Vägbeläggningars damningsbenägenhet

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Anders Gudmundsson
Per Jonsson
Erik Swietlicki

Since 2005 Sweden has an environmental quality standard for inhalable particles (PM10), based on an EC directive. In Sweden, road dust is an important local source of norm exceedance, which has highlighted the negative effects of studded tyres, but also initiated research and development for other ways to reduce the formation and distribution of road dust to our ambient air. More than 100 000 tons of road pavement is worn each season. Some of this material is PM10 from the start, while other material has the potential to be ground down by the traffic to PM10. Reducing road pavement dust formation propensity is therefore a potential measure studied in this project. Eight surfaces of SMA-type (stone mastic asphalt) were tested in the VTI road simulator for particle formation to determine both the impact of the largest stone size and the influence of rock material properties. As a complement to analyze the impact of technical properties of different stone materials, data from nine additional pavements tested in other projects were used. The results show that larger largest stone size generally leads to lower particulate emissions and that the stone material Nordic ball mill value is a useful measure for estimating a stone material dust formation propensity. In the pavements with 11 mm largest stone size, the Nordic ball mill value can explain 70% of the variation in PM10 at 50 km/h. The results are not conclusive, suggesting that some material may be more sensitive for changes in the largest stone size than others. Elemental analysis shows that particles larger than about 1 micron are completely dominated by elements originating in the aggregates of the pavement. Sulfur, which may originate from tyres and/or bitumen is usually a significant contribution to particles below 1 micron, while zinc, which can be traced to tyre rubber, is found in relatively small amounts mainly in the coarser fractions. Special tests in the Norwegian part of the project show that increased studded tyre percentage increases particle formation and that when non-studded winter tires and summer tires are tested on one of the Norwegian pavements, this results in about 15 times lower PM10 concentrations than with use of studded tyres and a higher proportion of fine particles. In all tests with studded tyres also ultrafine particles are formed. The source is still unknown, but tests with the porphyry pavements result in higher concentrations than for quartzite and mylonite pavements.

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