Adobe Blocks Reinforced with Vegetal Fibres: Mechanical and Thermal Characterisation

Abstract

The present study is based on the characterisation of adobe blocks of the central region of Portugal. It is recognised that the safeguarding of the existing building stock of constructions in the traditional adobe construction technique, through different levels interventions, should also preserve the historical and cultural identity of the area as well as the traditional construction techniques, starting from the ground itself. Soil, as a repository of valuable information on the history of the site, underpins the conservation and preservation process. However, the soil is a local expression of the site, and a precise knowledge of its characteristics is necessary to hypothesise building recovery strategies. For this reason, the characteristics of adobe blocks from old buildings in the village of Torres in Anadia, in a rural area that has not yet been the subject of scientific research, were evaluated. These adobe blocks were taken from the buildings to be used in the laboratory to determine the similar mixing rates for the new adobe mixtures by analysing the material’s chemical, physical, mechanical, and thermal properties, as well as its particle size distribution. In the study area, a wetland was identified characterised by a notable presence of vegetation, namely bunho and junco (Schoenoplectus lacustris L.). These fibres, which can be assimilated to Typha, are wild aquatic plants that can impair the biodiversity of wetlands but which, used as reinforcement for the production of adobe bricks, can stimulate new, more sustainable forms of economy in in the area, which is classified as rural. The fibres were divided into two groups of 10–30 mm and 30–60 mm in length, and compositions with an additional 1 to 3% of fibres were formulated. This experimental approach was useful for understanding how the length and quantity of these fibres influence the performance of the material, thus contributing to improving knowledge about the behaviour of adobe blocks in relation to the incorporation of vegetable fibre reinforcement. The research findings reveal that the length of the fibres and percentage of incorporation have a significant impact on the mechanical behavior of the material, particularly in relation to its compressive strength up to 50%. The tested formulations were also assessed with respect to capillarity, for which most of the formulations were classified as weakly capillary, with a capillary index (Cb) of less than 20. With respect to thermal conductivity, the incorporation of fibres led to a reduction of up to 20%. The characterisations demonstrate that the optimisation of adobe is the initial stage in attaining comprehensive insight into the heritage of traditional construction in the central region of Portugal, with a particular focus on the village of Torres and the ancient adobe construction technique.