EP1586706A2

EP1586706A2 - Method and device for producing asphalt mix

Info

Publication number: EP1586706A2
Application number: EP05008075A
Authority: EP
Inventors: Karl Gunnar Ohlson
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-04-14
Filing date: 2005-04-13
Publication date: 2005-10-19
Anticipated expiration: 2025-04-13
Also published as: CN1683715A; EP1586706A3; EP1586706B1; CN1683715B

Abstract

The invention refers to a method for producing an asphalt mix that includes a coarse fraction, a fine fraction, filler and a bituminous liquid with the following steps in the mentioned order:

a) mixing the coarse fraction and the bituminous liquid in a mixer,

b) discharging the filler to be spread over the coarse fraction and the bituminous liquid and

c) discharging the fine fraction over the filler and mixing,

d) discharging the ready mix from the mixer,

wherein the discharge of the fractions are optimized so that the mix behaves like a liquid in a test where a deformation of a specimen of the mix depending from the temperature of the specimen is measured, as known from EP 0 756 615 B1.

For increasing the viscous resource in batch plant mixed asphalt pavings, the invention teaches that, for conducting step a), the coarse fraction and the liquid binder are discharged and mixed simultanously over a first time period. Further, devices for carrying out such method are described.

Description

The invention refers to a method and a device for producing asphalt mix as known from EP 0 756 615 B1.
Reference is first made to WO 83/00700 which describes a method and apparatus for the production of asphalt concrete. According to this previous method, the aggregate is divided into a coarse fraction, a fine fraction and a filler portion. First, the coarse fraction and the bituminous liquid are mixed, then the filler fraction is added, and last, the fine fraction is added. The apparatus for carrying out such production method is described in detail. The mixing method of WO 83/00700 has been commonly known as "KGO II" mixing method. The known mixing method is characterized by force mixing. The filler is discharged at once, and then the mixing is conducted by the force of mixing paddles.
Reference is now made to the above mentioned EP 0 756 615 B1. In such patent, there is shown and described a test equipment and method for testing of asphalt specimens, called TOD test. The specimens are heated and the deformation in the specimens is determined. The deformation over temperature is plotted in a graphic. The curve of a specimen produced by the KGO II mixing method still shows sharp buckles and cracks. This shows the tendency of an asphalt to crack. In EP 0 756 615 B1, a new mixing method is given reducing such tendency to crack. The mixing method of EP 0 756 615 B1 - known as KGO III mixing method - is characterized by controlling the flow rate and time intervals for discharging the filler and the fine fraction. The filler discharge is such controlled that the filler is powdered over the liquid distributed over the surface of the coarse fraction. To understand this, one can compare the mixing methods with a preparation of a pancake dough. If the flour is discharged at once into the milk, a forced mixing is necessary. Nevertheless, the dough becomes lumpy. If, however, the flour is powdered over the milk when mixing the dough, lumps are avoided. The same technique is used in the KGO III mixing method. By such mixing, the bituminous liquid, the filler and the fine fraction material becomes enclosed in a combined suspension where the filler, the fine fraction and the coarse fraction are parts of a closed liquid volume. This condition is testable by the TOD-test. The flow rate and the time intervals for discharging the filler and the fine fraction are controlled in such a way that the closed liquid volume is established.
With the mixing method of EP 0 756 615 B1, one has changed from a force mixing to a flow mixing. Further details of the theory and the praxis of such flow mixing are given in "Method and means used in production of asphalt mix. Theory of suspension, mixing method, method of testing, method of analyses", dissertation at Lund University by Ohlson, Karl Gunnar, Institutionen för Trafikteknik, LTH, bulletin 132, available at the Lund University, Box 118, SE-22100 Lund (Sweden) under the code "CODEN LUTVDG/(TVTT-3110)/1-113/(1995)", Lund 1995. This dissertation is incorporated here by reference.
When trying to conduct the KGO III mixing method in practice, namely in some asphalt plants, especially such one as given in WO 83/00700, some problems have been raised. It was particularly difficult to find the optimised time intervals and flow rates for developing the closed liquid volume.
Further, reference is made to the European Patent Application 03023201.1 published on the priority date of the present application as EP 1 408 157 A2 and such being state of art according to Art 54(3) EPC, only. The aim of this state of art according to EP 1 408 157 A2 is to find optimal time intervalls and flow rates for production of a closed liquid volume of the mix.
An object of the present invention is to improve the mixing methods as known from EP 0 756 615 B1 in such a way that the intervall and flow rates can easier be optimized.
A further object of the invention is to increase the viscous resource in batch plant mixed asphalt pavings.
Such objects are achieved by the method according to claim 1 and by the device according to the claim 8.
Advantageous embodiments are given in the subclaims.
The invention especially refers to a start up procedure for starting production of asphalt mix in an asphalt plant. Beginning with such procedure, the optimized intervall and flow rates easily can be found by starting with a particular time schedule. The optimized adjustments of an asphalt plant can such be found easily by producing the mix, testing it with the TOD test and amending the intervall and flow rates, if necessary or advantageous.
When comparing the invention with the method according to EP 1 408 157 A2, it is clear that the order and intervalls for discharging and mixing of the different fractions are different. In EP 1 408 157 A2, the method is started by discharging the coarse fraction during 3s, then discharging the bitumen for 8s, then mixing coarse fraction and bitumen for 10s. The result of the mixing process is depending on the mixing time of each fraction before the next material is added. According to EP 1 408 157 A2, the discharge of bitumen starts after having discharged all the coarse aggregate into the mixer. Then, the mixing time starts at the time when all bitumen has been discharged into the mixer. Thus, the effective mixing time for mixing coarse fraction and bitumen, corresponds only to the mixing time of 10s.
According to the invention, the coarse fraction and the bitumen are discharged and mixed together in one step. The amount of coarse aggregate and of the bitumen are increasing simultanously. Thus, the mixing time for mixing coarse aggregate and bitumen starts at the time starting the discharge of the aggregate and the liquid. So, the efective mixing time starts earlier and can last longer. Since the amount of coarse aggregat and liquid are increasing simultanously, each particle of coarse aggregat will be better covered with liquid so that the closed liquid volume of the whole asphalt mix can be achieved more easily. The effect of the invention is visible by the TOD test. With the invention, one can achieve a smoother curve of the deformation versus temperature. The behaviour of a mix produced according to the invention is more like a liquid as compared with Fig. 1 a) of EP 0 756 615 B1. The known asphalt product still shows a sharp, sudden fall at a higher temperature. An aspalt product produced by the invention shows a smooth curve without sudden changes or flanks.
Embodiments of the invention are now explained in more detail with reference to the enclosed drawings in which:

Fig. 1: is a graph showing the viscous source of different road bitumen.
Fig. 2: is a diagramm showing an example of material composition of asphalt mix used by the invention.
Fig. 3: shows an example of a mixing time schedule used by the invention.
Fig. 4a: shows an test apparatus for testing the viscous resource of produced mix.
Fig. 4b: shows an diagramm, comparable with Fig. 1 of EP 0 756 615 B1, showing the deformation of a specimen over the temperature for a specimen produced with the invention. The diagramm represents an example of a characterisitc result from test of the viscous resource of produced mix.
Fig. 5: illustrates a first example of a device for producing asphalt mix.
Fig. 6: illustrates a second example of a device for producing asphalt mix.

The invention results from a discovery of that the property of viscosity that characterizes the unmixed bituminous liquid, figure 1 refers, is drastically reduced in the known process of mixing, this from lack of relevant time schedule for adding and flow rates of the different fractions of solids at discharge to the mixer.
"Viscosity resist flow by inertia. Inertia is a combined function of ductility and cohesion, properties recognized as the resource of durability of the bituminous liquid as the binder of paved mix".
One novelty of the invention is the time schedule for entering to the mixer the different fractions of the aggregate and the bituminous liquid of the mix, the mixing times of each fraction entered and the time of emptying the mixer of the ready asphalt mix that is characterized by the viscous resource of the unmixed bituminous liquid.
The basic components of asphalt mix are the following:

Bituminous liquid (road bitumen) of different viscosity, figure 1 refers;
Aggregate coarse fraction, particles mainly > 4 mm;
Aggregate fine fraction, particles mainly < 4 mm; and
Filler, particles mainly < 0.0074 mm.

In the known technology there are a number of different types of mixes used for paving work, each with different material composition that concern both the fine and the coarse fraction.
The composition of the mixes of an embodiment of the invention differs from the known by that, independent of the type of the mix, the fine fraction and filler, has more or less the same percentage in mix and the different types of the mixes are recognized by the difference in the size of the largest particles of the coarse fraction.
An example of material composition for use with the invention for production of asphalt paving of type surface layer, is shown by figure 2.
A time schedule, figure 3 refers, shows the order of discharge, the intervals between discharge, the rate of flow at discharge and the mixing time between discharge of each component added to the mixer. The production of asphalt paving mix by the shown time schedule, results in a paving characterized by the property of the viscosity of the bituminous liquid. The property of viscosity in the mix is shown by test on specimens drilled from the paving. Figure 4a) shows a test equipment, and figure 4b) represents a graph of viscous mix.
The time schedule of figure 3 is universal for starting up different make of asphalt plants and will function with all types of mix with the material composition of the invention. Trimming the schedule for adjustment of the respective asphalt plant capacity is allowed, the extent is however limited by the test on the viscous behaviour of the mix. Figure 4 b) refers.
Am embodiment of the invention requires the following mechanical changes to the asphalt plant:
1) an apparatus set to administrate the mixing process in accordance with the time schedule shown by fig. 3;
2) the device for discharge of the filler into the mixer to be furnished with an apparatus for regulating the flow rate of the filler at discharge to the mixer. Example: If there is a screw feed, the flow rate can be adjusted by lowering the revolution/minute of the screw, this by a frequency converter on the motor of the screw. Fig. 5 refers.
3) a device that prevent the aggregate material from being discharged in to area (C), figure 6 refers, where the material flow in the mixer is countercurrent to the flow of the discharged material.
The described invention is a technology here described by a time schedule, an example of mix composition, a method for trimming the asphalt plant and a method for testing the asphalt mix. By the method of testing, the limit to which the time schedule can be trimmed is also learned.
One embodiment of the invention provides a method for production of asphalt mix depending on a time schedule for entering to the mixer the different fractions of the aggregate and the bituminous liquid of the mix, the mixing times of each fraction entered and the time of emptying the mixer of the ready asphalt mix, this having the effect of the invention of the viscous resource of bituminous liquid, the time schedule being universal for different make of asphalt batch plants for discharges of the components to the mixer to be used when starting production by the invention. The time schedule includes
a) discharge the coarse fraction and the bituminous liquid simultaneous and mix over a timeperiod of 17s,
b) spread the discharge of the filler over a timeperiod of 17s,
c) discharge and mixing the fine fraction material over a timeperiod of 18s, and
d) discharge of the ready mix from the mixer.
By starting the production of asphalt mix with such time schedule, any type of asphalt plant easily can be adjusted to produce asphalt mix with increased viscous behaviour which is testable by TOD test. Such, the time schedule of the invention is universal for starting up production at any asphalt plant.
Further, a time schedule to weigh and discharge the material to the mixer can be provided including
e) to weigh up the desired amount of coarse fraction and fine fraction separately at the same time or one after the other to the weigh hopper of the plant
f) to discharge to the mixer, the coarse fraction together with the desired amount of bituminous liquid, discharge time and mixing time 17s
g) to discharge the desired amount of filler to the mixer, at the flow rate that spread the discharge over 17s.
h) discharge the fine fraction, the discharge time and mixing time, 18s, whereupon the mixer is emptied.
i) to repeat the time schedule for continuous production.
The apparatus that controls the discharge and mixing times makes those adjustable to the extent allowed for trimming of the plants capacity.
An example of a device for carrying out the method has a screw (D) for discharge of the filler into the mixer, wherein the flow rate is adjusted by the change of the revolution/minute of the screw by a frequency converter connected to the motor of the screw.
A further example of a device for carrying out the method has a wall fitted in the weigh hopper above the mixer or alternative in the mixer (A), depending on space, the function of this is to prevent the aggregate material from being discharges into area (C) of the mixer where the material flow in the mixer is countercurrent to the flow of the discharged material.
The invention results from a discovery that the property of viscosity that characterize the unmixed bituminous liquid is drastically reduced in the known processes of mixing, this from lack of a relevant time schedule for adding, and flow rates of the different fractions of solids at discharge into the mixer.
The invention is a technology of mixing the components of the asphalt mix without reduction in the viscous resource of the bituminous liquid. The technology is here described by a time schedule, an example of mix composition, a method for testing the asphalt mix of the viscous resource and devices that control the flow of the components in mix at discharged to the mixer. By the method of testing is also learned the limit to which the time schedule can be trimmed, as to the asphalt plants capacity.
The invention is important to the production of asphalt mixes. This as the viscosity of the bituminous liquid is a product of ductility and cohesion, a combination recognized as the resource of durability of the bituminous liquid as the binder of paved mix.

Claims

Method for producing an asphalt mix that includes a coarse fraction, a fine fraction, filler and a bituminous liquid with the following steps in the mentioned order:

a) mixing the coarse fraction and the bituminous liquid in a mixer,

b) discharging the filler to be spread over the coarse fraction and the bituminous liquid and

c) discharging the fine fraction over the filler and mixing,

d) discharging the ready mix from the mixer,

wherein the discharge of the fractions are optimized so that the mix behaves like a liquid in a test where a deformation of a specimen of the mix depending from the temperature of the specimen is measured,
characterized in that,
for conducting step a), the coarse fraction and the liquid binder are discharged and mixed simultanously over a first time period.
Method according to claim 1,
characterized in that, for starting production of the asphalt mix in an asphalt plant, the following time schedule is used universally in different types of asphalt plants and for different mix compositions:

a) discharging the coarse fraction and the bituminous liquid simultanously and mix over a first time period of 17s,

b) spreading the discharge of the filler over a second time period of 17s,

c) discharging and mixing the fine fraction material over a third time period of 18s,

d) discharging the ready mix from the mixer.
Method according to claim 2,
characterized in that the time schedule is thereafter amended to achieve and/or optimize the viscous behaviour of the mix.
Method according to any of the claims 2 or 3,
characterized in that the time schedule is then trimmed for adjustment of the respective asphalt plant capacity wherein the extent of trimming is limited by testing the viscous behaviour of the mix.
Method according to any of the preceding claims,
characterized in that
the filler and/or the fine fraction is discharged into a downwardly directed material flow in the mixer.
Method according to claim 5,
characterized by using a mixer with a mixing shaft extending in a horizontally direction and having paddles for driving the flow of the material to be mixed and by discharging the fine fraction material along a mixer wall extending essentially parallel to the shaft where the paddles are rotated in a downward direction.
Method according to any of the claims 5 or 6,
characterized by using a mixer with at least two mixing shafts having mixing paddles wherein the shafts and their paddles are rotating in opposite directions so that the paddles on the side near to the other shaft are moving upwards and the paddles located near to a wall of the mixer which wall extends essentially parallel to the shafts are moving downwards.
Device for carrying out the method according to any of the preceding claims, comprising a mixer,
characterized by
a control apparatus administrating the mixing process wherein said control apparatus is configured such that the coarse fraction and the bituminous liquid are discharged and mixed simultanously and that further steps b) to d) are conducted.
Device according to claim 8,
characterized by an regulating apparatus for regulating the flow rate of the filler at discharge into the mixer.
Device according to claim 9,
characterized in that the regulating apparatus has a screw for (D) for discharge of the filler into the mixer and an adjustment means for adjusting the flow rate of the filler by changing the revolutions per minute of the screw wherein said
adjustment means include a frequency converter for changing the revolutions per minute wherein the frequnecy converter is connected to a motor of the screw.
Device for carrying out the method according any of the claims 1 to 7, comprising a mixer,
characterized by a guiding means that prevents the aggregate material from being discharged in an area of the mixer where the material flow in the mixer is countercurrent to the flow of the discharged material.