TECHNICAL FIELD:

The present invention relates to a method for treating a gravel road to make it convenient to a greater extent than is the case today. Moreover, the invention relates to a dust binding emulsion to be used when treating a gravel road.

BACKGROUND OF THE INVENTION:

Gravel road maintenance has previously comprised watering, grading and adding of salt (calcium chloride) or lye in order to bind moisture to the gravel material and, thus, provide a dust-free environment for the road-users and those living around. This implied that the road-users' vehicles were subjected to heavy wear by the corrosion arising when the salt was allowed to affect the metal surfaces of the vehicles. Furthermore, if these gravel roads were wet, they also became smeary. This previously used treatment also required continuous maintenance in order to maintain the quality of the roadway.

In the field of road surfacing, the emulsion technology has made great progress in recent years. As a consequence, experiments have been made to find a substitute for salt in the field of emulsions.

The functional demands on a dust binding emulsion are that it should bind dust, it should have the capability of binding and hardening the gravel material and the driving surface of the road but it should have a softness so as to make the surface workable, that it should have the capability of securing the gravel material to the road base, and that the method of treating with the emulsion should keep the costs of maintenance at a positive price level.

The object of the invention is to provide a method for treating a gravel road with a dust binding emulsion, which solves the problems mentioned above and satisfies the functional demands in a cost-effective manner. A further object of the invention is to present a dust binding emulsion and the preparation thereof from a stock emulsion. The advantages obtained by the present invention are that the emulsion effectively binds the dust, the gravel roadway can be graded again and compacted, the previously yearly maintenance gravelling can be significantly reduced or be omitted, and the emulsion has resulted in an amount of bitumen, which within three

CORRECTED

years corresponds to a simple road surface. Moreover, maintenance can be reduced since the number of grading operations can be reduced by up to 50%. This results in environmental advantages, such as omitted use of salt, advantages for the road-users, such as less formation of rust on vehicles, improved local environment and road maintenance advantages, such as reduced costs.

SUMMARY OF THE INVENTION:

The invention relates to a method for treating a gravel road by applying a layer of gravel in the form of a measured amount of gravel and adding a dust binding emulsion, whereupon the emulsion is mixed with the gravel. Subsequently, compacting is effected. Furthermore, the invention relates to a dust binding emulsion and the preparation thereof for use in treatment of a gravel road, the dust binding emulsion having a composition as defined in the accompanying claims.

DESCRIPTION OF THE INVENTION:

The dust binding emulsion is prepared in two steps. The first step is a stock emulsion which is designated "special emulsion". This "special emulsion" contains as a basis 40-80% (usually 60%) soft bitumen MB 2000. Plasticised bitumen or soft bitumen consists of bitumen mixed with a plasticiser. The plasticiser should be an oil distillate recovered during the distillation process when preparing bitumen from crude oil. By varying the amount of plasticiser (fluxing agent), the viscosity of the final product can be adjusted as required. Soft bitumen is designated MB. The subsequent digits state the mean value of the kinematic viscosity at 60°C. Soft bitumen MB 2000 is prepared from base bitumen B180 (having the kinematic viscosity 180 mm^/s at 135°C) which is mixed with 20-30% heavy flux for obtaining the suitable viscosity. (A fluxing agent is mixed with bitumen as previously mentioned in order to obtain the desired viscosity of soft bitumen.) The kinematic viscosity of soft bitumen MB 2000 at 60°C should be 1600-2400 mm ² /s. Also base bitumen other than B 180 can be used for preparing soft bitumen, for example B 60, B 85 etc.

In order to further adjust the viscosity of this emulsion, 2-8% (usually 5%) plasticiser (light flux having a boiling point of 300-500°C) has been added to the mixture. These components together with 0.2-0.6% (usually 0.4%) emulsifier, for example LILAMULS® EM 44, which is a modified alkyl diamine, and 0.2-0.6% (usually 0.3%) of a diamine type adhesive, for example DIAMIN HBG, which is a saturated N-tallow

propylene diamine having a hydrocarbon chain length between C14 and C-|8. ^are then subjected to a mixing process in an emulsion mill and result, together with 30- 40% (usually about 35%) water, in the "special emulsion", i.e. the stock emulsion.

In the second step, the "special emulsion" is mixed with substantially equal parts of water and results in the dust binding emulsion which is used in the method. This second step is carried out when docking to a spreading vehicle. Thus, only the "special emulsion" is stored in the depots for considerations of space. The dust binding emulsion consists of:

soft bitumen 20 - 40% emulsifier 0.1 - 0.3% light flux 1 - 4% adhesive 0.1 - 0.3% and water 60 - 80%.

Preferably, the dust binding emulsion consists of:

soft bitumen 30% emulsifier 0.2% light flux 2.5% adhesive 0.2% and the balance water about 67%

When treating a gravel road, there should be supplied, in addition to the dust binding emulsion, additional surface course gravel which should comply with the ordinary grain distribution according to the building regulations issued by the National Road Administration, for a surface course gravel of the fraction 0-16 mm or 0-18 mm.

Before treatment, the gravel roadway should be in such a state that the correct amount of gravel and the correct camber in double or single inclination are available. The base of the road should have good drainage and no edges causing water to remain on the surface. Thus, an adequate gravel surface should be the basis for a treatment with a dust binding emulsion.

The dust binding emulsion consisting of the "special emulsion" mixed with substantially equal parts of controlled water, is spread on the gravel surface by a

spreading vehicle, whereupon a motor grader follows immediately, equipped with the earth moving system SYSTEM 2000 on the grader blade, and carries out a common gravel grading with the material. This implies that the dust binding emulsion is mixed with the gravel layer. The motor grader should also have a planer floatingly positioned, to make the surface as smooth as possible. The working depth of the grader should be between 2.0 and 3.5 cm. Optionally, the working procedure is repeated once more to obtain a thoroughly prepared material which spreads easily and which during and after breaking up of the emulsion is easy to compact. As "compacting device", use is made of a bogiecar with a water tank, which also serves to maintain the correct moisture in the mixture. The compacting is an operation which requires great accuracy for good results.

The method is carried out in the following steps:

Step 1 Gravelling, (7-15 l/m ² ), i.e. applying a measured amount of gravel, and grading and, optionally, watering of the roadway. Step 2.1 Spreading of the dust binding emulsion (0.5-2.0 kg/m ² , preferably 0.8-

1.2 kg/m ² ) Step 2.2 Immediately after spreading, mixing of the emulsion with the gravel material by means of a motor grader. The working thickness of the gravel material is 2.0-3.5 cm. Step 3.1 Spreading of the dust binding emulsion (0.5-2.0 kg/m ² , preferably 0.8-

1.2 kg/m ² ) Step 3.2 Immediately after spreading, mixing of the emulsion with the gravel material by means of a motor grader. The working thickness of the gravel material is 2.0-3.5 cm. Step 4 Compacting, after the surface has dried somewhat, by means of a watering vehicle, which is available in order to maintain the correct moisture of the gravel material when mixing. Some after-watering may be required.

Possibly, step 3.1 and step 3.2 may be excluded, i.e. only one spreading of the dust binding emulsion with subsequent mixing is carried out.

By immediate mixing after spreading of the dust binding emulsion is meant mixing before breaking up of the emulsion occurs. The term "immediate" should of course be understood in this manner.

After breaking up the dust binding emulsion, i.e. when the emulsion passes into two separate phases (soft bitumen and water), the water will evaporate (the surface dries) and the surface layer will contain a mixture of soft bitumen and gravel. During the time of the surface drying before compacting, certain restrictions apply on the distance to prevent the vehicles from becoming smeary.

A few hour after compacting, a convenient, permanent surface will be obtained, but still in the form of a gravel road which requires continued maintenance, although to a considerably smaller extent. The method yields a surface which is relatively firm down to a thickness of 2-3 cm.

If any cavities arise in a roadway that has been treated in this manner, they should be filled with a mixture of gravel and dust binding emulsion.

During a four-year period, a gravel road could be treated according to the following schedule:

Year 1 7-15 l/m ² gravel material of the fraction 0-18 mm or 0-16 mm and about 2 kg/m ² of the dust binding emulsion are applied to the roadway. Year 2 No gravel material or 3-5 l/m ² of the same fraction as in year 1 and about 1 kg/m ² of the dust binding emulsion are applied to the roadway. Year 3 No surface course gravel and no dust binding emulsion is applied to the roadway, possibly some grading and compacting. Year 4 The same as year 3 or, if required, the same as year 2.

Such a treatment as has been described above results in applying to the roadway 7-20 l/m ² surface coarse gravel and the base having obtained a measured amount of emulsion, which in respect of balance bitumen content corresponds to a simple type of road surface, e.g. Y1G, which is the designation of a simple surface treatment according to the building regulations of the National Road Administration. With regard to costs, year 1 will be more expensive than the traditional maintenance with calcium chloride as dust binding agent. In year 2, the costs will be comparable, while the saving and the profits owing to the new method begin in year 3.

LILAMULS® EM 44 and DIAMIN HGB are product names belonging to Berol Nobel

AB;

SYSTEM 2000 is a product name belonging to Sandvik AB.