PSI - Issue 64

Hamzeh Shdeifat et al. / Procedia Structural Integrity 64 (2024) 1360–1368 Shdeifat et al. / Structural Integrity Procedia 00 (2019) 000–000

1361

2

Nomenclature RC

reinforced concrete NSM Near Surface mounted CFRP carbon fibre reinforced polymer GT glass transition temperature CFRP carbon fibre reinforced polymer

1. Introduction Near surface mounted (NSM) CFRP strengthening of reinforced concrete (RC) beams has attained a great amount of interest due to its effectiveness in advancing the flexural and shear capacity. The method involves inserting CFRP laminates or bars into pre-installed grooves made on the concrete cover of the structural element to strengthen it (El Hacha and Rizkalla, 2004, De Lorenzis and Teng, 2007, Saadah et al., 2021). For instance, El-Gamal et al. (2016) conducted a study on effectiveness of NSM technique in enhancing the flexural capacity. Grooves were installed at the bottom of the RC beams, and CFRP bars were inserted into the grooves to increase the flexural capacity. The study reported a remarkable increase of 133% in flexural capacity. For assessing the shear capacity enhancements, Alwash et al. (2021a) have reinforced RC beams by inserting CFRP strips into pre-installed grooves on both sides of the RC beams. The results demonstrated an improvement in shear strength of 97%. Although CFRP strengthening is deemed as an effective technique, its durability is compromised when subjected to elevated temperatures. This lack of durability is ascribed to the low glass transition temperature (GT) of epoxy which is used as the binding agent between the CFRP material and the RC structure. When GT of epoxy is exceeded, a pronounced reduction in mechanical strength is displayed as the material transitions from stiff to viscous state. Gamage et al. (2005) reported a significant drop in bond strength when epoxy was subjected to temperatures beyond 60 ° C. Furthermore, Al-Safy et al. (2012) reported a loss in tensile strength of 31.8% and 89% at 40 and 60 o C, respectively. The lack of durability in epoxy within NSM CFRP applications under elevated temperatures has prompted the search for a resilient alternative with mechanical properties comparable to epoxy. Several studies have focused on the development of cement-based adhesive (CBA) as an alternative to epoxy since cement depicts a much better thermal resistance. Al-Abdwais et al. (2017) developed CBA and achieved 146.7% and 12.8% of epoxy compressive and tensile strength, respectively. Furthermore, samples bonded to CFRP using CBA failed the pull-out test at a maximum temperature of 255 ° C, whereas those bonded with epoxy failed at 140 ° C. Despite the better thermal resistance of CBA over epoxy adhesive, cementitious composites display cracks and significant strength loss around 600 ° C (Malhotra, 1956, Alarcon-Ruiz et al., 2005, Georgali and Tsakiridis, 2005, Arioz, 2007) To further investigate the matter using fire heating rate, we prepared CBA containing 0.075 wt% nano graphene, following the method described in the study by Alwash et al. (2021b). Subsequently, the CBA was applied into the installed groove on the NSM CFRP sample as depicted in Fig. 1.

Fig. 1. (a) Cross section; (b) side view; (c) top view.