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Contractor (June 2012) Transmission Gully – NZ’s First Concrete Road

28 Jun 2012

Rob Gaimster
Cement & Concrete Association (CCANZ)

It would be natural to assume that a decision almost 100 years in the making would have all bases covered. However, if the New Zealand Transport Authority (NZTA) and its partners choose an alternative to concrete as the primary material for Transmission Gully then an opportunity to future proof a key component of our infrastructure, and at the same time create a template for other major roading projects, may have been missed.

GULLY BACKGROUND

In early May an independent board of inquiry, administered by the Environmental Protection Agency (EPA), released its draft decision approving resource consent for the $1 billion 27km inland highway from Linden to just north of Paekakariki (MacKays Crossing).

Transmission Gully is part of the Wellington Northern Corridor which runs from Wellington Airport to Levin.  In 2010 it was designated one of seven ‘Roads of National Significance’ that the Government identified as essential state highways that require upgrading to reduce congestion, improve safety and support economic growth in New Zealand.

Transmission Gully is also seen as a means to secure an alternative strategic link for Wellington that improves regional network security, particularly in the event of a significant earthquake.

BENEFITS OF CONCRETE

The biggest road construction undertaken in the Wellington region since the motorway extension of the late 1970s, the traffic loads Transmission Gully is anticipated to carry, along with the topography over which its route will follow, pose many unique engineering challenges that will demand the very best in construction materials.

Across road construction and maintenance programs, whether it be for specific structural forms, bridge spans or pavement applications, concrete’s first cost-competitiveness and long term durability ensure it ranks highly and warrant serious consideration from the project’s decision makers.

BRIDGES

New Zealand has a proud bridge building history, and can boast many outstanding concrete bridges At the time of their construction these bridges led the world in design and engineering excellence. The iconic Grafton Bridge in central Auckland is a case in point, one which continues to adapt to meet the requirements of a busy metropolitan centre.

Reinforced concrete presents a wide range of options in terms of shape, form and finish, which when combined with its strength, durability and seismic performance ensure it continues to set the standard, both in New Zealand and internationally, for bridge construction.

In addition, advancements in high-performance and ultra-high performance concretes over recent years have pushed the capabilities of the material to enable increased durability. This takes the form of good long-term creep and shrinkage behaviour, excellent resistance to chloride ion penetration, and the ability to hold up well under freeze-thaw testing. In terms of compressive strength, these concretes also have the capability to sustain deformations and resist flexural and tensile stresses to an exceptional degree.

Such enhanced durability and strength enables cost-effective bridges with a service life over 100-years, which would be ideally suited to such a demanding project as Transmission Gully.

Similarly, the benefits of prefabricated concrete systems and elements, manufactured off-site and erected as required, as a component of Accelerated Bridge Construction (ABC), would also prove invaluable.  Becoming a common way to fast track bridge building in North America, ABC consists of a number of design, construction, and contracting practices which speed construction, improve safety, and minimize traffic disruption.

RIGID PAVEMENT

The benefits of rigid concrete pavements are well documented, and and being increasingly embraced overseas. They can be neatly grouped into economic and environmental categories.

Based on its durability, a concrete road’s extended service life and low maintenance, along with reduced fuel consumption achieved through less rolling resistance experienced by heavy vehicles, are persuasive economic reasons for the implementation of rigid rather than flexible pavements for Transmission Gully.
 
From an environmental perspective concrete roads require minimal maintenance and therefore cause less congestion and associated exhaust emissions. Also, a recent whole-of-life study identified concrete manufacture as requiring less primary energy, and therefore generating less greenhouse gases, than alternative roading materials.

Grind-and-groove technology has improved the surface noise characteristics of concrete roads, while continual reinforcement has removed the need for (and the annoying “thud, thud” of) expansion joints.

Proponents of concrete pavement are now placing greater emphasis of it albedo – the ratio of the reflected solar energy to the total solar energy received. Essentially, concrete’s light coloured surface has a greater albedo than darker alternative materials, which means greater radiation reflectivity and a slower rate of global warming.

FINAL DECISION

With the independent board of inquiry’s draft decision binding (it can only be appealed against only on points of law), and the final decision to be released in mid-June, construction on Transmission Gully could start in 2015 and be completed by 2021.

Close to 100 years from inception to realisation is a long time. Key decision makers across all stakeholder groups must be confident that all aspects of such a significant infrastructure project, including material choice, have been thoroughly considered.

Article appeared in Contractor magazine.