Two Edmonton bridges now spanned in concrete

Edmonton’s 102 Avenue bridge over Groat Road and its Terwillegar Park Footbridge have something in common: they now both bear concrete across their spans.

The 102 Avenue bridge will accommodate high volumes of vehicle traffic, while hikers and cyclists will traverse the Terwillegar Park Footbridge.

For the 102 Avenue bridge, which carries a $32-million budget, a high performance mix that offers greater strength and lower permeability than ordinary concrete was used. As well, water is less likely to corrode the deck prematurely due to the adoption of stainless steel reinforcing bars, said Michael Markowski, operations manager for general contractor Graham Construction.

Putting the concrete deck in place is "probably the most significant milestone" in the bridge’s construction, he added.

The 102 Avenue bridge’s centre span stretches 83 metres and also features two 15-metre abutment spans. The middle 40 metres were poured first to "lock in the girders and apply the required loads to the structure," Markowski explained. That was followed by the pours for the two end sections. Each section required close to 160 cubic metres of concrete.

Deck pours, requiring temperatures warm enough to allow the concrete to cure, usually take place between mid-May to October. It’s recommended that high performance concrete, which needs considerable water, undergo a 14-day wet cure and then a drying period prior to the application of the waterproofing membrane, said Markowski.

The envelope was pushed with the 102 Avenue bridge by pouring concrete in the latter half of March. Even though it was warmer than usual this spring, that meant, with help from AECOM and the City of Edmonton, installing external heating sources to prevent cool night conditions from hampering the process.

The last of the deck pours will address the cantilevered sidewalks that widen the 102 Avenue bridge to a total of 24 metres. The bridge is scheduled to open in the late fall.

Across the city, the $24-million, three-span, stressed-ribbon Terwillegar Park Footbridge, also under contract to Graham Construction, showcases concrete in a different way.

The deck consists of 86 precast concrete panels – each measuring 2.6 metres in length, five metres in width and 46.5 centimetres in depth — that rest on bearing cables. The transverse and longitudinal joints are filled with high-performance concrete that "effectively lock in the deck as a composite structure," Markowski explained.

In total, the 262-metre footbridge, which stands on two 9.2-metre by 3-metre piers, required approximately 3,000 cubic metres of concrete, which was locally sourced, according to city officials. The project is the longest stressed ribbon bridge in Canada and the second longest in the world.

"The stressed ribbon option was selected as the recommended option because it provided the highest score at the same time as having the lowest cost and shortest schedule. Main benefits included lowest impact on the river valley during construction, aesthetically pleasing design and minimal use of materials.

In addition, in public consultation meetings the option was found to gain the highest approval and generate the most excitement due to its pleasing form," city officials stated.

"In fact, the ribbon refers to the slender pre-stressed concrete decks that span gracefully from support to support. Like a stressed ribbon. It is like a suspension bridge made from pre-stressed concrete with the suspension cables inside the deck instead of above the deck as in an actual suspension bridge."

Among the work still to be completed as of late May was deck lights and handrail installation, post-tensioning cable installation, canopy column construction and installation and trail construction and paving at each end of the bridge. Designed to have a 75-year lifespan, the bridge is set to open in September.