Bonding capacity of jute fabric reinforcements of earthen structural elements. An experimental analysis

Raw earth is one of the earliest and most common building materials in the history of mankind. Earthen building techniques are still used in many developing countries since they are suitable to satisfy the need of low cost housing, of environmental comfort and are fit for self-build practice. Due to the limited tensile strength of earth masonry structures, the possibility of recovering the existing herit- age in seismic areas, as well as suggesting the use of these materials for new constructions, is conditioned by the ability to improve its mechanical properties. In the last years, strengthening systems have been developed for masonry structures consisting of fiber reinforced composites, with polymer or cementitious matrix. These externally bonded strips are applied in order to avoid collapse mechanisms as overturning of structural walls and, finally, to increase strength against the seismic actions and improve the ductility, both of the structural elements and of the entire construction. The Authors reconsider the opportunity of applying an externally bonded reinforcement keeping in mind the sustainability of earth building tech- niques and suggesting the use of a strengthening system made of jute fabric and a matrix of earth and 10% gypsum. The substantial equality of matrix and masonry substrate gives good compatibility and adhesion of the strengthening system. Composite material externally bonded strips are generally sub- jected to peel and tangential loads on the bonding surface. In order to improve the knowledge concerning this reinforcing technique, necessary to assess appropriate interventions on existing buildings, the results of an experimental campaign aimed to evaluate the adhesion properties of jute reinforcement under peel- ing action are reported in this paper. The experimental campaign includes peeling tests carried out in the Laboratories of the Universitat Politècnica de València and of the University of Florence. The results were interpreted in light of energy theory of peeling.