Guide for the Design and Construction of Externally Bonded Fibre Reinforced Inorganic Matrix Systems for Strengthening Existing Structures

The FRCM (Fibre-Reinforced Cementitious Matrix/Mortar) composites are nowadays used in structural rehabilitation interventions, more and more frequently, instead of classic FRP fibre reinforced composites (Fibre Reinforced Polymer), made with long glass, carbon or aramid fibres immersed in polymeric matrices (such as epoxy resins). In international literature the first are also called TRC (Textile Reinforced Concrete), TRM (Textile Reinforced Mortars), FRM (Fabric Reinforced Mortar) or even IMG (Inorganic Matrix-Grid Composites). In the following, since the acronym FRCM has been adopted in already approved Italian ministerial documents, it is preferred to continue using the same acronym. FRCM composites are the result of coupling nets, made with the same fibres mentioned above, or with others which have appeared more recently on the building materials market, with an inorganic matrix based on lime or cement mortar. Innovative fibres include basalt, PBO (Polyparaphenylene benzobisoxazole) and steel. In particular, this last material, very common in the construction field, is proposed again for use in FRCMs, in a version with highly enhanced mechanical performance, thanks to a particular processing process. The inorganic matrix has numerous advantages over the organic FRP matrix, especially for applications to masonry structures, given its greater affinity with this type of substrate. At the moment some guidelines are available in the international field for the qualification of FRCMs and for the design of structural reinforcement interventions carried out with such materials. In this connection the US acceptance criteria (ACI 434 - Acceptance Criteria for Masonry and Concrete Strengthening Using Fiber-Reinforced Cementitious Matrix (FRCM) Composite Systems, issued by ICC Evaluation Service, 2018) and the design guidelines (RILEM TC 250-CSM & ACI 549 - Guide to Design and Construction of Externally Bonded Fabric-Reinforced Cementitious Matrix (FRCM) and Steel Reinforced Grout (SRG) Systems for Repair and Strengthening Masonry Structures, pending approval) can be mentioned. In recent years, the scientific interest in the innovative applications of FRCMs for structural rehabilitation, on the one hand, and the special nature of the widely varied Italian building heritage on the other, have attracted the interest of numerous researchers operating in the fields of Structural Mechanics, Construction, Structural Rehabilitation and Seismic Engineering. It is clear that the drafting of an Italian Guideline for the design and construction of strengthening interventions with FRCMs could no longer be postponed; above all, the drafting of a wide ranging document usable for the different types present in the national building heritage, from the masonry to the concrete constructions, as well as for the many FRCM products currently present on the national market that are different in nature of the matrix and the net reinforcement. The CNR, through its Advisory Committee on Technical Recommendations for Construction, promptly felt this need and made efforts to satisfy it by setting up a Working Group in June 2016 with the task of drawing up a Guideline for the design and construction of externally bonded fibre reinforced inorganic matrix systems for strengthening existing structures. In July 2017, the CNR Advisory Committee approved a first draft of this Technical Document on a proposal from the Working Group. Subsequently, the Working Group expanded to include all interested Italian researchers already scientifically committed to the topic, and benefited from the invaluable contribution of the FRCM manufacturers. It was thus possible to draw up the present version of the Technical Document, broader than the initial draft and characterized by more advanced applications and more sophisticated approaches which are at the frontier of current international research on the topic of structural reinforcement with FRCM