Speaker
Description
The use of bio or geo-sourced materials is a sustainable solution to reduce the carbon footprint in the building sector. Among these, raw earth materials stand out thanks to its reversibility, local availability, and remarkable hygrothermal properties. Nevertheless, this material sometimes exhibits unpredictable mechanical responses due to its high sensitivity to water [1], which hinders a more widespread adoption. Raw earth is a composite material whose clay and silt particles, once hydrated, act as a binder for the granular skeleton. The cohesion of this porous medium and its mechanical properties are therefore strongly correlated with its hydric state [2]. During the construction of masonry structures, earth bricks are placed in contact with wet earth mortar, leading to water exchange through capillary flow (imbibition process) and evaporation (drying process) at the brick/mortar interfaces. This results in swelling and shrinkage of the material, which can induce significant local micro-cracking and severely affect cohesion. The extent of these micro-mechanisms is expected to be controlled by the microstructure and, in particular, by the properties of the pore network.
In this work, we characterize the hydromechanical coupling that leads to the cohesion between earth bricks and mortar to explain the counterintuitive observation that walls built with denser bricks, featuring better mechanical strength, thinner pores and higher capillary forces, may exhibit worse strength than looser bricks with worse mechanical strength, larger pores and lower capillary forces. The response of raw earth structures, including masonry, has primarily been studied at macroscopic and phenomenological levels. To our knowledge, no full-field micro-mechanical study of hydromechanical coupling at interfaces exists, despite the need to understand and quantify these processes at the local scale due to the material's strong heterogeneity. In our study, we track the evolution of raw earth microstructures (samples of dimensions Ø × h = 20 × 40 mm) during imbibition and drying tests using 3D operando measurements in a laboratory micro-tomograph as well as the multi-modal neutron+X-ray imaging platform NeXT at the institut Laue-Langevin [3]. The combined use of neutron and X-ray tomography allows us to characterize the hydro-mechanical behavior of brick-mortar interface during these processes by locally relating deformation and micro-cracking (visible through X-rays to the saturation rate visible with Neutrons. We are also studying the impact of the microstructure on this hydro-mechanical coupling by testing raw earth with different porosity levels, as well as different grain size distributions and mineralogical compositions.
| References | [1] Hall M, Djerbib Y Moisture ingress in rammed earth: part 1—the effect of soil particle-size distribution on the rate of capillary suction. Constr Build Mater 18:269–280. (2004) [2] Chauhan, P., El Hajjar, A., Prime, N., & Plé, O. Unsaturated behavior of rammed earth: Experimentation towards numerical modelling. Construction and Building Materials, 227, 116646 (2019). [3] Tengattini, A., Lenoir, N., Andò, E., Giroud, B., Atkins, D., Beaucour, J., & Viggiani, G. NeXT-Grenoble, the Neutron and X-ray tomograph in Grenoble. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 968, 163939 (2020). |
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| Country | France |
| Green Housing & Porous Media Focused Abstracts | This abstract is related to Green Housing |
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