Gap Graded and Stone Mastic Asphalt: The two existing standards for BCRA in Australia – by VicRoads and RMS NSW – are written around the dry mix process using a relatively high proportion of bitumen and crumb rubber additive in a coarse gap graded asphalt mix. The gap grading is employed to provide sufficient space (measured in VMA or voids in mineral aggregate) to accommodate the high proportion of bitumen and crumb rubber while maintaining sufficient air voids in the mixture to avoid instability at very low air void contents.