The ability of different operators to obtain similar results when performing laboratory tests on the same material is vital for producing accurate testing results. By conducting trials in triplicate for each of three different testing methods, a measurement of the bulk specific gravity (Gmb) of compacted hot-mix asphalt concrete (HMAC) cores was obtained. An analysis of the variability between operators was investigated using a total of almost 1,300 test results, using HMAC sampled from six projects in Arkansas. Three methods were used to determine the bulk specific gravity of compacted HMAC samples, including saturated surface dry (SSD) (as per AASHTO T166), height and diameter (as per AASHTO T269), and vacuum sealing (using the Corelok vacuum sealing device). In almost all cases, Gmb values determined using the height and diameter method were statistically different from those determined using the SSD and Corelok methods; further, statistical differences were noted in paired analyses between the SSD and Corelok methods. The Corelok method exhibited a lower degree of variability than the other two methods used, based on the standard deviation of test results obtained by different operators. In direct comparison with the SSD method, the Corelok exhibited a lower variability (standard deviation) in 81 percent of the cases. Overall, the Corelok method appears to offer a viable alternative for determining the bulk specific gravity of compacted HMAC. However, agencies seeking to use the Corelok must consider the effect of an apparent shift in Gmb values obtained on resulting HMAC volumetric and compaction properties.

Much attention has been given to the determination of bulk specific gravity (Gmb) of compacted hot-mix asphalt (HMA) specimens. For relatively open-graded HMA mixtures, such as those produced by Superpave® and stone matrix asphalt design methods, perceived potential shortcomings in traditional test methods may be pronounced. Recently, a new device was introduced for measuring Gmb that features the use of gamma-ray technology. To evaluate the efficacy of the device, 221 compacted HMA specimens were tested with three test methods: saturated surface dry (SSD) (AASHTO T-166), vacuum-sealing (Corelok), and gamma-ray technology (CoreReader). Each specimen was tested three times in each of the three methods. The specimens represented field-sampled and laboratory-prepared mixtures, 12.5-mm and 25-mm nominal maximum aggregate sizes, and a variety of aggregates typically used in Arkansas. Test results indicated that statistically significant differences exist between mean Gmb-values generated by each of the three testing methods. In general, the vacuum-sealing method yielded the lowest Gmb-values, followed (in order of low to high) by the gamma-ray and SSD methods. Significant differences in the variability of test results were not observed between test methods. In ease of testing and testing variability, the CoreReader gamma-ray device does not appear to offer significant advantages for determining the bulk specific gravity of compacted HMA cores. Further, departments of transportation wishing to replace or allow alternatives to traditional SSD-based tests should consider the impact of test results on existing volumetric property specifications.

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As part of their required curriculum, undergraduate students in the Civil Engineering Department at the University of Arkansas take a course that studies the materials commonly used in the construction of buildings, bridges, highways, and the like. This course is titled CVEG 2113 - Structural Materials. A focal point for this course is the examination of concrete, its production, engineering properties, and uses in structures.Since concrete can be delivered to a job site while still in a workable form, it is often necessary to perform a series of tests on the “fresh” material prior to its placement in a structure. Prior to the mid-1980's results from the field testing of concrete were often dubious. In an effort to improve the quality of testing, and thus the reliability and accuracy of the test data, organizations such as the American Concrete Institute (ACI) initiated programs to certify field testing technicians. With the students in CVEG 2113 already receiving instruction relative to testing, as well as having the opportunity to perform the applicable tests in the laboratory, it quickly became evident that ACI certification could, and should, be incorporated into the course syllabus. Being certified adds a tangible skill to a student's resume thus making the student more marketable for summer and long-term employment. The concrete industry benefits from an increased pool of highly qualified engineers. The Department of Civil Engineering benefits from an enhanced reputation from the perspective of both the students and industry.

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