Bitumen Film Thicknesses and Confinement Ratios in Chip Seal Surfacings

ABSTRACT A method for the direct measurement of the thickness of bitumen films between stone chips in a chip seal surface is reported. A range of simulated single layer seals were constructed with bitumen application rates of 0.77 to 2.07 lm−2 and chip (5.24 mm ALD) application rates of 143 to 275 m2m−3. Median film thicknesses ranged from 4.6 to 10.2 mm measured in a direction parallel to the surface and 1.6 to 3.6 mm normal to the surface. The assumption was made that the bitumen films between stones could be approximated as cylinders with the confinement ratios defined as, cylinder diameter/length. Median ratios ranged from 0.12 to 0.50 and 1.78 to 4.38 for orientations parallel and normal to the surface respectively. The distribution of values ranged to over 40. Tensile failure strength of bitumen films were both found to be highly sensitive to confinement ratio over the range of values observed in the seals. KEYWORDS: Chip SealFilm ThicknessConfinement RatioTensile Failure