ORIGINAL ARTICLE Technological study of ‘‘ghiara’’ mortars from the historical city centre of Catania (Eastern Sicily, Italy) and petro-chemical characterisation of raw materials Cristina M. Belfiore • Mauro F. La Russa • Paolo Mazzoleni • Antonino Pezzino • Marco Viccaro Received: 12 May 2009 / Accepted: 8 December 2009 / Published online: 13 January 2010 Ó Springer-Verlag 2009 Abstract This paper presents new petro-chemical data on some typical mortars found in many buildings in the his- toric city centre of Catania (Eastern Sicily). Extensively used in the architecture of the city from the second half of the nineteenth century until the mid-twentieth century, these mortars are characterised by a particular aggregate locally known as ‘‘agghiara’’ or ‘‘ghiara’’. This is the product of thermal transformation induced by the heating undergone by palaeo-soils, originally rich in organic mat- ter, covered by lava flows, which change their colour to reddish nuances. The volcanic origin of ghiara is a peculiar feature of the Etnean area. Mixed with lime, it gives to mortars an intense reddish colour, as well as hydraulic properties, which are comparable with those of the his- torically used pozzolana. This work aimed at complete characterisation of these ghiara mortars, for providing information on several important technological aspects. In order to get information on used raw materials, sampling of some ancient underground quarries, located both in the historic city centre and at the periphery, was also per- formed. Results led to the complete characterisation of the selected ghiara mortars and yielded information on some technological features and the composition of both newly formed and secondary phases, these latter due to alteration processes. The hydraulic properties of mortars have been related to the occurrence of amorphous phases within the ghiara aggregate, which were identified by means of SEM morphological observations. These phases, formed during the ‘‘firing’’ process of palaeo-soils, react with lime pro- ducing hydraulic compounds (C–S–H and C–A–H), which are responsible for the mortars durability. Keywords Ghiara mortars Á Catania Á Sicily Á Aggregate Á Amorphous phases Á Hydraulic properties Introduction Mortars consisting of lime mixed with pozzolanic additions (natural or artificial) were extensively used in the past to construct historical buildings (Bakolas et al. 1995a; Giua 1958). The practice of modifying lime mortars by adding materials, which contain reactive silicates and silico-alu- minates was already known to Roman builders, who used such mixtures to obtain hydraulic mortars. In particular, they used two types of aggregate with pozzolanic behav- iour: (1) natural, consisting of pyroclastic materials coming from the Pozzuoli volcanic area close to Naples (from which the name derives); (2) artificial, given by ceramic fragments (Bakolas et al. 1995a). Further studies have demonstrated that the hydraulic properties of mortars can also be related to the presence of amorphous phases, often recognised as opal, within the aggregate of the mixture (Benezet and Benhassaine 1999; Diamond 1976; Tunc ¸oku and Caner-Saltik 2006). Many of the mortars used in buildings of the Catania historical city centre were prepared by adding to lime a particular aggregate with pozzolanic properties, locally C. M. Belfiore (&) Á P. Mazzoleni Á A. Pezzino Á M. Viccaro Dipartimento di Scienze Geologiche, Universita ` degli Studi di Catania, Corso Italia 57, 95129 Catania, Italy e-mail: cbelfio@unict.it M. F. La Russa Dipartimento di Scienze della Terra, Universita ` degli Studi della Calabria, Via Pietro Bucci—cubo 12/B, Arcavacata di Rende, Cosenza, Italy 123 Environ Earth Sci (2010) 61:995–1003 DOI 10.1007/s12665-009-0418-5