DAMAGE EVALUATION ON STONE MATERIALS OF THE RICHINI COURTYARD (MILAN, ITALY)

It has been recognized that air pollutants interact with carbonate surfaces and cause major damage to architectural heritage. The focus of the present study is to evaluate the damage on the stone materials that have been used for the realization of Richini courtyard. The courtyard was designed in the seventeenth century by Francesco Maria Richini in the complex of Ca 'Granda Hospital, currently home to the University of Milan. Since 1990 has been the subject of an important conservative intervention. At a distance of twenty years after the restoration, "Richini Project" aims to make an assessment of the effectiveness and durability of the solutions used. This study lies in the framework of this project. At this purpose the quantification of soluble salts within the stone samples, collected on the four sides of the courtyard, has been performed by ion chromatography. A widespread sulfatation phenomenon has been put in evidence with differences in intensity among the sides because of different exposition to the atmospheric agents. Atmospheric particulate matter (PM) present on the stone surfaces has been examined. In fact PM is involved in the formation of the black crusts that sometimes cover the surfaces. A new methodology has been set up for the quantification of organic carbon (OC) and elemental carbon (EC), which are mainly responsible of the blackening of those areas. PM major inorganic constituents (cations and anions) have been also quantified and observations by SEM-EDX have allowed the identification of metals that may act as catalysts in the reactions of degradation.