Raw earth is one of the oldest building materials of mankind. Almost a third of the world’s population is living in an earth-based house. However, their use remains low compared to conventional materials such as concrete, steel, and wood. Although these geosourced materials are abundant, recyclable, and have a low environmental footprint, their use is very limited in the construction sector. This can be explained by the lack of data regarding their hygrothermal behavior. In this context, the present work aims to highlight the properties of cob construction material with straw addition. An experimental characterization of hygrothermal and microstructural properties has been carried out. Thermal conductivity, specific heat, sorption isotherms, moisture storage capacity, moisture buffer value (MBV), and water vapor permeability are obtained experimentally. Then, the collected data are used as input parameters of a numerical prediction model to numerically assess the thermal and hygric behavior. Cob is then compared to other more commonly used materials to highlight the benefits of its use within the context of the energetic and environmental transition. Our results will allow better understanding of the behavior of the new geosourced material thanks to experimental and numerical investigation.

The aim of this work is to explore the manufacturing of insulation structures using fused filament deposition of biosourced materials. The approach considers printing of Polylactic acid (PLA) and PLA-flax (PF) structures using varied infill density and printing temperatures. Differential Scanning Calorimetry and Thermal Gravimetry analysis are performed to study thermal behaviour of PLA and PF and derive weight content of fibres within PF. Thermal measurements show a strong dependence of thermal conductivity with infill density and slightly improved thermal insulation of PF compared to PLA. Moreover, both PF and PLA show a hydrophobic behaviour unlike conventional green concretes based on hemp or flax. In addition, both scanning electron and optical microscopies show marked morphological changes induced by the laying down process for PF. This latter exhibits a more complex and tortuous microstructure compared to PLA marked by the presence of inter-filament porosity. This work concludes with superior hygrothermal properties of PLA and PF compared to other biosourced materials such as hemp or flax concrete. This work also concludes with the beneficial role of flax fibres that provides better hygrothermal properties to the printed structures as well as on the need to optimize the infill characteristics including density and cell morphology density.