PSI - Issue 44

I. Boem et al. / Procedia Structural Integrity 44 (2023) 1260–1267 Boem I. and Gattesco N. / Structural Integrity Procedia 00 (2022) 000–000

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In the samples reinforced through the CRM technique, a thin layer of scratch was firstly sprayed on the masonry surface, then a preformed Glass Fiber-Reinforced Polymer (GFRP) mesh was positioned and a 30 mm thick mortar coating was applied. The GFRP mesh (Fig. 2a) was composed of long alkali-resistant glass fibers yarns weaved together and impregnated with a thermosetting resin. In the case with reinforcement at the intrados, L-shaped GFRP connectors (cross section 7x10 mm 2 , 57.6 mm 2 fiber area), provided with additional GFRP mesh devices (33x33 mm 2 grid pitch), were also introduced into holes drilled into the masonry through injection with thixotropic cementitious mortar (6/m 2 ). The adopted FRCM technique consisted in the spreading of a first, thin layer of mortar (about 4-5 mm), the application of a heat-sealed mesh made of dry carbon fiber bundles (Fig. 2b), impregnated on-site with a two component water-based adhesive resin with low viscosity, and the finishing with mortar covering (4-5 mm thick). The global thickness of the FRCM system resulted of about 8-10 mm. The characteristics of the fiber reinforcements are summarized in Table 1; for both systems, it was adopted a premixed hydraulic mortar, with average compressive strength f c,c = 8.6 MPa, tensile strength f t,c = 1.1 MPa and Young modulus E c = 8.5 GPa.

Table 1. Main characteristics of the fiber meshes. Glass AR Carbon Mesh type Woven, preformed Heat-sealed Grid pitch 66x66 mm 2 8x8 mm 2 Weight 500 g/m 2 200 g/m 2 Area of dry fibers 58 mm 2 /m 56 mm 2 /m Tensile strength 1182 MPa 1375 MPa Young modulus 58 GPa 102 GPa

Characterization tensile tests on both CRM (Fig. 2a) and FRCM (Fig. 2b) coupons were performed (at least 6 coupons for each type): the results are reported in terms of applied load per unit of width at the varying of the mean strain. It is observed that both tests sets attained to very similar mean values of resistance: 86.5 kN/m for CRM (C.o.V. 8.2%) and 95.3 kN/m for FRCM (C.o.V. 8.5%), in accordance to the similar tensile strength and equivalent fiber area per unit of width for two meshes (Table 1).

a b Fig. 2. Characterization tensile tests on (a) CRM and (b) FRCM coupons: strength per unit of width varying the mean strain. The behaviour of the bare textiles was also reported in dotted lines; moreover, the numerical curves of the composite overlays are plotted (multi-layer modelling). However, the trend of the curves showed some differences. The FRCM samples had a very limited un-cracked, rigid phase (up to 8-10 kN/m) followed by a rapid stiffness reduction due to the progressive, diffuse mortar cracking. In this phase, the graphs roughly overlapped with that of the bare carbon-fibers, till the attainment of the fibers failure at an ultimate tensile strain value of 1.68% (C.o.V. 9.3%). Differently, in CRM samples, the first un-cracked phase resulted more pronounced (up to 35-40 kN/m), due to the higher mortar thickness; then, the sequential occurrence of cracks determined an irregular trend, due to sudden load