PSI - Issue 64

Reza M. Fioruz et al. / Procedia Structural Integrity 64 (2024) 1142–1151 Firouz R. M. et. al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 5. Environmental contribution analysis for 1 kg of bonding adhesives, (a) CBA; (b) GPA.

6. Conclusions This study explored the performance of geopolymer materials as an adhesive for NSM CFRP strengthening of RC structures. Results of bond tests were presented for NSM CFRP samples with cement-based (CBA) and geopolymer (GPA) matrices. Special sand-coated CFRP strips were used as NSM reinforcement in all series. Despite the slight differences in ambient and thermo-mechanical pullout tests, samples with both adhesives showed an approximately similar behavior. The failure modes observed in all samples were essentially showing slipping of sand-coated CFRP strips through the adhesive medium. The average bond strength for tested samples with CBA and GPA matrices were 9.0 MPa and 8.2 MPa, respectively. Therefore, GPA samples could reach up to about 90% of the bond strength of those with CBA matrix at ambient temperature which shows a promising performance. Thermo-mechanical tests showed similar temperatures at the level of NSM CFRP at failure, which shows that the adhesives could delay the heat transfer to the CFRP. The average temperature for at the time of failure in the CFRP strip mid-height and top points for CBA samples were 150°C and 181°C, respectively, while 147°C and 183°C were recorded on GPA samples. The average surface temperature at failure and TUF in GPA samples were slightly higher (672°C), compared to the CBA samples (613°C). This could be attributed to the higher constant service load imposed on CBA samples, based on the average of the maximum pullout force at ambient temperature. The average heating time until failure (TUF parameter) for GPA and CBA adhesives was 36.7 min and 34.2 min, respectively. The LCA results showed a similar outcome for the CBA and GPA materials, in terms of CO2 emission. However, the GWP-Total index for both CBA and GPA were about 22% of that of the epoxy adhesive. By using GPA material with less volume of MK would result in an eco-friendlier geopolymer adhesive, but its impact on the bond performance must be assessed. For future studies, it would be interesting to assess the feasibility of using a geopolymer material with a low content of metakaolin as a “green adhesive”. This adhesive should have a lower environmental impact while preserving the necessary mechanical performance for bonding CFRP to concrete substrates. Also, it is recommended to explore the performance of geopolymer materials for NSM CFRP strengthening of flexural RC members, e.g. beams and slabs, in ambient and standard fire tests. Acknowledgements The authors would like to express their gratitude and appreciation to S&P Clever reinforcement Ibérica and Sika Portugal for supplying materials. The first author would like to thank the Fundação para a Ciência e a Tecnologia (FCT) for the financial support through the Research Grant SFRH/BD/145796/2019.