Mechanical properties of unstabilized earth compressed at high pressures

Abstract

Earthen construction is attracting the interest of civil engineers because of its “green” credentials of limited environmental impact and energy efficiency over the life cycle of buildings. Yet, the adoption of earthen materials in mainstream construction is hindered by serious drawbacks including relatively low strength and water infiltration. Among all earthen materials, compressed earth blocks are the most popular option because of the flexibility of the building process and the possibility to employ standard masonry construction techniques. Compressed earth blocks are currently produced by compacting moist soil inside a mould under pressures that range from 5MPa to 25MPa. This pressure is applied for few seconds, which is too short to allow full dissipation of the excess pore water pressures generated during compaction. In this paper, we propose an alternative compaction method that significantly improves the mechanical properties of compressed earth without resorting to chemical binders. A compaction pressure of up to 100MPa, higher than the pressures currently used, is applied and maintained constant for a longer period of time to allow consolidation of the soil. The attainment of high effective stresses increases the dry density of the soil and changes the material fabric in such a way that mechanical properties are highly enhanced [Olivier 1986; Houben 1994; Kouakou 2009]. Compressed earth samples were prepared according to the proposed compaction method at different water contents as to determine the compaction curves corresponding to different compaction pressures. After compaction, specimens were stored in a climatic chamber at constant temperature and humidity (25°C and 62%) until equalization. Unconfined compressive tests were subsequently performed on the equalized samples to investigate the effects of compaction pressure and dry density on stiffness and strength. The adopted compaction method resulted in mechanical properties that can compete with those of stabilized earth and standard masonry bricks.