![Rammed Earth]( "Rammed Earth") Rammed earth, also known as taipa, pisé de terre or simply pisé, is a technique used in the building of walls using the raw materials of mud, chalk, lime and gravel. It is an ancient building method that has seen a revival in recent years as people seek more sustainable building materials and natural building methods. Because of the nature of the materials used it is incombustible, thermally insulating and very strong and hardwearing. It also has the added advantage of being a very low cost and simple way to construct walls. Traditionally, rammed earth buildings are common in arid regions where wood is in scarce supply.
Evidence of the early use of rammed earth as been seen in Neolithic archaeological sites of the Yangshao culture and the Longshan culture in China along the Yellow River dating back to 5000 BCE. By 2000 BCE, the use of rammed earth architectural techniques was commonly used for walls and foundations in China.
In the 1800s in the United States, rammed earth was popularized by a book Rural Economy by S. W. Johnson. For example, it was used to construct Borough House Plantation and Church of the Holy Cross in South Carolina, which are two National Historic Landmarks of the United States.
Rammed earth is a green material for a number of reasons. It does provide good thermal mass, which implies good heat storage and absorption. It also controls humidity where walls contain clay which is exposed to an internal space. Humidity is held between 40% and 60% (coincidentally the lower and upper trigger points for asthma sufferers) as well as the ideal humidity for the storage of susceptible items such as books. When cement is used these effects are not present, and ecological benefits may not be realized. Cement adds to the global carbon dioxide burden at a rate of 1.25 tons per ton of cement produced. Given cement blocks and walls rammed with cement, the content may vary in cement content in a range between 5% and 13%, a 300 mm thick “earth” wall with cement in will typically have a higher emissions burden than a 115 mm concrete block wall, and therefore cannot seriously be considered green. However this may be substantially offset by the partial substitution of cement with alternatives such as ground-granulated blast furnace slag.
Rammed earth is not only an economically viable construction technique; it results in pleasant, energy-efficient buildings. The density and thickness of rammed earth means cold temperature penetration has a slow rate of thermal conductivity. Warmth takes almost 12 hours to work its way through a 14-inch (360 mm) thick wall. The walls provide good thermal mass, which helps keep indoor temperatures stable, particularly in regions with dramatic daily temperature changes. The half-day rate of heat transfer and thermal mass of the material makes rammed earth a particularly suitable material for passive solar buildings. Rammed earth has been a popular choice for buildings where temperature fluctuations need to be kept to a minimum. It can be used in cooler climates but must be protected from heavy rain and insulated with vapor barriers.
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