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15 the total mass of the samples (result expressed as a percent- Uncompacted Voids in Coarse Aggregate (Currently age). For Superpave specifications, after the percent of parti- AASHTO TP56), and cles with one or more fractured faces is determined, the aggre- Uncompacted Voids in Coarse Aggregate--Shovel Tech- gates are re-examined for two or more fractured faces. niques (AASHTO T19). ASTM D5821 was only performed on the three gravel sources 2.2.2 Relationship Between Percent included in the nine sources. Because of the limited data col- Coarse Aggregate Fractured Faces lected, ASTM D5821 was excluded from correlation matri- and Performance ces with other test methods and the rutting performance of mixes produced with each of the coarse aggregate sources. Cross and Brown (17) reported on the selection of aggre- Rut testing was performed on the nine mixtures using the gate properties to minimize rutting. The study was based on Superpave Shear Tester and Georgia Loaded Wheel Tester testing conducted on 42 pavements in 14 states; 30 of the 42 (GLWT). The uncompacted voids in coarse aggregate test pavements had experienced premature rutting. Rut-depth (AASHTO TP56) produced the best relationships with the measurements and cores were taken at each site. The cores rutting parameters from all nine mixtures and a reduced data were tested for density, asphalt content, and gradation. The set that had unusual mix properties (2). The results from percent with two crushed faces was determined separately AASHTO TP56 and ASTM D3398 were highly correlated. for the material retained on the 4.75-mm sieve and the mate- The authors recommended uncompacted voids in coarse rial passing the 4.75-mm sieve and retained on the 0.600-mm aggregate (AASHTO TP56) and flat or elongated particles sieve. The uncompacted void content was determined accord- on the 21 ratio to characterize coarse aggregate shape, angu- ing to the National Stone Association flow test, Method A (the larity, and texture. basis for AASHTO T304). Some of the cores were recom- Hand et al. (13) conducted round-robin testing to deter- pacted using the U.S. Army Corps of Engineers (USACE) mine the precision of ASTM D5821. The study was initiated gyratory compactor or Marshall hammer method (75-blow). because of concerns that insufficient fractured faces in the The measured rut depth at each site was converted to a rut- original crushed gravel source used at WesTrack may have ting rate by dividing the rut depth by the square root of accu- contributed to the premature failure of the coarse-graded sec- mulated equivalent single axle loads (ESALs). tions. The materials were collected from cold feed samples Data analysis indicated that none of the aggregate proper- taken during the construction and reconstruction of WesTrack. ties were related to the rutting rate when all of the data were Four materials were included in the study based on the coarse included. The authors felt that when air voids were less than aggregate fractions of (1) coarse blends of Dayton crushed 2.5%, rutting is likely to occur regardless of the other mix gravel produced in 1994 and placed in the tangents; (2) fine properties. Using the data from pavements with in-place air blends of Dayton crushed gravel produced in 1994 and voids greater than 2.5%, a relationship shown in Equation 1 placed in the tangents; (3) coarse blends of Dayton crushed (17) between the percent with two crushed faces in the coarse gravel produced in 1995 and placed in the curve sections; and aggregate and the rutting rate was developed. The relation- (4) the crushed andesite from Lockwood, Nevada, used in the ship produces an R2 = 0.42. Analysis of variance indicated coarse-graded replacement sections. The percent fractured the relationship was significant ( = 0.01). faces of the fine and coarse mixtures placed on the tangent Rut Depth (mm) ESAL = 0.03138 - 0.0025 sections were found to be equal. The actual values (98% one (1) fractured face and 96% two or more fractured faces) (Percent 2 Crushed Faces) exceeded the Superpave requirements for 10 to 30 million design ESALs. The study concluded, "CAA [coarse aggre- Kandhal and Parker evaluated the properties of nine coarse gate angularity] did not have an effect on the rutting perfor- aggregate sources (2). Nine tests were performed to evaluate mance of Superpave mixtures at WesTrack" (13). coarse aggregate shape, angularity, and texture including the A Canadian study was conducted in Saskatchewan to inves- following: tigate the effect of the percent fractured coarse aggregate par- ticles on rutting performance (18). The majority of Saskatch- Index of Aggregate Particle Shape and Texture (ASTM ewan's coarse aggregate comes from glacial gravel deposits. D3398), Aggregates with high fractured face counts are more expen- Image Analysis (Georgia Institute of Technology), sive. Ten pavements ranging in age from 2 to 9 years were Flat and Elongated and Flat or Elongated Particles by evaluated. Rut depths were measured and cores were recov- ASTM D4791, ered within and between the wheel paths. Cores were tested Flakiness Index (British Standard 812), for density, voids filled, asphalt content, coarse aggregate Elongation Index (British Standard 812), fractured face count, and uncompacted void content in fine Percent of Fractured Particles in Coarse Aggregate aggregate. The fractured face count was determined accord- (ASTM D5821), ing to Saskatchewan Standard Test Procedure 204-4. The