Properties of compressed earth blocks made of traditional materials from Benin

Abstract

The raw earth is a natural material originating from the slow decomposition of rocks and stones. It can be used as a construction material as cob, daub, wattle, adobe, moulded bricks, rammed earth or compressed earth blocks. The use of a specific technique depends on the vernacular habits and also on the climate to which the building will be submitted or on the intrinsic properties of the earth. In this paper, we study the thermal and mechanical properties of compressed earth blocks (CEB) made of raw earth from Benin. In order to improve the mechanical properties of this brittle material, especially the tensile stress, kenaf fibers are incorporated into the mix. To determine the influence of the fibers on the various properties of CEB, the fiber content and the fiber length was varied. The results show a strong influence of these parameters on the porosity and as a consequence on the thermal and mechanical properties (compressive and tensile strengths). The increase in the porosity of the material yields a decrease in the mechanical strengths whatever the fiber content, except for long fibers. This seems to demonstrate combined effects of the porosity decrease and of the resistance to traction efforts due to the fibers. The addition of fibers also induces a decrease in the thermal conductivity of the material mainly due to the increase in the porosity.