Why Is Epoxy Encapsulation the Best?
A fair question, 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 far less-expensive per cubic foot. However, the excess loading added to the structure is enormous.
The original specifications for a recent project in the northeast region of the United States illustrates the problem. Two methods were specified to encapsulate over 100 piles on a single pier.
- Method one 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 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 this solution, the static loading on the pier increased by over 3 million pounds.
Problems with Concrete Encapsulations
An additional problem with the excess size of concrete encapsulations becomes apparent in offshore structures, such as oil platforms. These structures are constantly exposed to hydrodynamic forces, thus increasing the surface area of structural members, dramatically increasing the effect of wave action on the structure.
Further, concrete encapsulations, due to their volume, their 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 it surrounds.
The bond strength between concrete and both the structural member and the jacket is far less than the bond strength of epoxy. 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 that have been in place since the early 1070s are reported to be in excellent condition. As the above differences illustrate, this type of performance simply cannot be matched by concrete encapsulation techniques.
