The report describes the evaluation of stone mastic asphalt (SMA). SMA was originally produced in Germany as a proprietary wearing course material, but recognition of its excellent performance led to its standardisation in 1984. SMA has been found to be very deformation resistant due to its stable aggregate skeleton structure. The voids in the stone matrix are filled with a mastic of bitumen/crushed sand/filler to which a stabilising agent, which is normally cellulose fibre, is added to prevent binder drainage. Experience in countries that have adopted SMA has shown it to be very durable. Following a study visit to Germany to gain more information on material design, production and construction practice, a demonstration trial was arranged at TRL to further evaluate the potential of this material.

The trial showed that SMA can be sesigned, produced and laid successfully by UK contractors using existing plant, and demonstrated clearly the feasibilty of its use in the UK, Furthermore with careful choice of aggregate size and grading SMA has the potential to meet UK surface texture requirements, to be laid as a thin layer, and it generates less tyre noise. The material could be used in carefully monitored road trials to build up experience before considering it for general use.

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