Impact of relative humidity on the mechanical behavior of compacted earth as a building material

• Three earthen materials have been tested in unconfined tests with cycles.
• Each earthen material have been confined at three different relative humidity.
• Axial strain has been measured by image correlation.
• Radial strain has been measured by non-contact sensors.
• Compacted earth exhibits a complex volumetric behavior.
• Its mechanical behavior appears to be strongly changed by the curing humidity.

Earthen buildings can provide an answer to face difficulties in modern constructions in both terms of sociology, economics as well as ecology. However, the difficulty to understand and to predict their long term behavior represents an obstacle to their spreading. In some cases for example, unsuitable repairs on old constructions can lead to catastrophic situations.More specifically, during their lifetime, earthen walls have to face important variations of indoor and outdoor relative humidity, which induces variations and gradients in their water content. In this context, this paper aims at addressing an important aspect, not yet fully understood: the impact of these variations on the deformability and the strength of unstabilized earth. To that purpose, unconfined compression tests, with and without unload–reload cycles, were performed on different compacted earth samples conditioned at different relative humidities. Tested samples were prepared from materials coming from different existing constructions and sieved at 10 mm. During the tests, the axial and radial strains were measured using non-contact sensors and an image correlation system. This study shows that earthen materials have a complex mechanical behavior, involving the phenomena of plastic straining and mechanical damage. Moreover, both of these phenomena show a strong dependence on the relative humidity at which the samples were stored, as well as on the activity of the clayey portion of the earth.