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Asphalt Maintenance

From the Minnesota DOT Asphalt Pavemnent Maintenance Handbook

The purpose of this handbook is to provide background information about the importance of pavement preservation and preventive maintenance, as well as present maintenance techniques for a variety of distresses and conditions. The major focus of this handbook is on preventive maintenance activities, which are performed while the roadway is still in good condition with only minimal distress, before the pavement falls into a condition where structural overlays, major milling or reclaiming, or replacement is necessary.

The most common flexible pavement distresses are cracking, roughness, weathering, raveling, rutting and bleeding. If the distresses identified in a pavement are related to structural deficiencies, the pavement section is most likely not a candidate for preventive maintenance treatment, and should be scheduled for rehabilitation or reconstruction. Maintenance treatments covered in this handbook include: Crack repair w/sealing, including clean and seal, saw and seal, and rout and seal; crack filling, full depth crack repair, fog seal, seal coat, double chip seal, slurry seal, microsurfacing, thin hot mix overlays, and potholes and pavement patching.

Today’s increasing budget constraints require that state and local agencies perform more work with less money. Historically, the emphasis of local highway departments has been on building new roads, but the new focus is on maintaining and preserving existing pavement surfaces. This shift has resulted in three types of pavement maintenance operations:

• Preventive Maintenance: Performed to improve or extend the functional life of a pavement. It is a strategy of surface treatments and operations intended to retard progressive failures and reduce the need for routine maintenance and service activities.
• Corrective Maintenance: Performed after a deficiency occurs in the pavement, such as loss of friction, moderate to severe rutting, or extensive cracking. May also be referred to as “reactive” maintenance.
• Emergency Maintenance: Performed during an emergency situation, such as a blowout or severe pothole that needs repair immediately. This also describes temporary treatments designed to hold the surface together until more permanent repairs can be performed.

All types of maintenance are needed in a comprehensive pavement maintenance program. However, emphasizing preventive maintenance may prevent a pavement from requiring corrective maintenance. Preventive maintenance is completing the right repair on the right road at the right time. Many pavement treatments can be used for preventive, corrective, or emergency maintenance. Figure 1-1 illustrates the differences among these three types of maintenance. As indicated on the graph, the main difference is the condition of the pavement when the treatment is applied. There are no clear boundaries between when a treatment is preventive versus corrective, or corrective versus emergency.

Although all three types of maintenance are important, this handbook focuses on preventive maintenance activities because these are the most costeffective and offer the best means for prolonging pavement service life. The remainder of this chapter describes the three maintenance types.

Preventive Maintenance and Pavement Preservation

A preventive maintenance program is a systematic approach to using a series of preventive maintenance treatments over time. One treatment will improve the quality of the pavement surface and extend the pavement life, but the true benefits of pavement maintenance are realized when there is a consistent schedule for performing the preventive maintenance.

An effective pavement preservation program integrates many preventive maintenance strategies and rehabilitation treatments. The goal of such a program is to extend pavement life and enhance system-wide performance in a cost-effective and efficient way. Studies show that preventive maintenance is six to ten times more cost-effective than a “do nothing” maintenance strategy.

Benefits of pavement preservation include improved customer service and substantial life cycle cost savings; treatments are especially cost-effective when applied early in the life of a pavement. In addition, by extending the life of a pavement section until it can be rehabilitated, preventive maintenance allows an agency to even out its maintenance budget from year to year, which otherwise can vary greatly. For example, the Michigan Department of Transportation has used preventive maintenance to balance out its construction program. They report that their program enables them to optimize the network condition with a given preservation budget, resulting in more stable funding needs.

Critical elements of a successful pavement preservation program are:

1. selecting the roadway
2. determining the cause of the problem
3. identifying and applying the correct treatment(s)
4. determining the correct time to do the needed work
5. observing performance

The program can then be adjusted according to the results. Preventive maintenance activities can include conventional treatments such as crack sealing, chip sealing, fog sealing, rut filling, and thin overlays. They can also include emerging technologies such as ultra-thin wearing courses, very thin overlays, and microsurfacing applications. Aside from crack treatments, all of these treatments leave the pavement with a new wearing surface. A fog seal provides a new wearing surface, although it generally has a lower friction number than the original surface.

When to Apply Preventive Maintenance Treatments

Waiting until after a failure occurs is not cost-effective or preventive maintenance. The effectiveness of a preventive maintenance treatment is directly related to the condition of the pavement. Conducting preventive maintenance activities on a sound pavement in good condition will be very effective in prolonging that pavement’s service life. Conducting an inappropriate repair (either method or timing) can actually accelerate the rate of distress development.

Preventive maintenance is generally planned and cyclical in nature. Its intent is to repair early pavement deterioration, delay pavement failures, and reduce the need for corrective maintenance and service activities. Although this type of maintenance is not performed to improve the load-carrying capacity of a pavement, it extends the pavement useful life and level of service. Figure 1-2 shows the relationship between pavement condition and time (or traffic). Often, preventive maintenance methods are designed to repair damage caused by the environment. Periodic renewal of the pavement surface can provide several benefits, including sealing the pavement surface (which prevents water from penetrating into the pavement structure), and controlling the effects of oxidation, raveling, and surface cracking. Environmental conditions remain fairly consistent over time, so the maximum time between preventive maintenance treatments should be based on time, rather than the amount of traffic on a roadway section.

To help choose the correct time to apply a treatment, a condition survey and non-destructive testing can be used. This provides a more rational approach to determining which pavements need treatment and when the treatment should be done. Using the output of the pavement condition survey, threshold limits can be developed to define when a treatment type should be implemented.