Earth construction: lessons from the past for future eco-efficient construction

TL;DR: In this paper, the authors highlight the importance of earth construction and highlight the environmental benefits associated with it, including economic issues, non-renewable resource consumption, waste generation, energy consumption, carbon dioxide emissions and indoor air quality.

About: This article is published in Construction and Building Materials.The article was published on 2012-04-01 and is currently open access. It has received 366 citations till now.

Summary

1. Introduction

• The construction industry is one of the largest and most active sectors throughout Europe representing 28.1% and 7.5% of employment respectively in the industry and in the European economy.
• Therefore, the use of more sustainable construction materials and construction techniques represent a major contribution to the eco-efficiency of the construction industry and thus to a more sustainable development.
• In the last decade almost one hundred research articles related to this subject have been published in Scopus journals mostly related to rammed earth.

2.1. The past

• There is no consensus about the date when man began to use earth construction.
• Other authors [9] mentioned that the use of earth for construction purposes dates from the period of El-Obeid in Mesopotamia (5000–4000 BC).
• Even the Great Wall of China whose construction began about 3000 years ago has extensive sections built on rammed earth.
• Adobe based buildings structures are common in Central America.
• Another good example is the city of Shibam in Yemen with earth buildings up to 11 floors that were built 100 years ago [13].

2.2. The present

• Currently almost 50% of the world’s population lives in earth based dwellings [14].
• The French laboratory CRATerre, founded in 1979 and linked to the School of Architecture in Grenoble, which acquired an institutional dimension in 1986 through the recognition of the French Government, was capable to maintain a strong and steady action in the promotion of earth construction.
• Earth construction is not only dependent on adequate training but also on specific regulations.
• In 2002 this document has been replaced by the Australian Earth Building Handbook [18].
• In New Zealand the earth building regulations are dependent on the building height.

2.3.1. Techniques

• Earth construction encompasses several techniques such as, the most usual being: wattle and daub; cob; rammed earth (including earth projection); earth bricks or compressed earth blocks (CEB); Hybrid earthen wall system that combines elements of rammed earth, cob and wattle and daub have been recently used in Portugal (Fig. 1).
• Adobe is a very simple earth building technique being the reason most ancient construction were made of adobe [25].
• This position is not unanimous because vegetable fibers could rot leading to the appearance of fungi.

2.3.2. Properties

• The soil used in earth construction consists only in its mineral phase excluding the organic phase usually present in the first layers.
• The stabilization processes aim at the reduction of the soil plasticity, improvement its workability and also the resistance to erosion.
• Binici et al. [33] shows that using straw fibers in adobe bricks reduces the compressive strength.
• One of the most interesting features of earth walls is not thermal insulation but its high thermal inertia, i.e., the ability to store and manage heat.
• (10) Suitable only for in situ construction.

2.3.3. Durability

• The durability of earth construction is illustrated by the fact that some of these buildings last for hundreds of years.
• Durability has also been assessed by accelerated aging tests and more recently from monitoring experimental sections of earth masonry built a dozen years ago.
• The main mechanism responsible for the erosion of earth walls have to do with the kinetic energy of the impact of rainfall [51].
• This justifies the worst durability behavior of earth walls oriented to the South, a direction usually associated with wind based rain.
• Bui et al. [53] evaluated the performance of 104 sections of rammed earth masonry with and without stabilization, which were exposed during for 20 years to natural climatic conditions (Fig. 3).

3.1. Economic advantages

• For less developed countries the cost-efficiency aspect remains of paramount importance.
• Zami and Lee [54] quotes several authors for whom ‘‘earth construction is economically beneficial’’, nevertheless one cannot take this as a guaranteed truth because the economics of earth construction depends on several aspects such as: construction technique, labor costs, stabilization process, durability, repair needs.
• This is not the case in less developed countries in which labor is available for a very low cost.
• According to Sanya [55] this provides a very important way to create decentralized job creation.
• In these countries the cost-efficiency is dependent on the nature and the amount of binder used in the stabilization process.

3.2. Non-renewable resource consumption and waste generation

• The use of soil for earth construction cannot be regarded as a use of a renewable resource; however, one must recognize that is very different from the extraction of raw materials needed for the construction materials used in conventional masonry.
• This is because generally the soil used in earth construction is located immediately below the organic layer of the soil.
• This very different of conventional masonry in which concrete blocks and ceramic bricks are always very distant of construction sites thus implying high transport distances responsible for the emissions of green house gases (GHGs).
• Even when the soil is stabilized with cement or lime, it can be reused in this type of construction, so the authors may thus consider earth construction hardly generates any waste.
• As a comparison the traditional ceramic brick masonry implies a relevant amount of wastes because the use of broken pieces takes place quite often in this kind of masonry.

3.3. Energy consumption and carbon dioxide emissions

• The increasing demand for worldwide energy is a major cause for the unsustainable development of their Planet.
• The rise in energy consumption has two main reasons, the increase in world population and the fact that there is an increasing number of people with access to electricity.
• Gonzalez and Navarro [60] mentioned a correct choice of building materials can reduce of almost 30% CO2 emissions, avoiding the emission of 38 tons of CO2.
• Therefore the use of local materials as it happens with earth construction should be prioritize.
• Building with a reinforced concrete structure and adobe walls, also known as Solution 4.

3.4. Indoor air quality

• Another advantage of the indoor air quality of earth buildings relates to its ability to control the relative humidity [69].
• Some investigations show that the earth blocks are capable of absorbing 10 times more weight moisture than ceramic bricks (Fig. 6).
• Relative humidity values above 60% are associated with the presence of mites and also asthmatic diseases [71].
• Therefore, it is easily understood that public health statistics in recent decades show an increase of almost 50% in the occurrence of health problems from respiratory conditions such as asthma [72].

4. Conclusions

• Earth construction exists since the early agricultural societies, a period whose current knowledge dates from 12,000 to 7000 BC.
• There are countless cases of earth buildings which were build 1000 years ago and made it to the XXI century.
• Nowadays, the majority of earth construction is located in less developed countries, unfortunately, the fact that earth construction is associated with low income status is probably one of the most important reasons that explain why less developed countries try to emulate the use of unsustainable construction materials in the majority of the developed countries.
• The use of cement for soil stabilization increases embodied energy, therefore, further studies about the environmental impacts of earth construction stabilized with non-Portland cement binders are needed.
• Investigations about soil stabilization with lime and pozzolanic aluminosilicate wastes should also be analyzed.

Figures

Table 1 Transportation energy [10].

Fig. 4. Embodied carbon in different masonry materials [61].

Fig. 5. Embodied energy for four different scenarios [62].

Fig. 3. Rammed earth masonry sections exposed during 20 years to natural climatic conditions. (a) Wall made with soil stabilized with 5% lime; (b) wall made with soil without stabilization (mixed soil); and (c) wall made with soil without stabilization [53].

Fig. 1. Hybrid earthen wall system.

Fig. 2. Procedures for determining soil favorability for stabilization [31].

Table 2 Carbon embodied in different wall types [65].

Fig. 6. Weight of moisture absorbed by different materials when relative humidity increases from 50% to 80% [69].

Fig. 7. Rammed earth wall, Hospital of Feldkirch, Austria [10].

Frequently asked questions

Q1. What are the contributions in "Earth construction: lessons from the past for future eco-efficient construction" ?

Earth construction has received in the last decade an increased attention by the scientific community illustrated by a tenfold increase of the published research articles when compared to the previous decade. In order to disclosure and highlight the importance of earth construction, this article reviews some of the environmental benefits associated with it. 

Q2. What are the future works mentioned in the paper "Earth construction: lessons from the past for future eco-efficient construction" ?

The use of cement for soil stabilization increases embodied energy, therefore, further studies about the environmental impacts of earth construction stabilized with non-Portland cement binders are needed. Earth construction is also responsible for an indoor air relative humidity beneficial to the human health ; therefore, earth construction has clear competitive advantages in the field of sustainability over conventional construction assuring it a promising future in the years to come. 

Q3. How much energy does the building sector consume?

Given that buildings consumes throughout its life cycle, more than 40% of all energy produced [58], the authors can easily see the high energy saving potential of this subsector and that this may represent in terms of reducing carbon dioxide emissions. 

Q4. What is the role of earthen structures in controlling relative humidity?

Earthen structures act as a relative humidity flywheel, equalizing the relative humidity of the external environment with that of the pores within the walls [10,45]. 

Q5. Why has the earth construction industry increased in the US, Brazil and Australia?

Earth construction has also increase substantially in US, Brazil and Australia largely due to the sustainable construction agenda, in which the earth construction assumes a key role. 

Q6. How many tons of CO2 would be saved by replacing concrete blocks?

The replacement of only 5% of concrete blocks used in the UK masonries by earth masonry would mean a reduction in CO2 emissions of approximately 100,000 tons [46]. 

Q7. How much CO2 would be produced by earth walls?

For a house with three rooms and an area of 92 m2 made with earth walls the values in represent a reduction of 7 tons ofCO2 compared to ceramic brick and a reduction of 14 tones of CO2 if aerated concrete blocks were used. 

Q8. How many tons of CO2 can adobe buildings produce?

According to these authors adobe buildings have the potential to reduce the production of almost 100 tons of CO2 emissions every year. 

Q9. According to Morton, what is the way to control the relative humidity of the indoor air?

According to Morton [46] the hygroscopic behavior of construction materials can be more effective in reducing the indoor air relative humidity than the use of ventilation. 

Q10. What is the main reason why earth construction is so popular in the developed countries?

the majority of earth construction is located in less developed countries, unfortunately, the fact that earth construction is associated with low income status is probably one of the most important reasons that explain why less developed countries try to emulate the use of unsustainable construction materials in the majority of the developed countries. 

Q11. What is the cost of earth construction in seismic regions?

earth construction in seismic regions needs to be associated with a reinforced concrete structure reducing its eco-efficiency. 

Q12. What is the main reason why earth construction is labor intensive?

These authors state that production and construction costs represent the most important part because earth construction is labor intensive. 

Q13. What is the common type of earth construction in the world?

The majority of earth construction is located in less developed countries, however, this kind of construction can also be found in Germany, France or even the UK that has an excess of 500,000 earth based dwellings. 

Q14. What is the main argument for the use of more sustainable construction materials?

the use of more sustainable construction materials and construction techniques represent a major contribution to the eco-efficiency of the construction industry and thus to a more sustainable development. 

Q15. What can be done to reduce the energy consumption of the building sector?

The appropriate choice of building materials can thus contribute decisively to reduce the energy consumption of the building sector. 

Q16. What is the main reason why earth construction is considered economically beneficial?

Even when the soil is stabilized with cement or lime, it can be reused in this type of construction, so the authors may thus consider earth construction hardly generates any waste. 

Q17. What are the main reasons why straw construction is becoming popular in the UK?

Other authors [39,41] show that straw construction complies with building regulations and the UK climate being a feasible option for this country. 

Q18. What are the main reasons why the authors have not used earth construction in the UK?

The same authors reveal that lack of scientific data and lack of experience by the mainstream construction industry in using these materials remain barriers to be overcome.