Investigating possible correlations between the porosimetry and insoluble residue content of Malta’s Lower Globigerina Limestone

The millenary use of Lower Globigerina Limestone (LGL) as the main building stone of the Maltese Islands is testimony to the importance of this resource to the local building industry. Today, the pressing need to conserve Malta’s rich patrimony of archaeological/historical masonry buildings and structures drives research in this field, particularly in view of the observed variable durability of this stone type. LGL has been described as a moderately weak calcarenite characterised by a predominance of calcite (86–99 %) and high porosity. In theory, these physical properties should make this type of stone particularly susceptible to deterioration involving (a) mechanisms of capillary salt-laden moisture accumulation and movement together with (b) thermodynamic changes in soluble salts during dissolution and crystallisation cycles. The study reported here forms part of a wider research programme aimed at characterising this resource. In this work, we assessed the durability of the LGL in a temperate Mediterranean climate characterised by two main factors, namely (i) a salt-laden marine environment and (ii) relatively short spans of heavy precipitation alternated with longer periods of virtual drought. The main aim of the study was to analyse macro/microporosity variations and minute, yet quantifiable, fluctuations in minor geochemical constituents of the stone with respect to observed weathering characteristics and accelerated crystallisation damage test results. This was achieved through systematic sampling and testing of retrieved core samples extracted from dimension-stone quarrying areas in Malta.