GB2452903A

GB2452903A - Bond coat

Info

Publication number: GB2452903A
Application number: GB0618422A
Authority: GB
Inventors: Alan Dinnen
Original assignee: Colas SA
Current assignee: Colas SA
Priority date: 2006-09-19
Filing date: 2006-09-19
Publication date: 2009-03-25
Anticipated expiration: 2026-09-19
Also published as: GB2452903B; GB0618422D0

Abstract

An emulsion comprises a binder and water, the binder comprising bitumen and a non-aromatic polymer. On application of the emulsion to a surface, it breaks to provide a bond coat which comprises the binder and which is non-tacky at ambient temperature. The emulsion is prepared via a process comprising mixing an aqueous phase with the bitumen and polymer. The emulsion may be used to provide a bond coat in the manufacture of a paved surface, such as a road pavement, a car park or a runway. A method of manufacture of such a surface comprises applying an emulsion on to a first surfacing material layer, allowing the emulsion to break thus providing a non-tack bond coat, and applying a second surface material layer on to the resulting broken emulsion bond coat at a temperature such that, on application of the second layer, the bond coat becomes tacky thereby forming a bond between the first and second surfacing material layers. The non-aromatic polymer is preferably rubber, especially polyisoprene.

Description

L

BOND COAT

Field of the Invention

The present invention relates to a bitumen-containing emulsion, which finds particular use in the production of paved surfaces such as road pavements, car parks and runways.

Background to the Invent ion

The structures of surfaces such as road pavements, car parks and runways typically comprise a series of layers of material such as bitumen or asphalt. In order to promote the development of a homogenous structure, bitumen emulsions are commonly sprayed between these layers.

Effective bonding between the different layers of such surfaces is particularly important in highly stressed areas of trafficking. This is because weak interface bonds that are further weakened by the action of traffic loading on the road, will create slippage of the layers in relation to one another thus creating a high tensile strain within the layers themselves and, therefore, the overall road structure. This results in the individual layers acting independently and not as a homogenous structure. In fact, it has been reported by Al Nageim and Al Hakim (Proceedings of the Third European Symposium on Performance and Durability of Bituminous Materials and Hydraulic Stabilised Composites, April 1999, published by Aeclificatio of Zurich, pages 725-736) that up to a 50% reduction in road life has been observed when complete debonding exists between the wearing and base layers of road structures.

It is, therefore, key that bonding between the layers in a road surface must be reliable and effective if the life time of the road is to be maximised. In addition, as the upper layers of road structures are sometimes constructed in stages, effective bonding between the existing and new surfaces is also key.

Traditionally, rapid-setting, cationic, bitumen emulsions of low bitumen content, for example approximately weight%, have been used to provide so-called "tack coating". Such materials are typically manufactured using a soft paving grade bitumen, for example 200 penetration grade, and provide a little extra binding capacity to an existing surface, which is often adequate to initiate adhesion between the layers in a road surface. Tack coating is traditionally carried out well upstream of the road paving operation.

Alternatively, so-called "bond coats" may be used to facilitate bonding between the layers in road surfaces.

Generally, bond coats have a higher binder or bitumen content than tack coatings, for example approximately 65 weight, and often contain binder modifiers such as polymers, for example styrene-butadiene-styrene (SBS).

Such conventional bond coats are usually applied at a higher rate of spreading, eg. 0.5-1.0 1/rn2, than the above-mentioned tack coatings, thus promoting improved adhesion and some waterproofing capability, which minirnises water damage in the underlying structure of the road.

The use of bond coats came to the fore with the introduction of thin asphalt road surfacings, which can be laid as thinly as approximately 1.5 cm. When designing thin surfacing systems, it is important to provide good adhesion to the base layer to prevent the upper layer(s) from peeling away. As previously mentioned, bond coats provide a degree of imperviousness to the road surface, which is desirable as thinner surface layers are more prone to infiltration of water than the traditional, dense, asphalt surface layers, which can be 4-5 cm thick.

There are various disadvantages associated with the use of known tack coatings and bond coats, in particular pick-up of the coating on the tyres of both paving machines and material delivery trucks, which may, in turn, cause d contamination of nearby road surfaces. There is, therefore, also an increased risk of heavy machines sliding or skidding on the coatings.

As a result, paver-integrated bond coat spraying devices have been developed so that bond coats can be applied immediately ahead of the surfacing mixture in a combined operation. However, such complex devices have operational and cost disadvantages, typically costing up to three times as much as conventional paving or spraying devices.

Therefore, bond coat systems which are not picked up on the tyres of vehicles such as paving machines or delivery vehicles, but which still provide a strong adhesive bond between the layers in a road surface are desired. In addition, a bond coat which may be spread using traditional spraying devices, therefore avoiding the use of expensive and complicated paver-integrated spraying devices, would also be desirable.

Summary of the Invention

According to a first aspect of the present invention an emulsion comprises a binder and water, wherein the binder comprises bitumen and a non-aromatic polymer, and wherein, in use when the emulsion is applied on to a surface, the emulsion breaks to provide a bond coat which comprises the binder and which is non-tacky at ambient temperature.

According to a second aspect of the present invention, a process for the preparation of the above-described emulsion comprises mixing an aqueous phase with bitumen and a non-aromatic polymer.

According to a third aspect of the present invention, an emulsion of the invention is used to provide a bond coat in the manufacture of a paved surface, such as a road pavement, a car park or a runway. a

According to a fourth aspect of the present invention, a method of manufacture of such a surface comprises applying an emulsion of the invention on to a first surfacing material layer, allowing the emulsion to break thus providing a non-tack bond coat comprising the binder, and applying a second surfacing material layer on to the resulting bond coat at a temperature such that, on application of the second layer, the bond coat becomes tacky thereby forming a bond between the first and second surfacing material layers.

The emulsion of the invention, when used to provide a bond coat in the manufacture of surfaces such as roads, overcomes the afore-mentioned problems associated with the use of known bond coats or traditional tack coating. More specifically, the emulsion according to the present invention, once broken, provides a non-tack binder or "bond coat" which, on heating, for example during the application of an upper surfacing layer on to the broken emulsion binder, becomes tacky thus forming a bond between the layers of the road surface. In addition, the emulsion according to the present invention may be applied using conventional spraying devices.

A further advantage of the emulsion according to the present invention and its use as a bond coat is that the emulsion is preferably substantially "solvent-free".

Detailed Description of the Invention

In the context of the present invention, the term "non-tack" means a substance of substantially no adhesive capability or stickiness at ambient temperature such that it is not picked up by objects placed on top of it. By ambient temperature is meant the air temperature of the location where the surface is being laid, which may be as low as approximately 0°C and as high as approximately 35- 40°C in some locations, and is generally in the range 10- 25°C. Such a substance must first be heated, preferably to a temperature of approximately 50°C or higher, more preferably to at least 60°C and most preferably to at least 70°C, before it will become tacky.

In the context of the present invention, the term "non-aromatic polymer" means a polymer containing no aromatic groups, either in its backbone or as substituents attached to the polymer backbone.

The emulsion of the present invention finds particular use in the provision of a bond coat in the manufacture of paved surfaces such as road pavements, car parks or runways. The emulsion comprises a binder and water, the binder itself comprising bitumen and a non-aromatic polymer.

The emulsion is typically a so-called ubitumenin water" emulsion. This means that when it breaks, ie. when the bitumen binder coagulates and is no longer present as droplets suspended in the water at which stage the emulsion cannot reform, the residual binder or "bond coat" is not tacky. The binder only becomes tacky at temperatures associated with the overlay of upper surfacing layers in the construction of roads, for example. Such temperatures are typically in the range 50°C or higher, and are more preferably 60°C or higher and most preferably 70°C or higher. On heating, the bond coat softens at its interface with the overlay thus achieving a bond. The break index of the emulsion of the invention is generally in the range 45-g, and preferably in the range 60-90 g, which is indicative of rapid breaking, le. generally less than 100 g. The break index is determined using a method based on NFT 66-017 (tentative French National Standard December 1983) as detailed in Annex 2.

The emulsion of the invention may be cationic or anionic. Preferably, however, the emulsion is cationic, as cationic emulsions generally have better breaking and adhesion properties than anionic emulsions. If the emulsion is anionic, the emulsion breaks comparatively slowly such as to be relatively ineffective in comparison with cationic emulsions.

The bitumen used in the emulsion of the present invention preferably has a consistency in the range 50-150 grade. These so-called "grades" are designations given to bitumens relating to the depth of penetration of a needle into the bitumen, which is a standard test in the art.

Thus, bitumen is generally supplied in a grade of up to around 300, which signifies a very soft bitumen, or in a grade as low as approximately 25, which signifies a very hard bitumen. The types of bitumen suitable for use in the emulsion of the present invention more preferably have a consistency in the range 50-100 grade and most preferably in the range 70-100 grade. Such bitumens are identified by the terminology "70/100" in the art.

The non-aromatic polymer used in the emulsion of the present invention is preferably selected from natural rubber, synthetic rubber and mixtures thereof. More preferably a polyisoprene is employed and, most preferably, a polyisoprene with an average molecular weight in the range 200000-1000000, which typically has a relatively broad weight distribution.

It has been found that binder modifiers conventionally used in the production of road surfacing materials, such as styrene-butadiene-styrene (SBS) and styrene-isoprene-styrene (SIS), form emulsions which, once broken, provide bond coats which are tacky at ambient temperature. Such modifiers are, therefore, unsuitable for use in the emulsion of the present invention. This is thought to be because of the different interactions between these types of polymer and the bitumen, in comparison with the polymer used in the present invention. It is therefore envisaged that other types of non-aromatic polymer, which are similar in their structure to the polymer used in the emulsion of the invention, will be suitable for use in the emulsion of the present invention.

The polymer used in the present invention is typically supplied in the form of a latex or water-based polymer dispersion. The concentration of the latex is generally in the range 45-70 weight of polymer as based on the total mass of the dispersion, and preferably in the range 50-65 weight. Suitable latexes are commercially available from Revertex (Malaysia) SDN, BERHAD under the trade name LATZ.

The binder, le. bitumen plus polymer, in the emulsion of the invention typically comprises 0.3-3.0 weight % of polymer, based on the mass of bitumen in the binder. More preferably, the binder will comprise 1.2-1.8 weight of polymer based on the mass of bitumen in the binder.

The amount of binder in the emulsion of the invention should be such that the emulsion is easy to apply using conventional paving machinery and forms an effective coating on the surface to which it is being applied.

Equally, however, it is envisaged that the emulsion may be applied by hand. The amount of binder is typically in the range 45-75 weight based on the total mass of the emulsion. More preferably, the binder is present in an amount of 60-70 weight % and most preferably 61- 68 weight % based on the total mass of the emulsion. However, if the emulsion is to be applied by hand the amount of binder in the emulsion will typically be in the range 45-55 weight based on the total mass of the emulsion.

Such binder proportions will provide emulsions having viscosities typically in the range 2-20°E (Engler; approximately 10 to 2 x iO m2/s; measured in accordance with BS 434:1984 as detailed in Annex 1), and preferably in the range 6-12°E. Such viscosities enable the efficient spreading of the emulsion of the invention whilst allowing it to form a comprehensive coating.

The emulsion of the invention typically has a Vialit Pendulum Peak cohesion value of greater than 1.0 J/cm2 and preferably greater than 1.2 J/cm2, as measured by the method detailed in Annex 3. This value is indicative of the energy per unit area which is needed to break a film of the emulsion binder under specified conditions of impact.

Therefore, the higher the cohesion value of the emulsion, the greater its strength.

The emulsion of the present invention may also comprise other substances commonly used in the manufacture of bitumen-based emulsions, for example water-soluble metal salts such as calcium chloride, which reduce settlement of the emulsion by increasing the density of the aqueous phase. The addition of salts such as calcium chloride also controls the emulsion viscosity during storage. This helps to reduce osmosis of water into the bitumen droplets, which may contain salt left over from inadequate de-salting of the crude oil from which the bitumen is derived prior to distillation. The swelling of the bitumen droplets through osmosis of water will result in an increased emulsion viscosity. Therefore, the presence of a salt such as calcium chloride reduces this problem. If the emulsion comprises a water-soluble metal salt such as calcium chloride, it will typically be present in an amount of approximately 0.1-1.0 weight % based on the total mass of the emulsion, and preferably in an amount of approximately 0.2 weight.

As previously mentioned, the emulsion of the invention is preferably substantially solvent-free. More specifically, it is preferably free from the types of solvent normally employed in traditional road surfacing materials such as those derived from petroleum oil, f or example kerosene. Such solvents have a damaging effect on the environment and the avoidance of their use through use of the emulsion according to the present invention is therefore advantageous. By "substantially solvent-free' is meant that the emulsion typically comprises less than 10 weight of one or more solvents other than water based on the total mass of the emulsion, and preferably comprises less than 5 weight% and more preferably comprises less than 1 weight of solvent other than water.

The emulsion according to the present invention is prepared by a process comprising mixing an aqueous phase with bitumen and a non- aromatic polymer. The polymer may be incorporated into either the aqueous phase or the bitumen, or may be added after emulsification. Preferably, however, the polymer is initially added to the aqueous phase, and the resulting polymer-containing aqueous phase is then mixed with the bitumen. As previously discussed, the polymer is typically incorporated into the emulsion using a polymer-in-water dispersion.

In the process for manufacturing the emulsion of the invention, an emulsifier is typically also employed. If employed, the emulsifier may be any of those conventionally used in the production of bitumen emulsions. Typically, the emulsifier is an amine, for example a fatty amine derivative such as those of the Redicote range available from Akzo Nobel, for example Amine EM44 which comprises a fatty alkyldiamine ethoxylate.

If the emulsion of the invention is to be provided in the form a cationic emulsion, an acid is also preferably added during manufacture of the emulsion in order to bring about dissolution of the emulsifier into the aqueous phase, thus promoting the emulsification process. Preferably, the acid employed for this purpose is hydrochloric acid. If the emulsion is to be provided as an anionic emulsion, however, an alkali such as sodium hydroxide is typically used for this purpose.

Typically, the emulsion of the invention may be manufactured using apparatus such as a colloid mill, in which energy is applied to the system by passing a mixture of hot bitumen and aqueous phase between a rotating disc, cone or flywheel and a stator. The emulsion may be manufactured in a batch or continuous process. If a batch process is employed, the aqueous phase is usually prepared in a tank into which heated water, and typically an emulsifier and other standard emulsion chemicals, such as hydrochloric acid, are metered and the solution is thoroughly mixed, before being dosed with the bitumen to the colloid mill. In comparison, in a continuous process, the materials are continuously dosed using individual dosage pumps into the colloid mill.

As previously stated, the emulsion of the invention may be used to provide a bond coat in the manufacture of paved surfaces such as road pavements, car parks and runways. The method of manufacture of such a surface according to the present invention comprises the steps of applying an emulsion of the invention on to a first surfacing material layer, for example a layer of bitumen or asphalt. The emulsion will break thus providing a non-tack bond coat which comprises the binder. Prior to the next stage in the method of manufacture, the emulsion is preferably in fully broken form. A second layer of surfacing material is then applied on to the binder at a temperature such that the binder will become tacky thereby forming a bond between the first and second surfacing material layers. The temperature at which the second layer of surfacing material is applied on top of the binder is typically at least 50°C, more preferably at least 60°C and most preferably at least 70°C. A homogenous, bonded structure results from this process.

A bond coat resulting from an emulsion of the invention, when incorporated in a road, or similar, structure by the previously-discussed method will typically have a mean interlayer torque bond strength of greater than 850 kPa and preferably greater than 1000 kPa, as measured by the method detailed in Annex 4. This value indicates the bond strength between the bond layer and the substrate layer, eg. bitumen or asphalt, to which it is attached.

Therefore, the greater the bond strength the better.

The present invention will now be described with reference to the following Examples, which provide two sample formulations of an emulsion according to the present invention. In the following Examples, the weight % values are based on the total mass of the emulsion unless otherwise stated. The viscosity and break index of the emulsions were determined as detailed in Annexes 1 and 2 respectively. The sieve residue value of the emulsion, which is indicative of the homogeneity of the emulsion and the likelihood of it clogging spreading equipment, was determined in accordance with a method technically equivalent to that contained in BS 434:1984 and which is detailed in Annex 5. The lower the sieve residue value the more homogeneous the emulsion and the less likely it is to clog spreading equipment.

Example 1

Specification Mm Max Unit

Binder Content 64.00 -weight Viscosity 6.00 12.00 °E Acidity 2.00 3.00 pH Break Index 60.00 90.00 g Sieve Residue 150 -0.30 weight % Formula Weight 70/100 bitumen 63.4 Emulsifier 0.2 Hydrochloric acid 0.3 Latex a 1.4 Calcium chloride 0.2 Water 34.5 Total 100

Example 2

Specification Mm Max Unit

Binder Content 49.00 51.00 weight Viscosity 2.00 6.00 °E Acidity 2.00 3.00 pH Break Index 60.00 90.00 g Sieve Residue -0.30 weight I.Lm Formula Weight 70/100 bitumen 49.0 Emulsifier 0.2 Hydrochloric acid 0.3 Latex a 1.1 Calcium chloride 0.2 Anti-settlement agent <0.1 Water 49.2 Total 100 a The latex used in the formulations of Examples 1 and 2 was LATZS, which is latex LATZ as detailed in the formula sheet of Annex 5, containing approximately 1.3 weight % of one or more stabilisers.

The present invention therefore provides an emulsion which finds particular use as a bond coat in the manufacture of surfaces such as road pavements, car parks and runways. The resulting bond coat has desirable properties such as low-pick up by construction traffic, good interlayer bonding and high cohesive strength. The bond coat may be spread using conventional spraying devices thus keeping operational costs to a minimum.

Claims

1. An emulsion comprising a binder and water, wherein the binder comprises bitumen and a non-aromatic polymer, and wherein, in use when the emulsion is applied on to a surface, the emulsion breaks to provide a bond coat which comprises the binder and which is non-tacky at ambient temperature.

2. An emulsion according to claim 1, which is substantially free of solvents derived from petroleum oil.

3. An emulsion according to claim 1 or claim 2, which is cat ionic.

4. An emulsion according to any preceding claim, wherein the consistency of the bitumen is in the range 50-150 grade.

5. An emulsion according to claim 4, wherein the consistency of the bitumen is in the range 70-100 grade.

6. An emulsion according to any preceding claim, wherein the polymer is selected from natural rubber, synthetic rubber and mixtures thereof.

7. An emulsion according to claim 6, wherein the polymer is a polyisoprene.

8. An emulsion according to claim 7, wherein the polyisoprene polymer has a molecular weight in the range 200000 to 1000000.

9. An emulsion according to any preceding claim, wherein the binder is present in an amount of 45-75 weight % based on the total mass of the emulsion.

10. An emulsion according to claim 9, wherein the binder is present in an amount of 60-70 weight and preferably 61-68 weight based on the total mass of the emulsion.

11. An emulsion according to any preceding claim, wherein the binder comprises 0.3-3.0 weight I of polymer based on the mass of bitumen in the binder.

12. An emulsion according to claim 11, wherein the binder comprises 1.2-1.8 weight % of polymer based on the mass of the bitumen in the binder.

13. An emulsion according to any preceding claim, having a viscosity of 2-20°C measured according to BS 434:1984.

14. An emulsion according to claim 13, having a viscosity of 6-12°C.

15. An emulsion according to any preceding claim, having a break index of 45-bOg measured according to NF T 66-017.

16. An emulsion according to claim 15, having a break index of 60-90g.

17. A process for the preparation of an emulsion as defined in any preceding claim, the process comprising mixing an aqueous phase with bitumen and a non-aromatic polymer.

18. A process according to claim 17, wherein the polymer is initially added to the aqueous phase, and the resulting polymer- containing aqueous phase is then mixed with the bitumen.

19. Use of an emulsion as defined in any of claims 1 to 16 to provide a bond coat in the manufacture of a paved surface.

20. Use according to claim 19, wherein the surface is selected from road pavements, car parks and runways.

21. A method of manufacture of a paved surface comprising the steps of applying an emulsion as defined in any of claims 1 to 16 on to a first surfacing material layer, allowing the emulsion to break thus providing a non-tack bond coat comprising the binder, and applying a second surfacing material layer on to the resulting bond coat at a temperature such that, on application of the second layer, the bond coat becomes tacky thereby forming a bond between the first and second surfacing material layers.

22. A method according to claim 21, wherein the surfacing material is selected from bitumen and asphalt.

23. A method according to claim 21 or claim 22, wherein the temperature at which the second layer is applied is at least 50°C.

24. A method according to claim 23, wherein the temperature is at least 70°C.

25. A method according to any of claims 21 to 24, wherein the surface so-produced is selected from road pavements, car parks and runways.