Image processing of the pozzolanic reactions in Roman mortars via X-Ray Map Analyser

A new semi-automated image processing procedure based onmultivariate statistical analysis of X-Raymaps hasbeen here used to compute the element distribution between andwithin specific phases, recognized inside a hydraulicRoman mortar sample. This new tool package, largely centred on functions implemented in ArcGis®, isbased on the semi-automated combined use of the Principal Component Analysis (PCA) and of the supervisedMaximum Likelihood Classification (MLC) of X-Ray maps.Three different micro-domains were selected within the investigated archaeological mortar, whose hydraulicproperties were reached by mixing an aerial lime with a pozzolanic aggregate from the Alban Hills (Lazio,Italy). Attention has been here focused on the cementitiousmatrix (CM), in order to assess the distribution of hydraulicphaseswithin the investigated domains. To this aim, three different X-Raymap arrays have been acquiredthrough a SEM–EDS device at 1024 ∗ 800 pixel resolutionwith amagnification closely ranging from 120 to 230×.Starting from these EDS X-Ray maps, the procedure included two different cycles of analysis: the first one processedthe entire selected domain in order to classify all the recognisable components (cementitious matrix, aggregateand pores); the second one allowed to investigate in more detail the element distribution within thecementitious matrix by means of a new MLC. In addition, the application of the kernel density function on thesole CM, allowed to obtain the density distribution of Ca, Al, Si,Mg, K and Fe within CMand to put into evidencethe effect of the differential hydraulic reactions developing between pozzolanic aggregate and hydrated lime.Finally, the use of raster calculator functions permitted to gain further derived maps showing, for instance, thevariability of the hydraulicity index (HI) within the three selected domains.Obtained results highlight as the used tool package proved to be powerful in the study of pozzolanic mortarssince it provides a simple visualization of the newly formed phases and their distribution within a restrictedbut compositionally complex system.