Mechanical Properties of Concrete Produced with Coarse Aggregates from Different Mineralogical Origins Using Ultrasonic Tests

The use of nondestructive techniques in the technological control of concrete allows to evaluate and monitor the condition of the material without interfering with its properties; therefore, it is highly desirable in on-site inspections. Among these techniques, ultrasonic testing stands out as one of the most promising by its speed and simplicity to obtain results. However, inferences of strength and stiffness properties using ultrasound parameters should be made with caution, since many factors may interfere with wave propagation. This research aimed to evaluate the behavior of parameters obtained by ultrasonic testing (velocity of wave propagation [V] and stiffness coefficient [C = density × V²]) as predictors of the strength (f_c) and stiffness (E_ci) of concrete produced with coarse aggregates from different mineralogical origins. To achieve the objective, 128 specimens were produced with four aggregate mineralogical origins and four water-cement ratios, with 8 replications each. The ultrasonic tests were performed with two-frequency transducers (45 and 80 kHz). Prediction models of f_c and E_ci were statistically significant (P-value < 0,05) for both frequencies. The model using [C] as independent variable present better correlation with E_ci (R² > 91,2%) and with f_c (R² > 82%) than the model using only [V]. General regression models (regardless of the gravel type) were also statistically significant (P-value < 0.05), with R² > 79% and prediction errors higher than those obtained for the specific models for different rock types.