Bitumen road paving

Road paving. This includes bitumen, cutbacks and fluxed bitumen as well as emulsions. Each of these products is subject to very special application techniques. This list is completed by the use of poured asphalt, even though this product is better suited to smaller surfaces sidewalks, courts, etc., than to pavements. Since the middle of the 1980 s, air-blown bitumen is no longer used for road construction. 

Asphalt emulsions are used in road paving for the production of a smooth, water-repellant surface. First, an asphalt O/W emulsion is formulated, which has sufficiently low viscosity to be easy to handle and apply, and which has sufficient stability to survive transportation, brief periods of storage, and the application process itself. The emulsion needs to be able to shear thin during application, and then break quickly when it contacts the aggregate. The asphalt emulsions are usually 40-70% bitumen and stabilized either by natural naphthenic surfactants released by treatment with alkali (for a somewhat similar situation involving bitumen processing see also [64]), or else by the addition of anionic or cationic surfactant [106]. Emulsified asphalt can be applied to gravel or rock even when wet [1,20,105,106]. 

As time passed, bitumen technology had to develop to adjust to new demands of the updated transport networks. Hence, bitumen used for road paving has been modified via the addition of polymers, in order to improve the mechanical characteristics of natural bitumen. However, there are some special uses in which traditional bitumen is replaced by design materials called synthetic binders (Figure 10.1). 

In 1903 an American Society for Testing and Materials (ASTM) Committee on Road and Paving Materials was formed to develop test methods and specifications for highway materials. Test methods for volatilization, penetration, and bitumen were developed by the Office of PubHc Roads and were... 

Bitumen modification, roads, roofing, paving, impact-resistant shingles. .. 

The principal use of coal tar in paving is as a seal coat to bitumen paving. Asphalt for paving comes in several forms determined by the intended application, ie, straight asphalts called asphalt cements (AC), asphalt emulsions, cutback asphalts, and road oils. 

Hard paving bitumens have very high stiffness modulus values and are used for the construction and maintenance of road and airport pavements or other kinds of bitumen surfaces. Hard paving bitumens constitute an extension of common paving bitumens. They are usually used in locations with very high daily traffic flow, when annual ambient temperatures are intermediate or high. 

Figure 3.3 Changes in bitumen composition and its ageing index (ratio of recovered viscosity, over initial viscosity, qj during mixing, laying and in service. (From Chipperfleld E.H. et al.. Asphalt characteristics in relation to road performance. Proceedings of the Association of Asphalt Paving Technologists, Vol. 39, p. 575. Seattle. WA. 1970.)...

Cut-back and fluxed bituminous binders are suitable for use in the construction and maintenance of roads, airfields and other paved areas. The bitumen used may be paving grade bitumen (in most cases) or by addition of polymer. 

In locations where trackout from an unpaved road to a paved road is a problem, chemical suppressants are generally a good choice. Watering aggravates the trackout problem with moisture and mud, whereas chemical suppressants, particularly bitumens and adhesives, leave the road dry. Finally, some mines have a dust problem in winter when temperatures are subfreezing but little moisture is present. The case for chemical suppressants over water in this case is clear. 

This application is similar to the use of geotextiles to prevent crack reflection in asphalt-paved roads. Here, the impregnation (which is an emulsified bitumen) is placed first, and then the geotextile and then the asphalt overlay (Fig. 11.13). 

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