The present invention relates to a bitumen emulsion, a pro¬ cess for its preparation, a breaking additive intended for use in the bitumen emulsion and the use of the bitumen emul¬ sion. More specifically, the present invention relates to a bitumen emulsion of an anionic or cationic type having a breaking additive, a breaking additive intended for use in the bitumen emulsion and the use of the bitumen emulsion as a binder in road building, road maintenance, recycling of old asphalt pavings or construction work.

A great number of methods for the breaking of bitumen emul¬ sions are known. However, they all suffer from the disadvan¬ tage that the breaking occurs immediately. In order to enable the use of bitumen emulsions for e.g. the manufacture of asphalt mixes it will be necessary to achieve a controlled delayed breaking. In this way a very stable bitumen can be used, which gives a good covering of the stone material, which allows mixing and paving as well as compaction without breaking.

Once the compaction having been carried out, the emulsion should break as fast as possible in order to avoid breakdown of the traffic. Another reason why a rapid breaking is desired is that cold asphalt mix made with emulsion is sensi¬ tive to water (i.e. rain) before the emulsion is broken.

One way to achieve this is disclosed by European Patent Application No 90850415.2. This method utilizes a breaking additive, which comprises a water-in-oil emulsion, in which an aqueous solution of a neutralizing salt is dispersed in a continuous oil phase. Thus this process is based on the use of water-soluble substances in order to achieve the breaking.

It is an object of the present invention to provide a bitume emulsion in which it is possible to use solids instead of aqueous solutions, which solids are known per se to break bitumen emulsions. However, bitumen emulsions will break immediately on the addition of such substances thereto. The problem has been to achieve a delayed breaking in order to permit paving and compaction before solidifying.

According to the present invention it has now been found that this problem can be solved by making a suspension of the solid breaking material as a breaking controlling additive which is mixed into the bitumen emulsion just before the wanted moment of breaking. The oil film then delays the contact between the breaking material and the bitumen emul- sion.

In accordance with the above the present invention thus relates to a bitumen emulsion of an anionic or cationic type having a breaking additive, which bitumen emulsion is charac- terized in that the breaking additive has been added to the emulsion in the form of a suspension of a breaking solid in oil.

According to an embodiment of the invention the emulsion is of the cationic type, in which case, for instance, the following alkaline materials can be used as breaking chemicals: Calcium hydroxide, calcium oxide, alkali metal tetraborate, alkali metal carbonate, alkali metal etasili- cate, cement (STS cement P) , alkali metal salts of sulphona- ted lignin, magnesium carbonate and magnesium hydroxide.

The term "alkali metal" as used above is intended to denote sodium and potassium, preferably sodium. Examples of a sodium salt of sulphonated lignin is Diwatex 30 from Hol en Kemi.

The period of delay can be varied to some extent by selectin different oils for the suspension. The selection of the oil is of great importance to the stability of the suspension. According to the present invention the oils which are used i this connection can be selected from mineral oils, synthetic oils and vegetable oils.

The principle of allowing the oil film to delay the contact between an emulsion breaking solid and a bitumen emulsion ca also be utilized if an emulsion of the suspension in water is made. Hence in accordance with an embodiment of the present invention the suspension of solid in oil is added as an emulsion in water. In this case, however, water-soluble salts cannot be used as breaking chemical since these will leach out through the oil film into the continuous aqueous phase. When such a breaking emulsion is mixed with the bitumen emulsion an immediate breaking is obtained, which is not desirable.

According to another aspect of the invention this relates to an breaking additive for use in a bitumen emulsion according to the invention, which breaking additive is characterized in that it comprises a suspension of a breaking solid in oil.

According to an embodiment of the breaking additive according to the invention the suspension of solid in oil is emulsified in water.

The bitumen emulsion according to the present invention is prepared by a process, which is characterized in the following steps a) preparing a suspension of a breaking solid in oil, b) mixing the suspension with a bitumen emulsion of an anionic or cationic type, the suspension optionally being emulsified in water before step b) .

The invention also relates to the use of a bitumen emulsion according to the invention in road building, road maintenance, recycling of old asphalt pavings or in construc¬ tion work such as roofing, coating and water-proofing.

The invention will be further described in the following by means of a number of working examples.

Example 1

A suspension consisting of 49% of calcium hydroxide in a naphthenic distillate (viscosity at 40°C 32mrrr/s, carbon type analysis C _A =30%, C _N =30%, C _p =45%) is made by dispersing by means of a high speed mixer of the type Ultraturrax ^® . When 2% of the above suspension is added to a bitumen emulsion BE65/5000 (Nynas Bitumen AB) a well-broken emulsion is obtained in which water has separated within 20 hours.

In order to further investigate the effect of the breaking additive a so-called run off and wash off test was performed. The test is carried out in the following way: A certain amount of breaking additive is added to a bitumen emulsion. The emulsion is then mixed with stone material which has become moistened with water. The mixture is mixed for 30 seconds and then poured into a funnel having a wire netting at its bottom. Liquid which flows out from the funnel during 30 minutes is collected. The water is evaporated and the residue is reported as "Run off" expressed as percent binding agent calculated on the amount of binding agent added. The mix is left in the funnel for additional 30 minutes, whereafter 200 ml of water is poured over the mass. The water is collected and evaporated. The residue is weighed and reported as "Wash off" in percent of binding agent added.

2% of the suspension above was added to a bitumen emulsion P91-212-01 (Nynas Bitumen AB) . 500 g of stone material (granite from Farsta; composition 52% 4-8 mm, 13% 2-4 mm and

35% 0-2 mm) were moistened with 20 g of water. 40 g of the above emulsion were added thereto. The mixture was poured into a funnel for measuring of "Run off" and "Wash off- according to the above.

Results: Run off: 0%, Wash off: 0.8%. The results can be compared with the case when no breaking suspension is added: Run off: 5%, Wash off: 11%.

Example 2

A suspension consisting of 38% of sodium metasilicate in a naphthenic distillate (viscosity at 40°C 200 mm ² /s, carbon type analysis C _A =25%, C _N =30%, C _p =45%) is made by dispersing by means of a high speed mixer of the type Ultraturrax ^® .

When 2% of the above suspension are added to a bitumen emul¬ sion BE 65115000 a broken emulsion is obtained, wherein the water has not separated within 24 hours.

2% of the above suspension were added to a bitumen emulsion

P91-212-01 and tests confirming "Run off" and "Wash off" were carried out in the same way as in Example 1.

Results: Run off: 0%, Wash off: 0%.

Example 3

A suspension consisting of 68% of cement in a naphthenic distillate (viscosity 32 mm ² /s at 40°C) is made by dispersing by means of a high speed mixer of the type Ultraturrax ^® . The suspension is then emulsified in water. The emulsion has the following composition: 47% of cement suspension, 47% of water, 3% of emulsifier Berol 79 and 3% of emulsifier Berol 540 (both emulsifiers from Berol Nobel AB) .

3,5% of the emulsion above was added to a bitumen emulsion P91-212-01. 40 g of the mixture were added to 500 g of moist

stone material (as in Examples 1 and 2) . The mixture was stirred for 30 seconds and poured into a funnel to test "Run off" and "Wash off".

Results: Run off: 0%; Wash off: 0.9%.