GB2255978A

GB2255978A - Coated aggregates

Info

Publication number: GB2255978A
Application number: GB9110947A
Authority: GB
Inventors: Anthony Stephen Collins
Original assignee: AYTON ASPHALTE Ltd
Current assignee: AYTON ASPHALTE Ltd
Priority date: 1991-05-21
Filing date: 1991-05-21
Publication date: 1992-11-25
Also published as: GB9110947D0

Abstract

A bitumen in water emulsion is mixed with particles of aggregate without heat, the emulsifying agent being selected relative to an adhesive agent so that the formed material may be stock piled without deterioration. In the mass of coated aggregate a portion of the emulsion has been broken to coat the aggregate particles with bitumen and a portion of the emulsion is unbroken. The coated mass may be laid at a site of use, e.g. in road making, and then compacted to break up the unbroken emulsion. The emulsifying agent is preferably a quaternary ammonium salt, e.g. N-tallow alkyl pentamethyl propylene diammonium chloride, and the adhesive agent is preferably a diamine, e.g. N-tallow alkyl trimethylene diamine.

Description

COATED AGGREGATES The invention relates to the coating of particles of aggregate, e.g. of the type used in road making or the like. More particularly, the invention is directed to the need to provide aggregate coated with a binder such as bitumen and which has an extended workability so that it can be stockpiled for future use but without the use of fluxes.

According to the invention in one aspect there is provlded a method of coating particles of aggregate with a bitumen-in-ater emulsion, the method comprising: a) including in the aqueous phase an emulsifying agent which will readily bond to the particles of the aggregate; b) including in the bituminous phase an adhesive agent which will adhere bitumen to particles of the aggregate; c) combining the aqueous phase and the bituminous phase to form a bitumen-in-water emulsion; d) mixing the emulsion with particles of aggregate in the substantial absence of heat, the emulsifying agent being caused to reversibly bond to the aggregate particles and thereby destabilise the emulsion, so bringing bitumen into contact with the particles, the adhesive agent causing the bitumen to adhere to the aggregate particles and displacing the emulsifying agent which is released and returned to the emulsion, whereby the mass formed comprises particles of aggregate to which bitumen is bonded and bitumen-in-water emulsion which is not yet broken.

Preferably the aqueous phase is acidified, although it is not essential. The emulsifying agent included according to the present invention may be selected from a wide range of substances and is preferably a quaternary ammonium salt. Preferably the emulsifying agent is water dispersible. Particularly preferred are diammonium chlorides, especially pentamethyl propylene diammonium chlorides, most preferably N-Tallow alkyl penta propylene diammonium chloride where the alkyl group has from say 1 to 40 carbon atoms in the chain. It is most convenient to include the quaternary ammonium salt as a 50% solution in water / isopropyl alcohol. The proportion of the included agent should be from about 0.18 by weight to about 15% by weight.

Other ingredients may be present in the water to form the aqueous phase of the emulsion; an example is calcium chloride.

The adhesive agent included in the composition to be the bituminous phase of the bitumen-in-water emulsion may be selected from a wide range of substances known to bind bitumen to particles of aggregate. Preferably the agent is a diamine, such as an alkyl trimethylene diamine (where the alkyl group has from 1 to 40 carbon atoms in the chain), and is most preferably N Tallow alkyl trimethylene diamine. The proportion of the included adhesive agent is from about 0.1% to about 1,5 by weight. Other ingredients which may be present in.the bituminous phase; examples include certain surface active agents.

The emulsion to be formed preferably conforms to British Standard BS434:Part 1: 1984, Table 2, Class h3. Preferably the bitumen is one which has a penetration grade conforming to BS3690:Part 1: 1989, Table 1, i.e. contains no added hydrocarbon diluents, and is capable of mixing with dry or damp aggregate at ambient temperature to produce coated bitumen macadams of a composition conforming to BS4987:Part 1: 1988.

The emulsion is formed simply by mixing the water phase and the bitumen phase under shear. The formed emulsion can be added to the aggregate by mixing at ambient temperature i.e. it is not necessary to introduce heat. This saves energy, pollution and reduces the dangers to which operatives are exposed.

Because o= the presence of the included emulsifying agent in the aqueous phase and the adhesive agent in the bitumen phase there is a two stage 'break' of the emulsion on to the aggregate to be coated. Initially adsorption of the quaternary ammonium ions from the aqueous phase onto the aggregate surface results in a decrease in emulsion stability, by lowering the emulsifier concentration in the aqueous phase and hence on the surface of the dispersed bitumen particles in the emulsion.Breaking of the emulsion commences with adhesion of bitumen to the aggregate surface being expedited by the adhesion agent Quaternary ammonium ions which initiated the breaking process are released from the aggregate surface into the aqueous phase and dynamic equilibrium in the remaining unbroken emulsion is restored, with a layer of bitumen coating the aggregate surface with good adhesion due to the presence of the diamine. The wetting agent in the bituminous phase has assisted in displacing the emulsifying agent from the bond therefor with the particles of the aggregate. The product comprises aggregate which is coated with bitumen, together with some unbroken emulsion which is available to be broken when the mass is later laid.

The aggregate may be selected from the wide range of materials suitable for use as road aggregates. The moisture content is not critical provided the aggregate is only surface damp, and the granulometry is normally selected from BS 4987 or other standards relevant to the type of material being produced.

In another aspect the invention provides a mass of aggregate which has been coated with a bitumen-in-water emulsion, wherein a portion of the emulsion has been broken to coat the aggregate particles with bitumen and a portion of the emulsion is unbroken whereby the mass is of extended workability.

The mass may be laid in the usual way, say up to two or more weeks after stockpiling, and then be compacted. The mechanical action of working the mass, (including the compaction) breaks the unbroken emulsion therein, and this together with evaporation of water causes the mass to harden.

In another aspect the invention provides a method of laying a mass as dfind, wherein the mass is laid at a site of use and the unbroken emulsion is then broken by the mechanical action.

The invention also includes the separate aqueous and bituminous phases of the emulsion.

Claims

1. A method of coating particles of aggregate with a bitumen in-water emulsion, the method comprising: a) including in the aqueous phase an emulsifying agent which will readily bond to the particles of the aggregate and be displaced therefrom.

b) including in the bituminous phase an adhesive agent which will adhere bitumen to particles of the aggregate c) combining the aqueous phase and the bituminous phase to form a bitumen-in-water emulsion d) mixing the emulsion with particles of aggregate in the substantial absence of heat, the emulsifying agent being caused to reversibly bond to the aggregate particles and thereby destabilise the emulsion, so bringing bitumen into contact with the particles, the adhesive agent causing the bitumen to adhere to the aggregate particles and displacing the emulsifying agent which is released and returned to the emulsion, whereby the mass formed comprises particles of aggregate to which bitumen is bonded and bitumen-in water emulsion which is not yet broken.

2. A method according to Claim 1, wherein the aqueous phase is acidified.

3. A method according to Claim 1 or 2, wherein the included emulsifying agent is a quaternary ammonium salt or the like.

4. A method according to Claim 3, wherein the salt is a diammonium chloride.

5. A method according to Claim 3 or 4, wherein the salt is N - Tallow alkyl pentamethyl propylene diammonium chloride.

6. A method according to Claim 5, wherein the alkyl group has from say 1 to 40 carbon atoms.

7. A method according to any of Claims 3 to 6, wherein the salt is added to the aqueous phase as a 508 solution in water/isopropyl alcohol.

8. A method according to any preceding Claim, wherein the adhesive agent is a diamine.

9. A method according to Claim 8, wherein the diamine is an alkyl trimethylene diamine.

10. A method according to Claim 8 or 9, wherein the alkyl group has from say 1 to 40 carbon atoms.

11. A method according to any of Claims 8, 9 or 10, wherein the adhesive agent is N - Tallow alkyl trimethylene diamine.

12. A mass of aggregate which has een coated with a bitumen-in water emulsion, wherein a portion of the emulsion has been broken to coat the aggregate particles with bitumen and a portion of the emulsion is unbroken whereby the mass is of extended workability.

13. A method of laying a mass according to Claim 12 wherein in that the mass is laid at a site of use and then compacted to break up the unbroken emulsion in the mass.