Earth construction: bird teaching

Abstract

The paradigm of earth being a traditional and a modern building material has been related to the fact that it is natural, ecological, recycled, abundant and economic. Among the traditional Portuguese building techniques, earth construction was always one very common. The construction built with these techniques must be preserved. In this context, the main objective of this research work is to give a contribution on the material properties characterization and, in particular, for the development of adequate rehabilitation and strengthening techniques for this type of construction, based upon a biomimetics study focused on the andorinha-dos-beirais nest. A structural numerical model of a nest using a finite element computer analysis program was done in order to understand the structural behavior of this kind of natural structures. In order to identify a possible occurrence of a certain agglutination phenomenon during the building process of the nest by the birds, an experimental identification/characterization study of nest’s material using samples taken in Vila Real area was carried out. The identification of the elementary chemical and the mineralogical compositions of the material were done by the scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and by the X-ray diffraction analysis, respectively. The identification/characterization of the organic composition was done using the colorimetric method, being the protein components detected by the biuret method and the polysaccharides/sugars components by the total sugar method. The identification of the type of polysaccharides/sugars and their amount was done by the anion-exchange chromatography method. In order to verify if the addition of polysaccharides/sugars into the nest’s material results in an improvement of the mechanical properties, in particular, of its compressive strength, mechanical tests were carried out on cubic specimens, The results show that there is a strong possibility of the bird andorinha-dos-beirais adds a certain amount of glucose into the clay material during the building process of the nest, which may increase the quality of this raw material.