Quantifying the Effects of Preservation Treatments on Pavement Performance (2018)

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1 Background Pavement preservation provides a means for maintaining and improving the functional con­ dition of an existing pavement segment through application of a preventative and responsive set of treatments that slow deterioration or correct isolated defects and thus defers costly pavement rehabilitation or reconstruction to a later time. While preservation is not expected to increase struc­ tural capacity of the pavement, it can lead to improved performance (e.g., slow cracking, reduce weathering, and attenuate degradation), longer service lives, and reduced life cycle costs (LCC). The FHWA defines preservation as work that is planned and performed to improve or sustain the condition of the transportation facility in a state of good repair, and which does not add capacity or structural value, but does restore the overall condition of the transportation facility (FHWA 2016). The key component of pavement preservation is preventive maintenance, which can extend the useful life of the roadway in a cost­effective manner. Preventive maintenance is not directly associated with a specific treatment; rather, it is associated with the condition of the pavement when the treatment is applied. A preventive treatment that is applied in a timely and proper manner is expected to have an effect on pavement performance in one of the following ways (Applied Pavement Technology, Inc. 2015): • Preventing or slowing down infiltration of moisture and incompressible material by applying treatments such as crack or joint seals, membrane seals, and certain patches. • Providing protection against aging and oxidation of bituminous surfaces by applying treat­ ments such as surface seals for asphalt surfaces. • Restoring surface integrity by applying treatments such as surface seals and partial or full depth slab repairs. • Improving surface texture by applying surface seals, thin asphalt overlays, and diamond grinding. • Reducing pavement roughness by applying treatments such as thin asphalt overlays and diamond grinding. The effects of preservation treatments are measurable and should be reflected in the overall models of pavement performance. Figure 1 shows a typical performance curve that illustrates the effects of applying preventive maintenance treatments. In addition to expected improving overall pavement performance when compared to that of pavement without treatment, pres­ ervation treatments could delay the need for rehabilitation as the threshold for rehabilitation would be reached later in time. While the effects of preservation are easy to illustrate, their implementation and measured benefits are not as easy to quantify for the following reasons: • There are questions about the effect of preservation on commonly used measures of pavement performance, such as ride quality and cracking. C H A P T E R 1 Introduction

2 Quantifying the Effects of Preservation Treatments on Pavement Performance • Preservation has not always been included as part of the pavement management systems used by highway agencies (also referred to simply as agencies) and it has not always been possible to distinguish between pavements that have and have not received preservation treatments. • The practice of preservation in most agencies has not always been consistent from district to district, and has varied over time as the interests of individuals and funding have changed. • The benefits of preservation are highly variable; they are affected by existing pavement condition, treatment type, material quality and consistency, quality of construction and workmanship, environment, and traffic. Variations in these factors could affect the benefits of preservation. Because of the these reasons, there was a clear need to identify and/or develop a common set of pavement performance measures that adequately quantify the effect of preservation on pavement performance, service life, and LCC. To accomplish this, the current generation of performance measures was evaluated to determine whether or not they can capture the effects of preservation treatments or if new measures needed to be developed. Although many highway agencies use performance measures, these measures are generally not used to assess the effect of pavement preservation on performance, service life, and LCC. Incorporating these measures in pavement and/or asset management systems would provide a means for selecting the right preservation treatment at the right time, thereby improving the use of resources. Performance Measures Key consideration in this research was a clear definition of performance measures. Much research has been conducted in recent years in an effort to clearly define performance measures, their attributes, and their uses. For example, NCHRP Report 551 (Cambridge Systematics et al. 2006) defines performance measures as indicators that can be used to measure progress towards a goal and NCHRP Report 708 (Zietsman et al. 2011) defines performance measures as quantifi­ able criteria used to measure progress towards goals. Similarly, performance measures have also been defined as indicators of system effectiveness and efficiency, or more generally as tools to support performance management (Amekudzi and Meyer 2011). Specific to pavements, per­ formance measures have been defined as ways to consistently assess their functional condition (Simpson et al. 2013). Literature also was extensively reviewed to identify the attributes that can be used to evaluate performance measures. For example, NCHRP Report 666 (Cambridge Systematics et al. 2010) identifies four criteria, Performance Based Planning and Programming Guidebook (Grant et al. 2013) Control (Untreated Pavement) Preserved Pavement Immediate Change in Condition Service Life Extension Target Level of Service Improvement in Performance Very Good Condition Good Condition Fair Condition Poor Condition Very Poor Condition Pavement Age Figure 1. Anticipated effect of a single preservation treatment on pavement performance.

Introduction 3 identifies seven criteria, and Natural Resources Management Gateway (U.S. Army Corps of Engi­ neers 2015) identifies 12 criteria against which a performance measure should be evaluated. Many of the criteria in these references are similar, and their differences relate to how the criteria are combined (e.g., a single criteria in one reference may be expressed as multiple criteria in another reference). The following are the main criteria that were considered when recommending performance measures in this project: • Is the measure feasible? In other words, can the measure be obtained or objectively calculated from data collected by agencies at a reasonable level of accuracy and repeatability? Can the measure be used on a broad set of pavement types? • Is the measure understandable? Many measures can potentially be developed or recom­ mended that communicate abstruse aspects of pavements. In order to facilitate widespread implementation of the research results, consideration was given to whether the recommended measures can be used by a wide group of practitioners. • Is the measure useful in decision­making? In order for the measure to be useful in decision­ making, it must, or can be, directly linked to agency practices and reflects the effect of preserva­ tion. For example, structural measures may be linked to agency decisions, but do not capture the defined effect of preservation (i.e., affecting functional but not structural condition). Based on the stated definitions and criteria, pavement performance measures are defined for this research as metrics that quantify the degree of achieving specific goals pertaining to perfor­ mance. Although these measures are often used to assess the current condition of the pavement, they provide a basis for the decisions needed to achieve specific goals for the asset (Cambridge Systematics et al. 2006; Zietsman et al. 2011; Amekudzi and Meyer 2011; Simpson et al. 2013). For a pavement performance measure to provide the basis for decision­making, it must have the ability to be forecasted over time considering that many agencies do not make treatment decisions based on single year evaluations. Therefore, when recommending performance mea­ sures, consideration was given to those indicators for which adequate data could be obtained to develop models as a function of time. Project Objectives and Scope The objectives of NCHRP Project 14­33, “Pavement Performance Measures that Consider the Contributions of Preservation Treatments” were to (1) identify and/or develop pavement performance measures that consider the contributions of preservation to changes in performance, service life, and LCC, and (2) prepare a guide document to facilitate implementation of these measures by state highway agencies. The approach for accomplishing these objectives consisted of the following activities: 1. Gathering/reviewing relevant information. a. Conducting a literature review. b. Conducting an internet survey questionnaire of highway agencies. c. Conducting follow­up telephone interviews of selected state Departments of Transportation (DOT) personnel. 2. Selecting performance measures. a. Establishing criteria for evaluating potential performance measures. b. Applying criteria to potential performance measures using findings from Step 1. c. Selecting recommended performance measures. 3. Evaluating the applicability of the recommended performance measures. a. Establishing a framework for determining preservation treatment contributions and benefits.

4 Quantifying the Effects of Preservation Treatments on Pavement Performance b. Gathering highway agency data and information necessary to carry out the evaluation. c. Assessing the contribution of preservation treatments to performance, service life, and LCC. 4. Developing a guide document to facilitate implementation of the selected measures, based on the findings from the activities listed earlier that provides: a. A step­by­step procedure, including flowcharts and examples, for establishing the initial condition jump and long­term performance for each applicable preservation treatment and for each measure. b. Step­by­step procedures, including flowcharts and examples, for incorporating into the highway agency’s business practices the effects of preservation treatment on pavement performance, service life, and LCC. 5. Developing the final report to document the entire research effort. Report Organization This report documents the entire research effort (including the guide document). This report presents the major findings, outcomes, conclusions, and recommendations from the research effort. The information presented in this report has been organized into five chapters. This chap­ ter provides background information, project objectives, and summarizes the approach used for conducting the research. Chapter 2 discusses existing practices, including general trends and major findings from the literature review and survey of state and provincial highway agencies, and recommends a set of performance measures. Chapter 3 details the evaluation process of the applicability of the recommended pavement performance measures, and Chapter 4 describes the process for developing the guide for implementation. Chapter 5 presents summary, conclusions, and recommendations for research. The references cited throughout the report are listed at the end of the report, and the guide document is also included as an attachment to the report. An appendix that presents case studies to illustrate the implementation of the recommended performance measures is also included.