Study On Recycling And Reuse Of Waste Concrete

This thesis deals with the key technologies in the recycling and resue of waste concrete as a new aggregate for concrete and concrete blocks. The following research work was carried out:(1) An extensive review of the past studies on application of waste concrete as new aggregates in producing new concrete and concrete blocks was performed.(2) An efficient recycling technology for producing recycled concrete aggregate (RCA) from waste concrete is proposed. Various physical and mechanical properties of RCA from this technology were investigated according to Standard and Test Method for the Coarse Aggregate of Normal Concrete (JGJ 52-2006). The test results indicate that RCA has the characteristics of low density, high water absorption and porosity , low strength and weak durability compared with natural aggregates (NA).(3) The behavior of recycled aggregate concrete (RAC) under uniaxial compression is experimental evaluated. Extensive tests were carried out on the prism compressive strength to cube compressive strength ratio, the cylinder compressive strength to cube compressive strength ratio, stress-strain curve, peak strain, ultimate strain and the modulus of elasticity as well as the Poisson's ratio. some new correlationship between various mechanical properties of RAC under uniaxial compreesion are proposed.(4) In addition to the uniaxial compression behavior, the other mechanical properties of RAC were studied, including the uniaxial tensile strength, the splitting tensile strength and the correlationships between them, the flexural strength, the fracture energy and the bond strength between steel reinforcement and recycle aggregate concrete as well as the thermal expansion coefficient and the residual compressive strength after high temperature.(5) By taking account into the distinct feathers of the RCA, a production process for concrete hollow blocks with RCA was developed.The compressive strength of the concrete hollow blocks was investigated. The test results indicated with suitable mix design, ideal compressive strength can be achieved. The influence of replacing cement with fly ash on the compressive strength and the improvement of the crack-resistance and the thermal insulation of the concrete hollow blocks made from RCA through adding fibers was also investigated. This study may provide a base for the recycling and reuse of waste concrete as new aggregatefor new concrete and concrete blocks in practice.