In This Issue...

Concrete Overlay Technology

Few people would argue with the widely-held view that many of the nation's highways and roadways are in disrepair.

The more controversial question is what to do about the situation. With the dual problem of limited funding and rising construction costs, agencies are increasingly turning to pavement preservation strategies, and within them, to overlays as a viable means of extending pavement life.

The "portfolio" of concrete overlay options has been around for considerable time, but the demand for overlays has increased sharply in recent years.

And, while many agencies have long understood the benefits of concrete, more are considering the versatile material because its first costs are increasingly competitive with those of asphalt.

Thinner by design ... Worker spreads concrete on a test project at the Illinois DOT's Schaumburg, Illinois-facility. Concrete overlays such as this one can be engineered to carry the load, even with a thickness as low as 2 in. (ACPA staff photo.)

Rising fuel prices, and the greater issue of volatile oil prices, continue to challenge state DOT’s, which already are facing the pressures of limited funding available to address the critical needs of the nation's surface transportation infrastructure.

But there is hope for agencies and roadbuilders facing this two-fold challenge. The concrete pavement industry has developed a number of tools for agencies as they shift their focus to maintenance and repair, rather than reconstruction.

As part of this shift, concrete overlay technology is becoming a common solution in the toolbox.

Paradigm Shift
Historically, there have been two fundamental ways of assessing costs of pavements: first costs (the short-term analysis based on materials and placement costs) and life-cycle costs (the long-term analysis factoring in maintenance and repair requirements, as well as inherent design lives). Concrete has historically offered the best value in a life-cycle cost analysis, but asphalt often appeared cheaper because its first costs were lower. Therein lies the historic reasons why asphalt was so often selected.

But the paradigm has shifted, largely because of the volatility in oil pricing, as well as the associated price spikes with asphalt oil. As a result, concrete pavements in a growing number of cases is less expensive on both the basis of first costs and life-cycle costs.

Concrete overlays have been proven to extend the life of the pavement structure by 15 to 20 years or more and now they are competitive at first cost. In contrast, a comparably-designed conventional mill-and-fill of an aging asphalt pavement might provide only 8 to 14 years of extended pavement structure life. These applications range from mainline paving and streets and local roads to parking lots, rest areas, and any other scenario where a traditional mill-and-fill might be performed as routine maintenance.

Fueling the Argument
Adding to the complexity of the issue, gasoline prices were supposed to peak at $3 per gallon in May 2007 and then drop off slightly before the summer driving season, according to the U.S. Energy Department. But gas prices at the pump have in most areas of the country exceeded $3 per gallon ... and a number of analysts and experts are predicting the situation to get worse.

This recent change in relative cost, on top of rising fuel prices, has caused many agencies to consider concrete pavement in many applications they previously had not, often times fueled by an alternate bidding system.

For Heavier Loads
Conventional concrete overlays 4 or more in. thick have been proven to perform nearly as well as newly constructed concrete pavements. In some cases, they can add as many as 30 years (or more) to the life of a pavement structure. Such structures are designed using common methods and formulations and assuming that the existing asphalt pavement is the subbase, with consideration of any additional layers (including pre-existing concrete if the existing pavement is a composite) and subgrade preparation from the original construction.

Because the existing asphalt performs well as a subbase, thicknesses can be substantially less than those used in new construction. Dowel bars and tie bars are often times necessary, as with a new design, so the cost savings (if a concrete overlay does not win at first cost) with conventional concrete overlays come primarily from the benefit of the excellent pre-existing foundation and the subsequent extension of service life of the pavement structure.

For Streets and Local Roads
The use of ultra-thin (UTW) concrete overlays over existing asphalt facilities only dates back to 1988, but their performance has often exceeded expectations. These thinner sections, typically 2 in. to 4 in. thick, are usually characterized by the use of high strength concrete, fiber reinforcement, and smaller panels. Another characteristic is the tenacious bond between the concrete and existing asphalt. Because of these characteristics, traditional design rules do not apply, so ACPA has developed a free on-line UTW design calculator.

UTW pavements provide a durable wearing surface, free of rutting and shoving, and are best suited for normal traffic loads on residential and collector streets and roads, parking lots, rest areas, general aviation airports, etc.

Because the design procedure is based on the UTW’s load carrying capacity, any design life can be effectively specified.  Due to the unique design of UTW overlays, dowel bars and tie bars are not specified, so the cost savings of an UTW versus a conventional asphalt mill-and-fill is immediately realized.

The cost savings are then made even greater with any extension in the service life that the UTW provides, which is controlled by the designer’s selection of load carrying capacity.

These two concrete overlay systems, as well as several others, are highlighted in the recent CP Tech Center publication “Guide to Concrete Overlay Solutions”, available for free download here.

For additional information, please contact Robert Rodden, ACPA’s Director of Technical Services, at 847-966-2272.

U.S. freight traffic will experience “staggering increases” during the next three decades according to John Horsley, Executive Director of the American Association of State Highway and Transportation Officials (AASHTO).

They are:
• Traffic volumes and freight movement rising with economic
growth;
• U.S. manufacturing output continuing to grow;
• Just-in-time strategies spurring shipping; and
• Growing international trade stimulating a rising tide of imports and exports.

Horsley warned that transportation’s economic edge is trailing and said the situation will not improve without intervention.  Truck traffic on the Interstate highway system is expected to double to 22,700 trucks per mile in 2035.

He also said the trucking industry experiences 243 million hours per year of delays, which costs $7.8 billion, according to the Texas Travel Institute. What needs to be done? Further investment in Interstates, along with rail incentives and water projects are needed, Horsley said, noting that innovative solutions with public- and private-sector collaboration are needed, as is a national rail policy.

Ultimately, findings from the AASHTO-commissioned research will be presented to the National Transportation Policy and Revenue Study Commission. Click here to download the report. (Source: AASHTO.)

Highway Officials Toughen Stance on Highway Fatalities ... The American Association of State Highway and Transportation Officials (AASHTO) is toughening its stance on highway safety.

AASHTO's Standing Committee on Highway Traffic Safety drafted a resolution to reduce highway fatalities by half over the next two decades. This more aggressive highway safety program is aimed at saving more than 50,000 lives over this time period.

By setting this goal, AASHTO hopes to inspire other safety organizations and state agencies to share this standard of achievement. Reaching this new target will require improving highway infrastructure, among other changes, according to the resolution.

The new goal for decreasing highway fatalities replaces an earlier target of reducing highway deaths to 1.0 deaths per 100 million vehicle miles of travel by the end of 2008.