Optimising The Hygroscopic, Thermal And Structural Performances Of Sustainable Bio-Based Earthen Materials: Cob As A Case Study

Research in various fields of architecture is currently focused on developing sustainable and eco-friendly living environments. Buildings and construction activities contribute significantly to CO2 emissions, accounting for approximately 38% of total emissions (UNEP, 2020). The residential sector alone contributes to around 7.9% of Greenhouse Gas (GHG) emissions, and heating and cooling systems in buildings consume approximately 20% of energy in developed countries (Pérez-Lombard et al., 2008). To address these issues, numerous studies have been published, exploring new construction materials that can reduce CO2 emissions and energy consumption. Many of these materials have shown promising results in achieving these goals.

Thermal comfort, defined as the state in which individuals are satisfied with the thermal environment (ASHRAE, 2004), has been a significant focus of research. It is influenced by factors such as air temperature, air velocity, relative humidity, mean radiant temperature, metabolic heat production, and clothing insulation (ASHRAE, 2004). Additionally, occupants' behavior can impact thermal comfort, with variations observed based on income levels and other social factors (Barkenbus, 2013). Different models have been developed to study and measure thermal comfort, including Fanger's model and the adaptive model, which have been widely adopted in international standards (ASHRAE, 2004; ISO, 2005).

Earth has been used as a construction material for centuries, but its demand has recently increased due to its sustainable and green building techniques (Colin MacDougall, 2008). Cob, in particular, is a low-carbon alternative to conventional concrete, requiring less energy for manufacturing and operation, resulting in lower GHG emissions (Senanayake & King, 2019; Schroeder H, 2016). Cob can be classified into wet methods (e.g., compressed earth blocks, rammed earth) and dry methods (e.g., adobe, wattle and daub, earthen-based plaster) (Hamard et al., 2016).

Compared to other earthen materials, cob exhibits higher material ductility and architectural flexibility during construction (Gomaa et al., 2021a, 2021b). Its thermal properties make it suitable for both cold and hot climates (O.O. Akinkurolere et al., 2006). The composition of cob typically includes subsoil, fibers, and water. Other materials such as clay, lime, or cement can be added to enhance its structural stability (Gomaa et al., 2021). Previous studies have focused on optimizing the structural performance of cob, while a few have explored its hygrothermal properties. This research aims to create an optimized cob mixture based on existing literature, considering both structural and hygrothermal