Comparison of Alternative Devices to Determine Aggregate Shape

About the report:

This study compared devices (with corresponding procedures) that may be used to classify flat and elongated (F&E) particle content for coarse aggregate sources. The comparison involved the traditional (and manual) proportional caliper and two digital calipers. The material used to conduct these comparisons was from aggregate sources used to produce stone-matrix asphalt during the 2003 and 2004 construction seasons in Virginia. Replicate tests were conducted for each source and each device. The same material was tested by multiple technicians from the Virginia Transportation Research Council's asphalt laboratory and the Virginia Department of Transportation's central materials laboratory. The central conclusions were: (1) the vertically operated digital caliper is a suitable alternative to the traditional manual proportional caliper; (2) the ROCLOG software facilitates data reduction; and (3) it is important to consider the full gradation analysis when characterizing F&E content of any aggregate source. This research also documented an estimated time-savings of 45 minutes per aggregate source when performing F&E testing with the vertically operated digital caliper. Given VDOT's standard requirements for aggregate testing, this translates into an annual time-savings of at least 30 hours per laboratory. With an advertised cost of less than $300 per device, the benefit to cost ratio for the vertically operated digital caliper is better than 4 to 1, and the investment is easily justifiable.

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