Portsmouth Memorial Bridge Micropile CP

LOCATION: Portsmouth, NH

STRUCTURE: Portsmouth Memorial Bridge

CLIENT: New Hampshire Department of Transportation

TECHNOLOGIES: Cathodic Protection Design

PROJECT ISSUES: Design and Implementation of Cathodic Protection System

CONTACTOR: Archer Western Contractors

Project Description:

Vector Corrosion Services (VCS) conducted a corrosion evaluation and cathodic protection (CP) design for the Portsmouth Memorial Bridge’s micro-piles.  The bridge was undergoing a complete rehabilitation, including new concrete caps on the 100 year old mass concrete piers.  VCS was asked to develop a CP system to protect micro-piles being installed into the original concrete piers.

Project Issue:

As part of the Portsmouth Memorial Bridge renovation, steel threadbar micro-piles were used to pin the existing, approximately 100 year old, concrete piers to bedrock below the river channel.  During the micro-pile installation, a concern arose that cracks, voids, or damage to the existing piers may have exposed the micro-pile steel casings directly to seawater.  This exposure would lead to corrosion activity and a reduction in the micro-pile service life.

Project Solution:

VCS performed corrosion testing on the micro-piles to determine the suitability of CP and to develop a replaceable system that will provide sufficient corrosion protection for 25 years.  Onsite testing was conducted and confirmed that corrosion of the micro-piles was a concern.  Polarization testing of the micropiles was conducted and the information was used to custom design the galvanic protection system utilizing bulk aluminum anodes placed around the piers.  VCS evaluated the CP installation and verified proper operation after installation.  VCS installed a monitoring station on each pier so that performance data from the CP system could be collected and analyzed.  These monitoring stations allow the New Hampshire Department of Transportation to collect information on the remaining life of the anodes and verify operation of the CP system.