Pavement Preservation Compendium II
Making High-Volume Roads Last Longer
by Tom Kuennen
Preservation techniques for local roads work for high-volume pavements, too - but top-flight discipline, designs, and materials are required.
Crack sealing, chip seals, slurry surfacings, and thin overlays are part of a standard pavement preservation "tool box" for low-volume, secondary roads. Now, a growing accumulation of research indicates these same techniques also work on high-volume roads, but with a catch: success demands a disciplined approach to these techniques rather than the seat-of-the-pants, intuitive procedures that often mark work done on low-volume pavements.
Where chip seals might have been done by agency forces using tried-and-true, "hand-me-down" procedures with off-the-shelf binder and chips, today's successful chip seal for high-volume roads likely will be designed in a lab based on existing conditions, climate, and traffic loads, with a binder that is polymer-modified, and chip attributes that specify shape size, moisture content, and placement.
And, rather than being installed by an agency's general maintenance crew, it may be placed by a contractor - or a highly trained agency crew - with the quality controls and material suppliers that can assure the quality materials demanded for long-term performance. Its performance may be warranted. And in some instances, the preservation treatment may be a proprietary product that is available only through a dedicated contractor, such as an ultra-thin bonded wearing course like Koch's NovaChip.
As agencies invest more in preservation for high-volume pavements, competition for that market is growing. A case in point: Rather than conceding the prevention market to chip seal interests, the hot-mix asphalt industry has been supporting research into thin asphalt overlays and how they fit into a pavement preservation program.
And, all treatments are benefiting from new research that identifies best practices for pavement preservation for high-volume roads, and establishes valid lifecycle cost-analysis that makes the argument for increased budget emphasis on prevention more effective.
Conventionally, chip seals and other surface treatments have not been associated with high-volume arterial, collector, or interstate-type pavements. Instead, with regional exceptions, the preferred application is an asphalt overlay, following years of minimal care - typically, pothole patching and occasional crack sealing. But a variety of surface treatments for high-volume roads exists, and experts say they have the potential to prolong pavement serviceability at minimal cost.
"Historically, the agency managers felt that the high-type asphalt and concrete pavements always needed an additional section of asphalt placed on them, and that chip seals, slurry seals, and other preservation treatments would not stand up to the traffic and loadings of those high-level pavements," said Jim Sorenson, senior construction and maintenance engineer, Federal Highway Administration Office of Asset Management.
"But with the advent of SHRP [Strategic Highway Research Program], 1988-1993, it was clearly demonstrated that preservation treatments were fully viable for any volume of road," Sorenson told Better Roads.
"There are the right techniques to use; for example, the chip seal must be properly designed, with good embedment and traffic speed held down. But on the Tacoma Narrows Bridge, with about 178,000 ADT [average daily traffic], Washington State DOT has been putting chip seals on the deck for years" noted Sorenson. "They don't want to add a lot of extra weight but need to keep friction up. Caltrans has main-line pavements on I-5 and I-80 where they did not think surface treatments would work, but the treatment has held up to the traffic."
Such surface treatments can afford to have a higher quality aggregate in them, because other costs are lower. "As a result, their durability is much better," Sorenson said. "The surfacings are not expected to carry the load or provide structural value, but to ward off the effects of aging and oxidation that Mother Nature sends. It's a matter of putting them down right, and they will serve the pavement and traveling community in a very positive fashion."
Some preservation practitioners think that multiple treatments can preserve the structural soundness, drainage, and overall condition of roads for long periods of time. "Don't think you can only mill out and replace," Sorenson told Better Roads. "You may be able to use fog seals, slurry seals or microsurfacing, or chip seals, bettering the pavement performance cost-effectively, because these treatments clearly are showing a return on investment."
"A lot of people use a one-size-fits-all approach," said Larry Galehouse, P.E., director, National Center for Pavement Preservation at Michigan State University. "It's not cost-effective to do business that way. We have to look at what treatment will correct the deficiency, for the least cost, for the best performance. Pavement managers have to jump in with both feet, and gain this experience. Right now, a lot of agencies don't have the institutional knowledge to take on preservation without some intense training. They have to cultivate the knowledge base within the agency, because there is a lot of poor practice out there."
One of the worst practices is waiting too long - that is, waiting for damage to develop - before preventive measures are applied, he said. "You've got to have a good pavement structure. If the pavement structure is sufficient to carry the load, we must keep the water out, maintain good skid resistance, and provide a smooth ride for the motorist. With pavement preservation techniques we will improve pavement performance and extend its life."
Most preservation actions used on asphalt or concrete low-volume roads are also suitable for higher-volume roads, Galehouse said. "For example, on good PCC pavements we can reseal joints, and on HMA, we seal the cracks," Galehouse told Better Roads. "We can seal edges to avoid edge drops between the driving lane and shoulder, something that's not done enough. We can microsurface and place thin bituminous lifts without concern for changing traffic volume."
Attention to preservation
Years of research, publicity, and politicking on behalf of pavement preservation in the post-interstate era are beginning to bear fruit as closer attention is being paid to pavement preservation in national forums.
Pavement preservation has been a strong topic of research at the annual Transportation Research Board meetings since 2000. The Federal Highway Administration and American Association of State Highway & Transportation Officials are putting resources into promoting pavement preservation in the context of transportation agency asset management.
The Foundation for Pavement Preservation was founded in 1992 and now is administered out of Austin, Texas. And Galehouse's NCPP, a strong resource for pavement managers, marked its first year of operation last fall.
Also driving the interest in prevention practices for high-volume roads is a growing emphasis in government on asset management.
The Midwestern Regional University Transportation Center in Madison, Wisconsin defines asset management as "a systematic process of operating, maintaining, and upgrading physical assets cost-effectively. It combines engineering and mathematical analyses with sound business practice and economic theory. Asset-management systems are goal-driven and, like the traditional planning process, include components for data collection, strategy evaluation, program selection, and feedback."
The asset management philosophy compels government agencies to borrow private-sector concepts of inventory, initial value, and net present value and apply them to their pavement system. That, in turn, helps them allocate their limited financial resources to optimize present and future road-system value. Asset management automatically puts the emphasis on life-cycle costing and how limited expenditures now can ensure optimal value later - and that is the very essence of pavement preservation practice.
However, experts warn, high-level pavement preservation programming will only work if the bureaucracy of the highway agency supports it, and that can be tough in cultures that have traditionally focused on construction and renovation, and treated maintenance as an afterthought.
FHWA moves forward
That pavement preservation deserves highest priority at the state DOTs was borne out last October, when the Federal Highway Administration strongly affirmed that pavement preservation expenditures are desirable and reimbursable under FHWA rules. In an October 8, 2004 memo obtained by Better Roads, FHWA Associate Administrator King W. Gee threw the weight of the FHWA behind pavement preservation.
"Timely preventive maintenance and preservation activities are necessary to ensure proper performance of the transportation infrastructure," Gee told division administrators and field services directors. "Experience has shown that when properly applied, preventive maintenance is a cost-effective way of extending the service life of highway facilities and, therefore, is eligible for Federal-aid funding."
And preservation gives states a path to optimizing their pavements for the long-term, he said. "By using lower-cost system preservation methods, states can improve system conditions, minimize road construction impacts on the traveling public, and better manage their resources needed for long-term improvements such as reconstruction or expansion. Preventive maintenance offers state DOTs a way of increasing the return on their infrastructure investment."
Eligibility of pavement preservation grew slowly during the 1990s, as Congress incrementally broadened the applicability of Federal-aid funding to preventive maintenance activities. "Congress' acknowledgement of preventive maintenance activities as an eligible activity on Federal-aid highways is a logical step that reinforces the importance of implementing a continuing preventive maintenance program," Gee said.
Gee urged FHWA offices to work proactively with states to establish a preservation program, likely to include joint repair, seal coats, pavement patching, thin overlays, shoulder repair, restoration of drainage systems, and bridge activities such as crack sealing, joint repair, seismic retrofit, scour countermeasures, and painting.
"Many other activities that heretofore have been considered routine maintenance may be considered Federal-aid eligible on an area-wide or system-wide basis as preventive maintenance (i.e., extending the service life)," Gee said. "This might include such work items as region-wide projects for periodic sign face cleaning, cleaning of drainage facilities, corrosion protection, spray-applied sealant for bridge parapets and piers, etc."
Most pavements in North America and the rest of the world carry low traffic volumes, and there is a rich history of surface treatments being used in their management.
In a 2005 TRB paper, Maintenance and Rehabilitation of Low-Volume Pavements in Washington State, Muench, White, Mahoney, Sivaneswaran, and Pierce confirm that "maintenance and rehabilitation practices on these roads are vital to their continued serviceability." They also noted that such low-cost strategies are vital because "low-volume roads are typically managed by agencies with extremely limited resources."
The authors researched their state's 30-year data base for low-volume pavement maintenance to reach their conclusion. "Records indicate that over two-thirds of WSDOT's low-volume pavements are bituminous surface treatments, while almost one-third are hot-mix asphalt surfaced pavements," they said. "These pavements, many of which have lasted in excess of 35 years, are in relatively good condition and are typically subject only to periodic rehabilitation treatments every 8 to 20 years and responsive pothole patching. This evidence suggests that the concept of a long-lasting low-volume pavement is viable and, in fact, already exists."
Many of those same practices can be used on high-volume roads as well. For example, chip seals can be used on interstate-type highways if done right, NCPP's Galehouse said.
"There are states that have successfully put chip seals on high-volume highways," Galehouse told Better Roads. "They have developed an institutional knowledge that lets them be successful. Texas, California and Montana have done them. Trucks will take their toll on any treatment, and chip seals are no exception. But if a chip seal is done right it can stand up to trucks, provided there are no structural deficiencies."
"There is no magic ADT number or threshold for chip seal use," said Steve Mueller, pavements and materials engineer, FHWA Resource Center, Denver. "Our new NCHRP Chip Seal Best Practice study shows that many countries are using chip seals on high-volume roads, and that's one of the report's major findings. It's an outstanding report which will advance the pavement preservation industry considerably."
Such seals tend to be polymer modified, Mueller told Better Roads at the 32nd annual Rocky Mountain Asphalt Conference and Equipment Show in February in Denver. "Polymer modification adds to the stickiness of the material, and holds the aggregates in on high-speed roadways. Public safety is a key issue here, and we certainly don't want to damage vehicles from chip loss. The fact is that we can build chip seals with very low rates of loss, and properly designed and constructed chip seals can be used on high-volume roadways."
That properly designed surface treatments can hold up to traffic and weathering is borne out by research that now is coming to fruition. At January's TRB meeting, proponents of pavement preservation gave an overview of just how well polymer-modified surface treatments can perform in different climates, based on 14 years of field experience. Visual surveys, photos, and data mining from the Long-Term Pavement Performance study's DataPave Web site were used to evaluate the condition of seven research projects after 13 or 14 years in service.
Preventive Maintenance Treatment Performance at 14 Years was authored by NCPP's Larry Galehouse, Helen King, and David R. Leach of Koch Pavement Solutions, Jim Moulthrop of Fugro Consultants, and Bill Ballou of the Foundation for Pavement Preservation. They concluded, "Perhaps the most compelling conclusion is that, after 14 years, the chip seal sections are generally giving longer than expected performance; reducing longitudinal, transverse, and fatigue cracking; and they are especially effective in sealing and protecting the centerline joints."
The slurry seals are showing signs of wear, but did provide sealing protection for most of their service life, and the pavements protected by the slurry seals are generally in better condition than the sections that were just crack sealed and the control sections, they said. "The results on the crack sealing sections are mixed, confirming earlier conclusions by ETG [expert task group] observers that the routed seals give better performance, and their performance may also depend upon the road condition before treatment," they said.
The contention that surface treatments will keep a top-flight road in top-flight condition also was borne out by the data. "The Michigan SPS-3 project, in the most severe climate, is among the best in overall condition," they said. "It was also one of the projects in the best condition before treatment. The Illinois, Michigan, and Missouri original pavements were in the best condition of the sections studied for this report, and the photos and surveys show that the preventive treatments have kept them in the best condition.
"The excellent condition of the Michigan SPS-3 project and some of the other test sections clearly illustrates that preventive maintenance treatments in all climates do provide protection and extension of service lives when appropriately applied," they said.
Chip seal best practice
That the best-designed chip seals can be used on high-volume pavements is illustrated in a new survey and practice presented in January at TRB. The paper, Chip Seal Program Excellence in the United States, by Dr. Doug Gransberg, P.E., University of Oklahoma-Norman, describes a survey of public highway and road agencies that use chip seals as part of their roadway maintenance program; the paper will become a part of the new NCHRP Synthesis Report 35-02 mentioned by the FHWA's Mueller, Chip Seal Best Practices, (see For More Information sidebar).
The survey was conducted to identify best practices in chip seal design and construction. "The study found that successful chip seal programs had much in common," Gransberg said. "The major findings were that they used chip seals as a preventive maintenance tool applying it to roads before distress levels were classified as moderate. It also found that they require their contractors to use the latest technology and exploit advances in material science such as the use of modified binders. Additionally, most of these case study programs use chip seals on both high- and low-volume roads."
Chip seals date to the 1920s, Gransberg said. "These early uses were predominantly as wearing courses in the construction of low-volume gravel roads," he said. "In the past 75 years, chip seals have evolved into maintenance treatments that can be successful on both low- and high-volume pavements. The popularity of chip seals is a direct result of their low initial costs in comparison with thin asphalt overlays, and other factors influencing treatment selection, where the structural capacity of the existing pavement is sufficient to sustain its existing loads."
Among those agencies reporting excellent chip seal performance were Arkansas State Highway and Transportation Department; Colorado DOT; Idaho Transportation Department; Nevada, Oklahoma, Texas and Washington State DOTs; and the cities of Austin and Lubbock, Texas.
"The most striking factor [is that] they use chip seals as a preventive maintenance tool by following a specific PM cycle," Gransberg said.
Research Gransberg uncovered in Texas shows that the design of a chip seal is paramount for performance. "One group followed formal design procedures...or local empirically developed procedures and utilized some form of input parameters, based on observed surface conditions, to calculate the rates of binder and aggregate application," he wrote. "The other saw chip seal as a commodity and merely ordered an estimated amount of material and specified application rates based on past experience."
The carefully designed chip seals significantly outperformed their more casually placed counterparts. "Only one of the excellent case studies did not formally design its chip seals, and those that did utilized a procedure that has been in use for an average of 21 years," said Gransberg.
All use modified binders, with polymers and crumb rubber being the most common modifiers, he said. "They all select roads whose distress level is rated at moderate or less and whose structural cross-section is rated as fair or better, using some type of pavement condition rating as the trigger point to consider the selection of chip seal to extend the life of the pavement," Gransberg said. "This further reinforces the use of this treatment as a PM technique rather than a repair method…these programs also follow-up to maintain their seals with routine crack sealing, and sometimes fog sealing, to maintain the integrity of the asphalt membrane for the life of the seal."
- Chip seals should be viewed as a preventive maintenance tool to be applied on a regular cycle, and in doing so, reinforce the pavement preservation benefits of the technology.
- Chip seals can be successfully used on high-volume roads if the agency's policy is to install it on roads before pavement distress becomes severe or the structural integrity of the underlying pavement is breached.
- Both hot asphalt cement and emulsified asphalt binders can be used successfully on high-volume roads; binders modified by polymers or crumb rubber seem to reinforce success.
- In-house maintenance forces should be used to install chips seals in areas where the greatest care must be taken to achieve a successful product.
- Requiring chip seal contractors to use state-of-the-art equipment and to control the rolling operation enhances chip seal success.
- Chip seal success requires an aggressive QC testing program combined with careful on-site inspections.
Cracks come first
In its Roadway Maintenance Surface Treatment Strategies (Recommended Guidelines), Caltrans says much the same thing for both contracted maintenance and that done by state forces. "Experience has shown when proper preparation has been done in areas scheduled for surface treatments (either by contract or by state forces), the life of the surface treatments can be greatly extended and helped in reducing lifecycle cost," the California DOT said. "It is critical that all necessary preparation work such as crack filling, pothole repair, patching, leveling, digouts, etc., be done prior to surface treatments being placed."
Caltrans calls crack filling and sealing "our first line of defense in roadway maintenance." The agency recommends cracks 0.25 inch or wider be filled or sealed before rainfall seasons or before the application of maintenance surface treatments such as fog seals, sand seals, slurry seals, chip seals, or maintenance overlays.
"Cracks should be cleaned before filling or sealing," the agency says. "When moisture is present or suspected, it is recommended that hot compressed air (hot lance) be used to prepare cracks immediately before filling or sealing materials are applied. All cracks should be squeegeed during filling and sealing (if product is left above the surface) to save materials, prevent road noise, improve ride quality, prevent bleeding or masking through future surface treatments, and prevent compaction problems on future overlays."
Caltrans also says crack fillers should be placed several months before future surface treatments, depending on local climatic conditions, to assure sufficient cure time for various crack-filling products.
Premium crack-sealing products should be considered, Caltrans says. "Crack-sealing operations can be very labor intensive," the agency advises. "A value engineering study which involved seven states (including California) concluded that 66% of the total cost for these projects was for labor, 22% for equipment, and 12% for materials. Therefore, it may be more cost-effective to use a more expensive product that will last longer."
Polymer modifiers key
Gransberg's findings of the desirability of polymer-modified binder in high-volume roadway chip seals was illustrated several years ago in South Dakota, which has had mixed success in surface sealing high-volume, high-speed roadways such as interstates.
"Chip seals and sand seals have been the treatments of choice [in South Dakota] but they have been less successful on high-volume/high-speed roadways," the FHWA said. "Chip retention is the major problem associated with these failures. The high number of broken windshields caused by loose chips has resulted in multiple claims on an individual project."
So a project was undertaken to investigate the use of chip seals for high-speed applications and to make recommendations to improve their performance. An extensive literature review was conducted to develop an understanding of the latest practices and experiences. Interviews were conducted within the South Dakota DOT to investigate chip seal practices and to determine areas for improvement.
Finally, test sections were constructed to evaluate the performance of standard and modified chip seal designs. The test sections consisted of 12 chip seal designs and included two aggregate types (quartzite and natural aggregate) and alternate chip seal designs with new gradations and other modifications and enhancements.
Recommendations were articulated in a January 2002 Transportation Research Board presentation, Evaluation of Chip Seals on High-Speed Roadways. Authors Daris Ormesher, P.E., South Dakota DOT Office of Research; and Monty J. Wade, P.E., and David G. Peshkin, P.E., Applied Pavement Technology, Inc., said polymer-modified binders are the key to successful chip seals on South Dakota's interstate-type, high-speed pavements. Performance can be enhanced through special considerations, such as the use of polymer-modified emulsions, precoated aggregates, or a fog seal cover.
They recommended use of a polymer-modified emulsion to obtain better adhesion, especially on high-volume roadways, and the use of a fog seal over the chip seal to help with retention.
Projects should be designed on a specific, individual project basis, and a higher emulsion application rate to achieve greater aggregate embedment should be considered, the authors said.
They also concluded that a tighter and more gap-graded aggregate gradation should be developed to ensure uniformity and provide a single layer of chips, and that the amount of fines (material passing the 0.075-mm [No. 200] sieve) in the chips should be limited. Testing should limit the amount of flat and elongated particles in the aggregate, and also should determine adhesion between the aggregate chips and the emulsion.
The authors said a surfaced pavement should be swept two hours after chip seal placement, and before opening to traffic; in the meantime, if used, the pilot vehicle should be run on the chip seal to assist chip embedment and orientation. An embedment check to ensure adequate embedment of the aggregate should be considered. And a choke stone layer of small chips over the chip seal to lock in the larger aggregate particles might be beneficial.
Microsurfacing vs. slurry seals
A major western contractor says high-performance microsurfacing is a superior choice for high-volume pavements.
"On interstates we recommend microsurfacing, because you can get traffic back on it quickly," said Brett Hone, project manager, Intermountain Slurry Seal, Salt Lake City, Utah. "Microsurfacing allows the contractor the capability to fill ruts by placing the aggregate more than one stone thick, then turn 80,000-pound trucks back on to the filled ruts within one hour. The degree of heavy truck-caused rutting is the key factor over whether microsurfacing or chip seals would be used."
Hone said chip seals still have applications for interstates. "We're still using chip seals on interstates and fog-sealing them after three days," Hone told Better Roads. "With the proper application they're a good solution; Utah DOT uses them every year. When you fog-seal the chip seal, it does a great job of holding the chip down, and gives the gray chips a black color for snow melt, and high contrast for striping."
For main arterial roads around town, Hone recommends slurry seals as a cost-effective maintenance product. "You would want to use a latex- or polymer-modified Type III slurry seal," he says, "because it has better bonding capabilities and the coarser Type III aggregate gives you a more aggressive surface for keeping skid numbers up high. And Type III slurry will cure out in less than four hours in the summer, which lets you get traffic back on it quickly. There is a little more downtime that way, but the cost savings compared to microsurfacing is half as much."
Intermountain has done fog-sealed chip seal projects with quarry-sourced 0.375-inch chips on I-70 and I-15 in Utah, and reports that they last four to five years. "After three years, on some applications, they will apply a rejuvenator sealant, prior to placing another wear surface down three years after that," Hone said.
For either microsurfacing or chip seal, the highway has to be in good condition. "The highway will have to be structurally sound," Hone told Better Roads. "Microsurfacing can fill in ruts, so long as you are confident the pavement has stabilized and is not subject to plastic deformation. My advice to states is to sit back and look at their wallet a little closer, and see where the money is going out the door. If they can maintain an asphalt surface by utilizing surface treatments in lieu of putting an overlay on top, they will be money ahead, because they can do twice as many lane miles with surface treatments. The key, though, is getting on them relatively quick, before they have oxidized and gotten brittle, and all the cracking has taken place."
Does joint sealing work?
Pavement joint and crack sealants are designed to protect pavement by minimizing water infiltration and by preventing the accumulation of debris. "Crack sealing is an effective technique for maintaining flexible [hot-mix asphalt] pavements," said the Transportation Research Board's forward-looking state-of-the-industry forecast on the occasion of the Millennium. "Research has indicated that, in conjunction with maintenance techniques such as slurry seals and chip seals, crack sealing will extend the life of a flexible pavement."
The practice of sealing joints in rigid pavements has been subject to controversy. Research conducted by the Wisconsin DOT indicated sealing joints in concrete highway pavements was not cost effective. "Anecdotal information supports this finding," the TRB panel found, adding "other information seems to show that joint sealant materials are vital to the protection of the pavement and that unsealed pavements deteriorate rapidly."
The challenge was thrown down at the 1996 Spring Convention of the American Concrete Institute in Sacramento, and subsequently was articulated in The Effect of PCC Joint Sealing on Total Pavement Performance, a paper by Steve F. Shober and Terry S. Rutkowski of the Wisconsin DOT.
Their research indicated that long-term pavement performance was not significantly affected by joint sealing, or its omission, and was not worth the expenditure of precious state maintenance funds.
"WisDOT believes the burden of proof has shifted," Shober and Rutkowski wrote. "No longer can anyone tout the merits of keeping water and incompressibles out of [pavement contraction] joints. Now, the burden is on researchers to prove through total pavement performance analysis that sealing PCC joints somehow enhances performance enough to be cost effective." In a subsequent paper they found that asphaltic concrete (HMA) crack sealing was cost-effective in some cases, especially in improving winter ride.
Realizing their findings constituted heresy to an establishment that maintained pavement joint sealing was intuitively valid, Shober and Rutkowski summoned up a scientific fallacy of the past.
"Centuries ago, the concept of a spherical earth was viewed as preposterous," they wrote. "Wisconsin's research has posed a position that may be viewed similarly, that is: total highway pavement performance is not significantly affected by joint sealing or lack thereof. The challenge awaits others to provide compelling research on this issue."
Into the fray stepped New York State DOT's outspoken innovative projects engineer John Bugler, and Burgess & Niple's engineer Martin P. Burke, Jr. In their 2002 TRB paper, The Long-Term Performance of Unsealed Jointed Concrete Pavements, Bugler and Burke said Shober and Rutkowski had not used a long-enough time frame.
"[I]t appears that WisDOT observations of test pavement performance were based on the mistaken assumption that the performance of pavements during their first 10 years of service was somehow indicative of their long-term performance," Bugler and Burke said. "Such an assumption entirely neglects the characteristics of the pavement growth/pressure phenomenon that typically becomes more destructive with pavement age. It also neglects the adverse long-term accumulative effects of surface and subsurface water movement on pavement pumping and step-faulting, especially for pavements without dowels serving heavy truck traffic." Unsealed pavement joints did not provide long-term cost-effective pavement performance, their research indicated. "As a result," Bugler and Burke said, "the use of unsealed pavement joints has been discontinued by many major users familiar with the long-term performance of such applications."
But joint sealing had to be done right, they said. "Care must be taken in choosing high quality sealant material, the type and size of sealant for the chosen pavement joint and panel characteristics, as well as effective installation and inspection procedures, and periodic sealant repair and replacement practices."
New Pavement Preservation Boss at FHWA
Tom Deddens, P.E., joined the FHWA's Office of Asset Management as pavement preservation and construction engineer in February. He will manage the pavement preservation program, as well as the program manager moving the FHWA's interests in performance specifications.
Deddens has 30 years' experience in the industry. He worked more than 10 years in the U.S. Army Corps of Engineers, and has since worked in the private sector for several consultants, and in industry as a district engineer for the Asphalt Institute. With the Asphalt Institute, he provided technical assistance and training opportunities to the states of Arkansas, Illinois, Kansas, Missouri, and Nebraska, including maintenance of hot-mix asphalt pavements, rehabilitation of pavements using HMA, advanced Superpave mix design, and construction of asphalt pavements.
Deddens is a qualified National Highway Institute instructor, having taught its course in Pavement Preservation: Selecting Pavements for Preventive Maintenance. He holds a bachelor of science degree (1975) from the University of Missouri-Rolla, and a master of science degree (1985) from the University of Kansas. He is a registered professional engineer in Kansas and Missouri, and has been professionally active in the Association of Asphalt Paving Technologists and American Public Works Association.
FHWA'S List of Preservation Methods
- Crack sealing.
- Fog seals (a combination of mixing-type emulsion and approximately 50% water, used to seal shoulders and patches).
- Rejuvenation (application of a rejuvenator agent in a procedure similar to fog sealing).
- Sandwich seals (application of asphalt emulsion and a large aggregate, followed by a second application of asphalt emulsion that is in turn covered with smaller aggregate and compacted).
- Sand seals (application of liquid asphalt or emulsions, covered with fine aggregate or sand, to improve skid resistance, prevent oxidation, and to seal against water infiltration).
- Chip seals (surface treatment in which the pavement is sprayed with asphalt emulsion and then immediately covered with aggregate and rolled).
- Slurry seals (an application of mixing-type asphaltic emulsion, sometimes with additives, mineral aggregate, and proportioned water, mixed and spread on clean pavement free of dirt and loose gravel).
- Microsurfacing (polymer modified asphalt emulsion, mineral aggregate, mineral filler, water, and other additives, properly proportioned, mixed, and spread on a pavement).
- Cape seals (application of slurry seal to a newly constructed surface treatment or chip seal).
- Thin and ultrathin hot-mix asphalt overlays (single-lift surface course, generally with a thickness of 1.5 inch or less).
- Joint sealing.
- Joint and spall repairs.
- Load transfer retrofit.
- White topping (similar to a thin HMA overlay, but using a fast-curing, high-durability concrete mix).
For More Information
More information about high-performance pavement preventive maintenance is available from a variety of sources. Begin with these:
Chip Seal Best Practices. The long-awaited National Cooperative Highway Research Program synthesis of best practice, NCHRP 35-02: Chip Seal Best Practices, should be available this spring. Visit this link to see if it has been announced. Alternatively, locate it with a Google search by inputting: "NCHRP 35-02."
NCHRP Report 523. Optimal Timing of Pavement Preventive Maintenance Treatment Applications describes a methodology for determining the optimal timing for the application of preventive maintenance treatments to flexible and rigid pavements. NCHRP Report 523 also presents the methodology in the form of a Microsoft Excel Visual Basic Application, called OPTime. It may be downloaded at no charge.
A Pavement Preservation Strategy. Wisconsin's carefully formulated philosophy on pavement preservation can be downloaded.
Transportation Asset Management. Asset management is getting much play and new tools exist for pavement managers. Visit the Transportation Asset Management Web site of the Midwest Regional University Transportation Center of the University of Wisconsin-Madison.
Capital Preventive Maintenance. The same center offers a strategy for getting support for preventive maintenance in your agency structure. Read Capital Preventive Maintenance, Project 03-01, February 2004.
Asset Management. There's more on asset management at the American Association of State Highway & Transportation Officials Web site.
The Great Unsealing. Steve Shober's controversial report on unsealed concrete pavement joints, The Great Unsealing, can be downloaded. Find many other useful WisDOT reports at the WisDOT Internal Pavement Studies web page.
The Case for Joint Sealing. Burke and Bugler's response to Steve Shober's critique of PCC joint sealing, The Long-Term Performance of Unsealed Jointed Concrete Pavements, can be downloaded.
Federal Highway Administration. The FHWA supports pavement preservation; visit its Web site.
Caltrans' Pavement Maintenance Manual. California's approach to prevention can be downloaded.
National Center for Pavement Preservation. Visit this new group's site.
International Slurry Surfacing Association. Browse their resources.
Asphalt Emulsion Manufacturers Association. Information on emulsions used in chip and slurry seals, both conventional and polymer-modified, may be downloaded.
Reprinted from Better Roads, April 2005. Better Roads can be visited online.