Quick Answer
Local soil can be used for rammed earth construction, but it's essential to test its suitability first, as it must be free from contaminants, have good compressive strength, and a stable moisture content.
Choosing the Right Soil
When selecting a local soil for rammed earth construction, look for a mix that contains at least 70% sand, 15% silt, and 15% clay. The ideal soil should have a pH between 6.5 and 8.5 and a moisture content of 10-15%. To ensure the soil meets these requirements, conduct a series of tests, including a sieve analysis, Atterberg limits, and a pH test.
Preparing the Soil
Once you’ve identified suitable local soil, it’s essential to prepare it for use in rammed earth construction. Begin by removing any debris, rocks, or other contaminants. Then, crush the soil to a uniform size and mix it with a small amount of water to achieve the optimal moisture content. The ideal mix should be workable, but not too wet or dry. A 1:1:1 sand-silt-clay mix, for example, can be achieved by adding 50-60% sand, 20-30% silt, and 20-30% clay.
Compaction and Curing
To ensure the rammed earth structure is stable and durable, compact the soil mixture in a 1-inch layer at a time, using a tamper or hand tool. Apply a moderate amount of pressure to achieve a uniform density. After compacting each layer, use a trowel or brush to smooth the surface and create a level base for the next layer. Allow the compacted soil to cure for at least 28 days before applying a finish, such as a natural plaster.
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