PSI - Issue 64

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

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Fig. 2. (a) Surface exposed to 400 °C for 1 hour; (b) side view.

The sample was subjected to a heating rate in accordance with ISO 834 nominal fire curve (ISO, 1999). Once the temperature reached 400 ° C, it was kept constant for 1 hour. As shown in Fig. 2a, the surface of the developed adhesive exhibited cracking after the exposure to 400 ° C. This deterioration further substantiates the susceptibility of the cementitious matrix to elevated temperatures. In contrast to cementitious adhesives, fly ash geopolymer exhibits superior thermomechanical performance at elevated temperatures, including up to 1000 ° C (Rickard et al., 2012, Zhang et al., 2020, Hager et al., 2021). FA geopolymer synthesis comprises of the dissolution of aluminosilicate in a strong alkaline solution to establish chemical bonds, forming the geopolymer gel, which subsequently bonds to unreacted FA particles to consolidate the structure (Phair and Van Deventer, 2002, Panias et al., 2007). FA geopolymer adhesives have been explored as an alternative to epoxy in NSM CFRP application by Hadi et al. (2020b). The samples underwent pull-out testing, and the results highlighted the promising potential of geopolymer adhesive as a bonding agent for NSM FRP applications. Furthermore, in another study, the FA geopolymer adhesive included 1% micro steel and 0.6% carbon fibre as additives. The bond strength of the FA geopolymer adhesive was reported to surpass the bond strength of epoxy by 4.1% and 9.6%, respectively (Hadi et al., 2020a). The results from both studies indicate that employing FA geopolymer adhesives in NSM CFRP application can be advantageous. Previous studies have assessed the thermomechanical performance of potassium-activated FA geopolymer at elevated heat using heating rate in the range of 5 to 10 ° C/min. The studies reported minor thermal degradation in the geopolymer (Hosan et al., 2016, Lahoti et al., 2018). Although FA geopolymers depict excellent thermal performance at elevated temperatures using low heating rates, It’s noted that higher heating rates can have significant impacts on the thermomechanical performance of FA geopolymers (Duxson et al., 2007). The objective of this study is to develop an ambient-cured FA geopolymer adhesive with a superior thermomechanical performance under severe heating rate, following fire temperature-time curve, for use in NSM CFRP applications. Geopolymer adhesives in this study are proportioned based on intrinsic parameters, and the evaluation criteria are based on the residual compressive strength and thermal shrinkage. 2. Experimental Work 2.1. Materials Fly ash class F was sourced from Ramagundam combustion power plant in Telangana, state of India, and ground slag was provided by Independent Cement and Lime Pty Ltd with a median particle size of 36.9 and 13.49 μm, respectively. Chemical composition of FA based on X-ray fluorescence spectroscopy (XRF) is detailed in Table 1. Potassium silicate liquid Kasil 2040 (K 2 SiO 3 ) grade D was purchased from Potters Chemicals Pty Ltd with modulus ratio of 2 (where Ms = SiO 2 /K 2 O, SiO 2 =27%, K 2 O=13.3% by mass). Potassium hydroxide pellets were purchased from Redox Ltd with a purity of at least 90%.