The present invention relates to road-surfacing material, and more par¬ ticularly to a road-surface layer, so-called road-dressing, applied to asphalted road constructions.

In Sweden, 8* of the road network is surfaced annually.

Various attempts have been made to increase traffic safety over a large number of years, by admixing light-coloured stone fractions with road- surfacing material.

For instance, a Danish material designated synopal has been admixed with the road-dressing material in an amount corresponding to 8% by weight.

This provides a relatively light-coloured surface. However, because synopal was found to be less tolerant to wear from studied tyres, quartzite was used in the road-dressing instead.

An ideal condition is one in which the road surface is light in colour and can be readily illuminated, so as to enable the road to be seen easily and also to enable objects on the road to be readily discerned. It is found, however, that light-coloured road-surfacing materials of the synopal kind do not brighten the road sufficiently when illuminated by conventional vehicle headlamps.

Accordingly, the present invention relates to a road-surfacing material which will fulfill the desire for light-coloured road BurfaceB.

The present invention thus relates to road surfacing material which is intended to be laid as a road-surface dressing on asphalted roads and which comprises a crushed rock-material, Buch as quartzite (SiO _a ), and a binder, such as pitch, and which is characterised in that it further comprises an additive material which will fluoresce when illuminated with ultraviolet light, said additive material having been produced by bringing a mineral substance to a molten state and doping said mineral substance with a doping agent whose presence will cause the mineral concerned to fluoresce, and which has been crushed and/or granulated to particle size which corresponds to the size of the quartzite particles.

The invention will now be described in more detail with reference to exemplifying embodiments thereof.

The inventive road-surfacing material comprises a conventional road Burface- dressing which has admixed therewith an additive material which will fluoresce when illuminated with ultraviolet light, said additive material being mixed with said road-dressing prior to applying the same.

A very large number of mineralβ which will fluoresce when irradiated with ultraviolet light are known to the art. The fluorescent effect of these minerals will vary in accordance with their place of origin, since the chemical composition of the mineralβ varies from place to place. Conse¬ quently, it is difficult, if not impossible, to locate a mineral mining or quarrying site from which the mineral extracted therefrom will have a considerable and fairly uniform fluorescent effect and which can be mined/quarried at reasonable, related costs.

Typical minerals possessing fluorescent properties are fluorspar (CaF _a ), limespar (CaC0 ₃ ), Scheelit (Ca O__), Willemit (Zn _a (SiO _a ) and Autunit (Ca(UO_,/PO_ ₁ ) ₃ ) - 10-12 HaO.

Fluorspar fluoresces with a blue light and is therefore lees suitable for use in the present context.

Willemite, Scheelite and Autunite fluoresce with a green-yellow light.

Scheelite, however, will fluoresce with a white light when the tungsten (W) is replaced with molybdenum (Mo).

Limespar can be used to great advantage, since when manganese (Mn) is present, limespar will fluoresce with an orange light. Orange is namely a colour rich in contrast.

According to the present invention, the fluorescent additive material is not an untreated mineral, but a mineral which has been treated to provide a fluorescent effect.

The treatment to which the mineral is subjected in accordance with the invention involves melting a mined or quarried mineral in a furnace of the kind used in the manufacture of mineral wool, i.e. a furnace of the elec- trosteel type. The molten material is then doped with a doping agent which will cause the mineral to fluoresce, by introducing said doping agent into the molten mineral-bath.

The melt may then be granulated or cast. Subsequent hereto, the solidified material is crushed to a particle Bize which corresponds to the particle size of the quartzite present in the road-surfacing material, i.e. a particle size of about 10-20 mm.

According to one preferred embodiment of the invention, the additive material includes one of the minerals limespar or Scheelite doped with manganese or molybdenum respectively.

The amount in which the mineral shall be added in order to provide a fluorescent effect will depend on the mineral concerned and also on the strength of fluorescence desired.

The proportions in which the additive material is admixed with the road- surface material are also significant. A larger proportion will naturally result in a greater fluorescent effect.

According to a preferred embodiment, the additive material is present in the road-surfacing material in an amount which corresponds to 2-25* by weight, preferably about 10-15* by weight.

Such mixing proportions will provide an adequate fluorescent effect while maintaining other properties of the road surface essentially unchanged.

The present invention is not limited to any particular mineral or doping agent.

Those minerals which will fluoresce are well known, and the concentrations in which the fluorescent substance is contained in such minerals in order to achieve fluorescence is also known.

Consequently, the skilled person is able to acquire this knowledge and is also capable of varying the proportion of the doping agent in the material, and also to vary the proportion in which the invented additive material is present in a road surface, so as to achieve the intended fluorescent effect.

Thus, in accordance with the invention, there is mined or quarried a selected, appropriate mineral which is cheapest with respect to the location of the processing plant. Naturally, the number of suitable minerals avail¬ able will be restricted to minerals which have a good fluorescent effect subsequent to treatment and which can be mined or quarried at locations in which the mineral concerned is highly concentrated and present in large quantities.

The present invention thus provides an additive material which, distinct from natural fluorescent materials, will produce a relatively smooth and uniform fluorescent effect.

A fluorescent road-surface will greatly enhance road safety. It is namely found that a fluorescent road-surface will also provide improved road- vision and improved ability to discern objects on the road, even under daylight conditions.

At sunset and at dawn, the natural light includes a large amount of ultra¬ violet light, which means that the light conditions of the inventive road- surface will be a considerable improvement on the light conditions afforded by a conventional road-dressing.

The invention, however, includes the concept of fitting automotive vehicles with lamps which emit a large proportion of ultraviolet light.

Such lamps are already available, as are also lamps of special configura¬ tion.

Furthermore, lamps which emit white light together with a significant proportion of ultraviolet light, such as discharge lamps, can be used in conventional vehicle headlamps.

In dark conditions, the optical effect thus achieved is highly pronounced.

The road surface will appear to glow in the dark, and objects present on the road will stand-out against the road surface, thereby enabling the objects to be discerned easily from a long way off.

By admixing a mineral, such as limespar for instance, in a proportion of about 10-15%, the resultant road-surface will obtain a wear-resistance which corresponds in all essentials to the wear-resistance of a conventional road surface.

The invention thuB fulfills the aforesaid objects.

As before mentioned, the invention is not limited to any particular additive material, and the choice of a suitable mineral for the purposes intended is therefore left to the person skilled in this art.

Neither is the invention limited to the described exemplifying embodiments thereof, since modifications can be made within the scope of the following claims.