###### Abstract  
This work aims to study the relationship between the compression resistance and velocity from ultrasonic pulses in samples of mortars with 25% of pozzolanic content. Pozzolanic cement is a low-priced sustainable material that can reduce costs and CO\({}_{2}\) emissions that are produced in the manufacturing of cement from the calcination of calcium carbonate. Using ultrasonic pulse velocity (UPV) to estimate the compressive resistance of mortars with pozzolanic content reduces costs when evaluating the quality of structures built with this material since it is not required to perform an unconfined compression test. The objective of this study is to establish a correlation in order to estimate the compression resistance of this material from its ultrasonic pulse velocity. For this purpose, we studied a total of 16 cement samples, including those with additions of pozzolanic content with different compositions and a sample without any additions. The results obtained show the mentioned correlation, which establishes a basis for research with a higher number of samples to ascertain if it holds true at greater curing ages. ultrasonic pulse velocity; compressive strength; non-destructive test; pozzolanic materials +
Footnote †: journal: Applied Sciences  
One of the applications of ultrasound testing is the evaluation of the compressive strength of mortars and concrete based on ultrasonic pulses velocity (UPV). UPV tests are an easily applied non-destructive method for calculating of the speed of propagation of ultrasonic waves. These values can be correlated with the compressive strength of the mortars and concrete as measured with direct compression tests. In general, the compressive strength and the velocity measured have a correlation, where an increase in velocity results in high values of compressive strength [3]. Many factors influence the models established to predict the compressive strength of concrete from UPV. Some of these factors include the nature of the cement, the influence of aggregate size, the water-cement ratio, and the use of active admixtures [4]. For example, [PERSON] [5] indicated that the UPV decreases with the increase of the water-cement ratio and increases with an increasing aggregate size. [PERSON]. [6] found that increasing the surface roughness of the aggregates led to an increase in the compressive strength of concrete and the speed of the ultrasonic pulses. Another factor to consider is the influence of the concrete mesostructure on wave propagation. Recent research [7] has shown that the complex heterogeneous mesostructure of a concrete slab affects the displacements associated with wave motion, leading to inaccuracies in the wave propagation model. The discrepancy between the actual and theoretical values increases with the proportion of the aggregates and the particle size of the aggregates. Research has been carried out to determine the relationship between compressive strength and UPV in different materials derived from cement. [PERSON] et al. [8] showed that ultrasonic speed can be used to study the quality of concrete reinforced with steel fibres and is an effective way of evaluating the level of consolidation during and after the curing period. [PERSON] and [PERSON] [9] analyzed the ultrasonic test methodology to determine the conversion factor for compressive strength in samples of various dimensions. [PERSON] et al. [3] studied concretes with different types of aggregates, achieving a simplified expression to estimate the compressive strength from UPV that was not affected by the kind of concrete and its composition. [PERSON] et al. [10] investigated whether it is possible to obtain a relationship between compression resistance and ultrasonic speed in concrete samples where the design characteristics are unknown.