Asphalt Construction Materials Testing
This section covers what NICET CMT asphalt questions test: mix design verification, volumetric calculations, binder and mixture performance tests, and field density acceptance. Expect calculation items and test-method sequencing, not just definitions.
Volumetric mix design
Superpave mix design uses the gyratory compactor (AASHTO T 312); Marshall stability and flow (T 245) still appear on older or agency-specific work. Key measurements are theoretical maximum specific gravity Gmm (T 209), bulk specific gravity Gmb of compacted specimens (T 166), and aggregate bulk Gsb. Air voids: Va = 100(Gmm − Gmb)/Gmm. VMA = 100 − [Gmb(100 − Pb)/Gsb], where Pb is binder percent by total mix mass. VFA = 100(VMA − Va)/VMA.
Worked example
A mix has Gmm = 2.500, Gmb = 2.360, and VMA = 15.0%. Va = 100(2.500 − 2.360)/2.500 = 5.6%. VFA = 100(15.0 − 5.6)/15.0 = 62.7%. Using Gsb in place of Gmm would give a meaningless air-void result, because Gmm is the zero-air-void reference for compacted mix.
Binder and moisture tests
PG binder grading includes rotational viscosity (T 316), DSR (T 315) for high-temperature rutting and intermediate fatigue, and BBR (T 313) for low-temperature cracking. RTFO (T 240) simulates plant aging; PAV (R 28) simulates long-term aging. Moisture susceptibility uses T 283: wet and dry indirect tensile strengths are compared, and TSR = wet/dry × 100, commonly required to be at least 80%.
Field density and acceptance
Field density is reported as percent of Gmm or percent of laboratory density. Nuclear gauge (T 355) and cores (T 166) are common. Record random location, lift, and temperature, and avoid segregated areas unless the specification directs otherwise.
Traps
Using Gsb instead of Gmm in air-void calculations; forgetting the ignition-oven binder correction; testing specimens before constant mass; comparing wet TSR to the wrong dry set; and reporting density without stating the reference (Gmm versus lab-compacted).