Pavement Life-Cycle

This section discusses the basic pavement life-cycle and how maintenance and rehabilitation affect this life-cycle. All pavement deteriorates over time. Typically, pavement deteriorates at an ever-increasing rate: at first very few distresses are present and the pavement stays in relatively good condition, but as it ages more distresses develop with each distress making it easier for subsequent distresses to develop. For instance, once a substantial crack occurs it is then easier for water to (1) infiltrate the HMA layer and (2) penetrate and weaken the subgrade. Additionally, freeze-thaw problems in the crack may develop and any expansive materials that get into the crack (such as dirt, sand or weeds) may make the crack even wider thus compounding the previous problems.

Effects of Maintenance and Rehabilitation

Maintenance and rehabilitation are the two principal treatments used to extend pavement life. These treatments have two main effects (Deighton, 1997^[1]):

1. They immediately improve the pavement condition. For instance, a slurry seal can eliminate most minor surface distresses.
2. They affect the future rate of deterioration. For instance, crack sealing prevents water from entering the pavement structure and subgrade through open cracks, which slows future deterioration.

In general, maintenance can slow the rate of deterioration by correcting small pavement defects before they can worsen and contribute to further defects. Beyond a certain point, however, defects become too large for correction by mere maintenance. At this point, rehabilitation can be used to effect a wholesale correction of a large number of relatively severe defects, which provides a step increase in pavement condition. Figure 1 illustrates this concept.

In general, there are several levels of treatment to correct pavement deterioration. These are (Deighton, 1997^[1]):

• Routine maintenance (e.g., filling cracks, potholes).
• Periodic maintenance (e.g., fog seals, slurry seals, BST applications)
• Rehabilitation (e.g., structural overlays)
• Reconstruction (e.g., design and construct an entire new road)
• Ancillary (leveling and spot repair, usually done in concert with other treatments)

Keep in mind that not all treatments will reset pavement condition to its original new-construction value. Determining how a particular pavement should be treated, when and to what extent are all decisions that can be made with the aid of a pavement management system (PMS).

Effects of Maintenance and Rehabilitation Timing

In addition to the basic concepts illustrated in Figure 1, the timing of maintenance and rehabilitation actions can greatly influence their effectiveness and cost as well as overall pavement life. In general, once a pavement needs treatment, the sooner a maintenance or rehabilitation activity is undertaken, the more cost-effective it will be. Figure 2 demonstrates this concept. Notice that for the first 75 percent of pavement life the pavement condition drops by about 40 percent. However, it only takes another 17-percent of pavement life for the pavement condition to drop another 40 percent. Additionally, in order to restore pavement condition to a predetermined level, it will cost 4 to 5 times as much if the pavement is allowed to deteriorate for even 2 to 3 years beyond the optimum rehabilitation point. This increase in cost is because (1) the pavement condition must be improved by a greater amount (e.g., “very poor” to “very good” versus “fair” to “very good”) and (2) it costs more money per unit of pavement condition increase (e.g., it costs more to go from “very poor” to “poor” than it does from “fair” to “good”).

Summary

Left alone pavements will typically deteriorates over time at an ever-increasing rate. Maintenance and rehabilitation can slow or reverse this deterioration. The degree to which this occurs is dependent on the type of maintenance or rehabilitation as well as the timing of such actions. In general, an early and systematic maintenance and rehabilitation plan is the most cost effective and results in the greatest extension of useful pavement life. This concept is further illustrated in Figure 3 below.

[[2]]Stevens, L.B.  (May 1985).  Road Surface Management for Local Governments – Resource Notebook.  Publication No. DOT-I-85-37.  Federal Highway Administration.  Washington, D.C.[[2]]