Innovative prefabricated bridge with Ductal® connections a first in Alberta
The project had numerous requirements such as high durability and flood resistance with a higher clearance and fewer piers than the previous structure. It also had to last 100 years. The owner (the City of Calgary) had serious environmental concerns too. In particular, the potential risk of a major concrete spill or formwork blowout over the sensitive Bow River ecosystem.
The project team offered an innovative solution that would mitigate this risk and meet the requirements: a full-depth, full-width precast concrete deck panel system with Ductal® ultra-high performance concrete (UHPC) connections. Importantly, this approach would: significantly reduce the volume of wet concrete placed over the river; reduce onsite formwork and temporary work platforms and; accelerate construction.
Fabricating the concrete panels in a controlled environment (Lafarge’s local precast plant) ensured a higher level of quality and tighter construction tolerances by comparison to cast-in-place methods. A total of 60 full-width (15m wide x 2.7m long) panels were assembled on site and field-casting of the Ductal® connections was completed in just 10 days.
The design included three-span, haunched steel girders with vertical curvatures; the girder depths were increased at the piers to enhance structural capacity. The haunched shape increased the main river channel opening and the bridge’s hydraulic capacity against flooding. Furthermore, in the case of a “one hundred year flood” event, only a small portion of girders would be submerged.
It was the first time that a solution of this kind was designed for a multi-span, continuous vehicular bridge in Alberta. The experience gained will provide long term value and potentially lead to more widespread adoption across Canada. Recently, the project team (including Lafarge/ Ductal® & Precast) was recognized by Alberta Transportation at the “2018 Minister’s Awards for Transportation Innovation”2; an annual event that recognizes “innovative people and organizations in Alberta who plan, design, construct, operate or maintain a roadway, transit service or related initiative”. The design team was presented with the prestigious “Award of Excellence for Design Innovation”.
The new bridge has been designed and built to last – ready to serve the public for the next 100 years and beyond.
Why Ductal® ?
A bridge deck system with prefabricated concrete panels and Ductal® connections is more durable than a traditional cast-in-place system and it facilitates Accelerated Bridge Construction (ABC).
ABC is an increasingly popular approach world-wide that uses innovative planning, design, materials and construction techniques in a safe and cost-effective manner to reduce onsite construction time when building new bridges or replacing existing bridges.
Thanks to Ductal’s superior properties including compressive strengths up to 200 MPa and ductility, it is an excellent solution for use in areas with harsh climates and environmental conditions, plus - the joints are no longer “the weakest link”. The reduction in splice length also helps to provide continuity of longitudinal reinforcement in a small joint width. Other benefits realized on this project (compared to traditional methods) included a higher level of quality control, reduced onsite formwork and reduced risks related to work over water and live, heavy traffic flow.
Innovation in Manufacturing process
The precast deck panel system was selected primarily to mitigate the risk of a major concrete spill or formwork blowout while placing the concrete deck over the sensitive Bow River ecosystem. With fabrication completed in Lafarge’s precast plant, there was reduced need for onsite formwork and temporary work platforms, thereby contributing to accelerated construction. Production in a controlled plant environment also ensured a higher level of quality and tighter construction tolerances compared to cast-in-place methods.
The 170-m long deck was subdivided into sixty, 250 mm-thick precast/prestressed deck panels which were fabricated three at a time and installed over a four-month period. Then, in preparation for the Ductal® connections, a pre-pour meeting was held to confirm the sequence and placement/location. As this was a new material for most of the project team, the meeting was critical to determine the batching, placing and curing procedures and review good construction practices - which would help to minimize or eliminate errors.
A pair of high shear mixers were used (in sequence), to blend the UHPC liquids, pre-mix powder and fibers. At the time of placement, Calgary was experiencing hot summer temperatures, therefore in order to ensure recommended temperatures, ice was used instead of water and batching and placing was performed at night. Furthermore, to reduce the risk of surface dehydration, the connections remained sealed from exposure to the external environment until after initial set. To facilitate ABC techniques, the contractor removed the forms after the Ductal® material had reached a strength of 100 MPa, enabling other work to resume on the deck and stay on schedule.
- City of Calgary’s time-lapse video: “12 Street S.E. Bridge Removal”: https://www.youtube.com/watch?v=s8c04toybQI
- FHWA - Accelerated Bridge Construction: https://www.fhwa.dot.gov/bridge/abc/
- “The City of Calgary 12 Street S.E. Bridge Prefabricated Deck Panels”, Azarnejad, A., Elmetwally, A., Murdoch, N., Hikita, K., Kroman, J., and White, P., CSCE, June, 2018
Excellence Awards proposed to Lafarge, the City of Calgary and CH2M (now Jacobs)
Location: Calgary, Alberta, Canada
Delivered in: 2017
Owner: the City of Calgary
General Contractor: Westpro (a division of Pomerleau)
Key figures: 264 tons of Ductal® (used to connect 60 precast concrete deck panels)
Structural Engineer: Jacobs
Precaster: Lafarge Canada Inc., a member of LafargeHolcim