PAVEMENT:New Jersey Turnpike asphalt nears 50 & strong

John Kunna, chief engineer at the New Jersey Turnpike says his predecessors did a superb job designing and constructing the turnpike’s pavement. And he says the Turnpike has generally done a good job since then of maintaining it. Full depth asphalt, most of it, was laid in 1950 and 1951, so it is approaching its half centenary. And it’s going strong. Kunna says there is no foreseeable need to rebuild the pavement totally, as has happened with many other portland cement concrete and asphalt pavements well before this.

For example, the concrete pavement of Illinois original toll road and West Virginia’s concrete, a few years younger than the NJ Tpk pavement is being totally replaced. The Pennsylvania Turnpike’s 61 year old pavement is all being ripped up and replaced with asphalt.

The NJ Tpk pavement structure is generally about a meter thick (40"). It started in 1950-51 with a 900mm (36") structure consisting of 450mm (18") of free draining sand with 150mm (6") of crushed stone, then 300mm (12") of asphalt. Most places have had a couple of 50mm to 60mm (2" to 2.5") overlays, giving it an asphalt depth of 400mm to 420mm (16" to 17") on top of a 600mm (24") sand and stone foundation.

Regular rehab consists of milling to improve skid resistance and every 12 to 15 years milling off approximately the top overlay and replacing it with a new 50mm to 60mm (2" to 2.5") wearing surface. The Turnpike has only 4.4m (14.5ft) clearance at the original overbridges thanks to the overlays which makes it a tight fit for many trucks but where bridges are replaced they get an extra 600mm (2') clearance

“We’ve seen very little base failure. Certainly we have surface failures that need work. But the basic pavement slab is in excellent shape and we can’t see any end to its life. It was an excellent design and it was excellently built. We have to be conscientious about regular crack sealing and to go back regularly to attend to the wearing surface. We got a bit behind where I thought we should be, but with the new capital plan we are going to attend to that.”

Kunna says that he thinks the generous depth of “free draining sand” in the foundation is probably the main reason for the long life of the base pavement, but credits good construction as well: “They made a special effort to do it right the whole length of the turnpike.”

The turnpike got behind on timely replacement of bridge decks, Kunna says, but it should now be able to catch up with a $20m/yr program. It has 500 bridges. A latex modified concrete now being used in decks should prolong their life by reducing water penetration.

“The larger capital program should enable us to do bridge deck replacement more efficiently. There is also major joint and bearing replacement, and some work to preserve sub-surface components of the bridges.”

The pavement of the toll plazas is concrete. In some cases the plaza concrete has been extended to replace asphalt on the approaches to Turnpike toll plazas. The braking and maneuvering there calls for the greater strength of concrete.

But in general travel lanes the turnpike engineers think asphalt is the clear choice, at least in this climate.