Stress Wave Propagation Characteristics Of Concrete Under Freeze-thaw Cycles

At present,the research of the durability of concrete are remarkable,but the safety inspection and the evaluation of concrete structure need to be improved.Nondestructive testing,as an economical,reasonable,simple and efficient test method,is often used in the inspection of concrete.The research of the stress wave propagation characteristics of concrete under freeze-thaw cycle,which can provide reference for the study on the durability of concrete,and has a very practical significance on the safety and operation of water conservancy project.Through the freeze-thaw test,the elastic wave velocity,dynamic elastic modulus of concrete should be test under freeze-thaw cycle.The focus of this paper is researching the effects of different water cement ratio,the dosage of air entraining agent,the number of freeze-thaw on the elastic wave velocity,dynamic elastic modulus,analyzing the relationship between elastic wave velocity and dynamic elastic modulus,establishing freeze-thaw damage model of concrete.The main contents of this paper include the following aspects:1)Taking the impact elastic wave of nondestructive testing technology to research the elastic wave propagation characteristics of concrete under freeze-thaw cycle,analyzing the effects of different water cement ratio,the dosage of air entraining agent,the number of freeze-thaw on the elastic wave velocity.The test results showed that the specimen without adding air entraining agent,with the increasing number of freezing and thawing,the elastic wave velocity of specimen will decrease;and the water cement ratio of specimens is smaller,the elastic wave speed is larger;the water cement ratio is larger,elastic wave velocity decreased faster.And specimens which adding air entraining agent,the elastic wave velocity have a certain impact.Though the elastic wave velocity will be decreased,the addition of air entraining agent can make the decay process of elastic wave velocity was more stable and smaller amplitude attenuation.2)Testing the dynamic elastic modulus of concrete specimens under freeze-thaw cycle,and analyzing the effects of different water cement ratio,the dosage of air entraining agent,the number of freeze-thaw on the dynamic elastic modulus.The test results showed that with the increasing number of freeze-thaw test,the dynamic modulus decreased;adding air entraining agent can make the dynamic elastic modulus of concrete decreased to a certain extent,but the addition of air entraining agent to theconcrete cause the dynamic modulus attenuation amplitude is smaller than that without adding air entraining agent.And the concrete performance is more stable.3)Through the analysis of freeze-thaw cycle between dynamic elastic modulus and elastic wave propagation characteristics of concrete,establishing the durability test model of concrete under freeze-thaw cycle,providing a new detection method of the thawing studies of concrete.Testing the function of the elastic wave velocity and dynamic elastic modulus of the 8 groups of specimens,and finding that the Power function fitting is better.Choosing dynamic modulus of elasticity and elastic wave velocity as damage factor to determine the damage degree of concrete freezing and thawing,and analyzing the degree of freeze-thaw damage of concrete.4)The relative dynamic elastic modulus and mass loss rate are used as the basis for judging whether the concrete is damaged or not.Combined with the test results,which could analyze the freeze-thaw damage of concrete.