This test method describes the procedure for determining the in-place density of asphalt mixtures by use of nuclear gauge. The density of the material is determined by the backscatter/air-gap ratio method. Density —The total density of asphalt mixtures is determined by the attenuation of gamma radiation where the source and detector(s) remain on the surface (backscatter method). The density in mass per unit volume of the material under test is determined by comparing the detected rate of gamma radiation with previously established calibration data.