Experimental Study On The Freeze-Thaw Damage Of Tunnels Sprayed Concrete

The water occurrence in the spray concrete will freeze and melt, alternating positive and negativetemperature changes causing microscopic damage of the material, frost heave fragmentation or destructionof instability.This thesis makes two sizes of100mm×100mm×400and100mm×100mm×300mm C25sprayed concrete test-piece,useing laboratory experiment and the damage mechanics theory analysismethod,with rapid freezing and thawing experiment and uniaxial compression experiment tested thequality、the specimen and the dynamic elastic modulus、ultrasonic velocity、axial compressive strength、elastic modulus and stress-strain curve of the experience of0、25、50、75and100times the number offreeze-thaw cycle.recording the strength and deformation of sprayed concrete freeze-thaw cycledegradation law.On the basis of the theory of macro damage mechanics and the result of uniaxialcompression and rapid freezing and thawing experiment,the damage evolvement equations areestablished,and the constitutive.Then，The damage evolvement equations for two stages are established，and the constitutive.Equations for two stages of rock subjected to freeze-thaw are deduced，accordingly.Byusing the constitutive model，the curves of uniaxial compression stress-strain are drawn，And comparedwith the stress-strain curves from experiment. The following conclusions are obtained:(1)The average weight of Sprayed concrete test-piece lost0.95%after bear100times of freeze/thawcycling, the average relative dynamic elastic modulus and ultrasonic wave velocity is96.01%and94.21%.The relative dynamic modulus of elasticity and the relative ultrasonic velocity losses average3.99%and5.79%respectively.Mass loss, the relative dynamic modulus of elasticity and relative ultrasonic velocitydecreased with the increase in the number of freeze-thaw cycle.(2)Tested prayed concrete prism test-piece under different freeze-thaw cycles of axial compressivestrength and elastic modulus. Before the freeze-thaw cycle, the prayed concrete test-piece of average axialcompressive strength is20.0MPa After100freeze-thaw cycle, its average axial compressive strength ofconcrete is12.0MPa, corresponding to the loss of40%.Before the freeze-thaw cycle, the average of thecompressive elastic modulus of concrete21.85GPa,after100freeze-thaw cycle, the average of thecompressive elastic modulus of concrete prism14.49GPa, corresponding to the loss of33.68%. Sprayedconcrete prism test-piece axial compressive strength and elastic modulus decreased with the increase in thenumber of freezing and thawing.(3)Different number of freeze-thaw cycle effects prayed concrete stress-strain curve trend is similar. With the increase in the number of freeze-thaw cycle, the peak stressf ccontinue to lower, increasing thepeak strainε cand ultimate strainε u, the curve tends to flatten.(4)Elastic modulus as the damage variable, and the establishment of a sprayed concrete freeze-thawdamage evolution equation, the relationship between freeze-thaw damage and freezing and thawing of thenumber of available functions once said.(5)Lemaitre equivalent strain hypothesis and its corresponding damage model, damage evolutionequation of the sprayed concrete in the different freeze-thaw cycles and their corresponding damage stress-strain constitutive relation, and constitutive model calculated the stress–strain curve with the experimentalcurves were compared, the results show that the damage constitutive relations established with theexperimental results are basically the same, damage mechanics model is reliable.Through this study,it can provide the necessary reference and reference for spray concrete freeze-thawdamage mechanics of tunnels concrete in cold regions.The result will be valuable to design andconstruction of cold region tunnels.