In 1993 under the Strategic Highway Research Programme (SHRP) a new mix design system was developed known as Superpave (Superior Performing Asphalt Pavements). United States rapidly made this Superpave mixture design as a new standard. Since the system was introduced, the Superpave system have been placed across the country A few initiative was undertaken to enhance the selection of materials and mixture design by developing a new technique mix design for traffic loading and environmental conditions, asphalt binder evaluation and mixture analysis. This idea come from where the common design system such as Marshall and Hveem is a common way to overcome pavement problem such as fatigue and low temperature cracking.
This Superpave system comes with a new compactor known as Superpave Gyrator densifying mixes in the lab. Hence, a few requirement of aggregate, binder and mixture compactive need to meet up in order to satisfy to traffic loading. The Superpave mix design system assesses the volumetric properties of compacted samples include air voids (Va), voids in mineral aggregate (VMA) and voids filled with asphalt binder (VFA), and dust to binder ratio.
The aggregates from a various stockpiles will be combine and selected by gradation to meet the requirement that need to be achieved in mix design. Then, by using a gyratory compactor, the aggregates will be mixed with asphalt binder to the specified gyratory compaction effort where the volumetric feature will be determine. The objective of this process is to assess how the mix will combine to satisfy if there is adequate space for binder to allow long-term resistance and sufficient aggregate structure to withstand densification and plastic deformation by traffic in the field.

2.3 Load Transfer on Flexible Pavement

Flexible pavement called flexible since the structure of the pavement bend or flexes to accommodate traffic loads beside the structure consists a layers, (subbase, base and surface coarse) which distribute the traffic loading stress to the soil (sub grade). Figure 2.1 show the load transfer to the lower layer by distributing load to grain by grain. The pavement structure received load from acting wheel and transfer to a wider area so the stress will decreases with the depth.