Danny Winters

Effectiveness of Fiber-Reinforced Polymer in Reducing Corrosion in Marine Environment

In this paper, results are presented from a long-term exposure study to assess the role of fiber-reinforced polymer (FRP) in mitigating corrosion in a marine environment. Twenty-two 1/3-scale models of prestressed piles cast with built-in chloride were exposed to simulated tidal cycles under outdoor ambient conditions for nearly 3 years. These included 8 carbon FRP (CFRP)-wrapped specimens, 8 glass FRP (GFRP)-wrapped specimens, and 6 controls. Embedded titanium reference electrodes and thermocouples were used to monitor the corrosion performance inside the wrapped region throughout the exposure period. The performance of the FRP was evaluated on the basis of bond and gravimetric tests conducted at the end of the exposure period. The results showed that the FRP-concrete bond was largely unaffected by exposure and both CFRP- and GFRP-repaired specimens significantly outperformed the controls. The underlying trend in corrosion rate measurements showed increases for the controls and reductions for the wrapped specimens. This was reflected by much lower metal losses in wrapped specimens compared with controls. These findings indicate that FRP is effective in reducing the corrosion rate in heavily chloride-contaminated prestressed concrete elements such as those exposed to a marine environment.

Effective Repair for Corrosion Control Using FRP Wraps

This paper presents results from a multiyear study to evaluate the role of prewrap substrate preparation on corrosion mitigation in a marine environment. Seventeen one-third scale prestressed piles were corroded to 20% metal loss to simulate severe corrosion. Subsequently, two types of prewrap substrate preparation were carried out: (1) full repair in which the delaminated concrete was removed and the section reformed and (2) epoxy injection repair in which the cracks were sealed and the surface cleaned. Specimens were then wrapped using carbon fiber-reinforced polymer (CFRP) and exposed to simulated tidal cycles at 60°C for 28 months. The postexposure wrap performance was evaluated from gravimetric testing in which the metal loss in all specimens was measured. Results showed that the performance of the full repair and the epoxy injection were comparable with relatively minor increased steel loss despite the severity of the exposure. In contrast, the steel in unwrapped controls exposed to the same environ...

Improvement in Fiber-Reinforced Polymer-Concrete Bond by External Pressure

An experimental study evaluated the improvement in the bond of fiber-reinforced polymer (FRP) and concrete to dry and wet substrates from applied pressure. In the study, 12 full-sized pile specimens, including four controls, were wrapped by using two different glass FRP systems–- a prepreg and a wet layup–-and two different layouts typically used for unidirectional and bidirectional fibers. Wrapping was conducted inside a partially filled tank to ensure that the bonded areas of the dry and wet regions were identical. Sustained pressure was maintained during curing by using pressure or vacuum bagging. Bond improvement was evaluated from more than 400 pull out tests. Results showed that external pressure led to improved bond in both the dry and submerged regions. However, vacuum bagging was better for prepreg systems, whereas pressure bagging was better for wet layups. Transverse fiber layout typically used with bidirectional fibers gave better bond in controls where no external pressure was applied.

Fiber-Reinforced Polymer Pile Repair Incorporating Cathodic Protection

Fiber-reinforced polymers (FRPs) are increasingly being used for corrosion repair. As barrier elements, FRPs can only slow down corrosion. Cathodic protection (CP) is the only proven method for stopping electrochemical corrosion of steel. But a new method repairs corrosion damage: a sacrificial CP system is incorporated within an FRP repair. The system was implemented in a demonstration project in which corroding piles supporting the Friendship Trail Bridge, Tampa Bay, Florida, were repaired. The repaired piles were instrumented so that performance of the CP system could be assessed. Results indicate that the CP system is effective in protecting the reinforcing steel. It also shows that corrosion rates are lower in FRP-wrapped piles. This lower rate can increase the life of anodes used by the CP system by more than 20%.

Comparative Study of Thermal Integrity Profiling with Other Nondestructive Integrity Test Methods for Drilled Shafts

Integrity testing of drilled shafts and similarly constructed concrete foundations has evolved to combat the blind nature of the construction process and to increase quality assurance. The more popular methods include cross-hole sonic logging (CSL), gamma-gamma logging (GGL), and more recently thermal integrity profiling (TIP) and sonic caliper. Thermal integrity profiling, developed at the University of South Florida in the mid-1990s, utilizes the heat of hydration of curing concrete to evaluate the integrity of drilled shaft foundations. Comparing the results of the different test types is difficult due to the varied nature of the different tests. This paper looks at various shafts constructed across the nation, which were tested with thermal and at least one other method. When compared with CSL and GDL test results, TIP agreed with four of six cases for CSL and two of five cases for GDL. In the one case were both sonic caliper and inclination data were available, TIP showed good agreement.

Controlling Mass Concrete Effects in Large-Diameter Drilled Shafts Using Full-Length Central Void

Mass concrete defines elements where heat formation due to exothermic hydration reactions can induce tension cracking as a result of excessive temperature differentials upon cooling. These conditions are anticipated in dams, large footings, and, in some cases, pier columns and caps where internal cooling systems can be used to moderate the effects. Until 2006, drilled shafts were not recognized by the Florida Department of Transportation as mass concrete due to the relatively small diameters (4 ft [1.2 m] diameter being the most common) and/or the perception that the surrounding environment was not conducive to producing mass concrete conditions. This paper presents the results of a full-scale shaft demonstration project where a 9 ft (2.74 m) diameter shaft was constructed with a 3.8 ft (1.17 m) diameter central void to control temperature and reduce costs. Peak and differential temperatures were shown to stay well within specified limits without the need for internal cooling systems.