Current State and the Potential Use for Future Construction
With Rammed Earth and its Variants.
In 2014 right after graduation I had the opportunity to attend a workshop for building with sustainable materials. Organized by BASE HABITAT, from the University of Linz in Austria, we were introduced to rammed earth construction by the master Martin Rauch.
In that moment i fell in love with the material and technique, so i pursue the : tropicalization” of this system in Mexico. Luckily i met my friend and tutor Quentin Branch in Oracle Arizona, an energetic man whom at his 70 + years he wakes up to ram a wall for fun, and has a deep sincere desire to share his knowledge to future generations, because like many others he sees the big opportunity that building with earth provides for us and our planet. Among several structures, I managed to built the tallest single wall in Mexico, 7 meters height, in a private house in Culiacán, Sinaloa, and i plan to build much more. It is on my best interest to contribute to the development of earth construction, and hopefully the following research will be as informative , inspiring.
Rammed earth has been used to make floors, walls and foundations for centuries. It’s still used today in some places. In fact, it’s experiencing a bit of a resurgence, and for good reason. It’s inexpensive, readily available, durable, sustainable, nontoxic and even fireproof.
Another advantage of rammed earth: It makes use of excavated soil. Every construction site has excavated soil that ends up at the landfill, now if we use locally available soil, it will help us to reduce cost and minimize environmental impact.
Unlike so many building materials, earth is one resource that isn’t going anywhere (rammed earth uses subsoil, not topsoil) — and isn’t going to hurt the planet. A “green” way to strengthen it just might strengthen its resurgence.
In the past few years, though, it’s become more common for designers to include rammed earth as feature walls in buildings
Building these walls, though, still requires an investment in specialized tools and labor
Today, disadvantages such as on site weather-dependency can be circumvented by using prefabricated elements. Possible load bearing problems solely due to pressure can be bypassed by pre-stressing the structure. By carrying out measures such as these, the building material – being ecologically sustainable and completely recyclable – will become an attractive alternative for contemporary construction methods.
Rammed earth is a widely used historic building material, found in Mediterranean regions, along the Silk Road, and in parts of the Himalayas. While guidelines exist for the construction of new rammed earth structures, there is very little guidance for the structural analysis of historic structures.
Many World Heritage sites contain structures constructed from rammed earth. Examples include Muslim fortresses dating from the 8th century throughout Spain and North Africa, Buddhist monasteries, some over 1000 years old in India, and parts of the Great Wall of China and the Potala Palace in Lhasa.
Evidence of ancient use of rammed earth has been found in Neolithicarchaeological sites of the Yangshao and Longshan cultures along the Yellow River in China, dating to 5000 BCE. By 2000 BCE, rammed-earth architectural techniques (夯土 Hāng tǔ) were commonly used for walls and foundations in China.
Interest in rammed earth declined after World War II when the cost of modern construction materials decreased. Rammed earth was considered substandard, and still is opposed by many contractors, engineers, and tradesmen who are unfamiliar with earthen construction techniques.
Having been used for thousands of years by many cultures, rammed earth is making a comeback, popping up in various modern buildings in universities to Swiss factory buildings by star architects. Now, Australian firm Luigi Rosselli Architectshave completed what they are calling the country’s longest rammed earth wall, as part of a residence for seasonal workers on a cattle ranch (no word on whether the ranch itself utilizes sustainable practices).
Among the pioneers of contemporary rammed earth construction are Anna Heringer in Germany, Quentin Branch from Rammed Earth Solar Homes in Arizona, David Easton from Rammed Earth Works in California, Martin Rauch from Lehmtonerde in Austria, Meror Krayenhoff in Canada, ASADURU Team in Cape Town, South Africa, John Oliver from Rammed Earth Construction in Australia, Mike Beukes from Rammteck in Africa, Tierradura and Multifuncional in Mexico.
Famous architects worldwide are supporting this movement and proposing buiildings with rammed earth such as Herzog de Meuron, Mauricio Rocha, Renzo Piano, Peter Zumthor, among others.
The future of earthen construction depends on the way it is adapted to our comfort needs, to the new standards and building codes. New strategies have been developed for innovation, combining traditional techniques with modern construction systems and new materials, changing the earthen construction paradigm. Nevertheless, earthen materials are still seen as an alternative and experimental resource, fulfilling some clients’ expectations and builders’ ambition to make different architecture.
Two major movements can be identified within the earthen construction evolution. One of the movements, found in the North American Southwest, approaches a high-tech system that makes the construction extremely expensive and less accessible, without fearing cement contribution. The other tendency, found in the Portuguese Southwest, keeps a traditional profile, with a low cost level. These differences have to do with country’s scale, construction market and available resources.
Key to affordability was the decision to use the rammed earth walls structurally, set out to the standard formwork dimensions, and to eliminate reinforcement, saw cutting to the top of walls and lintels and overfills. The unreinforced, load-bearing, rammed earth walls support the exposed concrete, first floor and ceiling level slabs and take the roof loads of the two-storey buildings. The use of load-bearing rammed earth influenced the building form; walls were always returned at the ends forming L or Π plan shape for structural stability.
The advice from rammed earth contractors was that walls with simple standard curves were not more expensive than straight walls, partly due to the scale of the job and largely dependent on the formwork owned by the particular contractor. Curving of walls also contributed to structural stability.
An ideal proportion of possible granularity, with a visibly very wide range of possibilities. One can read: clay between 10 and 40%, silt between 10 and 40%, sand between 35 and 65%, gravel between 0 and 40%. The size of the particles can vary from 5m to 10cm. Of course the granularity will also influence the aspect of the walls. Gravel and stones will be visible on the surface of the wall and this higher diversity of granularity can provide an interesting structure to the lot.
A pair of researchers at the University of British Columbia has discovered a way to strengthen rammed earth without using carbon-emitting cement — and create a second life for landfill-clogging waste materials at the same time.
By adding calcium carbide residue and fly ash as binding agents, then compacting the soil, forming walls and curing them for 60 days in a temperature- and moisture-controlled environment, they created walls 25 times stronger than walls built the same way but without binders.
When implemented without industrial additives, crude earth is a totally and infinitely recyclable material with a remarkably low environmental impact. In spite of that, raw earth construction is facing serious challenges, many of which stem from its still very limited use in modern construction. It suffers from a – ofen unjustified – poor image, in social and technical terms, and from the difficulty to pass some durability and mechanical performance tests which were designed for industrial materials, and which are not adapted to raw earth.
The picture is changing considerably when stabilization is taken into account. Te GWP of modern Portland cement is close to 830 grams CO2 per kg of cement, about 40 times larger than earth. Tus, even a moderate incorporation of cement – say, 5 to 10% – represents a significant increase in embodied carbon
Te conclusion of this analysis is clear. Stabilization of raw earth with Portland cement is not advisable in environmental terms.
Nearly 6% of all UK greenhouse gas emissions, and up to 8% of the world’s, are now sourced from cement production. If it were a country, the cement industry would be the third largest in the world, its emissions behind only China and the US. Climate change may possibly modify the architectural rules to be followed, but rather than massively transforming earth into a low quality concrete, it would be more appropriate to adapt the architectural practice and to look for new ways to improve strength and durability.
For building with rammed earth it is necessary to have a pneumatic tamper powered with a medium size air compressor, a bob cat for mixing large quantities, a hand/ manual tamper for leveling the layers of earth before compacting, a water tank and a hose with a pump, and either standard or custom formwork.
Formwork can range from simple to complicated systems and you can use plywood or steel ones. Like concrete formwork it is required to have sufficient strength, stiffness and stability to resist pressures it is subjected to during assembly, pouring the soil mix, and dismantling.
Productivity of rammed earth construction depends on several factors like site circumstances, weather conditions, workers proficiency and formwork system. Generally, Organization of formwork is one of the most time-consuming in rammed earth construction. Productivity rates quoted for rammed earth vary between 5hrs/m3 to over 25hrs/m3.
As for the human capital, most part of the job can be done by unskilled labour, Depending on the technology available , because nowadays prefabricated long walls can be done almost entirely by automatic machines, but the most common techniques which is using a pneumatic rammer empowered by compressed air, and the soiled poured with a bobcat, would be 4-5 people. It also depends on the position in charge, because ramming with a tamper is an easy to learn task, as well as setting up the forms and mixing the soil, but it is necessary to have an expert on site to make sure the design of the soil mix as well as the adequate humidity and proportions of material by layers are correct.
The mixed moist soil was poured in the formwork creating a uniform level of almost 15 cm, which after ramming was compressed to 10 cm. As soon as the first layer was rammed properly another was poured to be rammed, and so on. Both electric and hand metal rammers were used to ram the soil. The metal were composed of a steel rod with a flat steel plate, the weight of the rammers and the size of the plates differs to suit the purpose for example to ram the corners.
Despite global standards, regional codes and many scientific results, on both countries there is still a long path to promote more recommendations and standards to face warranty demands, to inspire and educate the public in general and also to instruct and prepare a specialized corp of technicians. This is part of a long process that could give to rammed earth a more prominent position in the construction scenario.
According to the New Mexico Building Code, the minimum compressive strength of a rammed earth wall is of 2.07 N/mm² and according to the Code Enforcement of Rammed Earth Structures of Zimbabwe (2001), the minimum values of compressive strength is of 1.5 N/mm² for one story buildings and thick wall of minimum 400 mm and compressive strength of 2.0 N/mm² for two level buildings.
Tested according to ASTM D698, it weighs 110 - 130 pounds per cubic ft. The earthen building materials industry accepts 300 psi as the minimum unconfined compressive strength for rammed earth, tested according to ASTM D1633 or C39.
The compressive strength of rammed earth is a maximum of 4.3 MPa (620 psi).
In my experience external walls of our rammed earth buildings are a minimum of 300mm (1 ft) thick, providing excellent protection from extremes in climate. The thickness and density of the material means that heat (or cold) penetration of the wall is very slow and the internal temperature of the building remains comparatively stable, with the end result of it feeling warmer in winter and cooler in summer than the outside temperature.
Thermal Storage This is a measure of the specific heat capacity expressed in volume terms and has units of J/m3 C. Houben & Guillaud (1994) claims that for rammed earth the thermal storage is around 1830 J/m3C. Thermal Resistance (R-value) The R-value is a measure of resistance to heat flow through a given thickness of a wall and is measured in m2 K/W. A 30 cm thick rammed earth wall has an R value between 0.35-0.70 m2 K/W (Berge, 2009). Generally, the more thermal resistance the material has the better insulating properties. Thick walls are required to provide sufficient high thermal mass. Improved insulation techniques are needed to increase the thermal performance of wall cross sections.
Rammed earth is hygroscopic. Wherever walls are clad externally, cladding systems and finishes must be vapour-permeable to allow evaporation. This is important for unstabilised walls, but less-so for stabilised walls where the stabilising agent will impair breathing. Nonetheless, it might be wise to consider vapour permeable solutions for both instances to reduce the chance of condensation build-up on the inside face of insulation.
SIREWALL has been the global technological leader of insulated rammed earth since its invention in 1992 and was the only practitioner for the first thirteen years. SIREWALL has four patents on this specific technology that leads the way in thermal and structural excellence in this emerging industry.
A new SIREWALL project has just opened for business, the Telenor ‘345’ head office complex near Islamabad, Pakistan.The overall scale of this project was 600,000 square-feet (5.57ha), by far the largest construction project implementing SIREWALL ever to be built. Although not all elements were created using strictly SIREWALL, the sheer scale—including a 10-foot high perimeter wall, 0.47 miles (750m) in length— is truly groundbreaking. It contains the new tallest rammed earth structure on earth, a tower of 100 feet tall, walls three feet thick!
The future of rammed earth seems to have to directions, one is a high technological approach of lightweight prefabricated walls and 3D printed earth structures on the other hand we envision a a vernacular low tech, mass available construction method for developing social housing in poor countries. An interesting combination of technologies for massive use is compressed earth blocks. In California, USA; David Easton from Rammed Earth Works has been working on a project, though, that could change that — a rammed earth block that’s made of quartz, recycled concrete, locally sourced earth and other materials. The result, the Watershed Block, could be used just like concrete blocks are today. CEBs are made from soil that is 15-40% non-expansive clay, 25-40% silt powder, and 40-70% sharp sand to small gravel content. The more modern machines do not require aggregate (rock) to make a strong soil block for most applications. Soil moisture content ranges from 4-12% by weight. Clay with a plasticity index (PI) of up to 25 or 30 would be acceptable for most applications In theory, this would mean that skyscrapers could be built out of blocks made of earth. But they’re more likely to be used in the day-to-day construction of rapidly growing cities, for example there is need for around 2 million new houses in Ghana per year, but most of the building is concentrated in the capital Accra, where land is very expensive. The aim of Hive Earth is a construction company based in Accra, Ghana is to build houses that our workers and the majority of Ghanaians and West Africans can afford. The prototype that should be ready by the end of the year will cost roughly $5,000 for a one-room house using the earth from the site, avoiding freight expenses.
Prefabricated rammed earth walls are being developed simultaneously in Austria by Martin Rauch and in United Stated by David Easton : “Simply speaking, there are many projects where classic rammed earth is just not practical. Slimming down has opened a lot of new doors. Whether it’s an art piece on the wall or a rain-screen cladding, rammed earth has a bright and bold new future.” - Easton. A revolutionary new technology under development is 3D earth printed houses ,Gaia is a highly performing module both in terms of energy and indoor health, with an almost zero environmental impact.For the realization of Gaia, RiceHouse supplied the vegetable fibers through which WASP has developed a compound composed of 25% of soil taken from the site (30% clay, 40% silt and 30% sand), 40% from straw chopped rice, 25% rice husk and 10% hydraulic lime. The mixture has been mixed through the use of a wet pan mill, able to make the mixture homogeneous and workable.The external casing, completely 3D printed on-site through the Crane WASP, has been designed with the aim of integrating natural ventilation systems and thermo-acoustic insulation systems in only one solution. The versatility of the computational design is in fact made possible in the construction practice thanks to the precision and speed of the 3D technology, obtaining complex geometries, difficult to replicate with the traditional construction systems. It took 10 days for the realization of the 3d printed casing, for a total of 30 square meters of wall whose thickness is 40 cm and the total cost of the materials used in the wall structure is € 900. Ramming requires little water, which can be an important consideration in dry climates with sacristy of fresh water. They require few other resources like aggregates or additives to improve their properties. - Earth can be recycled, is easy and agreeable to work. - Has good insulating properties if built with high thermal mass especially for hot climate. - Known fact earth gives off no harmful emissions. - Good for noise reduction and insulation. - Earth doesn’t burn, so rammed earth walls are fire proof. - Load bearing, which reduces the need for structural supports, therefore reducing building costs. In a world with increasing demand for housing in developing countries and the urgency to reduce carbon emissions earth construction in all its variants can contribute efficiently to the stabilization of our environment while supporting human conditions of life. The popularization of the material will lead us to the adequate regulation and availability of the technology to supply the needs of our civilization. I personally believe that there is an opportunity and a great potential for building on earth with earth.