Methodology to identify badly weathering limestone using geochemistry : case study on the lower globigerina limestone of the Maltese Islands

Abstract

This paper proposes a new objective method to classify building limestone into types of varying durability working on samples that are visually identical in appearance. Geochemical data were obtained for 90 samples of the Lower Globigerina Limestone of the Maltese islands. Multivariate analyses, including cluster analysis, principal components analysis and discriminant analysis allowed the identification of variables Si02 , Al203 , K20, Ti02 , Fe203 as indicators to distinguish between more durable 'franka' limestone and the less durable facies locally called 'soil'. This hypothesis was confirmed by differences in geochemical data from samples of both weathered and unweathered stone taken from abandoned quarry faces. In the less durable 'soll', Si02 concentrations are >3.4±0.3%, Al203 >0. 78±0.05%, K20 >0.13±0.01 %, Ti02 >0.06±0.002% and Fe20 3 >0.47±0.02%. However, some overlap occurs between the two stone types for all five components, demarcating another stone type we designated as 'intermediate'. The geochemical differences are reflected in mineralogical data and in acid-insoluble residues. This geochemical method is simple and innovative. It can be used to identify newly extracted limestone for use in building and also for replacement of deteriorated stones in old buildings.