The role of waxes as an additive to asphalt

The use of asphalt compositions as paving and covering agents for a wide variety of surfaces such as roads and airports is known. Such compositions contain a mixture of aggregate and asphalt in a specific ratio and are generally laid and compacted while hot to provide a dense and durable surface.

For many applications, asphalt (bitumen in English, asphalt in American) provides a sufficiently durable and adhesive binder for the aggregate. However, for high load applications, additives can be added to this asphalt in order to improve its mechanical properties. For this purpose, a variety of different additives have been proposed, including polymers, such as ethylene vinyl acetate copolymers, random or block copolymers of styrene and conjugated dienes (e.g. SBS copolymers). Recently, synthetic waxes containing a blend of synthetic aliphatic hydrocarbons have also been used in asphalt blends (WO99/11737). Such blends, compared to their corresponding wax-free counterparts, tend to be more resistant to deformation under high loads.

Fuels such as diesel and gasoline have damaging effects on bitumen. These fuels tend to dissolve or soften the bituminous components of asphaltene surfaces. As a result, with long-term use, the aggregate components of such surfaces tend to become less well bonded and thus the surface tends to disintegrate.

Surprisingly, we have now discovered that waxes can be used to improve the fuel resistance of asphalt.
Thus, the present invention provides the use of waxes as a hydrocarbon resistant, better lubricant resistant or fuel resistant additive to asphalt.

Suitable waxes include petroleum waxes and synthetic waxes, specifically, waxes with a softening or melting point of 50°C or more, better 60 to 150°C, and better 60 to 120°C. Examples of petroleum waxes include paraffin waxes and microcrystalline waxes. Such waxes are well known (see, for example, 3rd edition Kirk-Othmer, Encyclopaedia of Chemical Technology, vol. 24, pp. 473-476, which is included as a reference herein) and are generally obtained from crude oil and/or crude oil distillates using known techniques. Paraffin waxes are coarse crystalline products and are typically solid at room temperature (25°C). Microcrystalline waxes also tend to be solid at room temperature. However, in addition to being available from petroleum distillates, these waxes can also be naturally occurring, for example, in the form of ground waxes. Ground waxes can be refined and bleached to produce wild cherry wax, which is also suitable for use as a fuel-resistant additive.

Suitable synthetic waxes include hydrocarbon waxes, e.g. polyethylene waxes, which are preferably obtained in the Fischer-Tropsch synthesis process. Waxes with functional groups, such as chemically modified hydrocarbon waxes, as well as waxy esters and amides, can also be used.