Determining concrete compressive strength by combined non-destructive methods

The concrete is the most widely used construction materials at nowadays construction technology. Especially has a quite wide area of the building industry in our country. Due to concrete is a un-homogeneous material, the strength of concrete cannot be achieved at the site. In this sense, to control the mechanical properties of concrete in the site, non-destructive test methods can be used. They are useful for having no damage on concrete, however these test results sometimes gives deceptive results. To reduce these deceptive results, it was supported destructive test method to increase the accuracy of non-destructive methods (NDT). The purpose of this study, determining the a variety of characteristic strengths of concretes? controls with destructive and non-destructive testing methods, establish new relations compressive strength of concrete with the Schmidt rebound value and between the ultrasonic wave velocities. For this purpose, 101 concrete samples were prepared cube dimensions 150x150x150 mm3. After 7 and 28 days curing, Schmidt rebound and ultrasonic wave velocity tests were applied from non-destructive testing methods. Then the compressive strength of these samples was measured by breaking in the pressure device. New formulations and graph were obtained by doing a multiple regression analysis between ultrasonic wave velocity, Schmidt rebound number and compressive strength. These samples were measured NDTs at the end of 90 and 180 days at the site, compared 28 days test results. Furthermore, it was investigated the applicability and accuracy of obtaining formula and graph by taking core samples from present structures. In the first chapter of this study consisting of four chapters, it is introduced shortly to subject of concrete' s strength at the site. Material properties and experiments are given in second chapter, in the third chapter, the findings and considerations are discussed. After important conclusions and suggestions are emphasized in the last chapter, the study is completed. If the most important findings obtained from the study are summarized; the concrete strength can be determined by obtaining formulas as a non-destructive with an accuracy rate of 85% via formulas. It was obtained deviation 1.6% of high strength samples by the graph and 7.3% in the NDTs of the core specimens. These test results show that, NDTs are very good alternative for determining concrete strength at the site. Keywords: Concrete strength, Combined method, Schmidt hammer, Non-destructive test method, Ultrasonic wave velocity