Just like when building sandcastles, getting the moisture levels right is all-important for constructing houses from packed earth, UK researchers say.
The research, led by scientists from the Durham University School of Engineering, studied the strength of rammed earth construction, an ancient building technique that uses a mixture soil and water to build rock-solid walls.
“We know that rammed earth can stand the test of time, but the source of its strength has not been understood properly to date,” said project leader Dr Charles Augarde in a statement.
“By understanding more about this we can begin to look at the implications for using rammed earth as a green material in the design of new buildings and in the conservation of ancient buildings that were constructed using the technique,” he said.
The team found that the strength of rammed earth was greatest when only a small amount of water was present in the mix of sand, gravel and clay which is compacted to form the construction material.
To test the strength of rammed earth, the scientists subjected small cylindrical samples to different external pressures. The researchers found that the suction created between soil particles at very low water contents was a source of strength.
Rammed earth walls left to dry naturally after construction in a suitable climate will retain some water – over time this little bit of moisture gives the walls considerable strength, said the researchers.
With this understanding, preventing ancient walls made of rammed earth from absorbing too much water should help to preserve them.
Rammed earth is considered a green material as it reduces the reliance on cement and can be produced from locally sourced materials. It is an approved building technique in Australia and the US, and was used to build experimental low cost housing in Wiltshire, UK, after World War I.
Ancient Chinese used rammed earth construction around 4000 years ago to build walls around their settlements. Parts of the Great Wall of China and Alhambra Palace in Spain were also built using rammed earth.
The research is published in the journal Geotechnique.
The research, led by scientists from the Durham University School of Engineering, studied the strength of rammed earth construction, an ancient building technique that uses a mixture soil and water to build rock-solid walls.
“We know that rammed earth can stand the test of time, but the source of its strength has not been understood properly to date,” said project leader Dr Charles Augarde in a statement.
“By understanding more about this we can begin to look at the implications for using rammed earth as a green material in the design of new buildings and in the conservation of ancient buildings that were constructed using the technique,” he said.
The team found that the strength of rammed earth was greatest when only a small amount of water was present in the mix of sand, gravel and clay which is compacted to form the construction material.
To test the strength of rammed earth, the scientists subjected small cylindrical samples to different external pressures. The researchers found that the suction created between soil particles at very low water contents was a source of strength.
Rammed earth walls left to dry naturally after construction in a suitable climate will retain some water – over time this little bit of moisture gives the walls considerable strength, said the researchers.
With this understanding, preventing ancient walls made of rammed earth from absorbing too much water should help to preserve them.
Rammed earth is considered a green material as it reduces the reliance on cement and can be produced from locally sourced materials. It is an approved building technique in Australia and the US, and was used to build experimental low cost housing in Wiltshire, UK, after World War I.
Ancient Chinese used rammed earth construction around 4000 years ago to build walls around their settlements. Parts of the Great Wall of China and Alhambra Palace in Spain were also built using rammed earth.
The research is published in the journal Geotechnique.
