PSI - Issue 64

Sareh Akbarpoor et al. / Procedia Structural Integrity 64 (2024) 822–832 Sareh Akbarpoor/ Structural Integrity Procedia 00 (2019) 000 – 000

823

2

1. Introduction Reinforced concrete structures may be subjected to various incidents and loading conditions during their service lives, resulting in strength and stiffness degradation. Therefore, it will be necessary to adopt effective approaches to the repairing and strengthening of concrete structural members as a viable alternative to demolition and rebuilding, which are expensive and environmentally damaging approaches (Usman et al., 2021; Yaqub, Bailey, 2011). The application of advanced composite materials like fibre-reinforced-polymer (FRP) materials for repairing and strengthening purposes have attracted considerable attention recently (Zhou and Wang, 2019). This is attributed to the advantages offered by FRPs, including their high strength-to-weight ratio, corrosion resistance, and fatigue behaviour (Ma et al., 2017; Rezazadeh and Carvelli, 2018; Zhou and Wang, 2019). FRP composites can be applied to concrete members through Externally Bonded (EB) or near-surface-mounted (NSM) techniques. In EB FRP, reinforcement is bonded externally using adhesive, but premature debonding can reduce efficiency. Hence, NSM FRP serves as an alternative, involving embedding FRP reinforcement into grooves cut into the concrete surface with adhesives. NSM FRP systems offer advantages over EB FRP system, including shortened installation time due to reduced preparation work that only requires opening grooves (Yu et al., 2021; Coelho et al., 2015), increased bond strength due to a larger bonding area, and better protection from impacts, mechanical damage, and elevated temperatures (Al-Saadi et al., 2019; Yu et al., 2021; Zhang and Teng, 2013; De Lorenzis and Teng, 2007). In the NSM FRP strengthening system, the bond between FRP reinforcement and concrete is crucial for its effectiveness (Cruz et al., 2020; Al-Saadi et al., 2019), with the adhesive playing significant role in the transfer of shear stress between these materials (Yu et al., 2021). Hence, the choice of adhesive significantly impacts the NSM FRP system's efficiency. Common adhesives for NSM FRP systems include epoxy and cement-based adhesives. While epoxy adhesives offer superior mechanical properties, concerns have been raised regarding their poor resistance to high temperatures and moisture (Yu et al., 2021). As a result, cement-based adhesives have emerged as an alternative solution (Akbarpoor et al., 2024, Al-Abdwais and Al-Mahaidi, 2016a; Al-Abdwais and Al-Mahaidi, 2016b; Al Abdwais and Al-Mahaid,i 2017; Al-Abdwais et al., 2017; Yu et al. 2022; Mohammed et al., 2017; Alwash et al., 2021; Jadooe et al., 2017; De Lorenzis et al., 2002;). Despite the significance of understanding the bond behaviour of NSM FRP adhesive-concrete, limited studies have focused on this behaviour experimentally NSM FRP systems using cement-based adhesives. Some research studies tried to make some modifications to the cement-based adhesive, for example one of these adhesives was developed specifically for the NSM FRP system (Al-Abdwais and Al-Mahaidi, 2016a), with maximum bond properties between CFRP textile and concrete determined through pull-out testing. Also, other study (Al Abdwais and Al-Mahaidi, 2016b), on the bond properties of NSM CFRP laminates using the proposed cement-based adhesive (Al-Abdwais and Al-Mahaidi, 2016a), indicated a significant effect of bond length on bond stress and resulting failure mode at the adhesive-concrete interfacial zone. Subsequent research (Al-Abdwais and Al-Mahaidi, 2017) replicated this study for CFRP textile at both ambient and elevated temperatures (Al-Abdwais et al., 2017). Examination of the bond performance of both cement-based and epoxy adhesives at high temperatures confirmed the effectiveness of the cement-based adhesive over epoxy adhesive (Al-Abdwais et al., 2017). Despite the efforts made by researchers to develop or modify cement-based adhesives for the NSM FRP system and investigate their bond behaviour, there is a lack of adequate information on the bond behaviour of this type of adhesive and some practical mixes for developing cement-based adhesives in real applications. Therefore, this paper introduces a new modified cement-based adhesive for the NSM FRP system, offering good performance in terms of maximum bond stress and ductile behaviour, and compares its bond behaviour with the NSM FRP system using epoxy adhesives through pull-out tests.