There are two types of rammed earth mixtures:
Unstabilized Using only naturally occurring soil ingredients. A quality unstabilized mix can have high compressive strength, but will be susceptible to degradation from exposure to water.
Stabilized Using natural soil ingredients and a hydraulic cement binder. The proportion of hydraulic cement can range widely, in some cases equaling the proportion found in conventional concrete. Stabilized mixes tend to have higher strength and will be more resistant to water damage.
Rammed earth mixtures require careful formulation to ensure adequate compressive strength, integrity, and resistance to water. Research and testing should be performed with the specific ingredients to be used to determine the best mixture.
Rammed earth can be produced in several formats, all of which can be unstabilized or stabilized:
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Formed rammed earth Ingredients are placed into temporary wooden forms in relatively small (4-6 inch) lifts and tamped in consecutive layers, creating a monolithic wall. Rebar or other reinforcement materials are often added to improve tensile strength and performance in seismic conditions. Compressed earth blocks (CEBs) and masonry units Ingredients are placed into a block form and manually or hydraulically compressed. The individual blocks are mortared together to create a wall. Earthbag, or flexible form rammed earth Ingredients are placed into a polypropylene bag or tube, and the fabric acts as a flexible form while the mixture is being tamped, either manually or mechanically. The bag or tube typically remains in place after construction, though it is not usually functional after compression and curing. The bags can help to provide stability for mixes that are less than ideal, and they protect the mixture from erosion. Earthships, or rammed earth tires Ingredients are placed into a used car or truck tire, and the tire acts as a form while the mixture is being tamped, either manually or mechanically. The tire remains in place as FiLLCrt- ( auctj oz” CAV.J) 3CtujC£M TrrLiS
A pier foundation uses a grid of posts in the ground to support loads from the building above. In some cases, piers might elevate the building completely above the ground, but piers can also anchor perimeter beams at grade level.