In-situ versus laboratory characterization of stone degradation using x-ray fluorescence spectrometry and Raman spectroscopy
Résumé
Raman (micro)-spectroscopy and X-ray fluorescence spectrometry are powerful analytical techniques that allow for molecular and elemental analysis, respectively. These types of characterizations are essential to identify the salt or mix of salts responsible for the weathering of stones, bricks and mortars. Due to the evolving nature of salts, the process of sample extraction and storage in laboratory might alter the state of the degradation and lead to erroneous assumptions. Recent advances allowed for the development of portable devices for both x-ray fluorescence and Raman spectroscopy, which avoids these problems because they allow to perform measurements in-situ. Still, the use of miniaturized equipment involves sacrifices concerning the spectral resolution and geometrical precision. Here, a comparison is presented between in-situ and laboratory analysis to ascertain the amount and importance of loss of information caused by the change of method. The object of study was a 130 year old structure, the Villa Belza, located at the coast of Biarritz, France. The analysed façade suffered from severe weathering of different building materials, in-situ analysis were performed in nine different points, including natural stone, building stone and mortar. Subsequently, cores were drilled in each of these locations and transported to the laboratory for further study. The identification of elements and molecules by the proposed techniques is weighted against their importance as forensic tools and conclusions are drawn regarding the necessary accuracy for the case of the Villa Belza. The authors concluded that the difference in information quality could be diminished by altering acquisition parameters, and in-situ techniques were sufficient for the porposition of damage mechanisms.