Abstract
This work addresses the durability of structural epoxy adhesives and carbon fibre reinforced polymer (CFRP) laminates typically used in strengthening of existing reinforced concrete structures exposed to natural ageing. The experimental program included four natural (real) outdoor environments inducing ageing mainly caused by carbonation, freeze-thaw attack, elevated temperatures, and airborne chlorides from seawater. Moreover, a control (reference) environment (20 °C of temperature and 55% of relative humidity) and an environment involving water immersion of the materials under controlled temperature (20 °C of temperature) were also included in this investigation. The characterization involved the assessment of the physical, chemical and mechanical properties along a study period of up to two years. Furthermore, comparisons between the natural ageing tests developed in the scope of the present work and accelerated ageing tests existing in the literature were performed. Regarding to the epoxy adhesives, an increase in the glass transition temperature with the time was observed, while the tensile properties decreased, regardless of the outdoor environment. The CFRP laminates were marginally affected by the studied environments. Despite the remarkable dispersion of the results observed in the accelerated ageing tests for the period investigated, this testing protocol yielded higher mechanical degradation than under natural ageing.
Highlights
Structural repairing and strengthening of existing reinforced concrete (RC) structures with systems involving fibre reinforced polymer (FRP) materials are considered state-ofthe-art in civil engineering
Technique uses laminate strips or sheets which are externally bonded to the surface of the structural member to be strengthened, while in the near surface mounted (NSM) technique the reinforcements are inserted into grooves cut into the concrete cover of the structural member
This paper presents the results of an investigation on the durability of epoxy adhesives and Carbon FRP (CFRP) laminates subjected to four outdoor environments inducing ageing mainly by exposure to carbonation, freeze-thaw attack, elevated temperatures, and airborne chlorides from seawater for up to two years
Summary
Structural repairing and strengthening of existing reinforced concrete (RC) structures with systems involving fibre reinforced polymer (FRP) materials are considered state-ofthe-art in civil engineering. CFRP materials are commonly applied using the externally bonded reinforcement (EBR) technique or the near surface mounted (NSM) strengthening technique. The EBR technique uses laminate strips or sheets which are externally bonded to the surface of the structural member to be strengthened, while in the NSM technique the reinforcements (laminates or bars) are inserted into grooves cut into the concrete cover of the structural member. Epoxy adhesives are used as the bonding agent. Both techniques are suitable for flexural and shear strengthening. The use of prestressing combines the advantages of FRP systems with external prestressing, which leads to more efficient use of concrete and CFRP and reduction on the deflection and crack width, amongst other advantages [8,9]
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