Sandcastles give clue to ancient construction technique
Scientists have uncovered the secret to the strength of rammed earth, an ancient, environmentally friendly building technique used in structures as diverse as the Great Wall of China and the Alhambra in Spain. The findings, published in the journal Géotechnique, have implications for the conservation of historical rammed earth structures and the construction of new ones. Rammed earth is a mixture of sand, gravel and clay, plus a small amount of water that is compacted between forms to make walls. Now researchers at Durham University in the UK reveal that, just as a sturdy sandcastle requires just a small amount of water for stability, rammed earth's strength is linked to its moisture content. The scientists applied pressure to samples of rammed earth in the laboratory. Their analyses revealed that when the water content of the rammed earth is very low, the suction created between the soil particles gives the structure its strength. According to the researchers, in the right climate, when rammed earth walls are left to dry after construction, they retain a tiny amount of their water, and this is the source of their strength. 'We know that rammed earth can stand the test of time, but the source of its strength has not been understood properly to date,' commented Dr Charles Augarde of Durham University's School of Engineering. 'Without this understanding we cannot effectively conserve old rammed earth or make economic designs for new build. 'Our initial tests point to its main source of strength being linked to its water content. 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.' The Chinese started using rammed earth to build walls around their settlements around 4,000 years ago, and the technique subsequently spread around the world. The Durham researchers' findings should aid in the conservation of ancient structures and monuments built with rammed earth, for example by preventing too much water from getting into the material. Meanwhile, architects and builders are increasingly turning to rammed earth for the construction of new buildings, as the materials can be locally sourced and there is no need for cement. This is important for the environment, as cement production is responsible for 5% of the world's carbon dioxide emissions. 'This kind of research is very valuable as the construction industry analyses environmentally sound, traditional ways of building and adapts them for sustainable construction in the 21st century,' commented Tom Morton, secretary of Earth Building UK, an organisation that promotes conservation on construction of earth building in the UK. 'Such low-carbon technologies are most likely to succeed by marrying the expertise of our research universities such as Durham with the commercial understanding of the wider industry, and we are seeing a number of very exciting developments in this area.'
Countries
United Kingdom