By Dave Johnson, P.E.
Rising materials costs have the managers of our infrastructure seeking better and more cost-effective ways to manage assets. With these increasing costs, the value of our in-place materials rises and becomes more expensive to maintain at an acceptable level of service. Managers of these assets are seeing greater value in using a pavement management system to better maintain their system in a more cost-effective manner.
Typically, a pavement deteriorates at an ever increasing rate. Initially few distresses are present, and the pavement stays in relatively good condition. But as it ages, more distresses develop making it easier for subsequent damage to occur. Maintenance and rehabilitation are the two principal treatments used to extend pavement life. In general, maintenance can slow the rate of deterioration by correcting small pavement defects before they worsen and contribute to further defects. Beyond a certain point, however, defects become too large for correction by maintenance. At this point, rehabilitation can be used to effect a wholesale correction of a large number of relatively severe defects, thus improving the pavement’s condition.
Pavements deteriorate over time from exposure to traffic and environment. Maintenance and rehabilitation are employed to slow down the deterioration process or to return the pavement to a like-new state. Maintenance operations, such as crack sealing, chip seals and patching help slow deterioration by identifying and addressing specific pavement deficiencies that contribute to the overall deterioration. Rehabilitation is the act of reconstructing portions of an existing pavement to reset the deterioration process in those portions. For instance, removing and replacing the wearing course in a pavement provides new wearing course material on which the deterioration process begins anew.
Reconstructing an entire pavement, however, is not considered rehabilitation but rather new construction because the methods used are generally those developed for new pavement construction. Pavement life cycle, life cycle cost analyses, and pavement management are all employed when deciding on the type, timing, and extent of maintenance and rehabilitation actions.
In general, there are several levels of treatment to correct pavement deterioration. These include:
- Routine maintenance (e.g., filling cracks, potholes)
- Periodic maintenance (e.g., fog seals, slurry seals, surface treatments, and non-structural [thin] overlays)
- Rehabilitation (e.g., structural overlays or in-place recycling), and
- Reconstruction (e.g., design and construct a new road).
Pavement maintenance describes all the methods and techniques used to prolong pavement life by slowing the deterioration rate. Thus, the performance of a pavement is directly tied to the timing, type, and quality of the maintenance it receives. The Federal Highway Administration recognizes the following operations as preservation methods:
- Crack sealing
- Fog seals
- Sand seal
- Chip seal
- Slurry seal
- Cape seal
- Thin-lift overlay, and
- Ultrathin overlay.
Each option’s effectiveness is dependent upon a multitude of local conditions – weather, traffic, surface and subsurface conditions, etc. Maintenance options need to be evaluated and utilized locally, including the availability of a technology.
While pavement maintenance can slow the rate of deterioration, it cannot stop damage from occurring. Therefore the effects of deterioration eventually need to be reversed by adding or replacing material in the existing pavement structure. This process is rehabilitation.
Rehabilitation options depend upon local conditions and pavement distress types but typically include:
- Cold in-place recycling (CIPR)
- Hot in-place recycling (HIPR)
- Full-depth reclamation (FDR) and
- Hot mix asphalt (HMA) structural overlay.
Rehabilitation essentially reverses the effects of deterioration by adding, replacing or recycling material in an existing pavement structure. The inclusion of recycling techniques may be appealing on many levels. First, it reuses in-place materials that are commonly some of the best materials available. Second, it is often a very cost-competitive option compared to reconstruction. Third, the disruption to the public tends to be less as the road can typically be used during the rehabilitation work. Especially in urban settings, this can greatly reduce user costs associated with a project.
Both recycling and reconstructing correct a myriad of distresses in a single effort. However, with recycling, the agency may choose to stage the construction steps into appropriate phases over extended time. Staging improvements can reduce the funds needed to address a road today, while still correcting problems in the short term. Subsequent stages provide for a long-term solution, with the completion of all the planned stages.
A general pavement deterioration model is seen in the accompanying figure. It graphically displays that, in general, once a pavement needs treatment, the sooner a maintenance or rehabilitation activity is undertaken, the more cost-effective it will tend to be. Notice that for the first 75 percent of pavement life, the pavement condition drops by about 40 percent. However, it only takes another 12 percent of pavement life for the pavement condition to drop another 40 percent. Additionally, in order to restore pavement condition to a pre-determined level, it will cost four to five times as much if the pavement is allowed to deteriorate for even two to three years beyond the optimum rehabilitation point.
All rehabilitation or reconstruction projects should employ some level of economic evaluation to determine the most cost-effective method and timing. The use of a well designed pavement management system (PMS) that is tailored to the individual agency can be a highly useful tool in aiding the decision making process.
Pavement Management System
“Pavement management” refers to a systematic process of maintaining, upgrading and operating a network of pavements. Through an orderly analysis of pavement life cycles, a PMS can help determine the most appropriate time to treat a pavement; what the most cost-effective method may be; and how many dollars it may take to maintain a roadway system at a desirable condition.
Managers should be cautious to not view a PMS as a black box that has all the answers. The need for sound engineering judgment remains. A PMS can assist in making those judgments. The level of sophistication of the PMS can range from a simple paper-only database of information, to a user-designed spreadsheet, to a highly developed computer data system. Jurisdictional needs and budgets will have to be considered when determining the level of sophistication to pursue.
A PMS is a system that combines components and processes to generate suggestions to the user. The components are generally subdivided into network level (big picture) and project level (focused perspective) items. Examining the network level shows information such as the system’s inventory. This includes facility locations, surface types, past construction and maintenance activities, budgetary resources, and system conditions and goals.
At the project level, project limits, individual distress surveys, project budgets, engineering information, project designs, and permitting and right-of-way requirements are documented. All of these data are processed by the PMS to generate recommendations. The recommendations are then analyzed and reviewed to determine their effect on the system and their usefulness in helping to reach pre-established goals. This process is frequently iterative in nature as results are studied and alternatives explored.
In its highest form, that of a computer database, a PMS will generate reports, charts and tables. The reports may include predictions of future conditions and budgetary needs, historical conditions, and it may offer prioritization strategies. Charts or graphs and tables can be useful in summarizing the information from the reports in a format specified by the user.
Decision Making Tool
When a road system is viewed from a holistic perspective, it can be constructed, maintained and rehabilitated efficiently. To achieve the goal of building and maintaining a cost-effective and reliable road system, current pavement conditions, future maintenance and rehabilitation needs, anticipated new construction, and estimated financial resources are blended with historical conditions, and construction and maintenance activities into a decision-making system designed to assist engineers and planners in using and maintaining resources.
Typically when a PMS is implemented, it can be an invaluable tool in deciding where and when pavement construction, maintenance, and rehabilitation efforts should occur. When well done, a PMS helps to remove individual subjectivity from the process and to produce unbiased decisions. And it improves the overall quality of the road system while extending the available dollars for the system.
|Dave Johnson is a Regional Engineer for the Asphalt Institute.|