Chicago – A team of researchers compared two functionally equivalent rural bridges to evaluate sustainability and life cycle cost, and the steel bridge outperformed its concrete counterpart across the board.
Over the bridges’ life cycles, the steel bridge will result in 26.3% fewer embodied CO2e emissions, consume 8.7% less energy, and lead to 17.8% more recycled material, assuming the concrete is recycled at all, at the end of its service life. Plus, the steel bridge’s life cycle cost is 23% lower than that of the concrete bridge.
Michael Barker, PE, of the University of Wyoming’s civil & architectural engineering & construction management program led a team that evaluated two real bridges in Whitman County, Wash. Both bridges meet the two-lane rural crossing requirements and were built by the same crew. The study considered only the superstructures of these bridges to allow a direct comparison.
The Seltice-Warner bridge is a roughly 36-ft-long prefabricated, modular steel bridge with seven rolled beams and a corrugated gravel deck. Meanwhile, the Thornton Depot bridge is a 34-ft-long prefabricated, precast, pre-stressed concrete girder bridge with eight beams and a concrete deck. The Whitman County bridge crew built them within the last three years.
Researchers evaluated both bridges throughout the construction, maintenance, and demolition phases according to four sustainability criteria:
- Embodied carbon and equipment emissions (measured in kg of CO2e),
- Embodied and equipment energy consumption (measured in MJ),
- Waste management and recyclability (measured by percent weight recycled), and
- Life cycle cost (measured in present values).
Although “the decision on which bridge type to select is clear,” as the report says, researchers also developed a series of procedures to help society or a bridge’s owner consider sustainability for more expensive projects.
To view the full report, click here.
