Lesson 4: Hot Mix Asphalt – Mix Design CEE 595 Construction Materials Winter 2008 Reading Virtual Superpave Laboratory WSDOT Pavement Guide Interactive Lesson Outline Hot mix asphalt (HMA) description Superpave mixture design procedure Section 1 Hot Mix Asphalt (HMA)
CEE 595 Construction Materials
The SGC has an issue with internal angle of gyration (see SGC – Background). Basically, it’s a dimension that is not specified in instrument manufacture because it is assumed to be directly related to another specified dimension. Since this internal angle of gyration can vary between brands of SGCs and even between SGCs of the same brand, the industry is noticing that calculated bulk specific gravity (and thus the calculated air voids) of the same mixture can vary between SGCs even though the same number of gyrations is specified.
Given that measurements of laboratory bulk density are often used by owners for acceptance testing and by contractors for process control, how does one reconcile this problem so that an SGC can be used for quality assurance testing (in other words, if each machine measures differently, how can the owner and contractor compare numbers)?
For instance, a contractor’s machine may produce samples that indicate 4% air voids, while the agency’s machine may indicate 6% air voids, while a third party machine may indicate 5% air voids – all on the same mix.