Why is epoxy encapsulation the best?
There is a minimal surface area and weight increase when employing epoxy-filled FRP jackets.
A fair question is why fiber-reinforced polymer (FRP) epoxy encapsulation is the “best.” The answer requires examining the specific advantages over other methods.
Concrete vs. Epoxy Encapsulation
A less expensive encapsulation method involves utilizing concrete fill instead of epoxy. Concrete is indeed far more available and is far less expensive per cubic foot. However, the excess loading that is added to the structure is enormous.
The original specifications for a recent project in the northeast region illustrate the problem. Either of two methods were specified to encapsulate over 100 piles on a single pier.
Method one, which specified a steel jacket and a 3-inch annular space filled with concrete, increased the structural loading on the pier by over 13,300 pounds per pile. Method two, which specified an FRP jacket and a 9-inch annular space filled with concrete, increased the structural loading on the pier by over 31,000 pounds per pile.
Multiply this 31,000 by 100 piles and the result is astounding – as a result of such “solution,” the static loading on the pier has been increased by over 3 million pounds.
Problems with Concrete Encapsulations
An additional problem with excess size of concrete encapsulations becomes apparent in offshore structures such as oil platforms.
These structures are constantly exposed to hydrodynamic forces, and by increasing the surface area of each structural member, the effect of wave action on the structure is increased dramatically.
Further, concrete encapsulations, due to their volume, composition, and the thermal changes in the marine environment, exhibit a tendency to crack over time. These cracks can allow the intrusion of water and lead to the rapid failure of the encapsulation. An encapsulation thus breached lends little protection to the structural member that it surrounds.
The bond strength between concrete and both the structural member and the jacket is far less than that of epoxy. Again, a failed bond will lead to water intrusion and result in the ultimate failure of the encapsulation.
Observing a variety of such concrete encapsulation techniques led one researcher to state that “[s]ome older marine structures such as Pier 1 at the Boston Street terminal in Baltimore have become virtual museums of pile jacketing failure.” M. Arockiasamy, Ph.D., P.E., Evaluation of Conventional Repair Techniques for Concrete Bridges, p. 36 (1998).
Epoxy Encapsulations
Epoxy encapsulations have been in place since as early as 1971 and are reported to be in excellent condition. As the above differences illustrate, this type of performance simply cannot be matched by concrete encapsulation techniques.