Effect of the Inspection Conditions on the In-Situ Infrared Thermographic Examination of Facades with Adhered Ceramic Cladding

Transcription

1 Effect of the Inspection Conditions on the In-Situ Infrared Thermographic Examination of Facades with Adhered Ceramic Cladding Ecem Edis 1 Inês Flores-Colen 2 Jorge de Brito 3 ABSTRACT Ceramic based facade materials are widely used in Portugal. Some of the durability problems of ceramic facades are joint failures, delamination and efflorescence, and one of the reasons of this kind of problems is water/moisture caused by condensation, rising damp or precipitation. Infrared (IR) thermography is a well developed non-destructive examination technique in terms of detecting thermal and air infiltration problems, and the environmental inspection conditions are well studied. Inspection of moisture problems using IR thermography is a comparatively new field, and most of the studies either focus on applications on historical buildings or investigate the applicability on different materials in laboratory conditions. Environmental factors affecting in-situ thermographic inspection of moisture problems of different building technologies are not well studied yet. In-situ inspection of adhered ceramic facades to detect presence of moisture before the occurrence of any visible signs is a possible accomplishment of IR thermography. In relation with these facts, suitable inspection conditions in terms of solar heat gain for in-situ examination of adhered ceramic facade claddings by IR thermography are discussed in the paper. Parameters like characteristics of ceramic tiles or inspection time and their effects on the inspection of moisture problems present in the facade system are studied theoretically, and case studies are presented as well. KEYWORDS Infrared thermography, adhered ceramic facade cladding, in-situ inspection, environmental inspection conditions, moisture. 1 Istanbul Technical University, Faculty of Architecture, Istanbul, TURKEY, ecem@itu.edu.tr 2 DECivil-IST, Technical University of Lisbon, Lisbon, PORTUGAL, ines@civil.ist.utl.pt 3 DECivil-IST, Technical University of Lisbon, Lisbon, PORTUGAL, jb@civil.ist.utl.pt

2 E. Edis, I. Flores-Colen and J. de Brito 1 INTRODUCTION Ceramic based facade claddings are widely used in Portugal as one of the traditional materials. However durability problems such as cracking, efflorescence or detachment are also noted [LNEC, 2006; APICER, 2003]. Water/moisture caused by precipitation, condensation or rising damp is one of the reasons of this kind of durability problems. In building/construction sector, infrared (IR) thermography is one of the non-destructive examination (NDE) techniques that is used to detect thermal irregularities and air infiltration problems of building envelope, moisture and delamination problems and defective areas of mechanical and electrical systems [Balaras & Argiriou, 2002]. In the application of IR thermography, providing certain (environmental) conditions depending on the type of problem is required and important to perform the inspection. In the detection of thermal irregularities and air infiltration problems, these conditions are defined in standards such as in ASTM C [2003] or ISO 6781 [1983]. However, this kind of standardized procedures and conditions does not exist for detection of moisture problems. Either in adhered ceramic claddings or in other cladding technologies, detection of moisture within a system before the occurrence of visible signs such as efflorescence is important to take the necessary preventive measures. Due to its non-destructive nature, using IR thermography to detect the presence of excessive moisture can be beneficial. Considering this a research study based on in-situ inspections in Lisbon, Portugal, was conducted to adapt general IR thermographic procedures to its particular application in adhered ceramic claddings to detect moisture and also delamination problems [Edis et al., 2010]. As part of this research the effect of parameters such as ceramic type, amount of solar heat gain or inspection timing on in-situ IR thermographic inspection was studied and is presented here. 2 CERAMIC BASED FACADE MATERIALS European standard EN [CEN, 2006] classifies ceramic tiles into three main groups according to their water absorption characteristics as: (i) group I - water absorption lower than or equal to 3%, (ii) group II - water absorption between 3% and 10%, and (iii) group III - water absorption higher than 10%. Tiles with a high rate of water absorption (i.e. within group III) can either be glazed to prevent water absorption from the surface like the traditional tiles of Portugal (i.e. azulejo) or left unglazed like some veneering bricks. Tiles with lower absorption rate can also be glazed or polished for decorative purposes. Glazing increases water vapour diffusion resistance, as well as improving the water absorption from the surface. 3 DETECTION OF MOISTURE BY IR THERMOGRAPHY 3.1 Driving Forces Helping to Detect Moisture Problems by IR Thermography In IR thermography, objects whose temperature varies from the environmental temperature, in other words, objects which are not in thermal balance with the surroundings or readily absorbing moisture from the air, can be observed with an IR sensing system [Barreira & de Freitas, 2007]. The same applies to observing surface temperature variations of an object. In the detection of moisture within a system, there are generally two different driving forces that create observable surface temperature differences, which are: (i) evaporative cooling, and (ii) higher thermal inertia of water versus building materials thermal behaviour [Rosina & Ludwig, 1999], in other words increased heat capacity of moist material. In evaporation, depending on the relative humidity and temperature of air near the object surface, water content and physical characteristics of the object, and soluble salt content, surface cooling occurs in moist areas due to endothermic nature of evaporation [Rosina & Ludwig, 1999; Barreira & de Freitas, 2007]. When soluble salts are present in the material, evaporation rate decreases and therefore the decrease in surface temperature and temperature difference between moist and dry zones becomes less significant [Matias et al., 2008; Rosina & Ludwig, 1999]. High relative humidity of air, 2 XII DBMC, Porto, PORTUGAL, 2011

3 Effect of the Inspection Conditions on the In-Situ Infrared Thermographic Examination of Facades e.g. more than 80%, also prevents evaporation and temperature difference between moist and dry areas due to surface cooling becomes less significant [Rosina et al., 1998]. Specific heat capacity of water is higher than that of most construction materials [Rosina & Ludwig, 1999]. Therefore, the presence of moist increases the heat capacity of construction materials, which is the quantity of heat required to raise the temperature of a body of material by 1 ºK [Bolton, 2006]. In unsteady thermal conditions, different thermal capacities of the moist areas cause colder or warmer surface temperatures depending on being in the heating or cooling period, and these zones can be identified by thermography. The observation location in respect to the heating location affects the observed surface temperature distribution as well. Apart from these two driving forces that generate observable surface temperature differences, another physical fact is the increased thermal conductivity of moist material generating surface temperature differences under steady heat flux. The presence of moist thermal insulation in the case of stud walls can be detected with this approach as mentioned in ASTM C [2003]. However, in order to generate observable temperature differences, the thickness of the damp area should be large. Therefore, it is less favorable in detection of moisture within components that have smaller thicknesses, such as plaster or ceramic claddings. 3.2 Detection of Moisture by IR Thermography In Facades with Adhered Ceramic Cladding In facades with adhered ceramic cladding, the type of ceramic tile in terms of water absorption and surface treatment (i.e. glazed or unglazed) determines the driving force that can be used while detecting moisture problems by IR thermography. In most of the research studies on detection of moisture by IR thermography, porous materials such as render, aerated concrete or stone, which allow evaporation, were considered [Matias et al., 2008; Barreira & de Freitas, 2007; Rosina & Ludwig, 1999]. However, in adhered ceramic claddings, tiles that are unglazed and that have high water absorption rate (e.g. unglazed veneering bricks with high water absorption) can only be detected by using the evaporative cooling as the driving force. In the case of tiles that are glazed and/or that have low water absorption, the driving force that can generate observable surface temperature differences is the higher thermal inertia of moist material because of the high water vapour diffusion resistance and low water absorption of tiles, and it requires unsteady thermal conditions as mentioned in the previous section, either provided by an active or a passive approach. In the passive approach, the heat flux is generated by natural boundary conditions [Grinzato et al., 2002]. In the active approach, artificial heating is used and thermograms are taken during or after heating [Rosina & Robison, 2002]. The use of solar radiation, which is sometimes considered in the passive approach and sometimes in the active approach, is one of the feasible heating methods in the case of in-situ inspection of facades, especially of middle or high-rise buildings. However, apart from the other limitations related to inspected building such as uneven solar heat gain due to projections, one of the major drawbacks of using solar radiation is that the intensity of solar radiation is orientation dependant, influencing the amount of solar heat gain and inspection timing. 4 CASE STUDIES TO DETECT MOISTURE IN ADHERED CERAMIC CLADDINGS In the in-situ inspection of the case buildings presented here, a FLIR ThermaCAM B2 type IR camera with a spectral range of 7.5 to 13 µm, thermal sensitivity of 0.1 o C and field of view of 33.8 o was used. Air temperature and relative humidity was measured with Rotronic HydroLog-D and HydroClip SC05. Moisture content measurements were also made with Tramex s Survey Encounter, which is a surface moisture meter using electrical impedance to determine relative moisture content. While evaluating the condition of the facade and surface temperature variations during both in-situ IR thermographic inspection and assessment of thermograms, the reference method was used. In the reference method, surface temperature distribution at a particular location can be evaluated considering the general temperature distribution at that building. In addition, reference thermograms XII DBMC, Porto, PORTUGAL,

4 E. Edis, I. Flores-Colen and J. de Brito that were taken from other buildings with similar characteristics during inspections with similar environmental conditions can be used [ISO, 1983; Rosina & Ludwig, 1999]. 4.1 Moisture Detection in Facades with Unglazed Adhered Ceramics (Veneering Brick Application) The east facing facade of a building clad with veneering bricks and with reinforced concrete frame structure with brick/block infill walls was inspected during the rainy season, in April The 1 st inspection was performed in the morning hours of a cloudy day, before any solar heat gain. The 2 nd inspection was performed on the same day close to the sunset hours without direct sunlight on the facade. The exterior air temperature ( o C) and relative humidity (%) measured during the inspections and the weather forecast of the Meteorology Institute of Portugal (IM-IP) are given in Table 1. Table 1. In-situ inspection of veneering brick application - measured environmental conditions and weather forecast of IM-IP. Exterior air Exterior relative Sky temperature - o C humidity - % Inspection 1- morning Cloudy Inspection 2 - evening Light clouds Weather forecast of IM-IP Minimum: 14 Maximum: 20 - a.m.: periods with heavy clouds p.m.: sky with light clouds In the first inspection, surface temperature variations indicating a possible problem was observed as shown in Fig. 1-(a) and a surface moisture meter measurement was made at the location marked as Ar1 in the same figure. A general analysis of the temperature profiles 4 (, and in Fig. 1-(b)) and surface moisture meter readings (Fig.2-(a)) revealed that there were moisture content changes at that location and lower moisture content generally showed up in the thermogram as areas with colder surface temperature due to evaporative cooling. However, an exact correlation between temperature profiles and moisture meter readings cannot be found with a high probability due to efflorescence, i.e. white stains observed on the surface. The reliability of both methods decreases in the presence of efflorescence, since soluble salts decrease the amount of evaporation as aforementioned, and increase the measured moisture content in moisture meters using electrical impedance [Burkinshaw, 2002]. FLIR Systems Ar C C ~B,C ~F ~G,H Label Cursor Min Max (a) Time of creation: 10:35 a.m. (b) Figure 1. In-situ IR thermographic inspection of a veneering brick application: (a) thermogram of the facade taken during morning hours; (b) temperature profile of the thermogram in (a). In the second inspection performed after heat gain through solar radiation and exterior air temperature, surface temperature variations observed in the first inspection cannot be seen, rather the material difference at the substrate, i.e. the location of reinforced concrete structural members and 4 In the thermograms the name label marks the beginning of the temperature profile line and its direction in the temperature profile graph is from left to right. The cursor to mark a specific location on a line is presented with a + sign, and the place of the cursor is presented with a vertical line on temperature profile graph. 4 XII DBMC, Porto, PORTUGAL, 2011

5 Effect of the Inspection Conditions on the In-Situ Infrared Thermographic Examination of Facades infill walls, can be identified as given in Fig. 3-(a). Only at the location marked with the cursor on the temperature profile line, a similar surface temperature drop of about o C was observed. In the thermogram taken before heat gain, the temperature drop at this location was about 0.8 o C. This probably indicates that heat loss after solar heat gain masks the effect of evaporative cooling. ~B, C ~F ~G, H Ar1 (a) (b) Figure 2. In-situ IR thermographic inspection of a veneering brick application: (a) surface moisture meter readings with brick option; (b) photograph of the facade, location of analysis lines and approximate locations of cursors in relation with ceramic tile columns. FLIR Systems Ar C C Label Cursor Min Max (a) Time of creation: 7:18 p.m. (b) Figure 3. In-situ IR thermographic inspection of a veneering brick application: (a) thermogram of the facade taken during the late afternoon hours; (b) temperature profile of the thermogram in (a). Rosina & Ludwig [1999] reported that, while monitoring the walls of Santa Maria delle Grazie at Milano during the interior space heating period, the surface temperature difference between dry and damp zones increased as the interior air temperature increased. Rosina et al. [1998] also suggested that active direct heating of the wall either with radiation or convection should be avoided for a proper inspection. Considering this information and in-situ inspection data it can be said that, in the case of unglazed adhered ceramics, it is possible to distinguish damp and dry zones during the beginning of the heating period, before the heat gain of the substrate. However, after heat gain of the substrate, it is hard to observe and distinguish damp and dry zones of ceramic cladding with IR thermography. 4.2 Moisture Detection in Facades with Glazed Adhered Ceramics West facing facade of a building clad with glazed ceramic tiles and with infill walls within reinforced concrete structural frame, was detected in the rainy season, in May The first inspection was performed in the evening hours. The second inspection was performed in the morning of the following day before solar heat gain, when the sky was cloudy. The exterior air temperature ( o C) and relative humidity (%) measured during inspections and the weather forecast of IM-IP are given in Table 2. In the first inspection performed after heat gain, surface temperature increases were observed in zones close to the ground level. As seen in the thermogram and its temperature profile in Fig. 4-(a) and (b) ~F ~G, H XII DBMC, Porto, PORTUGAL,

6 E. Edis, I. Flores-Colen and J. de Brito respectively, the surface temperature difference ranged between 2.3 and 3.2 o C. A general moisture content control made with brick option of the surface moisture meter at each row showed that the moisture content increased when it got closer to the ground level as seen in Fig. 4-(c). Areas with higher moisture content showed up in the thermogram as areas with higher surface temperature since glazing prevented evaporation and increased thermal capacity caused by increased moisture content was the driving force generating observable surface temperature difference. Table 2. In-situ inspection of glazed ceramic application - measured environmental conditions and weather forecast of IM-IP. Exterior air Exterior relative Sky temperature - o C humidity - % Inspection 1- day 1, evening Inspection 2 - day 2, morning Cloudy Weather forecast of IM-IP Day 1 - Min.: 14, Max.: 22 Day 2 - Min.: 15, Max.: 22 - Day 1 - a.m. & p.m.: periods with heavy clouds Day 2 - a.m.: periods with heavy clouds FLIR Systems 27.8 C C st row 2 nd row 3 rd row (a) Time of creation: 8:30 p.m. (b) ) Label Cursor Min Max (c) Figure 4. In-situ IR thermographic inspection of a glazed ceramic application: (a) thermogram of the facade taken in the evening after heat gain; (b) temperature profile of the thermogram in (a); (c) photograph of the facade, location of the tile rows and approximate moisture contents. In the second inspection performed before solar heat gain, a similar surface temperature increase was observed at the same location but with a smaller temperature difference which ranged between 1.2 and 1.4 o C as seen in Fig.5. When assessed together with the thermogram taken in the evening after heat gain, it can be said that solar heat gain increases the observed surface temperature differences when there is a moisture content change, and thus identification of damp zones becomes easier. 5 DISCUSSION AND CONCLUSION Top ends of 6 th row (0-15%) 5 th row (0-15%) 4 th row (20-35%) 3 rd row (85-90%) 2 nd row (95%) 1 st row (95%) In-situ IR thermographic inspection of different ceramic types at different hours of the day to detect moisture problems confirmed the theoretical discussion made in section 3.2. that, in the case of reinforced concrete structural frame with brick/block infill walls clad with adhered ceramic tiles and when solar radiation is used for providing unsteady thermal conditions: 6 XII DBMC, Porto, PORTUGAL, 2011

7 Effect of the Inspection Conditions on the In-Situ Infrared Thermographic Examination of Facades Driving forces that generate observable surface temperature differences during IR thermographic inspection change according to the surface treatment and water absorption characteristics of the ceramic tiles; The effect of solar heat gain changes according to the characteristics of ceramic tiles and the driving force to generate temperature differences. FLIR Systems 22.8 C C 1 st row 2 nd row 3 rd row Label Cursor Min Max (a) Time of creation: 9:00 a.m. (b) Figure 5. In-situ IR thermographic inspection of a glazed ceramic application: (a) thermogram of the facade taken in the morning before solar heat gain; (b) temperature profile of the thermogram in (a). In unglazed ceramics with high water absorption rate like veneering bricks: The driving force that generates surface temperature differences is evaporative cooling in damp zones and damp areas are observed as colder areas in the thermograms; Heat gain either by solar radiation or convection initially increases the observability of damp zones. However heat gain of the substrate masks the effect of evaporative cooling especially when different materials, e.g. reinforced concrete and brick, are used as the substrate, and thus prevents performing an appropriate IR thermographic survey. Considering this, it can be said that in the case of unglazed ceramics it is better to perform an IR thermographic inspection in the morning hours, at the initial periods of heat gain. Depending on the orientation of the facade, cloudy sky conditions may be required to prevent direct sunlight on the surface which may cause false indications when using thermography. In addition, it should be kept in mind that the presence of efflorescence decreases the rate of evaporation and thus the observed surface temperature differences by IR thermography, and on the contrary it increases moisture content readings made with impedence type surface moisture meters. In glazed ceramics and in ceramics with low water absorption: The driving force that generate surface temperature differences is the increased thermal inertia, in other words increased heat capacity of moist material and damp areas are observed as warmer areas in the IR thermographic inspection since evaporation is not possible; Heat gain either by solar radiation or convection increases the observed temperature difference between moist and drier areas. Therefore performing an in-situ inspection becomes easier, although heat gain of the substrate has the same effect like in the veneering brick application as observed in in-situ inspection of other buildings which are not mentioned here. Considering this, it can be said that in the case of glazed ceramics and ceramics with low water absorption, it is better to perform the IR thermographic survey after solar heat gain. However it should be considered that the amount of solar heat gain is orientation dependant and feasible inspections may not be performed for every orientation. In conclusion it can be said that IR thermography is a possible NDE technique that can be used in the detection of moisture problems of adhered ceramic claddings, although reliability of this technique is affected by many different factors such as those mentioned here (efflorescence or orientation of facade), or by factors such as reflection or surface stains which are not mentioned here. In order to increase the reliability of this NDE technique, further field and laboratory research studies, which also cover destructive examinations, are required. XII DBMC, Porto, PORTUGAL,

8 E. Edis, I. Flores-Colen and J. de Brito ACKNOWLEDGMENTS The first author of this paper was financially supported by the Scientific and Technological Research Council of Turkey (TÜBĐTAK) during this research. The authors thank Building Physics group and Maria da Glória Gomes from IST, DE-Civil for the technical support and use of IR equipment. REFERENCES APICER, 2003, Manual of application of ceramic claddings (In Portuguese), Ed.s: Sousa, A. V., de Freitas, V. P., & da Silva, J. R., Associação Portuguesa da Indústria de Cerâmica, Coimbra, Portugal. ASTM, 2003, Standard practice for thermographic inspection of insulation installations in envelope cavities of frame buildings, ASTM - C , American Society for Testing and Materials (ASTM) International, USA. Balaras, C. A., & Argiriou, A. A, 2002, Infrared thermography for building diagnostics, Energy and Buildings, 34[2] Barreira, E., & de Freitas, V., 2007, Evaluation of building materials using infrared thermography, Construction and Building Materials, 21[1] Bolton, W., 2006, Engineering science (Fifth edition), Elsevier Newnes, Oxford, UK. Burkinshaw, R., 2002, What is the moisture meter trying to tell us, Structural Survey, 20[5] CEN, 2006, Ceramic tiles - Definitions, classification, characteristics and marking, EN 14411, European Committee for Standardization, Brussels, Belgium. Edis, E., de Brito, J., Flores-Colen, I., 2010, Diagnosis of exterior wall failures by in-situ inspection techniques - Inspection of facades with adhered ceramic cladding (Preliminary report), Universidade Tecnica de Lisboa - Instituto de Engenharia de Estruturas, Território e Construção (UTL - ICIST) DTC No. 06/2010, July. Grinzato, E., Bison, P. G., & Marinetti, S., 2002, Monitoring of ancient buildings by the thermal method, Journal of Cultural Heritage, 3(1) ISO, 1983, Thermal Insulation - Qualitative detection of thermal irregularities in building envelopes - Infrared Method, ISO 6781, International Organization for Standardization, Switzerland. LNEC, 2006, Technical guide of rehabilitation of housing (Vol. 2) (in Portuguese), Instituto Nacional de Habitação - Laboratório Nacional de Engenharia Civil, Lisbon, Portugal. Matias, L., Vilhena, A., Magalhães, A., Santos, C. P., & Veiga, R., 2008, Performance of masonry specimens in contact with salt water - Absorption by capillary rise and evaportaion phenomena, Proceedings of 1st International Conference on Construction Heritage in Coastal and Marine Environments, Laboratório Nacional de Engenharia Civil (LNEC), Lisbon, Portugal. Rosina, E., Ludwig, N., & Rosi, L., 1998, Optimal Environmental Conditions to Detect Moisture In Ancient Buildings: Case Studies in Northern Italy, Proceedings of Thermosense XX, pp , SPIE, Orlando,USA. Rosina, E. & Ludwig, N., 1999, Optimal thermographic procedures for moisture analysis in building materials, Diagnostic Imaging Technologies and Industrial Applications, SPIE, Vol. 3827, Germany. Rosina, E. & Robison, E. D., 2002, Applying infrared thermography to historic wood-framed buildings in North America, APT Bulletin, 33[4] XII DBMC, Porto, PORTUGAL, 2011