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Title:
WEARING COURSE FOR GRAVEL ROADS
Document Type and Number:
WIPO Patent Application WO/2012/057690
Kind Code:
A1
Abstract:
The present invention relates to a wearing course for gravel roads. A wearing course for gravel roads shall have a hard and even surface and yet be elastic in order to withstand traffic and weather, in order not to dust and to manage the ground frost in the winter. The wearing course shall also meet the environmental requirements of today. In order to achieve this, the material for the wearing course comprises wearing course gravel with a grain size of 0-18 mm and a mixture of clay and lignine in the form of a powder or a granulate.

Inventors:
JOHANSSON JAN (SE)
Application Number:
PCT/SE2011/051281
Publication Date:
May 03, 2012
Filing Date:
October 27, 2011
Export Citation:
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Assignee:
JOHANSSON JAN (SE)
International Classes:
E01C7/08; E01C7/36
Foreign References:
US20090103979A12009-04-23
DE202005015536U12005-12-15
GB338247A1930-11-27
AU769470B22004-01-29
Other References:
See also references of EP 2633122A4
Attorney, Agent or Firm:
VALEA AB (Malmö, SE)
Download PDF:
Claims:
CLAIMS

1. Wearing course for gravel roads, characterized in that the material for the gravel road wearing course comprises wearing course gravel with a grain size of 0-18 mm and a mixture of clay and lignine in the form of a powder or a granulate.

2. Wearing course according to claim 1 , characterized in that the wearing course gravel has a grain size of 0-16 mm.

3. Wearing course according to claim 1 or 2, characterized in that the amount of wearing course gravel constitutes maximum about 95 % of the total amount of the wearing course material.

4. Wearing course according to any one of claims 1-3, characterized in that the mixture of clay and lignine constitutes maximum about 14 % of the total amount of the wearing course material.

5. Wearing course according to any one of claims 1-4, characterized in that the amount of clay constitutes maximum about 10 % of the total amount of the wearing course material.

6. Wearing course according to any one of claims 1 -5, characterized in that the amount of lignine constitutes maximum about 4 % of the total amount of the wearing course material. 7. Wearing course according to any one of claims 1-6, characterized in that the wearing course further comprises additives of starch, kaolin, lime, cement, bentonite, vegetable substances, minerals or chlorides.

8. Use of a wearing course according to any one of claims 1-7 as a supporting border or edge for roads.

Description:
WEARING COURSE FOR GRAVEL ROADS

TECHNICAL FIELD

The present invention relates to a wearing course for gravel roads.

BACKGROUND OF THE INVENTION

The national road net in Sweden consists of about 70 000 km of paved roads, about 20 000 km of gravel roads and about 41 000 km of local roads, of which about 1 200 km are gravel roads. There is also about 76 000 km of state-subsidized private roads. Finally, there is about 200 000 km of gravel roads in the form of private roads and forest roads, which are important to rural areas and for forest transports; one of Sweden ' s most important export markets is forest products. Thus, an important part of the Swedish road net consists of gravel roads. According to an opinion poll from 2001 , only 15 % of the road-users were satisfied with the maintenance of the gravel roads.

A wearing course for gravel roads shall have a hard and even surface and yet be elastic in order to withstand traffic and weather, in order not to dust and to manage the ground frost in the winter. The wearing course shall also meet the environmental requirements of today.

A main reason for the poor standard of the gravel roads is, inter alia, that the binder which today is used in gravel road wearing courses, consists of fine-grained stone powder which is obtained during stone crushing and which for the major part consists of silt. The lasting- ness or wearing qualities of the wearing course are thereby poor, which requires frequent application of new wearing courses.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a wearing course for gravel roads with improved lastingness or wearing qualities, i.e. a wearing course having a hard and even surface, but which yet is elastic. This object is achieved by providing a material for the gravel road wearing course according to the invention which comprises wearing course gravel with a grain size of 0-18 mm and a mixture of clay and lignine in the form of a powder or a granulate.

Suitable graphs for the grain-size distribution of wearing course gravel already exist. Two such graphs are shown in the enclosed figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates the grain-size distribution for wearing course gravel, ready for road application and provided for dust binding with calcium and magnesium chloride.

Fig. 2 illustrates the corresponding values for the grain-size distribution for an "ideal gravel graph", ready for road application and with proposed value of acceptance illustrated.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The mixture of natural clay and lignine has other geotechnical and road technical properties than the previously used stone powder. The differences are seen in e.g. the different plasticity and hygroscopicity properties of the materials, i.e. in the ability of the materials, after deformation, to return to their original shape and in the ability of the materials to absorb moisture from the surrounding air respectively. Also, a clay contains many minerals such as aluminum oxide, silica, iron oxide, illite, vermiculite, smectite and others.

The best lastingness is achieved if about 0-10 % clay is mixed into the gravel road wear- ing course, i.e. maximum 10 % of the total amount of wearing course material, in combination with about 0-4 % lignine, i.e. the amount of lignine constitutes maximum 4 % of the total amount of wearing course material. The clay shall have a clay content of at least 50 %, i.e. at least 50 % of the clay particles shall be smaller than about 0,002 mm. The dust binding materials most used today however, are chlorides, e.g. calcium or magnesium chlorides. Chlorides have a negative influence on the environment, causing damages to the vegetation along the roads and are gathered in the underground water, and they cause corrosion on cars and damage concrete. Chlorides are not degraded or decomposed. Dust binding with bitumen is also possible. At dust binding, the law requires that the most non-polluting material is used, i.e. the vegetable materials. Lignine (ligno sulfonate) is such a material. Tests have been made also with e.g. starch, colza oil, linseed oil and soy. In US 2009/0103979 A1 there are mentioned compositions and methods for the manufacture of soy-based binding agents. These soy-based binding agents comprise, inter alia, one or more secondary stabilizers. Such a secondary stabilizer may in turn comprise e.g. lignine. From e.g. page 3, paragraph 0036, it is apparent that this lignine is present in liquid form, e.g. as lignine sulfonate, which is used as a wetting agent and as a soil stabili- zer in order to bind together, inter alia, soil particles. It is also apparent from several examples in the publication that lignine in one or other form is mixed with water before it is added to the soy-based material for the final use.

The present invention relates to, as defined, a wearing course for gravel roads. The com- ponents for the wearing course are mixed and distributed in dry condition. According to the present invention, lignine powder or granular lignine is used, i.e. lignine in dry condition is used. In view of prior art, it is new to use lignine in dry condition. The advantages thereby achieved are many. It is easier and not so costly to store and transport dry lignine compared to liquid lignine. Transport of the mixture of clay and dry lignine may be carried through in e.g. large sacks or as bulk. For transport of liquid lignine, tanks are required and transport of a large amount of water is a more expensive measure. From an environmental point of view, it is also a drawback that one has to transport a large amount of non- active component in the form of water together with an active component in the form of the lignine. It should be noted that it is easier and more economic to spread or distribute lignine, or mixtures comprising lignine, in dry condition instead of in liquid form.

A dust binding agent according to US 2009/0103979 A1 is adapted for distribution, inter alia, on top of the wearing course of a gravel road. In order to get a proper distribution of the dust binding material and get it to fairly penetrate into the surface of the existing wear- ing course and improve the lastingness thereof, the dust binding agent is distributed in liquid form. In the wearing course according to the present invention, the mixture of clay and lignine is mixed into the wearing course gravel before the wearing course material is distributed and thus, already carefully integrated with the wearing course gravel. By means of this integration into all wearing course gravel, through the entire wearing course, the mixture of clay and lignine gives rise to a stabilizing effect of the wearing course. The- re is no need to use liquid lignine in order to improve the homogeneity of the wearing course material. The homogeneity is already optimal.

It should also be noted that the distribution of the material for the wearing course means that totally different problems than the distribution of dust binding agents must be considered. The wearing course gravel which together with the mixture of clay and lignine in the form of a powder or a granulate constitutes the wearing course for gravel roads according to the present invention, consists primarily of crushed rock alternatively of crushed stone and gravel or moraine, and of a smaller amount of recovered material. It is of no interest at all to distribute this wearing course gravel in liquid form. The large amount of wearing course gravel, maximum about 95 % of the total amount of wearing course material, crushed down to a grain size within an interval of 0-18 mm at the most, alternatively e.g. about 0-8 mm or about 0-16 mm, means however, that the weight of the handled material is many times larger than the weight of dust binding agent even if the dust binding agent, as in the prior art, contains water. The equipment for distribution of wearing course material must be constructed to manage the larger weight and to permit distribution in other ways than dust binding agents. Distribution may e.g. be carried through by means of asphalt spreaders. For being able to control the grain-size distribution of the crushed material, said material is analyzed by screening in e.g. laboratories. The Swedish transport administration sets the requirements for the grain-size distribution of wearing course gravel. There already exist, as stated above, graphs for the grain-size distribution of wearing course gravel. Fig. 1 illustrates the grain-size distribution for wearing course gravel, ready for spreading or dist- ribution on the road and provided for dust binding with calcium and magnesium chloride. In fig. 2, the corresponding values for the grain-size distribution for an "ideal gravel graph", ready for road application and with proposed value of acceptance presented, are illustrated. The "ideal gravel graph" is based on Swedish and foreign experiences for 80 years and is well suited for addition of clay and lignine and chloride.

To the material for the wearing course, comprising wearing course gravel and a mixture of clay and powdered or granular lignine, other components, additives, can be added, e.g. starch, kaolin, lime, cement, bentonite, vegetable substances, minerals and chlorides. The object of these additives is to seal the wearing course such that no leaching occurs, i.e. such that water flows off on top of the wearing course layer after application thereof with- out penetrating down into said wearing course layer. Some substances can also be added during granulation. The mixing procedure may be carried through on situ or off situ for subsequent transport for distribution or spreading on the road from a lorry, tractor trailer equipped with a spreader or scraper. Alternatively, distribution may be carried through by means of the above-mentioned asphalt spreader, adjustment or trimming rod. In situ with special equipment.

The material can also be delivered in large sacks or as bulk for later spreading. It is obvious to a skilled person that the present invention can be modified and altered within the scope of the subsequent claims without departing from the idea and purpose of the invention. Thus, the wearing course according to the invention can be used also as a supporting border or edge for roads and then of course not only for gravel roads, but also for paved roads.