Bitumen is a petroleum product obtained by a process of refining the petroleum. Bitumen is a high molecular weight mixture of hydrocarbons, with a dark color; ranging in viscosity from a barely fluid, sticky to a brittle consistency. It is further characterized by hydrophobic properties (see DIN 55 946).
Because of its thermoplastic behavior, bitumen is easily worked at high temperatures.
For most applications, for instance in making asphalt mixes for road construction or bituminous roofings, the bitumen must be delivered in the heated, fluid state from the refinery and must be kept ready in insulated storage tanks.
It is known to make a powdery bitumen concentrate with a content in silica of 10 to 80% by weight by spraying the liquid bitumen onto the silica (German Patent 29 33 339).
The known bitumen concentrates are used in the industry to enhance the toughness properties of asphalt mixes employed for road construction.
The known bitumen concentrate suffers from the drawback that because of its high silica content, dilution by means of further bitumen (binder) always is required during processing.
Accordingly, there is a need for a friable, i.e. free-flowing, bitumen which can be added directly; that is without being molten first, to the mineral mix, without addition of further liquid or solid binder. Further, there is a need to avoid the often undesired stiffening due to the high proportion of silica.
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