A new system of performance based specifications is being used to an increasing extent in Sweden. The system takes into account the functional properties of the road surface which must be fulfilled during a certain time. There is also a need to describe the "functional properties" of bituminous hot mix testing. Since the late 1960s, development of bituminous surfacings in Sweden has largely been focused on improving wearing resistance to studded tyres. Much progress has been made especially in recent years, and the levels of rutting by wear observed earlier are unlikely to reoccur. The significant influence of aggregate quality is now well understood and aggregate tests exist that permit prediction of the performance of a particular type of surfacing. The correlation between aggregate wear tests and actual road wear is surprisingly good. New types of surfacings with a high stone content, such as stone-mastic asphalt, are being specified and used to an increasing extent. There are also certain benefits regarding wear of studded tyres in the form of improved skid resistance of road surfacings because of better micro and macro texture. A system for testing laboratory rolled slabs with well known composition, inserted in road surfacings or used in a road simulator, has been developed at VTI. The road simulator makes it possible to test road surfacings in a very cost-effective manner and the results correlate very well with road wear. Some examples of using the machine to solve particular problems are given. Research is also being directed towards testing other "functional properties" of different types ofbituminous mixes, such as stiffness, rutting by plastic deformation and cracking by fatigue, as well as durability properties such as ageing and stripping (water susceptibility). Lack of durability has been a problem especially with porous asphalt. This work is still in progress and only certain preliminary results are outlined as these properties are not always very easy to evaluate. (A)
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