Repair Mortars for Stone: Increased Compatibility Through Optimised
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Repair mortars for stone: Increased compatibility through optimised development Aurélie Isebaert A doctoral thesis submitted in partial fulfilment of the requirements for the joint doctoral degree in Doctor in Architecture and Urban Planning (University of Mons) and Doctor of Science: Geology (Ghent University) Supervisors Professor L. Van Parys, University of Mons Professor V. Cnudde, Ghent University Jury Professor T. Descamps, University of Mons Professor J.M. Baele, University of Mons Professor M. De Bouw, University of Antwerp Dr. H. Derluyn, Ghent University Dr. J. Hughes, University of Glasgow Professor D. Laplume, University of Mons Professor W. Quist, Delft University of Technology i This thesis was funded by both the Materials Research Institute, University of Mons and the Special Research Fund at Ghent University All images and content are by Aurélie Isebaert unless stated otherwise. ii Abstract Built heritage often demands interventions in order for it to resist weathering and deterioration. The materials applied on built heritage are aimed to be compatible with the original building material. Repair mortars for stone also need to fulfil this demand: the properties of every mortar should thus depend on the properties of the stone. Repair mortars are however not always chosen for their adapted properties, mainly because time and budget do not permit to determine what mortar recipe is (most) compatible and durable. In this thesis, a new system is introduced which, based on the requirements of the stone, will propose several potentially compatible mortar recipes. The number of potential mortar recipes which should be produced and tested is as such reduced. The system focuses on three properties of the mortar -permeability, colour and elasticity- since in terms of performance they proved to be the most influential for compatibility. As the system should be able to present mortar recipes, this thesis discusses the effect of the mortar components on each of these three properties. Their effect is determined by theory and experimental campaigns. This knowledge is used in this thesis for the development of an estimation method for both permeability and elasticity and the adaptation of an estimation method for colour. These estimation methods were implemented into an optimisation algorithm, able to create mortar recipes based on a database and the established estimation methods. Finally, this system as a whole was tested on various natural sedimentary stones. The thesis leads to the conclusion that the system presented here sets a solid base for an optimised mortar development. Future research can improve the system through the implementation of mineralogy as a compatibility parameter or by elaborating the estimation methods by including the effect of ageing. iii Samenvatting Bouwkundig erfgoed kan enkel verwering en alteratie weerstaan door de interventies die er op worden uitgevoerd. De materialen die worden toegepast op dit bouwkundig erfgoed moeten daarom compatibel zijn met de originele bouwmaterialen. Ook herstelmortels voor natuursteen moeten aan deze eis voldoen: de eigenschappen van elke mortel hangen dus zo af van de eigenschappen van de natuursteen. Maar herstelmortels worden niet altijd gekozen voor hun aangepaste eigenschappen. Dit is voornamelijk vanwege tijds- en budgetbeperkingen die niet toelaten om mortelrecept te ontwikkeln dat (het meest) compatibel en duurzaam is. In deze doctoraatsthesis wordt een systeem voorgesteld dat, gebaseerd op de eigenschappen van de steen, verschillende potentiële compatibele mortelrecepten voorstelt. Het aantal mortelrecepten dat zo geproduceerd en getest moet worden, wordt aldus gereduceerd. Het systeem concentreert zich op drie eigenschappen van de mortel - permeabiliteit, kleur en elasticiteit - aangezien ze vanuit het standpunt van gedrag het meest de compatibiliteit beïnvloeden. Aangezien het systeem mortelrecepten moet kunnen voorstellen, presenteert deze thesis het effect van de mortelingrediënten op elk van deze drie eigenschappen. Hun effect op de finale morteleigenschappen werd bepaald op basis van theoretische modellen en experimentele studies. In dit onderzoek werd deze kennis gebruikt voor de ontwikkeling van inschattingsmethodes voor permeabiliteit en elasticiteit en de aanpassing van een inschattingsmethode voor kleur. Deze inschattingsmethodes werden samen met een databank van zanden en bindmiddelen in een optimalisatiealgoritme geïntroduceerd, zodat het in staat is om mortelrecepten te ontwikkelen. Dit systeem werd in zijn geheel getest op verschillende sedimentaire natuurstenen. De thesis leidt tot de conclusie dat dit systeem een solide basis vormt voor een geoptimaliseerde mortelontwikkeling. Toekomstig onderzoek kan het systeem verbeteren door de implementatie van de mineralogie van de mortel als compatibiliteitsparameter of door de uitbreiding van de inschattingsmethodes met de veroudering van steen en mortel. iv Preface To research repair mortars for stone might seem a very specific topic, but it came quite naturally to me. I chose this topic because of my interest in materials, and, due to my background of conservator-restorer, more specifically into the new materials used to restore something which has ‘lived’ so long. The reasons for which we choose to use these materials and not others, the knowledge we have about them and what we expect from them versus what reality tells us, has fascinated me throughout my studies. The thesis presents the study of mortar components and their influence on the mortar properties, and sets a base for future research into the optimisation of compatible mortar recipes. In order to achieve this, this work presents the subject of repair mortars out of one angle, the optimisation of compatible mortars, but more than one field of research was required in order to bring this research forward and understand these materials better. Consequently, this thesis was written as a joint doctoral thesis between the Faculty of Engineering at the University of Mons and the Faculty of Sciences at Ghent University. The search for improved mortar recipes is mainly fed by an engineering approach, while the understanding of the mortar components, chemically and physically, are more appropriate to the natural sciences field. The subject required thus a multidisciplinary approach, and the reader will find himself looking at, for example, various measuring techniques for pore-related properties, as well as Darwin’s principle of survival of the fittest. I hope the reader with an interest in built heritage and natural stones will find this work and the conclusions it draws worthwhile and valuable, that it will help understand the behaviour and improve our expectations of these new materials we apply on old buildings. This preface cannot go by without thanking a number of persons who have helped me from close or from far these past four years. First of all, I would like to thank my two supervisors, Laurent Van Parys and Veerle Cnudde. Without them, this research would not be what it has become today. Their guidance, their questions and their suggestions have led me further than I thought myself capable of. Each in their own specific style, most likely inherent to their point of view as engineer or natural scientist, have reached out elements on occasions important for either fields. As the researcher performing a joint PhD, I have to admit that the combination of these two point of views was sometimes hard to reconcile. As a result, the thesis is neither a pure scientific work, nor a work completely written as an engineer. Perhaps, it also requires someone with another v background to attempt to study a subject as this one. I have great respect for both my supervisors, since it is mainly their belief in me that has allowed me to perform this research, demanding and exciting at the same time. During my four years as doctoral student, I was also guided by my doctoral advisory committee: Thierry Descamps, Jean-Marc Baele, David Laplume and Hannelore Derluyn, who had pertinent questions and remarks ready whenever I laid out results or questions. I would like to thank Marjorie Olivier and the Materials Research Institute at the University of Mons as well as the Special Research Fund at Ghent University for the funding of my research. I also have to thank the various students who have performed their Master thesis in the light of my research and whose results are included in this thesis. Quentin, Sandrine, Sophie, Laurent and Ivan, please know that without your contributions, some experimental campaigns would not have existed. Due to the multiple disciplines required for this research, I have had the opportunity to meet and work with many interesting persons from various fields. I would like to thank Michel Renglet for his invaluable advice concerning colour and colour measurements, Fanny Descamps and the department of Mining Engineering at the University of Mons for the use of the water permeameter, Jeroen Dils, Philip Van den Heede and Geert De Schutter from Labo Magnel at Ghent University for the use of their MIP equipment, Matthieu Boone and the entire team of UGCT for the use of the micro-CT scan and Mathijs Dumon and Eric Van Ranst for the XRD analysis at Ghent University. I also have to thank INISMA for the laser grain size analysis, and the BRRC for the use of their spectrophotometer. A thank you goes as well to Francis Tourneur who was willing to discuss with me all possibilities for these building stones of the Ursuline Convent in Mons. A special word goes out to my colleagues and ex-colleagues at both research groups. Mijn collega’s en ex-collega’s in Gent: Jeroen, Tim, Tom, Hannelore, Victor en Danielle, maar ook Wesley, Jan, Delphine en Marijn, zou ik willen bedanken voor de leuke momenten tijdens de middagpauzes, jullie grappen en de streken die jullie uithaalden, voor de tijd die jullie maar al te graag wilden steken in het scannen of de uitleg die jullie gaven bij een techniek die ik nog niet onder de knie had. Mes collègues à Mons, au début, cette petite flamande a dû travailler pour avoir un niveau suffisant en français pour comprendre vos histoires et vos blagues.