| Recycled aggregate concrete(RAC)refers to the waste concrete that has been crushed,sieved and cleaned,and then replaced partially or completely with recycled aggregates.It can effectively solve the problem of construction waste and realize the recycling of building materials." which is good for protecting environment and has a good application prospect.In recent years,countries around the world have attached great importance to the research and application of recycled aggregate concrete technology.Domestic and foreign scholars have carried out a large number of experiments and theoretical studies on recycled aggregate concrete,which is still limited to study the basic performance and the mechanical properties of RAC under uniaxial stress conditions.However,studies on the multiaxial strength and failure criteria of RAC have not been reported.Based on the analyse above,In this paper,a series of concrete multi-axial dynamic tests are carried out by the triaxial static and dynamic testing machine at the Dalian University of Technology.The variables are concrete strength grades(C20,C40,C60),replacement rates(30%,50%),strain rates(10-5/s,10-4/s,10-3/s,10-2/s)and stress rates.The stress states are uniaxial tension,uniaxial compression,biaxial compression-compression,biaxial tension-compression,triaxial compression-compression-compression.The main works and innovations are as followed:1.This paper carries out uniaxial compression(C),uniaxial tension(T)tests under different strain rates(10-5/s,10-4/s,10-3/s,10-2/s),studying failure modes and strength development rules of recycled concrete under uniaxial tension and compression,and analyzing the impact of strain rates on uniaxial strength.At the same strain rate,the strength of RAC with aggregate replacement rate of 30%is significantly higher than the replacement rate of 50%.2.The biaxial compression-compression tests of RAC at different strain rates 10-5/s,10-4/s,10-3/s,10-2/s)are carried out.This paper studies the difference of failure modes under different strain rates and stresses rates.The influence of strain rates,stress ratios and replacement ratios of RAC on the strength are studied.The strength criterion of recycled concrete under biaxial compression is proposed and the strain rate is introduced as a parameter.The biaxial compressive strength of RAC increases first and then decreases with the increase of stress ratios,which approximates the parabolic trend.Under different stress combinations,the sensitivity of concrete to strain rates is different.3.The experiments on biaxial tension-compression are carried out under different strain rates(10’5/s,10-4/s,10-3/s,10-2/s).The impact of strain rates,stress ratios and replacement ratios of RAC on the strength are discussed.The strength criterion of recycled concrete under biaxial tension-compression is proposed and the strain rate is introduced as a parameter.At the same stress ratio,as the strain rate increases,the tensile strength and compressive strength also increase.The greater the strain rate,the greater the magnitude of the increase.Corresponding to the same strain rate,the strength of RAC under different stress states are significantly different.The compressive strength decreases as the tensile strength increases.4.Triaxial compression-compression-compression tests of recycled aggregate concrete at different strain rates(10-5/s,10-4/s,10-3/s,10-2/s)were carried out to study the dynamic strength.The influence of strain rates,stress ratios and replacement rates on failure modes and strengths of recycled concrete is analyzed.The strength criterion considering strain rates and stress ratios is established in octahedral stress space,and the strain rate is introduced as a parameter.At the same strain rate,the maximum strength appears mostly between the stress ratios of-0.1:-0.5:-1 and-0.1:-0.75:-1.With the increase of strain rates,the strength of RAC under different stress states increases.When the strain rate is 10-2/s,the increasing magnitude of strength is the largest. |
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