NO165641B - PROCEDURE FOR THE PREPARATION OF A PRESSURE-RESISTANT AND HIGH-STABLE COATING MASS. - Google Patents

Abstract

A method of manufacturing and a use of a compression resistance and high stable surfacing mass for heavy loaded surfaces, especially for strong traffic and heavily loaded street and road sections and mainly comprising a stone material which is bound by an asphalt mass. The surfacing mass is manufactured by heating asphalt at least to the recommended temperature for mixing asphalt with a stone material, and before or after the admixing of asphalt with the stone material a fibre material is added, especially a mineral fibre having an average fibre diameter of between 1 mu m and 5 mu m in an amount of about 0.5-20% of weight in relation to the asphalt weight, and the fibre material is mixed homogenously so as to throughout provide substantially separate fibres in the asphalt phase. When admixing the fibre material before adhesion of the asphalt to the stone material the temperature of the asphalt is preferably increased to 20-40 DEG C above the temperature for mixing the asphalt mass into the stone material, and after a homogenous mixing of asphalt and fibre the asphalt mass is cooled to the said admixing temperature, whereupon the asphalt-fibre mass is mixed homogenously with the stone material.

Description

The present invention relates to a method for the production and use of a pressure-resistant and highly stable paving compound for heavily loaded surfaces, especially for trafficked and loaded street or road parts, and mainly containing a stone material which is bound by an asphalt compound.

The development of traffic on streets and roads, both in terms of traffic intensity and the weight of the individual vehicles,

has led to great demands on the stability of road surfaces. To a particularly high degree, this applies in exposed places such as in front of traffic lights, at road junctions, roundabouts, etc. where paving materials consisting of a stone material with asphalt as binder often show insufficient stability.

A lack of stability in the paving mass means that it is deformed, in particular because the vehicle wheels, due to wear and compaction of the paving mass, form sunken wheel tracks in the road surface, which requires expensive maintenance. In the exposed locations, the maintenance work is also very difficult to carry out and causes traffic disturbances to a greater degree than normal road maintenance.

Attempts have been made to solve the problem of insufficient stability by using so-called skeletal masses, i.e. masses where the grain size in the stone material is graded so that the load is mainly transferred via coarse stone grains, which collide with each other. In this way, the risk of deposits or compaction of the paving mass can be reduced by the fact that the stone particles in the stone material have less opportunity to regroup, the fewer stones that participate in the load transfer.

However, the requirement for the properties of the binder increases to a corresponding degree, and in reality the nature of the binder has become the most important factor for the coating mass. It is thus essential that the binder effectively locks the stone particles in their assumed positions and prevents displacement or regrouping of the stone particles. The binding agent capacity can be increased by adding a larger amount of binding agent in relation to the amount of stone material. However, then problems arise with the so-called asphalt runoff, which means that the hot asphalt during the mixture with stone material flows off the stone particles, which partly defeats the purpose of the binder increase, partly also causing problems during storage and transport. The stability of the paving compound is not increased significantly, possibly due to so-called cold flow in the asphalt.

Attempts have been made to solve this problem by adding a fine-grained filler material, but the result does not seem to be satisfactory. Obviously, the skeleton principle is partially lost when fine-grained filler material is added.

Attempts have been made to solve this problem by adding asbestos fibres. Asbestos fiber has not been shown to give skeleton masses a sufficient increase in stability with the contents that can technically be used. This is probably due to the asbestos fibers' ability to interlock and form larger aggregates. Knowledge of the health hazards of asbestos fibers also precludes the use of asbestos in road surfaces.

Swedish patent document 211,163 also describes a coating material containing mineral fibers with a diameter of between 5 and 15 ura. Nor have the proposed coarse mineral fibers proven to be usable. These probably tend to orient themselves parallel to the stone surfaces in the asphalt-stone mass and thus in the plane of the binder film. They therefore hardly contribute to the stability of the skeletal mass. None of the proposed methods have therefore come to any major practical application.

It has now surprisingly been shown that an addition of a mineral fiber material with a small fiber diameter, preferably a fiber material with an average diameter of less than 5 µm, and where the fibers are evenly distributed in the asphalt mainly as single fibers, greatly reduces or eliminates the binder or asphalt's above-mentioned cold flow problems. This results in a binder phase with properties that give the finished coating compound significantly increased stability compared to previously known coating compounds without the viscosity at the mixing temperature becoming too high for a quick and good mixture. The increased stability is due to an increased strength in the binder, which is probably partly due to the increased thickness of the binder film around the stone grains, partly also to the fact that the added fiber material, which is evenly distributed as individual fibers in the asphalt, has a reinforcing effect .

The invention thus relates to a method for producing a pressure-resistant and highly stable paving compound for highly stressed surfaces, preferably such as paving for streets and roads, especially paving at street intersections, in front of stoplights, in roundabouts and other heavily trafficked traffic junctions, which paving compound mainly contains a stone material which is bound by an asphalt mass, whereby asphalt

heated to a temperature that at least corresponds to the recommended temperature of 150-160°C for mixing the asphalt with stone material, parallel to this the stone material is heated to the recommended mixing temperature, the heated asphalt and the heated stone material are mixed to a homogeneous mixture in the proportions 15-25 parts by weight stone material per weight part asphalt, which method is characterized by the fact that 0.5 - 20% by weight, calculated on the amount of asphalt, of mineral fibers with an average fiber diameter of between 1 and 5 µm is added to the stone material or to the asphalt, and that the fiber material is treated with a wetting agent , e.g. cationic

—surfactant before adding the fiber material to the asphalt.

Many different types of material can be used as fibres, provided that the fibers do not melt in the asphalt, which during mixing with the stone material maintains a temperature of 140-170 or preferably 150-160°C, and on the condition that the fibers are relatively stiff and retain in the at least a significant stiffness in the hot asphalt. Mineral fibres, for example stone fibres, i.e. fibers produced by melting stone such as diabase and subsequent fibrating of the melt, have proven to be a particularly suitable material.

As stated above, the average fiber diameter must be less than 5 µm. When the average fiber diameter is below 1 µm, the beneficial effect of the fibers decreases noticeably, probably due to the fact that thin fibers are inevitably shortened significantly during the mixing operation. The average fiber diameter should therefore be between 1 and 5 ym. To give the desired effect, the fibers should be added in an amount by weight between 0.5 and 20% of the asphalt weight, which corresponds to approx.

0.03 - 1.2% by weight of the finished coating mass.

It is essential that the fibers are not in the form of tangles or other aggregates. This can be provided through a properly executed mixing technique. To facilitate the distribution of the fibers and avoid tangling and to provide an optimal wetting of the fiber surfaces with asphalt, it can be advantageous for the fibers to be surface treated with a suitable agent. For this purpose, any non-polar compounds can be used, for example wetting agents such as cationic surfactants in the form of tertiary or quaternary ammonium compounds.

It is also advantageous that the fibers are as dry as possible when mixed into the asphalt, and in order to achieve an effect similar to the aforementioned treatment with a wetting agent, it may be advantageous before mixing the fibers into the asphalt or paving compound to dry the fibers so that the main part of the water molecules that are normally absorbed to the surface of the fibers are removed.

The fibers can be mixed in by addition to the stone material before the asphalt is mixed in, or the fibers can be mixed into the finished asphalt-stone mass. However, a particularly good effect is obtained if the fibers are mixed with the asphalt mass before it is added to the stone material. This facilitates the mixing and homogenisation of the fibres, and the mixing of the fiber and asphalt material can take place in a very gentle way for the fibres, so that the fibers do not break into pieces.

An even and tangle-free distribution of the fibers in the asphalt is further favored if the asphalt is heated in connection with the mixing of the fibers, e.g. 20-40°C above the temperature of 150-160°C at which the mixture of asphalt and stone material takes place, after which the asphalt-fibre mixture is cooled to this temperature and mixed into the stone material. The increase in temperature lowers the viscosity of the asphalt and thus facilitates a homogeneous and gentle mixing of the fiber material, and this elevated temperature further facilitates the wetting of the fiber surfaces, and the dispersion of the fibers in the asphalt is faster and more efficient.

In order to assess the impact of the mixing of the fiber material on the stability of the asphalt pavement, a number of fiber masses were produced using three different methods and within each group with a different amount of mixed fiber material.

Example 1

In a mixing plant for asphalt compounds, it was introduced

3,100 kilograms of stone material with a given distribution of the average grain size. The stone material was heated to 160°C, and to the stone material was added 5.8 kg of a mineral fiber material designated as "INORPHIL 057", which material has an average fiber diameter of 3 pm, and in which the majority of the fibers lie within the range of 1-5 urn. There are no acceptable direct methods for characterizing the fiber length. Appropriately, the so-called thickening number (n^), which is calculated by the equation, is measured instead

where is the viscosity of a slurry of 1.5 g of dry fibers in 200 ml of ethylene glycol at 20°C, and where qQ is the viscosity of the same ethylene glycol without fibers, likewise at 20°C measured with the same equipment, namely Brookfield viscometer with spindle LV1 or equivalent. For "INORPHIL 057" the thickening number applies 1.0 - 5.0.

195 kg of asphalt was mixed into the mixture of the stone material and the fiber material.

After mixing, the mass was taken out and its stability or repacking tendency was measured. This happens in the following way: An appropriate amount of coating compound is laid out in a frame of angle steel 80 x 80 mm. The frame, whose length is 2 000 ml and width 4 00 mm, rests on a concrete floor. The coating compound is isolated from the concrete floor with an aluminum foil.

After two days at approx. 1 8°C, the height position is measured for eight points along the center line of the frame in relation to the frame. The distance between the points is 200 mm. The measuring points are made up of a 20 mm circular chip which is placed on the measuring point during the measurement.

A cylindrical roller with a width of 100 mm and a diameter of 350 mm, loaded with 200 kg, is then rolled five times forwards and five times back over the mass along the center line. The aforementioned measurement points are measured again and the difference to the original measurement is used as a measure of the repacking of the mass. The values are compared with the repacking in a normal mass, whereby the following assessment basis is used: "normal", 0.8 - 1.2 x the deformation of the normal mass "some repacking", 1.2 - 1.6 x the deformation of the normal mass "obvious repacking", more than 1.6 x normal mass

deformation.

In this case, the sample showed a clear repacking tendency.

Example 2 - 6

Example 1 was repeated with the same type of mineral fiber but with a different amount of fiber mixed in. The mixing amount and the result are indicated in the following table.

Example 7-9

In these examples, the mineral fiber material was mixed in

in the hot asphalt within the asphalt-mineral fiber mixture was added and mixed into the stone material. The results are shown in table 3.

Example 10-12

In these examples, the asphalt was heated to 190°C, after which the mineral fiber material was mixed into the asphalt, the asphalt-mineral fiber mixture was cooled to 160°C and was mixed into the stone material. The results are indicated in the following table.

Example 13

In this example, mineral fibers with an average diameter of 6 - 8 ym were used as a comparison, but were otherwise carried out in the same way as in example 1.

Example 14

In this case, the same type of mineral fiber was used as in examples 1 - 12, but in order to determine the influence of the fiber length, the fiber material was ground so that it received a thickening factor of 0.2.

From the above table, it appears that the smallest amount of fiber mixed in has a significant impact on the material's stability or repacking tendency. With an admixture of 0.3% by weight of fiber material of the specified type, according to examples 1 - 6, a clear post-packing tendency is obtained and according to examples 7 - 12, there is a certain post-packing tendency. In cases where the mixing percentage is approx. 0.5 or higher, on the other hand, you get a normal afterpack. This applies in particular when the mixing takes place according to examples 7-9 respectively. 10 - 12. The table also shows that coarse fiber according to example 13 gives a clear post-packing tendency, and that thus fiber with an average diameter of less than 5 ym has significantly better properties than coarser fibres. The table also shows that the fiber length has a certain impact, in that the milled fiber material used in example 14 gives a perceptible post-packing tendency.

The accompanying drawing schematically shows a plant for producing the coating compound according to the invention. In a tank 1 equipped with heating coils 2, an asphalt mass 3 is heated to normal mixing temperature, or as indicated above to a temperature that is 20-40°C above this mixing temperature. The hot asphalt is pumped using a pump 4 in batches into a mixing container 5, which is equipped with a stirrer 6, and to which mineral fiber is added in batches from a container 7. After stirring to a homogeneous mixture, the asphalt fiber mass is pumped using a pump 8 through a heat exchanger 9, where the temperature of the asphalt fiber mixture is corrected to the correct mixing temperature with the stone mass. In the case that the mixture of asphalt and mineral fiber has taken place at an elevated temperature, the mass is cooled, and in the case that the mixture has taken place at the normal mixing temperature of, for example, 150-160°C and some cooling has possibly taken place during the handling of the mass, some temperature increasing correction may be necessary.

The stone material is heated in a container 10 equipped with a heating device 11, and transferred from there in batches to a rotating mixing drum 12. The mass from mixing container 5 for asphalt and mineral fiber is likewise pumped in batches through heat exchanger 9 to the mixing drum 12, and mixed with the stone material at the same temperature on the two phases.

As previously indicated, the mineral fiber material can be added directly from the mineral fiber container 7 to the mixing drum 12 for asphalt and stone material, and in this case the asphalt is of course pumped directly from the asphalt tank 1 to the mixing drum 12.

It is understood that the description given above and the plant shown in the drawing only constitute illustrative examples, that many different modifications may occur within the framework of the subsequent patent claims.

Claims (6)

1. Method for producing a pressure-resistant and highly stable coating compound for highly stressed surfaces, preferably such as coating for streets and roads, especially coating at street intersections, in front of stoplights, in roundabouts and. other heavily trafficked traffic junctions, which paving mass mainly contains a stone material that is bound by an asphalt mass, whereby asphalt (3) is heated to a temperature that at least corresponds to the recommended temperature of 150-160°C for mixing the asphalt with stone material, parallel to this is heated the stone material to the recommended mixing temperature, the heated asphalt and the heated stone material are mixed into a homogeneous mixture in the proportions 15-25 parts by weight of stone material per weight part asphalt, characterized by the fact that 0.5 - 20% by weight, calculated on the amount of asphalt, of mineral fibers with an average fiber diameter of between 1 and 5 pm is added to the stone material or to the asphalt, and that the fiber material is treated with a wetting agent, e.g. cationic surfactant before adding the fibrous material to the asphalt. 2. Method according to claim 1, characterized in that the fiber material is added to the heated asphalt and mixed into a homogeneous mass of fibers dispersed in the asphalt, before the asphalt is mixed into the stone material. 3. Method according to claim 2, characterized by the asphalt being heated to a temperature that is 20-40°C above the recommended mixing temperature for asphalt mass before adding the fiber material to the asphalt, or before mixing the asphalt and the fiber material into the homogeneous mass. 4. Method according to any one of claims 1, 2 or 3, characterized in that the fiber material is completely dried before addition to the asphalt material. 5. Method according to any one of claims 2-5, characterized in that the asphalt concrete mixture is cooled to the recommended mixing temperature before mixing asphalt-Eiber mass with the stone material. 6. Method according to any one of the preceding claims, characterized in that the added fiber material is selected from a group of materials with a thickening number according to the above definition of between 1.0 and 5.0.