Ahmed H. Ali

Durability Assessment of Glass FRP Solid and Hollow Bars (Rock Bolts) for Application in Ground Control of Jurong Rock Caverns in Singapore

AbstractThis study was conducted to investigate the durability of two types of vinyl-ester/glass fiber-reinforced polymer (GFRP) rock bolts [solid and hollow (tubular) GFRP bars] that were subseque...

Service-life-prediction and field application of glass fiber-reinforced polymer tubular and solid bolts based on laboratory physical and mechanical assessment:

This paper presents the physical, mechanical, and durability characterization of glass fiber-reinforced polymer solid and tubular bars. These bars were subsequently used as rock bolts for ground control of the Jurong Rock Caverns in Singapore. The long-term performance of these bars was assessed under harsh environmental exposure (saline solution) simulating the subsea cavern water. The test parameters were (1) type of bars (solid and tubular), (2) temperature (20, 40, and 50℃), and (3) conditioning time (1000, 3000, and 5000 h). The measured tensile strengths of the bars before and after exposure were considered as a measure of the durability performance of the specimens and were used for long-term properties prediction based on a theoretical model. Moreover, microstructural analyzes using scanning electronic microscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry are also conducted to investigate the deterioration of fiber, matrix, and the fiber/matrix interface due to environmental conditioning. The results show the very high long-term durability of solid and tubular glass fiber-reinforced polymer rock bolts exposed to field conditions. The predicted tensile strength retention at a MAT of 32℃, with an RH of 100%, is 0.90 and 0.82 for a service life of 100 years for solid and tubular glass fiber-reinforced polymer bars, respectively. Based on the findings of this research, the tested glass fiber-reinforced polymer rock bolts were recommended as alternatives to stainless-steel rock bolts and successfully used as ground control in the Jurong Rock Caverns in Singapore.

Statistical analysis and theoretical predictions of the tensile-strength retention of glass fiber-reinforced polymer bars based on resin type

This paper presents experimental investigation, statistical analysis, and theoretical predictions of tensile-strength retention of glass fiber-reinforced polymer bars, made with vinyl-ester, polyester, or epoxy resins. The durability of glass fiber-reinforced polymer bars was evaluated as a function of time of immersion in alkaline solution. The aging of the three glass fiber-reinforced polymer bar types consisted of immersion glass fiber-reinforced polymer bar samples in an alkaline solution (up to 5000 h) at different elevated exposure temperatures. Subsequently, the physical and tensile properties of the unconditioned bars were compared with that of the conditioned bars to assess the durability performance of the glass fiber-reinforced polymer bars. Microstructure of all of the glass fiber-reinforced polymer bar types was investigated with scanning electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy for both the conditioned and unconditioned cases, to qualitatively explain the experimental results and to assess changes and/or degradation in the glass fiber-reinforced polymer bars. In addition, the long-term performance of glass fiber-reinforced polymer bars was assessed considering the effect of service years, environmental humidity, and seasonal temperature fluctuations. The test results showed that the tensile strength of the glass fiber-reinforced polymer bars was affected by increased immersion time at higher temperatures and the reduction in tensile strength was statistically significantly dependent on the type of resin system. The prediction approach of the glass fiber-reinforced polymer bars based on the environmental reduction factor (CE) after 200 years indicated that the CE values for vinyl-ester, epoxy, and polyester glass fiber-reinforced polymer bars can be conservatively recommended to 0.81, 0.75, and 0.71, respectively, for a moisture-saturated environment (relative humidity = 100%) and at 30℃. The polyester glass fiber-reinforced polymer bars experienced greater debonding at the fiber–resin interface than the vinyl-ester and epoxy glass fiber-reinforced polymer bars.

Effect of applied sustained load and severe environments on durability performance of carbon-fiber composite cables:

The research work reported in this paper involves investigation of the mechanical and durability performance of unstressed and stressed Tokyo Rope carbon-fiber composite cables for prestressing applications. This research is critical in order to establish the critical (allowable) stress and safety factors for the use of carbon-fiber composite cable tendons for prestressed precast-concrete members. The carbon-fiber composite cable specimens were exposed to simultaneous high alkali environment and sustained loading at different elevated exposure temperatures (22℃ and 60℃) for 3000, 5000, and 7000 h. The high alkali environment (12.8 pH) simulated the concrete pore solution and the elevated temperature was used to accelerate the aging process. The applied sustained stress on the carbon-fiber composite cable strands was equivalent to 40% and 65% of their guaranteed tensile strength. This was achieved through testing 171 carbon-fiber composite cable specimens subjected to stress levels of 0%, 40%, and 65% of their guaranteed strength, under tensile load. Also, 136 carbon-fiber composite cable specimens were tested to investigate the transverse shear strength. In addition, the durability characteristics of the constituent materials of the carbon-fiber composite cable strands were assessed to understand the long-term behavior of these materials. The results showed the effect of sustained stress on the degradation of carbon-fiber composite cable strands. Under sustained stress of 40% and 65%, the reductions in tensile strength were 10.6% and 12.3%, respectively. Scanning electron microscope results on epoxy resin indicated that no degradation is detected since the surface remains smooth without any pitting or loose material.

Durability and Long-Term Performance of Fiber-Reinforced Polymer as a New Civil Engineering Material

In recent years, fiber-reinforced polymer (FRP) composites have been increasingly used for civil engineering applications such as columns, beams, and slabs to all-composite bridge decks. However, the durability of FRP, especially under harsh environmental conditions, is now recognized as the most critical topic of research. The lack of a comprehensive database on durability of FRP materials makes it difficult for the practicing civil engineer and designer to use FRP composites on a routine basis. The current paper presents the most significant research work conducted and published on durability performance of FRPs, as internal reinforcement, in the concrete members. Its durability has been extensively investigated in the last two decades. A comprehensive review of the literature, including degradation mechanisms, accelerated tests for long-term performance, and the effects of environment parameters on the durability of FRPs will be presented and discussed. In addition, proposed service-life prediction models for FRP materials will be reviewed.