Strength tests of concrete specimens by the method of ultrasonic waves contain many variables such as the size of aggregate, water cement ratio, temperature, density of materials, among others, that affect the final strength of the specimen. However, it has become a fast nondestructive method to diagnose resistant of already built structures and detect anomalies such as cracks or discontinuities. This article finds a correlation between the readings of the ultrasonic waves and the compressive strength of concrete at 17.5, 21, 24.5 and 28 MPa for 7 and 28 days, with varying coarse and fine aggregates of Montería city so as to diagnose the concrete strength of the ancient structures that do not comply with the Regulation Colombian Earthquake Resistant Construction - NSR 10.