Comparative Study Of Ultrasonic And Elastic Waves Used To Analyze The Relationship Between Wave Velocity And Strain Of Existing Concrete

In reconstruction and reinforcement of existing buildings,it is often necessary to understand stress state of key members to ensure safety of project.In order to study efficiency and accuracy of the ultrasonic wave and elastic wave used to analyze the existing wave velocity-strain relationship of concrete,a corresponding auxiliary test device is designed and the test parameters is optimized firstly,and then the two test method are compared and analyzed through a concrete axial compression wave velocity test.Effectiveness and accuracy comparison of the test methods determines the main research method of this paper;the method is also used on further study on acoustic elastic coefficient of concrete under different water-cement ratios,air contents,pore water saturation,different ambient temperature and humidity.The acoustic elastic coefficient of tension of concrete is also studied;finally,the strain acoustic elastic coefficient is analyzed bases on the previous study.The main work and results of the paper are listed as follows:(1)The reasons of errors in the testing process of each method are analyzed,a special auxiliary test device is designed and manufactured,and the ultrasonic and elastic wave test parameters are optimized.The results show that:① for ultrasonic test,stable test result can be obtained when the test distance is set to 400mm-600mm and the coupling pressure is greater than 30kPa.moreover,when the test frequency is 50kHz,the measured wave velocity is more sensitive to stress variation;② for elastic wave test,when the test distance is set to 400mm～600mm and the coupling pressure is set to 30kPa-60kPa,stable test result can be obtained,moreover the impact of the impact energy on the wave velocity can be ignored.(2)Base on the foregoing configuration,two test methods are used to perform wave velocity tests under compressive stress on the concrete.Effectiveness and accuracy of the two methods are compared and analyzed.The research results show that the ultrasonic wave velocity and stress of the concrete under compressive stress have a good linear relationship,and the accuracy of fitting is good,and it can be used as a test method for further tests.For elastic waves,with the aid of test equipment and optimized parameters,the measured wave velocity can merely reflect the stress change law,but the fitting accuracy is relatively poor due to the limit of the used equipment.(3)The selected test methods and parameters are used to study the acoustic elastic coefficient of concrete under different stress status.Test results show that the acoustic modulus of elasticity of concrete under pressure increases with the increment of water-cement ratio,air content,and ambient temperature and decrease with the increment of humidity and water saturation.The acoustic elastic coefficient under tensile stress is greater than that under compressive stress;moreover,the voltage amplitude has a good linear relationship with the tensile stress.(4)Base on the acoustoelastic theory,a theory of measuring the strain acoustic elastic coefficient is proposed,and the strain acoustic elastic coefficients under different factors are summarized.