Encapsulation with epoxy-filled fiber-reinforced polymer (FRP) jackets is superior to and more cost effective than with concrete-filled steel jackets or concrete-filled FRP jackets.
Although less costly up front, concrete-filled jackets are less reliable than epoxy-filled FRP jackets over the long term; in addition, concrete-filled jackets often excessively load structures and increase the surface area of structures.
With regard to long-term reliability, the bond strength between concrete and the structural member and the jacket is far less than the bond strength of epoxy. A failed bond leads to water intrusion, eventually causing failure of the encapsulation.
Concrete encapsulations, due to their volume, their composition, and 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 it surrounds.
The original specifications for an encapsulation project in the northeast United States dramatizes the problem of excessive loading with concrete-filled steel jackets. Two methods were specified for encapsulating over 100 piles on a single pier:
- Method 1 – A steel jacket with a 3-inch annular space filled with concrete, resulting in an increase in structural loading on the pier by over 13,300 pounds per pile.
- Method 2 – An FRP jacket with a 9-inch annular space filled with concrete, resulting in an increase in structural loading on the pier by over 31,000 pounds per pile.
For 100 piles, steel jackets would increase the static loading on the pier by more than 1 million pounds while FRP jackets would increase the static loading on the piece by more than 3 million pounds.
The excess size of concrete encapsulations can be problematic in many structures. For instance, in offshore structures that are constantly exposed to hydrodynamic forces, such as oil platforms, increasing the surface area of structural members dramatically increases the effect of wave impact.
The decades-long performance and reliability of epoxy-filled FRP jackets encapsulation simply cannot be matched by concrete-filled-jacket encapsulation techniques.