Experimental Study On The Predictive Model Of Hydraulic Rubberized Concrete Mechanical Properties And Freeze-thaw Damage

There is an increase in water conservancy and hydroelectric Civil Engineering under construction and planned in China’s cold areas,with the development of water conservancy and hydropower industry,the Belt and Road Initiative,the marine power and national water security construction.Recycling scrap tyres as alternatives of materials to produce hydraulic concrete will result in environmental protection and improvement of concrete frost resistance.The addition of the rubber redistributes the microscopic structure of concrete,enhances the deformation adaptability of concrete,and reduces concrete strength to varying degrees.The incorporation rubber in concrete enhances the uncertainty of concrete freeze-thaw damage evolution and compression damage evolution of freeze-thaw damaged hydraulic rubberized concrete(HRC),making the freeze-thaw response and compression failure process of concrete macro and meso structures more complex.The incomplete of mechanical theory for HRC and the uncertainty of freeze-thaw damage mechanism,damage evolution law and damage constitutive relationship are important factors restricting the development and application of HRC.Therefore,the predictive models of HRC mechanical properties and freeze-thaw damage were studied based on the results of the mechanical tests and freeze-thaw cycle tests.The main work and achievements are as follows.(1)The effects of rubber content,particle size and pretreatment method on concrete strength and elastic modulus were studied through laboratory tests.The influence mechanism of the rubber on concrete strength and elastic modulus was clarified through the technology of CT and SEM,as well as analyses of void structure of hardened concrete.According to the test results,the calculation formula of compressive strength of HRC was proposed based on the existing that of normal concrete.On the basis,the calculation formulas of splitting tensile strength,flexural strength and elastic modulus of HRC were also proposed by establishing the relational equation between them and compressive strength.It was found that the formulas agreed well with the test results by comparing them with test results in peer researches.(2)The influence of rubber content on concrete stress-strain relationship under uniaxial compression was studied through the test of concrete complete stress-strain curve.Then,the calculation formulas of initial elastic modulus and peak stress of the curves were put forward,and the effect of rubber content on the damage evolution law of concrete under compression was revealed.On the basis,the constitutive model was proposed to predict complete stress-strain curve of HRC under compression,which have considered rubber content and the pretreatment.It was found that the constitutive model had good applicability by by comparing them with the test results,and it was applicable to rubberized recycled concrete of 16.2～32.6MPa with less than the content of 50%recycled coarse aggregate.(3)The freeze-thaw damage evolution law of HRC was studied based on the results of the freeze-thaw cycle tests,and the changes law of relative dynamic elastic modulus,mass loss rate and dynamic elastic modulus with rubber content,pretreatment and freeze-thaw cycles were clarified.On the basis,the formula of freeze-thaw durability index was proposed to evaluate frost resistance of HRC.The influence mechanism of the rubber on concrete frost resistance was revealed,through the technology of CT and SEM,as well as analyses of void structure of concrete.Based on Aas-Jakobsen fatigue formula,prediction models of freeze-thaw damage and durability life of frost resistance for HRC were proposed,which have considered rubber content,pretreatment and freeze-thaw cycles with parameterψ_n.It was found that the prediction models had good applicability by comparing them with test results in peer researches.(4)The influence law of rubber content,pretreatment and freeze-thaw cycles on stress-strain behavior of HRC under uniaxial compression were studied through the freeze-thaw test and the complete stress-strain curve test of concrete.The effects of rubber and freeze-thaw damage on the state of concrete compressive failure,and the compressive damage evolution law of concrete under the effects of rubber content,pretreatment and freeze-thaw cycles were clarified.The calculation formulas of the initial elastic modulus,peak stress and peak strain of freeze-thaw damaged HRC were put forward by considering the effects of rubber content,pretreatment and freeze-thaw cycles.On the basis,the compressive damage evolution equation and the complete macroscopic constitutive model of freeze-thaw damaged HRC were proposed.It was found that the macroscopic constitutive model agreed well with the test results.(5)Based on the concrete damage theory of statistical probability,the mesoscopic damage probability density function of freeze-thaw damaged HRC under compression was determined,and the compressive mesoscopic damage mechanism of concrete under the effects of rubber content,pretreatment and freeze-thaw damage was revealed.Through the correlation analysis between the probability density function of compressive mesoscopic damage for HRC and rubber content,pretreatment as well as freeze-thaw cycles,the parameters of the mesoscopic damage constitutive model of freeze-thaw damaged concrete under uniaxial compression were deterimined.On the basis,the compressive complete mesoscopic constitutive model of freeze-thaw damaged HRC was proposed.It was found that the mesoscopic constitutive model agreed well with the test results.