Earthen construction: an increase of the mechanical strength by optimizing the dispersion of the binder phase

Although of interest for its low embodied energy content for construction, earth is usually not used for modern construction due to the expensive, artisanal and complicated process and the high variability of the raw material. The transfer of techniques dedicated to cement concrete could help the industrialization of this material. The use of dispersant for an improved dispersion of the earth powder has been investigated for both dispersion of earth fine fraction and water (here named the binding phase) and mortar made with calibrated sand. An improvement of the rheology is observed with lower viscosity and yield stress. This leads to a very small improvement of the density however concomitant with a marked increase of the mechanical properties, Young modulus and compressive strength. The analysis of the microstructure of the mortar shows an increase of the largest pores, and a decrease of the clay platelets flocs. The evolutions of these properties are analyzed in terms of the Rumpf model at two different scales. The dispersant mainly acts on the platelet arrangement that defines the forces between particles, but also simultaneously decreases the permeability of this binding phase, therefore entrapping more air during the mixing of the powder and water. Clearly the use of a dispersant may be of interest for the processing of earth material on liquid state, decreasing the viscosity and/or allowing the reduction of the water content, and finally improving strength.