Damage evaluation method based on ultrasound technique for gangue concrete under freezing-thawing cycles

As a major industrial waste, gangue has significant environmental, economic, and social benefits when used in the preparation of concrete. The durability and bearing capacity of concrete structures in cold regions are affected by freeze-thaw damage. Therefore, the damage evolution behavior and degree of gangue concrete damage under a freeze-thaw environment should be accurately evaluated. In this paper, rapid freeze-thaw tests were carried out on gangue concrete with volume replacement ratios of 0%, 20%, 40%, and 60% coarse aggregate. The compressive strength and water absorption properties of gangue concrete were tested, and the changing rules of them were analyzed. In addition, the damaged layer thickness of gangue concrete was tested by ultrasonic nondestructive testing technology. The eigenvalue of the damage layer and the residual strength of the material in the damaged area were considered. The correction coefficient was introduced to modify the measured damaged layer thickness. A method for evaluating freeze-thaw damage in gangue concrete on the basis of damaged layer thickness was proposed. Results showed that the compressive strength and damage layer characteristic value of gangue concrete decreased gradually with the increase of freeze-thaw cycles, whereas the water absorption depth, damage layer thickness, and damage degree increased gradually; change rate increased with the replacement rate of gangue. With the increase of the replacement rate of gangue, the frost resistance of gangue concrete decreased obviously, whereas the damage deterioration rate increased. After introducing the damage layer correction coefficient, the accuracy of the evaluated degree of freeze-thaw damage increased significantly. Correction coefficient increased gradually with freeze-thaw time, indicating that the evolution of the residual strength of materials in the damage area decreased continuously and the actual degree of damage increased gradually. (C) 2020 Elsevier Ltd. All rights reserved.