CHAPTER 1—BACKGROUND

There are a number of ways in which the presence of water contributes to damage in asphalt and composite (asphalt surfaces on concrete) pavements. Being able to limit the damage to these pavement structures caused by the presence of water begins with an understanding of the sources of water. Starting with the surface layer, for example, water can enter the pavement structure through cracks, longitudinal paving joints, open-graded mixtures, and poorly consolidated asphalt layers. Water from the surface or outside the pavement structure (e.g., from shoulders or from beneath the pavement structure) can saturate and weaken aggregate base layers and subgrade soils. Moreover, pavement structures that restrict the positive flow of water away from the pavement section (due to such things as improper cross slopes, the buildup of materials or debris at the pavement edge, or the presence of a “bathtub” pavement cross section) can weaken pavement layers, leading to accelerated pavement damage and reduced pavement life. Finally, not adequately accounting for existing environmental conditions can also detract from pavement performance as a result of the presence of moisture. Examples of potentially adverse environmental effects include insufficient structural depth to account for freeze-thaw conditions, high water tables, perched water tables, or water trapped between poorly bonded or unbonded layers.

To overcome some of these moisture-related performance issues, various recommendations have been proffered that are predicated on three critical components: 1) keeping water out of the pavement, 2) making the paving materials less susceptible to moisture damage, and 3) removing water from within the pavement structure. Some of the guidance in each of these areas is available from the references below:

• Seal the pavement and minimize moisture infiltration (Peshkin et al. 2011; Gransberg 2010; Decker 2014).
• Reduce moisture sensitivity of paving materials:
  • – Reduce and control the mixture air void content (Kanitpong, Charoentham, and Likitlersuang 2012; Chen, Lin, and Young 2004).
  • – Include binder additives (e.g., hydrated lime and antistripping agents) to increase asphalt mixture resistance to moisture damage (Alavi et al. 2012; Solaimanian and Chang 2011; Santucci 2010; Kanitpong and Bahia 2008).
• Provide an adequate pavement drainage system and maintain the drainage system to ensure quick water removal (Cui et al. 2009; Hall and Crovetti 2007; Al-Qadi et al. 2004; Christopher and McGuffey 1997).

While there is an extensive number of references related to crack and surface sealing, asphalt mix design, the use of asphalt binders, drainage systems, practices for mitigating freeze-thaw damage, and so on, there is no single document addressing issues related to damage caused by water. NCHRP Project 01-54 was initiated to provide a concise, practical guide with accompanying training materials and technical tools to facilitate access to effective strategies in minimizing damage due to the presence of water in asphalt and composite pavements. The following objectives for NCHRP Project 01-54 formed the basis for the work:

• Develop guidelines detailing strategies to limit damage to flexible and composite pavements due to the presence of water.

• Assemble a 1-day training course for practicing engineers on the use of the guidelines.
• Develop a stand-alone web-based application to provide easy access to the guidelines content.
• Prepare a webinar covering the project content.

WORK APPROACH

The work was divided into two phases. The primary objective of the first phase was to collect information on the practices and experiences of state highway agencies (SHAs) and industry in mitigating damage in asphalt and composite pavements due to the presence of water. This information was collected through a detailed literature search/review and an online survey (including follow-up questions, as needed) with SHAs and industry personnel.

The literature search/review focused on recent or on-going studies examining the following topics:

• Material selection and testing (e.g., asphalt additives, asphalt mix design, aggregate base, treated base, and subgrade soils).
• Pavement drainage (e.g., design process, drainage systems).
• Pavement structure (e.g., pavement type selection, thickness design).
• Climate impacts (e.g., freeze-thaw, seasonal variation of in situ materials).
• Pavement performance (e.g., modeling, nondestructive testing, field testing).
• Construction specifications (subgrade soils, pavement structure, shoulder, and drainage systems).
• Preservation and rehabilitation (drainage systems and pavement structure).

Forty-five publications were reviewed and organized by the topics identified above; the review also compiled American Association of State Highway and Transportation Officials (AASHTO) and ASTM standards, agency and industry plans, and other documents relevant to the topic.

Two online surveys were used to gather information from practitioners, one for SHAs and the other for industry. Both surveys included questions about experience and practices for mitigating damage due to the presence of water. The surveys were organized to solicit information about experience in mitigating damage, roadway geometry requirements, drainage design details, pavement structural design requirements, material selection, pavement condition assessment, construction practices, drainage and pavement preservation and rehabilitation treatments, and an overall assessment of key activities for mitigating damage in asphalt and composite pavements due to the presence of water.

Together, information and recommendations gained from the literature review and from the surveys served as the basis for the development of the Guidelines document and the accompanying training and outreach materials.

OVERVIEW OF REPORT

This report provides background information on the development of the Guidelines document and the accompanying training materials and web application. Chapter 2 describes in more detail the work approach that was employed, with a focus on each specific product. Chapter 3 provides a discussion of the contents of the Guidelines document and other key products, while Chapter 4 provides an overall summary and describes the implementation benefits and barriers and recommended implementation activities.

Seven appendixes are included in support of this report. An annotated bibliography documenting the results of the literature review is included as Appendix A. The blank agency survey is included as Appendix B and the blank industry survey is included as Appendix C. The results from the thirty-nine responding highway agencies in the United States and Canada are summarized in Appendix D, and two example agency checklists for pavement design are presented in Appendix E. The results from the 12 responding industry organizations (representing asphalt and concrete pavement associations and material suppliers) are provided in Appendix F. Finally, the summarized results of the highway agency and industry survey responses are presented in Appendix G.

The Guidelines document and all accompanying training and outreach materials are available separately from NCHRP.