Study On Freeze-thaw Damage Of Different Types Of Concrete Based On Ultrasonic Velocity

In cold region,most of the concrete structure will be in freeze-thaw environment,due to the influence of the freeze-thaw damage in concrete structure appeared different degree of internal damage,the larger influence the service life of concrete structure and safety performance.Therefore,the freeze-thaw performance analysis of the concrete structure and the existing structure of nondestructive testing technology research is of great practical significance.At present,the research on concrete freeze-thaw damage is usually carried out by using dynamic modulus of elasticity.But this method is limited to laboratory testing and analysis,and it is not feasible to use it for actual testing.Ultrasonic technology on the freezing and thawing of concrete damage detection has more engineering practicality,is currently in the stage of strong research and development.The following research work is carried out in this paper.(1)For different types of concrete initial state wave velocity test and strength test,The results show that the fiber and slag-fly ash can effectively improve the dense degree of concrete,reduce the production of concrete defects,including slag and fly ash on the dense degree of concrete enhancement effect is better,slag-fly ash and steel fiber combination can further enhance the compactness of concrete.At the same time,adding steel fiber or slag-fly ash concrete,its strength is higher than ordinary concrete,the steel fiber has a modest increase,slag and fly ash enhancement effect is obvious,while adding fiber and slag-fly ash on concrete strength increase the most.(2)In this paper,the frost resistance of concrete with steel fiber and slag-fly ash was tested and the mechanism of freeze-thaw damage was explored.Analysis and calculation show that the mass loss rate and relative magnitude of the dynamic modulus of elasticity and ultrasonic wave velocity freezing-thawing resisting performance evaluation index,the three of the four groups of concrete antifreeze performance from low to high order are:Ordinary plain concrete,steel fiber concrete,slag-fly ash concrete,slag-fly ash steel fiber concrete.(3)Four sets of concrete strength test data were used to analyze the existing models of freezing and thawing strength of concrete,and the corresponding coefficient reference value was obtained.The fitting accuracy are: 0.9579,0.9846,0.9679,0.9846.Indicating that the fitting accuracy is high,can reflect the law of concrete strength attenuation.(4)Set up the dynamic elastic modulus and ultrasonic wave velocity for binomial model of concrete freeze-thaw damage model of damage variable,The coefficient of determination of the dynamic elastic modulus model is above 0.99,the coefficient of determination of the ultrasonic model is above 0.98,It shows that the model can reflect the freezing and thawing damage law of concrete,which provides a reference for predicting the degree of freezing and thawing damage of concrete.During the actual operation,the results obtained by the dynamic elastic modulus method are more stable,but is limited by the test conditions.The experimental results obtained by the ultrasonic method have a certain degree of fluctuation,but have little effect on the whole result,which can provide some reference for the evaluation and detection of the freezing and thawing damage of concrete.