###### Abstract
It is largely formed of natural aggregate (NA) that constitutes crushed concrete and the mortar adhering to it [28]. Furthermore, RA contains mortar fragments in its finer fractions [29]. The main advantage of this type of concrete is that it increases sustainability and reduces NA consumption [30; 31]. However, the high water absorption of RA and having less dense interfacial transition zones than ordinary concrete reduce the workability and strength of the resulting concrete [32; 33; 34]. Thus, it is essential to balance the sustainability and performance of concrete by defining an adequate RA content [35]. Another type of concrete whose use is also increasingly common is self-compacting concrete (SCC), which is characterized by an almost liquid-like behavior in the fresh state [36; 37]. The composition of the SCC must therefore have a large amount of fine particles (limestone filler, fine aggregate), a low proportion of small-size coarse aggregate, and an adequate amount of plasticizer [37; 38; 39]. SCC has a number of functional advantages, such as a high-pumping capacity and optimum adaptation to any type of formwork [38]. In addition, its use also has environmental benefits, since the absence of vibration saves energy and, therefore, reduces the carbon footprint of concreting [40; 41]. This type of concrete can also be manufactured with RA, and the studies conducted on its use have reached similar conclusions to the tests on conventional concrete [22; 40]. There are some studies in the literature that address the NDT of SCC containing RA through the UPV. On the one hand, some studies show the statistical dependence between UPV and the mechanical behavior of this type of concrete [21; 42; 43]. Thus, it was found that the linear-regression relationship is adequate to predict the compressive strength from the UPV [42; 43], although a more reliable estimate is obtained by complementing the UPV with another non-destructive measure such as the hammer rebound index [21]. These studies have served as a basis for the current focus on the use of algorithms that can predict the compressive strength of SCC containing RA from the composition of the concrete [44]. On the other hand, it has also been demonstrated that the UPV can be used to evaluate the durability behavior of this type of concrete and to predict its expected damage by external agents using linear simple-regression models [45]. However, further research is neededon the non-destructive evaluation of this type of concrete to ensure that SCC concrete components may be repaired or rehabilitated, which will in turn promote its usage. For this purpose, the utility of the UPV as an indicator of the overall mechanical performance of the SCC containing RA by considering multiple regression can be analyzed. In a previous study, the authors demonstrated the validity of the hammer rebound index to obtain an overview of the mechanical behavior of SCC with RA [46]. It was found that multiple-regression fitting of the hammer rebound index as a function of compressive strength, modulus of elasticity, splitting tensile strength, and flexural strength, using standardized values for all properties, showed that the hammer rebound index can be correlated with the mean weighted average values of compressive and bending-tensile behavior. So far, the scientific literature has only shown the validity of the UPV for estimating different concrete properties through simple regression on an individual basis, as detailed throughout this introduction. Therefore, the aim in this paper, using the same SCC mixes of the previous paper of the authors [46], was to evaluate whether UPV readings can be expressed through multiple regression as a function of all the mechanical properties, so that this non-destructive measure could be used to obtain an overview of the mechanical behavior of SCC containing RA.