The Application of Sonic Testing on Double-Leaf Historical Portuguese Masonry to Obtain Morphology and Mechanical Properties

Abstract

In order to perform a conservation or repair intervention of a historic building, knowledge of the mechanical properties of the historical materials and building components is essential. Obtaining these properties should be performed inflicting as little damage to the historical fabric as possible. Methods to do so are defined as non-destructive test methods (NDT). The paper investigates the use of sonic testing (NDT) on historical masonry. Nine double-leaf wallets were constructed according to a traditional Portuguese building method, using light ochre schist and mortar made of local soil and water. Three wall variations were present concerning plaster finishing and grouting strengthening. A testing procedure was developed for sonic testing to determine the morphology and mechanical properties. The wallets were also classified according to the Masonry Quality Index method (MQI), which can be used to identify strength and stiffness parameters of masonry by visual inspection without testing procedures. The method was used in conjunction with the sonic testing. In addition, compression tests with loading and reloading cycles were performed. Young’s moduli could be compared to those obtained by the MQI method and the sonic testing. The results revealed that the Young’s moduli of the sonic testing had a good agreement with those of the compression testing, although the former presented an overestimation due to testing on the outer leaves. The Poisson’s ratio presented inconsistent results due to a high scatter on experimental values. The sonic testing also showed a good indication of weak zones in the masonry. The MQI method produced less accurate results in terms of stiffness estimation but has potential and should be investigated further.