Construction and Building Materials

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1 Construction and Building Materials 24 (200) Contents lists available at ScienceDirect Construction and Building Materials journal homepage: Review The influence of the thickness of the walls and their properties on the treatment of rising damp in historic buildings Isabel Torres a, *, Vasco Peixoto de Freitas b a Civil Engineering Department, Faculty of Science and Technology of Coimbra University, Pólo II, Pinhal de Marrocos, Coimbra, Portugal b Building Physics Laboratory (LFC) Civil Engineering Department, Faculty of Engineering of Porto University (FEUP), Rua Dr. Roberto Frias, Porto, Portugal article info abstract Article history: Received 23 December 2008 Received in revised form 4 January 200 Accepted January 200 Available online March 200 Keywords: Rising damp Treatment of rising damp Ventilation of the wall base Historic constructions Intervention in older buildings increasingly requires extensive and objective knowledge of what one will be working with. In old buildings, rising damp in walls that are in direct contact with the ground leads to the migration of soluble salts that are responsible for many of the pathologies observed. Our research allows us to conclude that the most efficient way of treating rising damp is by ventilating the wall base [2,4]. This technique was experimentally validated to limestone walls 20 cm thick. As it experimental validation of different thicknesses and different compositions has not been possible, numerical investigation has been carried out in order to analyse their influence. In this paper we will present the results of the work developed in the Department of Civil Engineering of the University of Coimbra in collaboration with the Department of Civil Engineering in the Faculty of Engineering of the University of Porto. The main purpose is to analyse the influence of the thickness and composition of walls on the new treatment for rising damp in historic walls: the of the wall base. Ó 200 Elsevier Ltd. All rights reserved. Contents. Introduction Experimental study Numerical simulation Calculation program used Validation of the experimental work Properties of the materials Analysed parameters Influence of the wall thickness Obtained results concerning the influence of the thickness of the walls Influence of the composition of the walls Obtained results concerning the influence of the composition of the walls Conclusions Acknowledgements References Introduction Although many historic buildings in Portugal have undergone refurbishment to eliminate, or at least to minimise, the effect of rising damp, the results have not been satisfactory [6]. * Corresponding author. address: itorres@dec.uc.pt (I. Torres). In order to try to solve this serious problem that affects most of Portugal s historic constructions, the Building Physics Laboratory (LFC) of the Faculty of Engineering Porto University (FEUP) collaborated with the Department of Civil Engineer of the University of Coimbra to carry out experimental work to help ascertain the efficiency of a technique for treating rising damp in the walls of older buildings. The new technique consists of ventilating the base of walls of monuments and old buildings either through a natural /$ - see front matter Ó 200 Elsevier Ltd. All rights reserved. doi:0.06/j.conbuildmat

2 332 I. Torres, V.P. de Freitas / Construction and Building Materials 24 (200) Lateral infiltrations evaporation Rising damp Rising damp Fig.. Principle of peripheral ventilated system of wall base. Waterproofed faces damp was observed. The solution that is being implemented and monitored consists of:.58m 0.30m 0.0m Lime mortar Limestone A system in the inner face of all external walls and both faces of interior walls (mechanical ) (Fig. 3). A perforated tube measuring m was placed in the base of the walls. Air circulation is guaranteed by a hygro-regulable mechanical system that includes: two relative humidity and temperature probes, two relative humidity and temperature transmitters, a control module and data acquisition system. One of the probes is placed next to the exterior inlet grill and the other inside the piping. Each probe is connected to a relative humidity and temperature transmitter. 0.20m 2.00m Fig. 2. Physical model. process or by installing a hygro-regulated mechanical device. As it is not possible to avoid contact between the walls of historical buildings and water, it was decided to create a system in the base of the walls which would improve the evaporation conditions for water and reduce the water level at a lower rate. In order to reduce the rising damp, a ventilated peripheral system can be created and can be linked to a hygro-regulated mechanical device (Fig. ). The experimental validation of this new technique was obtained in laboratory with a physical model consisting of a prismatic system measuring.58 m 2.00 m 0.20 m, waterproofed on the two upper sides to prevent moisture in this direction, with walls made of limestone slabs measuring 0.30 m 0.20 m 2.00 m, with 0.0 m thick lime mortar joints, as we can see in Fig. 2 [,3]. The experimental campaign was limited to the configuration mentioned above and the experimental results were numerically validated by simulations where the characteristics of the walls and boundary conditions were introduced. An experimental study of walls made with other kinds of natural stone or of different thicknesses was not feasible. As an alternative, therefore, the calculation program was used to evaluate the changes in the moisture content inside walls, enabling us to perform numerical simulations to find the influence of thickness of the wall and its composition on the efficiency of the of the wall base. The wall-base system to treat rising damp is being implemented in a church in the north of Portugal, where rising The transmitters are connected to the control module that compares the data given by the two probes and activates or deactivates the extraction device, according to the following criteria: If the outside air exhibits a relative humidity higher than that of the air in the piping, the system is deactivated; If the outside air exhibits a relative humidity lower than that of the air in the piping, the system is activated. The data acquisition system is designed to store the values recorded by the probes so that the effectiveness of the proposed solution can be evaluated. Portugal s ancient buildings can in fact have walls up to.00 m thick and are made of various materials (Granite is used more in the north of Portugal, limestone in the centre and marble in the south). For our study we chose two kinds of limestone that we call (in Portugal) Pedra de Ançã and Dolomite and two other kinds of natural stone: Granite and Granite-. In these circumstances we think that the numerical analysis of the influence of these parameters on the efficiency of the of the wall base is of considerable interest. In this paper we will present the results of our study, which consisted of performing a large amount of numerical simulations for walls with different thickness (between 20 cm and.00 m) and different compositions (two kinds of limestone and two kinds of Granite). 2. Experimental study The experimental study carried out at the Building Physics Laboratory (LFC) of the Faculty of Engineering Porto University (FEUP) in collaboration with the Department of Civil Engineer of the University of Coimbra consisted on: construction of reservoirs with approximately 2.20 m 2.50 m 0.50 m made with cement blocks inside of which stone walls were built (Figs. 3 and 4).

3 I. Torres, V.P. de Freitas / Construction and Building Materials 24 (200) Fig. 3. Ventilation systems. Waterproofing stone wall Cement blocks 0.50m Waterproofing 2.20m Fig. 4. Configuration of the reservoirs. Configuration Configuration 2 FV FV The wall s base is immersed up to 8 cm and the gaps filled with sand A forced system is placed at the base of the wall Fig. 5. Different boundary conditions.

4 334 I. Torres, V.P. de Freitas / Construction and Building Materials 24 (200) Wall Ventilation box to allow air to enter freely (Fig. 7). This extraction system was left running for the duration of the test so that we could make sure the temperature and relative humidity inside the box were identical to the conditions we had in the laboratory. The continuous variation of the relative humidity and the temperature of the wall were monitored non-destructively by inserting probes into the wall at different heights and depths, as shown in Fig. 8. The probes were connected to a datalogger, providing an hourly register of these parameters. As an example, Fig. 9 shows the profiles of the relative humidity found in the second joint for configurations and 2. We have obtained similar profiles for all the layers of stone and all the joints of both configurations. 45 cm 20 cm cm 3. Numerical simulation 3.. Calculation program used 30 cm Fig. 6. Ventilation system. These experiments were meant to characterise how these walls were affected by rising damp in view of different boundary conditions. The tested configurations are shown in Fig. 5. To evaluate moisture transfer inside the walls, we inserted probes at different heights and different depths to measure relative humidity and temperature. These probes were then connected to a data acquisition and recording system. In configuration we measured the behaviour of a wall with both sides underground by placing sand on both sides of the wall up to a height of 45 cm above its base. In configuration 2, since we wanted to assess the effect of placing a system at the base of the wall, we placed a box on both sides of the wall (Fig. 6). We left two openings to which we attached flexible tubes to ventilate the box. We attached a mechanical extractor at one opening and left the other one free Calculation programs to evaluate changes in the moisture content and temperature inside walls are essential instruments for simulating the wall s behaviour in the presence of moisture, depending on the internal and external climatic conditions. The calculation program used in the numerical simulations for the experimental validation and for the subsequent simulations was WUFI-2D, developed in the Fraunhofer Institute for Building Physics, which is based on the following heat and moisture transfer equations [7 9]. ¼ rðkrtþþh vrðd p rð/p sat ÞÞ ¼ rðd /r/ þ d p rð/p sat ÞÞ ðþ ð2þ Fig. 7. Ventilation box with flexible tubes and mechanical ventilators. probes A - 5cm of depht probes B -0cm of depht 2B 2A B A 0B 0A 9B 9A 7B 7A 6B 6A 5B 5A 4B 4A 5.5 3B 3A 2B 2A 5.5 B A WATER Configuration A 0A 9A B 0B 9B 6.5 cm 7A 6A 7B 6B 5A 5B 4A 4B 3A 2A 3B 2B A B WATER Configuration2 A 0A B 0B 6.5 cm 9A 9B 7A 7B 6A 6B 5A 5B Forced 4A Forced 4B 3A 3B 2A 2B A B WATER Fig. 8. Position of the probes in the walls of configurations and 2.

5 I. Torres, V.P. de Freitas / Construction and Building Materials 24 (200) Configuration Configuration 2 Relative Humidity (%) 50 Relative Humidity (%) Time (hours) Time (hours) Fig. 9. Variation of the relative humidity in the second joint experimental results. where dh/dt [J/m 3 ] is the heat storage capacity of the moist building material, dw/d/ [kg/m 3 ] the moisture storage capacity of the building material, k [W/m K] the thermal conductivity of the moist building material, D / [kg/m s] the liquid conduction coefficient of the building material, d p [kg/m s Pa] the water vapour permeability of the building material, h v [J/kg] the evaporation enthalpy of the water, p sat [Pa] the water vapour saturation pressure, T [ C] the temperature and / [ ] is the relative humidity [7 9] Validation of the experimental work Fig. 0 gives some of the simulation results corresponding to configurations and 2 of the experimental device. The results show that in the simulation corresponding to configuration 2, the rising damp was slower and did in fact achieve lower levels Properties of the materials Use of the numerical simulation program requires knowledge of the boundary conditions and of the materials hygrothermal properties [4]. Some probes of pedra de Ançã, Dolomite and Granite were made and, in accordance with the respective European Standard, all hygrothermal properties needed (apart from specific heat) were determined experimentally. Table shows the properties of the Configuration 3 Configuration 4 Relative Humidity (%) 50 Relative Humidity (%) Time (hours) Time (hours) Fig. 0. Variation of the relative humidity in the second joint numerical simulations. Table Hygrothermal properties of the materials. Dolomite Pedra de Ançã Granite Granite- Bulk density (kg/m 3 ) Heat capacity (J/kg K) Porosity (%) Thermal conductivity (W/m K) Vapour diffusion resistance factor Water absorption coefficient (kg/m 2 p ffiffi s ) Free water saturation (kg/m 3 )

6 336 I. Torres, V.P. de Freitas / Construction and Building Materials 24 (200) materials that we need to introduce in order to perform each simulation. The properties mentioned above, in the heat and moisture transfer equations are obtained from these ones. 4. Analysed parameters 4.. Influence of the wall thickness In this first study our main goal was to analyse the influence of the wall thickness on the efficiency of the of the wall base in the presence of rising damp. In order to do that we considered a wall made of natural stone,.5 m in height. Maintaining the height constant we changed the thickness from 20 cm to cm. Fig. shows the 0 configurations studied. In all the simulations preformed the climatic conditions were the same and correspond to a sinusoidal function created by the program itself. Maintaining all the other conditions apart from the thickness, ten numerical simulations were performed for the configurations presented Obtained results concerning the influence of the thickness of the walls The simulation program provided the water content, the relative humidity and the temperature at all the points of the pre-defined grid and their evolution for the duration of the simulation. It also gave the heat and moisture flows along its surfaces. The results that seem to cast light on this first question, the influence of the thickness of the walls are given below. Only the results obtained for Pedra de Ançã are given, because the results for the other natural stones were very similar. Without With Thickness of the wall (cm) 20 Water content (kg/m 3 ) Height of the wall.50m Fig.. Studied configurations to analyse the influence of the wall thickness. Fig. 2. Water content variation along the transversal section of the walls of Pedra de Ançã (without ).

7 I. Torres, V.P. de Freitas / Construction and Building Materials 24 (200) Thickness of the wall (cm) 20 Water content (kg/m 3 ) Height of the wall.50m Fig. 3. Water content variation along the transversal section of the walls of Pedra de Ançã (with ). In Figs. 2 and 3 we present the water content profiles for the ten situations studied, for walls with thickness between 0.20 m and.00 m, after 2 years simulation. As expected, as the thickness of the wall increases the level achieved by the moisture front increases, in the untreated and treated walls alike. In fact by increasing the thickness of the wall we are increasing the absorption by capillarity and in order to restore the equilibrium between the absorbed flow and the evaporated flow the moisture front must increase. In order to analyse better the variation of the amount of water absorbed as a function of wall thickness, Table 2 was compiled. It shows the variation of the water content for each wall thickness and for each situation simulated (with and without treatment). The efficiency of the system is also included in this table. We considered that the maximum efficiency is obtained for the 20 cm wall and we calculated the relative efficiency for all the other thicknesses. In Fig. 4 we can again see the variation of the water content for each thickness at the end of the two-year simulation period, but now in graphic form. Analysis of the results enables us to conclude that the variation of the wall thickness influences the efficiency of the treatment system. The thicker the wall the smaller the variation of the water content with the introduction of the treatment system; that is to say, the efficiency of the system decreases. Anyway, it is clear that for any thickness of wall the height achieved by the moisture front falls when we introduce the treatment system. In fact, when we introduce the system most of the evaporation will occur inside the box, so lowering the level reached by the moisture front. The system becomes less efficient as the thickness of the wall increase Influence of the composition of the walls In this complementary study our main goal was to analyse the influence of the composition of the walls on the efficiency of the Water Content (kg/m3) Without With Thicness of the wall (cm) Fig. 4. Total water content variation at the end of 2 years of simulation. of the wall base, when in presence of rising damp. In order to do this we considered a wall made of natural stone, with.5 m in height and cm thick. Maintaining the height and the thickness constant, we changed the composition of the wall. Fig. shows the eight configurations studied. In all the simulations preformed the climatic conditions were the same and correspond to a sinusoidal function created by the program itself. Maintaining all the other conditions apart from the composition of the walls, eight numerical simulations were performed, for the configurations presented. The hygrothermal properties of the natural stones used are presented in Table. Table 2 Total water content at the end of the simulation. Thickness of the wall (cm) Water content (kg/m 3 ) Water content reduction by introduction of the (%) Efficiency (%) Without With

8 338 I. Torres, V.P. de Freitas / Construction and Building Materials 24 (200) Pedra de Ançã Dolomite Granite Granite- Without treatment Pedra de Ançã Dolomite Granite Granite- With treatment Fig.. Studied configurations to analyse the influence of the properties of the materials Obtained results concerning the influence of the composition of the walls Below we present the results that seem to cast light on this second question: the influence of the composition of the walls. Figs. 6 and 7 show the variation of the water content for the two-year simulation period, for the eight situations studied, which comprise the four natural stones and the two different configurations (with and without ). As the water content presents very different values for the four natural stones the results are presented in two separate graphics, 2 granite-without granite--without granite-with granite--with with two different scales. The first gives the results for the two kinds of Granite and the second gives the results for Pedra de Ançã and Dolomite. The graphics clearly show that when Pedra de Ançã or the Dolomite replaces the Granite the capillary ascension increases considerably. Table 3 presents the variation of the water content after the 2 years of simulation, in more precise detail. P. de Ançã-without P. de Ançã-with dolomite-without dolomite-with Water Content (kg/m3) Water Content (kg/m3) Time (Hours) Time (Hours) Fig. 6. Total water content variation for Granite and Granite-. Fig. 7. Total water content variation for Pedra de Ançã and Dolomite.

9 I. Torres, V.P. de Freitas / Construction and Building Materials 24 (200) Table 3 Total water content at the end of the simulation. Type of natural stone Water content (kg/m 3 ) Water content reduction by introduction of the (%) Without With Pedra de Ançã Dolomite Granite Granite Water Content (kg/m3) without with 20 cm thickness the decrease of the water content when we introduce the system is 30%, for the wall of cm the decrease is 20, 9% and for the wall of cm the decrease is.6%. Regarding the influence of the materials properties, the most important parameter is the absorption coefficient of water, which was expected, since it is the parameter that best characterises the movement of water in liquid phase, within construction materials. As far as the absorption coefficient of water increases there is no doubt that the capillary ascension increases but the efficiency of the treatment system does not vary greatly. We think that the system has some limitations like walls with thickness greater than m and when the walls are not homogeneous. Until now our studies have mainly focused homogenous walls and walls with thickness above m. 0 In Fig. 8 we can again see the variation of the water content for each kind of natural stone at the end of the two-year simulation period but now in graphic form. When we compare the properties of the materials and the obtained simulations we can conclude that, in fact, as the absorption coefficient increases so the capillary ascension increases, but the efficiency of the treatment system does not vary greatly. 5. Conclusions Granite 2-Granite 3-Pedra de Ançã 4-Dolomite Fig. 8. Total water content variation at the end of 2 years of simulation for Pedra de Ançã, Dolomite and Granite with and without treatment. The main conclusions of our study, which set out to analyse the influence of wall thickness and composition on the efficiency of of the wall base as a technique to treat rising damp are: In historic buildings, the traditional techniques for treating rising damp are not effective. Ventilation of the base of walls is a simple technology that offers great potential. Varying the wall thickness ( m) has a slight influence on the efficacy of the wall-base, while the improvement in the functioning of the wall after the introduction of the system is clear. We can see that for a wall of Acknowledgements The authors would like to thank the FCT-Fundação para a Ciência e Tecnologia for its support through the project POCI/ECM/ 57722/2004-Humidade na Construção, jointly funded by ERDF. References [] Torres MI, de Freitas VP. Treatment of rising damp in historical buildings: wall base. Build Environ 2007;42(): [2] Torres MI. Humidade ascensional em paredes. Master Thesis, FCTUC; 998. [3] Torres MI. Humidade ascensional em paredes de Construções Históricas. PhD Thesis, FCTUC; [4] Freitas VP, Torres MI, Guimarães AS. Humidade ascensional. FEUP Edições: Porto: ISBN [6] Torres MI, Freitas VP. Rising damp in historical buildings: a serious building pathology, construction in the XXI century: local and global challenges joint 2006 CIB W065/W055/W086, Roma, Outubro; [7] Holm A, Kunzel HM. Two-dimensional transient heat and moisture simulations of rising damp with WUFI-2D. In: 2nd International conference on building physics, Leuven, Belgium; p [8] Kunzel HM. Simultaneous heat and moisture transport in building components; one and two dimensional calculation using simple parameters. Dissertação de Doutoramento, University of Stuttgart; 994. [9] Krus M. Moisture transport and storage coefficients of porous mineral building materials. Theoretical principles and new test methods. Fraunhofer IRB Verlag; 996. p. 06. Further reading [5] Torres MI, Freitas VP. The influence of the thickness and the properties of the materials of the walls in the effectiveness of the wall base for the treatment of rising damp. In: IAHS world congress on housing, Sidney, Setembro; 2007.