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Limiting Damage to Flexible and Composite Pavements due to the Presence of Water: Guidelines (2025)

Chapter: 2 RESEARCH APPROACH

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Suggested Citation: "2 RESEARCH APPROACH." National Academies of Sciences, Engineering, and Medicine. 2025. Limiting Damage to Flexible and Composite Pavements due to the Presence of Water: Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/29201.

CHAPTER 2—RESEARCH APPROACH

This chapter presents the approach used in developing the three project deliverables: the Guidelines document, the training materials, and the web-based application. The Guidelines document is the primary product delivered in this research, but it is closely integrated with the training materials and the web-based application. The approach to developing each of these is briefly discussed in this chapter.

GUIDELINES DOCUMENT

As described in Chapter 1, the Guidelines document was developed based on the information obtained from the literature search and the agency and industry surveys. It includes best practices for limiting damage due to water in asphalt and composite pavements arranged according to design features (e.g., geometrics, drainage, and pavement structure), materials (e.g., material properties, mixture design, binder selection), construction (e.g., subgrade treatment, compaction requirements, testing, treatment to minimize reflective cracking), preservation (e.g., activity or treatment type and timing), and rehabilitation (e.g., maintain conditions, upgrade or address existing conditions, reflective cracking treatments), with accompanying appendices. Table 1 provides an outline of the technical content of the Guidelines document, which follows the different types of projects where pavement drainage is considered: new design, maintenance and preservation, and rehabilitation.

Table 1. Outlined content of the Guidelines document.

Chapter	Content
Introduction	Purpose – provide guidelines, practices, plans, and specifications for limiting damage to asphalt and composite pavements due to water Background – factors contributing to distress, impact on pavement performance, readily available information; however, no currently available guide document Scope – contents of guide document, case studies, design procedures, specifications, construction practices Audience – design, construction, and maintenance engineers and technicians at state highway and local transportation agencies Document organization – chapter number, title, and description How to use this guide and stand-alone application – summary of guide content and summary of functionality of stand-alone application Related documents
Sources of Water	Surface infiltration Capillary action and vapor movements Changes in depth to water table Seepage from high ground Pavement edge
Damage Mechanisms	Material softening/weakening Frost heave Stripping Pumping Moisture-related distress types in asphalt concrete and composite pavements

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Design Features	Roadway geometric design – Cross-slope – Longitudinal slope – Length of drainage path – Curb and gutter, shoulders Subsurface drainage – Need for subsurface drainage (e.g., collect and drain water from the surface, remove subsurface water, minimize erosion, intercept water, impact of climate zone, traffic, and subgrade permeability) – Types of subsurface drainage – Summary of drainage design procedures [e.g., rational method, Drainage Requirements in Pavements (DRIP), PAVDRN, others] – Design considerations (e.g., pavement type, infiltration rate, time to drain, grades, rain/storm events, subgrade conditions) – Subsurface drainage considerations (e.g., drainable base, edge drains, underdrains, ditches, daylighted base) Pavement design – Summary of pavement design procedures (new and rehabilitation) – Subgrade treatments (e.g., cement-treated, lime-treated) – Base type selection (e.g., aggregate, asphalt- and cement-treated) – Asphalt- and composite pavement-specific design considerations (e.g., reflective cracking mitigation) – Surface type considerations (e.g., dense-, open-, gap-graded) – Shoulder design considerations Freeze-thaw considerations – Freeze-thaw mechanism (subfreezing temperatures, presence of moisture, and frost-susceptible soils) – Heaving potential (uniform versus differential) – Methods for mitigating (e.g., increase depth, remove and replace with suitable materials, capillary break, load restrictions)
Material Type and Selection	Pavement structure – Base material types and properties (e.g., lean concrete, cement-treated, asphalt-treated, granular base) – Asphalt mixture properties and design Geosynthetics Drainage systems – Backfill material, pipe, outlets, headwalls, geotextiles, and so on – Laboratory testing procedures and recommended criteria
New Construction	Pavement layers – Subgrade treatment requirements (based on material properties) – Base placement and compaction – Asphalt placement and compaction requirements (e.g., tack coat, longitudinal joint compaction, construction joints) – Concrete construction requirements (e.g., joint details) – Construction quality control and acceptance testing requirements and monitoring procedures Drainage systems – Excavation, placement, compaction, and so on – Drainage system inspection – Construction quality control and acceptance testing requirements and monitoring procedures Roadway widening – Maintaining drainage between existing and new construction – Addressing permeability differences

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Maintenance and Preservation Strategies	Pavement – Reducing moisture infiltration by crack sealing and filling, patching, other preservation treatments Drainage – Cross slopes – Ditches – Subsurface drainage
Rehabilitation Treatments	Pavement – Treatment type, timing, and effectiveness – Pretreatment application requirements (e.g., tack coat, crack sealing) – Techniques for mitigating/addressing reflective cracking in composite pavements and asphalt overlays – Construction considerations Drainage rehabilitation – Retrofitted edge drains – Shoulder reconstruction (better-draining material) – Installation of new or replacement drainage system – Construction considerations
Benefits and Barriers	Summary of recommended practices Benefits of implementation Potential barriers of practices and features
Appendix A. Standard Plans	Drainage details Pavement cross-sections
Appendix B. Standard Specifications	Materials specifications Testing and evaluation requirements Construction specifications
Appendix C. Agency Fact Sheets	Agency fact sheets to describe: Description of practice Where and when to use Limitations Expected costs and benefits

The Guidelines document is packaged as a stand-alone report and is available separately from NCHRP. The Guidelines document was configured in a standard practice format such that it could be readily implemented by AASHTO, if approved after consideration.

WEBINAR

To help advance and promote the Guidelines document prepared under the study, a set of PowerPoint training materials was developed to support the delivery of a 90-minute webinar (including time for a question-and-answer session). This webinar could be presented through Transportation Research Board (TRB) or other organizations as a first step in the overall implementation of the Guidelines document.

TRAINING COURSE

A set of training materials was also developed for a 1-day, in-person workshop that focuses on the details of the Guidelines document. These materials cover the contents of the Guidelines document and feature a PowerPoint slide deck, an Instructor Guide, and a Participant Workbook,

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all of which were developed in general accordance with the protocols used by the NHI for consistency purposes only. The training course consists of the following eight modules:

Module 1 – Introduction
Module 2 – Sources of water and distress mechanisms
Module 3 – Design features
Module 4 – Material type and selection
Module 5 – New construction
Module 6 – Maintenance and preservation strategies
Module 7 – Rehabilitation strategies
Module 8 – DRAIN tool

STAND-ALONE WEB-BASED APPLICATION (DRAIN)

The project included the development of a web-based application, or “app,” in order to facilitate the broad use of the Guidelines document. The app, identified as DRAIN, guides the user through an assessment process in much the same manner as a user would access and run through the Guidelines. The user first indicates whether their project involves a new or an existing pavement and whether it is an asphalt or composite cross section. Additional inputs for new design include the type and characteristics of the subsurface soil, the climate in which the project is located, traffic levels, and sources of water. For existing pavements, the primary set of additional inputs includes the types of distresses present.

The primary output from DRAIN is whether subdrainage features are needed. But it bears mentioning that a key feature of the output is that the recommendations refer back to the Guidelines document, where additional information can be found.

The following are some of the key elements of DRAIN:

Accessible on all devices and operating systems.
Takes inputs about specific projects, materials, and drainage parameters.
Provides recommendations on drainage strategies based on user inputs
Provides links to additional guidance.

The DRAIN tool is available on the National Academies Press website (nap.nationalacademies.org) by searching for NCHRP Web-Only Document 433: Limiting Damage to Flexible and Composite Pavements Due to the Presence of Water: Guidelines.