If a 6"x4" asphalt sample is cut down to smaller dimensions (let's say to prepare a DCT testing specimen), does the Gmb value change from the original bigger sample? If it does change during testing, then what might be the factors affecting this change?
Bituminous Materials and binders specific gravity is much less than the gravel/sand aggregate and is sensitive to ambient temperature. ( AASHTO T 228 and ASTM D 70: Specific Gravity and Density of Semi-Solid Bituminous Materials-) roughly around 1.03 versus 2.6 to 2.65 of aggregate.
So depending on the mixture of these two components that are not uniform due to the random space filled with the binders the specific gravity of smaller samples is expected to vary.