Examining the reactivity of volcanic ash in ancient mortars by using a micro-chemical approach

A micro-chemical study of ancient mortars has been performed with the aim to evaluate merits and potential of Laser-Induced Breakdown Spectroscopy (LIBS) technique in determining composition of mixtures and evaluating the reactivity of volcanic aggregates, taking advantages from its micro-destructivity and no sample preparation requirements. LIBS maps have been acquired on areas of about 25 mm2on a set of mortars suitable characterised by the occurrence of volcanic rock fragments with a relevant range in grain size. Na, Mg, Al, Si and Ca have been detected and raw maps have been processed using appropriate image processing and statistical methods (i.e.: PCA, false colour images, self-organized maps). The compositional images have been evaluated and interpreted in the light of the supporting data obtained by classical optical microscope and SEM-EDS methods. Results evidenced the possibility to employ LIBS for a preliminary micro-chemical characterization of mortars, revealing also the potentiality of the method to provide compositional and spatial distribution data on aggregate grains and hydraulic phases.