerate the ion diffusion,simulating the diffusion mechanism of the recycled aggregate carrying the sulfate corrosion medium in the cement paste.Results indicate that the diffusion distance and the amount of sulfate ion increase with the increase of the water-to-binder ratio.And introducing mineral admixture to inhibit sulfate ion diffusion.Secondly,the effects of recycled aggregates with sulfate attack media on long-term mechanical properties,damping properties,shrinkage and frost resistance performance of concrete were investigated.Results indicate that the slump and mechanical propertiesdecrease with the increase of the replacement rate of recycled aggregate,while the damping properties and shrinkage rate are opposite The shrinkage of the specimens can reach 70% of the test age before the first 28 days of curing,while the shrinkage decreased slightly at 120 d The anti-freeze performance of concrete begins to decrease significantly when the number of freeze-thaw cycles is more than 50 times.The mechanical properties,shrinkage and frost resistance performance of concrete can be improved by recycled aggregate strengthening treatment.The acid treatment is the best,the slurry treatment is the second,and the polymer treatment is the worst.Finally,the micro-hardness tester,XRD and SEM-EDS were used to investigate the properties of interface transition zone between recycled aggregates with sulfate-corrosive media and mortar,and phase composition,distribution of internal corrosion products of concrete was investigated as well as in this paper.Results indicate that the interface hardness decreases with the increase of water-to-binder ratio and aggregate corrosion degree.Introducing mineral admixture can improve the interface structure.Corrosion products in concrete are mainly needle-shaped ettringite and short columnar gypsum.The amount of corrosion products decreases as the distance from the recycled aggregate increases,while increases as the curing time increases.The amount of corrosion products in concrete is relatively reduced when mixed by the acid treated and wrap treated recycled aggregates.