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

1143

2

Nomenclature RC

reinforced concrete

CFRP NSM CBA VOC BPA CO 2 LCA GPA PAN

carbon fiber reinforced polymer near surface mounted cement-based adhesive volatile organic compounds

bisphenol A carbon dioxide

life cycle assessment geopolymer adhesive polyacrylonitrile sodium silicate sodium hydroxide sodium oxide coefficient of variation

Na 2 SiO 3 NaOH Na 2 O COV LVDT

linear variable differential transformer

TC

Thermocouple time until failure

TUF GWP MK

global warming potential

metakaolin

1. Introduction The necessity to build and the limited resources of today’s world feature the importance of preserving the built environment. This favors the upgrading of current structures to provide accommodation for mankind. A significant part of existing structures is made of reinforced concrete (RC). Therefore, repair, strengthening, and rehabilitation of RC structures require continuous attention. However, these processes should also consider their environmental impacts. Hence, it is necessary to update the current strengthening techniques and promote eco-friendly solutions for the rehabilitation of RC structures. Carbon fiber reinforced polymer (CFRP) is an advanced material for strengthening RC structures. When applied according to the near surface mounted (NSM) strengthening technique, CFRP can increase significantly the load carrying capacity of RC structural elements (De Lorenzis and Teng 2007). The effectiveness of this technique in several applications, including flexural strengthening of RC beams and slabs was reported, being especially notable when using CFRP strips (Hosseini 2014, Dias et al. 2018). The transferring mechanism between CFRP and the concrete substrate is assured by epoxy resin (i.e. polymeric adhesive). However, the CFRP/epoxy resin systems are detrimentally affected by high temperatures, representative of fire occurrence, due to the lack of heat resistance nature of the adopted polymeric adhesives. Therefore, it is necessary to protect the strengthening zone(s) to do not be subjected to high temperatures (Azevedo et al. 2023), or implement alternative approaches such as using cement based materials instead of polymeric adhesives (Mohammadifirouz et al. 2022). Cement-based adhesives (CBA) for NSM strengthening were introduced as an alternative adhesive mainly for situations where fire occurrence must be considered (Al-Saadi et al. 2019). However, CFRP strips are generally produced with smoothed surfaces, and CBA have much smaller adhesion and cohesion than polymer adhesives, which penalize the bond stress transfer effectiveness between these two materials. One solution proposed and investigated in recent years by the authors is based on the application of a sand layer, coating the smoothed surfaces of CFRP strips (Mohammadifirouz et al. 2022). This creates an interlocking mechanism to facilitate the stress transfer at CFRP strip and CBA interface, which was proven to be effective through digital imaging correlation technique (Firouz et al. 2021). Moreover, several experimental investigations at the structural level were also supporting the effectiveness of using CBA in NSM strengthening technique (Al-Saadi et al. 2017, Al-Abdwais and Al-Mahaidi 2020, Al-Abdwais and Al-Mahaidi 2022). Furthermore, using CBA in NSM strengthening is also beneficial from the sustainability point of view. In fact, epoxy resins typically contain various chemicals, including solvents, hardeners, and curing agents, which can