The secret of a successful sandcastle could aid the revival of an ancient eco-friendly building technique, according to research led by Durham University.
Researchers, led by experts at Durham's School of Engineering, have carried out a study into the strength of rammed earth, which is growing in popularity as a sustainable building method.
Just as a sandcastle needs a little water to stand up, the Durham engineers found that the strength of rammed earth was heavily dependent on its water content.
Rammed earth is a manufactured material made up of sand, gravel and clay which is moistened and then compacted between forms to build walls. Sometimes stabilisers such as cement are added but the Durham research focussed on unstabilised materials.
The research, funded by the Engineering and Physical Sciences Research Council (EPSRC) and published in the journal Geotechnique, showed that a major component of the strength of rammed earth was due to the small amount of water present.
Small cylindrical samples of rammed earth underwent "triaxial testing" where external pressures are applied to model behaviour of the material in a wall. The researchers found that the suction created between soil particles at very low water contents was a source of strength in unstabilised rammed earth.
They showed that rammed earth walls left to dry after construction, in a suitable climate, could be expected to dry but not lose all their water. The small amount of water remaining provided considerable strength over time.
The researchers say their work could have implications for the future design of buildings using rammed earth as the link between strength and water content becomes clearer.
There is increasing interest in using the technique as it may help reduce reliance on cement in building materials (cement production being responsible for five per cent of man's CO2 output (1)). Rammed earth
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