Experimental Study On The Physical And Mechanic Behaviors Of Recycled High Performance Concrete

High strength and high performance of recycled aggregate concrete have received a great attention by researchers in recent times because of the defects of recycled aggregate concrete. The basic foundation of recycled concrete on the physical and mechanical properties are studied in this thesis, especially focus on the methods and effects of recycled high performance concrete, the interface features and the fatigue behaviors of two-layer recycled high performance concrete beams. The main contents of this thesis are introduced as follows:Firstly, the basic physics and mechanical behaviors of recycled aggregate concrete are tested and the results indicate: recycled coarse aggregate which has markedly higher water absorption and crushing value has more edges and is more rough compared to natural aggregate and shows more obvious adverse defects. Recycled concrete cube compressive strength, flexural strength, splitting tensile strength are lower than those of natural concrete. Fly ash content and recycled aggregate substitution rate are two main factors affecting recycled concrete 28 days compressive strength and flexural strength which is shown by orthogonal experiment.Secondly, the workability and mechanical properties of recycled coarse aggregate concrete is apparently improved by mechanical and chemical intensified methods combined with the secondary mixing method. The most obvious effect of method is the one treated with 5% HCL after washing with water to remove dust, then use mechanical strengthening method to remove loosed concrete mortar shells, and finally treated with1% EVA, the intensified recycled aggregate 24 hours water absorption decreased by22.7%, crushing value decreased by 26.5%, and the apparent density increased by 12.5%compared with un-intensified recycled aggregate. The interface structure and the hydration products of recycled concrete, natural concrete and recycled high performance concrete are tested by using the field emission scanning electron microscopy. The test results indicate: micro cracks and relatively weak transition zones are existed in the recycled aggregate-matrix ITZ. Recycled high performance concrete transition region is improved by intensified method.Thirdly, workability and effect of 28 days cube compressive strength and flexural strength of recycled high performance concrete are tested by changing water-cement ratio,sand ratio and intensified recycled coarse aggregate replacement ratio. An orthogonal test is studied to research the effects of slag, water-cement ratio, water reducing agent for early age shrinkage of recycled concrete performance. An optimal mix of recycled high performance concrete which is satisfied with workability and mechanical properties and shrinkage requirements is obtained.Finally, the fatigue tests of two-layer recycled high performance concrete beams are tested. The test results indicate: the bending fatigue life of two-layer recycled high performance concrete beam can be better obeyed two logarithm of Weibull distribution.When the stress level is 0.8,the anti-fatigue behaviors of high performance recycled aggregate concrete beams which use 30% replacement ratio is better than that of un-intensified recycled aggregate concrete beams. When stress level is 0.7,the two are similar.