(from APAI newsletter 11-2003)
ASPHALT’S SPEED OF CONSTRUCTION
BACKGROUND
Paving with asphalt cuts construction project time significantly and eliminates the long curing times of concrete. As a result, traffic flows more smoothly, impact on commerce is minimized, and safety hazards are reduced.
How it works
Asphalt paving projects can be planned and carried out to take advantage of low-traffic periods, like nights and weekends, minimizing the project’s impact on motorists, residences and businesses. In one state highway department comparison, asphalt crews placed more than 10 times the pavement surface that a concrete contractor did. The asphalt was placed in 11 nighttime-only shifts, while the concrete work went on around the clock for 12 days.
Major advantages
Asphalt projects are safer, because the work can be carried out during low-traffic periods to minimize worker and driver exposure to construction zones. And, a shorter project time simply increases safety. Asphalt is ready for traffic right after it is compacted and cooled, meaning that roads don’t have to remain closed for curing. This enhances traffic flow and minimizes closures and delays that frustrate motorists and cost money. Impacts on businesses are dramatically reduced when roadwork is completed rapidly.
FACT SHEET
1. Minimizes impacts on neighborhoods and businesses dues to road closures.
2. Improves safety—for both workers and motorists—by cutting total paving time.
3. Can be placed faster than other paving materials. Nearly 10 times as much road was paved with asphalt than concrete, in less time, in a Maryland Highway Administration comparison. Asphalt was placed only at night while concrete contractors worked around the clock.
4. Eliminates long curing times, allowing roads to reopen immediately.
5. Reduces road closures, cutting or eliminating costly traffic jams and back-ups.
SPEEDY ASPHALT PAVING SAVES LIVES, DOLLARS
“Stealth contractors” paving long stretches of busy commuter routes at night—and disappearing before the morning rush hour—are increasing road project safety while keeping homeowners and businesses happy nationwide. Fast and unobtrusive construction is one of the biggest benefits of Hot Mix Asphalt (HMA). With HMA, drivers, residents and business owners soon come to learn that traffic delays are significantly reduced, meaning access to shopping centers and homes often remains open throughout the paving project.
At the same time, the rapid construction of asphalt minimizes hazards to workers and drivers, improving safety and curbing traffic disruptions.
Even when a road must be closed for certain asphalt work, it reopens much sooner than one paved with concrete, which takes time to cure.
These benefits and more have been demonstrated time and again in independent studies, and by state and local highway departments grappling with ever-increasing demands on the nation’s roadways, on the one hand, and tight construction and maintenance budgets on the other.
Because it can be installed so rapidly, with minimal road closures and without the long preparation and curing time needed for concrete, asphalt is the pavement of choice for highway departments all over the United States.
Maryland highway officials, for instance, recently compared construction times of asphalt and concrete on a busy intersection. The asphalt crews prepared and placed 15,000 square yards of HMA in just 11 nights of work—while a concrete contractor managed only 1,800 square yards in round-the-clock operations that caused frequent, long-lasting lane closures and major traffic tie-ups.
This speed-of-construction advantage was also demonstrated dramatically in a recent resurfacing project in Oklahoma City, where two miles of eight-lane Interstate 40, near the city’s busy downtown, was resurfaced at night and on weekends, leaving the road open during high-traffic times. Haskell Lemon Construction Co., the asphalt contractor that performed the work, was nicknamed the “stealth contractor” by Oklahoma City drivers because the five-week project was completed without daytime traffic hassles or road closings.
HMA paving techniques, however, can slash user delay costs and provide significant advantages for community businesses, experts note. As just one example, they point to the recent reconstruction of nearly a mile of a busy commercial roadway in Wisconsin. Restaurants, car dealerships, strip malls and other businesses, as well as many residences lined the route but B.R. Amon & Sons designed the project to minimize shutdowns. “We kept all the driveways to the homes and businesses open,” said Tom Amon, the company president.
Even more important is the safety benefit of speedy asphalt paving work. A rapidly completed project that quickly restores smooth traffic flow minimizes the danger to both highway work crews and motorists, safety experts and highway engineers agree.
HOT MIX ASPHALT (HMA) LIFE-CYCLE COSTS
FACT SHEET
1. Reduces costs for initial construction.
2. Requires less maintenance over the life of the pavement.
3. Repaired and maintained cost-effectively with HMA overlays instead of complete
removal and reconstruction with concrete.
4. When maintenance is needed, HMA offers the widest variety of alternatives geared to
solve the precise problems on the roadway.
5. Can be overlaid to add structural capacity to account for increased traffic loading.
6. Eliminates the need for costly reinforcing materials, which are subject to corrosion, which
lead to more frequent and more costly repairs.
7. Properly designed and constructed HMA pavements will last 50 years or more with occasional resurfacing, relieving road agencies of the need for costly, time-consuming and disruptive reconstruction.
8. HMA can be recycled (milled and replaced along with fresh materials), saving dollars and preserving nonrenewable natural resources.
ASPHALT PAVEMENT LIFE-CYCLE COST
BACKGROUND
Smooth, flexible pavements constructed from Hot Mix Asphalt (HMA) stand up to the punishment of heavy trucks and other vehicles, significantly reducing initial and total costs over the entire life cycle of a road.
The cost of keeping motorists stuck in traffic during construction—known in the industry as user delay cost—should be considered in any analysis of life-cycle cost. On a busy interstate highway, traffic delays from a single construction project can easily cost a local economy more than two million dollars per day. With asphalt pavements, initial construction, maintenance, and rehabilitation all cost less. And, user delay costs are far less with HMA because construction, maintenance, and rehabilitation with Portland Cement Concrete (PCC) takes much longer.
How it works
HMA pavement design begins with a strong base layer that absorbs and diffuses the stress of heavy traffic, preventing the initiation of cracks. A smooth, load-bearing intermediate layer is topped by a smooth, rut-resistant surface layer that seals out moisture and deicing materials. Altogether, HMA pavements can handle the toughest traffic punishment.
Major advantages
Because construction cost less initially, and proper maintenance extends the life for decades, HMA pavements last long and cost less than concrete. HMA pavements require only periodic surface restoration, providing a smooth, durable pavement for decades. Maintenance is quick, cost-effective and less disruptive than with PCC pavements.
ASPHALT PAVEMENTS – A STANDARD OF EXCELLENCE
FOR SMOOTH ROADS QUESTIONS AND ANSWERS
What does it mean to have smooth roads?
Happy motorists. A national survey of motorists funded by the Federal Highway Administration showed that a smooth ride is the top priority of the traveling public. Smoothness enhances the perception of comfort and reduces annoyance for drivers and passengers.
Greater fuel efficiency. Results from an asphalt pavement test track in Nevada showed a significant reduction of frame, suspension, and engine component problems when the pavement smoothness was improved.
Less wear and tear on vehicles. Results from the same Nevada test track showed a significant reduction of frame, suspension, and engine component problems when the pavement smoothness was improved.
Longer pavement life. The Arizona Department of Transportation estimates that their new smoothness requirements will result in a 10 percent increase in the life of their pavements. What’s more, they are finding that it is costing them no more to build them this way.
How seriously do highway agencies take roughness?
Very seriously.
Georgia was recently identified as having the smoothest roads in the country. Ninety-five percent of the roads in Georgia are surfaced with Hot Mix Asphalt (HMA), and all of the roads tested had an IRI of less than 75 inches per mile.
Similarly, the Arizona DOT recently changed its smoothness specifications so that highways being built there are required to be 27 percent smoother than those constructed previously. They accomplished this by working with the HMA industry and offering incentives for pavements that were smoother than required. The contractors rose to the occasion and met the challenge of providing the public what it wanted.
How is road roughness measured?
The International Roughness Index (IRI) is one measure of ride quality. It is reported in inches of bumps per mile of road. To determine IRI, a mechanical device travels over a road or highway and measures the height of the bumps affecting ride comfort. The height of the bumps per mile of road is then added together. The higher the IRI, the rougher the road. Not all states use the IRI for measuring smoothness, but it will be used as a frame of reference for this discussion.
What is considered a smooth road?
According to a University of Michigan publication, airport runways and superhighways have IRI values in the range of 10 to 110 inches per mile, while damaged pavements run from 250 to 680 inches per mile.
To what standards are road contractors held when they build roads?
While some agencies have the same requirements for the smoothness of HMA and concrete pavements, many actually have stricter requirements for asphalt.
Asphalt pavements may be specified to have IRI values of less than anywhere between 60 to 80 inches per mile. The state of Georgia targets and IRI of 54 inches per mile on all newly constructed asphalt pavement.
Why are asphalt roads held to a higher standard?
Because they can be.
In a 1999 report to Congress, the General Accounting Office (GAO) noted, “Concrete roads may produce rougher (smoothness) readings than asphalt roads, even if the concrete road is of very high quality. Features such as joints between sections can contribute to the roughness of concrete highways.”
Highway agencies posed the challenge of building smoother roads, and the asphalt industry answered with the development of improved equipment and construction techniques.
How well do asphalt pavements perform?
Wisconsin. Construction records for the years of 1995 to 1999 indicate that asphalt pavements had an average IRI of 62 inches per mile, indicating that the road users are getting excellent value for their tax dollars.
Kentucky. Records dating back to 1981 indicate that asphalt roads in Kentucky’s system of parkways and toll roads as well as on its interstate highways are consistently performing to a level of ride quality better than required during construction.
Washington. In a study of 300 miles of Interstate 90 from Spokane to Seattle, the 55 sections of asphalt pavements had an average IRI of 55 inches per mile, with a range of 38 to 82 inches per mile. The surfaces of these pavements range in age from 2 to 12 years old and their roughness values are well below the maximum 110 inches per miles suggested by the University of Michigan for airports and superhighways.
Conclusion
Working with public agencies, the asphalt pavement industry is ensuring that asphalt is the standard of excellence when it comes to smooth roads.
RUBBLIZATION – ASPHALT’S ANSWER TO DETERIORATED CONCRETE PAVEMENTS
FAST FACTS
Rubblization is a road-user-friendly construction technique that turns a deteriorated concrete road into the base for a smooth, safe, quiet, durable pavement constructed of Hot Mix Asphalt (HMA). It minimizes 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 it is overlaid with Hot Mix Asphalt (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.
Rubblization saves time. If needed, the work can be accomplished at off-peak hours, without the round-the-clock road closures required to cure concrete pavements. Contractors report rubblizing up to one mile of deteriorated concrete pavement per day.
Rubblization saves resources. The rubblized roadbed is left in place, so that it does not have to be trucked off to a landfill. Instead of becoming waste, it has value as part of the new road structure.
Rubblization makes for smooth roads. The new asphalt pavement that is placed over the rubblized roadbed will remain smooth for years.
Rubblization works. Leading pavements researchers including Witczak, Rada, and Thompson who have tracked Rubblization projects over the course of years report excellent results. Many highway agencies have had great success in implementing it.
RUBBLIZATION – ASPHALT’S ANSWER TO DETERIORATED CONCRETE PAVEMENTS
QUESTIONS AND ANSWERS
Rubblization is a road-user-friendly construction technique that turns a deteriorated concrete road into the base for a smooth, safe, quiet, durable pavement constructed of Hot Mix Asphalt (HMA). It minimizes delays for motorists and allows for construction during “off-peak” hours. Rubblization with asphalt overlay is a very cost-effective technique.
What is Rubblization?
Rubblization is an effective means of rehabilitating deteriorated Portland Cement Concrete (PCC) pavement. The concrete is broken into pieces, and then it is overlaid with HMA.
Why rubblized concrete?
Fracturing the concrete into small pieces (2 to 6 inches, for the most part) reduces the likelihood that joints, cracks, and other defects in the concrete will “reflect through” the HMA overlay and impair performance. It is also a rapid means of concrete rehabilitation. Contractors report production rates of up to one mile per day.
What are the benefits of Rubblization?
Time savings. Rubblization is a natural choice when time is of the essence because it can be done very quickly. If needed, the work can be accomplished at off-peak hours, without the round-the-clock road closures required to cure concrete pavements.
Cost savings. Rubblization with an asphalt overlay is very inexpensive compared to other options. When the cost of delays to road users is considered, the savings become even more dramatic.
Environmental benefits. The rubblized roadbed is left in place, so that it does not have to be trucked off to a landfill. This not only saves landfill space, it eliminates many trips by trucks, saving diesel fuel and reducing traffic congestion.
Smoothness. The new asphalt pavement that is placed over the rubblized road bed will remain smooth for years.
How is the Rubblization done?
In general, there are two types of equipment used for Rubblization. Multiple head breakers utilize a number of large hammers, which pound on the pavement surface. Resonant breakers have vibrating hammers, which use a combination of force and vibration to break up the concrete. Next, rollers are used to further break the concrete and seat it into place. This is followed by the placement of an asphalt overlay.
When should Rubblization be done?
It is generally thought that Rubblization of concrete with an asphalt overlay is most economical when one of the following conditions exists in the concrete surface:
• Patching of 10 percent or more of the slabs.
• Severe D-cracking.
• Severe alkali-silica reaction (ASR) cracking
• Faulting continues to occur in spite of corrective actions.
In addition, the economic impact of delays to road users during construction should be considered. Rubblization and asphalt overlay can be accomplished speedily.
Are there any problems with Rubblization?
In a very few instances, wet soils may soften during the Rubblization process. If this happens, provisions should be made so that the fracturing process is adjusted to result in slightly larger pieces of concrete (12 to 18 inches) through the soft area. This is then followed by the normal procedure of rolling and overlay placement. A good engineering investigation will identify these areas so that they may be corrected by proper drainage before construction even begins.
Is Rubblization effective?
A 1992 paper by Witczak and Rada in the Transportation Research Record (TRR) states, “Rubblization of deteriorating PCC pavements followed by an AC (asphalt concrete) overlay is an excellent rehabilitation method that is equally effective for all types of PCC pavements.” In an award-winning 1999 article in TRR, Thompson documents the success of Rubblization in Illinois noting that it is a “viable and cost-effective rehabilitation option.”
Currently, more than half the state Departments of Transportation has implemented specifications for Rubblization. The state of Arkansas has embarked on a five-year program to rubblized approximately 360 miles of four-lane concrete Interstate highways. The preponderance of favorable research findings and practical experience clearly indicates the value gained by Rubblization of concrete pavement and overlaying it with HMA.
Conclusions
• Rubblization is an effective method of pavement rehabilitation when overlaying a deteriorated concrete pavement with HMA. It ensures pavement performance by preventing defects in the concrete from reflecting through the HMA surface.
• Rubblization combined with an asphalt overlay can be done rapidly, minimizing delays for motorists.
• Rubblizing and overlaying with asphalt is economical, making it attractive to public agencies that wish to use resources wisely.
• Once the asphalt surface has performed its many years of service, it may be milled up and recycled into a new surface, or it may simply be overlaid, taking advantage of the pavement already in place.
• Researchers have concluded that Rubblization is a technically sound approach, and many highway agencies have had great success in implementing it.
• Rubblization saves nonrenewable natural resources for future generations.
BIKE WAYS TO FREEWAYS, HOT MIX ASPHALT
IS THE VERSATILE PAVEMENT
QUESTIONS AND ANSWERS
In 1984, the Transportation Research Board’s Report 202 declared, “asphalt, more than any other single product, sustains the nation’s highway system and facilitates the flow of commerce.” While the authors of the report were concerned mainly with highways, they could just as well have said that Hot Mix Asphalt sustains “all” pavements, including parking lots, race tracks, airports, city streets, bike paths, and environmental liners.
Simply stated, there is a Hot Mix Asphalt (HMA) pavement design and material selection that’s right for just about every situation, from heavily traveled urban interstates to bike paths to reservoirs. HMA is the most versatile paving material available.
Where can HMA pavements be used?
Streets and highways. According to a report issued by the federal Bureau of Transportation Statistics (BTS), 94 percent of the 2.27 million miles of paved roads and highways in the U.S. are surfaced with asphalt. Asphalt pavement has won overwhelming acceptance by federal, state, county, and local road agencies because of its economy, durability, and smoothness.
Airports. Busy commercial airports such as Baltimore-Washington International, Oakland International, San Francisco International, McCarran (Las Vegas), Pearson International (Toronto), and Logan International (Boston) have main runways surfaced with HMA. Asphalt is also used extensively on runways at general aviation airports. Asphalt’s speed of construction makes it an ideal choice for rehabilitation of busy aviation facilities.
Race Tracks. Asphalt pavements provide smooth driving surfaces combined with the excellent traction demanded by professional stock car racing. Of the 33 NASCAR race tracks across the country, 31 are paved with asphalt surfaces. Of the 88 race tracks listed for the NASCAR Short Track series, 66 are asphalt, 21 are dirt or clay, and 1 is concrete.
Industrial applications, including cargo transfer points such as port container yards, timber yards, and rail transfer yards. A railroad-to-truck transfer yard in Minnesota was paved with a large-stone asphalt mix to withstand a pressure of 2080 pounds per square inch from the truck trailers parked on the facility. Coal storage pads in eastern Kentucky were constructed with 12 inches of HMA to handle 50-ton dump trucks and tracked loaders. A log handling facility in Washington State was constructed with 10 to 12 inches of HMA for gross loads of up to 240,000 pounds.
Hydraulic structures. HMA has been successfully used in the construction of erosion-resistant canal linings and watertight pond linings. It is safe for the storage of portable water since the asphalt is not soluble in water, and thus does not contaminate the water. It is used to line drinking water reservoirs in California and fish hatchery ponds in Oregon and Washington.
Bike paths, sidewalks, and recreational facilities. HMA is ideally suited for providing paths that are aesthetically pleasing and blend well with natural settings. It conforms easily to land contours and it does not tend to “fault” creating unexpected bumps to trip on. Tennis courts, basketball courts, running tracks, and playgrounds are often constructed of asphalt because it weathers well and the surface has enough “give” to be kind to athletes’ joints.
Can asphalt pavements be customized?
Yes. Recent years have seen an explosion in asphalt pavement technology. Conventional asphalt binders have evolved to include a wide range of modified binders, offering potential performance improvements in terms of rutting, cracking, and durability. “Designer asphalt” is becoming available with some firms offering colored asphalt and asphalt pavements that look like paving blocks.
Bikeways to Freeways
Questions & Answers
Page 2
As a result of developments in research and technology, a wide array of specialty mixes, designs, and products can now be tailored to meet specific customer demands. These include:
• Permeable mixes to reduce splash and spray and avoid hydroplaning;
• Impermeable mixes for railway roadbeds and hydraulic structures;
• Noise abatement’
• Rut-resistant SMA and Superpave designed mixes;
• Large stone mixes for roads, logging yards, container terminals, and other heavy-duty applications;
• Thin, flexible HMA pavements for maintenance and preservation;
• Extra high-stiffness base technology from Europe;
• High-strength mixes for intersections and airfields;
• Special anti-skid mixes for racetracks and hazardous locations;
• Perpetual Pavement designs; and
• Deep-strength, full-depth, and staged-construction design systems.
What materials are used in asphalt pavements?
HMA is comprised of a blend of about 5 percent asphalt and 95 percent aggregate (rock, gravel, and sand) by weight. The asphalt is a petroleum product, and the aggregate may be mined from a local quarry or gravel source. Each of these materials is required to meet certain standards to assure that they will perform their intended functions.
Below the asphalt layers, engineers and contractors my place crushed stone, gravel, or sand to act as a base layer over the soil. The soil itself is generally improved through compaction before construction of the upper layers.
Are the materials in all asphalt pavements the same?
No, they are tailored to the particular application. For instance, an asphalt pavement designed for an industrial application such as a cargo container yard would be designed primarily for strength. However, strength would not be as important for a pond lining where being watertight would be of most concern. Even for roads, the materials used on a heavily traveled interstate are different from those used on a country road with little traffic. The interstate would need to stand up to heavy trucks traveling at high speed, whereas the country road would be built to withstand weathering and to maximize economy.
Asphalt pavements have been used for over 100 years. Isn’t the technology pretty much the same now?
Continuous improvement is the name of the game, and the roads we drive on today are considerably different from those of our parents and grandparents. The goal now is to maintain the best and most extensive road network in the world while being environmentally responsible and accountable to road users. How is this being done?
New technology. 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 including SMA (Stone Matrix Asphalt), OGFC (Open Graded Friction Course), high-modulus HMA, dense-graded HMA, HMA with modified binders, and thin-friction lifts.
Perpetual Pavements. 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.
Recycling. 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 saves money, nonrenewable natural resources, and landfill space.
