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Portland cement concrete pavement: rehabilitation challenges and recommendations.

Portland Cement Concrete Pavement: Rehabilitation Challenges and Recommendations


The most challenging and pressing issue facing highway engineers today is rehabilitation of our Nation's highway infrastructure. Pavement rehabilitation is a relatively new and rapidly developing technology. It is only in the last few years that a variety of field and laboratory equipment, materials, design procedures, standards, and computer software has become available to aid the engineer in evaluating the pavement and design of several rehabilitation techniques such as overlays, full-depth repairs, and recycled mixtures.

With all these advances, however, many unanswered questions remain about pavement rehabilitation techniques and their effectiveness. Because pavement rehabilitation is still largely an art, the Federal Highway Administration sponsored a 3-day workshop in March 1990 to examine the state of the practice of concrete pavement evaluation and rehabilitation strategy selection. This article summarizes key workshop findings and recommendations. (1,2)(1)

Rehabilitation Strategies Should Be Selected Systematically

How does a highway agency select the most appropriate rehabilitation strategy for a given stretch of pavement? Ideally, this determination should be made in an organized and systematic manner, taking into account all relevant parameters and their respective impacts (e.g., existing pavement distress and initial cost, anticipated maintenance and future rehabilitation requirements, anticipated pavement serviceability, agency experience, and constructability for the given traffic and geometrics).

Many computerized (i.e., artificial intelligence systems) and manual programs are available to help agencies make informed decisions about rehabilitation. Most of these systems are based on a formal decision-making process, such as that recommended by the American Association of State Highway and Transportation Officials (figure 1).

The Expert System for Pavement Evaluation and Rehabilitation (EXPEAR) is a particularly noteworthy computerized system. EXPEAR leads engineers through a comprehensive evaluation of a pavement's present condition and development of one or more feasible rehabilitation strategies. The FHWA considers EXPEAR an excellent training tool for new engineers. Some modifications would be needed, however, to make the program applicable for routine design use with a particular State.

Regardless of the specific system used, the decision-maker should consider each project and pavement distress condition on its own merit. The decision-maker must assess the effectiveness of each treatment in terms of the project conditions, the cost involved (including initial cost, life-cycle costs, and user costs), constraints on strategy selection (including traffic volume), and various technical issues related to the specific strategy. The decision-maker must also know the repair's desired life expectancy and understand the effects on performance if the repair is not done.

Timing of Rehabilitation Is Linked to Strategy Selection

Besides the challenge of selecting the most appropriate type of rehabilitation for a particular pavement, the engineer faces the equally difficult decision of when to rehabilitate. These two decisions are inextricably linked: There is no one right time to rehabilitate a pavement, nor is there only one correct rehabilitation strategy to select at a particular time.

The type of rehabilitation that is most appropriate changes during the pavement's life as its condition declines. A tradeoff always exists between rehabilitating now and rehabilitating in the future when the pavement's condition will invariably be worse and will, therefore, require a more substantial improvement (figure 2). Each rehabilitation treatment raises its own issues regarding timing. Pavement design engineers and pavement management engineers should coordinate information during the process to select the appropriate rehabilitation treatments.

Predicting Rehabilitation Performance Requires Extensive Data

Perhaps the most challenging aspect of selecting a rehabilitation strategy is trying to predict how the rehabilitated pavement will perform. Rehabilitation performance prediction is much more difficult than new pavement performance prediction. This difficulty is due largely to the shortage of long-term performance data on rehabilitation projects and the many variables affecting a particular project's performance (e.g., traffic loading, materials variation, design features, quality of maintenance). The experience of specific agencies with certain rehabilitation techniques provides some guidance, as do national studies. However, these performance models need to be calibrated to rehabilitation practices within each State, thus reflecting the State's practices. These models must also be continually refined based on feedback from the State's pavement management program.

Custom Design Is Vital to Successful Pavement Rehabilitation

Successful rehabilitation depends on both the condition of the existing pavement and the selection of a strategy that is truly appropriate and cost effective for that pavement. Careful consideration and thorough evaluation is thus required for each individual pavement section. At a minimum, engineers should:

* Do a distress survey, noting distress types, rates of

change, severities, and quantities. Most PMS's only

sample pavement distresses. Therefore, the

pavement designer should perform a more detailed

distress survey for the total project section. * Identify the causes of distress. * Collect data on insitu structural condition using a

heavy load deflection device, such as a falling

weight deflectometer. * Collect data about past and current truck volumes

in order to estimate truck loading to date and future. * Collect data about climate. * Collect data about pavement materials and soil.

A pavement management system may recommend a pavement preservation treatment for a candidate project as part of the network analysis, but this does not replace the need for a custom design. This methodical approach, therefore, leads to custom design of the rehabilitation for a specific project. Applying the same rehabilitation treatment to every concrete pavement has led to poor overall performance and many early failures, because no rehabilitation design will work everywhere.

EXPEAR, mentioned above, uses a 10-step process for custom designing a rehabilitation project (figure 3). If these steps are followed, pavement engineers may be able to achieve a reliable and cost-effective customized rehabilitation design.

Each Rehabilitation Technique Raises Different Considerations

Highway engineers have a broad range of options available to them in selecting an appropriate rehabilitation strategy for portland cement concrete (PCC) pavement projects. When making their selection, engineers should be aware of the various design factors and technical considerations associated with each rehabilitation technique, as highlighted in the following paragraphs.

Routine or preventive maintenance only

This rehabilitation technique may be the most appropriate action for some projects. In general, rehabilitation is not warranted until annual maintenance costs exceed the cost savings of deferring rehabilitation. Generally, good maintenance will significantly extend the time before a rehabilitation alternative is needed.

Concrete pavement restoration

Concrete pavement restoration (CPR) is a system of repair methods to restore jointed concrete pavement to a high level of serviceability without an overlay. Individual CPR techniques have long been applied as maintenance. Today, CPR is considered to be a set of needed techniques that can provide a long-term pavement rehabilitation strategy. CPR may add significantly to a pavement's service life if it is applied, correctly and using proper techniques, before the pavement begins to manifest significant structural distress. CPR does not improve a pavement's structural capacity. Moreover, if signs of structural inadequacy are starting to appear at an increasing rate, CPR may not be the most cost-effective approach.

Pavement rehabilitation experts disagree as to which CPR methods should be used, when to use them, or whether to use them at all. Consequently, clear rules do not exist for determining what CPR should be done and when. To determine the need for any CPR technique, project conditions should be evaluated along with the extent and rate of change of the critical distress type. Decisions regarding what should be done must be based on an evaluation of expected traffic loadings, pavement design features, past repair history, current pavement condition, ability to handle traffic during repairs, and the estimated remaining performance life.

Conventional asphalt concrete overlay

Conventional asphalt concrete (AC) overlays may be effective in improving pavement structure and should be considered when there are structural deficiencies. However, reflection cracking is frequently a controlling factor in AC overlay performance life. This type of overlay typically requires thorough preoverlay repair. Rutting can also reduce its life. Thus, the service life of conventional AC overlays has often been less than expected. AC overlays, when applied in a timely manner, have been very effective in extending continually reinforced concrete pavement (CRCP) life, possibly because the increased thickness they provide reduce both daily temperature stresses and the stresses caused by traffic loads and minimal reflection cracking.

Saw and seal with AC overlay

This approach to reflection crack control has been used predominantly in the northeast section of the United States. It has been found to be very beneficial on moderately deteriorated jointed reinforced concrete pavements. However, the cost effectiveness of this approach on shorter jointed plain concrete pavements is still being debated.

Break and seat with AC overlay

This reflection crack control technique involves destroying slab action of jointed reinforced concrete pavements by reducing crack spacing and breaking the bond between the concrete and the reinforcing steel. Opinion is currently divided as to the overlay thickness over such pavements. Another question is whether the long-term reflection crack occurrence differs significantly from that of conventional AC overlay. It is recommended that States using this technique construct an uncracked control section with the same overlay thickness to verify that the procedures used are extending service life cost effectively. The Strategic Highway Research Program and other ongoing research should provide additional guidance in this area.

Crack and seat with AC overlay

This is the title given to the technique of controlling reflection cracks for jointed plain concrete pavements. The technique involves cracking the unreinforced slab into pieces about 2 to 3 ft. (.6 to .9 m) in length, seating the pieces and placing an AC overlay. This technique has achieved success in some States. There is divided opinion as to the required overlay thickness, with some believing it should be as thick as that placed over a rubblized concrete and others somewhat thinner. Additional research is needed to establish overlay thickness requirements for specific traffic levels.

Rubbilization with overlay

This approach involves reducing the existing concrete pavement almost to a granular base. To do this, the overlay must be designed as a new pavement. Overlays are predominantly AC, although PCC overlays can also be placed on rubbilized pavements. Rubbilizing must be uniform across the slab.

Bonded PCC overlay

This technique is most appropriate for pavements in relatively good condition; it requires a thorough pre-overlay repair. Use of a bonded PCC overlay should also be considered if the existing pavement is structurally inadequate for anticipated heavy traffic loadings. The specific reduction in service life due to debonding of the overlay has not been determined, although it is considered undesirable. Every effort must be made to achieve a full permanent bond; this may be particularly effective in extending the service life of thinner CRCP.

Unbonded PCC overlay

Unbonded overlays are most appropriate for pavements with a greater degree of structural or other deterioration. The technique uses a separation interlayer to absorb slab movement and prevent reflection cracking. This technique also has significant advantages where the base/subbase/subgrade material is very poor. Caution is advised, however, if the existing support is very non-uniform (i.e., unsupported joints in the old pavement). Also, when placed over a rigid base (old PCC or an AC pavement) shorter slabs and dowels are needed and drainage should be carefully considered. The performance of unbonded PCC overlays has been very good.


Because of its high cost, reconstruction is often considered a last resort unless it is warranted by other factors, such as the need for geometric improvements or maintenance of the existing pavement surface elevation. Reconstruction may also be the rehabilitation strategy of choice for pavements with very high traffic volumes, because of its long performance life and low maintenance requirements. Cost savings may be realized if the existing pavement can be recycled into the new pavement structure.

Numerous Technical Issues Affect Successful Rehabilitation

Careful evaluation of PCC rehabilitation strategies entails the consideration of a wide variety of technical issues. Some of the more significant of these issues include the following:


Opinion is divided as to whether drainage should be included on rehabilitation projects. At one time, drainage was included on every job as a form of "cheap insurance." Drains on some projects, however, have clogged, turning into moisture retention systems. Engineers have thus come to believe that in some instances drainage, rather than being either useful or harmless, can actually accelerate pavement deterioration. This perception underlines the need for indepth research in the area of drainage and edge drain design. The design of underdrains should be carefully engineered to take into account the existing condition at each proposed rehabilitation project.

Preoverlay repair

A correlation may exist between the types and amounts of preoverlay repairs made to a pavement and the thickness needed for the eventual overlay as well as the overlay's ultimate service period and life. It may be true that the better and more extensive the preoverlay repair, the thinner the overlay required. Engineers will need to assess this tradeoff between the extent of preoverlay repair and overlay thickness when considering this rehabilitation option.

Reflection cracking

Although several research studies have been conducted on various reflection crack control treatments, few, if any, techniques have proved reliably effective for high-traffic-volume pavements, and few States routinely incorporate reflection crack control treatments in overlay construction. Considering the substantial impact that reflection cracking often has on overlay life, this area deserves further investigation. The use of sawing and sealing of AC overlays has proved to be effective in several States.

Structural capacity of break/cracked and seated and rubbilized PCC

A significant unknown factor in designing overlays of break/cracked and seated and rubbilized PCC pavement is the structural capacity of the altered PCC layer. It is extremely difficult to directly assess a broken or rubbilized PCC layer's structural capacity after breaking from either visual examination or deflection testing. The current practice in some States is to measure deflections after the overlay is placed and to interpret the PCC layer's properties from these data. Additional research on the design of these overlays clearly is needed.

Management and Logistic Considerations Also Hamper Successful Rehabilitation

The challenges of pavement rehabilitation stem not only from technical issues, but also from management and logistic issues; some of these are explored below.

Fragmented lines of responsibility and communication

Within most agencies, responsibility for pavement rehabilitation is diffused among several different units or divisions. Each unit is responsible for a different aspect of maintenance or rehabilitation. In many cases, the units do not communicate during the rehabilitation process, and each, thereby, loses the opportunity to take advantage of expertise within the other units. The implementation of an effective pavement management system will do much to improve this situation.

Inadequate funding

A constraint that applies to all rehabilitation projects is availability of funding. The amount of funding appropriated for a given project is often inadequate. This can lead to serious problems in rehabilitation design and construction. In those States that have the capability to analyze either optimum or near-optimum strategies, the PMS recommendations should be used as input when analyzing the options and consequences when budget constraints prevail.

Lack of performance standards

A lack of State-specified performance standards results in contractor-dependent rehabilitation quality. States tend to get what they ask for: If they do not set standards, they get poor work performance; if they impose high standards, contractors generally meet them. States must provide contractors with specific work standards, guidance, and criteria that have been shown to be cost effective.

User considerations

What is a human life worth? What is convenience worth to the user versus the cost of additional delays caused by road repairs? Such concerns are very difficult to quantify, but represent a significant consideration when planning and performing a rehabilitation. Agencies must be aware of these considerations when determining rehabilitation timing and techniques and recognize that these concerns can affect rehabilitation cost.

Public perception of a State highway agency must also be taken into account. Some agencies opt to close a road once completely rather than close sections of the road every year. However, the public often sees no difference between full and partial closure, because both represent a significant inconvenience.

Rehabilitation Problems Will Increase in the Future

In the coming decade, pavement rehabilitation will become increasingly important and increasingly difficult due in part to two ongoing national trends: rising traffic levels and a dwindling pool of trained pavement engineers.

Increasing truck loadings

The loads applied to highway pavements are rising rapidly. For instance, truck loadings today on the Interstate system have often been three times as high as those estimated when the pavement was initially designed. Many highways have consequently reached and exceeded the end of their design life. Increasing truck axle weights are also causing rehabilitation treatments to deteriorate more quickly and underlying roadway problems to return much faster than in the past. This situation will be further exacerbated in the years to come.

Nevertheless, many current rehabilitation designs do not consider actual truck traffic volume or predicted growth. Such considerations are vital to ensuring a reasonable service life for proposed projects. Using automatic vehicle classification and weigh-in-motion equipment to determine on-site and network-level conditions will provide more accurate measures of actual and forecasted truck traffic loadings.

Deficit of trained engineers

Experienced engineers are retiring in large numbers, taking with them a wealth of knowledge and expertise that is not easily transferred to the next generation of pavement engineers. One way to help address the resulting shortage in qualified pavement engineers is to develop and improve the state of the art of pavement engineering and develop improved pavement rehabilitation advisory systems.

The development of effective pavement management systems, including feedback of performance information, will greatly assist in determining the most appropriate timing of maintenance and rehabilitation activities and determining the most cost-effective rehabilitation strategies.

These systems, however, cannot do the job alone. Trained personnel are needed to perform system analyses and provide input for improving systems. Therefore, the industry must attract engineering students to the pavement field. More courses in pavement rehabilitation and pavement management are greatly needed at both the undergraduate and graduate levels. Further, practicing engineers must keep up to date on the latest available technologies.


Perhaps the most significant conclusion reached at the workshop was that each rehabilitation project is unique and should be engineered and custom designed to achieve a reliable and cost-effective solution. The following are also needed to ensure highest-quality rehabilitation efforts:

* Implementation of an effective pavement

management system, including performance feedback. * Improved coordination among the units of a high

way agency in project selection, timing, cost

estimation, design, and construction. * Direct consideration of current and projected truck

traffic loadings. * Improved rehabilitation construction control and

practices. * Continued training to take advantage of

improvements to the state of the art in pavement design and

rehabilitation procedures. * Techniques, equipment, and materials that can

reduce the amount of time a traffic lane is closed for

testing or repair or that can improve the reliability

and service life of rehabilitation.

In addition, various research and development efforts (some of which are already under way) will provide useful information and results of extending the service life of PCC pavements:

* Using advisory systems in the area of pavement

evaluation and rehabilitation. * Examining full-depth repair design guidelines. * Studying the use of retrofit edge drains to determine

when and why they work. * Studying the use of AC and PCC overlays in different

climates and pavement types.

(1)Italic numbers in parentheses identify references on page 52.


[1]Workshop on Evaluating Portland Cement Concrete Pavement Rehabilitation Strategy: Summary Report. Federal Highway Administration, Washington, DC, March 1990 [2]Workshop Proceedings, March 27 through 29, Federal Highway Administration, Washington DC, March 1990

PHOTO : Figure 1.--Decision-making process.

PHOTO : Figure 2.--General pavement performance curve related to rehabilitation alternatives.

PHOTO : Figure 3.--EXPEAR: a 10-step process.

Nita Congress is a senior writer for Walcoff & Associates, a management consulting firm in Alexandria, Virginia, that specializes in technology transfer. She has written and edited numerous technical documents for the Departments of Transportation and Energy, the National Science Foundation, and the U.S. General Accounting Office.

Michael I. Darter, a registered professional engineer, is a professor of Civil Engineering at the University of Illinois and the Vice President of ERES Consultants, Inc., in Savoy, Illinois. Dr. Darter is a frequent consultant to several government agencies.
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Author:Congress, Nita; Darter, Michael I.
Publication:Public Roads
Date:Sep 1, 1991
Previous Article:University Transportation Centers Program: education and research for the 21st century.
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