Caractérisation et modélisation hygrothermique de la structure de murs de bâtiment en bois/argile renforcée par des fibres végétales

Abstract

Faced with the challenges of managing energy consumption in buildings and environmental issues, the reintegration of geosourced materials in construction proves to be a promising approach for sustainable and ecological construction. Cob, a traditional material composed of clay soil and plant fibres, stands out for its low carbon footprint and abundance of earthen materials, although its use is limited due to the lack of scientific references. The objective of this thesis is to provide a comprehensive characterization of cob formulated with 3% and 6% wheat fibres, followed by a numerical simulation of cob wall systems and cross-sectional wood/cob/wood cuts. The doctoral project is divided into three specific objectives. The first specific objective focuses on the characterization of clays, wheat fibres, and the formulation of cob samples by examining the water/clay ratio and the water/fibre ratio. The second specific objective aims to determine the hygrothermal and mechanical properties, porosity, and microstructure of cob and clay materials obtained in specific objective 1. As for the third objective, it aims to evaluate the hygrothermal behaviour of cob and wood/cob wall systems (materials obtained in objective 1) through numerical simulations with varying climatic data. Finally, an exploratory study was conducted on the fire resistance of cob samples and the thermal properties of cob samples stabilized with 2%, 4%, and 6% cement. The studies conducted to meet the various specific objectives have shown a significant improvement in the thermal performance of traditionally manufactured cob samples, with a reduced thermal conductivity ranging from 0.55 to 0.2 W/(m·K) and a specific thermal capacity ranging from 830 J/(kg·K) to 1600 J/(kg·K). These results highlight the potential of cob as a filling material in modern wood-frame structures, providing dual thermal regulation through the combination of wood and clay reinforced with fibres. The moisture buffer value (MBV) of clay samples, with or without fibre reinforcement, exceeds 2 g/(m²%RH), placing them in the excellence class according to NORDTest requirements. The open porosities of the samples ranged from 20% to 45%, with specific moisture capacities ranging from 0.014 kg/kg to 0.031 kg/kg. The mechanical properties of cob evaluated showed a significant increase in the compressive strength of red clay samples, from 1.8 MPa to 4.57 MPa, and that of beige clay samples, from 1.65 MPa to 4.61 MPa after 28 days. Flexural strength also increased with age for samples reinforced with 3% and 6% fibres, enhancing the ductility of cob samples. Preliminary fire resistance tests revealed that fibre-reinforced cob samples remain intact when exposed to high temperatures, although superficial cracks may appear, while fibreless samples break. The temperature on the unexposed side remains unchanged, demonstrating good thermal resistance. These results confirm those obtained from the hygrothermal simulation of cob wall systems with varying climatic data. The simulation results revealed stable interior temperatures in cob walls, reinforcing the idea that cob can contribute to sustainable and resilient construction. To promote the use of cob in cold and humid climate zones, the use of 3M™ 3015 air/vapor barrier membranes or rain barrier membranes is necessary to prevent the development of mold risks. The results of this study provide a solid foundation for future research aiming to optimize traditional cob formulations and develop innovative solutions to integrate these materials into modern construction. The development of building envelope systems with improved hygrothermal properties continues, and cob, with its environmental benefits and hygrothermal performance, could play a key role in transitioning to sustainable construction practices. The hygrothermal simulation results indicate that cob, as a filling material in wood-frame building structures, is an excellent regulator of interior temperature and humidity, making it suitable for specific applications in diverse environments.

Date	5 Dec 2024
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Claudiane Ouellet-Plamondon (Supervisor)