Pitch Perfect Stitch and Deck Pour-formance
The Bussell Highway Y-interchange deck and stitch pour took place on the 10th of July 2024 and marks one of the three last bridge deck pours on the Bunbury Outer Ring Road (BORR) project.
Published: 06 August 2024, Updated: 06 August 2024
In addition to there being approximately 360 cubic metres of concrete to be poured between the bridge deck and stitch pour, the Bussell Highway Y-interchange was one of the most technical pours on the project.
Y? Because it actually consisted of two separate concrete pours. One for the deck of the bridge itself and the other one for the stitch work.
Bird's eye view of the Y-interchange
Deck Pour
The deck pour is the more straight forward of the two. It is the process of pouring concrete to form the main horizontal surface of the bridge itself. It forms the deck onto which vehicles will eventually drive over.
As with all of the bridge deck pours on BORR, the Bussell Highway Y-interchange pour included the setting up of the formwork to shape the concrete, the installation of reinforcement steel (rebar) to provide the required strength and integrity, and then the pouring and curing of the concrete itself to create the solid, durable surface required.
Stitch Pour
The stich pour is the application of concrete to the sections that connect or ‘stitch’ together the separate elements and segments of the bridge deck. Stitch pouring ensures that the bridge is one continuous structure and is important for ensuring that the loads the bridge is intended to carry will be evenly distributed over the structure.
In the context of the Bussell Highway Y-interchange, the bridge has a slight curve, so standard straight teeroff beams don’t naturally meet in the middle. Therefore, a stitch pour was performed prior to the deck pour, which connected Tee-roff beams from adjacent spans together, along with the deck sections.
Bussell Highway Y-interchange deck and stitch pour
Two Pours at the Same Time
Due to the structure and design of the Y-interchange, the deck and stitch pour both needed to be carried out at the same time. The reason for this was that the concrete needed to ‘meet each other’ while still wet. This ensured that the two types of concrete would form a seamless join at the interface.
But it also meant that the two different and distinct concrete mixes needed to be poured simultaneously, rather than one after the other.
When the two types of concrete come together still wet it ensures a more seamless join at the interface.
Early Morning Concrete Pour
Apart from the technical complexity of the pour, the Y-interchange is also located in a unique spot of the BORR alignment. Due to the volume of concrete which needed to be poured, and to reduce impact on traffic as much as possible, the pour began early in the morning and was planned to be completed within one day.
What’s next?
In the next few weeks, the team will complete additional concrete pours on the abutment approaches leading up to the bridge. Other upcoming works include installing guardrails along the bridge and parapets along the western wall. This bridge is on track to open to traffic in late 2024 when the BORR highway is open and complete.
Early morning deck pour on BORR
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