Contact Damage And Nondestructive Test Of Concrete Materials By Using Sphere Indentation

Contact-induced damage is an important factor resulting in failure and strength losses of brittle materials. In order to understand further the behavior and micro- mechanism of contact damage in rock and concrete materials, experimental study and theoretical analysis on contact deformation and damage behaviors of rock, marble and concrete using steel or Al203 ball as indenter were presented. The damage zone under contact in the specimen was observed by using a bonded-interface technique. Subcritical crack growth in rock and concrete materials was investigated with the methods of controlling displacement and in-situ scout. It was found that the mode of contact damage in rock and concrete is not like tension-driven cone cracks in the brittle materials, such as glasses, fine-grain ceramics, but surface depression and semi-spherical shear-and compression-driven distributed damage zone beneath the contact zone. The micro-mechanism of damage for these quasi-brittle materials is 搃nterface microcrack initiation and propagation? In this paper, the equivalent impact method was first adopted to imitate the impact of moving particle on rock and mortar. It indicates that there is a critical impact energy for damage of rock and concrete materials, and that the impact crack-resistant and the working brought with cracks behavior of mortar under high energy level are better than those of rock. Nondestructive test to determine the surface elastic modulus, shear modulus, brinell hardness of brittle and quasi-brittle materials and compressive strength of concrete were investigated based on the analyses of Hertzian contact. It was indicated that the difference between the elastic modulus measured by sphere indentation and the bulk elastic modulus decreases with the degree of homogeneous and smooth. The relative error between them is below 10%. Compressive strength of concrete was also estimated according to the proportional relation between elastic modulus and compressive strength of concrete. The indentation method is convenient and feasible when the conventional method isn available or the measurement is required nondestructive. In view of the corrosion damage of rock and concrete materials by acid become more and more serious nowadays, the indentation stress-strain curves, elastic modulus and brinell hardness of materials in different environments and at different age were compared to evaluate the corrosion damage and the formula of damage degree described with indentation elastic modulus and brinell hardness was given to evaluate conveniently surface corrosion damage of materials. In conclusion, sphere indentation method is convenient and feasible to evaluate the contact damage and environment corrosion of rock and concrete materials. This paper provides a valuable reference for the engineering practice.