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Contractor (March 2015) Turn the Corner with Concrete Intersections

01 Mar 2015
Rob Gaimster
Cement & Concrete Association (CCANZ)

Ever pulled into the car park of your local shopping precinct, come to a stop at the traffic lights in the centre of town, or turned at a roundabout close to your kid’s school, only to feel as if you have driven over a cattle grid?

The car shudders, the driver and passengers are shaken, the keys jangle loudly beneath the ignition and the rear view mirror vibrates to distortion. Sound familiar?

Constructability of concrete pavements over a short time period allows for rapid re-use of the intersection.

In short, the rigidity of a suitably designed and constructed concrete pavement is well suited to withstand the loading and turning movements of heavy vehicles at busy intersections, which in turn means the expense associated with frequent maintenance is substantially reduced.

DESIGN CONSIDERATIONS

When planning to construct an intersection, the concrete pavement should cover at least the functional area. This includes the longitudinal limits of the approach and exit lanes, as the distress caused by braking of turning heavy vehicles extends beyond the physical area.

Concrete slab thickness will be influenced by traffic density and vehicle characteristics, but is most likely to be thicker in the physical (central) area of the intersection, compared to the approach and exit lanes.

The most important design aspect of concrete pavement intersection is jointing. However, by applying simple jointing fundamentals that consider spacing, type and layout concrete expansion and contraction can be managed effectively for long-term performance.

CONCRETE MIX

An appropriate concrete mix is essential to ensure a successful outcome for any concrete pavement. The capability to meet strength requirements within the specified timeframe is particularly crucial.

Adequate strength goes a long way to safeguarding a hard, durable, skid-resistant surface, as well as accommodating the tensile stresses resulting from shrinkage and loading.

CONSTRUCTION

The construction of concrete intersection pavements can incorporate a variety of methods, including fixed-form and slip-form equipment. The latter will most likely be used if the intersection is considered large enough by the contractor.

Although various types of equipment can be used, a relatively standard set of construction steps apply to the majority of concrete intersection project. These include, the removal of the existing intersection, subgrade / subbase preparation, setting forms, placing in-pavement objects, concrete placement, surface texturing and jointing.

UPTAKE & EXPERIENCE

Overseas experience with concrete pavement intersections has been encouraging. The concrete roundabouts constructed across New South Wales for instance have performed with very low maintenance demands.

In South Africa, Canada and the United States concrete pavement intersections are becoming more common place, supported in-part by the work of the relevant concrete associations.

Here in New Zealand, where investment in roading is at levels not seen for decades, the adoption of concrete pavements to provide long term durable solutions for road sections that are highly stressed merits consideration.

Article appeared in Contractor magazine.