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

1144

3

release fumes during the curing process. These fumes can contain volatile organic compounds (VOCs), such as formaldehyde, benzene, and toluene, which can be harmful if inhaled, affecting worker safety, and causing environmental issues (Huang, Zhu et al. 2018). Moreover, most of the commercially available epoxy resins are oligomers of di-glycidyl ether of bisphenol A (BPA), which are known to have a negative impact on human health including alterations in both immune and reproductive systems along with the modification in brain chemistry, and due to their chemical bond in polymer structures, the polymer release a small amount of BPA over time (Saba et al. 2016). Therefore, substituting the epoxy resins in strengthening application and reducing the usage of these materials contribute toward sustainable retrofitting of structures. However, although CBA seem to have less harmful environmental impacts compared to epoxy resins, cement production itself is associated with sustainability issues. The cement industry alone is responsible for creating up to 5% of worldwide man-made emissions of CO 2 , of which 50% are from the chemical process and 40% from burning fuel (Khodabakhshian et al. 2018). Therefore, the proposed strengthening technique could be further improved while the CBA itself is replaced by a more sustainable material. Geopolymer materials can constitute a more sustainable adhesive solution with adequate mechanical performance is using (Mohammadi-Firouz and Barros 2023). Geopolymer is an eco-friendly material that can attain relatively high mechanical properties, fire resistance and corrosion protection (Cong and Cheng 2021). Geopolymers can be engineered to have rheological properties required to a CBA to be applied in the NSM strengthening technique. This paper investigates the possibility of adopting geopolymer materials as adhesives in the NSM CFRP strengthening technique. The innovative aspect of this research of using geopolymers as an adhesive in FRP strengthening paves the way for sustainable alternatives in the rehabilitation and restoration of existing structures. An experimental work studying the bond performance of NSM sand-coated CFRP strips, using CBA and geopolymer adhesives is presented. Results of bond tests in ambient and thermo-mechanical conditions are presented and the relevant outcomes are discussed. Moreover, an LCA analysis was performed while the environmental impact of the three different types of practical adhesives for NSM, i.e. epoxy resin adhesive, CBA, and geopolymer adhesives (GPA) are compared. 2. Materials and methods To assess the feasibility of adopting a geopolymer material as an adhesive for the NSM CFRP strengthening technique, direct pullout bond tests were performed in ambient and thermo-mechanical conditions. The pullout samples were concrete blocks of 150×150×200 mm 3 of C25/30 strength class according to Eurocode 2 (CEN, 2004a). Average compressive strength of 33.8 MPa (COV of 3 %) was obtained from standard cylinders 150×300 after testing 4 samples at 28 days after casting. Grooves of 10 mm width by 25 mm depth were cut on the surface of concrete blocks, along the 20 mm edge for installing NSM CFRP strips. A bond length of 100 mm was adopted for all the prepared pullout samples. The bond test results of GPA samples are compared with those of CBA adhesives to verify the potential of using the geopolymer material for this application. Therefore, the material properties of CBA and GPA are presented here, followed by a brief overview of the development process of sand-coated CFRP strips. 2.1. The NSM bonding adhesive The CBA developed for this work consists of cement 52.5 I R, silica fume for improving microstructure (15% of binder in volume), and fine sand (maximum diameter of 1 mm) as the base ingredients. The flowability and shrinkage parameters were optimized using commercial products of polycarboxylate based superplasticizer and hydroxyl combination shrinkage reducing agents. To increase the flexural strength of CBA and resistance to spalling at high temperatures, Polyacrylonitrile (PAN) fibers were also added to the mixture (0.5% volume). Water to binder ratio of 17% was adopted for the mixture. A flow table test according to the BS EN 1015-3 (CEN, 2004b), performed with fresh CBA material resulting in 190 mm diameter. To evaluate the flexural strength of the material, 40×40×160 mm 3 prisms were prepared and tested in a 3-point bending setup, followed by compressive tests on the 40×40×40 mm 3 cubes from the same samples. An average compressive and flexural strength of 125.8 MPa and 15.8