###### Abstract
The relationship between the ultrasonic pulse velocity and the elastic characteristics of the material are, according to the following equation:  
\[c=\sqrt{\frac{E}{e}\ \frac{1-\mu}{(1+\mu)(1-2\mu)}} \tag{1}\]  
where \(c\) is speed of propagation, \(E\) is Young's modulus, \(e\) is the material density and \(\mu\) is the Poisson coefficient. Since there is a correlation between Young's modulus of a material and its resistance to compression, there will also be a correlation between this resistance and UPV, if the rest of the magnitudes involved are assumed to be invariable [11]. Many researchers like [PERSON] [12], [PERSON]'t et al. [10], [PERSON] et al. [13] and [PERSON] et al. [14] have shown that the relationship between compressive strength and pulse rate can be estimated by the following exponential relationship:  
\[Fc=A\times e^{B\times UPV} \tag{2}\]  
where \(Fc\) is the compressive strength (MPa), \(UPV\) is the ultrasonic pulse rate (km/s), and \(A\) and \(B\) are empirical constants. However, few studies have been conducted on the relationship between UPV and compressive strength in cement, mortars, or pozzolanic concrete. [PERSON] and [PERSON] [15] designed fifteen mixtures of concrete with different metakaolin contents and water-binder ratios (W-B). The hardened properties were tested for compressive strength and ultrasonic pulse rate (UPV), among other tests, and it was determined that compressive strength can be predicted based on UPV using multiple regression analysis. [PERSON] et al. [16] studied a roller-compacted concrete pavement (RCCP) material with different Class F fly ash content as a mineral admixture with different sands as fine aggregate, all tested at different curing ages. Through the results of UPV testing and compressive strength, he proposed the following relationship between both parameters:  
\[Fc=1.526\times e^{0.761\times UPV} \tag{3}\]  
The use of natural additions with different chemical compositions alters the behavior of the mixtures produced compared to materials without additions, with this behavior being more significant at greater curing ages, as can be seen in the study of [PERSON] et al. [17], who studied self-compacted concrete with natural zeolite. There is no consensus or unified formula for using UPV to predict compressive strength, despite the great benefits this would provide, since many factors influence the correlation between UPV and traditional compression tests. Furthermore, when we aim to apply this prediction technique to mortars or concrete with natural additions, such as pozzolans, we find little literature on the subject. This research aims to study the correlation between UPV and resistance to compression in mortar samples with natural pozzolanic additions to examine whether this methodology can be applied to these materials and thus initiate a line of research to determine if a unified formula can be developed to calculate compressive strength for mortars with these additions. The aim of this manuscript is not to suggest a generalized correlation applicable to other materials, but to obtain results for the most significant pozzolanic materials within the deposits shown to have the most appropriate physicochemical properties for use in high-strength mortars. With the implementation of this methodology, it is possible to reduce the cost of quality inspections, making them accessible to the entire population.