Member Company: LafargeHolcim
Selected Award Categories: Durability
Vermont’s first cast in place segmental concrete bridge, a 1,000-foot plus span, carries Interstate 91 over Vermont Rt. 30 & West River. Standing 100 feet above the river valley, the over 500-foot main span forms an open gateway anchored by curving cathedral piers. The project swapped two deteriorated steel bridges with a single 104.8’ wide concrete bridge. The span comprises concrete trapezoidal sections placed by a cantilever construction system. The platform space is formed from the top of each footing with a stone texture and a pattern that represents a white pine with 14 branches. The dome-shaped underside of the superstructure that runs the length of the bridge is sky-blue. Vermont’s Governor Phil Scott labeled it “the largest construction project since the interstate system was first built.”
Ternary concrete mixtures containing slag cement, portland cement , and micro-silica were used to increase strength and durability along with aesthetic reasons. Slag cement was used to reduce thermal gradients in the large mass footing and pier-table placements. For mass concrete, a (60%) slag cement replacement met heat and strength requirements which exceeded the (4000 psi) & (8000 psi) design requirements. The use of slag cement in ternary and other mixtures improved the workability of the low W/CM Ratio with the emphasis of reduced permeability for durability concerns replacement levels ranging from 20% to 60% throughout the project.
The project team incorporated slag cement into their mixes to achieve the durability and design requirements for a 100-year life as required by the Vermont DOT. Figg Bridge Engineers had confidence that slag cement would help achieve design goals and with the experience of PCL and Carroll Concrete, Vermont AOT knew they had the right quality minded team on this design-build high profile project.
(Owner, Vermont Agency of Transportation) (Architect/Engineer: FIGG Bridge Engineers) (Contractor: PCL Civil Engineers) (Concrete: Carroll Concrete) (Slag Cement: LafargeHolcim)