Accelerated Aging Behavior in Alkaline Environments of GFRP Reinforcing Bars and Their Bond with Concrete

Abstract

This study investigates the durability of glass fiber-reinforced polymer (GFRP) reinforcing bars (rebars) and their bond in concrete. Accelerated aging tests were first conducted on bare rebars that were either subjected to direct immersion in an alkaline solution or previously embedded in concrete before immersion in the solution (indirect immersion). Accelerated aging was conducted at different temperatures of the solution (20 °C, 40 °C and 60 °C) and for various periods up to 240 days. Residual tensile properties were determined for rebars subjected to direct immersion and served as input data of a predictive Arrhenius model. A large decrease in the residual tensile strength assigned to the alkali-attack of glass fibers was extrapolated in the long term, suggesting that direct immersion is very severe compared to actual service conditions. Short-beam tests were also performed on rebars conditioned under direct/indirect immersion conditions, but did not reveal any significant evolution of the interlaminar shear strength (ILSS). In a second part, bond tests were performed on pull-out specimens after immersion in the alkaline solution at different temperatures, in order to assess possible changes in the concrete/GFRP bond properties over aging. Results showed antagonistic effects, with an initial increase in bond strength assigned to a confinement effect of the rebar resulting from changes in the concrete properties over aging, followed by a decreasing trend possibly resulting from interfacial degradation. Complementary characterizations by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were also carried out to evaluate the effects of aging on the physical/microstructural properties of GFRPs.

Durability in Alkaline Environment of a Fiber Optic Sensor Bonded at the Surface of Reinforcing Bars for Distributed Strain Measurements in Concrete Structures

“…To verify if the DOFS instrumentation is resistant to alkaline environments at temperatures up to 60 °C (these ageing conditions are commonly used for durability studies on FRP rebars [6,8]), half-length of each instrumented sample was submitted to these harsh conditions. Before being partially immersed in the ageing solution, each specimen was first submitted to an initial tensile test using an Instron universal testing machine of capacity 250 kN.…”

“…The cell was filled with an alkaline solution composed of sodium hydroxide (NaOH) and potassium hydroxide (KOH), at concentrations of 0.1 mol/L (4 g/L) and 0.5 mol/L (28.05 g/L), respectively. This solution is commonly used in durability and corrosion studies [6,8], as it is suitable for simulating the pore solution of concrete at early age.…”

Environmental Durability of an Optical Fiber Cable Intended for Distributed Strain Measurements in Concrete Structures

“…The alkaline solution was composed of sodium hydroxide (NaOH) and potassium hydroxide (KOH) at the same concentrations as those adopted in previous durability studies [ 19 , 34 ] and specified in Table 1 . The pH of this solution is around 13.5, and is considered as representative of the alkalinity of concrete at an early age.…”

“…In addition, to evaluate the effects of ageing on individual components of the system, plain concrete cylinders (without cable) and samples of bare DOFS cable were also exposed to the same conditions. The alkaline solution was composed of sodium hydroxide (NaOH) and potassium hydroxide (KOH) at the same concentrations as those adopted in previous durability studies [19,34] and specified in Table 1. The pH of this solution is around 13.5, and is considered as representative of the alkalinity of concrete at an early age.…”

Improving Prediction Accuracy and Extraction Precision of Frequency Shift from Low-SNR Brillouin Gain Spectra in Distributed Structural Health Monitoring

“…The list of its varieties is constantly expanding [ 1 , 2 ]. Mechanical phenomena, both during concrete hardening and during operation [ 3 ] and ageing [ 4 ] of particularly critical concrete structures, such as hydraulic structures, are important data that require analysis and study. This is the scientific direction of structural health monitoring (SHM) [ 5 ], which is actively developing due to the emergence of new materials [ 6 ].…”