8. Determination of asphalt content of HMA by ignition method (AASHTO T-308): In this
test, an HMA sample (generally ranging in weight from 1.2 to 4 kg, for a range of nominal
maximum aggregate size [NMAS] of 4.75–37.5 mm) is weighed, it is placed inside an oven
maintained at 650°C, the asphalt binder is burnt off, the remaining aggregates are weighed,
and the asphalt content is determined on the basis of the two weights. Aggregate calibration
information, which accounts for loss of aggregates by burning, if any, can be input in the
ignition oven computer. The ignition oven reports the weight of the sample to the nearest
0.1 g, taking into consideration the temperature correction, and prints out the asphalt content
(using an onboard computer program) from the pre- and postignition weights, taking
the aggregate calibration factor into consideration. Important items are provision of methods
for reducing furnace emissions, availability of a self-locking oven door (which will
not open until the end of the test), an audible alarm and lights for indication of completion
of the test, as well as safety equipment such as a face shield and thermal gloves for the
operator. The asphalt-free aggregates can be used for running a sieve analysis and checking
gradation, although care must be taken to consider the breakdown of some aggregates and
the creation of some fines (if any) during the ignition test of some types of aggregates.
9. Determination of asphalt content by the nuclear method (AASHTO T-287): In this test
the amount of asphalt is indicated by the amount of hydrogen in a mix as measured with
a neutron source in the nuclear gage. The gage needs to be calibrated with both aggregate
and mix samples before using. A pan filled with consolidated HMA is placed inside the
nuclear gage, and the asphalt content is read off the equipment.