Adobe as a Sustainable Material: A Thermal Performance
J.D. Revuelta- Acosta,
A. Garcia- Diaz,
G.M. Soto- Zarazua
E. Rico- Garcia
Sustainable construction is achieved using natural resources, such as adobe, in such a way as to meet economic, social and cultural needs, but not depleting or degrading these resources to such an extent that they cannot meet these needs for future generations. Earth is a cheap, environmentally friendly and abundant building material and has been used extensively for construction around the world. Today the prevalence of earth as a building material may be attributed to its proven durability demonstrated by the number of ancient earthen buildings that remain standing today. Scientific work have demonstrated that adobe has low thermal conductivity and high heat capacity enabling earthen building thermal stability compared with concrete building. Computational fluid dynamics has been proposed as a new tool to study the thermal behavior of earthen building.
March 21, 2010; Accepted: June 02, 2010;
Published: July 27, 2010
At the World Summit on Sustainable Development in Johannesburg, 2002, the worlds
nations reaffirmed their commitment to support sustainable development. Sustainability
is not only satisfying present needs, but also ensure future generations can
satisfy theirs. This includes socio-economic and environmental targets and is
a concern to all sectors of human activity and development and housing is one
of the more energy demanding sectors (Viviancos et al., 2009; Martin
et al., 2010). Throughout a buildings lifetime (construction, use,
dismantling), it has a direct impact on the environment through resource and
energy consumptions. Some reasons for green building include reducing energy
consumption, greenhouse gas emissions, water use, waste production and many
more. The environmental impact of a building depends on the choices made during
the different phases of a buildings life, specifically; the choice of
construction materials has a strong environmental impact. As mention above,
selecting a material with a Low Life-Cycle Cost (LCC) and high technical performance
reduces the buildings impact on the environment (Collet
et al., 2006).
Our ancestors had the same request for comfort that we have today, but without
the availability of cheap plentiful energy resources that we now rely upon.
Buildings and houses in particular, were constructed from locally available
materials. Adobe bricks made from straw and unbaked clay were commonly used
in many regions of the world. However, the use of the adobe bricks began to
decline at the end of the 19th century, when the abundant supply of cheap manufactured
construction materials began. A renewed interest in earth construction began
during the oil crises of the 1970s, due to their lower demand for energy
during fabrication and because in climatic regions where they had been traditionally
used, provided a basic standard of thermal comfort (Alva-Balderrama,
2001; Parra-Saldivar and Batty, 2006). As a result, studies have been conducted
to identify other factors that may explain adobes excellent behavior as
a heat moderator. In this study, some historic facts, concerning with earth
construction, are presented along with scientific results on the matter. Finally
some future trends to study thermal properties of earthen construction are proposed.
Adobe is a common prehistoric building material, widely distributed in arid
and semi-arid lands where other construction materials are scarce. Generally
adobe is non-fired sun-dried mud bricks mixed with organic material and may
be stabilized with lime or cement. A variation of adobe is the compressed earth
which consists in monolithic masonry units made with earth and straw where consolidation
is achieved by mechanic means without chemical processes that change the materials
nature (Jimenez-Delgado and Canas-Gerrero, 2006).
EARTH CONSTRUCTION AROUND THE WORLD
Earth has been used as a construction material for thousands of years (Hall
and Djerbib, 2004) with its most primitive form dating back to the nomadic
years where humans lived a migratory life and often constructed temporary seasonal
shelters from brush and wooden frames covered with mud (McHenry,
1984). The walls of Jericho in Palestine (9000 BCE) are evidence of sun-dried
mud brick construction (Rodriguez and Saroza, 2006).
The Egyptian civilization was the first to use the raw earth for building since
the 10th Millennium BCE (Heathcote, 1995; Kemp,
1999; Atzeni et al,. 2007). Other constructions
made with earthen blocks date from 8000 to 6000 BCE have been found in Turkestan,
as well as blocks in Assyria date around 4000 BCE. Even today in Upper Egypt,
monumental structures about 3200 years old remain visible, such as the huge
earthen block fortification wall of Medinet Habu and the vaults of the storage
rooms in the temple area of Ramses II near Gourna (Gernot,
2009). In Spain, the long-standing tradition of earth building is seen in
monuments like the historic centre of the city of Córdoba and the Alhambra,
Generalife and Albaicín in Granada (Jimenez-Delgado
and Canas-Gerrero, 2006). The technique of constructing vaults and domes
from earthen blocks without supports was known to many cultures. For centuries,
Pueblo Indians in Taos, New Mexico, built their houses using mud and straw (Gernot,
2009). The historical core of the city of Shibam, Yemen, covering about
20,000 m2 was accessible through a single gateway that was built
entirely in adobe. Many houses resemble skyscrapers and date from the 15th century
(Gernot, 2009). In Scandinavia and in England, sod (grass
and the surface earth held together by its roots) construction was common in
the 17th and 18th centuries. Houses were constructed from blocks cut from the
top layer of loamy. The blocks were inverted and used as bricks to form walls
without the need for mortar (Gernot, 2009). European immigrants
then brought this technique to the United States of America (USA), where a large
number of sod houses were built in the 18th and 19th centuries (Gernot,
2009). Some settlers also adapted the same concept from North American Indian
nations such as the Omaha and Pawnee, who for centuries had used sod to cover
their round huts (Gernot, 2009). In New Mexico, silty
soil blocks were cut from riverbeds and used for building walls. These blocks,
are called terronis or terrones, were also used in Mexico and Central America.
It is interesting to note that the building codes in New Mexico still allow
buildings to be constructed with terronis. In Germany, earthen block work was
used in the 6th century BCE; adobe blocks 40x40 cm and 6 to 8 cm high were used
in the fort of Heuneburg near Lake Constance. Around 140,000 blocks and 400
m3 of mortar were used to construct the 3-m-high walls (Gernot,
Earth, is the most abundant resource in the central Mesaorian region of Cyprus.
Sun dried earthen blocks are the most common walling material in the construction
of load bearing walls. The original mixture is used as mortar and plaster. Earth
is also used as a plastering material for the final layer of the roof (Dincyurek
et al., 2003). The load bearing earthen walls support a timber roof
frame cover with reeds, straw and sealed with mud. Timber is also used as door
and window frames and panels (Dincyurek et al., 2003).
Earth has also been used as the raw basic building material throughout the
history of Mexico. This has allowed expedient and efficient architectural development,
while conserving natural resources and allowing a high degree of adaptation
to varying climatic conditions (Rodriguez-Viqueira, 2001).
The convergence of knowledge of pre-Hispanic civilizations with the building
traditions brought from Europe during the colonial period has resulted in a
vast array of earthen building types including farms, temples, monasteries,
palaces, government buildings, prisons and residences (Guerrero-Baca,
Earth as a material construction came to be widely used due to its abundant
availability, cost and simple construction techniques. One disadvantage of earthen
construction is that the resistant to water damage is much lower than that of
other building materials such as stone and terracotta. Yet, even when stone
began to be used as a building material and as stone-working technology developed
over the centuries, earth continued to be employed as mortar, sealer or plaster
in stonework and had continued use in the construction of dwellings (Olotuah,
2002; Jimenez-Delgado and Canas-Gerrero, 2006).
Earth construction is still used extensively today (McHenry,
1984; Houben and Guillaud, 1994; Hall
and Djerbid, 2004) and it has been estimated that over half of the worlds
current population reside in earthen based homes (Rodriguez
and Saroza, 2006; Binici et al., 2009). Many
of these people live in Less Economically Developed (LED) nations where other
materials may be unavailable or deemed too expensive, the use of earth in construction
is not limited to the LED world. The extent of earth construction in the More
Economically Developed (MED) world is greater than one might expect. For example,
it has been estimated that in Australia, approximately twenty percent of the
new building market is occupied with earth based construction projects (Easton,
1996). The prevalence of earth as a construction material may be attributed
to its proven durability demonstrated by the number of ancient earthen buildings
that remain standing today (King, 1996).
Energy savings: Presently housing consists of, approximately, 40% of
total energy demand in the European Union (EU) (Viviancos et al., 2009;
Martin et al., 2010). Therefore, reducing energy
consumption in heating and cooling of buildings is an issue of increasing interest,
with multiple organizations conducting research into this area. EU Energy Performance
of Buildings Directive (EPBD) was implemented in the legislation of Member States
on January 4, 2006. This directive is an important step for the EU to decrease
energy consumption (Viviancos et al., 2009).
Sustainable development includes socio-economic and environmental targets and
concerns all sectors of human activity. The major reasons for green building
are to reduce energy consumption, greenhouse gas emission, water use and waste
production versus traditional building. The choice of materials used in the
construction of a building has a direct impact on the environment (Collet
et al., 2006; Goodman-Elgar, 2008). As the
energy consumption of a building depends mainly on the buildings construction
and materials, building type, climatic conditions, occupancy behavior, insulation,
heating, cooling, heating water and lighting (Viviancos et al., 2009).
Earthen housing appears to meet the requirements of green construction, Shukla
et al. (2009) calculated the energy for construction and maintenance
of an adobe house. The entire house was constructed materials such as soil,
sand, cow dung and others that are not energy intensive. They found that approximately
370 GJ of energy can be saved per year using these construction materials. The
energy payback time for the adobe house was 1.54 years. The mitigation of CO2
in the environment was reduced by 101 tonnes per year. The adobe house was also
more environmentally friendly compared to conventional buildings. Chel
and Tiwari (2009) also found similar results for a mud-house construction.
Thermal behavior of adobe buildings: Adobe is able to absorb heat during
the day keeping the house cool and then release this stored heat at night, warming
the interior of the house. This behavior is due to the high specific heat capacity
of adobe which is an important factor that allows this material to reduce the
thermal gradient of earthen houses (Parra-Saldivar and Batty,
2006). On the other hand, the ability of adobe to conduct heat is highly
dependent on its moisture content, with a strong relationship between water
content and heat conduction (Rees et al., 2001).
|| Adobe thermal conductivity from different sources
Table 1 shows some experimental results. Actual adobe constructions
have wet-dry cycles due to rain and relative humidity that cause changes in
its thermal behavior. The presence or absence of internal walls is another important
factor that modifies room temperature and determines the thermal behavior of
the internal space of the building. In terms of temperature attenuation the
thickest internal wall shows the greatest effect for most climatic regions during
the year (Parra-Saldivar and Batty, 2006).
Advantages and disadvantages: Adobe material has relatively high thermal
conductivity (Parra-Saldivar and Batty, 2006). Even a poor insulating material
can insulate effectively if it is large enough, which is the case of adobe construction
(Baker, 1986; Martin et al.,
2010). Another advantage of adobe is its sound insulation (Binici
et al., 2009).
It is also mentioned that fiber reinforced mud brick houses have been found
to be superior to concrete brick houses in reducing large fluctuations of indoor
temperatures during the summer and winter (Martin et
al., 2010; Binici et al., 2009).
Demir (2008) showed that sawdust, tobacco residues
and grass can be used to improve the thermal and mechanical properties of adobe
bricks. The insulation capacity of brick increases with the increasing porosity
of the body clay. The organic residue additions were found to be effective for
pore-forming in the clay body and the clay maintained acceptable mechanical
Martin et al. (2010) conducted a field experiment
to investigate the thermal behavior of existing housing in Spain. They compared,
stone, adobe and wooden houses (modern). The results demonstrate better indoor
conditions in the traditional houses. In summer, thermal comfort was achieved
with no energy supply inside traditional houses but not inside the modern ones.
In winter, the indoor environment was more stable inside the traditional houses;
however no house was able to provide thermal comfort.
Porta-Gandara et al. (2002) carried out a study
for La Paz, Baja California Sur, Mexico and found that vernacular wall adobe
constructions have important energy savings compared to concrete housing. It
is important to underline that adobe walls are about 5.1 times thicker than
concrete block walls and this figure is very similar to the inverse ratio of
energy requirements. Due to the thick exterior walls of high thermal inertia,
the indoor environment inside them can be comfortable with less energy consumption
than new buildings (Martin et al., 2010).
Soils with a small clay component have been widely used as construction materials
since the earliest times and continue to be used in some LED countries and in
the so-called bioarchitecture (Atzeni et al., 2007).
The adobe production consists of molding a mixture of soil with 5 to 10% of
straw (Binici et al., 2009; Demir,
2008). The necessary quantity of water is about one quarter of the dry earth
volume. A soil will react very differently depending on the amount of water
it absorbs. The four fundamentals states are: dry, humid, plastic and liquid.
The adobe is produced at the plastic state which enables molding. When the soil
goes back to the solid state it reduces its volume, resulting in cracks in the
bricks. In order to stabilize the adobe, sand or straw are added to reduce the
size of the cracks. Mixing by the feet of humans or animals is the
most common for small scale production. Sometimes the adobe is produced by using
compressed soil in the humid stated to improve its mechanical behavior.
The thermal conductivity of the external wall is an important parameter. Future research needs to be conducted concerning the amount of heat storage in an external adobe wall. It is known that the moisture content of adobe materials has a large effect on the thermal conductivity of adobe materials. Additionally, the water contained within adobe has latent heat effects, which modify both the thermal conductivity and thermal capacity of the material. Energy storage occurs through the heat of crystallization arising from salts within the clay structure of the adobe material. Consequently, the effects of rain wetting and the absorption and evaporation of water vapor due to changes in relative humidity should be investigated. Understanding the thermal behavior of phase change materials, such as salts contained within the wall, would increase the accuracy of predicting the performance of adobe structures (Parra-Saldivar and Batty, 2006).
On the other hand, in order to decrease thermal gradients between day and night
some passive elements can be added, like bodies of water or gravel (Mier-Chaplea
et al., 2010; Alatorre-Jacome and Rico-Garcia,
2009; Soto-Zarazua et al., 2009) and then
evaluate their effect on the thermal behavior of earth housing or even any type
Computational Fluid Dynamics (CFD) is a sophisticated design and analysis tool
that uses computers to simulate fluid flow, heat and mass transfer, phase change,
chemical reaction, mechanical movement and solid and fluid interaction. The
technique enables a computational model of a physical system to be studied under
many different design constraints. The quality of a CFD study is a function
of not only the physics available in the software to model the system, but also
the understanding that the CFD modeler has of both the numerics and physics
contained in the software package. If used correctly CFD can provide an understanding
of the physics of a flow system in detail and does so through non-intrusive
flow, thermal and concentration field predictions (Norton
et al., 2007).
CFD represents another interesting tool to evaluate the thermal behavior of
adobe houses. This software allows the user to address the complicated geometry
and also evaluate the change in the rate of air exchange due to wind or thermal
buoyancy effect (Rico-Garcia et al., 2006, 2007,
2008). Therefore, it is necessary to utilize the power
of CFD to better understanding of the thermal behavior of earthen construction.
The worldwide tradition of earth construction has shown that it is possible to achieve long lasting and majestic buildings from single to multi storey.
One of the main advantages of adobe is that the raw materials are locally available. In fact adobe may be produced from the soil excavated from the building site reducing transportation and other energy intensive processes.
Adobe low thermal conductivity provides a more stable temperature behavior inside a house and reduces heat losses.
Moisture content in adobe and CFD have been proposed as new trends to gain fundamental knowledge about the thermal behavior of earth building.
This research was supported by the Mexican National Council of Science (CONACYT) and FIFI 2010, Engineering Department. Queretaro State University.
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