Aggregate Quality Requirements for Pavements (2018)

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3 1.1 Introduction and Background Aggregates constitute 70% to 100% by weight of all bound and unbound pavement layers in road applications and, accordingly, their types and properties significantly affect the end performance. This synthesis topic addresses the need to organize and compress available infor- mation related to different aggregate approval procedures and testing methods for construction of pavement layers. Recent advances were drawn from surveys of state specifications and also gathered from research publications to cover the current aggregate production and source information, agency selection practices, and use of different quality classes of aggregate materials in pavement layer construction, including sustainable practices dealing with recycled and blended aggregates and locally available and, as appropriate, marginal aggregate sources. Typical value ranges for aggregate quality tests were investigated to assess agency aggregate quality requirements and how they relate to end performance. Transportation agencies have diverse specifications and criteria for qualifying virgin as well as recycled aggregate sources. Sharing this information among the agencies may lead to better pave- ment design and construction practices, with improved resource utilization. Initial design as well as long-term and life-cycle performance requirements of the project can be linked to the quality of the construction materials used. As an example, aggregates with hard minerals and high abrasion/ polishing resistance under traffic are preferred for the construction of wearing surfaces of pave- ments and bridges. Note that particle size distribution or gradation is only determining single particle or aggregate assembly size requirements, which are not quality indicators. The concept of classifying aggregates in terms of quality is described in Figure 1-1 (Meininger and Stokowski 2011). As defined by the ASTM International in ASTM D8, an aggregate is “a granular material of min- eral composition such as sand, gravel, shell, slag, or crushed stone, used with a cementing medium to form mortars or concrete, or alone as in base courses, railroad ballasts, etc.” According to NCHRP Report 453: Performance Related Tests of Aggregate for Use in Unbound Pavement Layers (Saeed et al. 2001), unbound aggregate layers in flexible and rigid pavements generally serve to provide (1) a working platform, (2) structural layers for the pavement system, (3) drainage layers, (4) frost- free layers, and (5) “select fill” material (sometimes as part of the pavement working platform). Figure 1-1 lists unbound aggregate layers on the lower end of aggregate quality requirements where there is room to engineer effective and bulk volume uses of locally available and recycled aggregates. For example, as a working platform, unbound aggregate layers are often constructed on soft, unstable subgrade soils or bases to provide sufficient stability and adequate immediate support for equip- ment mobility and paving operations without developing excessive rutting. In flexible pavements, dense-graded unbound aggregate base/subbase layers serve as major structural components of the pavement system to provide load distribution, that is, dissipation of high wheel load stresses with depth, and ensure adequate support and stability for the asphalt surfacing. In contrast, open-graded C H A P T E R 1 Introduction

4 Aggregate Quality Requirements for Pavements granular layers are constructed in both rigid and flexible pavements for primarily drainage and frost protection purposes. Unbound aggregate base/subbase layers used in rigid pavement structures primarily provide uniform support conditions to the concrete slabs; the structural contribution of such layers is often not the primary design aspect. However, in both the asphalt concrete and Portland cement concrete (PCC) bound layer applications, aggregates play a major role not only in the volumetric design of these layers but also in their strength, stability, and performance. Coarse and fine aggregates are the construction building blocks of any pavement layer, unbound or bound, and are primarily responsible for the load-supporting capacity of a pavement. This synthesis report will focus on different aspects and quality requirements associated with the use of different sources of aggregates for pavement construction purposes. As a result, sig- nificant benefits could be derived from broader application and implementation of major find- ings from this synthesis. The report should be useful to transportation agencies in their efforts to identify, appraise, and use available aggregate sources in the most economical ways for the sustainability of intended roadway applications, especially when the availability of high-quality natural aggregates is decreasing and posing a challenge to many agencies (ACPA 2009, Langer 2011). Such advances will bring sustainability and offer economic and environment-friendly alternatives for road construction. 1.2 Study Approach Agency surveys and a review of research publications were conducted to identify different aggregate quality requirements/specifications and compiled into this synthesis report. Informa- tion was gathered through literature review on state, local, and international practices concerning Quality Application Lower Backfill and Bedding Subbase, Select Material, and Subgrade Improvement Base Course (Unbound and Stabilized) Stabilized (Asphalt, Portland Cement, and Lime-Fly Ash) Dense Graded Open Graded Aggregate Surfaced Roads (Gravel Roads) Chip Seal, Cover Material Portland Cement Concrete Lean Concrete Base (Dense or Open Graded) Structural Concrete Concrete Pavement Hot-Mix Asphalt and Warm-Mix Asphalt Dense Graded Open Graded Drainage and Riprap Higher Filter Aggregates Figure 1-1. Aggregate use and relative level of quality needed (modified from Meininger and Stokowski 2011).

Introduction 5 different aspects of aggregate quality requirements to satisfy desired pavement performance. The survey questionnaire had separate parts relevant to different aggregate quality requirements and approval procedures. The questionnaire was purposely designed to be comprehensive and at the same time brief, in an attempt to increase the survey response rate. The information was requested to encompass all engineering aspects highlighted in the previ- ous introduction and background section, primarily in the following categories: (a) aggregate selection process/guidelines for virgin, marginal, nontraditional as well as recycled, and blended aggregate sources; (b) the processes that are followed in controlling the quality of different sources of aggregates for pavement applications, with special focus on material properties and testing techniques/ranges; (c) current practices, innovations, and provisional standards that may allow the use of recycled, marginal aggregate sources for construction of pavement layers; (d) aggregate quality improvement techniques such as stabilization and blending that may allow the use of non- traditional large size and marginal aggregates; and, finally, (e) aggregate quality-related pavement distresses as well as environmental and performance concerns related to the use of recycled and artificial/byproduct aggregate sources. The synthesis survey questionnaire (see Appendix A) on aggregate quality requirements for pavements was sent to all 50 U.S. DOTs and 12 Canadian provincial agencies. The survey was not sent to any U.S. territories such as Guam or Puerto Rico. Figure 1-2 shows a map of the United States and Canada with all the surveyed states or provinces highlighted. In total, 45 state DOTs in the United States and eight Canadian provincial agencies (Alberta, British Columbia, Manitoba, New Brunswick, Ontario, Prince Edward Island, Saskatchewan, and Yukon) responded to the survey questionnaire (see Appendix B). A detailed compilation of all agency responses to the questionnaire is provided in Appendix C. 1.3 Outline of the Chapters This synthesis consists of six chapters: The description and production methods of recycled aggregate sources—including RAP, RCA, and artificial sources such SFS and BFS—are provided in Chapter 2. This chapter also summarizes findings from the survey for the quantities, types, and sources of aggregates used for pavement construction, as well as for the different methods taken by transportation agencies for evaluating use of nontraditional and marginal aggregate sources such as revising specifications and developing new and provisional testing methods. Chapter 3 covers the sampling techniques for quality assurance (QA) and quality checks on aggregates used in field applications. This chapter summarizes important aggregate properties, including mineralogy and physical, chemical, and mechanical properties, which make certain aggregate materials pass agency specifications for pavement applications. Different AASHTO, ASTM, and specialized agency specifications to identify different aggregate properties with a focus on quality and performance are listed. Aggregate shape, texture, and angularity properties affecting hot-mix asphalt (HMA) or concrete layer performance are discussed. Furthermore, the related quality tests are briefly reviewed and listed for importance according to agency practices. Chapter 3 also covers findings from the survey related to different numbers of samples and pro- cedures associated with a certain aggregate source used by each transportation agency. Finally, this chapter highlights currently used and new/emerging quality tests to characterize and accept nontraditional, marginal, recycled, and blended aggregate materials for pavement applications. Chapter 4 provides further details on how differently transportation agencies approve and/or certify different sources of aggregates. Whether an approved list of aggregates is available for use by an agency will be determined. A tiered approach was adopted to study and document different aggregate quality classes associated with specific pavement layer applications; for exam- ple, in the case of Superpave, mixture designs of surface and binder courses from aggregate

6 Aggregate Quality Requirements for Pavements quality perspectives are reviewed. Moreover, material sampling and laboratory testing proce- dures adopted by agencies, aggregate geology and mineralogy assessment, project acceptance criteria and performance requirements, prequalification, disqualification, and requalification techniques are included. Chapter 4 summarizes all the factors and properties that different transportation agencies consider when it comes to aggregate source approval and certification. Chapter 5 reports aggregate-related pavement performance records. The content of this chap- ter is based on findings from an extensive review of published literature, survey responses, and follow-up communications with the responding agencies. As part of the survey scope, it was also determined if an agency documents the overall impacts of using nontraditional, blended, and marginal aggregates. This chapter highlights the effectiveness of aggregate source approval procedures, certification policies, and performance-based specifications established by trans- portation agencies to ensure satisfactory field performance. This includes performance trends of in-service pavements (and experimental test sections) constructed with different aggregate sources. Techniques used by transportation agencies to measure performance of aggregates used in different pavement layers are discussed. Survey results regarding potential savings in cost, energy, and environmental impacts that emerge from using nontraditional and marginal Figure 1-2. Map of the United States and Canada showing all surveyed agencies (AB = Alberta, BC = British Columbia, MB = Manitoba, NB = New Brunswick, ON = Ontario, PE = Prince Edward Island, SK = Saskatchewan, and YT = Yukon).

Introduction 7 aggregate sources are also discussed by presenting performance metrics and case histories from previous and ongoing projects. Chapter 6 includes the conclusion and suggestions for future research, as well as knowledge gaps. This chapter portrays the current state of the practice in aggregate quality requirements for pavement design and construction through a technical assessment of the facts and information presented in Chapters 1 to 5. A short summary of the most important findings in each chapter is presented, and limitations for widespread implementation of promising methods or practices for classifying aggregate based on quality requirements are discussed.