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Predicting Hygrothermal Behavior of an Underground Stone Chamber with 3-D Modeling to Restrain Water-Related Damage to Mural Paintings

Predicting Hygrothermal Behavior of an Underground Stone Chamber with 3-D Modeling to Restrain... Cultural properties are variously influenced by their surrounding environmental conditions. One of the reasons for the deterioration of mural paintings in the Takamatsuzuka Tumulus was the humid microclimate on their surface. In order to control the deterioration of mural paintings caused by such problems, it is important to investigate the environmental factors from various aspects, such as the temperature, humidity, water content of cultural properties, wetting and drying cycles and so on. As for the research concerning hygrothermal behavior on mural paintings, these variables may not be thoroughly predicted by 1-D or 2-D for determination of the location and degree of the deterioration of mural paintings. This paper shows how a 3-D hygrothermal model developed with a view to analyzing the preservation measures that allow quantifying of the degree of drying and condensing processes occurred on the surfaces of the underground chamber. The findings show that for the purpose of preserving mural paintings within the underground chamber, the temperature difference between the surrounding mound and the protected object should be kept as constant as can be practically achieved. This method is applicable for estimating the effects of preservation measures for the conservation of other mural paintings. Keywords: hygrothermal behavior; 3-D modeling; condensation; dryness; water-related damage; Takamatsuzuka Tumulus 1. Introduction decided to preserve the mural paintings at the site. There are many important mural paintings in For this purpose, a climate chamber and conservation underground chambers in Asian countries. Among facilities were constructed in 1976 in order to keep the them, the under ground stone chamber of the mural paintings under the same conditions as when Takamatsuzuka Tumulus is well known for its beautiful they were found. During the period from the discovery paintings. The tumulus was discovered on 21 March of the mural paintings in 1972 to the beginning of 1972 in Asuka village (N: 34.47, E: 135.82), Nara the operation of the conservation facility in 1976, an Prefecture, Japan. The tumulus is a circular mound emergency preservation measure including a temporary with a diameter of 19 m and height of 5 m (Fig.1.(a)). shelter erected on the south side of the tumulus (see The stone chamber, which is 1.03 m wide, 1.13 m Fig.1.(b)) was adopted to control the hygrothermal high, and 2.65 m deep, is buried within a mound of soil environment in the stone chamber. Then, because of about 3 m below ground level. The mural paintings the difficulties in preserving the mural paintings on- were designated as national treasures in 1974 and site, the stone chamber was dismantled (from October a committee of specialists was organized for their 2006 to A ugus t 2007) to res tore the paintings in conservation. After extensive discussion, the committee temporary restoration facilities. In recent years, Asian scholars have begun to pay more and more attention to the research of cultural *Contact Author: Yonghui Li, Dr. Eng., Lecturer, 1), 2), 3), 4) heritage protection . The conservation of mural Key Laboratory of Urban and Architectural Heritage Conservation paintings in natural underground sites is difficult. As of Ministry of Education, Southeast University, we all know, the deterioration factors are all greatly Si Pai-Lou 2#, Nanjing, 210096, China influenced by hygrothermal behavior surrounding Tel/Fax: +86-25-83790530 the mural paintings. High temperature, humid air E-mail: liyonghui@seu.edu.cn; ogurad@archi.kyoto-u.ac.jp and condensation near such paintings will accelerate ( Received October 2, 2013 ; accepted March 11, 2014 ) Journal of Asian Architecture and Building Engineering/May 2014/506 499 5), 6), 7), 8) the risk of biological attack , and wetting and Fig.3., from April 1972 to December 1975. drying cycles inside the chamber greatly increase the 2.2 Equations 9) risk of physical and chemical deterioration , such In this paper, the basic analytical equation is a as detachment of lime plaster from the wall surface, coupled heat and moisture transfer equation, referred to 13), 14) salt deposition, etc. In order to restrain deterioration as Matsumoto M'model and shown in Eqs. (1) and of mural paintings caused by such problems, it is (2), which are based on heat and moisture movement important to investigate environmental factors from in porous materials. various aspects, such as temperature, humidity, the T Heat:    c   r T r  (1) ap Tg g water content of cultural properties, wetting and drying t cycles and so on.   The case study of Takamatsuzuka Tumulus has been Moisture:    gn T (2) w  T 9) 10), 11)  t described by previous papers with 1-D or 2-D numerical analysis, and the effects of post-excavation Here, (c ) is the apparent heat capacity of the ap preservation measures on the hygrothermal behavior material [J/m K], T is temperature [K], is thermal 10) of Takamatsuzuka Tumulus was analyzed . However, conductivity [W/m K], is moisture conductivity as for the research of hygrothermal behavior on the related to water chemical potential gradient (gas surface of the mural paintings, these variables may phase) [kg/ms (J/kg)], is moisture conductivity Tg not be thoroughly predicted by 1-D or 2-D for the related to temperature gradient (gas phase) [kg/ms determination of the location and the degree of the K], is density of liquid water [kg/m ], is water ρ µ deterioration of mural paintings, and a suitable design chemical potential [J/kg], is volumetric moisture method to prevent deterioration has not yet been established. The purpose of this paper is to review the case study of the Takamatsuzuka Tumulus by using a 3-D hygrothermal model, identify the impact of the hygrothermal environment on the deterioration of mural paintings in the underground stone chamber, a s we l l a s p r o po se a f a v o r a b l e d e si g n m e t h o d o f preservation measures for the conservation of mural paintings based on the measured temperature, humidity inside the chamber, and the material characteristics. Fig.1. The Excavation State and the End State of the Excavation 2. Model Description and Methods 2.1 Object Fig.1. shows the temporary conservation facilities d u r i ng a n d a t t he e nd o f t h e e x c a v a t i on i n 1 9 7 2 . About two weeks after the excavation, the south part of the stone chamber was exposed to the outside. Subsequently, a temporary conservation facility, connecting the front of the stone chamber, was erected to maintain the environmental conditions of the south part of the chamber as the same as those prior to its exposure. Soil and a waterproof sheet were applied to cover the south part of the chamber, except for the investigation area inside the stone chamber. The model (Fig.2.) shows a 3-D illustration with the Fig.2. Model of the Excavation State surrounding mound according to the measured size 12) of the Takamatsuzuka Tumulus . The excavated area filled with soil in Fig.2. is the state prior to excavation, while the excavated area exposed to the air refers to the state immediately after the excavation without any conservation measures. First, the authors analyzed the hygrothermal behavior in the stone chamber when the preservation measures were applied immediately after excavation, namely, a temporary shelter (2.75 m in width, 7.5 m in length, and 4.5 m in height) with a plastic corrugated roof erected in front of the excavated area. The exposed southern part of the chamber was Fig. 3. Model of the Excavation State and Diagram of covered with soil and a waterproof sheet as shown in Preservation Measures after Excavation 500 JAABE vol.13 no.2 May 2014 Yonghui Li 3 3 2 content [m /m ], g is gravity acceleration (9.8 [m/s ]), For the air in the stone chamber, heat and moisture is moisture conductivity related to water chemical balance equations are applied, in which one particle potential gradient [kg/m s J/kg)], is moisture indicates indoor air, as shown in (10) and (11): conductivity related to temperature gradient [kg/m s K]. T bo Heat: TT q  q  (10)  o noc sol b From this point, a series of subscripts and superscripts x will be used in the equations. Their meanings are: m1 p Moisture: cV S  p p cV N p p   (11) r  j mj j r r r b r subscript j is the surface of the soil, o is outdoor, t j1 (subscript r is in the stone chamber), subscript Sat Here, c is the volumetric heat capacity of air [J/ stands for Saturated, subscript l is Moisture in the liquid 3 2 m K], α is the moisture transfer coefficient [kg/m / phase, subscript g is moisture in the gas phase, subscript s Pa], S is the area of the wall surface [m ], V is the air b is the temporary shelter, subscript s is the surface in volume in the stone chamber [m ], N is air change rate contact with the air, superscript bi is inside surface of [1/s], c' is the moisture capacity of air [kg/m Pa]. the temporary shelter, superscript bo is outside surface For the air in the temporary shelter, heat and of the temporary shelter, superscript bs is ground moisture balance equations are applied, in which one surface in contact with the air in the temporary shelter. particle indicates indoor air; however, since the wall The relationship between water chemical potential μ of the shelter is damp proof, only heat behavior is and water vapor pressure p is as follows: considered. The equations are as follows: mm 23 T bs bs bi bi Heat: cV  S TT S  TT   R T lnp p  (3)    b  jj j b jj j b v sat t j 11 j (12) c V N T T c VN  T T bb o b r r r b Here, R is the universal gas constant for water vapor m2 [Pa m /kg K], P is the water vapor pressure [Pa]. p bs bs cV S  p p cV N p p Moisture:   b  j mj j b b b o b The ground surface of the surrounding mound is t j1 (13) treated as a bare area without considering the adjacent   cV N  p p rr r b bamboo forest. Combining temperature and water 2.3 Method chemical potential, the heat and moisture flux on the The stone chamber of Takamatsuzuka Tumulus boundary of the bare ground surface is as follows: consists of a single-layered tuff wall, approximately Heat:  (4)   r TT   r    q  q 0.6 m thick, which is surrounded by sandy clay T o s  o s sol noc  T  loam. Researchers have measured or calculated    rr     15), 16) Tg g  n n the equilibrium moisture content , moisture s s conductivity and thermal conductivity of the tuff and    T ''  (  )(  TT  )J  gn  Moisture: 17),  o sT o ss j T (5)    nn sandy clay loam of the Takamatsuzuka Tumulus   s s 18 ), 19) . T h e de t a i l e d d a t a use d a s t h e i npu t for t h e Here, is heat transfer coefficient [W/m K], r is a 10) model can be found in the author's previous paper . heat of gas/liquid phase change [J/kg], is moisture As the outdoor climate conditions, the authors use transfer coefficient related to temperature gradient [kg/ the data collected by Nara Local Meteorological 2 ' m /s K], is moisture transfer coefficient related to a 20) Observatories , from 1972 to 1975, including water chemical potential gradient [kg/m /s (J/kg)], q sol external temperature, air relative humidity, global is solar radiation [W/m ], q is nocturnal radiation [W/ noc solar radiation, precipitation and nocturnal radiation. 2 2 m ], J is rainfall [kg/m /s]. An explicit control volume method is adopted for The heat and moisture flux on the boundary of the the calculations with a time step of 30 seconds. In surface of the inner walls of the stone chamber is calculating the environmental conditions in the state expressed as follows: of emergency preservation measures following the   r TT  r    excavation of the mural paintings, the initial conditions Heat: T rs  r s of the model were determined by the relevant annual  T  (6)   rr   Tg g  nn c y c l e d a t a o f t h e y e a r p r i o r t o e x c a v a t i o n . T h e s s conditions for the calculation of the period from March    T '' (  ) (TT )  gn  6 to April 1 are shown in Fig.2. (the excavated place Moisture: (7)  r s Tr s  j T  nn  s s exposed to the air). The calculation of the period after The heat boundary condition of the inside surface of April 1 was conducted according to preservation the temporary shelter is as follows: measures as shown in Fig.3. Fig.4. shows the region of calculations and the boundary conditions. Boundary T bi  TT  (8)  conditions applied in the model for the ground level bb x and the inner surfaces of the stone chamber are of the The heat boundary condition of the outside surface third period, i.e. after April 1. At the bottom of the of the temporary shelter is as follows: calculation region, the boundary conditions refer to the first kind of boundary conditions (temperature is T bo  TT q  q  (9)  o noc sol b 14.6°C and water chemical potential is -7 J/kg). In x JAABE vol.13 no.2 May 2014 Yonghui Li 501   addition, the setting condition in the temporary shelter after excavation has been mentioned in the author's 10) previous paper . Fig.4. The Illustration of the Calculation Region and the Boundary Conditions 3. Model Validation 21) The analytical and measured values of indoor temperatures from 1972 to 1973 are both indicated in Fig.5.(a). The results show that the calculated annual average and phase difference of the indoor temperature are in good agreement with the observed data, except for the annual amplitude where the calculated values are smaller than the measured ones. The measured Fig.5. Comparison between Calculated and Measured temperature in the stone chamber is 13.6°C ± 2.8°C Temperature and Relative Humidity in the Stone Chamber (amplitude), while the calculated value is 13.5°C ± 2.5°C (amplitude). It is postulated that the three- time, Fig.6.b) shows low moisture content on the inner dimensional analytical model can reliably estimate surface of the south wall and the ceiling as well as both the temperatures inside the stone chamber. As for the east and west walls. Fig.6.(b) shows the lowest humidity, the calculated value is as high as 99%, moisture content of the surfaces of the stone chamber, as shown in Fig.5.(b), while the measured value is 3 3 which is 0.14 (m /m ) while the moisture content of constant at 95% RH (higher after opening the stone 3 3 other parts is 0.25 (m /m ). This is due to the external chamber for investigation). Considering the accuracy air reaching the south wall and the nearby ceiling. In of the measuring instruments, the three-dimensional other words, the temperature of the exposed part of model is considered as reliable in estimating the the chamber is higher than other parts during summer relative humidity. The following section discusses and lower in winter. Thus, the presence of external air the hygrothermal behavior in the underground stone causes a drying and wetting cycle throughout the year. chamber predicted by the model. Fig.7. shows daily minimum moisture content on the surfaces inside the stone chamber during the period 4. Results of 3-D Model Calculations from 1972 to 1975. The "daily minimum moisture 4.1 The Degree of Drying of the Surfaces Inside the content on the surface" is an index that reflects the Chamber extent of drying in the whole chamber. It can be seen Fig.6. shows the temperature and moisture content from Fig.7. that the volumetric moisture content of distribution on the interior surfaces of the stone 3 3 interior surfaces in the chamber falls to 0.13 (m /m ) chamber at 12:00 a.m. on August 15, 1973. As shown and drops every year. in the figure, the temperatures of the south, east and As mentioned above, repeated wet–dry cycles on the west wall and its nearby ceiling are around 15.5°C, wall surfaces enhance the damage to the lime plaster whereas the temperatures of the north wall and its layer. When the emergency preservation measures nearby ceiling, the east and the west walls as well as were used after the excavation, there was a risk of the floor are about 14.5°C. The temperature difference exfoliation of the mural paintings caused by dryness on the interior surfaces of the stone chamber is about near the corner around the ceiling, the south wall of 1.0°C (Fig.6.(a)). The maximal temperature inside the the chamber and a potential danger of water vapor chamber appears on the surface of the south wall and condensation on the north side of the chamber. the nearby ceiling, and the water in those areas will likely undergo an evaporating process. At the same 502 JAABE vol.13 no.2 May 2014 Yonghui Li Fig.6. Temperature and Moisture Content Distributions on Interior Surfaces of the Stone Chamber (12:00 a.m. August 15, 1973) Fig.7. The Daily Minimum Moisture Content on the Interior Fig.8. The Condensation Area and the Total Condensation Days Surfaces of the Stone Chamber from April 1972 to December 1975 Occurred on Interior Surfaces of the Stone Chamber (1973) and the pore air is near 99.999% RH. This definition of condensation is only used to evaluate the risk of severe condensation. The "area of condensation" is the ratio of the condensation area to that of the total indoor surface area when such condensation occurs (Fig.8.). This condensation occurred on the north wall, the ceiling, the east wall, the west wall and the adjacent floor. In 1973, the days of condensation at the lower part of the north wall and its nearby floor were the highest, reaching 90 days or more. Fig.9. shows the daily average of the area of dew condensation on the surfaces inside the stone chamber during the period from 1972 to 1975. It can be seen that Fig.9. Condensation Occurred on the Interior Surfaces of the the area of condensation in the stone chamber increases Stone Chamber from April 1972 to December 1975 from mid-June to the beginning of November. This is a seasonal occurrence every year with the maximum 4.2 The Extent of Condensation on the Surfaces area of condensation reaching 25% of the area. From Inside the Chamber the perspective of control of biological attack, it is easy Fig.8. shows the condensation area on the interior to accelerate the risk of such attack appearing in those surfaces and the number of condensation days during areas. the year 1973. In this study, condensation is assumed to occur when the water chemical potential reaches -5J/kg JAABE vol.13 no.2 May 2014 Yonghui Li 503 5. Discussions 5.1 Discussions on Adopted Preservation Methods after the Takamatsuzuka Tumulus was Excavated W he n e m e rg e n c y pre se r va t i o n m e a sure s we r e a d o p t e d a f t e r t h e Ta ka m a t su z u k a Tu m u l u s wa s excavated, the temperature control of the interior ambient did not solve the problems concerning the variation of hygrothermal conditions on the chamber surfaces. While the difference of the air temperature was small, the differences resulting from the interaction of thermal mass and the exposure conditions caused a wetting and drying cycle. From mid-June to the Fig.11. The Daily Maximum Temperature Difference of the beginning of November, condensation occurred on Whole Stone Chamber in 1973 the north wall side with its surrounding ceiling, the east wall, the west wall and the adjacent floor, while 5.2 Discussions on Suitable Preservation Methods evaporation continued on the south wall. The computer Thermal insulation is applied to ensure the favorable model shows that, in the worst case scenario, the stone preservation conditions postulated in the previous chamber will lose 50% water content compared with se c t i on. T he sha pe a nd l oc a t i on of t he t he rm a l the saturated condition, and in another worst case insulation layer is shown in Fig.12., with the increase scenario, condensation will cover 25% of the area of of the thermal resistance of the covered insulation the chamber. In other words, the drying and wetting 2 2 layer from 0.5 [m K/W] to 16.7 [m K/W]. Fig.13. cycle continues inside the chamber throughout the shows the annual maximum temperature difference year. Fig.10. shows the temperature distribution of the of the whole stone chamber in 1973 in relation to horizontal section (central height of the chamber) of thermal performance of the insulation layer (zero the Takamatsuzuka Tumulus on February 15, 1973 and insulation representing the excavation state in 1972). August 15, 1973 respectively. In winter (Fig.10.(a)), It can be seen that the temperature difference becomes the temperature of the south side of the surrounding smaller as the resistance of the thermal insulation layer mound of the stone chamber is lower than its north increases. side. In summer, (Fig.10.(b)), the temperature of the The authors further calculate the daily minimum south side of the surrounding mound of the stone moisture content and condensation area as shown in chamber is higher than its counterpart. Fig.11. shows Fig.14. in relation to the temperature difference of the the maximum temperature difference of the whole whole stone chamber compared with those shown in stone chamber in 1973. One can observe that the Fig.7. and Fig.9. outside surface temperature is 5.4°C higher than the Fig.14. shows the inverse relation between the stone chamber in winter, and 7.2°C higher in summer. growing temperature difference of the whole stone In other words, the emergency preservation measures chamber and the descending minimum moisture produce wetting and drying cycles to the chamber, content. Yet when the temperature difference is less resulting in further deterioration of the mural paintings. than 4°C, the area of condensation will become zero. Considering the conservation of mural paintings in This will happen when the thermal resistance of the the underground chamber, one must ensure that the covered insulation is about 7.0 [m K/W] (Fig.13.). difference between summer and winter has a limited Thus, favorable preservation of the mural paintings effect on the chamber conditions and maintain the in the Takamatsuzuka Tumulus requires covering the indoor temperature in the chamber as low as possible exposed stone chamber by insulated material with to inhibit fungal growth. thermal resistance of no less than 7.0 [m K/W]. Fig.12. The Position of Thermal Insulation Material in the 3-D Fig.10. The Temperature Distribution of the Horizontal Section Model (Red is the Thermal Insulation Material, and Yellow (Central Height of the Chamber) of the Takamatsuzuka Tumulus Represents the Stone Chamber) 504 JAABE vol.13 no.2 May 2014 Yonghui Li Acknowledgment This study was supported by JSPS (Japan Society for the Promotion of Science) KAKENHI (20560549), and NSF (National Science Foundation) of China (Grant No. 51108072 and Grant No. 51138002). The authors woul d l i ke t o t ha nk Prof. Ma rk Bom be rg for t he discussions concerning the choice of the conservation methods. References 1) Hejazi, M. (2008) The risks to cultural heritage in western and central Asia, Journal of Asian Architecture and Building Engineering, 7(2), pp.239-245. Fig.13. The Maximum Temperature Difference of the Whole 2) Matsumiya, K; Oikawa, K. (2013) Quantitative Analysis of Fire Stone Chamber in 1973 when the Thermal Resistance of the Spreading Potential for Surrounding Areas of Cultural Properties Covered Material Changes i n Kyot o Ci t y, Journa l of Asi a n Arc hi t e ct ure a nd Bui l ding Engineering, 12(2), pp.269-276. 3) Li, YH.; Xie, HR.; Wang JG.; Li XJ. (2013) Experimental Study of the Isothermal Sorption Properties of Late Qing and 1980s Grey Bricks in Wujiang, Suzhou, China. Frontiers of Architectural Research, 2(4), pp.483-487. 4) Shi X.; She W.; Zhou HL.; Zhan YS.; Shi F.; Chen W. (2012) Thermal upgrading of Hui-style vernacular dwellings in China using foam concrete. Frontiers of Architectural research, 1(1), pp.23-33. 5) Takatori, K., Takatori M., Kumeda Y., Kigawa R and Sano, C. (2010) Physiological and Biological Studies on the Growth of Fungi Isolated from Takamatsuzuka Tumulus (in Japanese), Science for Conservation, No. 49, pp.61-71. 6) Johansson, S., Wadsö, L., Sandin, K. (2010) Estimation of mould growth levels on rendered facades on surface relative humidity and surface temperature measurements, Building and Environment, Fig.14. The Maximum Area of Condensation and Minimum 45(5), pp.1153-1160. Moisture Content on the Interior Surfaces of the Stone Chamber 7) K. Sedlbauer. (2002) Prediction of mould growth by hygrothermal in 1973 when the Thermal Insulation Layer is Applied calculation, Journal of Building Physics, 25 (4), pp.321-336. 8) Gock, MA., Hocking, AD., Pitt, JI. and Poulos, PG. (2003) 6. Conclusions Influence of temperature, water activity and pH on growth of T hi s pa pe r de ve l ope d a 3-D m ode l of t he some xerophilic fungi, Source: International Journal of Food Takamatsuzuka Tumulus after excavation, based on the Microbiology, 81(1), pp.11-19. changed shape of the tumulus. The agreement between 9) Ogura D., Inuzuka M., Hokoi S., Ishizaki T., et al. (2008) Control the measured and predicted values of air temperature of temperature and humidity surrounding the stone chamber of Takamatsuzuka Tumulus during its dismantlement, International and relative humidity in the stone chamber by 3-D Symposium on the Conservation and Restoration of Cultural model was sufficient. The authors were therefore, Property, Tokyo, 2008, pp.75-81. able to use the 3-D model to predict the hygrothermal 10) L i YH., Ogu ra D., Ho k oi S. , Ish i z a k i , T. (2 01 2) E ffe c t s o f behavior of the underground stone chamber, and emergency preservation measures following excavation of mural ana lyze t he loca ti on and degre e of wa te r vapor paintings in Takamatsuzuka Tumulus, Journal of Building Physics, 36 (2), pp.117-139. condensation, wetting and drying cycles on the interior 11) Li YH., Ogura D., Hokoi S., Ishizaki, T. (2012) Numerical analysis surfaces of the chamber. Ultimately, the model enabled of heat behavior of stone chamber after excavation, Frontiers of the authors to propose a favorable preservation method Architectural Research, Frontiers of Architectural Research, 1(4), for the Takamatsuzuka Tumulus. The findings of this pp.375-379. research show that: 12) Archaeological Institute of Kashihara (Nara prefecture, Japan) Edit, (1972) Survey interim report of mural painting in The temperature difference of the whole protected Takamatsuka Tumulus, (in Japanese), pp.20-23. object is the main reason influencing the drying and 13) Matsumoto, M. (1978) Simultaneous heat and moisture transfer condensing process that occurred on the surfaces of and moisture accumulation in building materials, Dissertation, mural paintings. Kyoto University, Kyoto (in Japanese). To preserve the mural paintings in the underground 14) Matsumoto M, Hokoi S, Hatano M. (2001) Model for simulation of freezing and thawing processes in building materials [J]. chamber, the temperature difference of the whole Building and Environment, 36(6), pp.733-742. chamber should be kept to less than 4°C. 15) Khalil, M. and Ishizaki, T. (2007). Moisture Characteristic Curves A favourable method for the conservation of mural of the Soil of Takamatsuzuka Tumulus, Science for Conservation, paintings in the Takamatsuzuka Tumulus is to cover the No. 46, pp.13-20. exposed stone chamber by a layer of thermal insulation 16) Khalil, M. and Ishizaki, T. (2008) Moisture Characteristic Curves of Tuff Breccia Stone, Science for Conservation, No. 47, pp.11-19. material, positioned as shown in Fig.12. with thermal resistance of no less than 7.0 [m K/W]. JAABE vol.13 no.2 May 2014 Yonghui Li 505 17) Ishizaki, T., Miura, S., Inuzuka, M. and Khalil, M. (2006) Examination and Choice of Cooling Methods for the Mound of Takamatsuzuka Tumulus as Protective Measures against Fungi in the Stone Chamber (in Japanese), Science for Conservation, No. 45, pp.59-68. 18) Ishi z a ki , T., Inuz uka , M. a nd Mi m ura, M. 2006. Study on Geotechnical Properties and Moisture Regime of Takamatsuzuka Tumulus (in Japanese), Science for Conservation, No. 45, pp.69- 19) Kodai, K. 1984. The graph of base rock water permeability (in Japanese), Bulletin of the Geological Survey of Japan, 35(9), pp.419-434. 20) Japan Meteorological Business Support Cente r , Japan M eteorological A gency, (2007) Weather databas e ground observation, (CD-ROW). 21) Agency of Cultural Af fairs. (1987) National T reasure Takamatsuzuka Tumulus Preservation and Maintenance (in Japanese), pp.36-38. 506 JAABE vol.13 no.2 May 2014 Yonghui Li http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Asian Architecture and Building Engineering Taylor & Francis

Predicting Hygrothermal Behavior of an Underground Stone Chamber with 3-D Modeling to Restrain Water-Related Damage to Mural Paintings

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Taylor & Francis
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© 2018 Architectural Institute of Japan
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1347-2852
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DOI
10.3130/jaabe.13.499
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Abstract

Cultural properties are variously influenced by their surrounding environmental conditions. One of the reasons for the deterioration of mural paintings in the Takamatsuzuka Tumulus was the humid microclimate on their surface. In order to control the deterioration of mural paintings caused by such problems, it is important to investigate the environmental factors from various aspects, such as the temperature, humidity, water content of cultural properties, wetting and drying cycles and so on. As for the research concerning hygrothermal behavior on mural paintings, these variables may not be thoroughly predicted by 1-D or 2-D for determination of the location and degree of the deterioration of mural paintings. This paper shows how a 3-D hygrothermal model developed with a view to analyzing the preservation measures that allow quantifying of the degree of drying and condensing processes occurred on the surfaces of the underground chamber. The findings show that for the purpose of preserving mural paintings within the underground chamber, the temperature difference between the surrounding mound and the protected object should be kept as constant as can be practically achieved. This method is applicable for estimating the effects of preservation measures for the conservation of other mural paintings. Keywords: hygrothermal behavior; 3-D modeling; condensation; dryness; water-related damage; Takamatsuzuka Tumulus 1. Introduction decided to preserve the mural paintings at the site. There are many important mural paintings in For this purpose, a climate chamber and conservation underground chambers in Asian countries. Among facilities were constructed in 1976 in order to keep the them, the under ground stone chamber of the mural paintings under the same conditions as when Takamatsuzuka Tumulus is well known for its beautiful they were found. During the period from the discovery paintings. The tumulus was discovered on 21 March of the mural paintings in 1972 to the beginning of 1972 in Asuka village (N: 34.47, E: 135.82), Nara the operation of the conservation facility in 1976, an Prefecture, Japan. The tumulus is a circular mound emergency preservation measure including a temporary with a diameter of 19 m and height of 5 m (Fig.1.(a)). shelter erected on the south side of the tumulus (see The stone chamber, which is 1.03 m wide, 1.13 m Fig.1.(b)) was adopted to control the hygrothermal high, and 2.65 m deep, is buried within a mound of soil environment in the stone chamber. Then, because of about 3 m below ground level. The mural paintings the difficulties in preserving the mural paintings on- were designated as national treasures in 1974 and site, the stone chamber was dismantled (from October a committee of specialists was organized for their 2006 to A ugus t 2007) to res tore the paintings in conservation. After extensive discussion, the committee temporary restoration facilities. In recent years, Asian scholars have begun to pay more and more attention to the research of cultural *Contact Author: Yonghui Li, Dr. Eng., Lecturer, 1), 2), 3), 4) heritage protection . The conservation of mural Key Laboratory of Urban and Architectural Heritage Conservation paintings in natural underground sites is difficult. As of Ministry of Education, Southeast University, we all know, the deterioration factors are all greatly Si Pai-Lou 2#, Nanjing, 210096, China influenced by hygrothermal behavior surrounding Tel/Fax: +86-25-83790530 the mural paintings. High temperature, humid air E-mail: liyonghui@seu.edu.cn; ogurad@archi.kyoto-u.ac.jp and condensation near such paintings will accelerate ( Received October 2, 2013 ; accepted March 11, 2014 ) Journal of Asian Architecture and Building Engineering/May 2014/506 499 5), 6), 7), 8) the risk of biological attack , and wetting and Fig.3., from April 1972 to December 1975. drying cycles inside the chamber greatly increase the 2.2 Equations 9) risk of physical and chemical deterioration , such In this paper, the basic analytical equation is a as detachment of lime plaster from the wall surface, coupled heat and moisture transfer equation, referred to 13), 14) salt deposition, etc. In order to restrain deterioration as Matsumoto M'model and shown in Eqs. (1) and of mural paintings caused by such problems, it is (2), which are based on heat and moisture movement important to investigate environmental factors from in porous materials. various aspects, such as temperature, humidity, the T Heat:    c   r T r  (1) ap Tg g water content of cultural properties, wetting and drying t cycles and so on.   The case study of Takamatsuzuka Tumulus has been Moisture:    gn T (2) w  T 9) 10), 11)  t described by previous papers with 1-D or 2-D numerical analysis, and the effects of post-excavation Here, (c ) is the apparent heat capacity of the ap preservation measures on the hygrothermal behavior material [J/m K], T is temperature [K], is thermal 10) of Takamatsuzuka Tumulus was analyzed . However, conductivity [W/m K], is moisture conductivity as for the research of hygrothermal behavior on the related to water chemical potential gradient (gas surface of the mural paintings, these variables may phase) [kg/ms (J/kg)], is moisture conductivity Tg not be thoroughly predicted by 1-D or 2-D for the related to temperature gradient (gas phase) [kg/ms determination of the location and the degree of the K], is density of liquid water [kg/m ], is water ρ µ deterioration of mural paintings, and a suitable design chemical potential [J/kg], is volumetric moisture method to prevent deterioration has not yet been established. The purpose of this paper is to review the case study of the Takamatsuzuka Tumulus by using a 3-D hygrothermal model, identify the impact of the hygrothermal environment on the deterioration of mural paintings in the underground stone chamber, a s we l l a s p r o po se a f a v o r a b l e d e si g n m e t h o d o f preservation measures for the conservation of mural paintings based on the measured temperature, humidity inside the chamber, and the material characteristics. Fig.1. The Excavation State and the End State of the Excavation 2. Model Description and Methods 2.1 Object Fig.1. shows the temporary conservation facilities d u r i ng a n d a t t he e nd o f t h e e x c a v a t i on i n 1 9 7 2 . About two weeks after the excavation, the south part of the stone chamber was exposed to the outside. Subsequently, a temporary conservation facility, connecting the front of the stone chamber, was erected to maintain the environmental conditions of the south part of the chamber as the same as those prior to its exposure. Soil and a waterproof sheet were applied to cover the south part of the chamber, except for the investigation area inside the stone chamber. The model (Fig.2.) shows a 3-D illustration with the Fig.2. Model of the Excavation State surrounding mound according to the measured size 12) of the Takamatsuzuka Tumulus . The excavated area filled with soil in Fig.2. is the state prior to excavation, while the excavated area exposed to the air refers to the state immediately after the excavation without any conservation measures. First, the authors analyzed the hygrothermal behavior in the stone chamber when the preservation measures were applied immediately after excavation, namely, a temporary shelter (2.75 m in width, 7.5 m in length, and 4.5 m in height) with a plastic corrugated roof erected in front of the excavated area. The exposed southern part of the chamber was Fig. 3. Model of the Excavation State and Diagram of covered with soil and a waterproof sheet as shown in Preservation Measures after Excavation 500 JAABE vol.13 no.2 May 2014 Yonghui Li 3 3 2 content [m /m ], g is gravity acceleration (9.8 [m/s ]), For the air in the stone chamber, heat and moisture is moisture conductivity related to water chemical balance equations are applied, in which one particle potential gradient [kg/m s J/kg)], is moisture indicates indoor air, as shown in (10) and (11): conductivity related to temperature gradient [kg/m s K]. T bo Heat: TT q  q  (10)  o noc sol b From this point, a series of subscripts and superscripts x will be used in the equations. Their meanings are: m1 p Moisture: cV S  p p cV N p p   (11) r  j mj j r r r b r subscript j is the surface of the soil, o is outdoor, t j1 (subscript r is in the stone chamber), subscript Sat Here, c is the volumetric heat capacity of air [J/ stands for Saturated, subscript l is Moisture in the liquid 3 2 m K], α is the moisture transfer coefficient [kg/m / phase, subscript g is moisture in the gas phase, subscript s Pa], S is the area of the wall surface [m ], V is the air b is the temporary shelter, subscript s is the surface in volume in the stone chamber [m ], N is air change rate contact with the air, superscript bi is inside surface of [1/s], c' is the moisture capacity of air [kg/m Pa]. the temporary shelter, superscript bo is outside surface For the air in the temporary shelter, heat and of the temporary shelter, superscript bs is ground moisture balance equations are applied, in which one surface in contact with the air in the temporary shelter. particle indicates indoor air; however, since the wall The relationship between water chemical potential μ of the shelter is damp proof, only heat behavior is and water vapor pressure p is as follows: considered. The equations are as follows: mm 23 T bs bs bi bi Heat: cV  S TT S  TT   R T lnp p  (3)    b  jj j b jj j b v sat t j 11 j (12) c V N T T c VN  T T bb o b r r r b Here, R is the universal gas constant for water vapor m2 [Pa m /kg K], P is the water vapor pressure [Pa]. p bs bs cV S  p p cV N p p Moisture:   b  j mj j b b b o b The ground surface of the surrounding mound is t j1 (13) treated as a bare area without considering the adjacent   cV N  p p rr r b bamboo forest. Combining temperature and water 2.3 Method chemical potential, the heat and moisture flux on the The stone chamber of Takamatsuzuka Tumulus boundary of the bare ground surface is as follows: consists of a single-layered tuff wall, approximately Heat:  (4)   r TT   r    q  q 0.6 m thick, which is surrounded by sandy clay T o s  o s sol noc  T  loam. Researchers have measured or calculated    rr     15), 16) Tg g  n n the equilibrium moisture content , moisture s s conductivity and thermal conductivity of the tuff and    T ''  (  )(  TT  )J  gn  Moisture: 17),  o sT o ss j T (5)    nn sandy clay loam of the Takamatsuzuka Tumulus   s s 18 ), 19) . T h e de t a i l e d d a t a use d a s t h e i npu t for t h e Here, is heat transfer coefficient [W/m K], r is a 10) model can be found in the author's previous paper . heat of gas/liquid phase change [J/kg], is moisture As the outdoor climate conditions, the authors use transfer coefficient related to temperature gradient [kg/ the data collected by Nara Local Meteorological 2 ' m /s K], is moisture transfer coefficient related to a 20) Observatories , from 1972 to 1975, including water chemical potential gradient [kg/m /s (J/kg)], q sol external temperature, air relative humidity, global is solar radiation [W/m ], q is nocturnal radiation [W/ noc solar radiation, precipitation and nocturnal radiation. 2 2 m ], J is rainfall [kg/m /s]. An explicit control volume method is adopted for The heat and moisture flux on the boundary of the the calculations with a time step of 30 seconds. In surface of the inner walls of the stone chamber is calculating the environmental conditions in the state expressed as follows: of emergency preservation measures following the   r TT  r    excavation of the mural paintings, the initial conditions Heat: T rs  r s of the model were determined by the relevant annual  T  (6)   rr   Tg g  nn c y c l e d a t a o f t h e y e a r p r i o r t o e x c a v a t i o n . T h e s s conditions for the calculation of the period from March    T '' (  ) (TT )  gn  6 to April 1 are shown in Fig.2. (the excavated place Moisture: (7)  r s Tr s  j T  nn  s s exposed to the air). The calculation of the period after The heat boundary condition of the inside surface of April 1 was conducted according to preservation the temporary shelter is as follows: measures as shown in Fig.3. Fig.4. shows the region of calculations and the boundary conditions. Boundary T bi  TT  (8)  conditions applied in the model for the ground level bb x and the inner surfaces of the stone chamber are of the The heat boundary condition of the outside surface third period, i.e. after April 1. At the bottom of the of the temporary shelter is as follows: calculation region, the boundary conditions refer to the first kind of boundary conditions (temperature is T bo  TT q  q  (9)  o noc sol b 14.6°C and water chemical potential is -7 J/kg). In x JAABE vol.13 no.2 May 2014 Yonghui Li 501   addition, the setting condition in the temporary shelter after excavation has been mentioned in the author's 10) previous paper . Fig.4. The Illustration of the Calculation Region and the Boundary Conditions 3. Model Validation 21) The analytical and measured values of indoor temperatures from 1972 to 1973 are both indicated in Fig.5.(a). The results show that the calculated annual average and phase difference of the indoor temperature are in good agreement with the observed data, except for the annual amplitude where the calculated values are smaller than the measured ones. The measured Fig.5. Comparison between Calculated and Measured temperature in the stone chamber is 13.6°C ± 2.8°C Temperature and Relative Humidity in the Stone Chamber (amplitude), while the calculated value is 13.5°C ± 2.5°C (amplitude). It is postulated that the three- time, Fig.6.b) shows low moisture content on the inner dimensional analytical model can reliably estimate surface of the south wall and the ceiling as well as both the temperatures inside the stone chamber. As for the east and west walls. Fig.6.(b) shows the lowest humidity, the calculated value is as high as 99%, moisture content of the surfaces of the stone chamber, as shown in Fig.5.(b), while the measured value is 3 3 which is 0.14 (m /m ) while the moisture content of constant at 95% RH (higher after opening the stone 3 3 other parts is 0.25 (m /m ). This is due to the external chamber for investigation). Considering the accuracy air reaching the south wall and the nearby ceiling. In of the measuring instruments, the three-dimensional other words, the temperature of the exposed part of model is considered as reliable in estimating the the chamber is higher than other parts during summer relative humidity. The following section discusses and lower in winter. Thus, the presence of external air the hygrothermal behavior in the underground stone causes a drying and wetting cycle throughout the year. chamber predicted by the model. Fig.7. shows daily minimum moisture content on the surfaces inside the stone chamber during the period 4. Results of 3-D Model Calculations from 1972 to 1975. The "daily minimum moisture 4.1 The Degree of Drying of the Surfaces Inside the content on the surface" is an index that reflects the Chamber extent of drying in the whole chamber. It can be seen Fig.6. shows the temperature and moisture content from Fig.7. that the volumetric moisture content of distribution on the interior surfaces of the stone 3 3 interior surfaces in the chamber falls to 0.13 (m /m ) chamber at 12:00 a.m. on August 15, 1973. As shown and drops every year. in the figure, the temperatures of the south, east and As mentioned above, repeated wet–dry cycles on the west wall and its nearby ceiling are around 15.5°C, wall surfaces enhance the damage to the lime plaster whereas the temperatures of the north wall and its layer. When the emergency preservation measures nearby ceiling, the east and the west walls as well as were used after the excavation, there was a risk of the floor are about 14.5°C. The temperature difference exfoliation of the mural paintings caused by dryness on the interior surfaces of the stone chamber is about near the corner around the ceiling, the south wall of 1.0°C (Fig.6.(a)). The maximal temperature inside the the chamber and a potential danger of water vapor chamber appears on the surface of the south wall and condensation on the north side of the chamber. the nearby ceiling, and the water in those areas will likely undergo an evaporating process. At the same 502 JAABE vol.13 no.2 May 2014 Yonghui Li Fig.6. Temperature and Moisture Content Distributions on Interior Surfaces of the Stone Chamber (12:00 a.m. August 15, 1973) Fig.7. The Daily Minimum Moisture Content on the Interior Fig.8. The Condensation Area and the Total Condensation Days Surfaces of the Stone Chamber from April 1972 to December 1975 Occurred on Interior Surfaces of the Stone Chamber (1973) and the pore air is near 99.999% RH. This definition of condensation is only used to evaluate the risk of severe condensation. The "area of condensation" is the ratio of the condensation area to that of the total indoor surface area when such condensation occurs (Fig.8.). This condensation occurred on the north wall, the ceiling, the east wall, the west wall and the adjacent floor. In 1973, the days of condensation at the lower part of the north wall and its nearby floor were the highest, reaching 90 days or more. Fig.9. shows the daily average of the area of dew condensation on the surfaces inside the stone chamber during the period from 1972 to 1975. It can be seen that Fig.9. Condensation Occurred on the Interior Surfaces of the the area of condensation in the stone chamber increases Stone Chamber from April 1972 to December 1975 from mid-June to the beginning of November. This is a seasonal occurrence every year with the maximum 4.2 The Extent of Condensation on the Surfaces area of condensation reaching 25% of the area. From Inside the Chamber the perspective of control of biological attack, it is easy Fig.8. shows the condensation area on the interior to accelerate the risk of such attack appearing in those surfaces and the number of condensation days during areas. the year 1973. In this study, condensation is assumed to occur when the water chemical potential reaches -5J/kg JAABE vol.13 no.2 May 2014 Yonghui Li 503 5. Discussions 5.1 Discussions on Adopted Preservation Methods after the Takamatsuzuka Tumulus was Excavated W he n e m e rg e n c y pre se r va t i o n m e a sure s we r e a d o p t e d a f t e r t h e Ta ka m a t su z u k a Tu m u l u s wa s excavated, the temperature control of the interior ambient did not solve the problems concerning the variation of hygrothermal conditions on the chamber surfaces. While the difference of the air temperature was small, the differences resulting from the interaction of thermal mass and the exposure conditions caused a wetting and drying cycle. From mid-June to the Fig.11. The Daily Maximum Temperature Difference of the beginning of November, condensation occurred on Whole Stone Chamber in 1973 the north wall side with its surrounding ceiling, the east wall, the west wall and the adjacent floor, while 5.2 Discussions on Suitable Preservation Methods evaporation continued on the south wall. The computer Thermal insulation is applied to ensure the favorable model shows that, in the worst case scenario, the stone preservation conditions postulated in the previous chamber will lose 50% water content compared with se c t i on. T he sha pe a nd l oc a t i on of t he t he rm a l the saturated condition, and in another worst case insulation layer is shown in Fig.12., with the increase scenario, condensation will cover 25% of the area of of the thermal resistance of the covered insulation the chamber. In other words, the drying and wetting 2 2 layer from 0.5 [m K/W] to 16.7 [m K/W]. Fig.13. cycle continues inside the chamber throughout the shows the annual maximum temperature difference year. Fig.10. shows the temperature distribution of the of the whole stone chamber in 1973 in relation to horizontal section (central height of the chamber) of thermal performance of the insulation layer (zero the Takamatsuzuka Tumulus on February 15, 1973 and insulation representing the excavation state in 1972). August 15, 1973 respectively. In winter (Fig.10.(a)), It can be seen that the temperature difference becomes the temperature of the south side of the surrounding smaller as the resistance of the thermal insulation layer mound of the stone chamber is lower than its north increases. side. In summer, (Fig.10.(b)), the temperature of the The authors further calculate the daily minimum south side of the surrounding mound of the stone moisture content and condensation area as shown in chamber is higher than its counterpart. Fig.11. shows Fig.14. in relation to the temperature difference of the the maximum temperature difference of the whole whole stone chamber compared with those shown in stone chamber in 1973. One can observe that the Fig.7. and Fig.9. outside surface temperature is 5.4°C higher than the Fig.14. shows the inverse relation between the stone chamber in winter, and 7.2°C higher in summer. growing temperature difference of the whole stone In other words, the emergency preservation measures chamber and the descending minimum moisture produce wetting and drying cycles to the chamber, content. Yet when the temperature difference is less resulting in further deterioration of the mural paintings. than 4°C, the area of condensation will become zero. Considering the conservation of mural paintings in This will happen when the thermal resistance of the the underground chamber, one must ensure that the covered insulation is about 7.0 [m K/W] (Fig.13.). difference between summer and winter has a limited Thus, favorable preservation of the mural paintings effect on the chamber conditions and maintain the in the Takamatsuzuka Tumulus requires covering the indoor temperature in the chamber as low as possible exposed stone chamber by insulated material with to inhibit fungal growth. thermal resistance of no less than 7.0 [m K/W]. Fig.12. The Position of Thermal Insulation Material in the 3-D Fig.10. The Temperature Distribution of the Horizontal Section Model (Red is the Thermal Insulation Material, and Yellow (Central Height of the Chamber) of the Takamatsuzuka Tumulus Represents the Stone Chamber) 504 JAABE vol.13 no.2 May 2014 Yonghui Li Acknowledgment This study was supported by JSPS (Japan Society for the Promotion of Science) KAKENHI (20560549), and NSF (National Science Foundation) of China (Grant No. 51108072 and Grant No. 51138002). The authors woul d l i ke t o t ha nk Prof. Ma rk Bom be rg for t he discussions concerning the choice of the conservation methods. References 1) Hejazi, M. (2008) The risks to cultural heritage in western and central Asia, Journal of Asian Architecture and Building Engineering, 7(2), pp.239-245. Fig.13. The Maximum Temperature Difference of the Whole 2) Matsumiya, K; Oikawa, K. (2013) Quantitative Analysis of Fire Stone Chamber in 1973 when the Thermal Resistance of the Spreading Potential for Surrounding Areas of Cultural Properties Covered Material Changes i n Kyot o Ci t y, Journa l of Asi a n Arc hi t e ct ure a nd Bui l ding Engineering, 12(2), pp.269-276. 3) Li, YH.; Xie, HR.; Wang JG.; Li XJ. (2013) Experimental Study of the Isothermal Sorption Properties of Late Qing and 1980s Grey Bricks in Wujiang, Suzhou, China. Frontiers of Architectural Research, 2(4), pp.483-487. 4) Shi X.; She W.; Zhou HL.; Zhan YS.; Shi F.; Chen W. (2012) Thermal upgrading of Hui-style vernacular dwellings in China using foam concrete. Frontiers of Architectural research, 1(1), pp.23-33. 5) Takatori, K., Takatori M., Kumeda Y., Kigawa R and Sano, C. (2010) Physiological and Biological Studies on the Growth of Fungi Isolated from Takamatsuzuka Tumulus (in Japanese), Science for Conservation, No. 49, pp.61-71. 6) Johansson, S., Wadsö, L., Sandin, K. (2010) Estimation of mould growth levels on rendered facades on surface relative humidity and surface temperature measurements, Building and Environment, Fig.14. The Maximum Area of Condensation and Minimum 45(5), pp.1153-1160. Moisture Content on the Interior Surfaces of the Stone Chamber 7) K. Sedlbauer. (2002) Prediction of mould growth by hygrothermal in 1973 when the Thermal Insulation Layer is Applied calculation, Journal of Building Physics, 25 (4), pp.321-336. 8) Gock, MA., Hocking, AD., Pitt, JI. and Poulos, PG. (2003) 6. Conclusions Influence of temperature, water activity and pH on growth of T hi s pa pe r de ve l ope d a 3-D m ode l of t he some xerophilic fungi, Source: International Journal of Food Takamatsuzuka Tumulus after excavation, based on the Microbiology, 81(1), pp.11-19. changed shape of the tumulus. The agreement between 9) Ogura D., Inuzuka M., Hokoi S., Ishizaki T., et al. (2008) Control the measured and predicted values of air temperature of temperature and humidity surrounding the stone chamber of Takamatsuzuka Tumulus during its dismantlement, International and relative humidity in the stone chamber by 3-D Symposium on the Conservation and Restoration of Cultural model was sufficient. The authors were therefore, Property, Tokyo, 2008, pp.75-81. able to use the 3-D model to predict the hygrothermal 10) L i YH., Ogu ra D., Ho k oi S. , Ish i z a k i , T. (2 01 2) E ffe c t s o f behavior of the underground stone chamber, and emergency preservation measures following excavation of mural ana lyze t he loca ti on and degre e of wa te r vapor paintings in Takamatsuzuka Tumulus, Journal of Building Physics, 36 (2), pp.117-139. condensation, wetting and drying cycles on the interior 11) Li YH., Ogura D., Hokoi S., Ishizaki, T. (2012) Numerical analysis surfaces of the chamber. Ultimately, the model enabled of heat behavior of stone chamber after excavation, Frontiers of the authors to propose a favorable preservation method Architectural Research, Frontiers of Architectural Research, 1(4), for the Takamatsuzuka Tumulus. The findings of this pp.375-379. research show that: 12) Archaeological Institute of Kashihara (Nara prefecture, Japan) Edit, (1972) Survey interim report of mural painting in The temperature difference of the whole protected Takamatsuka Tumulus, (in Japanese), pp.20-23. object is the main reason influencing the drying and 13) Matsumoto, M. (1978) Simultaneous heat and moisture transfer condensing process that occurred on the surfaces of and moisture accumulation in building materials, Dissertation, mural paintings. Kyoto University, Kyoto (in Japanese). To preserve the mural paintings in the underground 14) Matsumoto M, Hokoi S, Hatano M. (2001) Model for simulation of freezing and thawing processes in building materials [J]. chamber, the temperature difference of the whole Building and Environment, 36(6), pp.733-742. chamber should be kept to less than 4°C. 15) Khalil, M. and Ishizaki, T. (2007). Moisture Characteristic Curves A favourable method for the conservation of mural of the Soil of Takamatsuzuka Tumulus, Science for Conservation, paintings in the Takamatsuzuka Tumulus is to cover the No. 46, pp.13-20. exposed stone chamber by a layer of thermal insulation 16) Khalil, M. and Ishizaki, T. (2008) Moisture Characteristic Curves of Tuff Breccia Stone, Science for Conservation, No. 47, pp.11-19. material, positioned as shown in Fig.12. with thermal resistance of no less than 7.0 [m K/W]. JAABE vol.13 no.2 May 2014 Yonghui Li 505 17) Ishizaki, T., Miura, S., Inuzuka, M. and Khalil, M. (2006) Examination and Choice of Cooling Methods for the Mound of Takamatsuzuka Tumulus as Protective Measures against Fungi in the Stone Chamber (in Japanese), Science for Conservation, No. 45, pp.59-68. 18) Ishi z a ki , T., Inuz uka , M. a nd Mi m ura, M. 2006. Study on Geotechnical Properties and Moisture Regime of Takamatsuzuka Tumulus (in Japanese), Science for Conservation, No. 45, pp.69- 19) Kodai, K. 1984. The graph of base rock water permeability (in Japanese), Bulletin of the Geological Survey of Japan, 35(9), pp.419-434. 20) Japan Meteorological Business Support Cente r , Japan M eteorological A gency, (2007) Weather databas e ground observation, (CD-ROW). 21) Agency of Cultural Af fairs. (1987) National T reasure Takamatsuzuka Tumulus Preservation and Maintenance (in Japanese), pp.36-38. 506 JAABE vol.13 no.2 May 2014 Yonghui Li

Journal

Journal of Asian Architecture and Building Engineering – Taylor & Francis

Published: May 1, 2014

Keywords: hygrothermal behavior; 3-D modeling; condensation; dryness; water-related damage; Takamatsuzuka Tumulus

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