Paving the road to the 21st century
Technology is a term that usually brings to mind the world of electronics and telecommunications. Computers. The Internet. Cell phones.
But as the end of the millennium draws near, technology as a force is far more widespread than that; indeed, it applies as much to the pavements being put down on our roads as to sophisticated consumer products.
Pavement used to come in two basic types, delineated by color: black (asphalt) or white (concrete). Cracking, buckling and potholes were seen as inherent evils – a necessary and costly byproduct of increasing traffic loads and harsh weather. Road repairs and traffic snarls, thus, were inevitable.
In an evolutionary sense, pavement can be compared to television. In the early 1970s, viewers had three or four channels from which to choose on a black-and-white set with rabbit ears – one that actually required the viewer to get up off the couch to manually change channels.
Today, viewers often can select from 50-plus channels, using a remote control loaded with bells and whistles and viewing a sophisticated television with SurroundSound that may even be capable of accessing the Internet.
“Smart” products are becoming the rage – diapers that change color when they’re wet to alert a baby’s caregiver; motion sensors that conserve electricity by turning lights on only when someone is in the room.
Pavement, which many might think of as nothing more than “boilerplate” technology – steamrollers, dump trucks, smelly asphalt mixers and sweaty workers with rakes and shovels – is undergoing a similar transformation, thanks to a well-coordinated, full-frontal technological assault known as the Strategic Highway Research Program (SHRP).
A $150 million catalyst SHRP was established by Congress a decade ago as a five-year, $150 million research program to improve the performance, durability and longevity of the nation’s roads and to make them safer for motorists and highway workers alike.
The massive research and development effort involves the National Research Council, federal research laboratories, universities, private industry, state departments of transportation and city and county road departments.
For years, the Federal Highway Administration has contracted out work to develop and evaluate innovative construction, maintenance and operations technology to universities, consulting firms and other researchers.
Individual research and development efforts had already been going on prior to implementation of SHRP, but the program was a catalyst, corralling these efforts into one omnibus initiative.
By 1992, more than 130 products or standards, including specifications, tests and equipment, had emerged. When ISTEA passed in 1991, it included a $108 million allocation for the FHWA to take on the task of helping state, county and local highway agencies implement and evaluate the new technology. (ISTEA was slated to expire on Oct. 1, but on that day the House passed a six-month extension. The Senate was also expected to act on the matter before it adjourns in November.)
As a result, how pavements are developed, which materials go into the asphalt or concrete and what specifications are needed for a given climate and traffic load, are receiving more attention than ever before.
The first hints of a big-time payoff are already starting to come in. A recently completed study by the Michigan DOT is one example. In 1992, the department began applying specific preventive maintenance treatments to 2,650 miles of both asphalt and portland cement concrete pavements at a cost of $80 million. MDOT has since determined that the expenditure has saved it $700 million on the rehabilitation and reconstruction projects that would have been necessary to bring the pavements up to their current condition.
Superpave is linchpin SHRP is divided into four major sub-categories: asphalt (the Superpave program), concrete and structures, highway operations and long-term pavement performance.
The Superpave (Superior Performing Asphalt Pavements) system is the most significant SHRP offshoot. It was started with three objectives: to investigate why some pavements perform well while others do not, to develop tests and specifications for materials that will perform better and last longer than conventional pavements and to work with highway agencies and the private sector to implement the new specifications. Superpave’s importance is largely attributable to the fact that asphalt pavements account for about 90 percent of all paved highways in the United States. In general, asphalt costs less than concrete and can be applied quicker; however, there are variables, and some studies allege that flawed standards are used to compare the two.
For instance, a New York DOT study, “Adapting the AASHTO Pavement Design Guide to New York State Conditions,” contends that AASHTO design procedures underestimate the performance of concrete pavements and overestimate that of asphalt, according to Bob Packard, director of engineering and design for the American Concrete Pavement Association (ACPA).
Regardless, Superpave has taken on the greatest prominence under the SHRP umbrella. The program is divided into five regions of the country, each with a “lead state” that will be at the forefront of experimental and pilot programs and serve as a laboratory of sorts for the other states in its region.
Specifications and software Superpave seeks to remedy two common problems: permanent deformation resulting from inadequate shear strength in the asphalt mix and low-temperature cracking, caused by asphalt shrinkage.
Three interrelated elements are being employed to deal with these problems: * specifications for asphalt binder, the black, sticky substance derived from petroleum that holds together the crushed stones and dust. More than two-thirds of the states are currently using Superpave’s binder specs; * a volumetric mix design and analysis system (used by two- thirds of the states in 1996 highway construction projects); and * mix analysis tests and a performance prediction system that includes computer software, weather database and environmental and performance models. The Superpave mix design system, which is based on volumetric proportioning of the asphalt and aggregate materials, uses a gyratory compactor for laboratory compaction of trial mixes. The compactor is a transportable device that fabricates test specimens by simulating the effect of traffic on an asphalt pavement.
Superpave is offering state DOTs its “mobile laboratories,” which travel around and help contractors tailor their asphalt mixes for local projects. Some contractors do not have all of the specialized equipment they need, but many are acquiring it, says Tom Harman, a pavement engineer with the FHWA. “The mix designs, by and large, are being done by the state departments of transportation because the equipment is very expensive,” says Rick Donovan, a senior geo-technical engineer with HDR, an Omaha, Neb.-based engineering firm.
Two specially developed pieces of equipment, the Superpave shear tester and the indirect tensile tester, will be used to measure specific engineering properties of the laboratory-compacted asphalt mix. The results will be entered into software modelsthat predict how many vehicles a pavement will carry or how much time will elapse before a certain level of rutting or cracking occurs.
Trying different recipes Experimenting with the mix may bring an added benefit besides longevity and reduced maintenance: less expensive snow and ice removal.
This is of keen importance to the Federal Aviation Administration, which is constantly exploring ways to ensure durable, maintenance-free runways.
In fact, the FAA and Chicago-based Superior Graphite, a manufacturer of carbon additives, graphite lubricants and other products used in manufacturing, are testing electrically conductive asphalt pavement, which uses synthetic graphite, asphalt and electricity to heat the runway surface and melt snow and ice. Chicago’s O’Hare Airport is one test site, and the New Jersey DOT is also considering the technology for its highways.
While some states have added alternative materials to pavements – chopped-up tires or glass, for example – Superpave for the most part sticks to traditional materials, according to FHWA’s Harman. Still, what constitutes “conventional materials” is open to question. Types of fine and coarse crushed stones used in hot mix asphalt will continue to differ by locality, says Harman, noting that granite is typical in New Hampshire, while limestone is often used in Maryland.
The Pennsylvania DOT experimented with “glassphalt” but discovered the pieces of glass would cut up vehicle tires, Harman says. Crushed glass cullet, ground-up tires and other alternatives may end up being more suitable for sub-pavement drainage layers.
The continued use of tried-and-true asphalt ingredients surely means that “in with the new” does not mandate “out with the old.” Recycled asphalt pavement (RAP), in use since the early 1970s, will play a major role in Superpave, Donovan says, often constituting 10 to 35 percent of an asphalt mix. But he cautions that the inconsistency in quality of recyclable asphalt cuttings may be a drawback to RAP.
If a contractor has multiple jobs calling for different quality levels (airport runways demand the highest quality mix, for instance, while parking lots are at the low-grade end of the spectrum), “what you end up with is a stockpile full of variable quality cuttings,” Donovan says.
One way to resolve this is to “recycle in place,” something that is practical for only large-scale jobs. A miller on site can grind up old asphalt as soon as it is removed, and the old asphalt is then mixed with virgin asphalt, blended with aggregates, heated, put through a spreader and reapplied.
New performance paradigm Interestingly, one of the ramifications of Superpave is how it muddies the waters of contractor performance. In other words, the old rules do not apply anymore, and evaluating how good a job a contractor did mixing up and laying down a batch of asphalt might get tricky.
Superpave’s new specifications, software and mix procedures theoretically will ensure that pavements last much longer before potholes, cracking and buckling take their toll. But at what point is “normal wear and tear” expected to manifest itself? If it is sooner than expected, what precedent is there to allege that a contractor used inconsistent mix formulations or improperly laid down the asphalt? And even this issue may have to wait, as state DOTs are now primarily doing the mixing.
“If a contractor is not designing (the mix), that gets to the heart of the problem,” says Don Barber, director of construction services for Kansas City, Mo.-based HNTB, an engineering and architectural firm. In other words, how is liability determined if the state DOT mixes up the asphalt? Donovan believes state highway departments may move more toward “pay-for-performance” contracts, which the FAA and other federal agencies have used for years, to ensure consistency in quality and adherence to specifications. “The critical part of any pay-for-performance (agreement) is to determine what variance is acceptable,” Donovan says, adding that too much mix inconsistency over long stretches of road could result in increased rutting and deterioration.
On the concrete front SHRP has also looked extensively at high-performance concrete, which lasts longer, requires less maintenance and allows for construction of bridges with fewer metal beams than regular concrete, thus reducing costs. A plethora of tests is being conducted to study such things as alkali-silica reactivity and chloride permeability.
The application of ultra-thin concrete pavement on top of deteriorated asphalt – also known as “whitetopping” has been going on for about six years and appears to be gaining in popularity.
The process involves milling off the asphalt surface and paving over it with two to four inches of concrete, which bonds to the underlying asphalt. More than 100 ultra-thin whitetopping projects have been undertaken in 21 states in the past five years, according to the ACPA. The Mississippi DOT recently used the process on Interstate 20, blending fibrillated fibers with concrete.
Still, in their enthusiasm for trying new mixtures and combinations, engineers must be vigilant about how certain additives – anti-corrosive agents, for example – may adversely affect cohesiveness or strength once a pavement has hardened, Donovan says.
“The thing you have to worry about with any kind of admixture is how it reacts with other admixtures – whether or not they are compatible with each other,” he points out. Some technologies, like cathodic bridge protection, which uses electrical current to aid in the rehabilitation of bridges corroded by salt, have been around for a while but will see increased use under SHRP because prices have dropped.
Underlying technology One thing is certain: Regardless of how pavement materials are mixed and what raw materials go into them, the pavements of the future will be augmented by the electronic hardware and software of the future – pavement sensors, microprocessors and communications systems tied into data banks containing the latest weather forecasts, traffic flow patterns, terrain information, anti-icing options and other relevant information.
And above the pavement, cameras, “message board” signs, satellites and weather monitoring equipment will all play a part in improving traffic flow.
In the meantime, the process of trial-and-error will continue, with discoveries, innovations, implementation hurdles and a continued need for consumer education. Politicians of every stripe will get in their share of posturing, from condemning “pork barrel” spending of transportation programs, to bringing home the bacon to their own constituents.
Ultimately, the results may be safer, longer-lasting streets and bridges that cost less to maintain and are up to the task of bearing the increasing traffic volumes of the 21st century.
Wisconsin winters are notorious for the damage they can inflict on roads. Highway E, a winding, two-lane asphalt road that serves commuters between Little Chute and Oneida, is a prime example.
Once called the worst stretch of road in Outagamie County, Highway E was plagued by cracking and heaving during the winter months. Similar problems occur elsewhere in the region where pockets of sub-base silt enclosed in the state’s thick clays become highly saturated and freeze.
In Wisconsin, heaving can start as early as November and remain a problem through March. During the winter months, the speed limit on a half-mile stretch of Highway E was often reduced from its normal 55 mph to 15 mph because of the cracks.
“We would put up flashing barriers and advance warning signs,” says Mike Marsden, Outagamie County highway commissioner. “It was really difficult to plow snow in the area.”
To solve its heave problem, Outagamie County decided to try a cellular confinement system made by Presto Products, Appleton, Wis. An expandable honeycomb-like structure made of high density polyethylene, the product is designed to produce a stiff base with high flexural strength, providing a base layer without deep excavation, thus avoiding the potential obstruction of underground utilities.
The technology was developed in the late 1970s in cooperation with the Army Corps of Engineers for building roads across unstable terrain. It was used to build sand roads for rubber-tire vehicles during the Persian Gulf War and has also been employed in slope and channel protection and earth retention. Outagamie County first used the system at its landfill to construct an access road into one of the landfill cells. That application was a success and led to the Highway E project.
On Highway E, an inch-deep cellular confinement system was installed in the area of the washboarding road. The asphalt pavement was removed and stored for recycling and final topping after reconstruction. The silty clay sub-base was cut down 18 inches below the water table level and covered with a geotextile.
Next, a six- to eight-inch layer of crushed stone was added. The confinement system was expanded, positioned and secured at the edges with granular fill. It was then in-filled with sand and topped with a 15-inch base course of crushed stone. A vibratory roller compacted the completed area, which was immediately ready for traffic.
“Because of our soil conditions, we always use a 15-inch base course on all of our roads,” Marsden says. “We probably could have gotten by with less, but we decided not to.” If the cellular confinement system had not been used, the county probably would have reworked the subgrade and added two feet of base course, Marsden says. But the system proved less expensive than using fill material, he adds.
Unpaved, Highway E performed well throughout the following winter and was surfaced with recycled asphalt in the summer of 1985.
Now, more than 10 years later, the road is still level and holding up well under all weather conditions, according to Marsden.
Highway E is scheduled to be rebuilt this year. The county will widen the highway, fill some valleys, improve sight distance and flatten curves, but the county will not alter the portion containing the cellular confinement system, Marsden says.
While it is true the pavements of the future will not benefit rural areas served by dirt or gravel roads, that does not mean that improvements are not in store for America’s country roads.
In Georgia, ongoing research expands the concept of using geotextiles for erosion control. Rather than using carpet fibers for erosion control on embankments or areas underneath guard rails, researchers are testing the practicality of using them in dirt roadbeds. The intent is to stabilize the roadbeds, making them safer in rainy or snowy conditions and reducing maintenance costs.
A combined effort among seven Georgia counties, the Georgia DOT and two carpet manufacturers is under way to use synthetic fibers or used carpet materials as bonding agents. Officials from GDOT’s Office of Materials and Research are serving as advisors to the seven counties – Candler, Habersham, Wilkinson, Brooks, Newton, Pike and Spalding. Researchers from the Atlanta-based Georgia Institute of Technology are also lending a hand.
For several months, researchers in each of the counties have been testing control sites to determine which of the agents will work best for bonding the roadbed.
Four separate sections of road are being tested in each county: a control section with no fiber or carpet materials; a section with shredded carpet that was scattered over the freshly tilled roadbed and then compacted with a layer of dirt; another in which shredded tape fiber was mixed into the tilled soil and compacted with a layer of dirt; and a fourth in which freshly tilled soil was combined with Fibergrid, a product developed seven years ago by Chattanooga, Tenn.-based Synthetic Industries to strengthen soil for pavement, slopes and other civil engineering work. The soil was then compacted with a layer of dirt.
“The first phase is over, and we are taking some of our findings back into a laboratory environment where we have less variability and can gather more conclusive evidence,” says Kemp Harr, a spokesman for the Tennessee company.
Dalton, Ga.-based Shaw Industries is supplying used carpeting for the project. The two companies, which are managing the research project, have donated the carpet and fiber materials.
One initial concern was whether the carpet used in the experiments could leach the toxic chemicals that are a byproduct of the manufacturing process into the ground.
However, only carpet produced in the last five years is being used in the experiments, and today’s carpet does not have the same toxic chemical ingredients as its predecessors, according to John Conyers, director of manufacturing for the Georgia-based textile firm.
Other counties have expressed an interest in participating in the research project, but Harr says county road testing is on hold for now. “We intend to continue monitoring our current test sites for long-range effects,” Harr says.
One of the busiest U.S.-Canadian border crossing areas is located where southeastern Michigan and extreme southern Ontario sit across from each other, separated by the Detroit and St. Clair rivers.
The original Blue Water Bridge, which connects I-94/I-64 in Port Huron, Mich., to Highway 402 in the village of Point Edward, Ontario, was built in the 1930s. Since then, not only has the traffic load exceeded its capacity, but the structure is in need of extensive renovation.
When the decision was made to build the Second Blue Water Bridge alongside the existing structure, extensive fiscal, regulatory and logistics planning was needed since the laws and interests of two different nations came into play. Drawings, construction procedures and scheduling all had to be thoroughly hashed out in advance.
The Federal Highway Administration and the bridge co-owners, the Michigan DOT and Blue Water Bridge Authority, all participated in the project, using the new AASHTO Load and Resistance Factor Design code as the primary design specification – its first major use in the United States. Approvals were required by five permitting agencies; 17 other agencies having jurisdiction also conducted reviews and approvals.
During construction, a major concern was ensuring the uninterrupted and safe continuation of shipping in the St. Clair River, a busy channel on the Great Lakes waterway. The contract for the main span stipulated that no work could proceed from the river, and no debris could fall into the river (for environmental reasons as well as for the safety of marine traffic). Therefore, cantilevered construction was used on the main span.
Moreover, jobsite safety was a major priority. The Ontario Ministry of Labor, Michigan Department of Labor and the contractors’ Health and Safety Committee worked to enforce numerous safety measures.
Away from secure platforms, workers were tied off using full body safety harnesses; a rescue boat was in the water and ready for use every workday; workers were trained in water rescue techniques; debris nets were strung under the bridge deck outwards from the shore to prevent debris from falling into the river or hitting a boater; specially trained workers and equipment for high-level rescues were available; and a full-time safety-superintendent was hired to regularly audit safety-related items.
St. Louis-based McCarthy and PCL Civil Contractors, headquartered in Alberta, Canada, built about 43 percent of the bridge. Canadian and American contractors then completed the re-maining portions of the bridge on their respective country’s sides.
“Constructing this international bridge over the St. Clair River required substantial coordination to ensure the project remained on schedule,” says Bruce Campbell, assistant project manager with MDOT.
Named the Second Blue Water Bridge, the U.S./Canadian bridge was designed by Modjeski and Masters of Harrisburg, Pa., and Buckland and Taylor of Vancouver, British Columbia, to blend with the existing bridge.
The new bridge, only the fifth of its kind in North America, features a continuous tied-arch design with two mainpiers located on the banks of the river for support. It is supported on H-pile foundations extending to bedrock below each pier. A total of 144 piles were driven up to 105 feet deep for the support of the main span.
Because of concern that the pile-driving operations would adversely affect local structures, all nearby houses and buildings were subjected to a pre-construction video-taping and detailed inspection.
The original bridge will now undergo two years of rehabilitation, while the new bridge will carry traffic traveling in both directions. A four span crossover structure connects the new bridge to the original bridge near the Michigan Toll Plaza.
When renovations are complete, traffic entering the United States will travel on the original bridge, while Canada-bound motorists will use the new bridge.
Traffic in suburban New York is bad enough under normal circumstances, but when construction of a new bridge takes place, motorists could easily find themselves in a gridlock nightmare.
That was the concern when the New York Department of Transportation needed to build a new bridge over the Long Island Expressway last year. To keep the traffic flowing and ensure contractors had sufficient time to do the job right, NYDOT chose to use pre-engineered bridge modules made by Baltimore-based Mabey Bridge & Shore.
The galvanized steel modules were trucked to the site and assembled in the desired configuration. The pieces were then put in place by a crane and pinned together without welding, almost like a giant erector set.
At the Long Island Expressway, NYDOT used dual three-lane bridges that crossed over a divided highway below. Each of the bridges was made of about 16 modular units, which weighed over 13 tons apiece.
About 15 men with the help of two cranes assembled the temporary bridges during one weekend in April 1996. While this assembly took place, one side of the expressway below was temporarily shut down to accommodate the cranes, while the other side was temporarily converted to handle two-way traffic.
Temporary center piers were put in place, and each modular bridge was constructed with two spans; about 110 feet and 125 feet for the southbound bridge; 103 feet and 117 feet for the northbound.
The new bridge, built between the two temporary bridges, was fabricated out of precast box beams in September 1996. The two temporary bridges were then disassembled in mid-November.