BPC achieved 62% carbon reductions during the Early Contractor Involvement (ECI) phase of constructing the Whakawhirinaki Silverstream Pipe Bridge, which carries a critical new drinking water pipe and shared path for cyclists and pedestrians across Te Awa Kairangi/ Hutt River.

As an ECI project, BPC could work directly with the designers to make carbon-reducing changes.

Most savings were related to reducing the weight of the super structure: replacing a concrete deck with a lighter steel deck. This allowed the supporting sub-structure to be reduced, requiring fewer piles and less steel.

Environmental risks significantly decreased as piling was no longer required within the river. Another improvement identified in the ECI process was to use geogrid reinforcing in the embankment. Rather than import the full volume from the quarry, only the structural core was imported, with the layers reinforced. Undercut material from site was then placed on the outer batters to provide the design profile. The result was less material imported from the quarry and it eliminated the need to cart undercut material off-site to landfill.

This demonstrates the benefits of PAS2080 principles in action, with significant carbon avoided through early collaboration between all parties: owner, designer, constructor and supplier.

Throughout construction the team reported on the projects carbon emissions, including Scope 3 emissions from materials, allowing the team to measure, understand and share the knowledge gained with industry.

Scope 3 GHG emissions relating to materials manufacture and transport made up 94% of all emissions, with emissions associated with materials manufacture (A1-A3) dominated by steel (88%), concrete (10%) and aggregate (2%).

Emissions relating to transportation were dominated by shipping of steel by cargo ship, representing 79% of A4 emissions, followed by the transportation of aggregate (11%), steel (8%), and concrete (2%) by trucks.

Water New Zealand has showcased BPC’s work on the project in its Embodied Carbon Guideline for industry as an example of good practice.