Behaviour of rammed earth structures: sustainable materials and strengthening techniques

In this thesis, a natural reinforcement method for earth structures is proposed. In particular, this research focused on the possibility of building and modeling a structural system made with rammed earth strengthened with jute fabric. In recent years, research has turned the attention towards the materials obtained from renewable sources, biodegradable and easily recoverable at the end of use. Earth is a natural traditional building material used all over the world and, as such, it has always been used in accordance with local traditions that are based on empirical knowledge. However, the preservation and enhancement of traditional earthen masonry, as well as the practice of construction with raw earth material for new buildings, needs a deep scientific knowledge of constructive techniques and of physical and mechanical properties of the material. The possibility of proposing earth material for new constructions is based on the use of reinforcement systems to yield appropriate renovations. Acting with suitable corrections and devices, earthen buildings can be used even in areas subject to seismic risk, guaranteeing acceptable safety. The aim of the reinforcement intervention is to increase resistance against the seismic actions and improve the ductility, both for the individual structural elements and for the construction. Artificial fiber composites are commonly used as reinforcement of masonry structures both in view of the seismic retrofitting of historical buildings and of the realization of new constructions which structural performances are adequate also in seismic areas. Correspondingly, biocomposites are being used as a reinforcement of earth buildings, being compatible with earth architecture from the point of view of environmental sustainability. This research work fits in the research field of FRCs (Fiber Reinforced Composites) as reinforcement method for masonry structures with the aim to extend and adapt to natural fibers, test methods and procedures of data treatment, useful to interpret the parameters that rule the materials behaviour and the interaction between parts. In order to design a reliable experimental technique to determine the necessary properties for the successive step of designing a reinforcement system, preliminary tests were necessary to assess the materials characteristics. Mineralogical, geotechnical and mechanical earth's characteristics were investigated, even with the use of eco-friendly additive. Tensile tests on jute yarns and jute strips were carried out. Test results were organized and statistically analyzed in order to interpret the basic laws of scale effects which influence is necessary to account for in the successive use of mechanical parameters. After materials characterization, the adhesion capacity of the reinforcement package composed by jute fabric and earth-gypsum matrix was investigated. Since the composite material strips, externally bonded to rammed earth supports, are generally subjected to peel and tangential loads on the bonding surface, the determination of the adhesion properties ii was considered a fundamental issue to produce specific rules that adequately support designers. In particular, an experimental campaign of peeling tests of jute fabric strips applied on prismatic earth specimens was carried out to evaluate the adhesion properties of the strengthening system. The results are compared with those obtained from single lap joint tests and interpreted with existing analytical models. In order to improve the knowledge concerning this reinforcing technique, necessary to assess appropriate interventions on existing buildings, an experimental program was carried out concerning the analysis of the mechanical behaviour of this type of reinforcements applied to rammed earth arches loaded asymmetrically. The arches were subjected to asymmetric load condition increasing up to incipient collapse characterized by the opening of four hinges. To verify the results obtained from the experimental tests the ultimate loads of the arches were calculated by limit analysis. Subsequently the arches were strengthened with jute fabric and tested again in order to verify the reinforcing ability of the fabric. The biocompatible reinforcement made with jute fabric and earthen matrix showed that it is possible to significantly increase the bearing capacity and the kinematical ductility of structural elements made with rammed earth.