Ultrasonic Identification Of Freeze-Thaw Damage For Concrete Based On Multi-Scale Homogenization Method

Freeze-thaw damage is one of the main reasons for the deterioration of concrete structures.Micro-cracks are generated inside concrete under the action of freeze-thaw cycles,resulting in deterioration of structural mechanical properties and durability.The relative change of ultrasonic pulse velocity can be used to detect the freeze-thaw microscopic damage of concrete materials,but the existing research results can only qualitatively evaluate the uniform freeze-thaw damage at the level of material.There is still a lack of research on the theoretical connection and quantitative relationship between ultrasonic pulse velocity and freeze-thaw microscopic damage.It is difficult to quantitatively characterize the changes in the internal structure of concrete materials under microscopic damage and quantify the microscopic damage of concrete materials through ultrasonic pulse velocity.In this paper,a multi-scale prediction model of ultrasonic pulse velocity for concrete materials is established based on the multi-scale homogenization method,and microscopic damage quantification parameters are introduced into the ultrasonic pulse velocity prediction model to determine the calculation scale of microscopic damage variables and the homogenization method of each scale under microscopic damage.A computational model of ultrasonic pulse velocity for quantitative characterization of concrete microscopic damage is proposed.The main research contents and conclusions are as follows:1.Based on the multi-scale homogenization method and the elastic formula of homogeneous multi-phase materials,a multi-scale prediction model of ultrasonic pulse velocity for concrete materials is established.According to the theoretical mechanism of ultrasonic pulse velocity changes and material properties,the main influencing factors of ultrasonic pulse velocity at different scales and the applicability of different homogenization methods are clarified.2.In this paper,the ultrasonic pulse velocity of concrete with different watercement ratios and different ages is measured through the ultrasonic pulse velocity detection test,and the ultrasonic pulse velocity of concrete materials in some existing studies is collected,compare them with the calculation results of the ultrasonic pulse velocity prediction model to verify the accuracy of the ultrasonic pulse velocity prediction model.3.In the freeze-thaw cycle test of mortar,the compressive strength,residual strain and ultrasonic pulse velocity of mortar at different degrees of freeze-thaw damage are measured.The changes of apparent morphology,residual strain,ultrasonic pulse velocity and compressive strength of mortars with different water-cement ratios during freeze-thaw cycles are analyzed.And the residual strain is used to quantitatively characterize the degree of freeze-thaw microscopic damage.The bilinear relationship between ultrasonic pulse velocity loss,compressive strength loss and residual strain is then established.4.The microscopic damage variable is introduced into the concrete ultrasonic pulse velocity prediction model,and the development degree of micro-cracks is quantitatively characterized by the residual strain of freeze-thaw damage.Based on different crack shape assumptions,the effects of calculation scale and homogenization method on the prediction results are compared and analyzed,and then a computational model of ultrasonic pulse velocity for quantitative characterization of concrete microscopic damage is proposed.