uu.seUppsala University Publications
Change search
Link to record
Permanent link

Direct link
BETA
Publications (10 of 24) Show all publications
Balksten, K., Mebus, U. & Thelin, C. (2015). Visby ringmur: att återuppbygga med autenticitet. Bebyggelsehistorisk tidskrift, 70, 43-61.
Open this publication in new window or tab >>Visby ringmur: att återuppbygga med autenticitet
2015 (Swedish)In: Bebyggelsehistorisk tidskrift, ISSN 0349-2834, ISSN 0349-2834, Vol. 70, 43-61 p.Article in journal (Refereed) Published
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

Abstract [sv]

Den 24 februari 2012 rasade en del av världsarvet Visby ringmur till marken. Muren är norra Europas bäst bevarade medeltida stadsmur. Den har byggts i flera steg under framförallt 1200-1300-talen med vissa senare tillägg. Den första lägre delen av muren byggdes som en skalmur med lös kärna. Murskalen murades med kalksten i fett kalkbruk och kärnan fylldes med småsten och lerbruk. Den påbyggda muren byggdes ovanpå den gamla.

Under murens 700-åriga historia har den flera gånger rasat och oftast har den på något sätt återuppbyggts. Även efter kollapsen 2012 beslöt man att återuppbygga muren då raset skett på en av de bäst bevarade mursträckorna i Östergravar. För att kunna besluta om åtgärd för återuppbyggnad och säkerställa en trygg och säker arbetsplats, var det viktigt att fastställa murens statiska verkningssätt. Likaså var det viktigt att utreda vad som kan ha orsakat kollapsen, om inte annat för att förhindra nya ras. Murens konstruktion dokumenterades med hjälp av studier på plats vilka kompletterades av arkivstudier, byggnadsarkeologiska undersökningar, laser scanning och georadar. Med hjälp av laserscanningen kunde murens geometri fångas och en analys av murens statiska verkningssätt utföras.

Resultatet visade hur muren uppförts i två etapper. Analysen visar att det är en koncentrerad last i murens nedre yttre skal. Kollapsed triggades sannorlikt igång av frostsprängning i murverket. Kombinationen av koncentrerad last i yttre murskalet, murens komplexa konstruktion med lös kärna och tunna murskal utan bindstenar som förankrar murskalen samt förlorad bindande förmåga i kalkbruket där fuktbelastningen varit hög, har resulterat i en dominoeffekt som förklarar rasets omfattning. För att möjliggöra återuppbyggnaden var det nödvändigt att montera ner delar av det återstående murverket och för att säkra muren under nedplockningen konstruerades av temporär stålstruktur som band den samman.

De medeltida materialen och konstruktionen med skalmursprincip och kalkbruk har visat sig vara mycket hållbara, varför den nya muren byggts upp med skalmur innehållandes bindstenar och med en kärna som är väl murad.

Under 1900-talet har omfattande restaureringsarbete utförts och ca 60 % av murens fogar täcks av cementbruk vilket har till följd att fukt blir instängt i murverket vilket leder till urlakat kalkbruk i fuktigt murverket.

När muren nu har återuppbyggts har det funnits en stark ambition att så långt som möjligt använda autentiska material och metoder. På Gotland finns en helt unik kunskap bevarad och utvecklad sedan medeltiden. Det är kunskapen att bränna och släcka kalk utifrån lokala förutsättningar gällande val av råvara, bränningsteknik, släckning och lagring samt tillredning av bruk. Genom att kunskapen om såväl som tillgängligheten på den lokala kalken existerar har det varit möjligt att återuppbygga Visby ringmur med perspektivet att den skall kunna bevaras i ytterligare 700 år.

Keyword
stadsmurar byggnadsvård byggnadshistoria världsarv murverk kalkbruk
National Category
Natural Sciences
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-274998 (URN)
Available from: 2016-01-27 Created: 2016-01-27 Last updated: 2017-11-30
Mebus, U., Balksten, K. & Thelin, C. (2015). Visby ringmurs fall och återuppståndelse 2012-2014. In: Jan Utas (Ed.), Byggnadshyttan på Gotland 2013/2014: (pp. 84-104). Visby: Byggnadshyttan på Gotland.
Open this publication in new window or tab >>Visby ringmurs fall och återuppståndelse 2012-2014
2015 (Swedish)In: Byggnadshyttan på Gotland 2013/2014 / [ed] Jan Utas, Visby: Byggnadshyttan på Gotland , 2015, 84-104 p.Chapter in book (Other (popular science, discussion, etc.))
Place, publisher, year, edition, pages
Visby: Byggnadshyttan på Gotland, 2015
Series
Byggnadshyttan på Gotland, ISSN 1654-7705 ; 7
Keyword
murverk, ringmur, kalkbruk, statik, lerbruk
National Category
Civil Engineering Art History Architecture
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-265320 (URN)
Projects
Visby ringmur
Available from: 2015-10-27 Created: 2015-10-27 Last updated: 2015-10-27
Thelin, C., Balksten, K. & Höst, F. (2014). Collapse and Rebuilding of a Medieval City Wall – Anassessment of the Structure and Material. In: : . Paper presented at SAHC2014 – 9th International Conference on Structural Analysis of Historical Constructions, Mexico City, Mexico, 14–17 October 2014. .
Open this publication in new window or tab >>Collapse and Rebuilding of a Medieval City Wall – Anassessment of the Structure and Material
2014 (English)Conference paper, Published 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.

Keyword
City wall, masonry structure, structural behaviour, lime mortar, two-leaf masonry wall
National Category
Natural Sciences
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-237222 (URN)
Conference
SAHC2014 – 9th International Conference on Structural Analysis of Historical Constructions, Mexico City, Mexico, 14–17 October 2014
Available from: 2014-12-01 Created: 2014-12-01 Last updated: 2015-01-19Bibliographically approved
Balksten, K. & Thelin, C. (2014). Construction and materials of Visby medieval city wall – risk of damage. In: Paulo B. Lourenco, Barry A. Haseltine, Graca Vasconcelos (Ed.), 9th IMC, Book of Abstract: . Paper presented at 9th International Masonry Conference 2014, Guimarães, Portugal, July 7-9, 2014. .
Open this publication in new window or tab >>Construction and materials of Visby medieval city wall – risk of damage
2014 (English)In: 9th IMC, Book of Abstract / [ed] Paulo B. Lourenco, Barry A. Haseltine, Graca Vasconcelos, 2014Conference paper, Oral presentation with published abstract (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.

Keyword
city wall, lime mortar, clay mortar, three-leaf wall, rubble core, masonry structure, deterioration
National Category
Arts
Research subject
History of Art
Identifiers
urn:nbn:se:uu:diva-237218 (URN)978-972-8692-85-8 (ISBN)
Conference
9th International Masonry Conference 2014, Guimarães, Portugal, July 7-9, 2014
Available from: 2014-12-01 Created: 2014-12-01 Last updated: 2015-02-12Bibliographically approved
Balksten, K., Lange, J. & Lindholm, M. (2014). Fuktproblem i salt- och frostskadat tegelmurverk: Fördjupd analys av Örgryte nya kyrka 2012. Göteborg: Göteborgs stift.
Open this publication in new window or tab >>Fuktproblem i salt- och frostskadat tegelmurverk: Fördjupd analys av Örgryte nya kyrka 2012
2014 (Swedish)Report (Other (popular science, discussion, etc.))
Place, publisher, year, edition, pages
Göteborg: Göteborgs stift, 2014
Series
Göteborgs stifts skriftserie, 2014:01
Keyword
Fuktskador, saltskador, tegel, murverk, kalkbruk, Örgryte, St Pauli
National Category
Natural Sciences
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-237223 (URN)9789197958103 (ISBN)
Available from: 2014-12-01 Created: 2014-12-01 Last updated: 2014-12-02Bibliographically approved
Balksten, K., Lindholm, M. & Lange, J. (2014). Increased salt and frost damages in solid neo-Gothic brickwork masonry due to low permeable restoration materials of the 20th century. In: Paulo B. Lourenco, Barry A. Haseltine, Graca Vasconcelos (Ed.), 9th IMC, Book of Abstract: . Paper presented at 9th International Masonry Conference, July 7-9, 2014, Guimarães, Portugal. .
Open this publication in new window or tab >>Increased salt and frost damages in solid neo-Gothic brickwork masonry due to low permeable restoration materials of the 20th century
2014 (English)In: 9th IMC, Book of Abstract / [ed] Paulo B. Lourenco, Barry A. Haseltine, Graca Vasconcelos, 2014Conference paper, Published 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.

Keyword
brickwork, lime mortar, cement mortar, salt damage, deterioration, facing bricks, moisture transport
National Category
Other Natural Sciences
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-237216 (URN)978-972-8692-85-8 (ISBN)
Conference
9th International Masonry Conference, July 7-9, 2014, Guimarães, Portugal
Available from: 2014-12-01 Created: 2014-12-01 Last updated: 2014-12-02Bibliographically approved
Balksten, K. (2014). Putsat för framtiden. Byggnadskultur (3), 38-40.
Open this publication in new window or tab >>Putsat för framtiden
2014 (Swedish)In: Byggnadskultur, ISSN 0348-6885, no 3, 38-40 p.Article in journal (Other (popular science, discussion, etc.)) Published
Place, publisher, year, edition, pages
Stockholm: Svenska föreningen för byggnadsvård, 2014
National Category
Natural Sciences
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-237231 (URN)
Available from: 2014-12-01 Created: 2014-12-01 Last updated: 2014-12-01
Balksten, K., Persson, C. & Eriksson, J. (2013). Lime burning tradition in field kilns: a case study of the Jämtland tradition in Sweden. In: : . Paper presented at 3rd Historic Mortars Conference HMC-2013, Glasgow, Scotland. .
Open this publication in new window or tab >>Lime burning tradition in field kilns: a case study of the Jämtland tradition in Sweden
2013 (English)Conference paper, Published 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.

Keyword
lime mortar, slaked lime, lime burning, lime kiln, workability
National Category
Natural Sciences
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-220112 (URN)
Conference
3rd Historic Mortars Conference HMC-2013, Glasgow, Scotland
Projects
Ökat brukande av ruiner genom säkrade murverk och komfortabelt klimat
Funder
Knowledge Foundation
Available from: 2014-03-11 Created: 2014-03-11 Last updated: 2014-03-12Bibliographically approved
Balksten, K. & Mebus, U. (Eds.). (2012). Bruk av ruiner: kulturarv, konstruktion, kalkbruk, komfort & kalsonger. Visby: Fornsalens förlag.
Open this publication in new window or tab >>Bruk av ruiner: kulturarv, konstruktion, kalkbruk, komfort & kalsonger
2012 (Swedish)Collection (editor) (Other academic)
Place, publisher, year, edition, pages
Visby: Fornsalens förlag, 2012. 143 p.
National Category
Natural Sciences
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-220106 (URN)9789188036841 (ISBN)
Funder
Knowledge Foundation
Available from: 2014-03-11 Created: 2014-03-11 Last updated: 2014-03-12Bibliographically approved
Balksten, K., Broström, T., Myrin, M., Thelin, C., Kettunen, R. & Mebus, U. (2010). Increased use of ruins through secured masonry and comfortable climate. In: Proceedings of the 7th International Conference on Science and Technology in Archaeology and Conservation, Petra, Jordan. Paper presented at 7th International Conference on Science and Technology in Archaeology and Conservation, Petra, Jordan. .
Open this publication in new window or tab >>Increased use of ruins through secured masonry and comfortable climate
Show others...
2010 (English)In: Proceedings of the 7th International Conference on Science and Technology in Archaeology and Conservation, Petra, Jordan, 2010Conference paper, Published 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.

Keyword
ruin, masonry, structures, mortar, stone, climate, comfort, Gotland
National Category
Building Technologies Energy Systems
Research subject
Conservation
Identifiers
urn:nbn:se:hgo:diva-1197 (URN)
Conference
7th International Conference on Science and Technology in Archaeology and Conservation, Petra, Jordan
Available from: 2012-01-19 Created: 2011-12-05 Last updated: 2017-01-25Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2994-1766

Search in DiVA

Show all publications