Rammed Earth As A Low Impact Building Environmental Sciences Essay

Rammed earth is widely used as a construction material from past many years. It is a monolithic type of construction which is built by compacting successive layers of soil. Rammed Earth as a material has a wide range of advantages and utilizations. So, an approach to explore the rammed earth construction in temperate climate of India by understanding the techniques and methods of construction, the properties of the material and the use of rammed earth in from past till present as well as in future in described. The essay is a brief study of the material, its history, technology, climatic response, feasibility and stand in today’s construction era. Experimental data have been included.

1. INTRODUCTION

SUSTAINABLE BUILDING

The sustainable building technology has seen a recent jump in interest in recent times. The rise in Global Warming has led Governments, to take speedy measures, to execute more environmental friendly practices. The government of UK has set up plans to reduce impact on earth by 60% by the year 2050 (DTI, 2007). Currently, the buildings in Europe contribute to 25-40% of the energy used by the society (UNEP, 2007).

The energy used in a building can be summarised by, the embodied energy of material, the energy spent in transportation, that used in construction, the energy consumed in the use of building and lastly, the energy used in disposal of the building at the end of its life. This energy consumption can be reduced by using low impact material, which carries low embodied energy. The embodied energy contributes to 10% of the total energy consumed by the building (UNEP, 2007). The use of locally available material can reduce the transportation energy. Different environmental building technologies, such as passive design for buildings can be used to reduce the energy in use of the buildings.

Thus the use and study of low impact building material has gained importance.

SUSTAINABLE MATERIALS

Sustainable materials have been used through centuries, but the environmental building technology, which has come out of the current environmental restraints, has set the revival of the old environment friendly materials. The locally available materials, which can be used without spending energy on transportation, manufacture of materials and even processing of raw materials, prove more economic, for energy consumption. Industrialised construction causes a lot of pollution. Thus the alternate methods of construction, viz, abode, rammed earth, stone, straw bale, hemp-lime, bamboo, cob, wood, earth-bag, wattle and daub among others.

The traditional building methods have employed use of the natural materials in the past. Now, these materials and technologies, through study and experiment, are being reinvented, for efficient sustainable low impact use. Rammed Earth is one such material which is being revived as a low impact building material. The significance of this material in the history of architecture is worthless. Michael Crichton, an author describes,

“If you don’t know history, then you don’t know anything. You are a leaf that doesn’t know it is part of a tree. ” This essay is an opportunity, to learn about the vernacular and modern use of Rammed earth. As rammed earth construction is found in different climatic zones, it also brings the necessity of considering the material’s relation with various climate types. It is important to study the properties, techniques (both vernacular and modern) of building in load bearing and framed construction and also their response to climate and geographical context.”

This essay explores Rammed Earth, as a low impact building material. The study of its historic social context and its appropriateness in today’s building scenario is also carried out. An analysis is made on the appropriateness of Rammed Earth, for contemporary architecture.

RAMMED EARTH

One of the oldest building methods, Rammed Earth is a (adjective) form of construction. Through centuries, this method has been used to build superior quality walls, which encompass the qualities a building should possess, viz. Strength, beauty and utility. Buildings made of rammed earth have stood strong for hundreds of years. In the past decade, the importance of rammed earth has considerably increased. In view of, the need of a more sustainable environment; as a material consuming less energy, yet providing a greater life span, ‘Rammed Earth’ is being re invented as another low impact, energy efficient building material.

The Rammed Earth walls are made using materials of earth, namely, lime, mud, gravel, chalk, etc. These constituents are easily available on any land, and hence, the Rammed Earth construction has been found on all continents, except, the Antarctica. Its favourability to any climate and measure of strength are proved by the many ancient earth buildings which still exist, eg. The Great Wall of China, China. Many earth structures sit in the foot of the Himalayas. Earth heritage can also be found in the countries of China, India, France, Morocco, Spain, South America, and Europe.

1.2 RAMMED EARTH CONSTRUCTION

Rammed earth walls are constructed by compacting soil in the formwork. Usually damp soil from the site is used directly, or sieved, to remove the larger gravels in the soil. This soil is then added with suitable proportions of stabilizers. Initially animal blood was used as a stabilizer, as opposed to the cement, asphalt or lime stabilizers of today. Straw is used as reinforcement, and mixed in the soil batches. A layer of soil of thickness 150mm is placed in the formwork and then compacted with rammers. Once this layer gets settled, other layers of same thickness follow. The required height can be achieved by moving the formwork upward as the layers settle. The wall hardens almost as soon as the form work is removed. Rammed earth takes 2 years to cure. It gains compressive strength as it cures. Thus the construction is best done in warm weather, so the walls can dry and harden.

1.3 PROPERTIES

Dry density

Strength (compressive, tensile, shear)

Durability

Shrinkage

Surface finish

Thermal insulation

Advantages

Distinct appearance

Natural and readily available

Low embodied energy (a level similar to brick veneer construction)

Unstablised earth is reusable post-demolition

High moisture mass, hygroscopic – helps regulate humidity

Use of local soils supports sustainability practices.

High thermal mass (though work is still underway to quantify its extent)

Airtight construction achievable

Traditional form of construction

Modern methods are widely tried and tested overseas eg Australia

Disadvantages

Concerns over durability – requires careful detailing

Poor thermal resistance – external walls require additional insulation

Not all soil types are appropriate

High levels of construction quality control are required

Longer than average construction period

Few modern examples exist in the UK – relatively untested in UK climate.

High clay content can cause moisture movement. Structures may need to accommodate this.

No UK codes of practice

Adding cement stabilisation can compromise environmental credentials

1.4 STABILISED EARTH CONSTRUCTION

Though rammed earth is considered a strongly sustainable material, it has some shortcomings in relation with durability. Some of the factors in natural earth which need improvement are, water resistance, shrinkage, external surface protection and strength. For overcoming this problem, stabilisers are used. In olden times, lime or animal blood were used to stabilise the material, while modern construction uses lime, cement or asphalt emulsions. Some modern builders also use bottles, tires, or pieces of timber.

Though stabilisers add to the carbon emission and thus the negative impact to some extent, they reduce uncertainty and risk. Hence, they are used. The most common stabiliser used is cement. It generally makes 6 to 7% of the total mixture.

Characteristics of Stabilised Rammed Earth

STRENGTH

Strength of unstabilised Rammed Earth is 1MPa and that of stabilised Rammed Earth is 10MPa. Stabilised Rammed Earth is suitable for both load bearing and framed structure.

FIRE SAFETY

Earth is a non-combustible material. Rammed Earth walls can sustain fire for 9 hours.

RESISTANCE TO MOISTURE

Earth walls can control humidity. Unclad internal walls can hold humidity 40% – 60% which is suitable for asthma patients, and storage of books.

SOUND INSULATION

Rammed Earth is effective for insulation. The design should accommodate provision of cavity walls for better sound separation.

CONSERVATION OF FUEL AND POWER

U-value of 300mm earth wall is ‘H 1.5 – 3 W/m2K, therefore insulation needs adding in external wall applications.

MATERIALS AND WORKMANSHIP

Material adequacy can be found out by sampling, lab testing or precedence. The quality of workmanship can only be derived against specification, test panels, etc.

1.5 DESIGN ISSUES

STABILISED RAMMED EARTH walls need added protection. Hence additional measures are required to be taken while designing rammed earth construction.

1.51 INSULATION

As discussed earlier, rammed earth has some shortcomings. Rammed earth has poor thermal performance, in some areas. Here, extra insulation is required.

Earth walls breathe. They absorb moisture and then let it evaporate. Rammed earth is hygroscopic. Wherever walls have external cladding, the cladding systems should be vapour permeable. It is wise to consider vapour permeable walls for both unstabilised and stabilised walls, to reduce condensation build up on the inside face of insulation.

When moisture is allowed to escape from the external face, the permeability is of less concern while specifying internally applied insulation.

External Insulation

Wall needs to be protected from weathering. Thermal mass should be exposed internally. Some types of insulation renders are described below.

Insulating render

rammed earth with insulating render

Figure: showing insulation

Source: http://www.greenspec.co.uk/rammed-earth.php.

Insulation Board and Render

rammed earth and insulation board and render

Figure: showing insulation

Source: http://www.greenspec.co.uk/rammed-earth.php.

Insulation materials: breathing insulation: cellulose slab, composite wood wool board (not cement-based), wood fibre board, cork, hemp, and hemp-lime.

Render: limecrete, mineral render, plaster, proprietary permeable renders.

Rain screen Cladding

rammed earth and rainscreen cladding

Figure: showing rain screen cladding

Source: http://www.greenspec.co.uk/rammed-earth.php

Insulation materials: breathing insulation: cellulose slab, composite wood wool board (not cement-based), wood fibre board, cork, sheep’s wool, hemp, and hemp-lime.Cladding: wood, tiles, slate, board and polymer-based render, proprietary cladding systems.

B) INTERNAL INSULATION

In case of internal insulation, the natural look of the exterior is maintained, but the available thermal mass on the inside is lost.

rammed earth internal insulation

Figure: Free standing studwork with infill insulation.

Source: http://www.greenspec.co.uk/rammed-earth.php.

Insulation materials: Cellular glass, Mineral wool slab, expanded polystyrene, Phenolic foam, Polyisocyanurate (PIR), Polyurethane (PUR).

1.52 WEATHER PROTECTION

Protection Given By the Roof

rammed earth overhanging eaves

Figure: The eaves provide protection from rain.

Source: http://www.greenspec.co.uk/rammed-earth.php.

Footings and Base

rammed earth footing and base

Figure: The DPC should be finished flush with the wall surface to avoid splash. Source:http://www.greenspec.co.uk/rammed-earth.php

2.0 HISTORICAL USE

“Archaeological evidence can date entire cities constructed of earth back over 10,000 years. All of the great civilisations of the Middle East were constructed with mud brick and rammed earth – Assyria, Babylon, Persia, and Sumeria. Rammed earth construction was used to construct countless monuments, temples, ziggurats, churches, and mosques. Many of these structures (the Great Wall of China being one) have stood the test of time and are still standing today.”

Rammed earth construction originated in China, in the Neolithic age. Rammed Earth remains have been found in the archaeological sites of Yangzhou and Langham cultures of the yellow river valley, dating back to 5000 BC. By 2000 BC, the use of this material spread across china. Rammed Earth was commonly used for building walls and foundations.

The 4000 year old, Great Wall of China has also been originally constructed in Rammed Earth, known there as ‘Taipa’. Its outer covering of stones and bricks, made later, gives it an appearance of stone wall. Foundations dating 5000BC have been discovered in Assyria. The core of the sun pyramid in Teotihuacan, Mexico, built between 300 and 900 AD, consists of approximately 2 million tons of Rammed Earth.

Rammed Earth developed as a construction technique in various parts of the world independently. It had great influence in the Middle East Countries, China and Europe. It also became popular in Africa and America. The Romans built many earth structures throughout Europe.

2.1 GLOBAL DISTRIBUTION

The early human shelters were caves. So, the use of earth construction is believed to have started as extensions to caves, such as mounds of earth at cave entrances, or cut earth, etc. The Rammed Earth building technique developed in several places independently. Man spread its use to different locations with his travelling for hunting.

Rammed Earth structures are made from soil removed from the ground. The soil which has appropriate proportions of clay soil and sandy silt, is suitable for construction. The regions with abundance of such soil make use of earth construction. This soil with silt, sand and clay together is found in various locations, but is usually found in hilly areas, edges of large river valleys, mountainous regions with glacial tilt. The Himalayan ranges have many still existing examples of Rammed Earth structures. Ladakh, Bhutan, Nepal are regions where Rammed Earth practices were popular. Rammed Earth continues to be promoted in the country of Bhutan.

Traditional Rammed Earth was prepared by ramming natural soil in small batches in a vertical formwork. The regions, which cannot provide soil favourable for preparing sun dried clay bricks, or timber; made use of rammed earth as a construction material. The desert sections of the Great Wall of China, Potala Palace in Lhasa, are made of Rammed Earth. Rammed Earth was also used to build fortification in North Africa and Spain.

In Europe, rammed earth technology was used in vernacular style in the late middle ages, and continues to be used in Africa today.

2.2 METHOD OF CONSTRUCTION

http://www.historicrammedearth.co.uk/indian_rammed_earth.png

Soil was removed from the ground and used for construction. It was sieved if found necessary. Straw and lime, mixed into the soil, were used as additives to increase the strength of structure. The soil was then dropped into a formwork in layers of 150mm high. The layer is compacted using heavy rammers. On compaction of one layer another layer is laid and the same procedure is carried out, till the formwork is full. The formwork is then moved vertically to accommodate more earth. Once the formwork is moved vertically, the horizontal timbers are removed from the wall, leaving characteristic holes.

Figure: Urdu manuscript showing Rammed Earth Construction.

Historic Formworkrammed earth formwork

Formwork is made up of timber sides. These are held together by vertical timbers connected to horizontal timbers which go through the wall. This formwork design is found in Nepal and Morocco. In some places, stones are placed over horizontal timbers to allow their removal. The traditional rammed earth wall can thus be constructed with little labour and without recourse to temporary works.

Figure: Rammed Earth Formwork

2.3 MODES OF FAILURE AND REPAIR TECHNIQUES

The strength present in unstabilised earth construction, also owes to a less understood phenomenon of suction. The pressure difference between air and water components of soil creates the interface of water and air to curve. This curve accommodates pressure difference, bringing about surface tension. The combination of surface tension and pressure difference creates a strong attractive force in the pores, thus strengthening the soil wall structure. (Jaquin P.A.)

A study on failures has been made extensively by Paul Jaquin of Durham University. Considering failure mechanism of historic structures can be utilised in taking measures for rectification and prevention for future. Cracking is the main mode of failure in Rammed earth structures. A study of presence of water, for strength is also important.

Water

A small amount of water can add strength to the structure. Excess of this water can also lead to failure. In the later case, structure becomes saturated, loses strength, then integration and finally leads to complete destruction of the building. When a structure is not maintained, Water enters a building. It can enter the wall when the roof is open. Slurry is formed on the top of the wall and the material moves downward, leading in complete erosion of the wall. The water flows through the walls and evaporates through the surface, leaving precipitated version of salt in the pores. This salt expands and cracks the pores and leads to removal of fine grained surface.

Use of permeable cement covering on the surface is not recommended, as water gets trapped and movement might occur. Use of less permeable material like brick wall also poses danger, if the water level increases leading to loss of structural integrity. The use of masonry to protect earth walls had been used in China and Spain to protect walls from the threat posed by artillery.

Cracking:

Cracks are formed in walls due to unsaturation of soil. The tensile stress in soil is less, which leads to this unsaturation.

Crack Stitching:

As a treatment to the cracks formed in buildings, crack stitching is applied. This method is applied with utmost care, so as to not induce any more stresses in the cracks. Hence ‘Soft Stitching’ is practiced. This involves application of similar material across the crack. This provides similar stiffness to the material, and thus works well in repair of large cracks in earthen structures

Crack stitching was carried out for a monument in Ladakh, India, by Jogn Hurd in 2004. The technique he used is as follows. A buttress is placed at the base of the slope. Soft ties are introduced across the crack to create structural integrity. A mud brick staple is constructed across the crack, to half the thickness of wall. Part of the staple is cut and hemp matting placed inside the cut. Mortared sundried bricks are then placed within the cut, forming a solid staple wall.

Seismic Protection:

Rammed Earth is constructed in horizontal layers. Once one layer is complete, the formwork is raised upward for another layer. Every layer is known as a lift. Historical evidence shows that materials such as, straw, lime, stones, brick are placed between lifts. These materials act as tie beams across the walls, tying them together and thus help in seismic protection (Hurd,2006). In some sites of Spain built in 1504, lengths of timber were placed in the wall while ramming. Their appropriate placement, proves an understanding of seismic design. These timers were first made circular, then covered in a lime and straw mortar, which was then rammed within the wall. These timbers were placed at 1.6m intervals, in a ring, throughout the building.

2.4 EXAMPLE

C:UsersVarunDesktopbasgo1.jpg

Figure: showing castle made of rammed earth at basgo, India. Source: http://www.historicrammedearth.co.uk/india.htm

“The site at Basgo consists of four distinct structures, three temples and a fort. The fort (Basgo Rabtan Lhartsekhar Castle) was built first and is the only structure made from rammed earth. The rammed earth section stands in the centre of the site, and consists of a mainly ruined set of walls, with no roof structure. A large crack is visible in the face of one of the walls which were repaired by in 2000. The castle withstood a three year siege in 1684, but may have been destroyed by invading Sikhs in around 1819 and definitely by 1843”.

3.0 CONTEMPORARY USE

The Rammed Earth construction received worldwide interest, owing to its non dependency on materials such as cement, ease of availability, and potential for recycling. The most important factor for its resurgence is its sustainable longevity. Rammed Earth is now being treated as a structural material and rules for designing have developed accordingly.

In the 15th century, rammed earth was brought to Europe. The 19th century, America saw resurgence of Rammed Earth as a construction Technology. The book ‘Rural Economy, by S.W. Johnson popularised it in the states. The famous historic landmark, ‘Burough House Plantation’ in 1821, is the largest complex of built Earth in the US.

After 1920, for almost 30 years government spent a lot of money on research of Earth structure construction. It even built low cost houses which became very successful. But, after WW2, the use of earth as a building material declined as modern building materials and technology were available at economic rates. Contractors and engineers found modern construction easier. Thus, use of rammed earth declined.

3.1 GLOBAL DISTRIBUTION

The modern era of Rammed Earth can be seen particularly in California, Western Australia and UK.

Australia has rich granite deposits and lateritic soils, suitable for construction of Rammed Earth. The property owners find all suitable material on their site itself, or nearby. This type of construction proves to be economical and long lasting. Thus the popularity grew in Australia.

The technique has observed growth in the southwest, around Tucson, Arizona and Las Cruces and Albuquerque, New Mexico, California, Colorado.

3.2 METHOD OF CONSTRUCTION

The method is similar to historic construction at large. All the old practices employed unstabilised earth, rammed on a raised masonry stem, protected by roof hangings. Today, concrete is used in the structure. A concrete stem must project 6inches above grade. Foundations are in the shape of an inverted T. In some places, rubble filled trenches are packed with reinforced concrete beam 10 inches thick and wider than the wall, to hold the ledges. Earth material is stabilised using Portland Cement in the weight of 5%. Softer earth plaster, stabilised with asphaltic emulsions, is used to clad unstabilised earth walls.

The formwork, now famous as concrete forming panel, is made of sturdy steel frame and special plywood inset, suited for rammed earth. Pneumatic ramming is used instead of the ancient hand ramming. The strength obtained by both is same.

3.4 EXAMPLE

C:UsersVarunDesktopCAMR2FM1.jpg

Fig: Rammed earth house in Bangalore, India. Source :http://rammedearth.blogspot.co.uk/2007/09/rammed-earth-in-india.html

“This is home was designed by Chitra Vishwanath Architects for Nishwath Hassan and Prakash Iyer, a Bangalore-based couple in their mid-30s. The walls are 9″ thick. They have sufficient self-weight to not need any other attachment or reinforcement. There is a nice rich mud mortar between the plinth beam (there’s a beam above the stone foundation) on which the bricks rest and then the rammed earth. The bricks or mud blocks can be optionally done away with. The self-weight of the wall structure is sufficient to hold it in place. In India we always have built in brick, stone and cement and reinforced cement concrete. Except for the roofs, beams and concrete columns (if there are any) steel is not used to reinforce walls. Our structural engineers say it’s not necessary. The load bearing capacity of the RE walls or any wall is dependent on their own strength and by self-weight they hold well in placeThe soil that was excavated from the basement was used to build the house. It was mixed by hand with sand and 5% cement then transported without the use of machinery. Its important that the design makes way for hot air (vertically up) and brings light into the right parts without using humungous openings. Helps in controlling cost of structure too. These Ecological homes that we make are cheaper than the conventional designer homes in the same city”

4.0 APPROPRIATENESS OF RAMMED EARTH IN DIFFERENT CLIMATE TYPES

The behaviour and function of rammed earth structures depend upon the climate they are exposed to. Rammed earth is an ideal choice for climates with distinct variation in day and night temperatures. Rammed earth is generally found in dry climates eg. Mediterranean rim, through central Asia and in parts of China and Himalayan regions. Whereas in tropical climates where the difference between day and night time temperatures is not much, Rammed earth does not work well. Although Rammed earth does not work well in excessively humid climates, evidence show that rammed earth structures can withstand severe rainstorm and snow fall for a short duration. A brief overview of different climates is given below.

Temperate Climates

Rammed Earth is placed in parts exposed to sunlight. The special properties of rammed earth alloy it to store the heat from the day, and release it at night, thus providing warmth. In these regions, walls are insulated to prevent heat loss.

Hot, Arid Climates

Buildings of high thermal mass work potentially here, in the deserts. The wall retards the passage of heat from the external face to the internal face. It even radiates the heat gained in the day time, back at night.

Hot Humid Climates

Night temperatures remain elevated in this environment, thus challenging the strength of rammed earth. rammed earth is placed away from direct sunlight so that it does not gain extra heat, as it will get overheated.

5.0 Tropical climate

5.1 Impact of climate

5.2 Local Availability of RE

5.3 Other uses of RE

5.4 Other factors deemed of interest.

Use http://www2.cemr.wvu.edu/~rliang/ihta/papers/11%20FINAL%20Paul%20Jaquin_paper_workshop.pdf

5.5 Vernacular style in temperate climate.

5.6 Whether it has been low impact

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5.7 Whether it is suitable for the climate

5.8 Which other materials are suitable for temperate climate.

6.0 Conclusion

Appropriateness in Contemporary architecture.

The likely future for the application of rammed earth is as:

– Thermal mass.

– Internal load-bearing unstabilised walls.

– External load-bearing stabilised walls.

(ref. Jaquin P.A. http://www.historicrammedearth.co.uk/Rammed_earth_structural_engineer.pdf)

( http://www.historicrammedearth.co.uk/india.htm)

( REF: http://www.greenhomebuilding.com/pdf/buildingstandards_sepoct98_ramearth.pdf)

(Ref: http://www.rammedearthliving.com.au/index.php?option=com_content&view=article&id=50:in-which-climates-does-rammed-earth-perform-the-best&catid=31:general&Itemid=46)

(reference: http://www.greenspec.co.uk/rammed-earth.php)

:http://www.greenspec.co.uk/rammed-earth.phpreference: ‘Rammed Earth: Design and construction guidelines’, Peter Walker et al, BRE 2005