Assessing the current and future condition of concrete structures is a recurring topic, and this applies to both new and old structures. Several non-destructive techniques are available for investigating and assessing the deterioration state of concrete structures. These techniques provide an interesting approach to predicting concrete properties such as strength, modulus of elasticity, and surface hardness without damaging the structure. When assessing the structure’s state of deterioration or concrete properties using NDT techniques, special attention should be paid to factors that can affect both destructive and non-destructive measurements. Among these factors, the parameters of the concrete mix and its components, particularly the maximum size of the aggregates, are considered to have the greatest influence on these measurements. Non-destructive testing is used to assess the performance status of structures based on correlation models developed on laboratory specimens; any extrapolation of these models outside the strength range or type of concrete for which they were developed must be done with caution in order to reduce the margin of error as much as possible. The applicability of these techniques is therefore restricted, necessitating the use of a calibration of these models. In this case, the validation of these models can be done using results obtained on the real structure; this step consists of comparing the results estimated using the developed regression model to the on-site results. Such procedure allows for the drawing of a correction coefficient of the correlation model that takes into account the influencing factors. The corrected curve will be more precise. The aim of this study is to highlight the influence of reducing the maximum size of coarse aggregates on the non-destructive rebound hammer and ultrasonic measurements, as well as the compressive strength. The rebound number, UPV, and the compressive strength results obtained on standard cylindrical specimens (16 × 32) cm of ordinary concrete, were compared to those obtained on specimens made from the same mix design but with the proportion of class 8/15 aggregates completely replaced by the same nature aggregates with a reduced diameter (class 3/8). This approach is used to derive a correction factor that takes into account the reduction in the maximum size of aggregates. This coefficient can be applied to calibrate and validate the associated correlation models. In the case of ordinary concrete, the results show that reducing the maximum aggregate size had no effect on the rebound index value. The variation in diameter, on the other hand, had an adverse influence on the ultrasonic measurements as compared to the compressive strength results. Indeed, when the ultrasonic values decrease due to a reduction in the maximum aggregate size, the compressive strength rises significantly.