Some Durability Considerations in the Design of the Confederation Bridge

Transportation to and from Prince Edward Island, Canada's smallest province, has been by ferry for the past century. The cost to operate the ferry system became an increasing burden for the Canadian government and a proposal call was solicited in 1987 to the private sector to construct and operate an alternate system to the Province of Prince Edward Island. A proposal was accepted for a private consortium to build a 12.9 km bridge from the mainland to Prince Edward Island. The bridge was completed in May, 1997. A precast concrete, post-tensioned segmental box girder structure was selected for the site. A requirement of the Government of Canada was that the design and construction of the bridge provide a structure with a design life of 100 years. The bridge is located in a harsh marine environment, with some 100 annual cycles of freezing and thawing. Ice floes which originate in Northern waters pass through the Northumberland Strait in the winter and early spring months. Water temperatures vary from about -2 deg C in the winter months to +18 deg C in the summer. The salinity of the water in the Northumberland Strait is approximately 3.5%. This paper presents some of the durability concerns which were considered during the design and construction of the bridge and describes how these concerns were addressed. The discussion covers concrete materials and mixtures, air content and slump, chloride ingress, alkali-aggregate reactivity, sulphate attack, freezing and thawing resistance, ice abrasion, salt scaling, thermal cracking, and concrete curing.