Issue 74

V. J. Kalyani et alii, Frattura ed Integrità Strutturale, 74 (2025) 89-114; DOI: 10.3221/IGF-ESIS.74.07

roller to ensure strong interfacial bonding. As shown in Fig. 4(h), a final layer of epoxy adhesive is applied over the GFRP to complete the lay-up. The mould’s top cover is repositioned (Fig. 4(i)), and uniform mechanical pressure is applied using nut-bolts and weighted plates (Fig. 4(j)) to enhance consolidation of laminate layers and minimize air entrapment. After curing for 24 hours under ambient conditions, the assembly is disassembled and the hybrid coupon specimen is carefully extracted. The mould is then reassembled for subsequent specimen preparation. To complete the test specimen, steel end tabs measuring 100 mm × 100 mm × 6 mm are bonded to both ends using the same adhesive, as shown in Fig. 4(k), to facilitate gripping during tensile testing. The final hybrid coupon specimens measure 500 mm in length and 100 mm in width, with an effective gauge length of 300 mm, satisfying the requirements of ASTM D3039 [25] for tensile testing. All experimental results of tensile test performed on coupon specimens of different configurations, reported in the present study correspond exclusively to specimens prepared using this second approach.

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Figure 4: Illustrative photographs of step-wise procedure for development of hybrid GFRP-SSWM wrap.

A total of 48 bond specimens are cast, prepared, and tested in this experimental investigation to evaluate the bond strength between concrete and various strengthening materials under ambient conditions. The specimens are primarily categorized into two groups based on the type of adhesive used: Sikadur 30 LP and Sikadur 330, consistent with the classification used for the coupon specimens. Within each adhesive group, the specimens are further subdivided according to the strengthening configurations employed for bond testing, as detailed in Tab. 3. Dumbbell-shaped specimens are cast using M25 grade concrete. A schematic representation of the specimen dimensions is shown in Fig. 5(a). The formwork is prepared from 17 mm thick white PVC sheets, as shown in Fig. 5(b). A uniform 1 mm gap is maintained between the two parts of each dumbbell specimen. A typical photograph of the casting of specimen is provided in Fig. 5(c). Specimens are demoulded after 24 hours, and subjected to water curing for 28 days. Following curing,

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