Several recent studies have shown that poured earth concrete has its place among the building
materials of tomorrow. Poured earth is a durable material, available locally. In addition, shaping
it by traditional tools from the concrete industry (for example concrete benches) would allow
its massive use for the building industry. One of the major challenges is to combine the
flowability of earth concrete thanks to its large quantity of water and at the same time promote
rapid solidification which would give the concrete a strength allowing it to support its own
weight 24 hours after being poured. Recently, certain works, such as those of Pinel et al.1 and
De Filipis et al.2, have attempted to give the material a short-term solidification (24 h) without
waiting for it to dry, in order to allow rapid unplugging. Based on the use of alginate or alkali-
activated slags, these developments have made it possible to move towards stabilization
processes with very low environmental impact. Among the panel of solutions available to lead
to short-term internal strengthening, we explore the use of a plaster/hydrated lime as an addition
to the earth. Plaster and/or hydrated lime mixtures are indeed known materials for stabilizing
soils, earth in particular. They have the advantage of having a more favourable CO2 balance
than cement, while being recyclable and available at low cost. Strengthening of such a material
was made possible by using a binder phase containing a hemihydrate material whose the setting
in earth environment was investigated through multiphysics approach using a combination of
techniques such as ultra sounds, scanning electron microscopy coupled with advanced image
analysis, calorimetry and rheometry. In particular the hydration degree of hemihydrate is
studied using different compositions containing admixtures enabling a control of their setting time and
flowability.

References:
1 A. Pinel, Transition liquide-solide dans des dispersions d'argiles contrôlée par un biopolymère :
Application à la construction en terre, Thèse de doctorat, INSA Lyon, 2017.
2 U. De Filipis, Stabilisation de la terre par activation alcaline : Etude des phénomènes physico-
chimiques et de leur influence sur les propriétés d’usage, Thèse de doctorat, INSA Lyon, 2021.