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Dynamic thermal performance of three types of unfired earth bricks
Accepted Manuscript Title: Dynamic thermal performance of three types of unfired earth bricks Author: Fayçal El Fgaier, Zoubeir Lafhaj, Emmanuel Antczak, Christophe Chapiseau PII: DOI: Reference:
S1359-4311(15)00929-1 http://dx.doi.org/doi:10.1016/j.applthermaleng.2015.09.009 ATE 7001
To appear in:
Applied Thermal Engineering
Received date: Accepted date:
18-6-2015 4-9-2015
Please cite this article as: Fayçal El Fgaier, Zoubeir Lafhaj, Emmanuel Antczak, Christophe Chapiseau, Dynamic thermal performance of three types of unfired earth bricks, Applied Thermal Engineering (2015), http://dx.doi.org/doi:10.1016/j.applthermaleng.2015.09.009. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Dynamic thermal performance of three types of unfired earth bricks Fayçal El Fgaier1; Zoubeir Lafhaj1*; Emmanuel Antczak2; Christophe Chapiseau3 Ecole Centrale de Lille, Laboratoire de Mécanique de Lille (CNRS UMR 8107), Villeneuve d’Ascq, 59651 Cedex, France 2 Université d’Artois, Technoparc Futura, 62400 Béthune, France 3 Briqueteries du Nord, 9ème Rue, Port Fluvial, Lille, 59003 Cedex, France *Corresponding author. Pr. Zoubeir LAFHAJ Tel./fax: +33 320335365. E-mail address: [email protected]
Highlights
Dynamic thermal performances were examined as function of wall thickness. Earthen wall cannot achieve the required level of building insulation. The ideal thickness ensuring optimum thermal inertia is determined. An earthen wall can achieve the optimum thermal inertia with a 0.3 m of thickness.
ABSTRACT The present work aims at studying the thermophysical properties of three types of unfired earth bricks through experimental investigation, and their dynamic thermal performance (thermal capacity, decrement factor and thermal lag) as a function of wall thickness. The objective is to to determine the ideal thickness of a raw earth wall, built by these bricks, to achieve the optimum values of thermal inertia. These bricks were industrially produced by the Briqueteries du Nord, which is a factory located in the north of France. The process used was the extrusion. The main difference between the three types of bricks is the origin of the soils, which were extracted from various quarries. It were characterized to determine their physical, chemical and geotechnical properties, and to identify its impact on development and production of unfired earth bricks. This work has identified the optimum thickness of the wall built by these unfired earth bricks (It was 0.3 m for two types of bricks and for the other one was 0.4 m). These thickness ensure the greatest heat capacity and a thermal lag between 10 and 12 hours, while taking into account the quantity of bricks necessary for the construction of such a wall and the habitable area.
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Keywords: Unfired earth bricks, Dynamic thermal performance, thermophysical properties, optimum thickness
1. INTRODUCTION The need to reduce CO2 emissions and to find more sustainable construction materials constitutes nowadays a major economic and ecological challenge. Earthen construction can contribute to reduce environmental problems. In fact, raw earth is one of the most widely used building materials in human history. It is estimated that almost a third of the world’s population lives in some type of earthen dwelling. It is one of the oldest building materials, used in many different ways around the world for centuries. Approximately 50% of the population of developing countries, the majority of rural populations, and at least 20% of urban populations live in earth homes (Houben and Guillaud, 1994). Unfortunately, this building material has been ignored for many years; this is due to the fascination for modern materials such as concrete, brick or steel. Second, it is due to the lack of international standards to evaluate the different products. Only some national reference documents and codes are used in the earth construction around the world, as mentioned by (Delgado and Guerroro, 2007). During the last few years, a growing interest has been appeared for earth as a sustainable material, and then has been studied in the engineering laboratories around the world in the aim of the certification of earth building products. The reason for this interest is that it presents several advantages that allows it to be a current response to energy and climate issues. Indeed, raw earth is an abundant natural and recyclable resource. It is low embodied energy building material, compared to fired clay bricks and concrete. It reduces the amount of energy required for construction as well as transportation needs (Morel et al., 2001). PachecoTorgal and Jalali (2012) have presented also the environmental benefits of earth construction. It includes a review about economic issues, non-renewable resource consumption, waste generation, energy consumption, carbon dioxide emissions and indoor air quality. Furthermore, Dethier and Eaton (2002) has described raw earth as the material of the future, with properties that are fully compatible with a modern lifestyle and attractive architectural design. Multiple research studies have outlined the economic benefits of earthen construction while reducing both the energy required to manufacture these products and environmental impact (Morel et al., 2001; Chel and Tiwari, 2009; Pittet and Kotak, 2009; Shukla et al., 2009; Zami and Lee, 2010). Moreover, the heat storage and humidity regulation properties of this material are additional benefits of earthen construction. They contribute to the thermal comfort and healthy environment of buildings. The thermal performance of these building materials have been studied in different research papers. In fact, Taylor and Luther (2004) worked on the suitability of rammed earth wall construction as an effective building envelope in regard to its thermal performance. Another study conducted by Parra-Saldivar and Batty (2006) presented the thermal performance of adobe constructions and the impact of various factors on its dynamic response. Also, Martin et al. (2010) compared the thermal behaviour of existing homes made of different construction materials in Spain, such as rammed earth, stone and wood. He demonstrated that traditional houses, built by the rammed earth technique, have a more pleasant indoor environment for the occupants and lower energy consumption compared to other construction techniques, mainly due to their thick walls that provide high thermal inertia. These previous studies have contributed to prove the thermal qualities of earth materials.
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However dynamic thermal performances (thermal capacity, decrement factor and thermal lag) of these materials have not studied as a function of wall thickness. In this context, this work presents an experimental and theoretical study to evaluate the thermal behaviour of three types of unfired earth bricks produced by the Briqueteries du Nord Company. The experimental study consists of measuring the thermal performance of these non-stabilised bricks, which the fabrication method and the utilised raw material are different. The dynamic thermal characteristics were determined as a function of wall thickness. The work presented in this paper aimed to determine the ideal thickness of a raw earth wall to achieve the optimum values of thermal inertia of such walls. Optimum thickness is a thickness that ensures the greatest heat capacity and a thermal lag between 10 and 12 hours, taking into account the quantity of bricks necessary for the construction of such a wall and the habitable area. In fact, Optimum thickness is defined linked to thermal inertia in this work. Heat capacity and thermal lag are very important characteristics to determine the heat storage capabilities of unfired earth bricks. An optimum thickness of wall can delay heat flow through the building envelope by as much as 10−12 hours, producing a warmer house at night in winter and a cooler house during the day in summer ((Ulgen, 2002; Taylor and Luther, 2004; Asan, 2006). 2. MATERIALS AND METHODS The Briqueteries du Nord company produces three types of unfired earth bricks (A, B and C). The differences between these three types of bricks derive mainly from the fabrication method and the utilised raw material. For the production of bricks (A) and (B), the shaping process is based on a vacuum extruder that produces a continuous bar, which is shaped in a metal mould. The raw bricks are then dried in chambers with controlled temperature and humidity. However, bricks (C) are produced according to artisanal techniques. It is shaped using a vertical mixer and a wooden mould. The brick surface is smoothed by water. The bricks are then stacked on carts by a robot and conveyed to drying tunnel with controlled air temperature and humidity. 2.1. Identification of soils properties The three different raw materials used in the manufacture of bricks were sampled from three company quarries, located in the north of France. The sampling, preparation and treatment method was identical for all three samples in order to enable their comparison. The samples' characterisation was intended to identify and determine their physical, chemical and geotechnical properties. Identification tests were used to classify the samples and understand the impact of their characteristics on development and production of unfired earth bricks, as well as the behaviour of these products in their utilization in construction. They were designated by A, B and C. The main physicochemical and geotechnical characterisation tests were performed on the three samples according to recommendations and international standards. 2.1.1. Particle Size Distribution Particle size distribution was determined using a wet sieving and a sedimentation test, according to standard (XP CEN ISO/TS 17892-4, 2005). It presents one of the main criteria in the selection of the suitable technique for earth construction (Delgado and Guerrero, 2007). Figure 1 shows the grain size distribution for the three selected soils used for brick manufacturing in this study. The grading curves show that the three samples are primarily fine soils. Indeed, they contain
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more than 10% fines (particles that pass through a 0.063 mm sieve). Soils A and B contain a significant amount of fine particles accounting for almost 95% of total mass. According to the distribution of granular fractions defined by standard (NF EN ISO 14688-1, 2003), the results indicated that the sample A consisted primarily of a fraction of 6% clay, 8% fine silt, 20% medium silt, 61% coarse silt and 5% sand. The soil B was a slight variation of the soil A, while the sample C contained a larger quantity of sand (15%). 2.1.2. Plasticity Atterberg limits were determined using a standard method for measuring liquid and plastic limits described in NF P94-051 (1993). Table 1 illustrates the Atterberg limits obtained for the three different soils (A, B, C). Plasticity index was also reported on this table.
According to the obtained results, the three soils have a different behavior depending on the moisture content. It can be observed that soils (A) and (B) have a high plasticity index value, which classifies them in the category of plastic soils. However, the low plasticity value of the soil (C) (PI = 3) indicates that the sample has weak plasticity. The main factors accounting for the behaviour of these soil are their low clay content and the abundance of quartz. 2.1.3. Chemical and mineralogical composition The mineralogy of the different soils was determined using X-Ray Diffraction (XRD) analysis (figure 2). The diffractogram of the soil (A) showed that it basically consisted of quartz, kaolinite, aluminosilicates and traces of illite and pyrite. The presence of kaolinite in the sample contributes to good shaping and drying properties of products (Kornmann, 2007). In contrast, the mineralogical composition of the soil (B) includes montmorillonite, which causes difficulties during drying due to significant shrinkage and capillary retention. The soil (C) consisted of a high proportion of quartz resulting in a relatively low plasticity as has been demonstrated, and the occurrence of a texture-layering phenomenon. The chemical composition of the samples was determined by X-Ray Fluorescence (XRF) technique. The mass percentages of oxides in the samples and the loss on ignition (LOI) data are presented in Table 2. The soil (A) contained a significant amount of silica, primarily from the alumina silicates and the quartz. It also showed a high concentration of Al2O3, generally related to clayey silicates, which contributes to good plasticity results (Kornmann, 2007). Other trace oxides (Mg, Na, Ti, etc.) have been detected in the chemical analysis of the sample. However, the soil (B) contained a smaller amount of silica and a larger amount of iron oxides, whereas silica and alumina were predominant in the soil (C). 2.1.4. Specific surface and SEM microscopic analysis Specific surface presents an important role in the characterisation of clayey materials. It enables understanding different soil behaviours such as shrinkage and swelling, as well as cation exchange capacities. It was determined through two adsorption techniques: Methylene blue method and Brunauer, Emmett and Teller (BET) Method. The obtained results (see table 3) show that the specific surface area is influenced by the measuring method. In fact, the methylene blue test consists in measuring the adsorption capacity and activity of the clayey fraction of samples, as specified in French standard (NF P94-068, 1998). It is used
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to determine the total ion exchange surface between the clayey fraction and the molecules of methylene blue. It basically includes the external surface between the clayey particles, and the internal surface corresponding to the interlayer space. The total volume of methylene blue solution (VBS) necessary to achieve total adsorption is provided in Table 3 for the different samples. The specific surface can be calculated according (Santamarina et al., 2002). Nevertheless, The BET Method is used to determine the volume of dinitrogen (N2) adsorbed by the sample at low temperature. The test principle is based on the theory of multilayer isothermal gas adsorption developed by Brunauer, Emmett and Teller (BET) in 1983 (Brunauer et al., 1983). This technique allows measuring the external surface area only, since the utilised gas cannot penetrate the layers of clay. For this test, we used Micromeritics ASAP 2010 instrumentation. The obtained results show that the specific surface area is influenced by the measuring method. Thus, the specific surface areas of soils (A) and (B) measured by the BET method were close to each other. However, based on the methylene blue method, the specific surface of the sample (B) produced a larger internal surface than (A), and therefore has a larger water or water vapour adsorption capacity, which subsequently can significantly affect mechanical behaviour (swelling problem). The methylene blue method was therefore used to determine the actual specific surface of these materials, in contrast to the BET method. The sample (C) had a smaller specific surface than the former two samples, primarily due to its microstructure. The difference in texture between the different studied samples is illustrated in Figure 3 by means of scanning electron microscopy (SEM) images. It show that soils (A) and (B) have a compacted microstructure, with the presence of some pores and cracks in the structure. The particle shape is poorly defined. It can be observed that the soil (C) has a discontinuous structure and a more open texture, with the presence of individual plates where the voids are more visible and connected.
2.2. Methods 2.2.1. Thermal conductivity and specific heat capacity The thermal conductivity (λ) of the bricks was determined based on standard NF EN 12664 (2001). The method consists in simultaneously measuring the heat flow and temperature on both faces of a sample subjected to a temperature gradient generated by two exchanger plates. The sample and flow meters assembly is surrounded by an insulating belt so as to limit the lateral heat flow losses and ensure a unidirectional flow in the central measurement area. The test apparatus used in this method is presented in Figure 4. Another element that characterises the thermal properties of materials is the specific heat capacity (c). The specific heat capacity is primarily determined based on a material's heat storage process. The measuring apparatus is the same as for measuring conductivity and only the imposed thermal stresses are different. In the initial state, the system is isothermal (the exchanger plates are at a temperature (θinitial) then it is brought to a final heat level (θfinal), also isothermal, by changing the setpoints of the bath thermostats. In-between these two states, the sample stores an amount of energy Q, which represents the variation of the material's internal energy, as expressed by the following formula, where C is the capacity (J/.K.m2), Δφ is the difference of the measured flows (W/m2) and dt is the acquisition time:
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Q
t fin
. d t C (
t in i
fin a le
J / m
in itia le )
2
(1)
Heat capacity is evaluated by calculating the integral of the difference of flows from the initial state (θinitial) to the final state (θfinal). The specific heat capacity is then derived as follows: c
C
J / k g .K
e
(2)
Where ρ is the brick density [kg/m3] and e its thickness [m]. 2.2.2. Thermal diffusivity and thermal effusivity Based on the thermal conductivity (λ) and the specific heat capacity (c), we can determine the thermal diffusivity (D) and thermal effusivity (E), which are both essential features for nonsteady thermal conditions. In fact, thermal diffusivity characterises the rate of heat transmission within the body by conduction. Thermal effusivity, on the other hand, is the speed at which the surface temperature of a material warms up (cold or hot feeling to the touch). These two parameters are important characteristics for the building comfort. They are calculated according to the following formulas: D E
c
. c
m
2
J.K
/ s 1
.m
(3) 2
.s
1/ 2
(4)
2.2.3. Dynamic thermal characteristics The dynamic performance of building materials is primarily used in the calculations of a building's heating and air conditioning needs, and subsequently for assessing the contribution of these materials to the overall energy performance. The dynamic thermal characteristics describe the thermal behaviour of a building component when subjected to conditions with variable limits. The faces of the component are assumed to be subject to temperatures or thermal flows of sinusoidal variations. These characteristics were determined based on the standard NF EN ISO 13786 (2008). Considering constant thermal properties of an homogeneous and isotropic layer and one-dimensional heat flux, the calculation principle was based on the quadrupole method (Maillet et al., 2000). This involves determining the heat transfer matrix (Z), which correlates the complex amplitudes of temperature and heat flow density on one side of the component and the complex amplitudes of temperature and heat flow density on the other side. 2 Z 11 Z q 2 Z 21
Z 12 1 . Z 22 q1
(5)
The data required for these calculations are the thickness of the material, its density, its thermal conductivity, its specific heat capacity and the period of thermal variations. Finally, the period of time taken into calculation is one day (86400 s), corresponding to the daily climatic variations. The dynamic thermal behaviour of the tested bricks are described by these parameters (NF EN ISO 13786, 2008): - The thermal capacity of the inner surface: this is the capacity of the inner face of a wall to absorb, store and restore calories. Essentially, it characterizes the internal thermal inertia.
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-
The decrement factor: this is the ratio between the temperature amplitude at position x to the amplitude of the excitation temperature. - The thermal lag: this is the time between the maximum excitation and the maximum response to the excitation at a given position x. In our case, the excitation is the cold temperature. The decrement factor and the thermal lag primarily characterise the thermal transmission inertia of the total thickness of the wall, which absorbs and phase shifts of temperature variations between the inside and outside.
3. TEST RESULTS AND DISCUSSION 3.1. Thermophysical characterisation of bricks The three types of unfired earth bricks were characterised at laboratory scale. Their thermophysical characteristics were determined and presented in Table 4. The results show that the density of bricks (A) and (B) is higher than that of (C), although the specific weight of the solid grains of the various samples is substantially the same, about 2.65 g/cm3. The density difference is caused by the manufacturing method of the bricks, specifically the extrusion conditions. The thermal conductivity of three bricks is around 0.9 W/m.K. This building material is not intended for thermal insulation. On the other hand, we note that the obtained specific heat capacity values are below the reference values found in the literature (Goodhew and Griffiths, 2005; Oti et al., 2010), but enable comparing the three types of bricks among themselves. The margin of error may be due to the use of an indirect method to determine this parameter. The thermal diffusivity calculation shows that the brick (C) has higher diffusivity than the (A) and (B). This means that the heat front will take longer to pass through the brick thickness. In fact, the difference lies in the volumetric heat capacity (ρ.c), since the thermal conductivity of the three bricks is practically equal. The calculated effusivity values show that unfired earth bricks, indeed provide a feeling of comfort. Concerning the dynamic thermal characteristics, the calculated values show that the thickness of the material has a significant effect on damping the thermal wave and shifting phase with it. Thus, a brick (A) with a 99 mm thickness has a decrement factor equal to 0.89 and a thermal lag of only 3.32 hours. This means that indoor temperature fluctuations will be great, as temperature peaks will be rapidly transmitted to the interior of the building. In general, a day/night thermal lag is sought, corresponding to thermal lag values of 10 to 12 hours. For the summer, this phase shift means that the external heat can be allowed to enter when the outside temperature begins to decrease, limiting the risk of overheating. It should be noted that in general, the walls used in earthen construction have greater thicknesses. Indeed, earthen walls are typically 300 - 450 mm thick, according to design requirements (Maniatidis and Walker, 2003, Walker et al., 2005, Goodhew and Griffiths, 2005). This is why the dynamic thermal characteristics were calculated based on the wall thickness. The presence of mortar joints used for the raw earth brick masonry can be neglected in calculations, as the wall can be considered as a homogeneous layer if the largest size of the non-homogenous layer does not exceed one fifth of the thickness of the layer of material (NF EN ISO 13786, 2008). 3.2. Dynamic thermal characteristics as a function of the wall thickness
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Figures 5, 6, 7 and 8 show the variation of the thermal resistance and dynamic thermal characteristics as a function of wall thickness. The three types of unfired earth bricks that were used for the different walls were studied. Earthen walls of large thickness cannot achieve the required levels of building insulation. Although thermal resistance increases linearly with the wall thickness, it remains lower than the values required by the thermal regulations in France (see Figure 5). Since the thermal conductivity of these three materials is almost equal, the three curves are practically superimposed. Results show that the thermal capacity of the inner surface increases almost linearly according to wall thickness, until it reaches its maximum value at a thickness of 0.3 m for bricks (A) and (B) and 0.35 m for the brick (C) (see Figure 6). From the standpoint of thermal capacity, a thickness exceeding these values is unnecessary. In fact, beyond these values, thermal capacity decreases asymptotically until it reaches a limit value (Sambou, 2008). The decrement factor decreases with increasing wall thickness until reaching a value close to 0 (see Figure 7). This means that wall thickness can mitigate the fluctuations of an external heat wave, and consequently, the indoor temperature remains practically stable and constant. The results of the thermal lag variation show that the ideal thickness to achieve the desired day/night phase shift of thermal comfort is between 30 and 40 cm for bricks (A) and (B), and between 40 and 47 cm for the brick (C) (see Figure 8).
4. CONCLUSION This paper presents a theoretical and experimental study to analyze the dynamic thermal behaviour of three types of unfired earth bricks. Based on the experimental study, it was determined that the thermal conductivity of these building materials is around of 0.9 W/m.K. Thermal resistance increases linearly with the wall thickness, it remains lower than the thermal requirements of current France building regulations. The dynamic thermal characteristics of the two walls built of bricks (A) and (B) respectively, extracted from the heat transfer matrix, indicate a similar performance and more better transient behaviour (heat capacity, decrement factor and thermal lag) in comparison to wall built by bricks (C). Indeed, an earthen wall built of bricks (A) and (B) can achieve the optimum values of thermal inertia with a 0.3 m of thickness. However, a higher thickness of 0.4 m is needed for a wall built by bricks (C) to ensure the greatest heat capacity and a thermal lag between 10 and 12 hours, taking into account the quantity of bricks necessary for the wall construction and the habitable area. This work will be completed by a subsequent study to investigate the effect of physical and chemical characteristics of raw materials on dynamic thermal performance of these building materials. Acknowledgment
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The authors would like to thank the Briqueteries du Nord Company for its contribution and its support for this work. REFERENCES Asan, H. Numerical computation of time lags and decrement factors for different building materials. Building and Environment 41 (2006): 615–620. Brunauer, S., Emmet, P.H., Teller, E. Adsorption of gases in multimolecular layers. Contribution from the Bureau of Chemistry and Soils and George Washington University; 1983: 60: 309-319. Chel, A., Tiwari, G.N. Thermal performance and embodied energy analysis of a passive house: Case study of vault roof mud-house in India. Applied Energ, 86 (2009) 1956-1969. Delgado, M.C.J., Guerrero, I.C. The selection of soils for unstabilised earth building: A normative review. Construction and Building Materials 21 (2007) 237–251. Dethier, J., Eaton, R. For a Sustainable New Contract between Nature and Builders. Paris: Centre Pompidou. 2002. Goodhew, S., Griffiths, R. Sustainable earth walls to meet the building regulations. Energy and Buildings 37 (2005): 451–459. Houben, H., Guillaud, H. Earth construction, Intermediate Technology publications 1994, London. Kornmann, M. Clay bricks and rooftiles - manufacturing and properties, 2007. Maillet, D., André, S., Batsale, J-C., Degiovanni, A., Moyne, C. Thermal Quadrupoles. Solving the heat equation through integral transforms. United Kingdom: John Wiley & Sons, 2000. Maniatidis, V., Walker, P. A Review of Rammed Earth Construction. May 2003. Martin, S., Mazarron, F. R., Canas, I. Study of thermal environment inside rural houses of Navapalos (Spain): The advantages of reuse buildings of high thermal inertia. Construction and Building Materials 24 (2010): 666-676. Morel, J.C., Mesbah, A., Oggero, M., Walker, P. Building houses with local materials: means to drastically reduce the environmental impact of construction. Building and Environment 36 (2001): 1119–1126. NF P94-051 (1993). Soils: investigation and testing. Determination of Atterberg's limits. Liquid limit test using casagrande apparatus. Plastic limit test on rolled thread. NF P94-068 (1998): Soils: investigation and testing. Measuring of the methylene blue adsorption capacity of à rocky soil. Determination of the methylene blue of à soil by means of the stain test.
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NF EN 12664 (2001). Thermal performance of building materials and products — Determination of thermal resistance by means of guarded hot plate and heat flow meter methods — Dry and moist products of medium and low thermal resistance. NF EN ISO 14688-1 (2003): Geotechnical investigation and testing - Identification and classification of soil - Part 1: identification and description. NF EN ISO 13786 (2008). Thermal performance of building components – Dynamic thermal characteristics – Calculation methods. Oti, J.E., Kinuthia, J.M., Bai, J. Design thermal values for unfired clay bricks. Materials and Design 31 (2010) 104–112. Pacheco-Torgal, F., Jalali, S. Earth construction: Lessons from the past for future eco-efficient construction. Construction and Building Materials Volume 29, 2012, Pages 512–519. Parra-Saldivar, M.L., Batty, W. Thermal behaviour of adobe constructions. Building and Environment. Volume 41, Issue 12, December 2006, Pages 1892–1904. Pittet, D., Kotak T. Environmental impact of building technologies, a comparative study in Kutch District, Gujarat State, India. Ecomateriales 4, Paths towards Sustainability conference, November 2009, Bayamo, Cuba. Sambou, V. Transferts thermiques instationnaires : vers une optimisation de parois de bâtiments. Thèse de doctorat préparée à l’Université Paul Sabatier. France, 2008. Santamarina, J.C, Klein, Y.H, Prencke, E. Specific Surface: Determination and Relevance.Canadian Geotechnical Journal, 39 (2002): 233-241. Shukla, A., Tiwari, G.N., Sodha, M.S. Embodied energy analysis of adobe house. Renewable Energy 34 (2009): 755–761. Taylor, P., Luther, M.B. Evaluating rammed earth walls: a case study. Solar Energy 76 (2004): 79–84 Ulgen, K. Experimental and theoretical investigation of effects of wall’s thermophysical properties on time lag and decrement factor. Energy and Buildings 34 (2002): 273–278. Walker, P., Keable, R., Martin J., Maniatidis, V. Rammed earth: design and construction guidelines. BREPress. 2005. XP CEN ISO/TS 17892-4 (August 2005): Geotechnical investigation and testing - Laboratory testing of soil – Part 4: determination of particle size distribution. Zami, M.S., Lee, A. Economic benefits of contemporary earth construction in low-cost urban housing – State-of-the-art review. Journal of Building Appraisal, 5 (2010): 259-271.
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Figure 1. Particle size distribution of soil samples Figure 2. XRD patterns of soil samples Figure 3. SEM images of soil samples Figure 4. Thermal measurement apparatus using the heat flow meter method Figure 5. Variation of thermal resistance
as a function of wall thickness
Figure 6. Variation of the thermal capacity of the inner surface as a function of wall thickness Figure 7. Variation of the decrement factor as a function of wall thickness Figure 8. Variation of the thermal lag as a function of wall thickness
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Soil (A) Soil (B) Soil (C)
Soil A Soil B Soil C
Table 1. Atterberg Limits of soil samples Water content Liquid limit Plastic limit Plasticity Index w (%) LL (%) PL (%) (PI=LL – PL) (%) 24 100 28 72 32 60 29 31 21 24 21 3
Table 2. Chemical composition of soil samples (% wt) SiO2 Al2O3 Fe2O3 K2O MgO CaO Na2O TiO2 64.22 14.59 5.66 3.08 1.51 1.04 0.35 0.90 50.72 12.83 15.03 2.63 2.27 1.61 0.28 0.80 73.97 8.52 3.22 2.00 0.73 4.18 1.01 0.77
LOI 8.75 14.11 6.03
Table 3. Specific surface areas of samples VBS (in g per 100 g of dry material)
Specific surface (Methylene blue method) (m2/g)
Specific surface (BET Method) (m2/g)
Soil (A)
4.45
108.88
46.56
Soil (B)
6.89
168.63
52.01
Soil (C)
2.36
57.85
16.08
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Table 4. Thermophysical properties of the three unfired earth bricks
Dimensions L x l x h (mm)
Brick (A) 219 x 99 x 60
Brick (B) 219 x 99 x 60
Brick (C) 222 x 104 x 60
Density (kg/m3)
2268
2186
1788
Thermal conductivity (W/m.K)
0.91
0.89
0.9
Specific heat capacity (J/kg.K)
662
712
545
Thermal diffusivity (10-7 m2/s)
6.06
5.72
9.23
Thermal effusivity (J.K-1.m-2.s-1/2)
1168.88
1176.95
936.49
Inner surface heat capacity (kJ/m .K)
45.16
46.60
32.84
Decrement factor
0.89
0.89
0.94
Thermal lag (h)
3.32
3.44
2.51
2
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S1359-4311(15)00929-1 http://dx.doi.org/doi:10.1016/j.applthermaleng.2015.09.009 ATE 7001
To appear in:
Applied Thermal Engineering
Received date: Accepted date:
18-6-2015 4-9-2015
Please cite this article as: Fayçal El Fgaier, Zoubeir Lafhaj, Emmanuel Antczak, Christophe Chapiseau, Dynamic thermal performance of three types of unfired earth bricks, Applied Thermal Engineering (2015), http://dx.doi.org/doi:10.1016/j.applthermaleng.2015.09.009. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Dynamic thermal performance of three types of unfired earth bricks Fayçal El Fgaier1; Zoubeir Lafhaj1*; Emmanuel Antczak2; Christophe Chapiseau3 Ecole Centrale de Lille, Laboratoire de Mécanique de Lille (CNRS UMR 8107), Villeneuve d’Ascq, 59651 Cedex, France 2 Université d’Artois, Technoparc Futura, 62400 Béthune, France 3 Briqueteries du Nord, 9ème Rue, Port Fluvial, Lille, 59003 Cedex, France *Corresponding author. Pr. Zoubeir LAFHAJ Tel./fax: +33 320335365. E-mail address: [email protected]
Highlights
Dynamic thermal performances were examined as function of wall thickness. Earthen wall cannot achieve the required level of building insulation. The ideal thickness ensuring optimum thermal inertia is determined. An earthen wall can achieve the optimum thermal inertia with a 0.3 m of thickness.
ABSTRACT The present work aims at studying the thermophysical properties of three types of unfired earth bricks through experimental investigation, and their dynamic thermal performance (thermal capacity, decrement factor and thermal lag) as a function of wall thickness. The objective is to to determine the ideal thickness of a raw earth wall, built by these bricks, to achieve the optimum values of thermal inertia. These bricks were industrially produced by the Briqueteries du Nord, which is a factory located in the north of France. The process used was the extrusion. The main difference between the three types of bricks is the origin of the soils, which were extracted from various quarries. It were characterized to determine their physical, chemical and geotechnical properties, and to identify its impact on development and production of unfired earth bricks. This work has identified the optimum thickness of the wall built by these unfired earth bricks (It was 0.3 m for two types of bricks and for the other one was 0.4 m). These thickness ensure the greatest heat capacity and a thermal lag between 10 and 12 hours, while taking into account the quantity of bricks necessary for the construction of such a wall and the habitable area.
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Keywords: Unfired earth bricks, Dynamic thermal performance, thermophysical properties, optimum thickness
1. INTRODUCTION The need to reduce CO2 emissions and to find more sustainable construction materials constitutes nowadays a major economic and ecological challenge. Earthen construction can contribute to reduce environmental problems. In fact, raw earth is one of the most widely used building materials in human history. It is estimated that almost a third of the world’s population lives in some type of earthen dwelling. It is one of the oldest building materials, used in many different ways around the world for centuries. Approximately 50% of the population of developing countries, the majority of rural populations, and at least 20% of urban populations live in earth homes (Houben and Guillaud, 1994). Unfortunately, this building material has been ignored for many years; this is due to the fascination for modern materials such as concrete, brick or steel. Second, it is due to the lack of international standards to evaluate the different products. Only some national reference documents and codes are used in the earth construction around the world, as mentioned by (Delgado and Guerroro, 2007). During the last few years, a growing interest has been appeared for earth as a sustainable material, and then has been studied in the engineering laboratories around the world in the aim of the certification of earth building products. The reason for this interest is that it presents several advantages that allows it to be a current response to energy and climate issues. Indeed, raw earth is an abundant natural and recyclable resource. It is low embodied energy building material, compared to fired clay bricks and concrete. It reduces the amount of energy required for construction as well as transportation needs (Morel et al., 2001). PachecoTorgal and Jalali (2012) have presented also the environmental benefits of earth construction. It includes a review about economic issues, non-renewable resource consumption, waste generation, energy consumption, carbon dioxide emissions and indoor air quality. Furthermore, Dethier and Eaton (2002) has described raw earth as the material of the future, with properties that are fully compatible with a modern lifestyle and attractive architectural design. Multiple research studies have outlined the economic benefits of earthen construction while reducing both the energy required to manufacture these products and environmental impact (Morel et al., 2001; Chel and Tiwari, 2009; Pittet and Kotak, 2009; Shukla et al., 2009; Zami and Lee, 2010). Moreover, the heat storage and humidity regulation properties of this material are additional benefits of earthen construction. They contribute to the thermal comfort and healthy environment of buildings. The thermal performance of these building materials have been studied in different research papers. In fact, Taylor and Luther (2004) worked on the suitability of rammed earth wall construction as an effective building envelope in regard to its thermal performance. Another study conducted by Parra-Saldivar and Batty (2006) presented the thermal performance of adobe constructions and the impact of various factors on its dynamic response. Also, Martin et al. (2010) compared the thermal behaviour of existing homes made of different construction materials in Spain, such as rammed earth, stone and wood. He demonstrated that traditional houses, built by the rammed earth technique, have a more pleasant indoor environment for the occupants and lower energy consumption compared to other construction techniques, mainly due to their thick walls that provide high thermal inertia. These previous studies have contributed to prove the thermal qualities of earth materials.
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However dynamic thermal performances (thermal capacity, decrement factor and thermal lag) of these materials have not studied as a function of wall thickness. In this context, this work presents an experimental and theoretical study to evaluate the thermal behaviour of three types of unfired earth bricks produced by the Briqueteries du Nord Company. The experimental study consists of measuring the thermal performance of these non-stabilised bricks, which the fabrication method and the utilised raw material are different. The dynamic thermal characteristics were determined as a function of wall thickness. The work presented in this paper aimed to determine the ideal thickness of a raw earth wall to achieve the optimum values of thermal inertia of such walls. Optimum thickness is a thickness that ensures the greatest heat capacity and a thermal lag between 10 and 12 hours, taking into account the quantity of bricks necessary for the construction of such a wall and the habitable area. In fact, Optimum thickness is defined linked to thermal inertia in this work. Heat capacity and thermal lag are very important characteristics to determine the heat storage capabilities of unfired earth bricks. An optimum thickness of wall can delay heat flow through the building envelope by as much as 10−12 hours, producing a warmer house at night in winter and a cooler house during the day in summer ((Ulgen, 2002; Taylor and Luther, 2004; Asan, 2006). 2. MATERIALS AND METHODS The Briqueteries du Nord company produces three types of unfired earth bricks (A, B and C). The differences between these three types of bricks derive mainly from the fabrication method and the utilised raw material. For the production of bricks (A) and (B), the shaping process is based on a vacuum extruder that produces a continuous bar, which is shaped in a metal mould. The raw bricks are then dried in chambers with controlled temperature and humidity. However, bricks (C) are produced according to artisanal techniques. It is shaped using a vertical mixer and a wooden mould. The brick surface is smoothed by water. The bricks are then stacked on carts by a robot and conveyed to drying tunnel with controlled air temperature and humidity. 2.1. Identification of soils properties The three different raw materials used in the manufacture of bricks were sampled from three company quarries, located in the north of France. The sampling, preparation and treatment method was identical for all three samples in order to enable their comparison. The samples' characterisation was intended to identify and determine their physical, chemical and geotechnical properties. Identification tests were used to classify the samples and understand the impact of their characteristics on development and production of unfired earth bricks, as well as the behaviour of these products in their utilization in construction. They were designated by A, B and C. The main physicochemical and geotechnical characterisation tests were performed on the three samples according to recommendations and international standards. 2.1.1. Particle Size Distribution Particle size distribution was determined using a wet sieving and a sedimentation test, according to standard (XP CEN ISO/TS 17892-4, 2005). It presents one of the main criteria in the selection of the suitable technique for earth construction (Delgado and Guerrero, 2007). Figure 1 shows the grain size distribution for the three selected soils used for brick manufacturing in this study. The grading curves show that the three samples are primarily fine soils. Indeed, they contain
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more than 10% fines (particles that pass through a 0.063 mm sieve). Soils A and B contain a significant amount of fine particles accounting for almost 95% of total mass. According to the distribution of granular fractions defined by standard (NF EN ISO 14688-1, 2003), the results indicated that the sample A consisted primarily of a fraction of 6% clay, 8% fine silt, 20% medium silt, 61% coarse silt and 5% sand. The soil B was a slight variation of the soil A, while the sample C contained a larger quantity of sand (15%). 2.1.2. Plasticity Atterberg limits were determined using a standard method for measuring liquid and plastic limits described in NF P94-051 (1993). Table 1 illustrates the Atterberg limits obtained for the three different soils (A, B, C). Plasticity index was also reported on this table.
According to the obtained results, the three soils have a different behavior depending on the moisture content. It can be observed that soils (A) and (B) have a high plasticity index value, which classifies them in the category of plastic soils. However, the low plasticity value of the soil (C) (PI = 3) indicates that the sample has weak plasticity. The main factors accounting for the behaviour of these soil are their low clay content and the abundance of quartz. 2.1.3. Chemical and mineralogical composition The mineralogy of the different soils was determined using X-Ray Diffraction (XRD) analysis (figure 2). The diffractogram of the soil (A) showed that it basically consisted of quartz, kaolinite, aluminosilicates and traces of illite and pyrite. The presence of kaolinite in the sample contributes to good shaping and drying properties of products (Kornmann, 2007). In contrast, the mineralogical composition of the soil (B) includes montmorillonite, which causes difficulties during drying due to significant shrinkage and capillary retention. The soil (C) consisted of a high proportion of quartz resulting in a relatively low plasticity as has been demonstrated, and the occurrence of a texture-layering phenomenon. The chemical composition of the samples was determined by X-Ray Fluorescence (XRF) technique. The mass percentages of oxides in the samples and the loss on ignition (LOI) data are presented in Table 2. The soil (A) contained a significant amount of silica, primarily from the alumina silicates and the quartz. It also showed a high concentration of Al2O3, generally related to clayey silicates, which contributes to good plasticity results (Kornmann, 2007). Other trace oxides (Mg, Na, Ti, etc.) have been detected in the chemical analysis of the sample. However, the soil (B) contained a smaller amount of silica and a larger amount of iron oxides, whereas silica and alumina were predominant in the soil (C). 2.1.4. Specific surface and SEM microscopic analysis Specific surface presents an important role in the characterisation of clayey materials. It enables understanding different soil behaviours such as shrinkage and swelling, as well as cation exchange capacities. It was determined through two adsorption techniques: Methylene blue method and Brunauer, Emmett and Teller (BET) Method. The obtained results (see table 3) show that the specific surface area is influenced by the measuring method. In fact, the methylene blue test consists in measuring the adsorption capacity and activity of the clayey fraction of samples, as specified in French standard (NF P94-068, 1998). It is used
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to determine the total ion exchange surface between the clayey fraction and the molecules of methylene blue. It basically includes the external surface between the clayey particles, and the internal surface corresponding to the interlayer space. The total volume of methylene blue solution (VBS) necessary to achieve total adsorption is provided in Table 3 for the different samples. The specific surface can be calculated according (Santamarina et al., 2002). Nevertheless, The BET Method is used to determine the volume of dinitrogen (N2) adsorbed by the sample at low temperature. The test principle is based on the theory of multilayer isothermal gas adsorption developed by Brunauer, Emmett and Teller (BET) in 1983 (Brunauer et al., 1983). This technique allows measuring the external surface area only, since the utilised gas cannot penetrate the layers of clay. For this test, we used Micromeritics ASAP 2010 instrumentation. The obtained results show that the specific surface area is influenced by the measuring method. Thus, the specific surface areas of soils (A) and (B) measured by the BET method were close to each other. However, based on the methylene blue method, the specific surface of the sample (B) produced a larger internal surface than (A), and therefore has a larger water or water vapour adsorption capacity, which subsequently can significantly affect mechanical behaviour (swelling problem). The methylene blue method was therefore used to determine the actual specific surface of these materials, in contrast to the BET method. The sample (C) had a smaller specific surface than the former two samples, primarily due to its microstructure. The difference in texture between the different studied samples is illustrated in Figure 3 by means of scanning electron microscopy (SEM) images. It show that soils (A) and (B) have a compacted microstructure, with the presence of some pores and cracks in the structure. The particle shape is poorly defined. It can be observed that the soil (C) has a discontinuous structure and a more open texture, with the presence of individual plates where the voids are more visible and connected.
2.2. Methods 2.2.1. Thermal conductivity and specific heat capacity The thermal conductivity (λ) of the bricks was determined based on standard NF EN 12664 (2001). The method consists in simultaneously measuring the heat flow and temperature on both faces of a sample subjected to a temperature gradient generated by two exchanger plates. The sample and flow meters assembly is surrounded by an insulating belt so as to limit the lateral heat flow losses and ensure a unidirectional flow in the central measurement area. The test apparatus used in this method is presented in Figure 4. Another element that characterises the thermal properties of materials is the specific heat capacity (c). The specific heat capacity is primarily determined based on a material's heat storage process. The measuring apparatus is the same as for measuring conductivity and only the imposed thermal stresses are different. In the initial state, the system is isothermal (the exchanger plates are at a temperature (θinitial) then it is brought to a final heat level (θfinal), also isothermal, by changing the setpoints of the bath thermostats. In-between these two states, the sample stores an amount of energy Q, which represents the variation of the material's internal energy, as expressed by the following formula, where C is the capacity (J/.K.m2), Δφ is the difference of the measured flows (W/m2) and dt is the acquisition time:
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Q
t fin
. d t C (
t in i
fin a le
J / m
in itia le )
2
(1)
Heat capacity is evaluated by calculating the integral of the difference of flows from the initial state (θinitial) to the final state (θfinal). The specific heat capacity is then derived as follows: c
C
J / k g .K
e
(2)
Where ρ is the brick density [kg/m3] and e its thickness [m]. 2.2.2. Thermal diffusivity and thermal effusivity Based on the thermal conductivity (λ) and the specific heat capacity (c), we can determine the thermal diffusivity (D) and thermal effusivity (E), which are both essential features for nonsteady thermal conditions. In fact, thermal diffusivity characterises the rate of heat transmission within the body by conduction. Thermal effusivity, on the other hand, is the speed at which the surface temperature of a material warms up (cold or hot feeling to the touch). These two parameters are important characteristics for the building comfort. They are calculated according to the following formulas: D E
c
. c
m
2
J.K
/ s 1
.m
(3) 2
.s
1/ 2
(4)
2.2.3. Dynamic thermal characteristics The dynamic performance of building materials is primarily used in the calculations of a building's heating and air conditioning needs, and subsequently for assessing the contribution of these materials to the overall energy performance. The dynamic thermal characteristics describe the thermal behaviour of a building component when subjected to conditions with variable limits. The faces of the component are assumed to be subject to temperatures or thermal flows of sinusoidal variations. These characteristics were determined based on the standard NF EN ISO 13786 (2008). Considering constant thermal properties of an homogeneous and isotropic layer and one-dimensional heat flux, the calculation principle was based on the quadrupole method (Maillet et al., 2000). This involves determining the heat transfer matrix (Z), which correlates the complex amplitudes of temperature and heat flow density on one side of the component and the complex amplitudes of temperature and heat flow density on the other side. 2 Z 11 Z q 2 Z 21
Z 12 1 . Z 22 q1
(5)
The data required for these calculations are the thickness of the material, its density, its thermal conductivity, its specific heat capacity and the period of thermal variations. Finally, the period of time taken into calculation is one day (86400 s), corresponding to the daily climatic variations. The dynamic thermal behaviour of the tested bricks are described by these parameters (NF EN ISO 13786, 2008): - The thermal capacity of the inner surface: this is the capacity of the inner face of a wall to absorb, store and restore calories. Essentially, it characterizes the internal thermal inertia.
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-
The decrement factor: this is the ratio between the temperature amplitude at position x to the amplitude of the excitation temperature. - The thermal lag: this is the time between the maximum excitation and the maximum response to the excitation at a given position x. In our case, the excitation is the cold temperature. The decrement factor and the thermal lag primarily characterise the thermal transmission inertia of the total thickness of the wall, which absorbs and phase shifts of temperature variations between the inside and outside.
3. TEST RESULTS AND DISCUSSION 3.1. Thermophysical characterisation of bricks The three types of unfired earth bricks were characterised at laboratory scale. Their thermophysical characteristics were determined and presented in Table 4. The results show that the density of bricks (A) and (B) is higher than that of (C), although the specific weight of the solid grains of the various samples is substantially the same, about 2.65 g/cm3. The density difference is caused by the manufacturing method of the bricks, specifically the extrusion conditions. The thermal conductivity of three bricks is around 0.9 W/m.K. This building material is not intended for thermal insulation. On the other hand, we note that the obtained specific heat capacity values are below the reference values found in the literature (Goodhew and Griffiths, 2005; Oti et al., 2010), but enable comparing the three types of bricks among themselves. The margin of error may be due to the use of an indirect method to determine this parameter. The thermal diffusivity calculation shows that the brick (C) has higher diffusivity than the (A) and (B). This means that the heat front will take longer to pass through the brick thickness. In fact, the difference lies in the volumetric heat capacity (ρ.c), since the thermal conductivity of the three bricks is practically equal. The calculated effusivity values show that unfired earth bricks, indeed provide a feeling of comfort. Concerning the dynamic thermal characteristics, the calculated values show that the thickness of the material has a significant effect on damping the thermal wave and shifting phase with it. Thus, a brick (A) with a 99 mm thickness has a decrement factor equal to 0.89 and a thermal lag of only 3.32 hours. This means that indoor temperature fluctuations will be great, as temperature peaks will be rapidly transmitted to the interior of the building. In general, a day/night thermal lag is sought, corresponding to thermal lag values of 10 to 12 hours. For the summer, this phase shift means that the external heat can be allowed to enter when the outside temperature begins to decrease, limiting the risk of overheating. It should be noted that in general, the walls used in earthen construction have greater thicknesses. Indeed, earthen walls are typically 300 - 450 mm thick, according to design requirements (Maniatidis and Walker, 2003, Walker et al., 2005, Goodhew and Griffiths, 2005). This is why the dynamic thermal characteristics were calculated based on the wall thickness. The presence of mortar joints used for the raw earth brick masonry can be neglected in calculations, as the wall can be considered as a homogeneous layer if the largest size of the non-homogenous layer does not exceed one fifth of the thickness of the layer of material (NF EN ISO 13786, 2008). 3.2. Dynamic thermal characteristics as a function of the wall thickness
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Figures 5, 6, 7 and 8 show the variation of the thermal resistance and dynamic thermal characteristics as a function of wall thickness. The three types of unfired earth bricks that were used for the different walls were studied. Earthen walls of large thickness cannot achieve the required levels of building insulation. Although thermal resistance increases linearly with the wall thickness, it remains lower than the values required by the thermal regulations in France (see Figure 5). Since the thermal conductivity of these three materials is almost equal, the three curves are practically superimposed. Results show that the thermal capacity of the inner surface increases almost linearly according to wall thickness, until it reaches its maximum value at a thickness of 0.3 m for bricks (A) and (B) and 0.35 m for the brick (C) (see Figure 6). From the standpoint of thermal capacity, a thickness exceeding these values is unnecessary. In fact, beyond these values, thermal capacity decreases asymptotically until it reaches a limit value (Sambou, 2008). The decrement factor decreases with increasing wall thickness until reaching a value close to 0 (see Figure 7). This means that wall thickness can mitigate the fluctuations of an external heat wave, and consequently, the indoor temperature remains practically stable and constant. The results of the thermal lag variation show that the ideal thickness to achieve the desired day/night phase shift of thermal comfort is between 30 and 40 cm for bricks (A) and (B), and between 40 and 47 cm for the brick (C) (see Figure 8).
4. CONCLUSION This paper presents a theoretical and experimental study to analyze the dynamic thermal behaviour of three types of unfired earth bricks. Based on the experimental study, it was determined that the thermal conductivity of these building materials is around of 0.9 W/m.K. Thermal resistance increases linearly with the wall thickness, it remains lower than the thermal requirements of current France building regulations. The dynamic thermal characteristics of the two walls built of bricks (A) and (B) respectively, extracted from the heat transfer matrix, indicate a similar performance and more better transient behaviour (heat capacity, decrement factor and thermal lag) in comparison to wall built by bricks (C). Indeed, an earthen wall built of bricks (A) and (B) can achieve the optimum values of thermal inertia with a 0.3 m of thickness. However, a higher thickness of 0.4 m is needed for a wall built by bricks (C) to ensure the greatest heat capacity and a thermal lag between 10 and 12 hours, taking into account the quantity of bricks necessary for the wall construction and the habitable area. This work will be completed by a subsequent study to investigate the effect of physical and chemical characteristics of raw materials on dynamic thermal performance of these building materials. Acknowledgment
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The authors would like to thank the Briqueteries du Nord Company for its contribution and its support for this work. REFERENCES Asan, H. Numerical computation of time lags and decrement factors for different building materials. Building and Environment 41 (2006): 615–620. Brunauer, S., Emmet, P.H., Teller, E. Adsorption of gases in multimolecular layers. Contribution from the Bureau of Chemistry and Soils and George Washington University; 1983: 60: 309-319. Chel, A., Tiwari, G.N. Thermal performance and embodied energy analysis of a passive house: Case study of vault roof mud-house in India. Applied Energ, 86 (2009) 1956-1969. Delgado, M.C.J., Guerrero, I.C. The selection of soils for unstabilised earth building: A normative review. Construction and Building Materials 21 (2007) 237–251. Dethier, J., Eaton, R. For a Sustainable New Contract between Nature and Builders. Paris: Centre Pompidou. 2002. Goodhew, S., Griffiths, R. Sustainable earth walls to meet the building regulations. Energy and Buildings 37 (2005): 451–459. Houben, H., Guillaud, H. Earth construction, Intermediate Technology publications 1994, London. Kornmann, M. Clay bricks and rooftiles - manufacturing and properties, 2007. Maillet, D., André, S., Batsale, J-C., Degiovanni, A., Moyne, C. Thermal Quadrupoles. Solving the heat equation through integral transforms. United Kingdom: John Wiley & Sons, 2000. Maniatidis, V., Walker, P. A Review of Rammed Earth Construction. May 2003. Martin, S., Mazarron, F. R., Canas, I. Study of thermal environment inside rural houses of Navapalos (Spain): The advantages of reuse buildings of high thermal inertia. Construction and Building Materials 24 (2010): 666-676. Morel, J.C., Mesbah, A., Oggero, M., Walker, P. Building houses with local materials: means to drastically reduce the environmental impact of construction. Building and Environment 36 (2001): 1119–1126. NF P94-051 (1993). Soils: investigation and testing. Determination of Atterberg's limits. Liquid limit test using casagrande apparatus. Plastic limit test on rolled thread. NF P94-068 (1998): Soils: investigation and testing. Measuring of the methylene blue adsorption capacity of à rocky soil. Determination of the methylene blue of à soil by means of the stain test.
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NF EN 12664 (2001). Thermal performance of building materials and products — Determination of thermal resistance by means of guarded hot plate and heat flow meter methods — Dry and moist products of medium and low thermal resistance. NF EN ISO 14688-1 (2003): Geotechnical investigation and testing - Identification and classification of soil - Part 1: identification and description. NF EN ISO 13786 (2008). Thermal performance of building components – Dynamic thermal characteristics – Calculation methods. Oti, J.E., Kinuthia, J.M., Bai, J. Design thermal values for unfired clay bricks. Materials and Design 31 (2010) 104–112. Pacheco-Torgal, F., Jalali, S. Earth construction: Lessons from the past for future eco-efficient construction. Construction and Building Materials Volume 29, 2012, Pages 512–519. Parra-Saldivar, M.L., Batty, W. Thermal behaviour of adobe constructions. Building and Environment. Volume 41, Issue 12, December 2006, Pages 1892–1904. Pittet, D., Kotak T. Environmental impact of building technologies, a comparative study in Kutch District, Gujarat State, India. Ecomateriales 4, Paths towards Sustainability conference, November 2009, Bayamo, Cuba. Sambou, V. Transferts thermiques instationnaires : vers une optimisation de parois de bâtiments. Thèse de doctorat préparée à l’Université Paul Sabatier. France, 2008. Santamarina, J.C, Klein, Y.H, Prencke, E. Specific Surface: Determination and Relevance.Canadian Geotechnical Journal, 39 (2002): 233-241. Shukla, A., Tiwari, G.N., Sodha, M.S. Embodied energy analysis of adobe house. Renewable Energy 34 (2009): 755–761. Taylor, P., Luther, M.B. Evaluating rammed earth walls: a case study. Solar Energy 76 (2004): 79–84 Ulgen, K. Experimental and theoretical investigation of effects of wall’s thermophysical properties on time lag and decrement factor. Energy and Buildings 34 (2002): 273–278. Walker, P., Keable, R., Martin J., Maniatidis, V. Rammed earth: design and construction guidelines. BREPress. 2005. XP CEN ISO/TS 17892-4 (August 2005): Geotechnical investigation and testing - Laboratory testing of soil – Part 4: determination of particle size distribution. Zami, M.S., Lee, A. Economic benefits of contemporary earth construction in low-cost urban housing – State-of-the-art review. Journal of Building Appraisal, 5 (2010): 259-271.
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Figure 1. Particle size distribution of soil samples Figure 2. XRD patterns of soil samples Figure 3. SEM images of soil samples Figure 4. Thermal measurement apparatus using the heat flow meter method Figure 5. Variation of thermal resistance
as a function of wall thickness
Figure 6. Variation of the thermal capacity of the inner surface as a function of wall thickness Figure 7. Variation of the decrement factor as a function of wall thickness Figure 8. Variation of the thermal lag as a function of wall thickness
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Soil (A) Soil (B) Soil (C)
Soil A Soil B Soil C
Table 1. Atterberg Limits of soil samples Water content Liquid limit Plastic limit Plasticity Index w (%) LL (%) PL (%) (PI=LL – PL) (%) 24 100 28 72 32 60 29 31 21 24 21 3
Table 2. Chemical composition of soil samples (% wt) SiO2 Al2O3 Fe2O3 K2O MgO CaO Na2O TiO2 64.22 14.59 5.66 3.08 1.51 1.04 0.35 0.90 50.72 12.83 15.03 2.63 2.27 1.61 0.28 0.80 73.97 8.52 3.22 2.00 0.73 4.18 1.01 0.77
LOI 8.75 14.11 6.03
Table 3. Specific surface areas of samples VBS (in g per 100 g of dry material)
Specific surface (Methylene blue method) (m2/g)
Specific surface (BET Method) (m2/g)
Soil (A)
4.45
108.88
46.56
Soil (B)
6.89
168.63
52.01
Soil (C)
2.36
57.85
16.08
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Table 4. Thermophysical properties of the three unfired earth bricks
Dimensions L x l x h (mm)
Brick (A) 219 x 99 x 60
Brick (B) 219 x 99 x 60
Brick (C) 222 x 104 x 60
Density (kg/m3)
2268
2186
1788
Thermal conductivity (W/m.K)
0.91
0.89
0.9
Specific heat capacity (J/kg.K)
662
712
545
Thermal diffusivity (10-7 m2/s)
6.06
5.72
9.23
Thermal effusivity (J.K-1.m-2.s-1/2)
1168.88
1176.95
936.49
Inner surface heat capacity (kJ/m .K)
45.16
46.60
32.84
Decrement factor
0.89
0.89
0.94
Thermal lag (h)
3.32
3.44
2.51
2
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