SE532658C2 - Method for preparing an asphalt pulp - Google Patents

Description

532 E58 EP 1, 398.35l B1 shows a method directed to the preparation of semi-hot and hot asphalt mass, loaded into a mixer, in which method all aggregate a heated bitumen is added to a foaming agent in the form of a polymerized fatty acid, whereupon the obtained the binder mixture is added to the unit as a foam. US 2005/0018530 A1 shows a method aimed at preparing asphalt pulp in the lower area of hot asphalt pulp, in which method the unit is supplied with the asphalt pulp in two batches. More specifically, a dried first amount of aggregate which is substantially free of fines in the mixer is first charged, then heated and liquid bitumen is added, then wet aggregates comprising water, sand and fines are charged in the mixer, whereupon the bitumin is allowed to self-expand. However, the resulting asphalt mass according to these two techniques has negative features. The biggest negative feature is that the filler in the EP script and the fine material in the US script absorbs a very large part of the bitumen / binder mixture because the filler is present in the asphalt mass when the bitumen / binder mixture is foamed / self-expanded. When such an asphalt mass is laid on the road, a relatively small proportion of bitumen / binder mixture will be bound to the stones in the unit and a relatively large amount of bitumen / binder mixture will be bound to fine material or the filler. When the paved asphalt is trafficked, the bitumen / binder mixture that is bound to the fine material or filler risks being quickly splashed away from the asphalt. Thus, a hot asphalt mass is not obtained according to any of these methods which have similar characteristics as conventional hot asphalt mass, in terms of, for example, wear resistance, adhesion, etc.

Brief Description of the Objects and Features of the Invention The present invention aims to obviate the above-mentioned disadvantages and shortcomings of prior art methods for preparing asphalt masses and to provide an improved method. A basic object of the invention is to provide an improved method for preparing an asphalt mass of initially defined type, which gives an asphalt mass, prepared in the vicinity of the lower limit for hot asphalt mass, with similar or better properties than conventional hot asphalt mass , for example in terms of wear resistance, adhesion, cavity occurrence, heat / toughness, of the laid asphalt.

A further object of the present invention is to provide a method, odor by reducing dust emissions. rigid etc., which emit less smoke and It is another object of the present invention to provide a method which is better for both the environment and the working environment in that energy consumption is lower and that emissions of carbon dioxide and nitrogen oxides are lower.

A further object of the present invention is to provide a method which provides a more easily worked asphalt mass, both in terms of preparation and laying.

According to the invention, at least the basic object is achieved by means of the initially defined method, which is characterized by the steps of charging the mixer with dry aggregate comprising stone material substantially free of filler, then charging the mixer comprising said dry aggregate, with a foamed binder mixture, when the latter leaves a pre-foaming chamber (12) and is loaded into the mixer (15), whereupon mixing of said aggregate and said foamed binder mixture takes place, and then loading the mixer with a filler, whereupon final mixing of the asphalt mass takes place. which is foamed Thus, the present invention is based on the insight that it is crucial for the asphalt created by the asphalt mass that the binder mixture is allowed to adhere to the stones in the aggregate in thick layers / membranes before the strongly absorbent filler is added to the asphalt mass.

Preferred embodiments of the present invention are further defined in the dependent claims. Preferably, the binder mixture comprises bitumen, an adhesive in the form of a fatty acid and a foaming agent in the form of water, whereupon a strong and long-lasting foam is obtained, which contributes to an easy-to-work asphalt mass which adheres. to the stones in the unit in thick layers before the filler is added.

Additional advantages and features of the invention will be apparent from the other dependent claims and from the following detailed description of preferred embodiments.

Brief Description of the Drawings A more complete understanding of the above and other features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic side view of a mixer according to the invention, and selected parts of an asphalt mass plant, and Fig. 2 is an enlarged schematic view from above of the mixer according to figure 1.

Detailed description of preferred embodiments Reference is initially made primarily to Figure 1.

Asphalt pulp consists for the most part of a unit 1, or stone material, usually amounting to at least 80% by weight, preferably about 90% by weight, of the total weight of the pulp. of the asphalt- The unit is further divided into different fractions, or size classes, partly in fractions containing filler, sand and stone, 0-4, 0-8, 0-11, 0-16 and 0-22, partly in fractions as in mainly contains only sand and stone, 8-11, 11-16 and 16-22. Where the numbers denote the hole size in millimeters of a grid, for example O-2, for example 4-8, 532 658 which passes through the unit and a grid which does not pass through the unit. The amount of aggregate from each fraction is determined primarily by the final application for the specific asphalt mass, ie. where and for what purpose the final asphalt is to be used. In a commonly used asphalt mass, about half of the aggregate is derived from fractions containing filler, such as O-4 and O-8, and half from fractions which are substantially free of filler, such as 4-8, 8-11 and 11-8. 16.

Evaluate fraction of the aggregate 1 is stored in a specific raw material silo 2, two of which are shown. When preparation of a new batch of asphalt mass begins, predetermined amounts of aggregate 1 are unloaded from the respective raw material silo 2 onto a conveyor belt or the like, whereupon the aggregate is led to a drying unit 3. In the embodiment shown, the drying unit 3 consists of a countercurrent drying drum, which has a slight slope downwards and rotates during operation. The unit 1 is fed into a first, upper end of the drying unit 3 and is fed out into a second, end, operation. lower as a result of the countercurrent drying drum rotating at the drying unit 3, the unit 1 is exposed to heat and heated to a temperature between 100 and 130 ° C, approximately about 120 ° C, after which the unit 1 dries. In the drying unit 3, among other things, the unit 1 is "thrown" in the form of a casting curtain through the heat flow created by a heat source in the drying unit 3. In the casting curtain, the filler, moisture and flue gases are separated from the unit 1 and leave the drying unit 3 via a flue 4, arranged in the first, upper end of the drying unit 3. Along the flue 4 is arranged a separator 5, which comprises a filter (not shown). In the separator 5, the filler 6 is collected and led to a filler silo 7, and moisture and flue gases are filtered and released via a chimney 8. Furthermore, in the drying unit 3, the unit which is substantially free of filler is heated further to reach the desired temperature mentioned above.

The heated unit consisting of stone material substantially free of filler is then transported by a lift 9, or the like, to a unit silo 10. Said unit silo 10 may be shaped in such a way that the heated unit again sorted into different fractions, ie. in individual compartments in unit silo 10, as shown in Figure 1, or in such a way that it comprises only one compartment. The unit silo 10 is acquired in such a way that the unit is allowed to fall through a number of grids with successively decreasing hole diameters, whereby the unit of a certain size passes a grid but not subsequently and is then led to the corresponding size or fraction section in the unit silo 10. Thus it is collected the smallest fraction on the far left in Figure 1, in aggregate silo 10, and the largest fraction on the far right in Figure 1. Filler 6 is usually designated as particles smaller than 0.063 mm, however, the filler 6 may be allowed to be slightly larger, for example smaller than 0, 08 mm, without affecting the method according to the invention.

Furthermore, sand and stones are the part of the unit which has sizes larger than the filler, and usually less than 22 mm, and is hereinafter referred to as stones. It should be pointed out, however, that it is central to the invention that the filler 6 preferably comprises the dust which is separated from the unit 1 during the heating / drying.

The other essential component of an asphalt mass is a binder mixture, which acts to hold the aggregate together in the asphalt finally obtained. The amount of binder mixture in the asphalt mass is similar to the amount of aggregate 1 depending on the purpose and application of the finished asphalt, and amounts to between 3 and 10% by weight, 5-7% by weight, preferably approximately of the total weight of the asphalt mass.

According to a preferred embodiment of the invention, the binder mixture comprises a binder, an adhesive and a foaming agent.

Preparation of said binder mixture comprises the step of guiding the binder via a line 11 towards a pre-foaming chamber 12. Thereafter, the adhesive is supplied to the binder via a line 13 arranged connecting to said binder line 11, whereupon the mixture of binder and adhesive is loaded into the foaming chamber 12. Thereafter, the foaming agent is charged via a line 14 directly into the foaming chamber 12, to be mixed there with the binder and the adhesive. The binder is heated to a temperature of between 130 and 200 ° C, preferably 180 ° C, before being mixed with the adhesive in line 11. The adhesive and the foaming agent can preferably have the same temperature as the environment, which facilitates the handling of the same.

The binder preferably consists of bitumen, which can, for example, be extracted from crude oil or from naturally occurring bitumen, or produced in another manner known in the art, or consist of mixtures thereof. Preferably, so-called penetration bitumen is used, in contrast to emulsion binders and viscosity binders which are conventionally used in cold and semi-hot asphalt, respectively.

One measure for classifying bitumen of different bitumen varieties, or bitumen compositions, is so-called penetra- Bitumen from different classes is used for different purposes and applications, tion. combined with different mixtures of aggregates as mentioned above. The penetration rate for a certain type of bitumen is measured by pushing a needle into a test piece of bitumen with a certain force and for a certain time and at a certain temperature, and the depth that the needle reaches is measured in tenths of a millimeter, dmm. Bitumen is usually used with a penetration rate of between 50 and 430 dmm. A frequently used bitumen type has a penetration number of l60-220 dmm.

The adhesive added to the binder mixture preferably constitutes at least 0.6% by weight of the total weight of the binder mixture, and comprises a fatty acid, such as tall oil fatty acid. The foaming agent added to the binder mixture constitutes between 1 and 10% by weight, preferably 4-5% by weight, of the total weight of the binder mixture. Reference is now made, in connection with the description of the method according to the invention for preparing an asphalt mass, also to Figure 2.

The method according to the invention comprises the steps of loading in a mixer 15 aggregates which comprise stone material substantially free of filler. Said aggregate consists, for example, of preselected amounts from each aggregate fraction which are temporarily stored in aggregate silo 10, whereupon said aggregate is dry-mixed to obtain a homogeneous aggregate mixture. According to one embodiment, the dry mixing is carried out for three seconds. Thereafter, the mixer 15 is charged with a foamed binder mixture, whereupon mixing of said aggregate and said foamed binder mixture takes place to obtain thick binder mixture layers on each rock / particle in the aggregate. According to an exemplary embodiment, the charging of foamed binder mixture and the mixing of the same with the unit is carried out for four seconds. The mixer is then charged with a filler 6, after which the final wet mixing of the asphalt mass takes place to obtain a homogeneous asphalt mass. According to one embodiment, the filling of the filler 6 is carried out for two seconds and the final wet mixing is carried out for sixteen seconds. The above times are examples of a batch of asphalt pulp which is prepared in a mixer 15 intended for 2.5-5 tons of asphalt pulp. The process temperature in the mixer is preferably between 100 and 120 ° C during the preparation, more preferably about 100 ° C. It should be pointed out that the said process produces hot asphalt mass, even though the current temperatures are in the boundary area around the current definition of the transition from semi-warm to hot asphalt mass.

In Figure 1, an aggregate scale 10a is arranged below the aggregate silo 10, in order to be able to determine how large an amount of the respective aggregate fraction is to be charged in the mixer 15.

The binder mixture is liquid when it is in the pre-foaming chamber 12. When the binder mixture is loaded into the mixer 15, it is sprayed via a nozzle 16 under high pressure into the mixer 15, for example with a pressure of 3-10 15 20 25 30 35 532 B58 6 Bar. When the binder mixture comes out at atmospheric pressure, which usually exists in asphalt mass mixers, the binder mixture expands up to about 20 times and thus forms a foam, which over time will settle as the foaming agent evaporates. Binder mixture should preferably remain, at least in part, in this foamed form for most of the remaining mixing time.

Foamed binder mixture is more advantageous than liquid binder mixture, as the temporarily increased volume also gives a reduced viscosity, which makes the binder mixture easier to mix with and distributed more evenly on the unit. Thus, a better coating of the binder mixture is obtained on the unit with less energy input. According to the method according to the invention, more specifically, the binder is made to foam by adding a foaming agent.

The foaming agent can be any material, mixture of materials, or that causes the heated binder to foam. Crucial is the foaming agent's ability to expand when it is heated above its boiling point, and consists primarily of water. The foaming agent content is reduced / evaporated in the binder mixture during the entire preparation and application time, and when the application is complete, a navigable path is obtained immediately which does not require further curing. It should be noted, however, that the finished asphalt may contain and is permitted to contain a certain amount of foaming agent.

The task of the adhesive is to repel the foaming agent from the stones in the unit in order to obtain a better bonding / adhesion between the adhesive and the unit. In addition, it has also been shown that the adhesive also means that the binder mixture foam has a longer survival before it collapses. In addition, the adhesive also has a lubricating effect in the asphalt mass both when it is prepared in the mixer 15 and when the asphalt mass is laid out. In the first place, Thus, thanks to the adhesive and the foaming agent, the asphalt mass has a good processability, ie is easy to pack during laying, despite a laying temperature lower than 10 ° C, preferably between 80 and 100 ° C.

The filler 6, which is added to the asphalt mixture after the addition of the foamed binder mixture, preferably constitutes between 3 and 8% by weight of the total weight of the asphalt mass. The filler 6 loaded into the mixer 15 during preparation consists at least in part of the same material as the aggregate, usually granite or the like, but may also comprise other material. For example, so-called rock-rich aggregate, where a small amount of filler can be discerned in the heating process step, may require that a certain amount of limestone filler be added to the filler 6 loaded in the mixer 15. The limestone filler may conventionally constitute a maximum of 50% of file the clay 6 which is loaded into the mixer 15. Other additives to the filter 6 which are loaded into the mixer 15 are cellulose fillers, which preferably constitute a maximum of 1% by weight of the total weight of the asphalt mass.

The advantage of adding the filler 6 after the foamed binder mixture and the aggregate which is substantially free of filler has been mixed is that thick binder membranes / layers are obtained on each stone in the aggregate, after which the filler 6 enters these membranes and sucks. up the part of the binder mixture that is not attached to the stones in the unit. This results in a dense asphalt where rainwater does not seep through the asphalt and risks blasting the asphalt or washing off the binder. By means of the method according to the invention, an asphalt mass is obtained which gives a packed asphalt with a cavity of about 3%.

Another advantage of the present invention is that it has been shown that the process temperature in the mixer 15 does not have to be raised as in the usual way when recycled asphalt is added to the asphalt mass during the preparation.

In the mixer 15 according to the invention at least one mixer shaft 17 is arranged which carries a number of vanes or mixer arms 18. Preferably, a mixer 15 according to the invention comprises two cooperating mixer shafts 17 arranged in parallel, which are individually rotatably supported in a container 19, included in the mixer 15, and arranged to rotate in opposite directions. More specifically, the mixer shafts 17 rotate in such a way that the asphalt mass is moved from the outside / from the bottom and inwards / upwards. Each mixer shaft 17 preferably comprises eight vanes 18 arranged in pairs, and where the vanes 18 in each pair have a diametrically spaced position relative to the mixer shaft 17. The mixer shaft 17 is arranged at such a height in the container 19 that a larger subvolume of the asphalt mass which is prepared is above the mixer shaft 17 than below. In addition, the vanes 18 have an active entrainment surface 20 which has an axial length, across the mixer shaft 17, which is 1.5-4 times larger than its width. each entraining surface 20 preferably extends from a free outer end in the radial direction to said mixing shaft 17, and along its length preferably has a uniform cross-section. In said cross-section, the entraining surface preferably has a part which is flat and substantially parallel to the mixing shaft 17, and a part which is curved in the opposite direction to the direction of rotation R of the mixing shaft 17, as seen in Figure 2. In addition, each vane 18 is bent in the free outer end like a shovel. The mixer according to the invention “lifts and moves” the asphalt mass, in contrast to mixers according to previous technology which only “knead” the asphalt mass.

Possible modifications of the invention The invention is not limited only to the embodiments described above and shown in the drawings, which have only illustrative and exemplary purposes. This patent application is intended to cover all adaptations and variants of the preferred embodiments described herein, and accordingly, the present invention is defined by the wording of the appended claims and their equivalents. Thus, the equipment can be modified in any conceivable manner within the scope of the appended claims.

For example, the binder mixture may contain various additives in addition to those mentioned in the description above, for example wax to obtain a stiffer asphalt mass.

It should also be pointed out that all information about / concerning terms such as upper, lower, etc., shall be interpreted / read with the equipment oriented in accordance with the figures, with the drawings oriented in such a way that the reference numerals can be read correctly way. Thus, such terms only indicate mutual relations in the embodiments shown, which conditions can be changed if the equipment according to the invention is provided with a different construction / design.

It should be pointed out that even if it is not explicitly stated that features from a specific design can be combined with the features in another design, obviously when possible. this shall be considered

Claims (19)

532 G58 13 Patent claims A method for preparing an asphalt mass in a mixer (15), which method is characterized by the steps of: - loading the mixer (15) with dry aggregate comprising stone material substantially free of filler, 4 then loading the mixer (15), comprising said dry aggregate, with a foamed binder mixture, which is foamed as it leaves a pre-foaming chamber (12) and loaded into the mixer (15), whereupon mixing of said aggregate and said foamed binder mixture takes place, and - then charging the mixer (15) with a filler (6), after which final mixing of the asphalt mass takes place. Method according to Claim 1, characterized in that the process temperature in the mixer (15) is between 100 ° C and 120 ° C. Method according to claim 1 or 2, characterized in that said unit, during a process step preceding loading of unit in the mixer, is heated to between 10 ° C and 130 ° C and thus dried. Method according to claim 3, characterized in that at least parts of said filler (6) are separated from said aggregate during said drying. Method according to any one of the preceding claims, characterized in that the asphalt mass comprises at least 80% by weight of said aggregate, based on the total weight of the asphalt mass. Method according to one of the preceding claims, characterized in that the asphalt mass comprises between 3 and 10% by weight of binder mixture, based on the total weight of the asphalt mass. 532 658 14 Method according to one of the preceding claims, characterized in that the binder mixture comprises a binder, an adhesive and a foaming agent. Method according to claim 7, characterized in that preparation of the binder mixture comprises the steps of: - first guiding the binder in a conduit (11) towards a foaming chamber (12), - then loading adhesive into said conduit (II), whereupon the mixture of bitumen and adhesives are charged into the foaming chamber (12), and then charge foaming agents into the foaming chamber (12). Method according to claim 8, characterized in that the binder has a temperature of between 130 ° C and 200 ° C, before it is led in the line (11) towards the foaming chamber. Method according to one of Claims 8 to 10, characterized in that the binder is bitumen. Method according to one of Claims 8 to 11, characterized in that the binder mixture comprises at least 0.6% by weight of adhesive, based on the total weight of the binder mixture. Method according to one of Claims 8 to 12, characterized in that the adhesive comprises a fatty acid, such as tall oil fatty acid. Method according to one of Claims 8 to 13, characterized in that the binder mixture comprises between 1 and 10% by weight of foaming agent, based on the total weight of the binder mixture. 53.? 658 15 Method according to one of Claims 8 to 14, characterized in that the foaming agent is water. Method according to any one of the preceding claims, characterized in that the asphalt mass comprises between 3 and 8% by weight of said filler, based on the total weight of the asphalt mass. Method according to any one of the preceding claims, characterized in that said filler comprises particles with a size of less than 0.063 mm. Method according to any one of the preceding claims, characterized in that at least parts of said filler consist of the same material as said aggregate. Method according to any one of the preceding claims, characterized in that said filler comprises a maximum of 50% by weight of limestone filler, based on the total weight of the filler. Method according to any one of the preceding claims, characterized in that said filler comprises a maximum of 1% by weight of cellulose fibers, based on the total weight of the asphalt mass.