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Analysis of the Moisture Content of Masonry Walls in Historical Buildings Using the Basement of a Medieval Town Hall as an Example Procedia Engineering 172 ( 2017 ) 363 – 368 Available online at www s[.]
Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 172 (2017) 363 – 368 Modern Building Materials, Structures and Techniques, MBMST 2016 Analysis of the moisture content of masonry walls in historical buildings using the basement of a medieval town hall as an example Anna Hołaa, *, Zygmunt Matkowskia, Jerzy Hołaa a Wroclaw University of Technology, Faculty of Civil Engeneering, Wybrzeze Stanislawa Wyspianskiego 27, 50-370 Wroclaw, Poland Abstract The paper concerns the issue of analysing the moisture content of thick masonry walls in historical buildings The research methods, including non-destructive methods, which are useful in the assessment of such objects, were first indicated Then, the exemplary results of tests conducted in the basement of a medieval town hall with the use of some of the previously mentioned methods were presented Based on the authors' own research, the developed correlative relation between the mass moisture of brick walls in the analysed building and the dimensionless parameter which was measured using the non-destructive dielectric method was also presented This relation was used to assess the mass moisture of brick walls in this building It can also be successfully used for non-destructive testing of the moisture content in walls of other buildings dating back to the turn of the XIV/XV century © 2017 Published by Elsevier Ltd This is an open access article under the CC BY-NC-ND license © 2016 The Authors Published by Elsevier Ltd (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the organizing committee of MBMST 2016 Peer-review under responsibility of the organizing committee of MBMST 2016 Keywords: historical buildings; walls; mass moisture; moisture content testing methods Introduction The masonry walls of historical buildings - made of ceramic brick or stone - are often characterized by a high thickness and a lack of damp insulations It refers primarily to horizontal insulations, which began to be executed in a modern way at the beginning of the twentieth century The lack of damp insulations causes direct and prolonged contact of a wall with the ground As a result, water molecules that are contained in the substrate along with salts * Corresponding author Tel.: +48-71-320-40-95 E-mail address: anna.hola@pwr.edu.pl 1877-7058 © 2017 Published by Elsevier Ltd This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the organizing committee of MBMST 2016 doi:10.1016/j.proeng.2017.02.041 364 Anna Hoła et al / Procedia Engineering 172 (2017) 363 – 368 dissolved in them penetrate elements of the masonry wall making it damp These elements are both ceramic brick and mortar from joints, and in walls made of stone these joints are usually of a large width Capillarity, the process of which was described inter alia in [1,2,3], causes water molecules to be transported into the wall and into its higher parts In the case of a masonry wall with a large thickness, from which evaporation of moisture is naturally difficult, the degree of moisture content gradually increases with time Table shows the degrees of moisture content of masonry walls acquired in literature [4,5] Table Degrees of moisture content of masonry walls in relation to the value of mass moisture content [4,5] Degree of moisture content I – masonry wall with permissible moisture content Mass moisture content [%] 0-3 II – masonry wall with elevated moisture content >3-5 III – medium damp masonry wall >5-8 IV – very damp masonry wall > - 12 V – wet masonry wall > 12 The effect of long-term and excessive moisture in a masonry wall is, among other things, susceptibility to frost erosion which progresses with time and in consequence, the chipping of fragments of bricks and mortar, as well as the crystallization of salts These processes cause the gradual reduction in the strength of a wall, reduction of its cross section and also its load bearing capacity [4,6,7] Methods of testing the moisture content in the masonry walls of historical buildings In historical buildings, actions against the process of masonry wall destruction are often only taken when there is a need to bring back the utility value of an object One of the first actions that aims to restore the former glory of a building object should include the execution of moisture content tests of masonry walls and the determination of moisture distributions along their height and across their thickness with regards to the quantitative approach The non-destructive methods which are recommended for these tests [4, 5, 8] enable measurements to be carried out in any number of places, at multiple times and at different times and also without damage to the historic tissue Support using destructive methods is usually necessary, however, the amount of tests made in such a way should be kept to a minimum Figure summarizes the methods of testing the moisture content in masonry walls that are accepted in cases of historical objects Fig Methods of testing the moisture content of masonry walls that are accepted in cases of historical buildings Anna Hoła et al / Procedia Engineering 172 (2017) 363 – 368 365 Tests of the moisture content of masonry walls, combined with the assessment of salinity are not only crucial in the selection of an appropriate method of protection against damp and the removal of harmful salts from a wall, but they also facilitate the estimation of costs of actions which accelerate the drying of masonry walls They are also, which is very important, a reference level for moisture content tests performed at a later time, which enables the effectiveness of drying actions and executed damp-proof protections to be assessed An example of moisture content tests in a historical building In order to highlight the above issues, the article presents the results of tests of the moisture content of damp brick walls in the unused basement of a medieval town hall located in northern Poland The impetus for the execution of these tests was the decision to restore the basement and open it to the public Figure shows a general view of the town hall, the renovated basement walls and also the damp basement walls Fig Town hall located in northern Poland: (a) general view; (b) renovated basement walls; (c) damp basement walls 3.1 Description of the basement and carried out tests The external and internal walls of the basement of the town hall are made of ceramic solid brick with lime mortar and their thickness is in the range of 700 - 2200 mm The external walls in some places have stone foundations of a height not exceeding 1300 mm above the floor level The lime mortar that fills the wide joints between the stone elements is rotten and its losses even reach 150 mm into the masonry wall The vaults of the basement are brick cross or staple - while the floors are brick or ground Tests of the moisture content of the masonry building walls were carried out using two methods: non-destructive dielectric, which enables the average moisture content of the wall to be specified to a depth of about 100 mm from the surface, and also the destructive drying-weighing method The number of tests performed with the latter one was reduced to a minimum due to conservation restrictions Tests conducted using the destructive method were used to establish the correlative relation between the mass moisture content of the assessed walls and the dimensionless indications used for non-destructive testing with a gauge based on the measurement of dielectric properties of a material For this purpose, non-destructive measurements of the moisture content of the masonry wall were carried out in more than thirty locations Then, in the same places, samples from a depth of 10-100 mm were taken from the wall and their moisture content was determined using the drying-weighing method On the basis of the obtained results, the correlative relation between the indications of dielectric gauge X and mass moisture content Um of the wall was determined and is shown in Figure 366 Anna Hoła et al / Procedia Engineering 172 (2017) 363 – 368 Fig The correlative relation between the indications of dielectric gauge X and mass moisture content Um of the wall Non-destructive tests of the mass moisture content of brick walls in the town hall were carried out in a total of hundreds of places and at a height ranging from 200 to 2000 mm from the level of the floor They allowed the mass moisture distribution along the height of the walls to be determined Moreover, in some selected places destructive tests were carried out across the thickness of the walls and involved the execution of boreholes and taking samples of the damp wall 3.2 Test results and their analysis Based on the conducted tests, it was concluded that the mass moisture content of the masonry walls in the basement of the town hall varies depending on the height at which the measurements were carried out and depending on the depth from which the samples for testing were taken Figure shows the obtained exemplary, but typical for the tested brick walls, distributions of the mass moisture content at the height of the internal and external walls obtained using the non-destructive dielectric method As can be seen, the highest value of the subsurface weight moisture content appears in the walls in the area of the floor In many measuring points located in this area, the measured high values classify the tested masonry walls as very damp according to the classification found in literature regarding the degree of moisture content [4, 5] The moisture content of masonry walls decreases with the distance from the floor The distribution of the subsurface moisture content of the external walls differs significantly from the distribution, which is characteristic for internal walls This is due to the fact that the external walls are damp from the bottom and from their side (a lack of horizontal and vertical damp insulation) In turn, Figure shows the exemplary distributions of the mass moisture content of a brick wall across its thickness, which were specified using the destructive method These tests indicate that the moisture content inside the masonry walls is much higher than the one measured in the subsurface area, and its value increases with an increase of depth from which the samples were taken for testing Based on the conducted tests, it was concluded that the mass moisture content inside the masonry walls enables the tested walls to be classified as wet It is worth Anna Hoła et al / Procedia Engineering 172 (2017) 363 – 368 mentioning that the highest value of the mass moisture content inside one of the external masonry walls was equal to 29%, which indicates a full saturation of the wall with water Fig Exemplary distributions of the mass moisture content of the brick wall obtained using the non-destructive dielectric method along the height of the walls (a) internal; (b) external 367 368 Anna Hoła et al / Procedia Engineering 172 (2017) 363 – 368 Fig Exemplary distributions of the mass moisture content of the brick walls across their thickness, specified using the destructive weighingdrying method: (a) external walls - the test was conducted for half of the thickness of the wall and at a height of 1500 mm above the level of the floor; (b) the internal walls - the test was performed across the entire thickness of the wall at a height of 400 mm above the level of the floor The carried out moisture content tests showed the image of the dampness of the brick walls in the basement of the town hall, which was a result of capillary actions of water from the ground This image is a consequence of a lack of horizontal and vertical damp insulations, which clearly indicate that before the beginning of repair works of the basement, the flow of the moisture from the ground to the external and internal walls should be stopped by the execution of secondary damp insulations This will enable these partitions to be dried to an acceptable moisture level during their usage Conclusions Tests of the moisture content of thick walls in historical buildings are necessary in the case of buildings for which decisions to restore their intended use were undertaken Non-destructive methods, and especially the dielectric method, are recommended for such tests The use of destructive methods should be limited to the necessary minimum, for example, to determine the correlative relation between the tested mass moisture content and dimensionless indications of devices used for non-destructive testing The correlative relation between the indications X of the GANN UNI gauge used in tests, which relied on measurements of the dielectric properties of the material, and also the mass moisture content Um, was determined on the basis of conducted experimental tests of the walls of the medieval town hall This relation, which is described with a mathematical equation, was used for the non-destructive evaluation of the moisture content of the brick walls in the basement of this building and can also be used for the non-destructive evaluation of the moisture content of brick walls in other medieval buildings On the basis of non-destructive tests of the basement walls in the medieval town hall, which were carried out with the use of the dielectric method, and also with the help of the previously determined correlative relation, it has been shown that the external walls in the area of the subsurface are very damp (Um > 8%) up to a height of 1400 mm which was measured from the floor level, while the internal walls are only very damp to a height of 200 mm Furthermore, it has been proven with the aid of the destructive test method that the mass moisture content inside the examined walls is high and qualifies them as wet (Um > 12%) References [1] M S Camino, F J Leon, A Llorente, J M Olivar, Evaluation of the behavior of brick tile masonry and mortar due to capillary rise of moisture, Materiales de Construccion 64(314) (2014) [2] J Kubik, Przepływ wilgoci w materiałach budowlanych, Oficyna Wydawnicza Politechniki Opolskiej, Opole, 2000 [3] M Raimondo, M Dondi, G Guardini, F Mazzanti, Predicting the initial rate of water absorption in clay brick, Construction and Building Materials 23 (2009) 2623–2630 [4] J Adamowski, J Hoła, Z Matkowski, Probleme und Lösungen beim Feuchtigkeitsschutz des Mauerwerks von Baudenkmälern am Beispiel zweiter grosser Barockbauten in Wroclaw, Bautechnik 82(7) (2005) 426–433 [5] A Goetzke-Pala, J Hoła, Influence of burnt clay brick salinity on moisture content evaluated by non-destructive electric methods, Archives of Civil and Mechanical Engineering 16(1) (2016) 101–111 [6] E Franzoni, Rising damp removal from historical masonries: A still open challenge, Construction and Building Materials 56 (2014), 123–136 [7] C Gentilliani, E Franzoni, S Bandini, L Nobile, Effect of salt crystallization on the shear behavior of masonry walls: An experimental study, Construction and Building Materials 37 (2012) 181–189 [8] A Pala, Investigations of moisture content in saline lime mortar by nondestructive dielectric method, 43rd International Conference, November 5-7, 2013, Olomouc, Czech Republic: proceedings, L Pazdera and P Mazal (Eds.) Brno: Brno University of Technology, (2013), pp 103–110 ... general view; (b) renovated basement walls; (c) damp basement walls 3.1 Description of the basement and carried out tests The external and internal walls of the basement of the town hall are made... the basement and open it to the public Figure shows a general view of the town hall, the renovated basement walls and also the damp basement walls Fig Town hall located in northern Poland: (a) ... section and also its load bearing capacity [4,6,7] Methods of testing the moisture content in the masonry walls of historical buildings In historical buildings, actions against the process of masonry