The use of polymer stabilised earth foundations for rammed earth construction

This paper presents a case study as part of a Professional Doctorate research project discussing an ecological approach to housing in South Africa, where polymer stabilised earth foundations have been used to support single story rammed earth walls, in a house in South Africa. Rammed earth was chosen as a construction method for its low embodied energy and thermal mass characteristics. The subsurface strata upon which the house was built comprised of clayey, gravely, sandy soils that have resulted as a result of decomposition of granitic rocks. In order to ensure solid founding conditions the foundations were excavated to a depth of one and a half metres before the excavated material was stabilised and backfilled. The material was stabilised to 600mm below top of floor level with 2% Portland cement and above that with a 5% polymer bitumen mixture reinforced with horizontal steel reinforcing rods. This foundation avoids the use of reinforced concrete and as a result a significantly smaller carbon footprint, while fulfilling the functional requirements of supporting the building and preventing rising damp. The polymer has, as it major component is bitumen emulsion, provided a waterproof layer. Rammed earth walls of 500mm thickness were constructed on the foundation up to 4.2 meters in height and initial observations suggest that the foundations are satisfactory with no settlement or cracking detected.