Condition Assessment and Determination of Methods for Evaluating Corrosion Damage in Piles Encapsulated in Protective Jackets on the Hampton Roads Bridge-Tunnel

About the report:

The primary purpose of this study was to assess the condition of piles that had been encapsulated in fiberglass and mortar jackets on four bridges that are part of the Hampton Roads Bridge-Tunnel (HRBT).  Since these four bridges contain a total of approximately 1,800 piles, it was not feasible to conduct detailed testing and evaluation of each pile.  Therefore, a necessary objective of the study was to consider visual, non-destructive, and destructive techniques and recommend those that were most effective and efficient in assessing pile condition under the fiberglass jacket systems.  A secondary purpose of this study, at the request of the Virginia Department of Transportation’s State Structure and Bridge Engineer, was to assess the effectiveness of the fiberglass jacket and mortar system in resisting corrosion and to make specific recommendations about application of these or similar systems on Virginia bridges in the future.  To accomplish the purposes of this study, 52 HRBT piles were systematically selected for study.  These piles represented a variety of conditions, ages, types, and locations.

Destructive and non-destructive methods were used to evaluate the piles.  Destructive methods included chloride analysis and jacket autopsy.  Non-destructive methods included cross-hole sonic logging, ground-penetrating radar, sonic echo, impulse response, half-cell potential, electrical resistivity, ultrasonic pulse velocity, and visual assessment.

No single test method was able to assess completely the condition of the jacketed piles.  However, a combination of half-cell measurements, sonic echo, impulse response, and chloride analysis was useful in evaluating the condition of jacketed piles.  Ultrasonic pulse velocity was used to determine the velocity of sound through the piles, which was used in the calculations for sonic echo, impulse response, and cross-hole sonic logging.  Resistivity measurements were used to evaluate the susceptibility of the concrete and mortar to corrosion.  Ground-penetrating radar was ineffective in determining the condition of the underlying pile while the jacket was intact because of signal reflection and attenuation caused by steel mesh reinforcement in the mortar.  Cross-hole sonic logging was not a practical evaluation method for this application because of the difficulty in placing the transducers on the piles.

The HRBT piles that were evaluated displayed corrosion activity ranging from severe section loss of a vertical tendon to no corrosion activity.  A majority of the piles exhibited corrosion, but only a small portion showed substantial corrosion-induced damage.  The jackets hid corrosion damage, causing the severity of the actual condition of the piles to be underestimated when assessed visually.

The study recommends that jackets with mortar fill not be installed on piles with prior corrosion damage, as the jacket will obscure future damage and may accelerate corrosion.  The HRBT structure is such a vital structure in southeastern Virginia that the closure of two lanes of traffic would cost users approximately $2.9 million per day.  Thus, it is extremely important that the HRBT piles stay in good structural health and that the Virginia Department of Transportation retain the capability to monitor their condition.

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