Experimental Study On Mechanical Properties Of C30 Recycled Coarse Aggregate Self-compacting Concrete

In recent years,the output of commercial concrete is increasing continuously,and the demand for aggregate is increasing day by day.Secondly,the accelerated urban development will lead to a large number of building demolition and reconstruction,which will produce a large number of waste concrete.If it can be recycled and used instead of natural sand aggregate to prepare self-compacting concrete,it will not only protect the environment,save natural resources,but also improve the concrete construction conditions and save construction costs.Therefore,recycled aggregate is formed from waste concrete by crushing,and Recycled Coarse Aggregate Self-Compacting Concrete(RCASCC)is prepared.The basic mechanical properties and flexural properties of simply supported beams are studied in this paper.The specific contents are as follows:On the one hand,the influence of shape index,particle size distribution and substitution rate of recycled aggregate on the working performance and mechanical properties of RCASCC is studied.The working performance and basic mechanical properties of RCASCC under different substitution rates of recycled coarse aggregate are analyzed through the testing of working performance and basic mechanical properties.The stress-strain constitutive equation of RCASCC is proposed.The results show that:(1)SCC can be prepared with recycled coarse aggregate to meet the specifications.It is suggested that fly ash should replace 20% of cement.The shape index of recycled coarse aggregate is close to needle-sheet shape,and the particle size distribution of recycled coarse aggregate is the best when the big stone is reduced by 20%.The shape index and particle size distribution have great influence on the working performance of RCASCC,but little influence on its mechanical properties.(2)The failure process and failure morphology of RCASCC.Similar to NC,the fluidity of RCASCC decreases with the increase of substitution rate,and the overall strength index shows a downward trend.It is suggested that the substitution rate of recycled coarse aggregate is about 50%.(3)The ratio of axial compressive strength and splitting tensile strength to cubic compressive strength of RCASCC is 0.823 and 0.096,respectively.It is suggested that the constitutive relationship of RCASCC can be controlled by NC uniaxial compressive constitutive equation.The parameters a and b are 0.7 and 7 respectively.On the other hand,the flexural properties of RCASCC simple-supported beams are tested.The differences between RCASCC simple-supported beams and SCCL simple-supported beams before and after particle gradation adjustment are compared and analyzed through failure mode,crack distribution,assumption of flat section,bearing capacity,load-deflection curve and load-strain curve of steel bar and concrete.The results show that:(1)RCASCCL-50%,RCASCCL-JP,SCCL three simple-supported beams are RCASCCL-50%,RCASCCL-JP and SCCL.It is similar to NC simply supported beam in failure mode and failure process;(2)The current design code of concrete structure is still applicable to the calculation of RCASCC flexural members;the addition of recycled aggregate will reduce the bearing capacity significantly,but the adjustment of particle size will increase the bearing capacity significantly;(3)the addition of recycled aggregate will not have a greater impact on deflection and deformation,but will significantly increase the reinforcement.Limit strain,and particle size adjustment will reduce the deflection and deformation,and will reduce the ultimate strain of tension steel bar and concrete,making its ductility worse.