Influence Of Recycled Aggregate With Chloride Corrosion Medium On Performance Of Concrete

The popularization and application of recycled concrete could meet the sustainable development strategy of China,which is of great significance to save resources and protect the environment.Based on the wide range of the chloride salt environment and the application of road deicing salt,the recycled aggregate is affected by the complex service of the parent concrete and inevitably carries a certain amount of corrosive medium such as chloride.Previous studies have shown that chloride corrosion is the main factor leading to deterioration of durability of concrete structures and corrosion of steel bars.It can be seen that recycled aggregate with chloride will inevitably have an impact on the performance of concrete,but there is a lack of research on this aspect at present.Based on this,the influence of recycled aggregate with chloride on the performance of concrete is studied in this paper.The main contents and results are as follows:Firstly,the effects of recycled aggregates with chloride and mineral admixtures on the long-term mechanical properties,shrinkage and chloride penetration resistance of concrete were studied.The results show that the higher the replacement rate of recycled aggregate,the worse the mechanical properties,shrinkage and resistance to chloride penetration of concrete.With the increase of corrosion degree of recycled aggregate,the later strength and resistance to chloride penetration of concrete decreases.The mechanical properties and resistance to chloride ion penetration of recycled concrete can be significantly improved by mixing fly ash and mineral powder.On this basis,the effects of recycled aggregate with chloride and hydration environment on steel corrosion were studied.The results show that measures such as reducing the corrosion degree of recycled aggregate and water-binder ratio,and mixing fly ash can reduce the risk of steel corrosion in concrete.Then,based on chemical titration method and SEM-EDS line scanning method,the leaching characteristics of chloride carried by recycled aggregates in different hydration environments were studied.The results show that chloride ions carried by recycled aggregate can be leached into cement mortar,the leached chloride ions are still mainly distributed around the recycled aggregate,and the amount of leached chloride ion are affected by the pH of solution,the corrosion degree of recycled aggregate and the mass ratio of recycled aggregate to solution.On this basis,the recycled aggregate with chloride salt is simulated by corroded mortar bar,the diffusion mechanism of chloride ions in cement mortar was studied by constant potential accelerated test method.The results show that the chloride ion content at different depths of recycled concrete increases with the increase of corrosion degree of recycled aggregate.Reducing the water-to-binder ratio and mixing fly ash can inhibit the diffusion of chloride ions.According to the characteristics of chloride ion diffusion carried by recycled aggregate,a simplified diffusion model is established.Finally,the interfacial properties of recycled aggregate concrete with chloride were studied by microhardness,SEM-EDS and XRD.The results show that the weak interface of recycled concrete is LG-XJ(old aggregate-new mortar).With the increase of water-binder ratio,the interfacial hardness of LJ-XJ(old mortar-new mortar)and LG-XJ(old aggregate-new mortar)decreases,and the width of transition zone increases,while the addition of fly ash can significantly improve the interfacial properties of later stage.The higher the corrosion degree of the recycled aggregate,the worse the performance of the LJ-XJ interface and LG-XJ interface of concrete in later stage.The chloride ion carried by recycled aggregate can participate in the hydration reaction of cement at the interface and generate expansive products such as Friedel salt.The higher the corrosion degree of the recycled aggregate is,the longer the age is,the more expansive products are produced.The addition of fly ash can improve the chloride binding ability of mortar,reduce the chloride ion diffusion rate and reduce the harm of chloride ion to concrete.