Evaluation of three different mobile Raman microscopes employed to study deteriorated civil building stones

Three different Raman spectrometers were used to analyse the original composition and the degradation products formed on natural outcrops and building materials under influences of urban and industrial pollutants and a marine environment A Renishaw portable Raman instrument was used to check the efficiency of two ultramobile instruments for the identification of the products of decay of diverse carbonaceous stones taken from three areas located at different distances from the coast. Satisfactory results were obtained in measurements of original compounds such as quartz and calcium carbonate. Differentiation between the polymorphic forms calcite and aragonite was possible with the Renishaw RA100 and BWTEK BWS415 i-Raman instruments, the ones provided with higher spectral resolutions. Concerning the degradation products, gypsum (CaSO₄·2H₂O) and amorphous carbon (soot) were detected in samples from three locations, but the most damaged stones are those of Aixerrota, which show higher amounts of both decay products, identified by the three Raman instruments, as the main agent responsible for stone decay. Some nitrate compounds were determined in a mortar sample from the location of the highest impacted environment (Aixerrota), and whewellite (CaC₂O ₄·H₂O) and weddellite (CaC₂O ₄·2H₂O) appeared in some sandstones from Arriluze and joint mortars from Aixerrota derived from micro-organism activity. However, the ultramobile equipments were not capable of detecting the presence of nitrates and oxalates, due to high fluorescence (DeltaNu) and thermo-decomposition (BWTEK) problems.