2.4.2. Rebound Number

To determine the rebound number of specimens of the six concrete mixtures used in this study, tests were carried out according to the NMX-C-192-ONNCCE-2018 standard [54], in which a procedure is established to determine the rebound index for hardened concrete using a device known as a sclerometer or rebound hammer, to evaluate the compressive strength as well as the surface uniformity of the concrete. The results are considered relative rather than absolute values, but the test has the advantages of being non-destructive and widely used worldwide, and is used for evaluating the compressive strength of in-situ concrete [55] and in conjunction with the UPV test to predict the compressive strength of concrete in studies according to the findings of Amine et al. [56]. A rebound hammer, abrasive stone, spatula, flannel and brush were used to carry out the test. The test surface preparation was at least 150 mm in diameter and 100 mm thick. The surface was free of any layer other than concrete (see Figure 3).

**Figure 3.** Rebound Number test.
