Asphalt is a mixture of aggregates and bitumen as a binder, which depending on its composition, contains a different proportion of voids. By varying its components in terms of type and quantity, the asphalt can be produced with very different properties and can therefore be adapted to the respective application to a large extent.
The quality requirements are to be coordinated with…
- the later stresses caused by traffic and weather with summer and winter temperatures.
- the manufacturing process must be taken into account (e.g. asphalt mix production, temporary storage, transport, installation, and compaction at high temperatures).
Aggregates
There is high demand for hot asphalt mix required for building purposes. But not all asphalt mix is the same, particularly when it comes to aggregrates. The choice of aggregates is based on aspects such as weather resistance, strength, affinity (adhesion) to the binding agent, resistance to polishing and color, as well as local availability and transport costs.
Aggregates for the production of asphalt mix, natural solidification, and sedimentation rocks as well as industrially produced aggregates (e.g. blast furnace slag, steel mill slag, metal mill slag) and recycled building materials are suitable, provided they meet the respective requirements.
For use in road construction, the ” Technical delivery conditions for aggregates in road construction ” (TL Rock-StB) only differ according to the grain size:
- Coarse aggregates (over 2 mm),
- fine aggregates (2 to 0.063 mm) and
- Filler (smaller than 0.063 mm).
Previously common terms such as “sand”, “chippings”, “noble chippings” or “crushed sand” are no longer used due to European requirements. The requirements associated with the earlier terms, e.g. on the fracture surface or origin, are now regulated by means of characteristic values in the form of categories.
Aggregates for road construction must meet the requirements of TL Gestein-StB and be CE-marked. The CE marking is accompanied by an in-house production control (FPC), the correct and standard-compliant implementation of which is regularly monitored by an approved, neutral certification body.
Requirements and tests related to the…
- Grain size distribution, grain shape, the proportion of broken grain surfaces, and the purity of the delivery grains,
- Weather resistance (resistance to frost exposure and to frost and de-icing salt exposure) as well as resistance to heat exposure as a result of drying in the asphalt mixing plant,
- Resistance to shattering and polishing (loss of fine roughness) of coarse aggregates.
The requirements are regulated in the TL Asphalt-StB and are defined with different values depending on the type of asphalt mix and traffic load.
Binder:
Standard binders in asphalt road construction are road construction bitumen and polymer-modified bitumen, in accordance with the TL Bitumen-StB. There, the requirements for the individual types of binder are specified and the test methods for checking these requirements are named.
In the case of road construction bitumen, the individual grades are named using the penetration limits or, in the case of polymer-modified bitumen, the penetration limits and the minimum value for the ring and ball softening point.
Bitumen:
- is stored and processed in hot liquid at temperatures well below its flashpoint. Due to the transport temperature of over 100 ° C, but well below the flashpoint, bitumen is classified in class 9 of the ” Hazardous Goods Ordinance on Road, Rail and Inland Shipping ” (GGVSEB). According to DIN 4102-4, asphalt is assigned to building material class 1 (flame retardant),
- is not a hazardous substance in the sense of the Hazardous Substances Ordinance,
- is proven to be harmless to health. In the course of a so-called “ human bitumen study ” it was found that emissions from hot bitumen do not pose any health risks; there are no abnormal lung function findings,
- is a non-water-polluting substance according to appendix 1 of the ” Administrative regulation water-polluting substances ” (VwVwS).
Therefore, among other things, in the ” Guidelines for structural engineering measures on roads in water catchment areas ” (RiStWag) it is pointed out that layers of asphalt are considered to be environmentally safe on the basis of existing investigations and that building materials that contain washable components may be used if they have hot bitumen (see. Use for sealing drinking water reservoirs or for lining drinking water pipes, etc.).
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