Miguel Gómez-Heras

The combined influence of mineralogical, hygric and thermal properties on the durability of porous building stones

It is a common practice to test building stones against an isolated decay factor when assessing the durability of building stones. Accordingly, the interpretation of results is often driven by the considerations of a limited number of properties thought as relevant to the action of that specific decay factor. In this way, the role of the synergies of decay processes and agents is often neglected. Contrarily, when different decay factors are included in the same experiment and the stone properties are examined conjunctly, the difficulties of isolating the effects of a specific decay factor or of isolating the contribution of “relevant” stone properties become apparent. The aim of this paper is to assess the combined contribution of mineralogical, hygric and thermal properties to the durability of different stones after exposure to laboratory-simulated cyclic decay combining wetness and temperature variations. For this purpose, 10 stone types were selected to emphasize the impact of the mineralogical heterogeneity on stone decay, in particular the coexistence of calcareous and siliceous grains and the occurrence of clays. The results emphasize the importance of considering the relations between decay factors and highlight how stone properties must be considered as a whole in order to assess and understand the durability of building stones.

Understanding the decay of stone-built cultural heritage

The problem of the decay and conservation of stone-built heritage is a complex one, requiring input across many disciplines to identify appropriate remedial steps and management strategies. Over the past few decades, earth scientists have brought a unique perspective to this challenging area, drawing on traditions and knowledge obtained from research into landscape development and the natural environment. This paper reviews the crucial themes that have arisen particularly, although not exclusively, from the work of physical geographers — themes that have sought to correct common misconceptions held by the public, as well as those directly engaged in construction and conservation, regarding the nature, causes and controls of building stone decay. It also looks to the future, suggesting how the behaviour of building stones (and hence the work of stone decay scientists) might alter in response to the looming challenge of climate change.

Evolution in the use of natural building stone in Madrid, Spain

Many types of stone have been used for construction in Madrid. In historical times, their use was determined by the proximity of the geological resources, the ease of quarrying and transportation links to the city. More recently, as transport connections and quarrying techniques have improved, quality and durability have become key determinants of building stone selection. Local flint was used intensively from the ninth to the eleventh century, when it was replaced by Redueña dolostone, used in turn until the seventeenth century. Granitic rocks from the Guadarrama Mountain Range that crop out in the northern and western area of the province increasingly began to be used in the city from the sixteenth century. Traditionally known as Berroqueña stone, this building stone was quarried in a number of areas; the primary point of supply was Zarzalejo, and from the eighteenth century the granite used was mainly quarried in the Alpedrete area. Eighteenth century advances in underground quarrying made it possible to extract a limestone (Colmenar stone) located in the southeastern part of the region. Together with Berroqueña stone, this limestone became one of Madrid’s traditional building stones, and both, highly esteemed for their excellent petrophysical properties and durability, are still used today.

Impacts of fire on stone-built heritage

Abstract Fire is a major threat to stone-built cultural heritage and this paper is a review of the existing research into fire damage on building stone. From early research based on anecdotal evidence of macroscopic observations, scientists have moved on to develop various techniques for approaching the investigation of fire damage to stone (high-temperature heating in ovens, lasers, real flame tests), different aspects of the damage that fire does have been learned from each, developing understanding of how microscopic changes affect the whole. This paper seeks to highlight the need for a greater awareness of the threat that fire poses (and the need to take precautionary measures in the form of fire-suppression systems), of the immediate effects, and of the long-term management issues of natural stone structures which have experienced fire.

Soluble salt minerals from pigeon droppings as potential contributors to the decay of stone based Cultural Heritage

This paper describes the salt content and pH evolution in solutions produced by the water-soluble extraction of accumulated pigeon droppings. Results demonstrate that these accumulations contain 4 % of soluble salts. Therefore, they are a plausible source of salts commonly found on buildings. These salts comprise halite, sylvite, potassium calcium sulphate, aphthitalite, apatite group minerals, weddellite and gypsum. The interaction of solutions formed from pigeon droppings with porous limestone was also studied. A noticeable deterioration in limestone due to acid attack was observed, including surface etching of rock-forming minerals.

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.

An urban geomonumental route focusing on the petrological and decay features of traditional building stones used in Madrid, Spain

The stone traditionally used to build cities contributes to their personality and attests to the geological substrate on which they stand. While stone decay in the built heritage can be attributed to a number of causes, anthropic activity has a particularly significant impact. The geomonumental routes project is one of the initiatives proposed in recent years for urban routes that convey geological fundamentals by observing the rocks present in heritage structures. Its innovative approach addresses traditional stone properties, original quarrying sites and mechanisms of decay. Madrid’s Royal Palace is a fine example of the use of traditional building stone in the centre of the Iberian Peninsula. In the geomonumental route proposed, the building doubles as an in situ laboratory that affords an overview of the main petrological properties of the two traditional stones most commonly used in the city’s built heritage, the forms of decay they are subject and the factors underlying such alterations. This route constitutes a tool for showing the main petrological features and decay forms in traditional building stones found in urban heritage façades, with a special focus on anthropic impact, primarily air pollution and the use of conservation treatments that time has proven to be unsuitable.

Underlying issues on the selection, use and conservation of building limestone

Abstract An argument is presented that, despite popular assumptions, many limestones, especially the wide range of clastic and, in general, granular limestones, do not decay in a steady and predictable pattern in response to slow dissolution. Instead these stones, especially when used in construction in polluted environments, invariably decay episodically through physical breakdown. Most commonly this is accomplished through a variety of salt weathering mechanisms that, if unconstrained, can lead to the rapid, catastrophic decay of building blocks and their complete loss – a process that has driven the extensive programmes of stone replacement that are typical of buildings constructed of these stones. In polluted environments, especially those rich in sulphur and particulates, the most common constraint on accelerated decay has been the rapid development of gypsum crusts that, for example, could rapidly ‘heal’ the scars left by contour scaling. It is ironic, therefore, that any reduction in pollution could conceivably lead to increased erosion by retarding this healing process. Because of this temporal variability of decay and its translation into spatial complexity, it is important that further research is undertaken to understand controls on the decay of these important building stones so that future conservation strategies can be appropriately informed.

Chapter 4.1 – Student Learning Styles

Abstract The existing literature in Earth science fieldwork demonstrates a particular concern to optimize the learning environment during fieldtrips and to encourage as much as possible the interactivity that should be inherent to fieldwork. Most of the studies on fieldwork learning focus on strategies during the fieldtrip, whereas only a few focus on the preparation, and yet this stage is crucial for students to get maximum benefit from the fieldwork experience. A wide recognition exists of the impact of students’ preferred learning styles in education outcomes; the aim of this study is to explore the impact that preferred learning styles have on the students’ perceptions of their performance during fieldwork and its preparation. Sixty undergraduate students participated, filling in a questionnaire with five sections (learning styles, two sections on their perception of novelty spaces in geography fieldwork, social behavior and their evaluation of fieldwork as a learning experience). The implications of this for educational practice are then examined in the conclusions, seeking to establish the best ways to interact with different learner types, for the best outcome.

Use of Fiber Optic and Electrical Resistance Sensors for Monitoring Moisture Movement in Building Stones Subjected to Simulated Climatic Conditions

Moisture is critical to the weathering of stone buildings and almost all weathering processes in building stones are influenced by the presence of moisture—especially the cyclic process of repeated ingress and egress of moisture that promotes their decay. Therefore, monitoring the moisture distribution in building stones is essential in understanding the material behaviour and degradation mechanisms associated with stone decay. In this study two real-time monitoring systems, viz. fiber optic sensor probe for relative humidity and electrical resistance sensors are compared by placing them, together with commercially available thermistors and humidity probe, at different depths in a limestone block in order to characterise patterns of moisture and temperature changes with depth from the exposure surface. This surface was then exposed to simulated wetting by a water spray, short-term cycles of heating and cooling beneath an infrared lamp to mimic solar radiation, and an intermittent air flow across the surface of the block. The experiment was conducted within an environmental chamber that kept ambient air temperature at 20°C. Results indicate that variations in external environmental factors, such as wind and intermittent heating cycles, can significantly affect the temperature and moisture variations in building stones.