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Who’s Afraid of Raw Earth? Geotechnical Understanding and the Future of Earth Construction

Carved gypsum arabesque at Beit al-Hikma Academy in Tunisia

Carved gypsum arabesque at Beit al-Hikma Academy in Tunisia

I had the pleasure of speaking at two earthen architecture events in the past couple of weeks that highlighted the different approaches in earth architecture between the developed and developing world, and the opportunities and challenges ahead. The first was a one-day raw earth architecture symposium at the Beit al-Hikma Academy in Tunisia. The second was an international conference on rammed earth at the University of Western Australia.

The buildings and streets of the Medina of Tunis are still providing an effective response to the climate more than one thousand years later. Which of our contemporary cities will be able to make similar claims?

The buildings and streets of the Medina of Tunis are still providing an effective response to the climate more than one thousand years later. Which of our contemporary cities will be able to make similar claims?

In the developing world, which contains the majority of traditional raw earth building stock, capitalizing on the advantages of earthen building materials moving forward will require overcoming the perception of earth as a traditional building material out of step with contemporary architecture. In the developed world, where there is a great deal of excitement about earth as the basis for low carbon future in architecture, the challenge is in weaning ourselves from the use of cement stabilizers that drive up the carbon footprint of rammed earth, compromising our reasons for using it in the first place. Addressing both of these issues will require cultural as well as technical shifts. 

Rooftops at the Medina of Tunis 

Rooftops at the Medina of Tunis 

The symposium in Tunis bridged the technical and poetic aspects of historic and contemporary earthen architecture, covering the preservation of heritage earth buildings in Morocco and Yemen, as well as the future of earth building in the region. Among the buildings presented by Salma Samar Damluji were the raw mud brick buildings of Wadi Daw'an in Yemen. Karim Ladiji, a Tunisian architect who has since relocated to Los Angeles, presented the first rammed earth building in Tunisia in at least a century. I gave an overview of stabilized rammed earth in North America, with the implications that this has on its environmental impacts. And of course, the role that we expect Watershed Block to play in the future of earth construction. 

Courtyard house, Medina of Tunis 

Courtyard house, Medina of Tunis 

The day after the symposium we walked through the Medina of Tunis, a Unesco World Heritage site constructed around the Zitouna mosque.  Led by Zoubeir Mouhli, director of preservation for the Medina, we visited a number of typical earthen courtyard buildings developed in response to the extreme heat of the North Africa. The region has an abundance of earth architecture that provides beautiful climatically appropriate and comfortable spaces inside and out. Most of the earthen construction is hundreds of years old, uses structural vaults to minimize resource use, and requires no chemical stabilizers: an amazing display of appropriate technology. In this context, it is ironic that much of the conversation at the symposium at the Beit al-Hikma centred around the challenges of overcoming the perception of earth as a traditional material not aligned with technological progress. Although earth building may be all the rage in Europe, North American and Australia, it still takes convincing that earth can be the material of the future in places where it is tied to architecture of the past. 

After a brief stop in Dubai, I arrived in western Australia, where the rebirth of rammed earth took place in Australia the 1970's with visionary practitioners like Stephen Dobson leading the charge. Since then, rammed earth has taken hold in and around Perth, and has spread widely throughout the country, used for high-end and more affordable construction alike. The conference itself was a unique blend of academic researchers and practitioners. Unlike North Africa, where earth builders must fight the perception as a traditional material out of step with technological progress, in Australia, as in North America, earth construction is viewed as an ecologically appropriate contemporary response to climate and energy concerns, which accounts for a big part of its growing popularity. 

Structural masonry groin vaults,  Medina of Tunis

Structural masonry groin vaults,  Medina of Tunis

The irony is that to meet building codes, most rammed earth mix designs in Australia, as in North America, incorporate 8-10% Portland cement, which increases the embodied energy of rammed earth 2-3X over unstabilized earth. As I argue in one of the two papers I presented at the conference, the embodied carbon of rammed earth construction varies linearly with the addition of Portland cement, and incorporation of 9% Portland cement in rammed earth mixes makes the embodied carbon of rammed earth roughly equivalent to that of masonry construction (thanks to Peter Walker’s former Bath University student Clare Lax for this last statistic). This should be sobering news to us as we celebrate the spread of rammed earth over the past 50 years. If the challenge of the first 50 years of the rammed earth resurgence was to gain the confidence of clients and building inspectors, the challenge of the next fifty years is to transition to raw earth construction that uses natural clay and clay-derivative binders to reduce its carbon footprint. In short, curbing our addiction to carbon-intensive Portland cement is essential if rammed earth is to deliver on its ecological claims. 

Rammed earth stabilized with 8-10% Portland cement is now a commonplace residential  construction material in Western Australia

Rammed earth stabilized with 8-10% Portland cement is now a commonplace residential  construction material in Western Australia

The shift from cement-stabilized to raw earth construction will require overcoming both cultural and technical challenges. There is ample historical and contemporary evidence to support the claim that raw earth can be used to produce durable buildings. At the conference I presented the raw earth demonstration wall I constructed at MIT back in 2005, which is showing some signs of age but proves that natural clay binders work as well in New England as they have in the Fujian province in China, the Rhone Valley, Andalusia, and a host of other places in the world where raw earth buildings have endured for hundreds of years with no cement binders. 

St Thomas More Church in Margaret River, Australia completed by Ramtec (Stephen Dobson)  in 1990.

St Thomas More Church in Margaret River, Australia completed by Ramtec (Stephen Dobson)  in 1990.

Despite ample built evidence that attests to the durability of raw earth buildings around the world, a generation of engineers trained in steel and cement systems are understandably uneasy when faced raw earth construction, in which natural unprocessed clays or geopolymers replace cement. These engineers are inclined to treat rammed earth as a kind of weak soil cement.

Mobilizing raw earth construction techniques in the developed world will require a better understanding of the behaviour and categorization of natural clays as well as their behaviour in different soil systems. Charles Augarde’s presentation in Margaret River differentiated between the typical structural engineering approach versus a geotechnical approach. The engineering approach generally considers rammed earth as a weak soil cement, which is a pragmatic way of relating the behaviour of rammed earth to more familiar structural systems at the cost of increasing the embodied carbon. In contrast, the geotechnical approach considers the behaviour of natural clay binders in soil systems. It is clear that the geotechnical approach will need to inform the structural approach as we transition to raw earth construction. Happily, presentations by Charles, his current and past doctoral students at the Durham University (UK), as well as the research presented by Daniela Ciancio and Chris Beckett, prove that the primary research that will inform this shift is already underway at university labs around the world. 

The one building that caused a buzz at the symposium in Tunisia as well as the conference in Australia was the Ricola Krauterzentrum, a 3,200 square metre rammed earth herb processing centre designed by Herzog and DeMeuron completed in 2014, earning it the distinction as the largest rammed earth building in Europe. Martin Rauch installed the rammed earth using prefabricated panels of raw earth in front of a load-bearing reinforced concrete moment frame capable of providing seismic performance that meets the Swiss building codes, which among the most aggressive in the world. A striking example of both the architecturally expressive potential of earth construction as well as a hybrid structural systems that draws from the past and future in equal measure, the Krauterzentrum is a significant step toward the meeting the challenges of a raw earth future.