Advances on the use of non-destructive techniques for mechanical characterization of stone masonry: GPR and sonic tests

Abstract

The main aim of the present work is to use NDT (non-destructive test) for characterization of stone masonry and obtaining information regarding the related mechanical parameters. Due to historical and cultural value that historic buildings embody the maintenance and rehabilitation work is important to preserve the appreciation of history. The preservation of buildings classified as historic and cultural heritage is of social interest, as they marked the history of society. Considering the object of research as a historic building, it is not recommended to use destructive investigative techniques. This paper focuses on the application of geophysical methods, namely Ground Penetrating Radar (GPR) and sonic tests for civil engineering purposes as NDT research options. The GPR comprises a generator of electromagnetic pulses, transmitting and receiving antennae and a control unit with signal displaying and recording facilities. The sonic tests are performed with an instrumented hammer and accelerometers for body and surface waves reception, namely, P, S and R. This work allowed understanding the behavior of two-leaf stone masonry walls by relating the NDT parameters with mechanical properties. To assist this analysis, the compression test results will be used. Simultaneously to the application of NDT's were carried on destructive tests on the stone masonry, like compression tests, to obtain compressive strength, Young's modulus and Poisson's ratio. These data will be correlated with the NDTs’ results. The use of other techniques in line with the GPR method is widely used in order to address limitations of the GPR. The GPR presented radargrams suitable for the structural constitutive type of the walls and the zones identified with the presence of more resistant structural elements validate the results obtained by the sonic tests. With the sonic test results it is possible to calculate values of Poisson's ratio, Young's modulus and shear modulus, to characterize the material. For sonic tests, the highest velocity points are in the header block, from the direct configuration test. The sonic test resulted in characteristic values ​​of propagation velocities of the sonic waves in the analyzed walls, with these results obtained values ​​of Young's modulus that supported the mechanical tests. In this way, it is highlighted that the synergy of the tests provides more coherent results for future correlations with the mechanical data. Both NDTs used presented coherent and related results, one technique corroborating the results of the others. The correlation between mechanical parameters and NDTs’ results will be investigated resorting to artificial neural networks’ techniques (ANN), which is the next step of this work.