Paving a better way
Asphalt industry takes aim at safety, cost savings

By Sam Barnes

The asphalt industry continues to search for ways to build better highways that save money and create longer-lasting pavements. Perpetual pavements, stone matrix asphalt mixes, Superpave and rubblization top the list of innovations.

The most recent endeavor is the Open-Graded Friction Course, touted to improve safety and reduce noise levels on urban pavements.

Don Weathers, executive director of the Louisiana Asphalt Pavement Association, said several test sites across the country are placing OGFC to test its assertions.

"We had representatives from the Texas Department of Transportation at the recent Transportation Engineering Conference talking about their test sites," Weathers said. "They've had some real success with the product." TXDOT is promoting OGFC's noise reduction aspects..

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OGFC is an open texture material that allows water to disburse laterally and vertically through the pavement, instead of creating hazardous driving conditions by sitting on top of the pavement.

"This improves safety conditions," Weathers added. "Trucks don't have the spray come off their tires because the water is not sitting on top of the pavement, and there is less pooling of water, which can cause hydroplaning."

The OGFC also reduces traffic noise, which reduces or eliminates the need for concrete sound walls in urban areas.

"It was used in Louisiana many years ago but some the performance was not that good because the asphalt we used then was un-modified," Weathers said. "But now, with the use of polymers we get a product that is more durable and longer lasting."

The Georgia Department of Transportation has effectively used OGFC as a 1.5- to 2-in.-thick overlay on top of existing stone matrix asphalt (SMA) pavements.

"It has about 20 percent air voids, which allows water to seep through and run off the pavement," Weather said.

Some states have pilot programs currently examining the effectiveness of OGFC.

"It's just a hot mix without the fines, and is placed on top of the final wearing course as a top coating," he said.

"They can go out every 10 years and replace it. The cost is not going to be significant because we're already making it; we're just eliminating the sands in the mix," Weathers said.

Some limited testing has been authorized in Louisiana, but more is planned for the future.

Other innovations. Recent initiatives in asphalt pavement design have produced a new approach to road building that could extend the design life of an asphalt pavement to 50 years or more - while improving safety and cutting both the time and cost of construction and maintenance.

Perpetual Pavements are asphalt pavements that use multiple layers of durable, recyclable asphalt. They stand up for decades under the steady punishment of heavy trucks. In addition, they provide a consistently safe and smooth roadway for parents driving minivans full of kids to soccer. When the surface layer needs repair, structural additions, or maintenance, it can be milled off for recycling and replaced in a timely and cost-effective manner.

But the road structure never needs to be entirely removed or replaced.

Developed by the Hot Mix Asphalt (HMA) pavement industry, Perpetual Pavements meet the driving public's demand for durable roads that won't crumble under today's increasing traffic and thus won't need costly and disruptive reconstruction. The concept is similar to that of a house that periodically may need to be painted or re-roofed, but that still stands the test of time.

The design starts with strong HMA base layer, flexible enough to prevent bottom-up, structural fatigue cracks. A strong load-bearing layer is applied over that, and the surface is constructed with a special asphalt mixture designed to resist ruts. This sturdy pavement system is designed to prevent the need for reconstruction for 50 years or more.

The surface can be periodically milled off for recycling, then quickly replaced, effectively giving motorists a new road.

As a long-lasting and smoother paving material, Perpetual Pavements using HMA could spell dramatic savings for state and federal transportation agencies striving to balance tight road budgets. And, because asphalt pavements are 100 percent recyclable, Perpetual Pavements offer further advantages, as well as economic benefits.

Perpetual Pavement combines the well-documented smoothness and safety advantages of asphalt with an advanced, multi-layer paving design process, that with routine maintenance, extends the useful life of a roadway to half a century or more.

Perpetual Pavements use multiple layers of durable asphalt to produce a safe, smooth, long-lasting road. The Hot Mix Asphalt (HMA) design begins with a strong, yet flexible bottom layer that resists tensile strain caused by traffic, and thus stops cracks from forming in the bottom of the pavement.

A strong intermediate layer completes the permanent structural portion, and a final layer of rut-resistant HMA yields a surface that lasts many years before scheduled restoration.

HMA also offers new technology. New, specially designed pavement types include Superpave, SMA (Stone Matrix Asphalt), OGFC, high modulus HMA, dense-graded HMA, HMA with modified binders and thin-friction lifts.

According to the APA, continuous improvement is the name of the game, with a goal of maintaining the best and most extensive road network in the world while being environmentally responsible and accountable to road users.

In the 1980s and 1990s, a new approach to selecting and evaluating HMA materials was developed under the Strategic Highway Research Program (SHRP). Called Superpave, this approach to designing asphalt mixtures holds promise to improve the performance of asphalt pavements.

Partnerships between public agencies, private industry and research institutions have resulted in other new pavement types, such as those mentioned earlier.

The "perpetual pavement" concept is that a pavement can be designed and built so it will only need periodic resurfacing over a period of more than 50 years. This approach will spare motorists time and money by minimizing the need to completely rebuild roads.

HMA is the most recycled material in the U. S. Reclaimed asphalt pavement is incorporated into new asphalt pavements that perform as well as, or better than, pavements constructed of all-new materials. Also, certain kinds of waste materials from other industries, including roofing shingles and tire rubber, can be used successfully in HMA pavements. Both approaches save money, nonrenewable natural resources and landfill space.

Rubblization. Rubblization is a construction technique that turns a deteriorated concrete road into the base for pavement constructed of Hot Mix Asphalt (HMA). It strives to minimize delays for motorists and allows for construction during "off peak" hours.

With rubblization, a deteriorated Portland Cement Concrete (PCC) pavement is broken into pieces and then overlaid with HMA. Fracturing the concrete helps to ensure that joints, cracks and other defects in the concrete will not "reflect through" the HMA overlay and impair performance.

If needed, the work can be accomplished at off-peak hours, without the round-the-clock road closures required for other pavements. Contractors report rubblizing up to one mile of deteriorated concrete pavement per day.

The rubblized roadbed is left in place so that it does not have to be trucked to a landfill. Instead of becoming waste, it has value as part of the new road structure. Leading pavement researchers including Witczak, Rada and Thompson, who have tracked rubblization projects during the past several years report excellent results.

A+B+C bidding. The recent adoption of the "A+B+C" method of bid letting has greatly impacted the asphalt industry.

"A" is the estimated cost of construction and "B" the time factor of the project, while "C" represents the merger of two ideas - the Alternate Design/Alternate Bid process and a lifecycle cost analysis.

"The marriage of the two is relatively new," explained Bill Temple, DOTD's chief engineer. "Other states do alternate design, but Louisiana is the only state that does alternate design/alternate bid based on lifecycle cost analysis."

For years, the DOTD has applied lifecycle cost analysis to decisions on which type of pavement to use for a particular roadway. However, the new component factors in maintenance over a 30 or 40-year period as well as user delay, a much more ambiguous factor.

Although maintenance figures come from DOTD historical data, the user delay costs are more difficult to define.

"One type of pavement might interrupt traffic less than another, so we would want to give credit for that," Temple said. "It is a very difficult thing to calculate because you are trying to calculate something that hasn't happened yet. It's not exact."

Although the new method represents more design work for DOTD and the lifecycle cost analysis is "a bit of trouble also," said Temple, it allows more competitive bidding. "To open up as much competition as possible, we do the life cycle cost analysis, and, for those alternates that are within 20 percent of each other, we would allow them to compete in an alternate bid/alternate design."

Factored into the bids are the state's estimates of lifecycle costs, including maintenance and user delays, based on a 30- or 40-year analysis period.

"For example, if we say it costs us $3 million to rehabilitate the concrete over the next 30 years and $5 million to rehabilitate asphalt over the next 30 years, it tends to equalize everything. Rather than this agency selecting a pavement type, we do alternate design, alternate bid and let the industry chose the pavement type."

Representatives of the asphalt industry say it's about time the logic of product selection is determined by marketplace competition instead of some "administrative decision," said Don Weathers, president of the Louisiana Asphalt Pavement Association. "John Q Citizen doesn't care if it's black or white, concrete or asphalt, they just want it to be smooth. We are simply trying to make the playing field level."

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For more technical information about Open Graded Friction Course and other asphalt innovations, go to: www.asphaltalliance.com