| With the fast development of China’s economy and urban construction,a large amount of solid construction waste will be produced every year,such as abandoned concrete,slag powder and fly ash.Although the practice of recycling waste concrete to prepare recycled aggregate is energy saving and environmental protection,it is often limited in practical application due to the defects of recycled aggregate itself.At the same time,the annual growth of cement production leads to high carbon emissions,and the greenhouse effect has not been effectively alleviated.To that end,strengthen regeneration aggregate performance,for the purpose of this study adopts the carbide and the strengthening of the heating process of recycled aggregate modified strengthen treatment.According to different aggregates,the new high performance materials,such as cement based recycled clean slurry,slag and fly ash based polymer recycled slurry,cement mortar,slag and fly ash based polymer recycled mortar,cement concrete,slag and fly ash based polymer recycled concrete and coupling reinforced concrete,were developed respectively.Due to net pulp,mortar and concrete at home and abroad about regeneration comprehensive report still less,the lack of carbonizating,such as heating and heating-carbonation coupling strengthening process on the mechanical properties of the specimens,especially the dynamic mechanical properties of research,this study proposed renewable clean pulp,mortar and concrete specimens as test object,carbonization time,replacement ratio and heating temperature,alkali modulus as the variables,the regeneration of net pulp,mortar and concrete working performance and quasi static mechanics performance,coupled with strain rate,replacement ratio and heat-carbonation strengthening technology for the variable,to explore the coupling to strengthen the dynamic mechanical properties of recycled concrete,At the same time,combined with scanning electron microscopy（SEM）technology,the microscopic morphology of concrete was explored to reveal the failure modes and failure mechanisms of RAC,SF-GRAC and CRAC under axial compression,providing experimental proof and data support for the effective utilization of recycled aggregate.The main experimental contents and results of this study are as follows:（1）The carbonizating,heating or heating-coupling carbonizating processing recycled aggregate,carbonization time（0 h,3 h,6 h,12 h,24 h）and the heating temperature（room temperature,200℃,400℃,600℃,800℃）for the study of the variables and the physical properties of the recycled aggregate,and combining with the replacement ratio and alkali modulus（0.8,0.95,1.1,1.25）,and other variables to explore regenerate mixed with recycled aggregate net pulp,mortar and the performance of recycled concrete.The results show that the apparent density and crushing index of the recycled aggregate after carbonization and heating treatment will increase,the water absorption rate of the recycled aggregate after carbonization treatment will decrease,but the water absorption rate after heating will increase.Both the addition of recycled aggregate and the heating process can degrade the workability of each specimen,while carbonization can improve the working performance,while the alkali modulus has no obvious effect on the working performance.（2）The regeneration of micro powder and recycled fine aggregate respectively to replace gelled material and natural fine aggregate,40 mm to 19 group size is 160 mm*40 mm*40 mm prism specimens and 20 groups of prism net pulp slurry on flexural,compressive test specimens,explore the heating temperature,carbonization time,replacement ratio and modulus of alkali and other variables of net pulp regeneration and regenerate the influence law of the key mechanical properties of mortar.The results show that the bending strength and compressive strength of RMP and RAM increase with the increase of carbonization time,and the strength of RMP and RAM is higher under the coupling of high-temperature carbonization.The addition of recycled fine powder and recycled fine aggregate will decrease the flexural strength and compressive strength.With the increase of temperature,the flexural strength and compressive strength of SF-GRMP and SF-GRAM firstly increased to the peak value and then decreased.The increase of the basic modulus will significantly reduce the flexural and compressive strength of SF-GRMP and SF-GRAM,and the appropriate base modulus is 0.8.Under the comprehensive consideration,renewable powder single strengthened the 24 h carbonization process recommended or 600℃heating processing,24 h and recycled fine aggregate is recommended carbide or 400℃heating single reinforcement technology,coupling strengthening process Suggestions regeneration of micro powder with 600℃（the recycled fine aggregate was 400℃）of recycled fine aggregate for 24 h after heating carbonization coupling processing,the suggested control in 10%recycled micro powder,recycled fine aggregate is recommended to replace rate control at 25%.（3）The use of recycled coarse aggregate to replace natural aggregate,the group of 20 size forΦ100 mm*200 mm cylinder specimen of quasi static axial compression test,study to explore the heating temperature,carbonization time,replacement ratio and modulus alkali variables on quasi-static compressive properties of recycled concrete.The results show that the quasi-static compressive strength,elastic modulus and toughness of RAC increase with the carbonization time,and the strength is higher under the coupling action.The addition of recycled coarse aggregate can reduce the quasi-static compressive strength,elastic modulus and toughness of RAC.The quasi-static compressive strength,elastic modulus and toughness of SF-GRAC first rise to the peak and gradually decrease with the increase of temperature,and then decreased with the increase of alkali modulus.It is suggested that 0.8 alkali modulus should be used as the alkali activator for concrete specimens.After comprehensive consideration,it is recommended to adopt the single strengthening process of 24 h carbonization or 400℃heating to regenerate coarse aggregate.24 h carbonization after 400℃heating to regenerate coarse aggregate is the best coupling strengthening process,and the replacement rate of regenerated coarse aggregate is controlled at 25%.（4）Coupled to strengthen modification of recycled aggregate to replace natural aggregate in 25 group size forФ100 mm*50 mm cylinder specimen for dynamic axial compression test,to explore the strain rate(19s-1、27s-1、40s-1、64s-1、107s-1),recycled coarse aggregate replacement ratio,strengthening the technology’s influence on the dynamic compressive properties of recycled concrete are studied.The test results show that the relationship between pressure and strain rate is exponential.CRAC,NAC and RAC are all strain rate-sensitive materials.The impact compressive strength and dynamic toughness of specimens rise with the increase of strain rate,but decrease with the increase of replacement rate of recycled coarse aggregate.The dynamic compressive strength and impact toughness of CRAC specimens prepared with recycled coarse aggregate after coupling treatment are effectively improved,and the stress-strain curve is very close to that of ordinary concrete.（5）Through the analysis of the axial compression failure mode and dynamic impact damage mode,from the perspective of quasi static study carbonization time,recycled coarse aggregate replacement ratio and heating temperature and alkali modulus of variables such as the influence of quasi static failure modes of concrete,from the dynamic perspective to explore the strain rate,replacement ratio and strengthening process variables such as the influence of dynamic failure mode of concrete.The results show that the carbonization treatment of recycled coarse aggregate can improve the quasi-static compressive property of concrete,while the the replacement ratio of reclaimed coarse aggregate and the alkali modulus rises will degrade the quasi-static compressive property of concrete.When the temperature is not higher than 400℃,the strength and stiffness of specimens can be improved by heating recycled coarse aggregate,but too high temperature will degrade the aggregate itself and accelerate the damage of concrete.The failure modes of CRAC,RAC and NAC are the trend of surface crack,corner crack,matrix breakage and specimen smashing.The addition of recycled coarse aggregate will degrade the impact resistance of concrete,and the impact resistance of impact specimens prepared by reinforced recycled aggregate is more excellent.（6）SEM technology was used to explore the micro-morphology and failure mechanism of concrete under quasi-static and dynamic compression.The test results show that both carbonization and heating can generate materials to fill the interface transition zone of recycled coarse aggregate,thus improving the microstructure of recycled aggregate and improving the compressive performance of concrete.Excessive incorporation of recycled aggregate will lead to looser microstructure,and even cracks can be seen directly through the aggregate at the micro scale.However,if the alkali modulus is too large,the occurrence of geopolymerization will be affected,resulting in more reactants such as fly ash and slag not participating in the reaction,and the fly ash and slag can also be seen attached to the surface of aggregate from the microscopic perspective. |
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