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Stabilisation de matériaux de construction durables et écologiques à base de terre crue par des liants organiques et/ou minéraux à faibles impacts environnementaux

Abstract : In the climate change mitigation context, unfired earth materials are a valuable alternative to cement concrete for reducing the construction sector related CO2 emission. However, this millenary construction material still has to meet current standards on mechanical and water resistance requirements. Hence, most industrial applications and papers on unfired earth stabilization use cement and lime for the stabilization of earth. But (Van Damme et al., 2017) pointed out the fact the high embodied energy of mineral binders and the high amount used for earth stabilization lead to doubt about the environmental friendliness of those solutions given their low improvement of the mechanical strengths. Yet, ancient earthen buildings and vernacular construction techniques in the worldwide showed the stabilization potential of some biopolymers. The so-called organic binders are food industry byproducts, which use for ancient earthen building renovation and vernacular techniques are recently revealed in some studies. Our study aims to propose a stabilization of earth for modern buildings with a good compromise between mechanical and water resistance performance on the one hand, and environmental impact on the other hand. A discussion on the relevance of proposing unfired earth bricks stabilized with cement and hydrated lime as an alternative to hollow concrete blocks led to limit the binder's content to 4% wt. of the dry soil. Preliminary tests on nine biopolymers have identified a few promising organic binders upstream, including ovalbumin (egg white protein), which does not require pre-activation. Thus, this organic binder as well as Portland cement and hydrated lime were used at 0, 2, and 4% to stabilize two soils (B and N) from the Occitanie region with different mineralogical characteristics. The results on compressive strength showed that the curing is necessary to guarantee the effectiveness of the mineral binders. In addition, the increase in manufacturing dry density at least equal to that of unstabilized soils' ones considerably improves the effectiveness of the stabilization. The improvement in dry compressive strength is greater on soil B, which is mainly composed of kaolinite, than on soil N, which is composed of montmorillonite and chlorite. However, on water resistance (wet compressive strength), it is the soil N that is better. Overall the formulations, those with 4% cement and ovalbumin at a manufacturing density equal to that of the soils alone, comply with the minimum resistance criteria both in the dry and wet state given in the French standard (XP P 13-901, 2001) standard. The surprise of this study is that ovalbumin gives much better mechanical performances and better durability (water resistance) than cement and lime for the same contents. In terms of hygrothermal performance, we have observed that the addition of binders reduces the hygroscopic capacities of soils. But they remain good according to the Nordtest criterion up to 4% addition of binder. It's worth mentioning that ovalbumin reduces soil hygroscopy much more than other binders. The thermal conductivity measured on mixtures with densities equal to the density of soils alone does not change. This confirms the observations made in the literature about the correlation between the dry density of materials and their thermal conductivities. Classical mineralogical analysis techniques (XRD, IR spectroscopie, and TGA) were used in order to explain the mechanisms of the stabilizations. But they only highlighted the well-known mechamisms of the stabilization with mineral binders unlike the ones of ovalbumin for which further investigations are still required.
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Kouka Amed Jérémy Ouedraogo. Stabilisation de matériaux de construction durables et écologiques à base de terre crue par des liants organiques et/ou minéraux à faibles impacts environnementaux. Matériaux. Université Paul Sabatier - Toulouse III, 2019. Français. ⟨NNT : 2019TOU30199⟩. ⟨tel-02628530⟩

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