WO1998038250A1

WO1998038250A1 - Method and fibre pellets for producing fibrous asphalt

Info

Publication number: WO1998038250A1
Application number: PCT/NO1998/000066
Authority: WO
Inventors: Ingvar Tuft
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-02-28
Filing date: 1998-02-27
Publication date: 1998-09-03
Anticipated expiration: 1999-08-28
Also published as: NO970951D0; AU6125298A; NO970951L; NO305760B1

Abstract

In a method for producing fibrous asphalt, aggregate, fibre pellets and bitumen are mixed at a temperature at which the bitumen is liquid. Hydrous fibre pellets are added, whereby, since the temperature at which bitumen is liquid is higher than the boiling point of the water, the heating causes evaporation and expansion of the water in the fibre pellets with associated rapid dissolution of the fibre pellets and dispersion of the fibres. Fibre pellets for use in the method contain most preferably approximately 20 % by weight of water, and moreover consist substantially of a fibrous material which is held together by a binding agent.

Description

Method and fibre pellets for producing fibrous asphalt

The invention concerns a method for producing fibrous asphalt, wherein aggregate, fibre pellets and bitumen are mixed at a temperature at which the bitumen is liquid. The invention also concerns fibre pellets for use in the method.

The terms "bitumen" and "asphalt" are interchanged to a certain extent. In order to avoid misunderstandings, in this patent application bitumen will be used to describe the pitch-like petroleum-containing binding agent, while asphalt will be used to describe the mixed mass which is employed in the finished product.

Asphalt is produced by mixing bitumen and aggregate, usually in the form of stones of different sizes, at approximately 180°C. The hot mass is mixed in a mixer, whereupon it is spread over a base and pressed to form a hard and solid mass. The finished product, the asphalt or the asphalt coating, thereby consists of stones embedded in bitumen.

The wear and tear on roads, particularly due to studded tyres, has led to a strong desire to produce asphalt with the greatest possible wear resistance. It has been found that the most wear-resistant asphalt is obtained when it contains a great quantity of large stones, typically stones with a diameter up to 16 mm. The use of aggregate containing a high proportion of large stones, however, causes the bitumen to easily run off during production, with the result that cavities are formed between the stones.

A known remedy for the above-mentioned problem is to add fibre to the asphalt mixture. The fibres cause the bitumen to have a pulpy consistency so that it does not easily run away. Asbestos fibre has been employed, but this has been abandoned due to the health risk associated with asbestos. Cellulose fibre is therefore used, either in loose form or as pellets. Cellulose fibre in loose form, however, has the disadvantage that it requires a great deal of space during transport. Moreover, in drum mixers, which are a standard type of asphalt mixer, loose fibre will be caught up in air filters, and it may also burn up.

Known fibrous pellets consist of fibre and a binding agent, which may be bitumen or a semi-liquid oil. When these known fibre pellets are employed, there is no occurrence of the above-mentioned problem of the fibres being caught up in filters or burning up during the mixing. In order to achieve rapid dissolution and dispersion of the pellets, known bituminous fibre pellets contain a relatively large amount of bitumen, typically 50% by weight. Nevertheless there is uncertainty associated with dissolution of the pellets, and the attainment of a homogenous mixture requires a longer mixing time than in the production of asphalt which only contains bitumen and aggregate, or bitumen, aggregate and loose fibre. The required mixing time depends on the kind of mixer employed, but in general experience shows that compared with the production of asphalt with loose fibre the required mixing time increases by between 20 and 30% when known fibre pellets are used.

On account of costs of transport, storage and handling, it is desirable that the proportion of fibre in the pellets should be as large as possible, and in this connection the high bitumen content is therefore undesirable.

NO 173 191 (Rettmeier) describes a granulate for introducing a fibrous filler material into liquid bitumen. The granulate includes fibres of the fibrous material, the fibres being coated and agglomerated to the granulate by a binding agent which has a binding effect on the fibres outside the said liquid bitumen and which loses its binding effect in the liquid bitumen in order thereby to cause dissolution of the granulates in the liquid bitumen, thereby obtaining a substantially homogeneous dispersion of the fibres in the liquid bitumen. The binding agent may be bitumen, and the fibres may be cellulose fibres or wood fibres.

The object of the invention is to provide a method for producing fibrous asphalt wherein fibre pellets are employed, where the required mixing time is reduced compared with the required mixing time with the use of known fibre pellets. It is a further object to provide fibre pellets for use in the method, and that the use of these fibre pellets results in reduced transport costs compared with known fibre pellets.

The objects are achieved according to the invention with a method and fibre pellets for use in the method of the type mentioned in the introduction, characterized by the features which are stated in the claims.

Thus the invention consists in the mixing of aggregate, fibre pellets and bitumen at a temperature at which the bitumen is liquid, and is characterized by the addition of hydrous fibre pellets, whereby, since the temperature at which bitumen is liquid is higher than the boiling point of the water, the heating causes evaporation and expansion of the water in the fibre pellets with associated rapid dissolution of the fibre pellets and dispersion of the fibres.

As mentioned at the beginning, asphalt is produced by mixing bitumen and aggregate at a temperature of approximately 180°C. The pressure inside the asphalt mixture is atmospheric or slightly higher.

It is a well-known fact that water which is heated up at atmospheric pressure from ambient temperature to approximately 180°C undergoes a very rapid evaporation and volume expansion. When the hydrous fibre pellets are heated up according to the invention to 180°C, the water causes the fibre pellets to undergo an explosive dissolution, with associated dispersion of the fibres.

The production of asphalt may also be undertaken at other temperatures than 180°C, and it is obvious that the effect of the water's evaporation and expansion and the explosive dissolution of the fibre pellets are also not dependent on exactly this temperature. The reason for producing asphalt at 180°C is that this temperature represents a sensible choice regarding the balance between the bitumen's viscosity, evaporation or burning off of solvents in the bitumen and heating economy.

In the production of asphalt both by the known method and by the method according to the invention, the order in which bitumen, aggregate and fibre are added is immaterial per se for the result, i.e. the finished asphalt mixture. Both in the production of asphalt by the known method, where either loose fibre or bituminous fibre pellets are employed, and by the method according to the invention, however, the shortest mixing time is achieved by first heating up the aggregate, then adding the fibres and finally adding hot bitumen. In this way the fibres are dispersed in the aggregate, and the bitumen is uniformly dispersed in the mixture of aggregate and fibre.

As mentioned, experience shows that the mixing time required in the production of asphalt with known bituminous fibre pellets is 20 to 30% longer than in the production of asphalt with loose fibre. It has been found that when producing asphalt by the method according to the invention, the dispersion of the fibres is just as good as in the use of loose fibre, and that the required mixing time is therefore also the same as in the use of loose fibre. It has further been found that in the method according to the invention, asphalt can be produced in a drum mixer without the fibres being caught up in filters or burning up as occurs when loose fibre is used. Thus the invention provides a method for producing asphalt wherein the advantages of employing fibre pellets are obtained with the same mixing time as in the use of loose fibre.

Fibre pellets according to the invention consist of a substantially fibrous material which is held together by a binding agent in addition to containing water. The explosive dissolution of the fibre pellets will be more or less dependent on the water content, and neither the method according to the invention nor the fibre pellets according to the invention is dependent on a specific water content. It has been found, however, that the water content of the fibre pellets should be between 5 and 40% by weight, more preferred between 10 and 30% by weight, further preferred between 15 and 25% by weight and most preferred approximately 20% by weight. This water content of 20%) by weight has been shown to represent a good balance between consideration of dispersion of the fibres in the production of asphalt at 180°C, and a desire that the water content should not be higher than necessary on account of the costs of transport of the pellets.

The fibre pellets can be prepared by known methods and known devices. In a preferred embodiment a water-soluble binding agent is employed, this being highly advantageous with regard to the compatibility with the water in the pellets.

In a preferred embodiment the fibre pellets contain wood fibre, and lignin is used as the binding agent.

Paper contains fibres of different types, such as cellulose fibres, and may also contain filler materials such as clay. Some types of paper, however, mainly contain wood pulp, and it has been found that this type of paper, and particularly paper which contains mechanically ground wood pulp, is highly suitable for the production of fibre pellets according to the invention. If this type of paper is used as the basic material for the pellets, it is not necessary to add extra binding agent, since lignin which exists in the mechanically ground wood pulp is adequate as a binding agent. Some types of newspaper contain mainly mechanically ground wood pulp, and it has been found that this newspaper is highly suitable as a basic material for production of fibre pellets according to the invention. The newspaper also contains printer's ink, and it has been found that this printer's ink acts as a binding agent and is advantageous in the production of the pellets.

By means of the invention the fibre pellets can be produced in a simple and reasonably priced manner, since collected newspaper is easily available at a low cost. At present there is an excess of collected newspaper, with the result that the production of fibre pellets according to the invention also provides environmental benefits.

Compared with the known fibre pellets described at the beginning, up to 50% of which typically consist of bitumen, by means of the invention fibre pellets are obtained with a higher fibre content, which compared to the pellets mentioned at the beginning provides lower transport costs.

The invention will now be explained in more detail in connection with a description of a specific embodiment.

An asphalt of the known type SKA 16, i.e. a so-called skeleton asphalt with up to 16 mm large aggregate, contains 8% by weight of stone filler materials with a size up to 0.074 mm, 20% by weight of stones with a size 0-8 mm,

17%) by weight of stones with a size 8-1 1 mm, 55% by weight of stones with a size 1 1-16 mm, 6.2% by weight of bitumen and 0.25% by weight of fibre.

In the production of this asphalt according to an embodiment of the invention, all the stone materials are heated to 180°C in a drum mixer with a capacity of 180 tons per hour. Hydrous fibre pellets according to the invention are then added. The water's evaporation and expansion cause an explosive dissolution of the pellets, with the result that the fibres are uniformly dispersed in the aggregate. The released water disappears mainly as steam via ventilation of the drum. Finally bitumen is added with a temperature of 180°C. The drum mixer feeds mass in and out continuously, with a dwell time of approximately 2 minutes, which is sufficient to produce the finished asphalt. Fibre pellets according to the invention can be prepared by granulating newspaper which contains mechanically ground wood pulp, and adding 40% by weight of water. This mixture is fed into an extruder with a temperature of approximately 105°C, where by means of a feed screw the mixture is pressed through a nozzle plate with openings of approximately 3 mm, thus forming strands, while at the same time approximately half the water is pressed out of the mixture or evaporates. On the outside of the nozzle plate the strands are cut into lengths of approximately 4 mm. Fibre pellets are thereby produced consisting of approximately 20% by weight of water and the rest mainly of mechanically ground wood pulp, held together by a binding agent composed of lignin, some printer's ink and also smaller proportions of other components which were in the newspaper. These other components which were originally in the newspaper may be colouring matter, small amounts of clay, cellulose, resin, various oils and also other components. As long as these other components occur in small amounts they are of no importance for the properties of the fibre pellets.

In the above the invention has been explained with reference to a specific embodiment. It is obvious, however, that the invention may be varied within the claims, and it is quite possible, for example, to produce hydrous fibre pellets in which, for example, starch is employed as a binding agent instead of lignin.

Claims

PATENT CLAIMS

1. A method for producing fibrous asphalt, wherein aggregate, fibre pellets and bitumen are mixed at a temperature at which the bitumen is liquid, characterized in that hydrous fibre pellets are added, whereby, since the temperature at which bitumen is liquid is higher than the boiling point of the water, the heating causes evaporation and expansion of the water in the fibre pellets with associated rapid dissolution of the fibre pellets and dispersion of the fibres.

2. A method according to claim 1, characterized in that fibre pellets are added containing between 5 and 40%) by weight of water, more preferred between 10 and 30% by weight of water, further preferred between 15 and 25% by weight of water and most preferred approximately 20% by weight of water.

3. Fibre pellets for use in the method for producing fibrous asphalt according to claim 1 or 2, wherein aggregate, fibre pellets and bitumen are mixed at a temperature at which the bitumen is liquid, characterized in that the fibre pellets contain between 5 and 40%) by weight of water, more preferred between 10 and 30% by weight of water, further preferred between 15 and 25% by weight of water and most preferred approximately 20% by weight of water, and moreover substantially consist of a fibrous material which is held together by a binding agent.

4. Fibre pellets according to claim 3, characterized in that the fibrous material contains or substantially consists of wood pulp, preferably mechanically ground wood pulp.

5. Fibre pellets according to claim 3 or 4, characterized in that the binding agent is water-soluble.

6. Fibre pellets according to claims 3 to 5, characterized in that the binding agent is substantially lignin.

7. Fibre pellets according to claims 3 to 6, characterized in that the binding agent contains printer's ink.

8. Fibre pellets according to claims 3 to 7, characterized in that the fibrous material contains or substantially consists of fibre which is made from paper which is made from wood pulp, preferably mechanically ground wood pulp. 9. Fibre pellets according to claims 3 to 8, characterized in that the fibrous material is composed of granulate of paper, especially newspaper.

10. Fibre pellets according to claims 3 to 9, characterized in that they are made of a mixture substantially of water and granulate of paper, especially newspaper.

AMENDED CLAIMS

[received by the International Bureau on 14 July 1998 (14.07.98); original claims 1-9 replaced by new claims bearing the same numbers; remaining claim unchanged (2 pages)]

1. A method for producing fibrous asphalt, wherein aggregate, fibre pellets and bitumen are mixed at a temperature at which the bitumen is liquid, characterized in that fibre pellets containing between 10 and 40% by weight of water are added, whereby, since the temperature at which bitumen is liquid is higher than the boiling point of the water, the heating causes evaporation and expansion of the water in the fibre pellets with associated rapid dissolution of the fibre pellets and dispersion of the fibres. 2. A method according to claim 1, characterized in that fibre pellets containing between 15 and 25% by weight of water are added.

3. Fibre pellets for use in the method for producing fibrous asphalt according to claim 1 or 2, wherein aggregate, fibre pellets and bitumen are mixed at a temperature at which the bitumen is liquid, characterized in that the fibre pellets contain between 10 and 40% by weight of water, and moreover substantially consist of a fibrous material which is held together by a binding agent.

4. Fibre pellets according to claim 3, characterized in that the fibre pellets contain between 15 and 25% by weight of water.

5. Fibre pellets according to claims 3 or 4, characterized in that the fibrous material contains or substantially consists of wood pulp, preferably mechanically ground wood pulp.

6. Fibre pellets according to claims 3 to 5, characterized in that the binding agent is water-soluble.

7. Fibre pellets according to claims 3 to 6, characterized in that the binding agent is substantially lignin. 8. Fibre pellets according to claims 3 to 7, characterized in that the binding agent contains printer's ink.

9. Fibre pellets according to claims 3 to 8, characterized in that the fibrous material contains fibre which is made from paper which is made from wood pulp, preferably mechanically ground wood pulp.