Why asphalt

courtesy of the National Asphalt Pavement Association

WHY ASPHALT? What makes asphalt better than other pavement alternatives?

Always the least expensive pavement: You're not alone when you choose Hot Mix Asphalt (HMA) pavements for your citizens. HMA's popularity tells its own story. Of the 2.27 million miles of paved road in the United States, 94 percent is surfaced with HMA, including 65 percent of the Interstate system.
     Today's HMA pavements are smoother than ever before, so HMA satisfies your customer -the road user -who, most of all, wants smooth pavements, according to recent research sponsored by the federal government.
A smooth asphalt pavement saves in vehicular wear and makes drivers happy. HMA pavements go down quickly and are open to traffic faster, saving labor costs and costs due to user delays. And use of reclaimed asphalt pavement (RAP) in the road base, base course, or surface course can make those dollars go even farther, while sustaining the environment.
     But one of the best reasons to choose HMA is its intrinsic low cost. Compared to Portland Cement Concrete (PCC), HMA always is the least expensive pavement medium in initial cost. This means more miles in your jurisdiction can be paved or overlaid in a season, faster, and with lower road user costs.
     But to most road agencies, long term costs are even more important. And given the right design, HMA is the also lowest priced pavement in the long term. Here's why.

HMA for short term, for long term: HMA is your best buy all of the time in both the short term and the long term. Real-life experience bears this out.
     For example, in the short term, a three-year analysis conducted by the Florida Department of Transportation showed first-cost, initial construction of an HMA pavement to cost $544,981, compared to a first-cost of the same pavement in Portland Cement Concrete of $765,729. And in the long term, following usage and proper maintenance, Florida DOT calculated the residual value of the HMA pavement to be 203 percent higher than the PCC pavement.
     Rigid pavements may not be as trouble-free in terms of placement and longevity as alleged. PCC boosters say it has lower maintenance costs than HMA, thus justifying its higher initial cost, but the Florida Department of Transportation calculated its routine annual maintenance costs on the above pavement as $132 per lane mile for asphalt pavement and $261 per lane mile for concrete pavement.
     Initial costs of HMA pavements are substantially lower than PCC. In a notable reconstruction of a suburban intersection in Maryland, the Maryland State Highway Administration evaluated the costs and performance of both pavement types under the same conditions.
     At the intersection of U.S. 40 and Maryland 213, contractors milled 8 inches of old pavement and placed 15,000 square yards of new HMA in 11 nights, with minimal lane closures. There, PCC forces also installed 1,800 square yards of material, working around-the-clock with long-time lane closures.
     Not counting user delay costs now a prime consideration in state DOT work ?on this project the PCC pavement cost nearly three times as much per square yard ($104.25) as the HMA pavement ($36.11). And when revisited in 1998, the HMA pavement looked as smooth as new, while the PCC pavement was badly broken and in need of repair.

Side-by-side, HMA shines: It's the long term that interests most road agencies. In new research presented at the January 1999 Transportation Research Board meeting by researchers at the Center for Transportation Research, University of Texas-Austin, the paper "Pavement Type Selection and its Current Practices in North American Highway Agencies" (Beg, Zhang, Hudson), showed that HMA is the highest-ranked pavement type when state and provincial Canadian agencies consider new pavements.
     Asphalt concrete pavement on granular stone base is the most widely considered pavement alternative, with 94 percent "yes" responses in this new survey of U.S. and Canadian road agencies. These same agencies state that "life cycle costs" are the most significant criterion used in selecting pavement type (66 percent), compared to "initial cost" (17 percent), and "both life cycle and initial costs" (17 percent).
     Long-term pavement studies on HMA interstate sections in Jasper and Poweshiek counties in Iowa show that HMA pavements ? instead of needing extensive maintenance are cost-effective in the long run.
     Based on Iowa Department of Transportation records, a life-cycle cost analysis rolled all costs back to 1957 dollars per one-way, two-lane mile; 1957 was the earliest year that interstate sections in the study were constructed. A discount rate of 4 percent was selected for use to stay consistent with discount rates used by the Iowa DOT.
     Even though user delay costs and residual values were not counted, the studies showed that the HMA pavements provided more than 22 years of service without the need for reconstruction or rehabilitation, and that they had a lesser rate of increase in cost for maintenance than adjoining concrete pavements. If user delay costs and residual values had been counted, they would have made HMA look even better.
     Similarly, an apples-to-apples comparison on Ohio's Interstates showed HMA pavements provided 25 to 34 years of continuous service before rehabilitation. They also were less costly to construct and maintain than adjoining PCC pavements. As in Iowa, they had a lower rate of increase in cost for maintenance than adjoining concrete pavements. Clearly, PCC pavements are more expensive to maintain, and this affects their long-term life-cycle costs.

Maintenance: CPR for PCC: That's because PCC "maintenance" includes time?, money? and labor-intensive operations like CPR, which almost always will be more expensive than conventional HMA maintenance like crack sealing and pothole patching.
     In road maintenance parlance, CPR means Concrete Pavement Restoration. Far from being a maintenance activity, CPR refers to a variety of intensive construction actions, such as joint repair and sealing, slab jacking, and grinding.
     For example, joint repair requires pavement sawing, debris material removal, placement of load-transfer dowels and baskets, mixing, transport and placement of PCC patch material, subsequent curing (perhaps over days), re-sawing of the expansion joint, and sealing of the joint. All these activities are accompanied by lane closures which seem excruciating to the motorist.
     Because they can conform to gradual shifts, HMA pavements aren't as likely to be harmed by adverse soil conditions like expansive clays as much as rigid PCC slabs, which may break up or fault. When a PCC pavement's slabs have faulted, the ride becomes unacceptably rough. Remedy requires lane closures as specialty contractors with large, expensive diamond grinding equipment are employed. Slowly moving down the lane, the grinding equipment precisely "shaves off' the jarring surface to smooth it.
     In the worst case, faulted slabs actually will pump wet material to the surface as trucks pass over them. Often, saturated subgrade materials will spurt from under the slab and onto the shoulder or driving surface, quickly undermining the pavement. Remedying such extensive faults requires "slab jacking," in which holes are drilled in the slabs and cement grout is pumped into the voids beneath the pavement. Slab jacking can be ineffective because it can crack the slab. Again, lane closures can be excruciating.
     Even local PCC pavements which don't require such drastic CPR measures still need maintenance. D-cracking needs to be patched. Joints lose their sealants, and need to be resealed.
     HMA maintenance techniques, on the other hand, are relatively brief and uncomplicated. Periodic patching or crack sealing can be conducted when necessary at minimal cost and disruption to traffic. When needed, milling and thin overlay can be accomplished quickly and economically, often overnight, without disrupting traffic flow. And 100 percent of the reclaimed HMA can be recycled.

It all adds up to HMA: Initial costs, maintenance costs, long-term costs, user delay costs, residual costs. They all add up to one thing: HMA is the lower-cost pavement, hands down.
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Sidenote:
HMA's Low Cost Keeps Fort Worth in "Black": Fort Worth is using Hot Mix Asphalt (HMA) more and more on its city streets, reports the Texas Hot Mix Asphalt Pavement Association.
Fort Worth finds that HMA's low initial cost permits them to put a major dent in its road-maintenance backlog. The city has some 5,600 lane miles of roadway to manage and maintain, of which as much as 30 percent may be classified as being in poor condition, said George Behmanesh, Assistant Director of Transportation.
Fort Worth is implementing a Pavement Management System (PMS) to give it an inventory of every street and pavement condition within its network. The city has two programs to address street needs: An HMA overlay program, funded through the annual budget, and reconstruction from a 1998 bond package.
The bond package is intended to help fund the major rehabilitation and reconstruction of streets. Voters approved a $120 million dollar bond package, of which $80 million is earmarked for streets and appurtenances.
The majority of the street reconstruction work over the four-year period will be done using Hot Mix Asphalt in order to "stretch their dollars," Behmanesh said. HMA will be used for total reconstruction projects as well as for in-place reconstruction of existing HMA streets.