The current precision values given in Florida Method FM 5-563 for the determination of asphalt binder content by use of the ignition oven are based on laboratory-fabricated specimens with known binder contents and gradations. A study was conducted to determine precision values for both asphalt binder content and gradation for use with plant-produced mixtures. This approach would encompass the variability associated with (a) differences in an asphalt mixture within the truck bed, (b) collection of samples from the truck, (c) splitting of the mixture into samples for testing, (d) differences in ignition oven equipment, and (e) the operator. The current precision values include only the variability associated with the last two items and the variability associated with batching and mixing of laboratory-prepared specimens. Twelve laboratories tested nine different mixtures containing a wide variety of gradations and aggregate types. The results of the study indicate that the allowable difference between two test results for asphalt binder content should be no greater than 0.32% within a laboratory and 0.44% between laboratories. New graphs were developed for the within-laboratory and between-laboratory precision values for aggregate gradation. Separate graphs were developed for dense-graded Superpave mixtures and open-graded friction course mixtures, as it was determined that allowable tolerances differ significantly for each type of mixture.
Samenvatting