Research On Multi-generation Utilization Effect Of Carbonized Modified Recycled Coarse Aggregate In Freeze-thaw Environment

Using carbonization modification technology to treat multi-generation coarse recycled aggregate(MCRA)from freeze-thaw(F-T)environment and apply it to structural concrete has multiple meanings,such as improving the utilization level of MCRA,promoting the realization of"double carbon"goal and"zero emission"of waste concrete.However,the properties of carbonized modified multi-generation recycled aggregate concrete(CMRAC)prepared by carbonized modified multi-generation coarse recycled aggregate(CMCRA)are rarely reported.Focusing on the multi-generation utilization effect of carbonized modified coarse recycled aggregate in F-T environment,this study tested the physical properties(apparent density,crushing value,water absorption and soundness)of three generations of MCRA and CMCRA in F-T environment.Three generations of C40 MRAC and CMRAC were prepared at100%replacement rate respectively.The mechanical performance indexes(compressive strength and flexural strength)and the frost resistance indexes(strength loss rate,mass loss rate and relative dynamic modulus of elastic)of MRAC and CMRAC under the action of fixed flexural tensile stress(35%F_f)were tested.The specific research contents are as follows:(1)The effect of F-T damage of MRAC on the application potential of MCRA under F-T environment was studied.The results showed that the F-T damage of MRAC had an adverse effect on the acquisition rate and physical properties of MCRA.The F-T damage threshold of coarse recycled aggregate based on MCRA2 and MCRA3 that can be used as structural concrete was0.359 and 0.317,respectively.The MCRA obtained from MRAC with F-T failure cannot be reused as coarse aggregate for structural concrete.(2)The effect of carbonation modified MCRA on the multi-generation utilization of waste concrete was discussed.The mechanical and frost resistance of MRAC and CMRAC were compared,and the service life of concrete in cold areas was obtained.The results showed that carbonization modification improved the physical properties of CMCRA.In the same generation,the mechanical and frost resistance of CMRAC were better than MRAC,but still worse than NAC.After carbonization modification,the compressive strength of CMRAC1,CMRAC2 and CMRAC3 increased by6.59%,7.14%and 14.12%respectively compared with MRAC1,MRAC2 and MRAC3,and the flexural strength increased by 3.91%,9.16%and 23.10%respectively.Carbonization modification can greatly improve the service life of CMRAC in cold areas,CMRAC1,CMRAC2 and CMRAC3 can be used in cold areas for 76,64 and 52 years respectively.(3)The sustainability of MRAC production mode and CMRAC production mode were compared and analyzed by using emergy phase diagram method.Four emergy analysis indexes were calculated and obtained:emergy investment ratio(EIR),emergy yield ratio(EYR),environmental load ratio(ELR)and emergy sustainability index(ESI).The results showed that the CMRAC production mode had better economy,and reduced the environmental burden while ensuring the performance.With the increase of multi-generation utilization times of concrete,ESI gradually increased and the sustainable development ability of concrete was enhanced.The comprehensive comparative analysis of the performance,environmental load and economic benefits of MRAC and CMRAC showed that it was feasible for MCRA in F-T environment to be used in structural concrete after carbonization modification.The research results can not only directly guide the production and engineering application of MCRA and MRAC,but also provide new theories and methods for the design and maintenance of new MRAC structure,and provide necessary experimental data and theoretical basis for the revision of relevant technical standards in the future.