Asphalt is a mixture of minerals, filler and bitumen. For environmental reasons only the filler and bitumen are of interest. Filler normally consists of natural limestone and/or silicates. However, nowadays filler also contains large amounts of fly ash of different origin, which may contain components harmful to the environment. Roadgrade bitumen, although it incorporates very small quantities of polycyclic aromatic hydrocarbons (PCA) (0,0081-0,005%), is a safe product for human beings, animals and vegetation. This is proved by extensive investigations throughout the world, by the use of asphalt in the construction of drinking water basins and tanks, and of bitumen coating in waterpipes and wine tanks. Bitumen is also used (as cutback or emulsion) to prevent erosion by accelerated germination of seeds for the vegetation of dikes, sand plains, etc. It indicates that asphalt is an environmental friendly product. However, when fly ash containing fillers are used lixiviation of harmful components in fly ash can be dangerous for the environment. However lixiviation of such components is largely retarded or prevented when used in asphalt due to the coverage by bitumen.
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