EXAMINING THE REACTIVITY OF VOLCANIC ASH IN ANCIENT MORTARS BY USING A MICRO-CHEMICAL APPROACH

Abstract

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 mm2 on 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.