Image analysis and flatbed scanners. A visual procedure in order to study the macro-porosity of the archaeological and historical mortars

This paper describes a low cost method that allows to identify, map and quantify the macro-porosity (Ø ≥ 1/16 mm) of mortar samples taken from the Roman hemicycle theatre in Sibari (South Italy). A specific tool connected to flatbed scanner has been devised for this purpose: it makes possible to acquire images of thin sections through transmitted polarised light. These images can then be elaborated by an ordinary image analysis software programs in order to extrapolate the required information. The technique can be used on mortars which have been buried underground for a considerable period of time (archaeological mortars) or on mortars exposed to sub-aerial weathering (historical mortars). In this way, carbonatic binder dissolution phenomena, and the consequent porosity increase, can be verified and studied in detail.