GB2234512A - A road surfacing composition and its use - Google Patents

Abstract

A road surfacing composition comprising aggregate and a binder which is applied as a hot melt to a substrate comprises bitumen and a viscosity modifier comprising a wax and is characterised in that the viscosity modifier is present in the binder in a amount such that the penetration value at 25 DEG C (as hereinbefore defined) of the binder is in the range of 0.3 pen25-2.0 pen25 where pen25 is the viscosity of the binder without viscosity modifier and such that the viscosity at a predetermined spraying temperature is at least 25% lower than the viscosity of the binder without viscosity modifier. Suitable viscosity modifiers include micro-crystalline wax or montan wax or coal tar wax but not paraffin wax, oil slack wax, paraffimic or aromatic resins or atactic polyethylene. The binder usually contains 1-15 wt% wax based on total binder and optionally may contain a non-volatile solvent.

Description

A ROAD SURFACING COMPOSITION AND ITS USE The present invention relates to a composition to be used in road surfacing, in particular to a surface dressing binder to which chippings are applied, which is substantially free of volatile solvent.

Conventional means of applying road surface dressing binders involve reduction of viscosity at the time of application by spraying. This is done by either raising the temperature, addition of a volatile diluent, emulsification or a combination of these. Whichever method is used, the binder must have a sufficiently low viscosity to give a good transverse distribution and adequate wetting properties. Bitumen consists of a continuous base fraction known as the maltenes fraction, and a dispersed asphaltenes phase.

Cut-back binders use a volatile diluent, generally kerosene, and high temperature to reduce the viscosity.

After application the kerosene is no longer required but its presence leaves the surface dressing soft and thus prone to hot weather failures. Because the layer of bitumen composition is fairly thick and becomes covered with chippings in use evaporation of the solvent is often slow so that the final properties of the composition are not attained quickly. The volatile nature of the kerosene, necessary so that it can eventually be lost after application, creates a considerable fire hazard at the point of application where the temperature of the binder, which has a flash point typically between 60-700C, may be as high as 1600C. Cut-back binders are preferred, especially in heavy traffic situations, because of their rapid adhesion to inorganic materials.

Sulphur has been suggested as a component for road binder compositions. However its use can result ir. the evolution of hydrogen sulphide gas which is undesirable.

Other compositions containing bitumen which are free of volatile solvent are known for a variety of applications. In GB-A-2,037,299 waxes including microcrystalline waxes are used to reduce the surface tackiness of particulate bitumen. The particles are mainly for use in filtration beds for aqueous effluent treatment but it is stated that they may also be useful for use in road construction, although there is no description of how they might be used. The particles are formed by a process including the step of cooling the fluid bitumen mixture using water. Such particles would be wet and thus unsuitable for use in road surfacing compositions which utilise a molten bitumen composition since the water would boil and cause frothing. The wax is incorporated in high amounts in order that the wax migrates to the surface of the particles to render them non-tacky.The composition of the example uses 40% by weight wax based on wax plus bitumen. Such compositions would not retain the features of bitumen required in a road surfacing composition. Hard bitumens are preferred, having penetration values in the range 15-25 at 250C.

In US-A-4,738,998 hot melt adhesives comprising 35-80% by weight bitumen, 15-50% ethylene-vinyl acetate copolymer (EVA) and 5-308 (preferably 15-25%%) wax, including microcrystalline wax, are disclosed for use in laminating materials to produce thermal insulation. The bitumens are very hard, having penetration values less than 1. The EVA makes the compositions even harder. The wax is probably incorporated as a solvent for the EVA copolymer modified binder which has very high melting temperatures. Such compositions are unsuitable for road surfacing compositions.

In US-A-4,267,085 a molten mixture of bitumen containing a wax and/or ethylene-vinyl acetate copolymer is injected to form a layer between railroad ties and the road bed, to reduce the maintenance of the bed. The wax used can be any type of petroleum wax, from paraffin waxes to microcrystalline waxes or synthetic waxes such as low molecular weight polyethylenes, polypropylenes or polybutylenes. These compositions contain relatively hard bitumens, for instance, having penetration values (at 250C) in the range 10 to 30. The compositions must be hard to perform the function required. In practice the compositions contain a high proportion of wax; where microcrystalline wax is used it is present in an amount of 30% based on wax plus bitumen. Such compositions would be too hard for road surfacing and would not have the properties of bitumen required of road surfacing compositions.

Bitumen containing rust prevention compositions containing highly volatile solvents such as white spirit are known. Such compositions are applied in enclosed factories and are dried in ovens so that the vapours from the solvent can be confined. The compositions are applied relatively thinly so that the solvent evaporates relatively quickly. Solvent-free compositions have been developed. For instance, in JP-A-53-064239 solvent-free rust prevention compositions for the undersides of car bodies applied as hot melt compositions comprise bitumen having a penetration value in the range 10 to 40, optionally in admixture with softer bitumen of penetration value 50 to 100, microcrystalline wax and process oil.

Evans et al in Am. Chem. Soc. Div. Petrol. Chem.

Preprints 16, D5-D17 describe the disadvantageous effects of the presence of waxes in asphalts. Andreev et al in Stroit. Malev. Detali Izdeliya 19, 189-197 state that the presence of greater than 3% by weight paraffin waxes gave disadvantageous properties to bitumens for rubberoid roofing materials but that low molecular weight polyethylene waxes gave satisfactory materials. The polyethylene waxes were found to give a more favourable penetration index, presumably therefore lowered that index.

Kolbanovskaya et al in Kolloid Zh. (1968) 30 522-6 describe the effect on the rheological and adhesion properties of a range of asphalts by the addition of paraffin waxes. Addition of more than 3% of wax appears to have disadvantageous effects on bitumens not having a well-developed asphaltene structure that is, tended to cause the asphaltenes to coagulate or flocculate and thus to distabilise the compositions. For bitumen compositions with high amounts of wax the adsorption of asphaltenes onto marble was adversely affected. The incorporation of paraffin waxes increased the viscosity of the bitumen compositions 20-300 below the softening point. From this disclosure it might be concluded that the presence of paraffin waxes would be undesirable in a road surfacing composition.

A new road surfacing composition according to the present invention comprises aggregate and a binder which is applied as a hot melt to a substrate comprises bitumen and a viscosity modifier which comprises a wax and is characterised in that the viscosity modifier is present in the binder in an amount such that the penetration value at 250C (as hereinafter defined) of the binder is in the range of 0.3 pen25-1.5 pen25 where pen25 is the penetration value of the binder without the viscosity modifier and such that the viscosity (as hereinafter defined) at a predetermined spraying temperature is at least 25% lower than the viscosity of the binder without the viscosity modifier.

The compositions are preferably for use as road surface dressings, which the binder is applied hot, usually by spraying, onto a road surface (the substrate) and chippings are then applied to the binder and become embedded in it. Alternatively the binder may be premixed with the aggregate and the hot melt is then spread onto the road surface, for instance as a hot-rolled asphalt carpet. Alternatively the compositions may be coated chippings, that is may comprise chippings precoated (as the substrate,) with hot melt binder and then at some later stage applied to the road surface. Such coated chippings are applied hot or cooled to the road surface.

The measurement of the penetration value of the binder at 250C is carried out by penetrometer according to BS2000 pt49:1983. Higher penetration values indicate softer compositions.

The measurement of the viscosity of the binder at the predetermined spraying temperature is carried out by a rotary viscometer (UK/LV spindle 6). The spraying temperature is a temperature at which the binder is dispensed from a mixing vessel eg is projected through the spray jets of the apparatus or is contacted with the aggregate. It is termed the spraying temperature for convenience although that application may be by other methods eg by pouring. Application of the binder of a road dressing is however, conventionally by spraying.

The predetermined temperature may be that conventionally used for the application of the binder for instance a temperature in the range 120 to 2000C, more usually in the range 140 to 1600C. However the temperature at which the binder can be applied may be reduced on the invention and so the predetermined spraying temperature at which the viscosity measurements are carried out is not necessarily the same temperature at which the binder is utilised.

We have found that the invention is of particular benefit in compositions based on relatively soft asphalts, such as those having penetration values at 250C of at least 70dmm or at least 80dmm, preferably at least 100dmm and most preferably around 200 or 250-300dmm.

Such bitumens are used as bases for road dressing binders. The penetration values are measured by BS2000 pt 49.1983.

The invention is also of use for binders based on bitumen having lower penetration values, such as one used in hot-rolled asphalts or coated chippings. Usually such bitumens have penetration values of more than 25, preferably more than 35dmm, most preferably 50dmm or more. Such bitumens usually have penetration values less than 100dmm, preferably less than 70dmm.

The invention also provides processes for producing the compositions by mixing the binder components at a temperature above the softening point of at least one of the components, usually at a temperature above the softening point of the wax, and then discharging the binder mixture as a fluid from the mixing apparatus and contacting the binder with the aggregate. Mixing is usually carried out in the conventional apparatus for this purpose. For road dressings the liquid composition is discharged from the mixer and then the aggregate is applied. For hot-rolled asphalts and coated chippings the aggregate is mixed with the binder and then discharged from the mixing apparatus. The asphalt is then laid hot and the coated chippings usually allowed to cool before application.

The invention further provides a process for applying the new compositions to the surface of a road in which the binder is applied as a hot melt followed by application to the binder of the aggregate (chippings).

Application at a temperature above the softening point of the binder is for instance by spraying. The equipment can be conventional equipment used for road dressing operations. The application temperature is usually above 1000C, preferably above 1200C, and usually does not need to be higher than 2000C. Most preferably the temperature is around 140-1600C.

In a further aspect of the invention a new process for surfacing a road comprises mixing the binder as a melt with aggregate and laying the hot composition on a road surface.

In a further aspect of the invention a new process for producing coated chippings comprises coating aggregate particles with the binder as a hot melt and then cooling the coated particles before applying them to the road.

The viscosity modifier comprises a wax and, optionally, a non-volatile solvent. Any non-volatile solvent is preferably present in an amount by weight of no more than the amount of the wax. The non-volatile solvent may serve to increase the penetration value (ie soften the composition) whilst maintaining relatively high softening point (ring and ball) so that the composition is less susceptible to brittleness at cold temperatures and less susceptible to high temperature failure (eg in hot summers).

The introduction of appropriate wax and optionally non-volatile solvent into the binder gives the composition a profile of viscosity change with temperature which is similar to solvent cut-back compositions at high temperatures, ie at application temperatures, to allow for easy handling of the molten composition and its application by conventional spray or other means. The composition has a much higher flashpoint than a conventional solvent cut-back composition so that it is less hazardous and more pleasant to use. Because the wax is not lost by evaporation it remains in the composition on the road and acts as a filler or integral part of the binder on solidification.The solidified road surfacing compositions have been found to have similar low temperature viscosity to the bitumen itself, improved penetration value and improved flow properties especially immediately after application compared to conventional solvent cut-back compositions, without any damaging loss of adhesion to the road surface or to the chippings and without affecting any of the other ambient temperature properties unfavourably.

Where the bitumen is the base for a road surface dressing and thus has a fairly high penetration value it has been found that the desired viscosity properties can be achieved by the incorporation of a microcrystalline wax or a montan wax optionally in combination with non-volatile solvent. Similar waxes which would be expected to provide the desired properties include aromatic-type or highly branched and/or crosslinked waxes eg coal tar waxes and any thermoplastic organic substance having a similar low molten viscosity and the ability not to affect substantially the bitumen medium at ambient temperatures. It has been found that for these bitumens however paraffin waxes, oil slack waxes, paraffinic and aromatic resins and atactic polyethylene de not provide the desired properties. Such substances, do not give both good high temperature (ie at predetermined spraying temperature) viscosity and good properties on cooling, but tend to produce poor depression of spraying temperature viscosity and/or give cooled compositions which are too hard or non-adhesive, ie have too high values for the penetration values at 250C and thus provide road surfaces which are brittle and subject to damage at low temperatures. Furthermore it appears that the viscosity of the binders including viscosity modifiers, including microcrystalline and other useful waxes have improved properties when they are subsequently subjected to higher temperatures: in some such circumstances it has been found that the viscosity may not fall as much as would be expected (ie from the viscosity profile with falling temperature after initial mixing).

Without being bound by theory, it is believed that the paraffin waxes are compatible with the maltenes phase of those bitumens suitable for road building applications so that at higher temperatures the wax is completely miscible with or soluble in the liquid maltenes phase.

At lower temperatures the wax also remains dispersed homogeneously and as crystals throughout the maltenes phase and thus has an effect on the low temperature viscosity as well as the high temperature viscosity of the bitumen. The microcrystalline (and other useful) waxes are believed to be less compatible with the maltenes phase at the lower temperatures and are dispersed as a heterogeneous (dispersed) phase in the continuous phase which consists substantially only of the maltenes. At such low temperatures the viscosity, including the penetration value of the binder is thus determined primarily by the maltenes and is similar to the binder without the wax. At the higher, predetermined spraying temperatures, these waxes may be completely miscible and interact with the maltenes phase to reduce the binder viscosity by the desired amount.

The advantageous properties of microcrystalline wax may be in part due to the fact that it solidifies over a broad range of temperatures and so gives a smooth transition in the viscosity curve with cooling of the composition. Paraffin wax in contrast solidifies over a narrow temperature range and gives a discontinuity in the viscosity curve.

It is expected that similar effects may be observed in lower penetration value bitumen containing binders, for instance for use in hot rolled asphalt compositions and for coating chippings. Suitable combinations of viscosity modifier and bitumen can be found which give binders which have the desired viscosity properties. The binder preferably has a penetration value at 250C in the range of 0.5 pen25-1.5 pen25. The viscosity at the predetermined spraying temperature is preferably less than 50% of the viscosity of the binder minus viscosity modifier at that temperature.

The binder compositions usually contain 1 to 15% by weight wax based on total binder, preferably 5 to 12%, most preferably 8-10% wax. Higher amounts tend to detract from the other properties required of the bitumen and lower amounts may be insufficient to give the desired effect.

The compositions are preferably substantially free of volatile organic solvent.

The compositions otherwise have the same basic components as conventional road surfacing compositions and thus comprise any of the known types of bitumen as well as known fillers, anti-stripping agents, etc. The incorporation of the wax may lead to a minor reduction in the tackiness of the compositions and thus to a reduction in the adhesion to the aggregates used as chippings or to the road surface. It may therefore be advantageous to incorporate tackifier components to counteract this effect. Tackifiers generally comprise resins having acid groups, usually carboxylic groups. Alternatively or additionally bitumens with high acidic group contents may advantageously be incorporated into the composition.

The binder compositions may also contain polymers to affect the final properties of the road surfacing compositions, for instance which may provide a harder but less brittle composition. EVA, SB or SBS copolymers may be useful for such applications. Such polymers are for instance incorporated in amounts up to 10%, but usually in amounts less than 8% or 6%.

The following example illustrates the invention: EXAMPLE A mixture was formed by blending a mixture of 79.5% by weight 200 penetration bitumen at 160cm in a vessel with a propellor stirrer with 10% by weight microcrystalline wax and 10% by weight tall oil still residue (combined tackifier and adhesion agent) and 0.5% by weight of a conventional fatty amine anti-stripping agent. The mixture was stirred until homogeneous, at 1500C. The viscosity at 1500C was 63 cP(UK/LV viscometer spindle 6).

When cold the composition had a penetration of 219 dmm (100 g/5s/25 OC) . The bitumen itself had a penetration value of 181 dmm.

The viscosities with falling temperature were performed using the Carri-med CS100 controlled stress rheometer, with software version 4.3, in the flow operating mode, with 2cm diameter, 4 degree cone and flat plate. Samples were loaded molten onto the 2cm 4 degree cone which was then placed onto the rheometer and allowed to reach equilibrium at 800C. Samples were loaded molten onto the 2cm 4 degree cone which was then placed onto the rheometer and allowed to reach equilibrium at 800C.

Sample mass and rheometer gap settings were chosen to be correct at 500C. The samples were then subjected to a sheer stress of 10,000 dyne/cm2 (1000 N/m2) whilst being cooled from 800C to 200C at a constant rate over a period of 12 minutes. The results are shown in the figure line (d), with similar viscosity profiles of comparative compositions containing paraffin wax replacing the microcrystalline wax (c), with kerosene as cut back in place of wax and tackifier to give similar higher temperature viscosities and with the bitumen alone (a) and bitumen with the tall oil still residue (base binder) (b).The viscosity profiles show that although each of the additives microcrystalline wax, paraffin wax and kerosene give reduced high temperature viscosity, the solvent cut-back composition has reduced viscosity at lower temperatures as well which is undesirable, and the paraffin wax gives a composition which is too hard and brittle at lower temperatures, eg below 400C.

EXAMPLE 2 The binder used in Example 1 containing microcrystalline wax was loaded into a hot binder distributor and the temperature of the composition in the tank was maintained at around 1500C. The composition was applied by spraying onto a surface at a rate of 1.08 l/m2, followed by applying 6mm lightly coated "Temple" chippings. Rolling chippings into the binder speeded up adhesion which was satisfactory after 5 minutes. The dressing was found to adhere satisfactorily to both damp and dry areas on the road surface. Two weeks later the surface looked sound.

During application the composition evolved far less fumes than a conventional solvent cut-back composition, so that visibility was not hampered.

EXAMPLE 3 The penetration value, LVT viscosity at 1600C, and ring and ball softening point of a composition containing 10% micrystalline wax and 5% non-volatile solvent as viscosity modifier were measured and compared to a similar composition, containing 10% paraffin wax as viscosity modifer, the base binder free of viscosity modifies and the bitumen itself.The results are shown in the following table: Composition Penetration Value LVT Ring & ball (250C) dmm viscosity softening pt (OC) at 1600C(cPs) Penetration grade bitumen 181 81 38 Base binder 238 66 36 10% Paraffin wax 74 40 55 10% microcrystalline wax] 58 non-volatile solvent z 280 40 48 The results show that the penetration values at 250C for the composition of the invention is within the desired range compared to the base binder whereas that of the paraffin wax-modified composition is too low and would be brittle. The viscosity at 1600C is however low so that the composition can be sprayed. The softening point of the composition of the invention is fairly high, which ensures that the composition is less likely to fail in use at high temperatures. The paraffin wax-modified composition has adequate high temperature properties which would deteriorate if solvent were incorporated to compensate for the inadequate low temperature properties.

Claims (13)

1. A road surfacing composition comprising aggregate and a binder which is applied as a hot melt to a substrate comprises bitumen and a viscosity modifier comprising a wax and is characterised in that the viscosity modifier is present in the binder in an amount such that the penetration value at 250C (as hereinbefore defined) of the binder is in the range of 0.3 pen25-2.0 pen25 where pen25 is the viscosity of the binder without viscosity modifier and such that the viscosity at a predetermined spraying temperature is at least 25% lower than the viscosity of the binder without viscosity modifier.

2. A composition according to claim 1 which is substantially free of organic solvent.

3. A composition according to claim 1 or claim 2 in which the penetration value at 250C is in the range 0.5 pen25-1.5 pen25.

4. A composition according to any preceding claim in which the binder has a viscosity at the predetermined spraying temperature of less than 50% of the viscosity at that temperature absent the viscosity modifier.

5. A composition according to any preceding claim in which the bitumen has a penetration value (25"C) of at least 70dmm, preferably at least 100dmm, more preferably in the range 200-300dmm.

6. A composition according to any preceding claim in which the bitumen has a penetration value (250C) in the range 25-100dmm, preferably in the range 35-70dmm.

7. Process of surfacing a road comprising applying to the road a molten binder composition as defined in claim 1 and then spreading aggregate onto the binder.

8. Process of surfacing a road comprising mixing a binder as defined in claim 1 as a hot melt with aggregate and then laying the mixture on the road.

9. Process according to claim 7 or claim 8 in which the composition is as defined in any of claims 2 to 6.

10. Process according to any of claims 7 to 9 in which the temperature of the binder as it is applied to the road is at least 1000C, preferably in the range 1200C to 2000C.

11. Process of producing coated chippings for road surfacing comprising coating aggregate particles with a binder as defined in claim 1 as a hot melt and then cooling the coated particles.

12. A process for producing a composition according to any of claims 1 to 6 by mixing the binder components at a temperature above the softening point of at least one of the bitumen and wax components, preferably of the wax, discharging the binder as a fluid from the mixing apparatus and contacting the binder with the aggregate.

13. A process according to claim 12 in which the mixing temperature is above 1000C, preferably in the range 1200C to 2000C, more preferably in the range 1400C to 1600C.