MacKay and Macdonald Bridges: Forensic Investigation and Rehabilitation of Concrete Foundations
Location: Halifax, NS
Client: Halifax Harbour Bridges
Duration: Continuous
Key Personnel: Wib Langley, Heather Geldart, Ted Moffatt.
Project Description
The two bridges spanning Halifax Harbour, the Macdonald and the Mackay Bridges, are some of the busiest sections of roadway in the province. As such, their continued maintenance and upkeep is essential for transportation throughout the region. The Angus L. Macdonald Bridge, opened in 1955, is a 75-year-old structure, and the A. Murray MacKay Bridge, opened in 1970, is a 55-year-old structure. With the structures continuing to age, and the conditions within Nova Scotia, the concrete pier foundations require observation, testing, and service life extension.
Harbourside’s Role
W.S. Langley, as a division of Harbourside Geotechnical Consultants, was responsible for the condition assessment of the pier foundations for both bridge structures. This meant not only visually assessing the concrete but also involved the extraction of cores, and rigorous laboratory testing. This comprehensive testing included (but was not limited to) the following:
Halifax Harbour Bridges Concrete Pier Testing
Alkali-silica reactivity (long term testing).
Compressive strength testing.
Tensile strength testing.
Damage Rating Index (DRI) testing.
Petrographic examination.
Testing for volume of permeable voids and absorption.
Service Life Extension
In addition to thorough testing of the concrete conditions, W.S. Langley and Harbourside Geotechnical Consultants developed the concrete mixture proportions for rehabilitation of the pier foundations. This was by means of concrete encapsulation. The repair concrete was designed with a 75-year service life.
Unique Challenges
It is critical that any work involving the Halifax Harbour Briges has as little impact on traffic flow as possible. These bridges function as two of the main transportation arteries within the city of Halifax. Their proper functioning is crucial for businesses, commuters, and shipping. Although much of this work occurred below the bridge deck, proper care had to be taken to avoid any unnecessary disruptions above. Under certain instances, work had to coincide with other pre-planned closures so as to further mitigate disruptions. These conditions posed restrictive timing, and necessitated efficient workflow, and meticulous planning.
Social Impact
Ensuring that the Macdonald and MacKay bridges continue to be serviceable well into the future helps to safeguard transportation throughout HRM. This is especially important as the city continues to expand and grow. Halifax is one of Canada’s fastest growing cities, and it also happens to be one of the most congested when it comes to traffic. Its transportation infrastructure needs to remain in peak condition in order to avoid exacerbating this problem. Extending the lifespan of both these bridges is a key piece of this.