Abstract
Structural cold-curing adhesives are widely used to strengthen Reinforced Concrete (RC) structures with Fibre Reinforced Polymers (FRPs). The performance of these adhesives, and therefore the performance of the strengthening system, may be affected by temperature, as ambient-cured structural adhesives usually have low glass transition temperature (Tg). This paper presents a comprehensive experimental investigation on the influence of temperature on mechanical properties and Tg of a structural epoxy adhesive. The experimental program was divided in four groups of specimens. In Group 1, the effect of curing and post-curing temperature on Tg of the epoxy adhesive was investigated. In Groups 2–4, the effects of testing temperature, curing temperature and post-curing temperature, respectively, on adhesive mechanical properties were studied. Experimental results confirm that curing and post-curing temperature affected Tg differently depending whether the applied temperature was below or beyond the epoxy Tg. Similar behavior was observed in the mechanical properties of the epoxy, as they showed improvements when curing process (curing and post-curing) temperature was below Tg and they were negatively affected when curing process temperature was beyond Tg. Besides, tensile and compressive mechanical properties were negatively affected by testing temperatures beyond 20 °C.
Highlights
Structural epoxy adhesives are widely used to bond Fiber Reinforced Polymers (FRPs) to concrete in both Externally Bonded Reinforcement (EBR) and Near-Surface Mounted (NSM) strengthening techniques [1,2]
A reduced number of studies have investigated the influence of testing temperature on the mechanical properties of cold-curing epoxy adhesive typically used in civil engineering [9,10,11,12,13,14,15,16,17,18,19,20]
Results of the differential scanning calorimetry (DSC) tests performed on specimens of Group 1 are presented in Fig. 5a in the form of curves showing the variation of the heat flow versus temperature
Summary
Structural epoxy adhesives are widely used to bond Fiber Reinforced Polymers (FRPs) to concrete in both Externally Bonded Reinforcement (EBR) and Near-Surface Mounted (NSM) strengthening techniques [1,2]. Cold-curing adhesives are the most widely used, as its use is easier and they present good mechanical properties after the required curing time (which depends on the curing agent and temperature). It is a feature of commonly used ambient-cured structural adhesives to have glass transition temperatures (Tg) ranging between 40 ◦C and 70 ◦C [6]. A reduced number of studies have investigated the influence of testing temperature on the mechanical properties of cold-curing epoxy adhesive typically used in civil engineering [9,10,11,12,13,14,15,16,17,18,19,20]. Firmo et al [9]
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