Chapter 11: Selecting a Pavement Preservation Treatment

1.0 Introduction

This chapter describes how to choose a pavement preservation strategy to preserve the condition of a highway system and extend its service life. It identifies factors involved in selecting feasible treatment types and presents a means of evaluating those various treatment types to determine which is best suited to specific pavement distresses. Topics related to the materials and procedures used in these treatments are discussed in greater detail in Chapters 2 through 10.

1.1 Determine the Feasible Treatment Options

Once the pavement condition has been quantified, test results collected and analyzed, and other available data reviewed, feasible treatments can be identified. In this context, feasibility is determined by whether a treatment can address the pavement’s functional and structural condition while also meeting any future needs. 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 1 illustrates a matrix of treatment options.

Once the feasible options have been determined, each option is evaluated for suitability. Treatment options may be eliminated by factors such as deflection, pavement, curvature, roughness, and permeability. The most inexpensive option that satisfies maintenance requirements within its limitations should be considered first.

At this point, a life-cycle analysis or other cost-effectiveness calculation should be made. That analysis is discussed in the next section.

Link to PDF of Figure 1: A Maintenance Treatment Matrix

Accessible versions of the matrix are available at:

1.2 Select the Most Cost-Effective Feasible Option

It is likely that there will be several feasible treatments for the existing conditions. To make the final selection, a life cycle or other cost effectiveness calculation should be made. In comparing these different treatments, consider the treatment placement cost, the life of the treatment, and whether the treatment will extend the life of the pavement. Additional factors to consider when analyzing and comparing treatment options include:

Cost effectiveness
Traffic conditions
Construction limitations
Weather
Curing times
Specific local issues

The most desirable treatment is the one that provides the greatest benefit for the lowest life-cycle costs – that is, whether that benefit is measured in terms of improving pavement condition, extending the pavement’s service life, or extending the life of the treatment.

Reconstruction and maintenance costs rise as a pavement ages. However, if maintenance and rehabilitation (M&R) are carried out too early, the costs are prohibitive. There is an optimal time at which maintenance can provide maximum cost-effectiveness. Figure 2 shows a typical cost- effectiveness relationship with respect to timing of treatment applications.

Chart shows that total cost falls with optimal timing of maintenance and rehabilitation.

Figure 2: Treatment Timing Versus Cost (3)

1.2.1 Cost Effectiveness

A simple way to estimate the cost-effectiveness of a proposed treatment is to calculate the equivalent annual cost (EAC) using the following equation (82):

EAC = Unit Cost of Treatment / Expected Life of Treatment

At this stage, the treatment that meets the performance requirements with the lowest EAC may be selected. Other, more complex, methods exist (140) and may be used to calculate whole-life costing.

1.2.2 Choosing from the Maintenance Treatment Matrix

The main factors to consider when selecting between acceptable treatments listed in the treatment selection matrix are:

Performance
Constructability
Customer satisfaction

Performance and constructability factors include: the expected life of a treatment, seasonal effects on a treatment, existing pavement conditions, 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 field reviewer or local supervisor assigns ratings based on his or her individual experience and 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 you from following proper procedures. 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, smooth riding surface, noise level, dust, and general appearance. These factors allow a feasible option to be evaluated on factors other than cost and performance. Under some conditions, the most cost-effective and long-lasting treatment may not be the right treatment for the pavement.

The rating factor is the weight assigned to a specific treatment’s attribute based on overall importance to the job success. The higher the rating, the greater the impact of the treatment’s attribute on the job’s success. The sum of all rating factors must equal 1.0. Since the maximum scoring factor for each attribute is 5.0, the maximum possible score for any alternative treatment must also be 5.0 – 5 times the sum of the rating factors. Figure 3 illustrates a blank ratings evaluation worksheet; Figure 4 shows a worksheet comparing chip seal and microsurfacing for a particular job. Based on the results of the worksheet (Figure 4), a microsurfacing treatment (Total Score of 3.55) would be chosen over the chip seal (Total Score of 2.90) for this job. This rating process should be repeated for all potential treatments that meet the feasibility requirements.