The microscopic study of the mortar's binders

The study of some artificial materials constituting the historic buildings, such as mortars, is very interesting because they maintain and transmit to us, not only the aspect of an artifact, but also the constitutive material, whose study, allows us to draw information on the ancient technologies used to realize the artifact itself. The information that we may obtained from the study of these materials, contribute to the knowledge of our past and our history, and also provide useful data for the conservation of Cultural Heritage. The mortars are materials used in architecture with very different functions: as bedding mortars of bricks and stone blocks, as filling of the nucleus of the walls themselves, as rendering of walls, support for mural paintings, up to material to join decorations etc. All these kinds of mortars can display different structure and composition. Purpose of this study is to characterize, through observations of thin sections under optical microscope in transmitted light, several typologies of mortars which differ in type of binder: air hardening lime (calcic, magnesian), air hardening lime with addition of materials providing hydraulic characteristics, gypsum binders, natural hydraulic lime, Portland cement, Roman cement. Petrographic thin sections of mortars realized with these different type of binders were realized and observed under optical microscopy in transmissed light. The main characteristics such as texture (micritic, sparitic, sparitic or amorphous), structure (homogeneous, with lumps, in plagues, oriented, etc), reaction rims, formation of new crystalline phases were described for each type of binder.