Study On Salt Frost Deterioration Mechanism And Durability Of Recycled Concrete Under Low Humidity Curing

Low carbon development is related to the global green future.In the era of achieving the strategic goal of "carbon peak,carbon neutral",the promotion of low carbon zero carbon technology is an important support for the green transformation of the construction industry.Recycling waste concrete to produce recycled concrete is the only way for sustainable development of the construction industry.At present,the key problem that restricts the wide application of recycled concrete has changed from mechanical property doubt to whether its durability can meet the complex service environment.In order to explore this problem,the durability deterioration mechanism of recycled concrete under service conditions must be deeply explored from macro-meso perspectives.In this paper,the research method of combining macro and meso tests,theoretical analysis and model calculation is adopted.Focusing on the actual durability problems faced by recycled concrete in cold climate conditions in northwest saline soil areas of China,the evolution characteristics of macro and meso parameters in the low humidity curing process of recycled concrete are considered,At the same time,the relationship between the deterioration of the macro mechanical properties of recycled concrete and the meso structural parameters under the action of freeze-thaw and salt freezing is deeply explored.Based on the macro and meso tests,the damage deterioration model of recycled concrete under freeze-thaw is established,and the uniaxial compression constitutive model of recycled concrete under freeze-thaw action is established on the basis of uniaxial compression tests.The specific research contents are as follows:(1)The evolution of the strength of the recycled concrete under low humidity curing characteristics was studied,the curing process of aggregate and recycled aggregate moisture migration under the influence of recycled concrete evolving law of porosity and pore distribution were analyzed,it was concluded that the interface transition zone and the correlation between the pore structure performance,has been clear about the characteristics of recycled concrete pore distribution and the mathematical relationship between the compressive strength,The internal mechanism of macroscopic mechanical property enhancement of recycled concrete is revealed.(2)The freeze-thaw cycle and salt-freeze cycle tests of recycled concrete were carried out.By analyzing the variation characteristics of apparent damage,mass loss rate and relative dynamic modulus of recycled concrete during the test,the macroscopic performance deterioration law of recycled concrete under the influence of aggregate composition and aggregate water migration under different freeze-thaw media was explored.By introducing the composite damage coefficient λs of recycled concrete,the linkage effect mechanism of sulfate erosion on the freezing resistance of recycled concrete is elucidated,and the deterioration mechanism of macro properties of recycled concrete under salt freezing is revealed.(3)By using nuclear magnetic resonance(NMR)and microhardness testing of nondestructive testing technology,the mesoscopic structure of recycled concrete in freeze-thaw and frost and circulation in the process of the quantitative analysis of pore structure and interface performance,considering porosity,pore distribution,interface transition zone width and strength parameters evolution characteristics,summarizes the recycled concrete mesoscopic structure degradation law of development.Established a comprehensive consideration pore structure integrity and particularity of the pore,a comprehensive parameter η as describe the mesoscopic structure deterioration and damage variables,illuminates the recycled concrete pore structure damage and the correlation between macro performance degradation,from the perspective of mesoscopic reveals the freezing and thawing and the durability of recycled concrete under the action of deicer-frost degradation mechanism.(4)Based on the continuum damage mechanics and thermodynamics principles,the material parameter ζ of recycled concrete was proposed,which considered the comprehensive pore parameters and the effects of freeze-thaw damage,and the freeze-thaw damage deterioration model of recycled concrete was established.By conducting recycled concrete under uniaxial compression test,analyzes the replace rate of recycled aggregates and recycled concrete under the influence of the moisture content of uniaxial compression damage deterioration law,build the recycled concrete under uniaxial compression damage constitutive model,the model calculation results and the test results of fitting effect is good.