New Materials For the Rehabilitation of Cultural Heritage

In this lecture some of the most recent intervention techniques for strengthening the cultural heritage constructions are presented and discussed. Many historical buildings are located in seismic active areas so that it is mandatory to define novel techniques that allow to increase the seismic capacity by respecting the requirements of the conservation. In the last decade the interest of composite materials for the restoration and rehabilitation of ancient masonry buildings was continuosly increased. In particular textile strips of carbon or glass fibers were considered to provide aids for the masonry in those zones subjected to tensile stresses. The fibers are embedded in situ in thermosetting resins. Other composite products concern FRP meshes that are used to reinforce a mortar coating applied on both masonry surfaces. Moreover stainless steel thin strips or strands are also used in particular techniques easy to be applied and that do not modify appreciably the actual seismic response of the structure. Different techniques for confining masonry columns so to increase the compression capacity and the ductility are presented. They concern the realization of hoops with FRP strips, with stainless steel thin strips and with stainless steel strands. The last one may be used also for exposed columns (not plastered) because the strands can be hidden with the mortar joint repointing. For increasing the in-plane shear resistance of masonry walls four strengthening techniques are discussed: two uses FRP composites and two uses stainless steel devices. The application of FRP strips on the masonry surface through adequate adhesives provides good in-plane shear performances, even though the lack of confinement may be crucial for multi-leaf masonries. The realization of a mortar coating reinforced with FRP meshes on both masonry surfaces allowed to increase considerably both the shear capacity and the ductility of the wall. Moreover, the transversal connectors provide good confinement to the masonry so that the technique is effective also for multi-leaf masonries. A strengthening method is based on the use of stainless steel thin strips that provide both the needed transversal confinement and the ties necessary to form a truss system for increasing the in-plane shear resistance. Finally a strengthening technique is made with a grid of stainless steel strands (or FRP wires) disposed on both surfaces of the masonry and connected together through steel elements. Good transversal confinement is provided and the shear resisrance is significantly increased. For out-of-plane flexure of the masonry the techniques with good confinement may guarantee good performances, even though further experimental studies are needed to support the theoretical results.