Shotover Wastewater Treatment Plant Upgrade

A third stage of upgrades to Shotover Wastewater Treatment Plant aim to improve wastewater capacity in the Queenstown Lakes District, with a range of improvements designed to provide for future growth in the area through to the year 2048.

Overview

Allied Concrete’s Queenstown plant supplied a programme of lower-carbon structural mixes for the Shotover Wastewater Treatment Plant (WWTP) upgrade, delivered by McConnell Dowell. The supply included the largest Ecrete™ pour completed to date in the Otago/Southland region, alongside high-strength mixes designed with supplementary cementitious materials to reduce embodied carbon without compromising strength, durability, or programme.

What we delivered

• Largest regional Ecrete™ pour placed on the project, supporting significant embodied-carbon reduction at element level.

• 2399.60 m³ of concrete supplied to date for the upgrade works.

• Mix designs targeting 30–35% fly-ash replacement while achieving specified 40 MPa and 45 MPa strengths across the works.

• Approximately 327.5 tonnes of fly ash incorporated, representing an avoided footprint of ~271.7 t CO₂ based on typical cement emission factors.

Behind the build: how the lower-carbon concrete supply worked

Our strategy centred on clinker reduction using fly ash, with production planning and quality control tuned to the project’s pour sequence. Cylinder testing confirmed target strengths and early-age performance. Pumpability and set times were adjusted to suit large structural pours and site logistics. Documentation accompanied each supply so the project team could track sustainability contributions alongside standard records. The key was a repeatable, plant-ready approach, not one-off trials, so every pour met environmental and operational requirements.

Why it matters

Reducing embodied carbon on critical infrastructure only counts when it is done at scale and without compromise. At Shotover WWTP, the combination of high-strength concrete with 30-35% SCM content, a milestone Ecrete™ pour, and quality assurance performance shows what regional plants can already deliver using proven materials and processes. The learnings from this supply are now informing other public projects across the South Island.

All Shotover WWTP images/video courtesy of McConnell Dowell.

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