Relationships between the density and strength of rammed earth

The renewed interest in rammed earth as a building material demands that its properties be better quantified. Based on 219 stabilisation experiments, this study examines the relationship between the maximum dry density and uniaxial compressive strength of rammed earth and identifies the determinants of each parameter. A building code criterion value for strength of 2 MPa was used as the threshold of stabilisation success, and a corresponding density criterion value of 1·5 t/m³ was adopted based on the data. Multivariate modelling revealed that clay–silt content was the only determinant of density, whereas clay–silt content, sand content, linear shrinkage, and stabiliser (lime and cement) quantity all influenced strength. As a predictor, density explained a unique component of the variation in strength when controlled for the effects of soil properties and stabilisers. Similar value ranges of soil properties favoured passing both the strength and density criteria, indicating that selecting a soil to maximise stabilised strength will also maximise density. The density value of 1·75 t/m³ is the most suitable value of density to be incorporated in any future earth building code because it corresponds to the 2 MPa strength criterion and exceeds the density needed to pass durability test criteria and wall acoustic standards.