JoAnn Cassar

Deterioration of the Globigerina Limestone of the Maltese Islands

Abstract The Globigerina Limestone occurs as two types of building stone: the resistant ‘franka’ and the easily weathering ‘soll’. Research on both fresh and weathered samples has led to an understanding of the main differences in these two types of stone. The causes and mechanisms of deterioration have also been established. ‘Franka’ and ‘soll’ differ in geochemical and mineralogical composition and in physical properties. The ‘soll’ is richer in the non-carbonate fraction, which occludes some of the pore space, resulting in a lower overall porosity and a higher proportion of small pores. The ambient local environment, heavily loaded with sea salt, particularly sodium chloride and sulphates, readily induces deterioration in ‘soll’, whereas ‘franka’ tends to resist better in this aggressive environment. The weathering process of Globigerina Limestone in general has been explained as a sequence of steps, from the formation of a thick and compact superficial crust, to the loss of this crust, to the initiation of alveolar weathering. Understanding the deterioration mechanisms of Globigerina Limestone permits criteria for proper conservation treatment to be established.

Limestone in the Built Environment

Limestone is a highly successful and widely used building material, found in many important historic buildings and new monuments around the world. Whilst its success reflects its durability under a wide range of environmental conditions, there are still important questions surrounding the selection, use and conservation of building limestones. In order to make best use of new limestone today, and to conserve old limestone most effectively, we need to bring modern research methods to bear on understanding the characteristics of different limestones, what mortars to use, and how key limestones have responded to polluted atmospheres. This volume brings together recent inter-disciplinary research on these issues, illustrating the diversity of innovative techniques that are now being applied to furthering our understanding of building limestones.

The use of limestone in a historic context – the experience of Malta

Abstract The Maltese Islands measure only 316 km2, have a population of just over 405 000 and are situated in the central Mediterranean. They are composed of sedimentary rocks, of which the Globigerina and Coralline Limestones have been used as building materials since prehistoric times. This paper gives an overview of the use of these materials, and other imported materials, for building from prehistoric times to the present day, and also looks at the exploitation of the underground environment through the ages.

Methodology to identify badly weathering limestone using geochemistry: case study on the Lower Globigerina Limestone of the Maltese islands

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 SiO2, Al2O3, K2O, TiO2, Fe2O3 as indicators to distinguish between more durable ‘franka’ limestone and the less durable facies locally called ‘soll’. 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’, SiO2 concentrations are >3.4±0.3%, Al2O3 >0.78±0.05%, K2O >0.13±0.01%, TiO2 >0.06±0.002% and Fe2O3 >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.

Tangible versus intangible in e-learning on cultural heritage : from online learning to on-site study of historic sites

The revolutionary development in digital theory and technology calls for non-trivial decisions in bridging between the virtual and real worlds. The field of conservation of cultural heritage thus provides various challenges, especially with regards to learning, study and investigation of tangible heritage through applications of intangible ICT technologies. This paper examines the interaction between e-learning, and the actual on-site learning and study of historic buildings and sites, with an emphasis on their visual characteristics. In this context, the paper presents some aspects of application of a methodology which allows basic documentation, monitoring and primary analysis of data on cultural (built) heritage sites by general public through educational process enabled by an e-learning platform.

Ammonium Oxalate Treatment Application in the Presence of Soluble Salts: Laboratory Results on Soft Limestone

Ammonium oxalate treatment of calcareous stone has, in recent years, emerged as a conservation treatment with both consolidating and protective properties through the surface conversion from calcium carbonate to calcium oxalate. This treatment on Maltese Globigerina Limestone has also produced positive results, increasing the acid resistance while retaining the water transport properties of the stone. Furthermore, treatment in the presence of sodium chloride did not impede the conversion. This paper focuses on ammonium oxalate treatment application in the presence of sodium chloride as well as sodium sulphate and sodium nitrate, in a comparative study where the treatment was applied to quarry samples of this soft Limestone under laboratory conditions. The resistance to salt crystallisation and the water absorption properties were subsequently studied. This stage in the understanding of ammonium oxalate treatment of calcareous stone under different soluble salt content conditions is an important step towards carrying this treatment forwards to real site conditions where soluble salts are naturally present in the stone and where desalination may prove to be difficult or impossible. Results obtained were positive in all respects and show that ammonium oxalate treatment may be relevant in the treatment of this stone type.

Physical characteristics of Globigerina Limestone using ultrasonic and thermographic methods

The Globigerina Limestone of the Maltese Islands, widely used in construction and for restoration purposes, comes in a variety of types, with the Franka and Soll types (local terms) being the end members. The Soll type manifests widespread and often serious problems of durability and weathering resistance. The Franka type tends to be more durable. The selection of these materials is generally entrusted to quarry workers and builders, who primarily use visual criteria. This can lead to unsuitable stone being used. The current study uses ultrasonic and thermographic methods to distinguish between the two types at the extreme ends of the range, and to determine how their water absorption characteristics (fundamental when durability is being considered) can be evaluated. Results show that the Franka and Soll types behave very differently; ultrasonic testing showed that the Franka type possesses a significantly higher velocity compared with the Soll type; the thermographic technique verified that the Soll type absorbs less water by capillarity. Having an objective test to distinguish between stone types can lead to fewer errors in the choice of stone; such errors at present are possible because of the subjectivity of the methods used, with ensuing grave economic and practical consequences.

Introduction to the Stone Cycle and the Conservation of Historic Buildings

This Thematic Set of papers relating to the life cycle of building stone was initiated by a call for papers in order to better recognize the contribution that the disciplines, and practitioners, of engineering geology and hydrogeology make to the conservation of historical buildings, which is intrinsically multidisciplinary. The call for papers particularly focused upon the issues of different stone types used in historical buildings, as well as the performance, durability and conservation of stone in historical settings. The response was overwhelming, with many more abstracts submitted than could possibly be published in the Quarterly Journal of Engineering Geology and Hydrogeology ( QJEGH ). Accordingly, the papers were divided into two sets, with one set destined to appear in QJEGH as described herein and the second set to appear in a Geological Society Special Publication (Cassar et al. 2014). The presence of a particular paper in one set or the other is not a reflection on quality, but merely a reflection of the need to divide the papers into two sets each of which reflects subtly differing themes. History has been written in stone, from prehistoric monuments to modern-day buildings, and all types of stone, limestones and sandstones, granites and marbles, have been utilized to build, to clad, and to decorate. The buildings that are symbols of a city, a region, or a country are mostly built of stone. We immediately think of England when we see an image of Stonehenge; the Acropolis symbolizes Athens; the Coliseum Rome; Machu Picchu Peru; and the Taj Mahal India. The immense varieties and diverse properties of building stone, its workability and its (im)permanence have been observed and studied since time immemorial. Vitruvius, in the first century BC, writing in the Ten Books on Architecture , Chapter VII (Stone), says the following: ‘The stone in quarries …

Geomaterials: aggregates, building stone and earthworks: papers from 50 years of QJEGH

Numerous papers included within the broad subject of geomaterials have been published in QJEGH over the past 50 years. These have been compiled and divided here into three main categories: aggregates, building stone and earthworks. The aim of this review is to provide a comprehensive summary of the relevant papers published in QJEGH with a view to identifying the main areas of interest historically, now and in the future. Some clear trends are evident from the survey and review; for example, there has been a steady interest in building stone and in particular its deterioration, a decline in papers on earthworks and an increase in those on ground improvement (also covered here). It is also noted that methods of characterizing geomaterials are becoming more sophisticated with advancing technology. The review makes relevant links with other Special Publications from the Geological Society, including also Engineering Geology Special Publications.

Introduction to stone in historic buildings: characterization and performance

Interest in natural building stone, especially as used in historic buildings, is significant. This is demonstrated by the large number of publications that annually appear on stone, its properties, use, behaviour and treatment, and in the conferences on these subjects that are held in all parts of the world. In 2012 and 2013, the 12th International Congress on the Deterioration and Conservation of Stone (New York, USA), CRYSPOM III – Crystallization in Porous Media (Troia, Portugal), Natural Stone Research and Heritage Stone Designation (Vienna, Austria), the EGU General Assembly Vienna 2012 Monuments under Threat and the International Conference on Built Heritage 2013: Monitoring Conservation Management (Milan, Italy) were held. Besides the proceedings, which usually result from such conferences, numerous other publications on stone and stone buildings regularly find their way into the public domain. Not least amongst these are a number of Geological Society Special Publications (SP) including SP205 Natural Stone, Weathering Phenomena, Conservation Strategies and Case Studies (Siegesmund et al. 2002), SP271 Building Stone Decay: From Diagnosis to Conservation (Přikryl & Smith 2007), SP331 Limestone in the Built Environment: Present-Day Challenges for the Preservation of the Past (Smith et al. 2010) and SP333 Natural Stone Resources for Historical Monuments (Přikryl & Torok 2010). This current volume, SP391, seeks to bring to the attention of the various professionals in the field – geologists, architects, engineers, conservators and conservation scientists – recent work centred on the characterization and performance of this important resource, and its use in historic buildings. This volume has wider relevance, including to those interested in the heritage of stone