A special concrete mix used in the Tauranga Harbour Link Project is the winner of the 2010 Supreme Concrete Sustainability Award.

Tauranga Harbour Link Project was the construction of a second bridge between Tauranga and Mount Maunganui, completed at the end of 2009.

The New Zealand Concrete Conference award was given in Wellington last week to the concrete's maker, Fletcher Construction.

Designated ‘Mix M', this concrete is designed to survive 100 years in harsh marine conditions, and was employed extensively in the second stage of the Harbour Link Project to form beams used in the off-ramps, bridges and land spans.

Mix M achieved top honours in concrete sustainability for its specially blended and extensively trialled mix of Golden Bay cement, fly ash (a waste product from coal burnt at Huntly Power Station), and microsilica 600, which enabled demanding durability, high early strength, and high workability requirements to be met.

The use of fly ash and microsilica resulted in a significant reduction in cement requirements and a corresponding reduction in the carbon footprint of the concrete beams.

CCANZ chief executive Rob Gaimster says Mix M was a significant step forward in concrete mix design and durability modelling; one which combined enhanced environmental credentials with superior performance.

'Not only was the mix design sophisticated in optimising cement replacement, but by sourcing its fly ash from within New Zealand, and using microsilica slurry rather than more energy intensive powder, Mix M scored additional sustainability marks.”

The team behind Mix M also received the Excellence in Civil Concrete Construction Award.