Trb superpave Abstracts 2002

ABSTRACT

In recent years, a significant percentage of coarse-graded Superpave asphalt mixtures have exhibited tender mix behavior. While the underlying causes of the phenomenon are not well understood, many experts believe the main cause of the tender zone problem is related to the amount of fluids, particularly excess moisture, in the asphalt mixture.

Unfortunately, the accurate determination of moisture in an asphalt mixture is considered by some asphalt technologists to be a difficult prospect. The purpose of this research was to determine if the tender mix behavior exhibited by some coarse-graded Superpave mixtures was related to moisture content, and to develop procedures to accurately measure moisture in an asphalt mixture. The research indicated that conventional oven drying (110ºC) was an acceptable alternative to the standard distillation procedure (ASTM D1461). The use of the microwave oven procedure for determining moisture content also appeared acceptable, although in this research there was a significant problem with the glass containers breaking. The best sampling container for determining moisture content after a storage period was a 4-liter aluminum paint can. When the paint can was used and sealed, the moisture content after 72 hours of storage at room temperature was statistically equal to the moisture content determined immediately after sampling the asphalt mixture. Other containers studied (paper grocery bag and plastic oven bag) indicated lower moisture content values after storage and a consistent loss of moisture the longer the sample was stored.

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Establishing Variability for Hot-Mix Asphalt Construction in Arkansas

Kevin D. Hall, Associate Professor

Department of Civil Engineering

University of Arkansas

4190 Bell Engineering Center

Fayetteville, AR 72701

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Stacy G.Williams, Research Assistant Professor

Department of Civil Engineering

University of Arkansas

700 W. Research Center Blvd.

Fayetteville, AR 72701

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[e-mail]

ABSTRACT

The Arkansas quality control / quality assurance (QC/QA) specification for hot mix asphalt (HMA) construction was initially developed from data and experience gained with the Marshall method of mix design. The implementation of Superpave, coupled with the initiation of the largest asphalt construction program in the state’s history, resulted in questions relating to the suitability of the QC/QA specification. Research was undertaken to revise the existing program or create a new specification. The first step in the effort was to establish typical HMA construction variability, in terms of the pay factors used in Arkansas: air voids, voids in the mineral aggregate (VMA), binder content, and field density.

Six projects were randomly sampled and tested by three operators: the contractor, the agency, and the research team. Six specimens were prepared by each operator at each of four testing times within each project. The results of the testing showed that the six projects bracketed a wide variation in mixture quality as defined by the HMA properties. The testing data was normally distributed, validating a typical assumption regarding construction. Analyses showed testing variability among the three operators could be absorbed into the overall variability of test properties, rather than being considered a distinct factor. Three levels of HMA quality were identified by the mean and standard deviation of test data. These quality levels are expected to form the basis for any revision to the existing QC/QA system, or for the development of a new QC/QA system for Arkansas HMA construction.
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Measurements of Aggregate Texture and its Influence on HMA Permanent Deformation

Thomas Fletcher1, Chandan2, EyadMasad3, and Krishna Sivakumar4
1 Graduate Research Assistant

3 Assistant Professor (Corresponding Author)

Department of Civil and Environmental Engineering

Washington State University

Pullman, WA 99164

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2 Graduate Research Assistant

4 Assistant Professor

Department of Electrical Engineering and Computer Science

Washington State University

Pullman, WA 99164

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ABSTRACT

Aggregate shape has great effects on the performance of asphalt mixes. Building well performing asphalt pavements requires developing methods to rapidly and accurately quantify the different properties of aggregate shape, and most importantly, relate these properties to performance. Aggregate texture has been identified by several studies to be the shape property that has the most significant influence on asphalt mix performance. This study presents a new procedure for measuring aggregate texture using image analysis techniques. The main advantages of this new procedure are the ability to capture the different sizes of texture elements, separating the true texture from the color variations on aggregate surface, and applicability to characterize fine and coarse aggregates. The developed procedure is used to measure texture for a wide range of fine and coarse aggregates, and the results are compared with asphalt mix performance. The analysis shows that the developed procedure yields detailed information on aggregate texture in a short time. The texture measurements have very good correlation with the resistance of asphalt mixes to permanent deformation measured in the laboratory using different wheel tracking devices.

KEYWORDS: Aggregate, Texture, Image Analysis, Asphalt Mix, Performance
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Simple Performance Test for Permanent Deformation of Asphalt Mixtures

Kamil E. Kaloush, Ph.D., P.E. (corresponding author)

Assistant Professor

Arizona State University

Department of Civil and Environmental Engineering

PO Box 875306, Tempe, AZ 85287-5306

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Matthew W. Witczak, Ph.D., P.E.

Professor

Arizona State University

Department of Civil and Environmental Engineering

PO Box 875306, Tempe, AZ 85287-5306

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e-mail: [e-mail]