Use of Non-Destructive Methods in Structural Analysis of Petrous Materials - Ultrasonic Testing and Ground Penetrating Radar (GPR)

Abstract

In the extractive and transformation processing industry of ornamental rocks, the presence of discontinuities, grain size, porosity and textural anisotropies in the explored blocks is an economic risk factor. This study aims the identification and possible quantification of these elements. The existence of a low-cost, non-intrusive and fast inspection method for the evaluation of blocks would facilitate their use avoiding their wastage. For this purpose, two nondestructive methods (“P” Wave Ultrasonic Testing and the Ground Penetration Radar (GPR)) were tested on a limestone rock block and compared the models obtained. The portable ultrasound equipment used was a Proceq Pundit Lab (Portable Ultrasonic Non-Destructive Digital Indicating Tester) which is based on the pulse rate method with 54 KHz to provide information about the uniformity, cavities, cracks and defects of the material concerned by the measurement of the ultrasonic wave time and the measurement of the pulse rate. The equipment used for the GPR data acquisition was a PULSEEKKO GPR (SENSORS & SOFTWARE), with a system of two bistatic antennas (transmitter and receiver) with a frequency of 1 GHz, using the reflection method with a common offset and with an antenna separation of 0,15 meters [m]. To make a comparison of the results valid and representative, both tests were performed with 0,10 m spacing between measurements, according to a pre-defined and common grid. In the case of the ultrasonic test, velocity color maps were created based on the results of the measurements, and through this colors differences it was possible to detect and locate some of the individual and visible fractures, but also not visible fractures on the surface of the tested face. By increasing the distance between transducers, the measurement depth also increases, creating maps of the same face at different depths. This method allows us to create several GPR profiles (radargrams) were obtained because of the processing, and were used to create 2, 2,5 and 3D models to identify the existing structures, their vertical and horizontal limits and spatial relationships between them.