Experimental Study On Mechanical Properties And Bending Toughness Of Hybrid Fiber Recycled Concrete

With the rapid development of the construction industry,people’s demand for concrete also increases sharply,and the production of concrete is often accompanied by a large amount of natural material consumption and serious environmental pollution.The recycled concrete is the concrete is made of construction waste Concrete which made of construction use waste recycling and processing as aggregate is called recycled concrete.Its appearance solves the problem not only saves construction resources,but also saves a lot of land resources for the treatment of construction waste.However,due to the low strength and poor performance of recycled concrete,its application in the engineering field is limited.In order to accelerate the promotion of recycled concrete,these problems need to be solved urgently.Adding fiber into concrete is one of the most widely used modification methods at home and abroad.In this paper,through to 30 groups concrete specimens of cube compressive strength test,splitting tensile test and four-point bending test,have a comprehensive study of the recycled aggregate replacement rate and fiber proportion on the basic mechanics performance and the influence of flexural toughness of the specimens,which make up the shortage of the research in hybrid fiber recycled concrete in our country,the main research contents and conclusions are as follows:(1)through the relevant test,the analysis summarizes the recycled aggregate replacement rate and fiber mixing ratio on the mechanical behavior of hybrid fiber recycled concrete,the results show that the mixed recycled aggregates will lead to the decrease of compressive ultimate load of the specimens,split strength ultimate load,flexural limit load,and with the increase of recycled aggregate replacement rate,the greater the load reduced.Among them,the reduction range of compressive load is0.2%~12.5%,the reduction range of tensile load is 1.7%~13.3%,and the reduction range of bending load is 0.1%~28.4%.This is because the strength of recycled aggregate is low,which leads to the performance decline of recycled concrete.The addition of fiber will increase the ultimate load of the specimen,the lifting range of compressive load is 0.6%~19.1%,the lifting range of tensile load is 1.8%~70.9%,and the lifting range of bending load is 18.9%~106%.This is because the fiber forms a stress framework in the matrix,which can bear and transfer stress more reasonably,thus improving the performance of the specimen.(2)the sensitivity of recycled aggregate to fiber is greater that is,the enhancement of fiber to the performance of recycled concrete is greater than that of raw concrete,and this trend will become more obvious with the increase of the replacement rate of recycled aggregate.The reason is that the surface of recycled aggregate is attached with a layer of old mortar,which makes it more rough compared with the raw aggregate with smooth surface,and increases the bond strength between aggregate and fiber,so that thefiber plays a better role.(3)the addition of recycled aggregate will reduce the energy absorption value of the concrete beam,thus reducing the toughness index of the concrete beam,but the recycled aggregate has no significant effect on the deflection deformation of the specimen;The addition of fibers will enhance the toughness of concrete beams,increase the energy absorption value and deflection deformation value of concrete beams,and there is an optimal ratio of fibers.Group 7 has the best toughening effect for this test(PVA0.5SF1.5).(4)through IBM SPSS Statistic data analysis software of the test data are analyzed,the study found that: in the main variables,the fiber with the performance of hybrid fiber recycled concrete specimen of the proportion of leading role,and the IBM SPSS Statistic can precisely control error,the analysis results and the test match degree is high,can be used as a test.