Inorganic Stabilisation Methods for Extruded Earth Masonry Units

Addressing the challenges of embodied environmental impact of materials has led to growing interest in the use of earth as a construction material and the use of commercial methods of extruding bricks has potential to overcome many of the barriers of adoption. Without the usual firing process, the bricks could have a significantly lower embodied environmental impact and similar dimensions (approximately 100mm thick), to conventional masonry. However, the wider adoption of 100mm thick unfired earth masonry is dependent on its suitability for use in structurally load-bearing applications. Currently the greatest barrier to earth masonry adoption is the durability of the material when subjected to high moisture contents. Accidental or intentional wetting of a 100mm thick load bearing unfired earth wall could lead to disproportionate collapse unless the moisture resistance is improved.

To overcome the concern of elevated moisture contents, a standard approach is to chemically stabilise the soil through the addition of either cement or lime. While there has been research into the use of cement and lime for other forms of earth construction, the use for extruded earth bricks has not been investigated in depth. The source materials and inherent physical properties of extruded earth bricks are different to other forms of earthen construction therefore the suitability of cement and lime to stabilise soil for the purpose of extruded earth bricks requires investigation.

This research demonstrates the improvement in 28 day compressive strength, with a range of cement or lime contents and three initial curing temperatures. Small scale bricks are used for testing purposes and are tested in both the ambient environmental conditions and following 24 hours of full submersion in water. Key factors such density and moisture content, are shown to be important for compressive strength development but the effect of stabilisation and the specific stabiliser used has been shown to be more important than density and moisture content alone.