Study On Constitutive Relation Of Recycled Aggregate Concrete Under Complex Stress State

In recent years,Chinese economy developed rapidly with ever increasing sum of buildings.As the main material of modern buildings,concrete demand became bigger and bigger.Since 2006,Chinese annual concrete consumption accounted for more than 50 percent of the total amount in the world.At the same time,hundreds of millions of construction waste are generated annually in our country,which accounts for 30-40 percent of municipal waste and 50-60 percent of that is waste concrete.Considered from saving resources and protecting environments,by recycling and processing waste concrete to make a new reusable concrete which called recycled concrete was a good idea.Therefore,the studying and using of recycled concrete is necessary.To put the recycled concrete into use in actual projects,a thorough research of its mechanical properties is needed,thereby to establish the related specifications.As an important mechanical property index of concrete,the research value of constitutive relation under complex stress states is very high.In coastal and offshore engineering national key laboratory's structural laboratory of Dalian University of Technology,the author conducted static loading experiment of uniaxial and multiaxial under various stress ratios on recycled concrete by using the concrete dynamic triaxial testing machine.The stress states include uniaxial tension,uniaxial compression,biaxial compression,biaxial tension and compression,triaxial compression and triaxial tension and compression.Main research works are as follows:1.Through the uniaxial tension and uniaxial compression adopting fiction reducing measure experiments on recycled concrete with three different strength grades?C20,C40,C60?and two replacement ratios?30%,50%?,it presented the failure modes,stress-strain curves and stress-strain curve equations containing parameters of recycled concrete under uniaxial tension and uniaxial compression states.Under these states,recycled concrete's failure modes respectively are tension failure and columnar damage.Compared with regular concrete,recycled concrete under uniaxial tension state has more rougher failure surface,and its brittleness is more stronger under uniaxial compression state while the geometrical shape of their stress-strain curves is roughly same.2.Through the biaxial compression experiment under the condition of 5 kinds of stress ratios which is??=?₂:?₃=-0.1:-1;-0.25:-1;-0.5:-1;-0.75:-1;-1:-1?and biaxial tension and compression experiment under the condition of 5 kinds of stress ratios which is??=?₁:?₃=0.05:-1;0.1:-1;0.25:-1;0.5:-1;1:-1?on recycled concretes with three different strength grades?C20,C40,C60?and two replacement ratios?30%,50%?,it presented failure modes,strength rules,strain rules,elasticity modulus rules as well as stress-strain curves and the equivalent uniaxial stress-strain curve equation containing parameters of recycled concrete under biaxial compression and biaxial tension and compression states.Under these states,recycled concrete's failure modes respectively are flake damage and tensile failure.Variation of recycled aggregates' replacement ratio will not change the macro failure pattern of recycled concrete.Recycled concrete's strength and stress-strain relationship under biaxial stress state are influenced by stress ratio and recycled aggregates' replacement ratio.3.Through the triaxial compression experiment under the condition of 5 kinds of stress ratios which is??=?₁:?₂:?₃=-0.1:-0.1:-1;-0.1:-0.25:-1;-0.1:-0.5:-1;-0.1:-0.75:-1;-0.1:-1:-1?and triaxial tension and compression experiment under the condition of 3 kinds of stress ratios which is??=?₁:?₂:?₃=0.1:-1:-1;0.25:-0.25:-1;0.25:-0.5:-1?on recycled concretes with three different strength grades?C20,C40,C60?and two replacement ratios?30%,50%?,it presented failure modes,strength rules,deformation rules,elasticity modulus rules as well as stress-strain curves and the stress-strain curve equation containing parameters of recycled concrete under triaxial compression and traxial tension and compression states.Recycled concrete's strength and stress-strain relationship under triaxial stress state are influenced by stress ratio and recycled aggregates' replacement ratio.