Experimental Research On Mechanical Properties And Damage Constitutive Relationship Of Waste Glass Concrete Under Sulfate Freeze-thaw Coupling Environment

With the progression of the country ’s macro-strategies such as ’ The Belt and Road’ and ’ Maritime Silk Road ’,many large-scale concrete structure projects have been constructed rapidly.Combined with China ’s geographical characteristics,the complex service environment has brought severe challenges to more and more large-scale concrete structure projects.In this paper,based on energy saving and emission reduction,waste glass is broken into appropriate particle size and reused in concrete.Orthogonal test is designed to develop waste glass concrete with better basic mechanical properties than reference concrete.In this paper,the safety of waste glass concrete in sulfate freeze-thaw coupling environment during engineering construction and service is taken as the research background.The deterioration damage characteristics,dynamic mechanical properties and creep properties of waste glass concrete under various complex environments such as sulfate erosion,freeze-thaw damage,long-term load and impact load are studied.The main research contents and results are as follows :(1)Based on orthogonal test,the water-cement ratio,the amount of waste glass particles and the amount of waste glass powder were used as experimental factors,and the compressive strength,splitting tensile strength and flexural strength of concrete were used as the basic mechanical evaluation indexes.Combined with the stress-strain relationship and energy dissipation law in the process of concrete compression,the effects of water-cement ratio,waste glass particles and waste glass powder on the compression characteristics of concrete were analyzed.The optimum mix ratio of waste glass concrete with the best comprehensive performance was analyzed and optimized,which provided a basis for subsequent research on the durability of waste glass concrete.(2)Ordinary concrete and glass concrete were placed in clear water and sulfate solution respectively for long-term indoor test of concrete freeze-thaw cycle.The mass change,longitudinal wave velocity,compressive strength and elastic modulus of concrete in different solutions and different freeze-thaw cycles were studied,and analyzed from the microscopic scale by scanning electron microscopy(SEM).The results show that the freezing and thawing of clear water mainly causes the process of crack damage caused by unloading of internal stress caused by the phase change of clear water in concrete.Freeze-thaw in sulfate environment not only has internal stress caused by water phase change,but also has complex interaction between freeze-thaw and sulfate erosion.In the early stage of freezing and thawing,sulfate alleviates the damage of freezing and thawing,and aggravates the damage of concrete in later stage of freezing and thawing.Waste glass concrete GC has better freeze-thaw resistance than ordinary concrete OC in either clear water or sulfate solution.(3)The dynamic compression tests of ordinary concrete and waste glass concrete under sulfate freeze-thaw coupling environment were carried out by using a SHPB test device with a diameter of 74 mm.The dynamic compressive strength,peak strain,elastic modulus and energy evolution of concrete under different strain rates and different freeze-thaw cycles were studied.The results show that the waste glass effectively delays the decrease of dynamic compressive strength and resistance of concrete to sulfate freeze-thaw.At the same number of sulfate freeze-thaw cycles,the damage degree of concrete GC is significantly less than that of OC,and the DIF of concrete GC is greater than that of ordinary concrete.Waste glass has an enhancement effect on concrete and has a more obvious strain rate effect.Under the same conditions,the absorption energy density of concrete GC is greater than that of concrete OC,waste glass effectively improves the energy dissipation capacity of concrete,thus improving the strength and impact resistance of concrete.(4)When the concrete is subjected to high strain rate,the low-frequency Maxwell body of the ZWT model is too late to respond,loses its function and no longer affects the dynamic mechanical properties of concrete.Based on the improved ZWT model,the dynamic mechanical behavior of concrete can be better described.Combined with the established sulfate freeze-thaw damage factor,the model better characterizes the dynamic mechanical properties of ordinary concrete and waste glass concrete under the coupling of sulfate freeze-thaw and impact load.(5)Uniaxial creep tests of ordinary concrete and waste glass concrete under sulfate freeze-thaw coupling environment were carried out by using rock compression rheometer test device.The evolution of creep parameters such as instantaneous strain,instantaneous deformation modulus,creep strain,creep deformation modulus,steady-state creep rate and long-term strength of it with various freeze-thaw cycles were studied.The results show that the creep failure strength of OC and GC concrete in creep test is lower than that of static uniaxial compressive strength.The sensitivity of creep parameters to constant load stress increases significantly with the increase of freeze-thaw cycles,and the creep modulus of concrete GC is larger than that of concrete OC.The mutation point of creep ratio gradually moves forward with the increase of freeze-thaw cycles,and the critical stress of OC specimen is always lower than that of GC specimen during the whole freeze-thaw cycle.(6)A nonlinear viscoelastic model is established by introducing a fractional-order Abel dashpot in series with the Kelvin model.The damage variable is introduced to construct the sulfate-freeze-thaw-damage viscous element,and a nonlinear viscoelastic-elastic-plastic damage creep mechanical model that can describe the concrete specimen in the sulfate freeze-thaw environment is established.