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  • 1.
    Balksten, Kristin
    Högskolan på Gotland.
    Beständighetsproblem för kalkputs2005In: Byggnadshyttan på Gotland 2003-2004 / [ed] Håkan Lindkvist, Visby: Byggnadshyttan på Gotland , 2005, p. 23-30Chapter in book (Other (popular science, discussion, etc.))
  • 2.
    Balksten, Kristin
    Högskolan på Gotland.
    Det gotländska bruket av kalk2008In: Från Gutabygd 2008: årsskrift för den gotländska hembygdsrörelsen, Visby: Gotlands hembygdsförbund , 2008, p. 125-140Chapter in book (Other (popular science, discussion, etc.))
  • 3.
    Balksten, Kristin
    Högskolan på Gotland.
    Handlaget minst lika viktigt som verktyget2005In: Byggnadskultur, ISSN 0348-6885, p. 24-25Article in journal (Other (popular science, discussion, etc.))
  • 4.
    Balksten, Kristin
    Chalmers.
    Kalkputs: porstrukturens betydelse för beständighet2005Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    When restoring historic lime plaster it can be difficult to reach the required durability. Today newly made lime plaster can fall off due to frost damages after only a couple of winters. To understand and solve these problems, the subject has been studied from different perspectives. Several factors in the production step are making an influence on the durability of lime plaster: 1. A binder, suitable for the building, must be chosen along with sandthat gives good material properties in both fresh mortar and in plasters. 2. The lime/sand ratio and the mixing technique should be chosen from the properties in the lime and the sand, in order to get a mortar with good workability. 3. The craftsmanship should be adjusted to the mortar, the weather and the underlying materials. A plaster with good frost resistance has a certain pore structure. The plaster should have some round air pores that contain air even when the material is filled capillary with water. Such air pores give the water a free space to expand when it is freezing. If the air pores are missing, the ice crystals may damage the plaster when expanding. To increase the chance of making a frost resistant lime plaster, the lime/sand ration must be adjusted so the lime can fill up well in the sand. Otherwise a collapsed pore system can easily occur, which means an open pore system without distinct air pores. A collapsed pore system contains many pores well connected with each other. Such a system is easily damaged by frost. To increase the chance of success, it is of great importance to work the surface of the lime plaster at the right time and in the correct way. Before working on a surface the mortar must be aloud to stiffen. Only then a homogeneous material can be created; cracks due to shrinkage can be pressed together and the result is a more compact material with an open surface. The time necessary for mortars to stiffen is related to the water content of the mortar, the suction of the underlying surface and the weather conditions. If the surface is worked on while the mortar is still fresh, the binder can form a hard lime shell on the surface. Inside thematerial a lack of binder can appear. Such plasters have a very low frost resistance. Other durability problems related to plaster are damages in the underlying materials, i.e. rotten wood in covered constructions or leached lime in old joints. Such damages can occur if the covering mortar is made of strong hydraulic lime or cement, since they form plasters with a low permeability in comparison to lime. Due to mentioned findings, it is important to study how a pore structureis influenced by materials, mixture and craftsmanship. Only then it is possible to understand how damages can be decreased.

  • 5.
    Balksten, Kristin
    Högskolan på Gotland.
    Norrlanda, Othem och Fardhem kyrkor: utvärdering av putsarbeten på tornen2009In: Byggnadshyttan på Gotland. 2007/2008 / [ed] Håkan Lindkvist, Visby: B , 2009, p. 91-112Chapter in book (Other (popular science, discussion, etc.))
  • 6.
    Balksten, Kristin
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Putsat för framtiden2014In: Byggnadskultur, ISSN 0348-6885, no 3, p. 38-40Article in journal (Other (popular science, discussion, etc.))
  • 7.
    Balksten, Kristin
    Gotland University, Department of Integrated Conservation.
    Tekniska anvisningar: Putsarbeten2007Book (Other (popular science, discussion, etc.))
  • 8.
    Balksten, Kristin
    Chalmers Tekniska Högskola.
    Traditional lime mortar and plaster : Reconstruction with emphasis on durability2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Lime mortar and plaster have been investigated with the aim to improve the knowledge on how to make them as durable as before the cement technology was developed. The background was the durability problems experienced for newly produced lime plaster on the medieval churches on the island of Gotland, Sweden. In some cases the new lime plaster façades showed severe frost damages after only one winter. Although the lime was burnt and produced according to old local traditions, the lime mortar was still mixed and worked onaccording to methods developed for lime-cement mortar. This often led to a very porous lime plaster with a lime shell in the surface and such a plaster has been shown to be sensitive to frost expansion. Field studies were combined with laboratory studies of thin section specimens. Optical microscopy and scanning electron microscopy have been important analytical methods showing the porosity and the structure of the binder and aggregate materials. The investigations have been carried out on both historic and on newly made reference mortar and plaster. The field studies were carried out mainly on Gotland, using local materials. The influence of the raw materials, i.e. lime, aggregate and blending ratio was investigated. The focus has been on the workability of the fresh mortars as well as the pore structure of the carbonated plaster. The craftsmanship, meaning mixing and application of mortar and working the plaster surface, was studied in order to clarify its final pore structure. The pore structure in a material determines many of its technical properties, such as moisture transportation, compressive strength, permeability and frost resistance. All these properties are closely connected to the durability of the mortar and plaster. The permeability of the plaster has an impact also on the durability of the covered construction materials. Behind low-permeable plasters made with hydraulic binder, examples of extensive damages of rotten wood and leached lime have been shown. The investigations have shown the importance of choosing a mortar adjusted to the building construction. They also showed the importance of choosing a blending ratio adjusted to the specific binder and sand used in order to get a mortar with a suitable pore structure and good durability. It has also shown the importance of knowing when and how to work on the plaster surface in order to obtain a homogenous material that is well receptive for lime wash and has a good frost resistance. The combination of all the investigations has led to a method for reconstructing historic mortar and plaster with good durability.

  • 9.
    Balksten, Kristin
    Gotland University, School of Culture, Energy and Environment.
    Understanding historic mortars and their variations: a condition for performing restoration with traditional materials2010In: 2nd Conference on Historic Mortars - HMC 2010 and RILEM TC 203-RHM final workshop / [ed] J. Válek, C. Groot and J.J. Hughes, Prague: Inst. of Theoretical and Applied Mechanics, Acad. of Sciences of the Czech Republic , 2010, p. 11-18Conference paper (Refereed)
    Abstract [en]

    In order to design a restoration mortar with properties and composition similar to the original mortar, it is important to analyze the historic mortar in several ways. A combination of analyses give information about the mixing ratio between binder and aggregates, chemical composition of the mortar, additives, tool marks, application technique etc. This paper shows the variations in Swedish medieval lime mortars with a high content of binder. By analysing historic mortar with a combination of ocular investigations, microscopically studies of thin section specimens, Scanning Electron Microscopy and X-Ray Powder Diffraction, all the information needed for designing a restoration mortar, with composition and properties similar to the historic mortar, is gained.

  • 10.
    Balksten, Kristin
    et al.
    Chalmers.
    Broström, Tor
    Gotland University, School of Culture, Energy and Environment.
    Permeability in lime plaster in relation to durability of covered materials2004Conference paper (Refereed)
    Abstract [en]

    In restoration of old buildings, lime plasters are used for reasons of authenticity and for technicalreasons as well. In many traditional constructions, there is wood behind the plasters or there is old limemortar in the masonry. For the durability of both these underlying materials, it is important that therelative humidity, RH is not too high under a long time of exposure. This can lead to an accelerateddegradation process of wood and leaching of lime in mortars. To prevent this, the plaster must have aproper permeability.The permeability of a material determines its ability to transport gas and moisture. In lime plasters,permeability affects hardening, carbonation as well as durability of the underlying materials. In thepresent paper, eleven mixtures of lime mortar were studied. The binders used were lime slaked in fourdifferent ways, hydraulic lime and cement.The following measurements were made to analyse the permeability and the pore structure of thesamples. Gas permeability and draining curves give an indication of rate of carbonation. Vapourpermeability shows the ability of plaster to transmit moisture at different RH. Thin sections were madefor microscopically investigations of the samples.The investigations show that both the vapour permeability and gas permeability decreases with anincreased amount of hydraulic binder in the lime plasters. Even small amounts of hydraulic binderhave a significant effect.By connecting these results with examples from reality, the picture becomes clearer. In the medievaltown Visby in Sweden, there are several examples of both rotten wood and disintegrated lime mortars.It is constructions from 13th to 19th centuries and low permeable cementitious plasters have coveredthem all, during the middle of the 20th century.

  • 11.
    Balksten, Kristin
    et al.
    Gotland University, School of Culture, Energy and Environment.
    Broström, Tor
    Gotland University, School of Culture, Energy and Environment.
    Myrin, Malin
    Tyréns AB.
    Thelin, Carl
    Tyréns AB.
    Kettunen, Rebeca
    Gotland Museum.
    Mebus, Ulrika
    Gotland Museum.
    Increased use of ruins through secured masonry and comfortable climate2010In: Proceedings of the 7th International Conference on Science and Technology in Archaeology and Conservation, Petra, Jordan, 2010Conference paper (Other academic)
    Abstract [en]

    This paper presents a unique scientific research project, funded by the KK-foundation in Sweden together with several companies participating in the project. A primary goal is to find methods to examine and take care of open masonry constructions thereby enabling an increased use of them in a safe and comfortable way without diminishing their cultural values. A second goal is to establish a long-term cooperation/network of researchers, conservators, engineers, antiquarians and craftsmen that can keep and develop the knowledge. The project takes place in year 2010 and 2011. This paper presents a model of cooperation as well as the ongoing experiment and expected results. The project is divided into three major parts:1) Description and assessment of historic masonry as load bearing structures. 2) Assessment of stone and mortar in old masonry and finding the methods to secure and preserve them. 3) The climate in the ruin with respect to comfort and preservation. The goals for the different parts of this research project are to find the best possible solutions of how to: a) Evaluate the construction of complex masonry structures to enable new additions that are appropriate with respect to statics. b) Find efficient methods to evaluate and conserve the status of the materials (stone, mortar) and walls in old masonry to grant safe accessibility. c) Create a comfortable climate in an open masonry structure without closing it. These three research areas all focus on the historic masonry which at the same time forms the climate shell, the bearer of plaster and the historical setting to the activities that are to take place in the ruin.

  • 12.
    Balksten, Kristin
    et al.
    Chalmers.
    Klasén, Kenth
    The influence of craftsmanship on the inner structures of lime plasters2005Conference paper (Refereed)
    Abstract [en]

    The use of traditional lime plaster in restoration of old buildings is motivated by bothtechnical and historic reasons. The plasterer deals daily with a multivariable problem wherethe variables are related in such a complex way that we are not even close to findingconverging solutions by traditional scientific methods. The decisions and actions of thecraftsman will have an influence on both the surface structure and the inner structure of thelime plaster. The present paper will focus on the time between application of mortar andworking on the surface to make a floated finish. In total, 32 lime plaster surfaces have beenanalysed. Half of them have been worked on after they have stiffened up and half of themhave been worked on while they are still fresh. The results clearly show that the time betweenapplication of mortar and working the surface is a critical parameter. If you wait until theright time, you receive a more homogeneous and compact material with an open surface anda higher frost resistance.

  • 13.
    Balksten, Kristin
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Lange, Johanna
    Lindholm Restaurering.
    Lindholm, Martin
    Lindholm Restaurering.
    Fuktproblem i salt- och frostskadat tegelmurverk: Fördjupd analys av Örgryte nya kyrka 20122014Report (Other (popular science, discussion, etc.))
  • 14.
    Balksten, Kristin
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Lindholm, Martin
    Lange, Johanna
    Increased salt and frost damages in solid neo-Gothic brickwork masonry due to low permeable restoration materials of the 20th century2014In: 9th IMC, Book of Abstract / [ed] Paulo B. Lourenco, Barry A. Haseltine, Graca Vasconcelos, 2014Conference paper (Refereed)
    Abstract [en]

    In Gothenburg many stone buildings of brickwork were built during the neo-Romanesque and neo-Gothic period in the late 19th century. The masonry was solid with a wall of bricks often covered with facing bricks with a hard burned water repellent surface. At Örgryte new church the bricks were put in lime mortar but the surface of the joints was made with a thin cement mortar layer. Salt problems are known in this church since early 20th century and the subsequent need of maintenance have led to several extensive restorations with replacement of external facing bricks and internal lime plaster during the years. In each restoration more low permeable facing bricks and more low permeable cement mortars have been chosen, followed by new problems inside the wall as the water transport properties in the wall has changed. Whereas salts have caused problems mainly on the surface, the restoration materials have caused problems with frost and salt damages in bricks and lime mortars in the wall core behind them.

  • 15.
    Balksten, Kristin
    et al.
    Chalmers.
    Magnusson, Sophia
    The pore structure in lime plaster as a key to understanding moisture transportation properties and frost damages2004In: 10th International Congress on the Deterioration and Conservation of Stone, 2004Conference paper (Refereed)
    Abstract [en]

    The pore structure is of great importance for a materials ability to hold and transport gasand moisture. In lime plaster, it affects hardening, carbonation as well as durability againstfrost damage. In the present paper, eleven mixtures of lime mortar were studied withrespect to frost damages. The binders used were lime slaked in four different ways,hydraulic lime and cement.Several analyses were made to characterize the transport properties and the porestructure of the materials; density, porosity, sorption curves, capillary water suction andthin sections. This study shows that there is a correlation between pore structure andimportant material properties. By studying these parameters, it is possible to get a goodpicture of the materials ability to resist frost damages. The study also gives an indication ofwhat materials in the mortar such as binders, aggregates and water, give a good porestructure.

  • 16.
    Balksten, Kristin
    et al.
    Chalmers Tekniska Högskola.
    Magnusson, Sophia
    Chalmers Tekniska Högskola.
    Transportegenskaper hos kalkputs: en jämförelse mellan elva brukstyper2002Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 17.
    Balksten, Kristin
    et al.
    Högskolan på Gotland.
    Mebus, Ulrika
    Bruk av ruiner: kulturarv, konstruktion, kalkbruk, komfort & kalsonger2012Collection (editor) (Other academic)
  • 18.
    Balksten, Kristin
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Mebus, Ulrika
    Gotlands museum.
    Thelin, Carl
    Tyréns.
    Visby ringmur: att återuppbygga med autenticitet2015In: Bebyggelsehistorisk tidskrift, ISSN 0349-2834, ISSN 0349-2834, Vol. 70, p. 43-61Article in journal (Refereed)
    Abstract [en]

    In February 2012, one part of the medieval city wall and Unesco World Heritage of Visby collapsed. It is the best preserved medival city wall of nothern Europe. The wall was built in several stages in the 13th, 14th and partly even 15th centuries. The first wall was made as a lower three-leaf wall with two shells built of lime stone and fat lime mortar and a soft and porous rubble core of lime stone and clay mortar. The second wall was built higher on top of the old one. It was mostly built as a solid wall in lime stone and lime mortar.

    During its 700 year long history parts of the wall has collapsed and been rebuilt many times and after the collapse 2012 it was decided that also this collapsed part of the wall should be rebuilt. To determine a procedure for the rebuilding and to secure a safe work site, it was necessary to define the construction and structural behaviour of the wall. Furthermore, what caused the collapse needed to be identified, in order to assess and predict the risk of future damage to other parts of the wall. An investigation into the construction of the wall was carried out through archival research, building acheology and on-site examinations. Laser scanning made it possible to describe and study the geometry of the wall and the damage in detail, and a structural analysis was carried out.

    The results show that the wall was built in two stages, making its construction complicated. The structural analysis indicates that there is a concentration of forces to the outer masonry leaf of the lower part of the wall. The collapse was most likely triggered by freezing of the water contained in the masonry. The combination of high stress levels in the outer masonry leaf, due to the construction of the wall, with a loose core, thin outer masonry leaf and insufficient binding stones and weak adhesion in the bedding lime mortar in the lower part of the wall, resulted in a domino effect that explains the extent of the collapse. To secure the wall during dismantling, a temporary steel structure was constructed.

    The medieval types of construction and material in a two-leaf masonry wall have proven to be durable if correctly implemented, with sufficient binding stones and a core in order, and will therefore be used for the rebuilding.

    As restorations have been made during 20th century the joints of lime mortar has been partly repointed with strong cement mortar, followed by leached lime inside from the mortar in the wall.

    As the rebuilding took place it has been a desire to use as authentic materials and constructions as ever possible. On Gotland there is a unique knowledge preserved and developed since middle ages how to handle the local lime, from burning, slaking, storing to mixing mortars. This knowledge and avalibility of local traditional materials has made it possible to rebuild the wall with the perspective and wish that the wall built 2014 shall stand another 700 years.

     

    Keywords: Visby city wall, medieval wall, masonry structure, structural behaviour, lime mortar, two-leaf masonry wall

  • 19.
    Balksten, Kristin
    et al.
    Chalmers.
    Myrin, Malin
    Göteborgs Universitet.
    Lime-based Repair Mortars: Influence by Surface Working Methods onBehaviour and Durability of Mortar2006Conference paper (Refereed)
    Abstract [en]

    The main purpose of this study was to observe the influence by different surface working methodson behaviour, durability and appearance of lime-based stone-repair mortars.The findings are based on:

    - Observations made during restoration work

    - Observations from field stations

    - Microscopic analysis of thin sections of mortar

    - Parallel studies on lime plaster

    The results show clear differences in durability, appearance and behaviour of lime-based mortar dependingon at which stage of the drying process the mortar is worked on. For achieving durable mortar it is importantto avoid the development of a surface lime-film. The study implies that the mortar, only when worked on at aspecific stage of drying, will be durable and have a structure, texture and porosity compatible with the surroundingstone material.

  • 20.
    Balksten, Kristin
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Persson, Christina
    Göteborgs Universitet.
    Eriksson, Jonny
    Göteborgs Universitet.
    Lime burning tradition in field kilns: a case study of the Jämtland tradition in Sweden2013Conference paper (Refereed)
    Abstract [en]

    This study focuses on the local lime tradition in the region of Jämtland, in central Sweden. Local lime was used when building the medieval stone churches and since they are in a need of restoration there is subsequently a need for understanding the use of local lime. The geology of Jämtland contains several layers of limestone in the folded mountains. There is a broad spectrum ranging from pure Silurian limestone to clay containing Ordovician limestone, giving all kinds of lime from pure air lime to strong hydraulic lime. The preserved historic mortarshave mostly been made with the hydraulic lime. Several old field kilns have been preserved in the forest landscape as prehistoric monuments, showing the model of the local lime burning tradition. This paper discusses the process of identifying the historic lime kiln constructions and their burning technique. It also describes the process of slaking this hydraulic binder in order to produce a lime mortar with workability and compatibility required from a restoration mortar. Newly-produced samples of lime mortar have been compared with historic ones in thin section microscope for further understanding.

  • 21.
    Balksten, Kristin
    et al.
    Department of Chemical and Biological Engineering, Environmental Inorganic Chemistry, Chalmers University of Technology.
    Steenari, Britt-Marie
    Department of Chemical and Biological Engineering, Environmental Inorganic Chemistry, Chalmers University of Technology.
    A method to recreate historic mortars applied at Norr­landa church on the island of Gotland, Sweden2008Conference paper (Refereed)
    Abstract [en]

    In this work, scanning electron microscopy analysis of lime slaked in different ways and analysis of thin section limeputty and mortar specimens by light microscopy was combined with practical tests and field studies in order to evaluatethe impact of the slaking technique on the properties of the lime putty, and also the structure of the fresh and carbonatedmortar. The lime slaking methods studied were wet slaking and earth slaking. These techniques give lime putties withvery different consistency and workability. The aim of this work was to use microscopy techniques to explain thesedifferences in properties and to investigate if it is possible to use these analytical methods to recognize the lime slakingtechnique used in a historical lime mortar.The results obtained by electron microscopy show significant differences in structure between the lime puttiesstudied. The earth slaked lime consists of relatively large particles that are packed in a porous system as compared to thewet slaked lime with very small particles closely packed in a dense structure. After storing, the wet slaked lime gives aputty, that has a dense and clearly defined stratified structure, whereas the earth slaked lime is porous and has nostratification. The earth slaked lime is tixotropic and has a light, smooth consistency reminding of well whipped creamcompared to the wet slaked lime that has a strong orientation and a rather stiff consistency reminding more of pudding.Microscopy investigations of thin section mortar specimens showed how the lime affects the mortar concerninghomogeneity, density, pore structure and crack patterns.

  • 22.
    Balksten, Kristin
    et al.
    Gotland University, School of Culture, Energy and Environment.
    Steenari, Britt-Marie
    Department of Chemical and Biological Engineering, Environmental Inorganic Chemistry, Chalmers University of Technology, Gothenburg, Sweden.
    The influence of particle size and structure in hydrated lime on the properties of the lime putty and lime mortar2010In: International journal of architectural heritage, ISSN 1558-3058, Vol. 4, no 2, p. 86-101Article in journal (Other academic)
    Abstract [en]

    In this work, scanning electron microscopy (SEM) analysis of lime slaked in different ways and analysis of thin section of lime putty and mortar specimens by light microscopy was combined with practical tests and field studies to evaluate the impact of the slaking technique on the properties of the lime putty as well as the structure of the fresh and carbonated mortar. The lime slaking methods studied were wet slaking and earth slaking, giving lime putties with very different consistency and workability. The aim of this work was to use microscopy techniques to explain these differences in properties and to investigate if it is possible to use these analytical methods to recognize the lime-slaking technique used in a historical lime mortar. The results obtained by SEM show significant differences in structure between the lime putties. The earth-slaked lime consists of relatively large particles that are packed in a porous system compared with the wet-slaked lime with very small particles closely packed in a dense structure. After storing, the wet-slaked lime gives a putty that has a dense and clearly defined stratified structure, whereas the earth-slaked lime is porous and has no stratification.

  • 23.
    Balksten, Kristin
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Thelin, Carl
    Tyréns.
    Construction and materials of Visby medieval city wall – risk of damage2014In: 9th IMC, Book of Abstract / [ed] Paulo B. Lourenco, Barry A. Haseltine, Graca Vasconcelos, 2014Conference paper (Refereed)
    Abstract [en]

    The City Wall in Visby was built in two periods in 13th and 14th century. The first wall was made as a lower three-leaf wall with two shells built of lime stone and fat lime mortar and a soft and porous rubble core of lime stone and clay mortar. The second wall was built higher on top of the old one. It was mostly built as a solid wall in lime stone and lime mortar. Due to its construction and form, a major part of the force is carried by the outer shell of the wall. As restorations have been made during 20th century the joints of lime mortar has been partly repointed with strong cement mortar, followed by leached lime inside from the mortar in the wall. In February 2012 a part of the wall collapsed and fell down as the outer shell of the masonry collapsed. This paper presents an analysis of the wall structure and its materials as well as the increased risk of damage due to the restorations of the 20th century.

  • 24.
    Legnér, Mattias
    et al.
    Gotland University, School of Culture, Energy and Environment. Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Del Curto, Davide
    Politecnico di Milano, Italien.
    Balksten, Kristin
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Valorization and management of the built heritage of fortified towns: The cases of the UNESCO World Heritage Sites of Sabbioneta, Italy, and Visby, Sweden2016In: Sguardi ed esperienze sulla conservazione del patrimonio storico architettonico: Proceedings of the International Conference Preventive and Planned Conservation Monza, Mantova - 5-9 May 2014, Milano, 2016, p. 29-43Conference paper (Refereed)
    Abstract [en]

    The purpose of this paper is to discuss the challenges of managing complex built heritage by comparing site-bound policies in a historical perspective. The World Heritage Sites of Mantova-Sabbioneta, Italy, and Visby, Sweden, are used as cases. Their defensive structures attract numerous visitors, however they have proven to be difficult to maintain because of size, complexity and organizational problems. Questions asked in this paper are: Exactly how was built heritage in these places valorized throughout the 20th century? What has the UNESCO nomination of the sites meant for the valorization process? The small Renaissance town of Sabbioneta and the medieval inner city of Visby both have preserved city walls. Management of them demands resources but also cooperation of stakeholders, here identified as monuments offices, plan- ning departments, property owners and citizens.

    By making transnational comparisons of the management of sites an in- creased knowledge on how to manage fortified towns without decreasing their economical, historical and aesthetic values may emerge. Today the heritage of Visby and Sabbioneta is so obvious that we risk taking their values for granted, but the valorization of these sites have actually sprung out of the development of modern urban society. World heritage sites need to be managed in sustaina- ble ways if their values are to be preserved. (Pedersen 2002, Clark 2010)

    An important aim with the paper is to begin comparing the management of fortifications at these sites. Each case is presented, followed by a comparative discussion of challenges to management today. 

  • 25.
    Mebus, Ulrika
    et al.
    Gotlands museum.
    Balksten, Kristin
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Thelin, Carl
    Tyréns AB.
    Visby ringmurs fall och återuppståndelse 2012-20142015In: Byggnadshyttan på Gotland 2013/2014 / [ed] Jan Utas, Visby: Byggnadshyttan på Gotland , 2015, p. 84-104Chapter in book (Other (popular science, discussion, etc.))
  • 26.
    Strandberg-de Bruijn, Paulien
    et al.
    Lund Univ, Div Bldg Mat, S-22100 Lund, Sweden.
    Donarelli, Anna
    Swedish Natl Heritage Board, S-62122 Visby, Sweden.
    Balksten, Kristin
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History, Conservation.
    Full-scale Studies of Improving Energy Performance by Renovating Historic Swedish Timber Buildings with Hemp-lime2019In: Applied Sciences, E-ISSN 2076-3417, Vol. 9, no 12, article id 2484Article in journal (Refereed)
    Abstract [en]

    With an increased focus on reducing greenhouse gas emissions, energy saving is of great importance in all sectors of society. EU directives set targets for member states to reduce energy use in buildings. Energy saving in historic buildings requires special measures, balancing energy-saving renovations against the preservation of heritage values. Traditional constructions are open to vapor diffusion and generally work differently from modern constructions. Modern materials in traditional constructions sometimes damages the original material as they are usually diffusion-tight. The aim of this study was to investigate whether hemp-lime could be used as an insulation material to improve the energy efficiency of historic timber building envelopes with a rendered facade in Sweden. The objective was to determine the actual energy savings for space heating. An additional objective was to determine the actual thermal transmittance and to study thermal buffering through in-situ measurements in a full-scale wall renovated with hemp-lime. Two full-scale wall sections were constructed at the Energy and Building Design laboratory at Lund University: A traditional post-and-plank wall with a lime render (80 mm), and a post-and-plank wall with a hemp-lime render (90 mm). Energy use for space heating was monitored continuously over a period of one year. The wall with a hemp-lime render required 33% less energy for space heating than the traditional post-and-plank wall with a lime render. This was accomplished without changing the framework, appearance or material in the render and without drastically changing the hygric properties of the facade. From the gathered data, the thermal transmittance (U-values) for both walls was calculated using two different methods, one based on material properties and the other based on energy use data. For both walls, thermal transmittance based on actual energy use data during the heating period was lower than what was expected from their material properties. This indicates that more material properties than thermal conductivity and material thickness need to be taken into account when performing energy use calculations. With hemp-lime, a renovation can be accomplished without damaging the timber structure and wooden slats, and it can be done with local traditional materials and building methods with no difference in appearance to a traditional lime render. This allows for heritage values to be preserved, while also allowing the building to comply with modern standards and with increased thermal comfort and reduced energy use.

  • 27.
    Thelin, Carl
    et al.
    Tyréns.
    Balksten, Kristin
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Höst, Folke
    Tyréns .
    Collapse and Rebuilding of a Medieval City Wall – Anassessment of the Structure and Material2014Conference paper (Refereed)
    Abstract [en]

    In February 2012, a part of the medieval city wall of Visby collapsed. The wall was constructed in several stages in the 13th and 14th centuries. It was decided that the collapsed part of the wall should be rebuilt. To determine a procedure for the rebuilding and to secure a safe work site, it was necessary to define the construction and structural behaviour of the wall. Furthermore, the cause of the collapse needed to be identified, in order to assess and predict the risk of future damage to other parts of the wall. An investigation into the construction of the wall was carried out through archival research and on-site examinations. Laser scanning made it possible to describe and study the geometry of the wall and the damage in detail, and a structural analysis was carried out. The results show that the wall was built in two stages, making its construction complicated. The structural analysis indicates that there is a concentration of forces to the outer masonry leaf of the lower part of the wall. The collapse was most likely triggered by freezing of the water contained in the masonry. The combination of high stress levels in the outer masonry leaf, due to the construction of the wall, with a loose core, thin outer masonry leaf and insufficient binding stones and weak adhesion in the bedding lime mortar in the lower part of the wall, resulted in a domino effect that explains the extent of the collapse. To secure the wall during dismantling, a temporary steel structure was constructed. The medieval types of construction and material in a two-leaf masonry wall have proven to be durable if correctly implemented, with sufficient binding stones and a core in order, and will therefore be used for the rebuilding.

  • 28.
    Mebus, Ulrika (Editor)
    Riksantikvarieämbetet.
    Balksten, Kristin (Editor)
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History.
    Visby ringmur: kulturarv som rasar och återuppbyggs2015Report (Refereed)
    Abstract [en]

    In February 2012, a part of the medieval city wall of Visby collapsed. The wall was originally constructed in several stages in the 13th and 14th centuries. It was decided that the collapsed part of the wall should be rebuilt. To determine a procedure for the rebuilding and to secure a safe work site, it was necessary to determine the construction and structural behaviour of the wall. Furthermore, the cause of the collapse needed to be identified in order to assess and predict the risk of future damage to other parts of the wall. An investigation into the construction of the wall was carried out through archival research and on-site examination. Structural analysis was carried out using laser scanning to describe and study both the geometry of the wall and the damage in detail. The results showed that the wall was built in two stages, making its construction complicated. The structural analysis also indicated that there is a concentration of forces to the outer masonry leaf of the lower part of the wall. The collapse was most likely triggered by freezing of the water contained in the masonry. The combination of high stress levels in the outer masonry leaf due to the construction of the wall, having a loose core, thin outer masonry leaf and insufficient binding stones as well as weak adhesion in the bedding lime mortar in the lower part of the wall, resulted in a domino effect that explains the vast extent of the collapse. To secure the wall during dismantling, a temporary steel structure was constructed. The medieval types of construction and material in a two-leaf masonry wall have proven to be durable if correctly implemented with sufficient binding stones and an ordered construction of the core. These medieval materials and techniques have therefore been used in such a way for the rebuilding. For more complete information in English, we refer to appendixes 1–3 at the end of this report.

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