06 fevereiro 2009

Rammed Earth_With a veneer of science_David Oliver

Rammed Earth - with a veneer of science
David Oliver, an australian architect from Queensland has spent a significant part of his professional life applying science to the simplicity of rammed earth construction. He is now recognised as a world leader in rammed earth technology and a significant driving force behind environmentally sustainable design in Australia. Along the way, David, who is based at Mooloolaba, on Queensland's Sunshine coast, has lifted the standing of the still-simple rammed earth technique to the same level as other 'conventional' construction methods.
David is the principal of his own architectural firm and its companion consultancy which is the vehicle for his pioneering technical work in rammed earth construction. He believes rammed earth will become ever more widely accepted and used over the next decade as more people become aware of it, and as the relative cost of other building materials increases - something he believes is inevitable.
"I believe rammed earth construction will become accepted as standard throughout Australia, with sub-contractors and builders who will specialise in the technique."

"There are already more than a dozen contractors around Australia specialising in rammed earth construction."
"Rammed earth has significant environmental and aesthetic appeal, and construction costs are comparable to the cost of building in cavity brick. It also has very good thermal modulation and acoustic insulation properties."
"The aesthetic appeal is very strong because rammed earth construction reflects, without interpretation, the natural colours of the locality."
"The colours of rammed earth buildings vary from district to district, depending on the colours of the materials available in the local area."
"Perhaps the strongest environmental benefit from rammed earth construction is that there is no firing involved, as there is with brick and cement, so the product is very low in embodied energy.
"I expect the cost-balance to change to significantly favour rammed earth construction over the next ten years, as the cost of energy increases and carbon and energy taxes are imposed."
Rammed earth was relatively labour intensive - about 60 percent of the cost of rammed earth construction is labour, David said. A wall can be constructed at about the rate a tradesperson could lay a brick wall.
David attributes his initial interest in earth construction techniques to 'romanticism'. "I was of the 60's generation, which was strong on idealism, and as an architect imbued with a good measure of idealism, earth construction appealed.

"My interest developed long ago before 'sustainability' became an issue."
When he started investigating the potential of earth construction, it soon became apparent that, largely because of the labour requirement of many forms of earth construction, rammed earth was the only commercial option in the Australian context, and since the 1980s, David and his associates have concentrated on rammed earth techniques.
"Initially I started designing for rammed earth construction and trying to get other people to construct the buildings, but that proved very difficult so we decided to learn how to do it ourselves. That also proved difficult. We found there was a global lack of knowledge about what made one building successful - that is, structurally sound - and another not. We could identify the problems but no-one seemed to know the answers."
In 1985, David travelled through the western provinces of China to learn more about the traditional earth construction methods used there and the following year he gained a Churchill Fellowship which enabled him to visit France, Germany, Britain and south-west USA to learn first-hand about the earth building techniques used in those countries.

"Some of the rammed earth buildings I saw in France were stately homes and mansions which have stood for more than 300 years. Rammed earth was used in France in the mid 17th century where suitable raw material was available and many of those buildings are still in use and still recognised as outstanding examples of the architecture of the period. On that study tour, I found that Australians knew as much as there was known about what was involved in successful rammed earth construction. We were then, and still are, at the cutting edge of modern earth building".
David's focus on rammed earth led eventually to technical definitions of the 'mix' of ingredients necessary for reliable construction; a development which he sees as the key to the potential of rammed earth as a modern construction material. "We set out to work out why some mixes worked and others didn't, and the end result is a physical and chemical definition of the necessary mix characteristics based on standard engineering analyses".
He is also involved in the final stages of trialling additives which will stabilise clays -an essential ingredient of the rammed earth 'mix' - and so prevent degradation of rammed earth construction by water. "Too much water can, in some instances, destabilise the clay particles and break down the mechanical bond formed between the particles. We have identified and patented additives which prevent that."
David believes identification of the additives, and definition of the physical and chemical characteristics of the construction mix, are the two biggest steps forward in the technical development of modern rammed earth construction: "We have taken the guess work out of the process. We are still using the traditional methods - compacting earthen material between forms which determine the shape of the construction - but in the past, determining the material to be used was a matter of trial and error or traditional experience. We realised very early on that to work in the modern context, with formal engineering and structural specifications to meet, we needed to be absolutely certain that we could produce consistent, high-quality results every time, building after building, no matter where they were located.
"If rammed earth was to be accepted as a modern building technology, it needed to be applicable to all areas and had to be able to be analysed and understood so engineering tests could be undertaken. At the same time, we wanted to use local material. Knowledge of the essential physical and chemical characteristics of successful rammed earth mixes enables us to develop a technical description of the ideal mix, and we are able to blend local materials to produce mixes with those characteristics."
Access to that information was now available through David's consultancy service for architects, engineers and builders interested in working in rammed earth, David said.
"Using our knowledge of the characteristics required, we are able to combine local materials, usually from several quarries, to achieve a mix with the necessary physical and chemical properties.
The materials included in a mix, and the proportions to be used, were determined on the basis of standard engineering tests of physical and chemical characteristics, said David. "Once we have worked out the mix, construction is a simple matter of dampening and compaction, as has been done for centuries, although we use modern technology for the compaction and do use one or two additives. We add a very small proportion of cement - about five percent by weight - to maximise erosion resistance, and the new additive to prevent bio-degradation as a result of excess moisture will become a standard part of the mix."

"The mix consultancy is done long-distance, in much the same way as a soil test. The builder or the consultant identifies a source of material he or she thinks might be suitable and sends our company a sample. We do an analysis and if something is lacking, we tell them what else to look for. Alternatively, they might send us several potential ingredients and we analyse the raw materials and develop the mix that way. Once we have all the components, we calculate the proportions and after that it is up to them."
"The construction technique is very simple. The key to success, and the soundness of the building, lies in the mix used."
With the technical side under control, David and his associates set out to promote awareness and appreciation of rammed earth construction through its use in prestige buildings. "We formed a construction company specialising in rammed earth techniques and set about winning a major project to boost its profile. We needed to show that rammed earth was good structurally and, from a design perspective, complied with current design and technical requirements, and was cost effective. We reasoned that a major project would increase public awareness of rammed earth and we would see a 'trickle-down' effect, which has happened.
"We needed to convince people we could build practical, commercial structures."

David Oliver is head of Greenway Architects and CEAC building consultancy. For contact details, see the Alternative Directory under Architects or Earth Builders or Ethical Building/Design Advisory Groups.
All Photos were taken from http://www.stabilisedearth.com.au/index.html website, an australian rammed earth building company created in 1986 by Ian and Tina Collect.

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