Abstract

Abstract:IntheProvenceregion(south-easternFrance),alargepartofthebuildingheritagewaserectedusingabioclasticlimestonecalled ‘‘Pierre du Midi’’. Under this common name, the heterogeneity of the material and, specifically, its stability upon climaticexposure depend on the actual extraction location. In some cases, building stones are affected by spalling decay which is commonlyrelated to the presence of clay minerals although without quantitative support. The present study aims at characterizing andquantifying the clay mineralogy of eight ‘‘Pierre du Midi’’ samples showing various spalling degrees.The combination of transmission electron microscopy (TEM) coupled to energy-dispersive X-ray spectrometer (EDX) and of X-ray diffraction (XRD) full-profile modeling of 00‘ reflections patterns is used for quantitative phase analysis. Identification of clayminerals present in the , 4 mm fractions is performed on the basis of qualitative analysis of experimental XRD patterns recorded inbothair-dried(AD)andglycolated(EG)states.Thecrystal-chemistryofclaymineralsisthenrefinedfromTEM-EDXanalyseswhichare used as an essential constraint for the modeling of both AD and EG XRD patterns.Theresultshighlightthatthecomplexclaymineralogyoflimestonescanbeunraveledandquantifiedwhenusingthepresentcoupledapproach.Finally,thecontrastingsensitivityofsamplestospallingdecaycanbeexplainedbytheoverallproportionofexpandablelayers,essentiallypresent inFe-rich mixed-layers,inthe clayfraction.A content ofexpandable layers higherthan0.80 wt. % resultsina highsensitivitytospallingdecay,whereas rocks withlessthan0.20wt. % ofexpandablelayersremainessentially unaffected.Key-words: clay minerals; building stone; spalling decay; XRD profile modeling; TEM-EDX; mixed layer minerals; intra-crystalswelling; Fe-montmorillonite.

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