Influence Of Recycled Concrete Aggregates Attached Old Mortar On The Deterioration Mechanism Of Concrete

Concrete structures are subjected to long-term erosion by the external environment during service,resulting in the gradual penetration of corrosive media into the matrix,when the waste concrete is broken into recycled aggregate for reuse,the old mortar attached to the surface of the recycled aggregate will inevitably carry the corrosive medium,and this layer of attached old mortar is difficult to completely remove,which means that the recycled aggregate will carry the corrosive medium,react with the hydration product to generate expansion corrosion products,and then affect the performance of concrete.Among these corrosive media,sulfate corrosive media are the most common,and concrete sulfate erosion is also the focus of durability research.Based on this,this paper takes recycled aggregates from different sources as the starting point to study the effect of recycled aggregate-carrying sulfate corrosive media on concrete properties,and the deterioration mechanism of concrete properties under the coupling of recycled aggregate-carrying sulfate corrosive medium and dry-wet cycle.(1)Research on the quantification of regenerated aggregates attached to old mortar and soluble ions.Taking three recycled aggregates from different sources as the research objects,the content of old mortar adhered to recycled aggregates and the soluble ion content in hydration environment were quantitatively characterized,and the correlation analysis between the adhesion amount of old mortar and the dissolution amount of soluble ions was established.The results show that the ion carrying content of recycled aggregate is mainly related to the service environment of the parent concrete,and the content of adhesion old mortar of recycled aggregate is approximately positively correlated with sulfate ion carrying capacity.(2)Study on the influence of recycled aggregate carrying corrosive medium on the properties of concrete.The effects of regenerated aggregate substitution rate,source and strengthening method on the working properties,mechanical properties and frost resistance of concrete were studied.The results show that the removal of old mortar and the mixed slurry of cement and silica ash can effectively inhibit the loss of slump,while the lifting effect of recycled aggregate treated with pure cement slurry is not large.After 150 freeze-thaw cycles,the strengthening treatment of recycled aggregates can significantly reduce the compressive strength loss and mass loss rate of concrete specimens.The mixed slurry of recycled aggregate coated cement slurry and silica ash is the most effective for improving the mechanical properties of concrete.(3)Study on the deterioration mechanism of concrete by coupling sulfate corrosion medium carried by recycled aggregate and dry and wet cycle.The dissolution characteristics of ionic form of recycled aggregate-carrying corrosive medium in hydration environment were studied,and the influence and deterioration mechanism of concrete sulfate erosion by coupling the corrosive medium carried by recycled aggregate and dry and wet cycle were studied.The results show that the ion dissolution amount and diffusion distance of sulfate corrosion medium carried by recycled aggregate are mainly affected by the carrying amount of old mortar and the density of slurry of recycled aggregate.Reducing the water-adhesive ratio of the outer coating slurry and optimizing the cementitious material composition of the outer coating slurry are conducive to inhibiting the diffusion of harmful ions;The strengthening treatment of recycled aggregates,especially the reinforced treatment of cement-coated and silica-ash composite slurry,can effectively improve the sulfate erosion resistance of recycled concrete.The higher the adhesion rate of the old mortar,the worse the interface quality of concrete,and the treatment of cement-coated and silica-ash composite slurry can effectively improve the interface quality.