Experimental Study On Modification Of Recycled Aggregate And Recycled Concrete Properties

In the process of production and crushing of recycled aggregate,some internal damage will occur,which leads to the low mechanical properties and has an i MPact on the application of recycled concrete.In view of the above problems,this thesis intensifies the pretreatment of recycled aggregate by five strengthening schemes,namely,sodium silicate,silane,polyvinyl alcohol,sodium silicate-silane and sodium silicate-polyvinyl alcohol,so as to improve the aggregate performance and further solve the environmental i MPact and resource shortage caused by construction waste.On the basis of C30 concrete,the reinforced recycled aggregate and unreinforced recycled aggregate were mixed with 25% replacement rate respectively for mix design.Then,the cube and prism specimens of recycled concrete and reinforced recycled concrete are made respectively.The cube compressive strength,crack strength and four-point bending strength of the samples were tested,and the microstructure of the samples was analyzed by scanning electron microscope.The strengthening mechanism and improvement effect of the chemical solution on the recycled aggregate were proposed.The main research work of this thesis is as follows:(1)In view of the performance defects of RCA(recycled coarse aggregate),the basic properties of particle grading,apparent density,water absorption rate and crushing index were determined,and the following conclusions were drawn.The properties of RCA were lower than that of NCA(natural coarse aggregate),after an intensive processing of RCA has a lot to improve the performance of,RCA4(sodium silicate-silane strengthen recycled aggregates)is to improve the effect of apparent density and crush index the best group,RCA3(PVA strengthen recycled aggregate)is bibulous rate is to improve the effect of the best group.(2)In view of the poor mechanical properties of concrete caused by the defects of recycled aggregate,three mechanical properties tests,namely compressive strength,splitting tensile strength and flexural strength,were carried out,and the following conclusions were drawn:RC(recycled concrete)of the intensity are lower than C(natural concrete),reinforcement of RC,its performance has been greatly promoted,RC4(sodium silicate-silane strengthen recycled concrete)is to improve the effect is the best one group,increased by 23%,the compressive strength of the splitting tensile strength increased by 18%,the flexural strength increased by 14%.(3)The microstructure of NCA is very co MPact without cracks;The microstructure of RCA is loosely arranged and angular,and there are obvious cracks.The microstructure of the five groups of reinforced recycled coarse aggregate is much more smooth,among which RCA4 has the best filling effect on the crack of aggregate,thus verifying the data of the aggregate performance test.(4)The internal ITZ of C is staggered and lapped by several hydration products,and its structure is co MPact with only a few pores and almost no cracks in aggregate.Both new and old ITZs exist in RC and RC1-RC5(reinforced recycled concrete),which leads to more pores in the transition zone than C,and RC1-RC5 is better than RC.Among them,RC4 is the group with the tightest hydrate distribution and structure in the interface transition zone,thus verifying the data of concrete mechanical properties test.