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Much research has been devoted over the past 30 years to the development of construction materials that can lower the environmental and economic costs of buildings over their entire life by reducing embodied energy, minimizing air conditioning needs and cutting down demolition waste. In this respect, raw earth is an attractive material because it is natural and largely available. In its simplest form, this material consists of a compacted mixture of soil and water which is put in place with the least possible transformation. Raw earth construction has been practised in ancient times but has only recently been rediscovered thanks to modern technology, which has improved fabrication efficiency. If properly manufactured, raw earth exhibits comparable mechanical characteristics and better hygro-thermal properties than concrete or fired bricks. After a brief historical overview, we discuss the advantages of raw earth construction in terms of environmental impact, energy consumption and indoor air quality together with the main obstacles to its wider dissemination. We also review the hydro-thermo-mechanical behaviour of raw earth in the context of the recent geotechnical literature, by examining the dependency of key parameters such as strength, stiffness and moisture retention on: (a) material variables (e.g. particle size and mineralogy), (b) manufacturing variables (e.g. density and stabilization) and (c) environmental variables (e.g. pore suction, ambient humidity and temperature). [ABSTRACT FROM AUTHOR]

This paper investigates the synergic effect of both hydrated lime and guar gum stabilisation on the mechanical, thermal and hygroscopic properties of a compressed earth material for building applications. The stiffness, strength and compression energy at failure of both unstabilised and stabilised earth samples were measured at different curing times by means of compression tests. The moisture-dependent thermal conductivity was instead determined via the hot disk technique at a constant temperature of 25 °C and at the three different relative humidity levels of 0 %, 50 % and 95 %. The specific heat capacity was measured by means of calorimetry tests at the three temperature levels of 32–34 °C, 34–36 °C and 36–38 °C. The moisture adsorption-desorption curves were measured by performing a cyclic variation of relative humidity between 0 % and 95 % at a constant temperature of 25 °C via the dynamic vapour sorption (DVS) technique. Results from the experimental campaign show that the proposed stabilisation methods increase both the peak compressive strength and compression energy at failure while the addition of the biopolymer guar gum induces a progressive reduction of stiffness. The thermal properties of the earth are only marginally affected by the addition of hydrated lime and guar gum, with stabilised samples exhibiting similar levels of thermal conductivity and specific heat capacity to those of the unstabilised ones. Finally, the biopolymer stabilised samples exhibited a similar hygroscopic behaviour to that of unstabilised ones, whereas the addition of hydrated lime deteriorates the moisture adsorption capacity of the material. • Earth samples are stabilised with hydrated lime and the biopolymer guar gam. • Biopolymer stabilisation increases strength and compression energy while reducing stiffness. • Lime stabilisation increases stiffness and strength but reduces ductility. • Lime and guar gum stabilisations marginally affect the thermal properties of the earth. • Moisture adsorption is preserved by guar gum stabilisation and reduced by lime stabilisation. [ABSTRACT FROM AUTHOR]