Soil-based construction materials are of interest as structural building materials due to their green credentials, as well as being present in many historical structures. For effective conservation of the latter, and to motivate greater uptake for new construction, understanding of the mechanical and hydraulic properties of these materials is in need of improvement. Earthen construction materials can be considered to be manufactured unsaturated soils, and advances in understanding can be made by considering them from a geotechnical point of view. This paper presents initial results from a major programme of testing, seeking improved properties for earthen construction materials, where unusual organic compounds have been employed as stabilisers. Two gums (guar and xanthan) used as stabilisers for a soil mixture are shown to have significant effects on certain mechanical properties, some of which can be explained, and other aspects which are in need of further investigation.

This paper investigates the mechanical behaviour of a hypercompacted unstabilized earth material manufactured by compressing a moist soil to very high pressures up to 100 MPa. The hypercompaction procedure increases material density, which in turn improves mechanical characteristics. Samples were manufactured at the scale of both small cylinders and masonry bricks.The effect of ambient humidity on the mechanical characteristics of the material was investigated at the scale of cylindrical samples, showing that both strength and stiffness are sensitive to environmental conditions and tend to increase as ambient humidity reduces. The strength of the bricks was instead investigated under laboratory ambient conditions by using different experimental configurations to assess the influence of sample slenderness and friction confinement. Additional tests were also performed to evaluate the influence of mortar joints and compaction-induced anisotropy. Overall, the hypercompacted earth material exhibits mechanical characteristics that are comparable with those of traditional building materials, such as fired bricks, concrete blocks or stabilized compressed earth.

A geotechnical perspective of raw earth building.

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