34 aggregates should wear nonuniformly; that is, they should not become rounded or polished smooth under traffic. Because the rate of aggre- gate polishing is closely related to the types of minerals the aggregates contain, a high percentage of hard mineral grains is desirable in the aggregates to provide polishing resistance. Also, asphalt pavement wearing surfaces often exhibit dissimilar friction characteristics under similar traffic conditions, whether they are constructed with aggregates of different rock types or of the same rock type but from different sources. The purpose of this study was to develop objective and practical methods to assess the polishing–abrasion characteristics of carbon- ate and noncarbonate coarse aggregates for use in pavement surface layers. This would provide the Virginia Department of Transportation (DOT) district materials engineers with needed tools to exercise sound judgment in the selection of aggregates for use in surface courses that would permit cost savings where appropriate and pro- vide justification for the use of higher-cost aggregate when necessary. To achieve this goal, samples of coarse aggregate from 10 sources across Virginia DOT’s western districts were evaluated by using laboratory techniques to assess their abrasion–polishing (A-P) ten- dencies. The techniques included petrographic examination, acid- insoluble residue of the carbonate rocks, and two procedures using the Micro-Deval (MD) apparatus to subject the particles to abrasive wear. Also, an image analysis system was used to evaluate the changes in particle morphology resulting from the abrasion testing. BACKGROUND Virginia DOT specifications call for nonpolishing aggregate for use in most surface layers. However, Virginia DOT materials engineers have few methods or tools with which to assess the polishing characteristics of aggregates to distinguish between polishing and nonpolishing aggregates. This is a problem primarily in the western part of Virginia where the predominant source materials for aggregates are carbonate rocks composed primarily of relatively soft minerals that have long been considered to be polishing aggregates. Various tests are used to evaluate aggregates for abrasion resistance. Among these tests, the most common is the Los Angeles test that measures the ability of aggregates to withstand impact and abrasion. However, because of some criticism about its inability to render accurate aggregate degradation results (3–5) the MD apparatus is gradually gaining acceptance by agencies as an alternative abrasion resistance–durability test (6–10). Hossain et al. present a detailed literature review and test results on this topic (5). They conclude that the MD test can accurately differentiate between well- and Modified Micro-Deval Procedure for Evaluating the Polishing Tendency of Coarse Aggregates D. Stephen Lane, Cristian Druta, Linbing Wang, and Wenjing Xue Coarse aggregates in asphalt concrete should be tough and durable to withstand hot-mix asphalt production, transportation, construction, traffic loads, and environmental effects. The morphology of such aggre- gates plays an important role in aggregates’ mechanical properties and influences asphalt pavement skid resistance, an essential characteristic of pavement performance. The predominant aggregate resources in western Virginia are carbonate rocks. The mineral components tend to be relatively soft, and when subjected to abrasive wear under traffic, the aggregate surface polishes fairly rapidly. This situation leads to smoothing of the surface and creates potential safety issues due to loss of surface friction. Considering all aspects, the increasingly popular Micro-Deval (MD) apparatus was used to assess the abrasion–polishing (A-P) resistance of coarse aggregates suspected to show a range of polishing character- istics. Although the conventional focus of the MD test is on attrition or degradation (mass loss) reflecting particles’ durability, such attrition or degradation also induces a polishing effect on susceptible particles and consequently was selected for this study. Hence, a suite of carbonate and noncarbonate coarse aggregates from 10 Virginia sources was tested in the MD with the standard procedure and a cyclical A-P procedure. Also, two-dimensional digital aggregate images, before and after abrasion, were obtained and analyzed with the use of specialized software to characterize morphological parameters (shape, angularity, texture). Testing results showed that wear-resistance aggregate groupings based on the A-P procedures were consistent with the polishing tendency based on lithologic characteristics. Abrasion effects induced by both MD pro- cedures were subjectively discernable. Trends could be perceived in the image analysis data, but the differences were not statistically verified. In both asphalt concrete and hydraulic cement concrete, mineral aggregates are the main component to withstand the traffic and envi- ronmental loads. When used in asphalt pavement surface layers they need to be rough-surface-textured to provide skid resistance as well as resistant to polishing under wear by vehicle tires (1, 2). To main- tain a high level of pavement surface friction (skid resistance), D. S. Lane, Virginia Center for Transportation Innovation and Research, 530 Edgemont Road, Charlottesville, VA 22903. C. Druta, Virginia Tech Transporta- tion Institute, 3500 Research Transportation Plaza, Blacksburg, VA 24061. L. Wang, 301N Patton Hall, and W. Xue, 200 Patton Hall, Via Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061. Corresponding author: D. S. Lane, stephen.lane@vdot. virginia.gov. Transportation Research Record: Journal of the Transportation Research Board, No. 2232, Transportation Research Board of the National Academies, Washington, D.C., 2011, pp. 34– 43. DOI: 10.3141/2232-04