There are many factors that are considered in the process of selecting an appropriate treatment for a pavement. These include pavement age, condition, traffic levels, expected future plans, as well as available funding and agency policy. At the network level, a general relationship exists between pavement condition and pavement age. For a properly constructed new pavement, the only treatments that are required are routine maintenance. Then, as the pavement ages, it may become a candidate for preventive maintenance, rehabilitation and eventually reconstruction. The purpose of this chapter is to provide guidance on treatment selection. The first step in determining the appropriate maintenance treatment is determining, based on the life cycle and pavement condition index of the existing pavement, a maintenance strategy. The most appropriate maintenance strategy for a treatment applied to a relatively new pavement differs from the strategy for a treatment being applied to a pavement nearing the end of its life cycle. Figure 1 illustrates the treatment strategies employed based on the condition index of the existing pavement.

Once an appropriate strategy has been chosen, a specific maintenance treatment must be selected to address the specific distress mechanism for the pavement. The most important factors to consider when choosing a maintenance treatment include:

1.Will the treatment address the distresses present? (i.e., Will it work?)
2.Can the required preparation for the treatment be carried out?
3.Is the treatment affordable and cost effective?
4.Will the treatment be performed before the situation being addressed changes?

SELECTION PROCESS

There are three basic steps in the maintenance treatment selection process. These steps include:

1.Assess the existing conditions.
2.Determine the feasible treatment options.
3.Analyze and compare the feasible options with each other.

Assess the Existing Conditions

The first step of the treatment selection process is to perform an evaluation of the existing conditions. This evaluation can be broken down into three processes, which include:

1.Visual site inspection and/or inspection of project information from a database and/or records.
2.Testing of the existing pavement.
3.Define the performance requirements for the treatment.

Any field distress, manual may be used to identify pavement distress mechanisms.

It is helpful to assess pavements using a pavement assessment form of some kind. A well-developed form promotes uniformity in the assessment process. The reviewer should fill out the pavement assessment form, on site, for each pavement being considered for treatment. Figure 2 (2) illustrates an example of a pavement assessment form .

Determine the Feasible Treatment Options

Once the pavement condition has been quantified, test results collected and analyzed, and other available data are reviewed, feasible treatments can be identified. In this context,easibility?is determined by a treatment''s ability to address the functional and structural condition of the pavement while also meeting any future needs. Note that feasibility is not a function of affordability, because at this stage of the selection process the primary purpose is to determine what treatments might work. Figure 3 illustrates the Caltrans matrix for treatment options while Figure 4 illustrates an alternative maintenance treatment matrix.

Once the feasible options have been determined, the limitations of each of the options should be taken into account in relation to its suitability vs. the other feasible options. Treatment limitations are imposed by such factors as deflection, pavement, curvature, roughness and permeability. The most inexpensive option that satisfies the maintenance requirements within its limitations should be considered first. At this point, a life cycle analysis or other cost effectiveness measure should be made as discussed in the next section.

Select the most suitable treatment that satisfies technical performance requirements in the most cost effective manner.

ANALYZE AND COMPARE THE FEASIBLE TREATMENT OPTIONS

It is likely that there will be several treatments that are identified as feasible. In comparing these different treatments, thought should be given to the treatment placement cost, the life of the treatment and whether or not the treatment extends the life of the pavement. Additional factors to consider when analyzing and comparing treatment options are: the cost effectiveness, traffic level, construction limitations, and any factors, such as weather, curing times or local issues, that affect a specific treatment. The most desirable treatment is the one that provides the greatest benefit (whether that benefit is measured in terms of improvement in condition, extension of pavement life, or even, more simply, the life of the treatment) for the lowest life cycle costs. At this point a life cycle or other cost effectiveness measure should be made Reconstruction and maintenance costs rise as a pavement ages. However, if maintenance and/ or rehabilitation (M&R) is carried out too early the costs are prohibitively high. There is an optimum time at which maintenance can be performed to provide the maximum cost effectiveness. Figure 5 shows the cost effectiveness relationship with respect to timing of treatment applications.

Cost Effectiveness

Caltrans calculates cost effectiveness using the Caltrans Pavement Survey (2) system. However, for initial assessment a more simplified approach may be employed (5). A more simplified approach is useful as costs and actual bid prices fluctuate. One simplified approach that can be used is the equivalent annual cost (EAC). In this method an equivalent annual cost is calculated using the following equation (5):

EAC = Unit Cost of Treatment / Expected Life of Treatment(9.1)

At this stage the treatment that meets the performance requirements with the lowest EAC is selected. Other, more complex, methods exist (7) and may be used to calculate whole of life costing.

Choosing from the Maintenance Treatment Matrix

The main issues to consider when selecting between accepted treatments listed in the Caltrans treatment selection matrix are:

1.Performance and Constructability
2.Customer Satisfaction

Performance and constructability factors include the expected life of a treatment, seasonal effects on a treatment, existing pavement conditions, the existing pavement structure and the EAC calculated for the treatment. The contractor''s experience, materials availability and weather limitations should also be taken into account. Each of these items is rated on a scale of 1 to 5. The ratings are based on the fact that a treatment is suitable when it is properly applied; however, project limitations such as climate conditions and material limitations may prohibit proper procedures being followed. In situations where new products or material sources are being introduced, a risk factor should be considered, and a lower rating given to these materials. Similarly, if a contractor is unfamiliar with the new product or new material a lower rating should be given, despite the technical properties of a new product.

Customer satisfaction factors are social factors and include: traffic disruption, skid resistance achieved and noise level. Aesthetic factors such as dust and general appearance are also included.

The rating factor is the weight, based on overall importance to the job success, assigned to a specific treatment''s attribute; the higher the rating the more significant the attribute''s impact on the job''s success. The sum of all rating factors must equal 1.0. Figure 6 illustrates a blank ratings evaluation worksheet while Figure 7 shows an example of a worksheet comparing a chip seal and a microsurfacing for a particular job. Based on the results of the worksheet (Figure 7), a microsurfacing treatment (Total Score of 3.55) would be chosen over the chip seal (Total Score of 2.90) for THIS job. This process should be repeated for all potential treatments that meet the feasibility requirements.