Sorption properties of biobased and raw earth materials: investigation of temperature and dry mass measurements

• Autor(a) principal: Costa, Inês Filipa da Mota
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/34366
• topic: Compacted earth; Earth plaster; Hemp concrete; Drying-method; Temperature; Hygrothermal behaviour; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Civil

Relative humidity influence strongly the indoor air quality and human comfort. Therefore, the hygrothermal behaviour of building materials is an important parameter and there has been a growing interest in studying passive solutions to regulate the indoor relative humidity. Since earth materials have the ability to absorb and release water vapour, they can be used to moderate the amplitude of indoor relative humidity and therefore to improve the indoor air quality and consequently save energy. Many researchers have been focussed on studying the hygrothermal properties of earth building materials, but it is still a scientific challenge to characterize precisely the hygrothermal coupling of those materials. This dissertation focuses on two main objectives, developed and studied in three different porous materials: compacted earth, earth plaster and hemp concrete. The first one is to analyse the effectiveness and the influence of three different drying-methods (oven-drying at 60°C, oven-drying at 105°C and vacuum-drying), and recommend one standard method, for each material studied, since there is no clear guidance to determine the correct dry mass of biobased and earth materials. Complementary to the first objective, it is evaluated the impact of drying/wetting cycles using the same three drying-methods. The second objective is to study the evolution of sorption curves with temperature, for biobased and raw-earth materials. The analysis of the results showed that the first drying process affects the moisture uptake of all the studied materials, from there forward. Oven-drying at 60ºC and vacuum-drying are the methods that produce less impact in the porous network. More specifically, vacuum-drying is the method that allows less impact in the first drying of compacted earth and hemp concrete, and both, vacuum-drying and oven-drying at 60°C, are suitable for a non-impact drying of earth plaster. However, they are not completely efficient in drying earth materials since hysteresis is observed in drying/wetting cycles. Using oven-drying at 105°C it is not observed hysteresis and therefore, this is the most effective method, but it is the method that most presents impact in the porous network after the first drying. Analysing the influence of temperature on the absorption curves, the results show that temperature cycles have no relevant impact on the hygrothermal behaviour of earth materials. Comparing the sorption curves of the three materials plotted at the same temperature, the influence of temperature is more relevant than the materials itself for compacted earth and earth plaster. The same cannot be stated for the hemp concrete.