Thermo-hygric weathering of Carrara Gioia marble monitored with NonlinearResonant Ultrasound Spectroscopy

International audienceCarrara marble is widely used, in buildings and sculptures, in ancient and recent works. Yet, it can developdeteriorations over time, such as bowing, cracks, expansion, reduction of mechanical strength, when it isexposed to environmental conditions. Previous studies have shown that these deteriorations can resultfrom exposure to temperature variations, and that they can be enhanced by additional humidity variations.However, the mechanisms at stake at the microstructure level are still not well-understood.This work is therefore focused on the understanding of the degradation mechanisms induced on marble bytemperature and humidity fluctuations. Laboratory experiments are carried out on Carrara marble samplesfirst heated at different temperatures (23 – 250 °C) and then undergoing hygric cycles.The mechanical state of Carrara marble samples is monitored with Nonlinear Resonant UltrasoundSpectroscopy (NRUS), through the evolution of resonant frequency and of nonclassical nonlinearity. Thefirst parameter is related to sample stiffness, and the latter is highly sensitive to any change occurring at themicrostructure level (micro cracks, friction, capillary effects, etc.). Additionally, microstructuralcharacterization (mercury intrusion porosimetry, optical microscope and SEM observations) is made on thethermally-damaged marble samples to link the evolution of the NRUS parameters to the changes occurringin marble microstructure.Results show that the nonclassical nonlinearity exhibits an original behaviour with thermal damage as itdecreases for highest heating temperatures. This could be due to the loss of intergranular contacts betweencalcite grains as marble undergoes a progressive granular decohesion. Nonclassical nonlinearity alsoexhibits a great sensitivity to fluctuations in relative humidity. However, adsorption-desorption cycles showthat these changes are reversible. Thus, relative humidity fluctuations alone do not induce permanentdamage in Carrara marble

Gene fusion in Helicobacter pylori: Making the ends meet

10.1007/s10482-005-9021-2Antonie van Leeuwenhoek, International Journal of General and Molecular Microbiology891169-18