Evaluating the performance of sonic and ultrasonic tests for the inspection of rammed earth constructions

Abstract

There are many examples of historical rammed earth constructions for which the development of valid methods for evaluation of their conservation state is a major concern for conservation agencies of all around the world. On the other hand, rammed earth is attracting the attention of modern architecture trends because of its outstanding performance from an ecological perspective. Thus, the development of reliable non-destructive tests for the inspection of new and existing rammed constructions is of major interest. Ultrasonic and sonic tests are among the most commonly used. While the former has been the subject of numerous studies in rammed earth soil, sonic tests still requires further experimental development. In general, both tests demand a more precise study of their performance according to different states of loading and damage to evaluate the state of structural degradation. Additionally, the procedure commonly used to apply both tests need to be revised in order to provide a more reliable and precise assessment of the time-of-flight of elastic waves. Therefore, on the one hand, this paper evaluates and compares the sensitivity of both non-destructive inspection techniques to different levels of damage induced on the tested samples and possible heterogeneous properties such as compaction energy distribution during the manufacturing process. On the other hand, an automated procedure for the analysis of the experimental recordings and the identification of the time-of-flight of sonic and ultrasonic waves is developed to facilitate the applicability of these techniques. This new procedure consists of a simple signal analysis algorithm that avoids the time-consuming task of manual inspection of the signals and reduces uncertainty in the final results. The results show that sonic test is a valid a promising tool for the inspection of this type of constructions. It performs better than ultrasonic test, which could also be used in practice with some limitations.