PSI - Issue 11

Luigi Ascione et al. / Procedia Structural Integrity 11 (2018) 202–209 L. Ascione et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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reinforced polymer composites (FRP) are currently the most popular but present some drawbacks such as their poor resistance to high temperature and UV radiation, difficulty of application onto wet surfaces, and absence of vapor permeability. Fabric-Reinforced Cementitious Matrix (FRCM) composites are currently increasing their popularity. They showed good results for strengthening RC and masonry structures and can overcome the issues connected to the use of polymers matrices. In the technical literature, such composites are also referred to as TRC (Textile Reinforced Concrete), TRM (Textile Reinforced Mortars), or IMG (Inorganic Matrix-Grid composites). Despite their widespread application, the FRCM mechanical behaviour and failure mechanisms have not been adequately investigated. The occurrence of debonding mechanisms at different interfaces (Focacci et al. 2016) and the complex interaction between shear and tensile stresses determine important difficulties in the definition of reliable criteria for the homologation, acceptance, design, and quality control of these materials when applied as structural strengthening systems. The American ACI 549.4R-13 is currently the only available guideline for design and construction of these systems. In Italy, two new guidelines providing acceptance criteria and design provisions for externally bonded Fabric Reinforced Cementitious Matrix (FRCM) systems for repair and strengthening of masonry and concrete structures will be published soon by the Ministry of Public Works. They considered the most recent results obtained by many researchers (Ascione et al. 2015, Bellini et al. 2017, Carozzi et al. 2017, De Santis et al. 2017, Focacci et al. 2017, Valluzzi et al. 2014). The preparation of the two guidelines required a considerable effort due to variety of composite materials, both fibres and matrices, considered. This paper presents the essential features of these two guidelines. Comparisons with the American guideline are also reported together with some considerations regarding the different approaches followed. The composite materials (i.e FRCM systems) treated by the Italian guidelines consist of: 1) an inorganic matrix, 2) a reinforcing mesh, 3) organic additives (if any). Their thickness is usually between 5 and 20 mm. Polymeric microfibers, dispersed in the matrix with various aims, mainly for controlling the shrinkage, are also allowed. It is mandatory that the FRCMs are: (1) provided by a single Manufacturer, who assumes responsibility for the declaration of performance; and (2) marketed by the same Manufacturer or Distributor, as defined in the EU Regulation no. 305/2011. In particular, the Manufacturer has to be equipped with a permanent internal production control system, in agreement with UNI EN ISO 9001: 2000. The matrix, comprising cement or lime, is reinforced with open-mesh textiles realized with continuous fibres of different materials: 1) steel (mainly UHTSS, Ultra High Tensile Strength Steel), 2) aramid, 3) basalt, 4) carbon, 5) glass, 6) polyparaphenylene benzo-bisoxazole (PBO). The overall organic component weight percentage, compared to the weight of the inorganic binder (cement and/or lime), shall be explicitly indicated by the Manufacturer on the pre-packaged bags in which the binder is contained for commercialization. This percentage cannot exceed 5%. An organic coating/impregnation of the dry fabric is allowed, which does not fall within the aforementioned 5%. The net distance between the bundles/yarns or strands cannot be greater than 3 times the thickness of the composite and cannot be greater than 20 mm. Fig. 1a shows an example of a balanced carbon reinforcing mesh with bundles spaced at 10 mm on centre in both longitudinal and transversal direction. 2. Characteristics of the FRCMs