scope:

INTRODUCTION

Application of wet lay-up Fiber reinforced polymer (FRP) systems in the repair industry is well accepted. These applications include structural strengthening of structures such as parking garages, buildings, bridges, etc. which have experience some form of structural deficiency, many due to corrosion. Emergence of new resin chemistries is allowing these technologies to find new types of applications, such as reinforcement of piles submerged underwater, where corrosion of steel rebar is the major cause of damage.

Research by Suh, et al.¹ investigated a prepreg (water activated resin) technology as well as an existing epoxy technology in understanding effectiveness of FRP wraps in corrosion reduction in submerged piles. This study included laboratory testing as well as two field tests. The authors also studied short term and long term bond strengths when these products were applied on two bridge piles. Finally, eccentric testing on submerged and dry columns was performed. The results show that both systems slow down the corrosion rate, irrespective of whether carbon or glass is used. The bond strength and failure mode of these systems in wet conditions was low and the author suggests that improvements in bond strength are necessary to make these wraps more desirable. Also, though eccentric column testing was performed on these systems, the studies do not clearly show how the underwater wraps compare to applications in dry conditions.

In another paper by Mullins, et.al.² the materials used, application experience, and bond data for the two field projects mentioned above1 are summarized. The authors do not provide any data on material properties of these products when fully cured under water. Also, though the author mentions that interaction diagrams can be developed for column strengthening, no correlation is offered to show how experimental data of columns wrapped underwater compare to theoretical calculations.

Other work, which demonstrate how composites protect reinforced concrete from corrosion of steel, was done by Gadve, et al³ and includes a pull-out testing of a 330mm rebar was placed inside a concrete cylinder with induced corrosion using NaCl and a current. The results show that rebar corrosion drastically slowed down when concrete cylinders were wrapped with both CFRP and GFRP. Another paper by Masoud and Soudki4 focus on the results of evaluation of the corrosion activity in unrepaired and FRP repaired specimens, using non-destructive and destructive techniques. The data shows that corrosion potential decreased with the progress of corrosion, and the FRP repair caused a higher rate of decrease of the corrosion potential with time than that observed for the unrepaired specimens. Another research by Spainhour and Wootton⁵ show that the type of resin used in the FRP can affect the resistance of the reinforced member from corrosion.

Repairs with FRPs were shown to greatly improve the strength and ductility of repaired corroded members and reduced the rate of post-repair corrosion in work completed by Bonacci, et al⁶. Moreover, subjecting the repaired column to extensive, postrepair corrosion resulted in no loss of strength or stiffness and only a slight reduction in the ductility of the repaired member⁷.

Not much research however has been done in understanding how curing process underwater of wet lay-up systems may affect their ability to strengthen and protect reinforced concrete from rebar corrosion. Since underwater pilings require continuous corrosion maintenance at the water to air interface caused by cyclic wet and dry exposure of these areas with tidal height change and large marine organic growth, FRP solutions are a desirable option to asset owners. FRP jackets have been successfully used in many projects to protect concrete and wood pilings in these types of environments. However, the issue with these jackets is that they are size specific and require multi step process.

Research data in this report is presented for a new prepreg, wet lay-up carbon FRP (CFRP) product and epoxy primer, which cure in the presence of moisture and are UV resistant. The CFRP system provides a great advantage to FRP jackets since they are easy to handle and non-size specific. The product is saturated in a moisture-free, controlled environment using specialized saturating machines, which ensure continuous levels of fiber to resin ratios. The prepreg rolls are hermetically sealed and opened when ready to be applied/laid-up for field application. The epoxy primer has a high viscosity and tack and is applied on concrete surface by heavily saturating a polyester felt fabric, which acts as a carrier of the primer and makes it easy to be applied underwater.

The intent of this paper is to show the material properties of this system when fully cured under-water, confinement strengthening effectiveness when the product is applied and cured underwater, while meeting existing ACI 440's8 design equations, and bond degradation when exposed to various harsh environments.