Quantifying the flexural stiffness changes in the concrete beams with externally bonded carbon fiber sheets under elevated environment temperature

Abstract

Structural strengthening solutions typically employ externally bonded reinforcement (EBR) systems with carbon fiber (CF) sheets because of these materials’ lightweight, corrosion resistance, and electromagnetic immunity. However, elevated ambient temperatures can negatively impact the mechanical performance of EBR, as documented in the literature. Therefore, American bridge design specifications assume a concrete surface temperature of 60 °C (140 °F), which reflects the extreme conditions that bridge structures may experience, particularly in regions with intense sunlight and high ambient temperatures. Therefore, sustainable design solutions require a reliable quantification of the effects of temperature. This study extends a recently developed bending test layout and builds the analytical modeling procedure to quantify the stiffness degradation under repeated temperature and mechanical loads. The explicitly obtained equivalent stresses in the tensile concrete determine the stiffness measure independent of the loading condition and sequence. This test program used 12 laboratory samples. All beam samples faced the mechanical load repetitions and entire unloading. Three selected beams were additionally treated at 60 °C for 10 hours in a heating chamber between the loading repetitions. These tests identified a substantial (three times) decrease in the bonding performance of the CF sheets after eight heating rounds. Scanning electron microscopy (SEM) identified the corresponding microstructure changes.

Keywords

• Carbon fibers
• Externally bonded sheets
• Reinforced concrete
• Bending test
• Temperature effect
• Analytical model