Rob Gaimster of the CCANZ and NZRMCA puts forward a case for concrete roading as the country spends billions of dollars over the next decade on state highways and Roads of National Significance.
WHILE CONCRETE ROAD PAVEMENTS are in widespread use throughout the world, New Zealand pavements are still largely constructed using asphalt (and chip seal) – despite growing evidence that concrete is cheaper, lasts longer, and offers various environmental benefits.
CCANZ has contributed to the debate by commissioning economic consultants Infometrics to investigate the high-level case for building concrete pavements. It was found that in a baseline scenario comparing the economics of asphalt and concrete pavements, concrete came in around 25 percent less expensive.
If our approach to pavement construction is to evolve and take advantage of the benefits afforded by concrete, a look at a recently completed pavement trial in the American state of Ohio as well as a large project in New South Wales’ Hunter Valley is worthwhile.
These undertakings have been used by the Portland Cement Association (PCA) in the United States and Cement Concrete and Aggregates Australia (CCAA) respectively to argue the case for concrete pavements.
In 2004 the Ohio Department of Transportation began a long-life pavement test on US-30, a four lane divided highway in the State’s north-east. The objective was to compare concrete to a ‘perpetual’ asphalt pavement solution.
The trial made use of west bound lanes constructed with asphalt, and east bound lanes constructed with concrete. The scope and length of the trial were the same for both west and east bound lanes, as was the same contractor.
Since 2004 the west bound asphalt lanes have required numerous repairs, as well a complete re-surfacing that cost US$1.8 million. The east bound concrete lanes have not required any repairs, and have none scheduled.
From an up-front cost perspective, in 2004 concrete was 8% more expensive than asphalt, however, if the costs of repairs are accounted for over the past 12 years then concrete has proven to be a cheaper option.
Over that 12 year period the volatility of oil, and in turn asphalt, has been significant. At the time of the trials completion the construction costs for both options were virtually identical.
Concrete pavement was chosen for a major portion of the Hunter Expressway, a forty kilometre, four lane, dual carriageway that provides a direct and efficient route for freight movements for the busy Port of Newcastle. Handling 75 percent of the State’s total international trade, the level of heavy traffic demands a pavement offering superior strength and durability.
A range of foundation support conditions required a variety of pavement solutions and consequently two forms of concrete pavement were used in different job sections – Plain and Continuously Reinforced concrete pavement.
The first form was a Plain concrete pavement consisting of a 280mm thick 35 MPa base constructed over a 150mm thick 5 MPa subbase. The second form was a Continuously Reinforced concrete pavement consisting of a 250mm thick 35 MPa base constructed again over a 150mm thick 5 MPa subbase. In both cases the base was debonded from the subbase with a 7mm spray seal over a wax curing compound.
The Plain concrete pavement contains no steel reinforcement and utilises a system of transverse and longitudinal jointing to manage cracking behaviour, while the Continuously Reinforced concrete pavement has continuous longitudinal reinforcing steel.
An interesting initiative that was undertaken on some of the concrete pavements was a Diamond Grinding surface treatment, a process that cuts narrow longitudinal grooves into the surface after the concrete has hardened to deliver a surface texture that produces a smoother vehicle ride with increased traction and lower perceptible traffic noise.
As demonstrated by the Ohio trial, the decision to go with concrete pavement options along the Hunter Expressway is anticipated to yield significant cost savings over the pavement’s extended life resulting from less maintenance and associated traffic disruption.
New Zealand applications
The Roads of National Significance programme represents one of the country’s biggest ever infrastructure investments, designed to enable economic growth and future prosperity.
Such a massive undertaking, coupled with interest in Public Private Partnerships that encourage involvement from well-resourced contractors, offers an ideal opportunity to explore the potential of concrete pavements.
This opportunity can take many forms, either long stretches of pavement or niche applications such as motorway on/off ramps, intersections and roundabouts. Alternatively, a trial similar to that conducted on US-30 in Ohio could be undertaken at a suitable location.
Regardless of the route taken, now is a watershed in terms of road construction in this country, one which deserves to be explored thoroughly for long-term gain.