M., Favero-Longo, S., Pérez-Ortega, S., Ascaso, C., Haghighat, Z., Talebian, M., Fadaei, H., De los Ríos, A., 2017. Lichen colonization and associated deterioration processes in Pasargadae, UNESCO world heritage site, Iran. International Biodeterioration & Biodegradation, 117: pp. 171–182.
UNI., 2006. 11187:2006 – Beni culturali – Materiali lapidei naturali ed artificiali – Pulitura con tecnologia laser. Milan: UNI – Ente Nazionale Italiano di Unificazione.
77
EFFECT OF FIRE ON THE DURABILITY OF A POROUS CALCARENITE: THE CASE STUDY OF A TOBACCO FACTORY IN TRICASE (LECCE, SOUTHERN ITALY)
Emilia Vasanelli1, Angela Calia1, Giovanni Quarta1, Davide Melica2, Maurizio Masieri1, Antonio Monte1, Francesco Micelli3
IN: SIEGESMUND, S. & MIDDENDORF, B. (EDS.): MONUMENT FUTURE: DECAY AND CONSERVATION OF STONE.
– PROCEEDINGS OF THE 14TH INTERNATIONAL CONGRESS ON THE DETERIORATION AND CONSERVATION OF STONE –
VOLUME I AND VOLUME II. MITTELDEUTSCHER VERLAG 2020.
1 CNR-ISPC National Research Council – Institute of Science for Cultural Heritage, University Campus, Prov.le Lecce Monteroni, 73100, Lecce, Italy
2 Conservation Scientist via Carlo D’Angiò 31, 73043 Copertino (Lecce), Italy
3 University of Salento Dept. Innovation Engineering University Campus, Prov.le Lecce Monteroni, 73100, Lecce, Italy
Abstract
Thermal decay induced by fire produces chemical and mineralogical alterations, which are often accompanied by discoloration changing the aesthetic characteristics of the stone surfaces. It may compromise also the load-bearing capacity of the masonry elements and lead to stability problems.
Here we report on the investigation of the fire effects on a soft calcarenite used within a masonry building.
Mineralogical transformations of iron hydroxides were detected through XRD and accounted for red discolouring. They were confirmed by DSCTGA analyses and indicated a temperature around 300 °C affecting the stone. Microstructural modifications were investigated by means of optical microscopy and UPV propagation test. A quantitative determination of physical parameters such as color, bulk density, porosity and water uptake was also performed. Implications of thermal stress with the mechanical properties were assessed through uniaxial compressive tests. Thermal effects on the stone microstructure were not microscopically evident. On the contrary, UPV decreases indicated a microfissuring, but this slightly affected porosity, water uptake and compressive strenght.
Introduction
Stone materials involved in fires may be affected by a variety of phenomena, which can change their original properties and related performance in buildings. Depending on the temperature, both chemical and mineralogical trasformations may occur and lead to stone colour changes (Kompaníková et al. 2014). In addition, volume variations due to phase transitions (Calia et al, 2015), different thermal expansion of adjacent minerals (Vázquez et al., 2015) or strongly anisotropic thermal properties of some minerals (e. g. calcite) (Siegesmund et al., 2000) may affect the stone microstruture and lead to microfissuring, which may increase the stone susceptivity to weathering and compromise its load-bearing performance (Sippel et al., 2007). Thermally induced effects on the microstructure strongly depend on the inherent stone characteristics and have a high incidence on low porosity materials, due to the dense packing of crystals and grains (Yavuz et al., 2010). Thermal behaviour has been studied for a variety of stones, which mainly include compact materials (Martinho et al., 2018), while poor literature deals with heating damage on porous stones (Gomez-Heras et al., 2006; Brotóns et al., 2013; 78Franzoni et al., 2013). In this paper we present the results of a case study where the effect of a fire on highly porous calcarenites were assessed by using integrated investigation techniques.
Material
The study was carried out on the stone materials used within the masonry of the ACAIT (Azienda Cooperativa Agricola Industriale del Capo di Leuca) industrial building (Fig. 1). The building was a factory for the processing of the tobacco, in the province of Lecce (Southern Italy). It was built in the early 1900 and dismissed at the end of the 1980s. The factory is a remarkable example of the industrial archaeological heritage relating to the tobacco manufacturing, a flourishing activity in which Puglia region had a leading role on a national basis in the past century.
The original building developed on the ground floor only and it has undergone several enlargements over the years. Like all industrial buildings, it has a simple and modular layout, composed of large rooms with corner-vaulted (“volta a spigolo”) roof, typical of the local tradition, load-bearing pillars and masonry walls with regular local limestone ashlars.
Figure 1: The building of the tobacco factory ACAIT affected by a partial collapse.
Figure 2: Detail of the stone from the collapsed vaults, which shows a yellow-beige-color (Y) passing to a reddish one (R) across the thickness of the masonry unit.
In 2018, after a strong rainstorm, part of the structure collapsed (Fig. 2), involving in a first time one vault and part of the two adjacent ones and in a second time (about 7 days later) the remaining part (five vaults) of the room. The collapse evidenced the inner structure of the vaults and external walls. The latter were two leafs walls without horizontal connections, filled with incoherent material (pieces of rocks and debris).
The vault collapse revealed traces of an historic fire, which were hidden by the presence of plasters, in the form of fumes and a diffuse reddish color across the thickness of the masonry units up to some centimeters from the surface (Fig. 2).
In the framework of a diagnostic activity supporting a restoration project in view of a building reuse, the study of the fire damage on the stone was undertaken.
Methods
Collapsed blocks measuring 21x20x50 cm were taken from the site and samples were obtained from both the unaltered and altered portions, having yellow-beige (Y) and reddish colour (R), respectively (Fig. 2).
The following analyses and tests were performed.
— Thin-section samples were observed in plane-polarised and cross-polarised transmitted light by means of an optical microscope (Eclipse LW100 Nikon) at magnifications of 50x e 100x.
— X-Ray Diffraction analyses (XRD) were performed on both the whole rock and insoluble residue. The insoluble residue was separated by a chemical attack of the grinded stone with HCl-3N in order to remove the carbonates
