Pavement Remaining Service Interval Implementation Guidelines

CHAPTER 2. RSI CONCEPT OVERVIEW

CONSTRUCTION NEEDS PROCESS

The basic process used to determine future pavement construction needs is illustrated in figure 1. Most pavement construction activity planning is based on an annual fiscal time cycle used by an agency. The steps shown in this figure are cyclical and depend on the time cycle appropriate to the type of pavement asset. The process starts with input data that are fed into the expectancy model to predict future changes in the construction trigger models. The outputs from the predictions are used to select the most appropriate construction strategy, which is used to develop construction plans and specifications. The feedback cycle starts with documentation of the actual condition observed over time as well as the actual construction activities performed. Monitoring measurements provide updated inputs for the next planning cycle and also refine expectancy models.

Figure 1. Flowchart. Future pavement construction needs process.

Within the context of the process illustrated in figure 1, the fundamental elements required to replace the existing RSL terminology with the new RSI terminology include the following:

• A controlled vocabulary to define pavement construction events.
• A common basis for when the future construction event is needed.
• How future needs are determined to differentiate between different levels of
  business decisions.
• The location and extent of the needed treatment.

The logic of this structure is based on separating the definitions of what future construction event is needed from how the need is determined.

Construction Event Terminology

The objective of construction event terminology is to uniquely define what type of predicted future construction event is needed. This vocabulary is needed to describe the construction treatments to promote database integration and increase levels of aggregation at local, district, State, and national levels. Moreover, the terminology requires the identification of three attributes: time when a treatment is needed, type of construction treatment, and reason for the construction treatment.

The time (or the year) when a treatment is needed is specified since this is the basis for budget planning. This is meant to replace prediction models based on traffic applications. Traffic application rates used in the modeling process need to be converted to a time basis. Converting traffic application rates to a time basis is a complex process based on considering the design lane (which receives the most truck loadings), multilane facilities, damaged lanes (which are the lanes in the worst condition), and other local factors that influence pavement damage from vehicle and environmental effects.

The following examples highlight definitions of construction events based on the expanded paradigm of common pavement improvements included in many pavement management systems (PMSs):

• Crack sealing: Application of sealants in surface cracks.
• Joint sealing: Application of sealants in preformed joints.
• Surface treatment: Application of a layer of material of intended uniform thickness less than 0.5 inches (12 mm).
• Thin overlays: Application of a material layer of intended uniform thickness greater than 0.5 inches (12 mm) and less than 2 inches (50 mm) and which does not increase the thickness of the bound material layers by more than 25 percent.
• Thick overlays: Application of a material layer of intended uniform thickness greater than 2 inches (50 mm) or increases thickness of bound pavement layers by more than 25 percent.
• Concrete pavement restoration (CPR): Application of full- or partial-depth joint repairs, slab replacement, dowel bar retrofit, or other restoration treatments.
• Grinding: Removal of portions of the surface layer of a pavement without placement of a new material layer.
• Grooving: Cutting grooves in the surface of a pavement without application of a new material layer.
• Milling: Removal of bound portions of a pavement that is associated with placement of a new material surface layer.
• Undersealing: Injection of cementitious material underneath bound pavement layers.
• Reconstruction: Removal and replacement of all bound layers of an existing pavement.
• Addition of lanes: Construction of additional lanes to the facility designed to permit greater traffic capacity.
• Addition of tied shoulders: Removal and construction of portland cement concrete (PCC) shoulders tied to adjacent PCC pavement structures.
• Shoulder widening: Extending the width of the existing shoulder with use of similar materials.

The definitions only describe what type of construction treatment is being applied to the pavement. An indication of the reason(s) why a future construction event is predicted is needed to complete the definition since pavement improvements are based on different needs. The following examples highlight controlled terminology that can be used to explain the basis of predicted time to a threshold event:

• Roughness exceeds y in terms of International Roughness Index (IRI). The y value is the generally accepted limiting value for pavement roughness in terms of IRI.
• Cracking exceeds the limit requiring major rehabilitation.
• Cracking exceeds the limit requiring reconstruction.
• Rut depth correction requires major rehabilitation.
• Rut depth correction requires reconstruction.
• Skid resistance reaches the safety limit.
• PCI reaches threshold x. For systems based on a PCI-based index, x represents the various thresholds between rehabilitation and reconstruction.
• Pavement serviceability rating (PSR) reaches x. For systems still using the PSR/Present Serviceability Index (PSI) concept, x is the terminal serviceability value considered by the agency appropriate for the route.

Typically, an agency will develop a decision matrix to use as part of its pavement management process. This matrix will associate types of pavement deficiencies requiring construction actions with types of construction best suited to correct them. For example, if the roughness exceeds the IRI threshold, then a typical approach would be placing an overlay to correct the roughness.

RSI IMPLEMENTATION FRAMEWORK

The framework for implementing the new RSI terminology is illustrated in figure 2. The key components of the framework that must be addressed by SHAs to develop, implement, maintain, and update a construction needs analysis methodology that includes generic agency and RSI implementation issues.

These components should be tailored to the individual agency requirements related to budgeting process, types of pavements in use, common types of pavement deficiencies requiring correction, construction contract instruments, and other considerations.

The generic agency issues address the establishment of the agency’s RSI protocol, the identification of an RSI coordinator, and the dissemination of the RSI concept within the agency. These issues only need to be addressed once, with periodic monitoring and revising to ensure they are still appropriate; however, they are vital to the success of an agency’s RSI program. These generic agency issues are discussed in more detailed in the appendix.

Figure 2. Flowchart. Agency RSI implementation.

The RSI implementation issues focus on a step-by-step approach that is necessary to successfully establish the RSI concept within the agency. These RSI implementation steps are discussed in the following two chapters of this report.