Petro-archaeology of Gallo-Roman lime mortar. Attempt to reconstruction and interpretation of the “chaînes opératoires”: from material to ancient craftsmanship ; Pétroarcheologie du mortier de chaux gallo-romain. Essai de reconstitution et d'interprétation des chaînes opératoires : du matériau au métier antique

Petro-archaeological research on Gallo-Roman lime mortars is based on a simple analytical methodology: observations with optical microscopy in transmission, which brings us a maximum of data about the material and the various stages of the “chaîne opératoire”. This work enabled us to draw the general features of the craftmanship (common practices of the ancient structores and tectores), to establish the relations between mortar composition and its “primary” and “secondary” architectural function, then to perceive what are the markers and motivations of the formula adaptations. The importance of the geological environment is shown, because it induces economic and technical choices, requiring sometimes raw material replacement. It poses also the geographical limits of the innovations propagation, often related to local problems of raw materials supply. The concepts of “wanted”, “missed” and “involuntary” properties make it possible however to understand what, in the complex system of the trade of the lime mortar, will be generating of formula durability, or a contrario of formula variability, in answer to the apparent and immediate material quality. Currently, only a mortars study according to their employment and for a restricted “area” makes it possible to perceive chronological evolutions with value of dating. The study of the construction mortars in Arelate (Arles, France) appears exemplary: mortars resulting from the same local inheritance show perfectly circumscribed uses in time, enabling us to advance assumptions of dating for badly dated masonries or to date masonries still prone to controversy. ; La recherche pétroarchéologique sur les mortiers de chaux gallo-romains s'appuie sur une méthodologie analytique simple, fondée sur les observations en microscopie optique en transmission, apportant le maximum d'informations sur le matériau et les différentes étapes de sa chaîne opératoire. Ce travail nous a permis de tracer les traits généraux du métier (les pratiques communes des structores et tectores ...