Experimental Study on the Compressive Strength of Big Mobility Concrete with Nondestructive Testing Method

An experimental study of C20, C25, C30, C40, and C50 big mobility concrete cubes that came from laboratory and construction site was completed. Nondestructive testing (NDT) was carried out using impact rebound hammer (IRH) techniques to establish a correlation between the compressive strengths and the rebound number. The local curve for measuring strength of the regression method is set up and its superiority is proved. The rebound method presented is simple, quick, and reliable and covers wide ranges of concrete strengths. The rebound method can be easily applied to concrete specimens as well as existing concrete structures. The final results were compared with previous ones from the literature and also with actual results obtained from samples extracted from existing structures. 1. Introduction The direct determination of the strength of concrete implies that concrete specimens must be loaded to failure. Therefore, the determination of concrete strength requires special specimens to be taken, shipped, and tested at laboratories. This procedure may result in the actual strength of concrete, but may cause trouble and delay in evaluating existing structures. Because of that, special techniques have been developed in which attempts were made to measure some concrete properties other than strength, and then relate them to strength, durability, or any other property. Some of these properties are hardness, rebound number, resistance to penetration or projectiles, resonance frequency, and ability to allow ultrasonic pulses to propagate through concrete. However, the term “nondestructive” [1–3] is given to any test that does not damage or affect the structural behavior of the elements and also leaves the structure in an acceptable condition for the client. However, a successful nondestructive test is the one that can be applied to concrete structures in the field and be portable and easily operated with the least amount of cost. Among the available nondestructive methods, the rebound hammer is the most commonly used one in practice. The rebound hammer test is described in ASTM C805 [4] and BS 1881: Part 202 [5]. The test is classified as a hardness test and is based on the principle that the rebound of an elastic mass depends on the hardness of the surface against which the mass impinges. The energy absorbed by the concrete is related to its strength [6]. Despite its apparent simplicity, the rebound hammer test involves complex problems of impact and the associated stress-wave propagation. There is no unique relation between hardness and strength of concrete,