Quick Answer
Aggregates such as sand, gravel, and crushed stone enhance the stability of rammed earth mixes by improving their density and strength, while also reducing the risk of erosion and settlement. The ideal aggregate-to-soil ratio typically ranges from 10 to 20% by volume. Proper selection and proportioning of aggregates are crucial to achieving a stable and durable rammed earth structure.
Aggregate Selection and Proportioning
When selecting aggregates for rammed earth mixes, it’s essential to consider the local availability, cost, and properties of the materials. A general rule of thumb is to use aggregates with a maximum particle size of 1/4 inch (6 mm) to prevent excessive voids and ensure good compaction. A typical aggregate mix might consist of 10% crushed stone (by volume) to improve density and strength, 5% sand to enhance workability, and the remaining 85% soil to maintain the thermal mass and insulating properties of the rammed earth structure.
Formwork and Compaction Techniques
To ensure a stable and even rammed earth wall, proper formwork and compaction techniques are crucial. The formwork should be designed to prevent excessive settlement and erosion, with a minimum wall thickness of 6 inches (150 mm) and a maximum height of 12 feet (3.6 meters) per layer. A combination of hand tampering and mechanical vibration can be used to compact the rammed earth mix, achieving a dry density of at least 100 pounds per cubic foot (1,600 kg/m³) to prevent erosion and settlement.
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