Apparatus for producing a heated reproduction asphalt mixture

Disclosed are a method of and an apparatus for producing a heated reproduction asphalt mixture, in which a new material and a normal-temperature waste material, the water content of which is set at a limited range of values, are adapted to be mixed together in the ratio of (90 to 40):(10 to 60) in terms of weight. The temperature of heating the new material by means of a dryer is controlled to range from 190.degree. C. to 350.degree. C. so as to be in conformity with the above mixing weight ratio. Both the materials are mixed and kneaded together in a mixer at a kneading temperature of 150.degree. C. or more. The gas generated within the mixer is exhausted toward a chimney in a state wherein the amount exhausted is made adjustable.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of and an apparatus for producing 
a heated reproduction asphalt mixture, which are adapted to produce a 
reproduction asphalt mixture by utilizing a waste asphalt pavement 
material produced following a remedy, etc. of an asphalt pavement. 
2. Description of the Prior Art 
A waste asphalt material which is produced as a result of remedy, repair, 
or the like of an asphalt-paved road has hitherto been attempted to be 
reused. Conventionally, a mixing system of drum-dryer type which is 
adapted to make much use of such waste asphalt material to an extent of 80 
to 100 percent by weight was generally employed for that purpose. Such 
mixing system, however, has the following drawbacks. First of all, the 
system is expensive in respect of its equipment. Secondly, the asphalt 
material is deteriorated due to the reheating of the waste asphalt 
material by a flame or a high temperature air. This necessitates using a 
softening agent in order to increase the penetration. Besides, the waste 
asphalt material necessarily is stopped from being heated up to a required 
value of temperature, in order to prevent the asphalt material from being 
degraded. This results in production of a reproduction asphalt mixture 
which is short of heating. Thus, the product becomes unstable in terms of 
property. 
Further, in the prior art, when the waste material is kneaded while it is 
heated, a large amount of water contained therein is instantaneously 
vaporized. This causes generation of a gas containing a large amount of 
water and dust. The generation of such a gas contaminates the operating 
environment to become a cause of air pollution. As attempts to solve these 
problems, several techniques have hitherto been made public, which 
includes a production method and apparatus disclosed in Japanese Patent 
Unexamined Publication Nos. 117102/83 and 120757/85. Besides, a technique 
adjusting the internal pressure of the dryer to make stable the quality of 
an aggregate material delivered from the dryer has also been proposed in 
Japanese Patent Examined Publication No. 53963/84. 
The techniques which are disclosed in Japanese Patent Unexamined 
Publications Nos. 117102/83 and 120757/85 each features heating of only a 
new material by means of a dryer with a waste material being introduced at 
room temperature and at a relatively low mixing rate of weight. Further, 
the former technique of No. 117102/83 is also characterized by causing a 
gas generated at the time of kneading the new material and the waste 
material to be exhausted towards the chimney side by way of a duct. On the 
other hand, the latter technique of No. 120757 also has a feature in 
respect of a blade structure within the dryer for heating the new material 
in addition to controlling a mixing weight ratio between the new and waste 
materials, as above. Any of the above-mentioned old techniques, however, 
made no attempt to combine or synthesize a part or all of such techniques, 
although it has its own features. Further, no disclosure has yet been made 
of a technique which is based on the consideration of an optimum weight 
percentage for mixing of the waste material, water content in the waste 
material, etc. 
SUMMARY OF THE INVENTION 
Accordingly, the object of the present invention is to provide a method of 
and an apparatus for producing a heated reproduction asphalt mixture, 
which excels the advantages of the prior art, and in which the mixing 
ratio in terms of weight between waste and new materials is selected to 
fall within an optimum range while the water content in the waste material 
is kept at a limited range of values, so as to stabilize the quality of 
the resulting reproduction asphalt mixture; and, on the other hand, 
reduction in the installation cost can be achieved, elimination of causes 
of the air pollution is fulfilled and, at the same time, the improvement 
in quality of the mixture is made through controlling the temperature of 
heating the new material within a dryer to a value which permits it to be 
commensurate with said mixing ratio. 
To attain the above object, according to the present invention, there is 
provided a method of producing a heated reproduction asphalt mixture, 
which is adapted to cause a base material to be reproduced and a new 
material to be mixed together in a mixer to produce a heated reproduction 
asphalt mixture, the former material being prepared by crush/breakage and 
subsequent classification from a waste asphalt pavement material composed 
of filler bitumen and aggregate material, and the latter material being 
composed of crushed or broken stones, sands, asphalt, normal-temperature 
filler, etc., said latter material being heated by a dryer up to an 
optimum temperature and introduced into the mixer, the method comprising 
the steps of selectively determining the mixing ratio of new aggregate 
composed of crushed stones, sands, etc. contained in the new material to 
the base material to be reproduced from the ranges of (90 to 40):(10 to 
60) in terms of weight, setting the heating temperature for the new 
aggregate such that when the weight of the new aggregate is selected to be 
90 percent, it is set at approximately 190.degree. C. and that, as the 
weight of the new material is selected to be a smaller value toward 40 
percent, it is sequentially raised from 190.degree. C. toward 350.degree. 
C., the base material being maintained at all times at normal temperature 
while its water content is suppressed to 2 percent or less, mixing the new 
aggregate and the base material to be reproduced in the mixer while both 
the materials are maintained to have a temperature of 150.degree. C. or 
more by way of heat exchange therebetween, thereby causing part of the 
filler bitumen in the base material to be reproduced to be transferred 
onto the surfaces of the new aggregate to thereby perform a primary 
coating, subsequently introducing new filler and new heated asphalt into 
the mixer, and kneading together the new aggregate, base material to be 
reproduced, new filler, and new asphalt, thereby causing the new filler 
bitumen to be transferred onto the surfaces of the new aggregate and base 
material to be reproduced to thereby perform a secondary coating. 
Further, according to the present invention, there is provided an apparatus 
for producing a heated reproduction asphalt mixture, improved from an 
asphalt plant of batch system comprising a new-aggregate handling means 
including a supply means, a dryer, a sieving means, a storage means and a 
measuring tub means, a new-asphalt handling means including a supply means 
and a measuring tub means, a new-stone-powder handling means including a 
supply means and a measuring tub means, a mixer for mixing with each other 
a new aggregate, new asphalt and new stone powder, exhaust ducts connected 
to the dryer, sieving means and mixer, and a bag filter and a cyclone 
collector for collecting dusts from the associated ducts by use of 
exhausters, the apparatus comprising a base-material-to-be-reproduced 
handling means including a supply means, a storage means, a measuring 
means, and an introduction-into-the-mixer means, the base material to be 
reproduced being prepared by crush/breakage and subsequent classification 
from a waste asphalt pavement material, the dryer having therein a heated 
hopper section constituting an aggregate discharge section, the heated 
hopper section having a corner at which the gas is most likely to stagnate 
and at which there is disposed a pressure sensor for controlling a 
pneumatic pressure, whereby the rate at which the gas is exhausted by 
means of the exhauster is made variable and controlled in accordance with 
the operation of the pressure sensor so as to cause the internal pressure 
of the dryer to be maintained at a constant level in corresponding 
relationship to the amount of combustion gas fed into the dryer from a 
burner thereof and the amount of vapor generated from the new aggregate 
therein, the level being substantially the same as that of the pneumatic 
pressure prevailing outside the dryer and indicating a water column of 
minus one to several millimeters when numerically expressed, the dryer 
being in the form of a hollow cylinder extending from a raised aggregate 
introduction port to a lowered aggregate discharge port by way of an 
intermediate inclined portion where the new aggregate can be permitted to 
slide and shift toward the lowered discharge port while it is being 
revolved along an inner surface of the dryer, the dryer having disposed 
therein the burner in such a manner that a flame thereof is directed 
toward the aggregate introduction port from a central part of the 
cylindrical dryer in the vicinity of the aggregate discharge port thereof, 
the dryer having an inner wall surface section corresponding to a flame 
section of the burner, the inner wall surface section being provided with 
auxiliary blades having a shape permitting the new aggregate to be moved 
along the entire inner peripheral wall surface without hindering the 
advance of the flame of the burner, the dryer having another intermediate 
wall surface section located at a position remote from that corresponding 
to the flame section of the burner, the another intermediate inner wall 
surface section being provided with agitating blades permitting the new 
aggregate to be uniformly distributed over the entire cross-sectional zone 
of the cylindrical dryer, the dryer having a third inner wall surface 
section in the vicinity of the aggregate introduction port, the third 
inner wall surface section being provided with nonreturn blades capable of 
checking the backward flow of the new aggregate, the measuring tub means 
and mixer being covered by a covering means from which is led out the 
exhaust duct connected to the bag filter and the cyclone collector via the 
exhauster, the exhaust duct being provided at its intermediate portion 
with an automatic opening/closing mechanism constituted by a damper as 
well as a blower mechanism. 
The present invention adopts an asphalt mixing system of batch type which 
is small in the installation cost and which does not necessitate the use 
of any softening agent or the like to provide a product of stable quality, 
the invention being characterized in that the waste material is introduced 
at normal temperature while the rate at which it is introduced for being 
mixed with the new material is comparatively small. That is, the invention 
has the following features. The new material and the normal-temperature 
waste material, the water content of which is set at a limited range of 
values, are adapted to be mixed with each other in the ratio of (90 to 
40):(10 to 60) in terms of weight. On the other hand, the temperature of 
heating of the new material by means of the dryer is controlled to range 
from 190.degree. C. to 350.degree. C. so as to be in conformity with the 
above mixing weight ratio. The new and waste materials are mixed and 
kneaded together in a mixer at a kneading temperature of 150.degree. C. or 
more. The gas generated within the mixer is exhausted toward a chimney in 
a state wherein the amount exhausted is made adjustable. The heating 
temperature inside the dryer is controlled by causing the internal 
pressure of the latter to be kept at a level substantially the same as 
that of the external pressure and, to this end, discharging the exhaust 
gas within the dryer toward the chimney in a state wherein the amount 
discharged is made adjustable. On the other hand, the blades of various 
configurations are provided on the inner peripheral surface of the dryer 
so as to enable the new material to be exposed to the flame with high 
efficiency.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An apparatus for producing a heated reproduction asphalt mixture will now 
be described with reference to the drawings. 
An aggregate material to be reproduced is prepared by crush/breakage and 
subsequent classification from a waste asphalt pavement material. That is, 
the waste asphalt pavement material is conveyed by means of, for example, 
a truck not shown up to a storage tub 39. It is then carried by means of a 
conveyor 38 up to a jaw crusher 37 in which it is crushed into pieces. Of 
these pieces, the large ones which have been obtained by way of a sieving 
device 36 are further crushed by means of an impact crusher 35 and then 
fed into a sieving device 34. The base material which has been obtained by 
way of the sieving devices 36 and and 34 is classified according to the 
particle size. The base material thus classified is fed into buckets 31, 
32 and 33 and then is fed into an aggregate receptacle 28 (waste material 
receptacle). Then, the aggregate material is fed into an aggregate 
measuring tub 17. On the other hand, new aggregate which is composed of 
crushed stones and sands is stored in an aggregate receptacle 20 in a 
state wherein it is classified. The new aggregate is then fed from the 
aggregate receptacle 20 into a dryer 1 in which it is heated up to a 
moderate temperature. Thereafter, the new aggregate is conveyed upwards by 
means of a bucket conveyor (not shown) disposed inside a heated elevator 
24. The new aggregate material, thereafter, is fed into the aggregate 
measuring tub 17 via a shaking sieve 25 and a heated receptacle 26. The 
new aggregate material and the aggregate material to be reproduced have 
their respective weights so measured as to a predetermined mixing ratio as 
expressed in terms of weight. 
The exhaust gas which contains the vapor and dusts generated within the 
dryer 1 is exhausted out of a chimney 14 by way of an exhaust duct 9 
equipped with exhausters 12 and 13. The exhaust duct 9 is equipped with a 
cyclone 10 and a filter 11 which are intended to remove the dusts and the 
like from the exhaust gas. 
On the other hand, stone powders are upwardly conveyed by means of a bucket 
conveyor not shown which is installed inside a stone-powder elevator 30. 
They are temporarily stocked in a stone-powder receptacle 29 and then are 
fed into a stone-powder measuring tub 19. Further, a new asphalt also is 
fed into an asphalt measuring tub 18. The mixture of the new aggregate and 
the base material to be reproduced, both of which are blended at the 
later-described mixing weight ratio, and predetermined amounts of stone 
powders and asphalt are thrown into the mixer 2 and are heated and kneaded 
together with the latter. The mixer 2, the aggregate measuring tub 17, the 
asphalt measuring tub 18 and the stone powders measuring tub 19 are 
covered by a covering 27 and thus are received therein. The interior of 
the covering 27 is allowed to communicate with a duct 15 by connecting one 
end thereof to the covering 27. An opening/closing valve 8 and an 
exhauster 16 are equipped to the duct 15, the other end portion of which 
is allowed to communicate with the interior of the exhaust duct between 
the cyclone 10 and the filter 11. Another opening/closing valve 6 and 
another exhauster 13 are also equipped to another exhaust duct between the 
filter 11 and the chimney 14. To the opening/closing valve 6 is connected 
the amount-of-exhaust-gas controlling device 5, to which there is 
connected a pressure sensor 3 which constitutes a pressure sensing means. 
It is to be noted in this connection that the amount-of-exhasut-gas 
controlling device 5 is also connected with exhausters 12 and 13 so as to 
control the amount of gas exhausted. Further, an automatic opening/closing 
device 7 is connected to the opening/closing valve 8 as well as to the 
exhauster 16 so as to control the degree of opening as well as the number 
of rotations. 
Next, the general description of the structure of the dryer 1 will now be 
described below. 
The dryer 1 has a cylindrical rotary member 1a which is pivoted to a 
stationary lower end structure 1b and a stationary upper end structure 1c 
and which is driven to rotate by means of a drive mechanism 40. The 
stationary lower end structure 1b is provided with a discharge port 22 for 
discharging the new aggregate as well as with a burner 23 while, on the 
other hand, the upper end structure 1c is provided with an inlet port 21 
for introduction of the new aggregate into the dryer 1 as well as with the 
exhaust duct 9. The rotary member 1a consists of three sections--a flame 
section located at the side of the burner 23, an introduction section 
located at the side of the inlet port 21, and an intermediate inner wall 
section located between those two sections. The flame section, the 
intermediate inner wall section and the introduction section are provided, 
on its cylidrical inner wall surface, with auxiliary blades 4a, agitating 
blades 4b and nonreturn blades 4c, respectively. The flame section, as 
shown in FIG. 2, is provided, on its cylindrical inner wall surface, with 
the auxiliary blades 4a having a substantially L-shaped cross section in 
such a manner that they are arranged in a manner extending from the 
cylindrical inner wall surface radially about a center 41 of the cylinder 
of the burner 23. The agitating blades 4b having a base 42 shaped, in 
cross section, like L, on which lateral plates 43 are fixed having gaps 44 
therebetween. The introduction section, as shown in FIGS. 5 and 6, is 
provided, on its cylindrical inner wall surface, with the nonreturn blades 
4c in such a manner that they are arranged in a manner extending from the 
cylindrical inner wall surface radially about the center 41 of the burner 
cylinder and being inclined with respect to an axis thereof. 
The action of this embodiment will now be described below. 
The respective mixing amounts of the new aggregate and the base material to 
be reproduced are measured in the aggregate measuring tub 17 so as to bear 
a predetermined mixing weight ratio. Where the amount of the base material 
is too large, a reproduction asphalt of good quality can not be obtained. 
For this reason, the following mixing weight ratios are experimentally set 
taking, for example, the particle size of the base material into 
consideration. That is, the new aggregate is selected to have a weight 
part of 90 to 40 whereas the base material to be reproduced is selected to 
have a weight part of 10 to 60. For example, the base material is, 
selected, for being mixed with the new aggregate, to have a weight part of 
10 when the weight part of the new aggregate is 90. Further, the base 
material is selected to have a weight part of 60 when the new aggregate 
has a weight part of 40. As stated before, the new aggregate is fed into 
the aggregate measuring tub 17 after it has been heated with the dryer 1 
at a moderate predetermined temperature. On the other hand, the base 
material to be reproduced is fed in a state wherein it is kept at normal 
temperature. At the time of mixing those two types of material, desirably, 
the mixture is maintained at a temperature of 150.degree. C. or more. 
Therefore, when the weight part of the new aggregate is 90, the new 
aggregate is heated at about 190.degree. C. When the weight part of the 
new aggregate is 40, this aggregate is heated at about 350.degree. C. 
Concerning the values of weight part falling within the intermediate range 
between 90 and 40, the setting thereof is performed while the gradient of 
change in weight part of from 90 toward 40 is brought into corresponding 
relationship to the gradient of rise in temperature of from 190.degree. C. 
toward 350.degree. C. While the base material to be reproduced is fed in a 
state of having been kept at normal temperature as mentioned above, the 
content of water therein desirably is 2% or less. The upper limit of 
temperature of heating the new aggregate when the base material to be 
reproduced is added 60% is 350.degree. C. In order to heat the new 
aggregate up to a temperature higher than 350.degree. C., it is necessary 
to improve the facility. Besides, the quality of a composite heated 
reproduction asphalt material is likely to be degraded. For this reason, 
limitation inevitably is imposed upon the heating temperature for the new 
aggregate. 
The above-mentioned mixture is thrown from the aggregate measuring tub 17 
into the mixer 2 while, on the other hand, the new asphalt and stone 
powders as measured are also thrown from the asphalt measuring tub 18 and 
the stone powder measuring tub 19 into the mixer 2, whereby these 
materials are mixed with each other. It is to be noted that the new 
asphalt is added in an amount obtained by subtracting from an optimum 
amount of asphalt the amount obtained through multiplying the amount of 
asphalt extracted from the base material to be reproduced by the 
percentage of asphalt to be mixed. During the time period in which the 
mentioned materials are mixed by means of the mixer 2, the heat exchange 
is performed between the new aggregate and the other materials. As a 
result, the mixture in the mixer 2 is maintained at a desired mixing 
temperature of about 150.degree. C. Under the conditions wherein the 
mixture is kept at such a temperature, the filler bitumen in the base 
material to be reproduced is allowed to transfer onto the surfaces of the 
new aggregate. Thus, a primary coating is effected. After the gas of ducts 
produced at this time has been exhausted, the new filler bitumen (asphalt 
and stone powders) is allowed to transfer onto the surfaces of the new 
aggregate. Thus, a secondary coating is effected. Thus, a heated 
reproduction asphalt mixture is obtained. This asphalt mixture is of 
substantially the same quality as that of a new asphalt mixture and thus 
can be used for pavement of a road as it stands. 
While the heated reproduction asphalt mixture is produced as above through 
operation of the mixer 2, during the mixing operation a large amount of 
vapor, dust and blue smoking are generated. When such vapor, dust and blue 
smoking are leaked outside the apparatus, they will become a cause of air 
contamination. To prenent this leakage, the mixer 2 and measuring tubs 17, 
18 and 19 are covered by use of the covering 27 as stated before. By so 
doing, the mentioned gas is sucked into the duct 15 by operation of the 
exhauster 16 and is introduced into the exhaust duct 9. Thus, after having 
its dust and the like removed by means of the filter 11, the gas is 
emitted from the chimney 14. The gas which is emitted by way of the duct 
15 is controlled, in terms of the amount exhausted, by the operation of 
the automatic opening/closing device 7 adapted to automatically operate 
the opening/closing valve 8. That is to say, the automatic opening/closing 
device 7 is so constructed as to cause the opening/closing valve 8, which 
is automatically opened/closed by electric power or air, to be kept "open" 
for a specified period of time and at the same time to cause the exhauster 
16 to rotate when the gas which contains vapor, dust and the like enters 
the interior of the covering 27. It is to be noted that, after said gas is 
exhausted into the duct, the opening/closing valve 8 is closed by use of, 
for example, a timer or the like in a specified period of time. 
The new aggregate is introduced from the aggregate receptacle 20 into the 
dryer 1 by way of the introduction port 21 and is caused to rotate within 
the rotary member 1a. During the rotation step of this rotary member 1a, 
the nonreturn blades 4c function not only to prevent the new aggregate 
from being backwardly moved toward the stationary upper end structure 1c 
but also to cause the new aggregate to be transferrred to a central part 
of the interior of the dryer 1. The agitating or scarifying blades 4b 
function not only to upwardly scarify the new aggregate dropping onto the 
bottom zone of the inner peripheral wall surface of the rotary member 1 
but also to allow the new aggregate to drop, as if it were hails, from the 
gaps 44 between the lateral plates 43 as it rises toward the top zone. The 
auxiliary blades 4a of the flame section function to scoop the new 
aggregate while it rises along the inner peripheral wall surface, so that 
the new aggregate is caused to rotate along the inner peripheral wall 
surface without being allowed to drop even at the top zone of the inner 
peripheral wall surface of the rotary member 1a. Thus, no new aggregate 
hinders the advance of the flame of the burner 23. Thus, the new aggregate 
is heated, while they are caused to rotate by the blades 4a, 4b and 4c, up 
to the above-mentioned temperatures (190.degree. C. to 350.degree. C.), 
thus to be discharged into the elevator 24 by way of the discharge port 
22. Although a combustion gas which contains vapor, dusts, etc. is 
introduced into the dryer 1 from the burner, it is sucked and exhausted 
into the exhaust duct 9 by means of the exhausters 12 and 13 as stated 
before. In this case, the amount of the vapor produced within the dryer 1 
varies depending upon the water content, etc. in the new aggregate. In 
order to increase the heat efficiency of the dryer, the material is 
preferably low in water content. More particularly the water content is 
required to be suppressed at 2% or less. 
The exhaust-gas-amount controlling device 5 is disposed for the purpose of 
solving the above-mentioned problem. More specifically, the variation 
internal pressure of the dryer 1 is sensed by the pressure sensor 3. 
Namely, the exhaust-gas-amount controlling device 5 is constructed such 
that, by sensing the internal pressure variations occurring due to the 
variations in quantity of the vapor in the dryer and the combustion gas 
sent thereinto from the burner 23, it controls the degree of opening of 
the opening/closing valve 6 in the exhaust duct 9 so as to make the level 
of the internal pressure approximately equal to the external pressure. 
This prevents the unnecessary entry into the dryer of the above-mentioned 
cooling air, etc. It is to be noted in this connection that it is 
desirable to differ the internal pressure from the external one of the 
dryer 1 to an extent of minus 1 to minus several millimeters of water 
column. It is also to be noted that the pressure sensor 3 desirably is 
disposed at a position inside the dryer in the vicinity of the new 
aggregate discharge port 22 where the gas is most likely to stagnate. This 
is for the purpose of sensing the pressure with high accuracy at the 
position where the pressure has the greatest effect upon the property of 
the heated new aggregate as discharged. Besides, the exhaust-gas-amount 
controlling device 5 is connected to the exhausters 12, 13 as well so as 
to control the rate of exhaustion from the dryer in accordance with the 
degree of opening of the opening/closing valve 6. This prevents the dust 
from being leaked outside the dryer 1 and, at the same time, suppresses 
the degree of increase in pressure loss of the filter 11, etc. to enable 
the elongation of the service life. 
As will be apparent from the foregoing description, the present invention 
has the following advantages. 
(1) The asphalt mixture which contains the base material to be reproduced 
and the new aggregate was compared with an asphalt mixture not containing 
any base material to be reproduced but containing the new aggregate while 
the amount of the former material to be added was varied. The products 
obtained has uniform values involved, each of which cleared a reference 
value. 
TABLE 1 
______________________________________ 
Amount Added Of Base Material To Be Reproduced 
And The Results Of Test On The Physical Properties 
Of The Same 
______________________________________ 
Comparison Example Example 
Example No. 1 No. 2 
______________________________________ 
Amount Added 
0 20 30 
Of Base 
Material To 
Be Reproduced 
(wt %) 
Density (g/cm.sup.3) 
2.392 2.400 2.412 
Void (%) 4.0 4.0 3.7 
Stability (kg) 
1,160 1,260 1,360 
Flow Value 25 25 30 
(1/100 cm) 
Dynamic 1,250 2,700 2,300 
Stability 
(times/mm) 
______________________________________ 
Example Example Reference 
No. 3 No. 4 Value 
______________________________________ 
Amount Added 
30 50 -- 
Of Base 
Material To Be 
Reproduced 
(wt %) 
Density (g/cm.sup.3) 
2.411 2.422 -- 
Void (%) 3.8 3.5 3-6 
Stability (kg) 
1,390 1,380 &gt;750 
Flow Value 29 29 20-40 
(1/100 cm) 
Dynamic 2,900 2,700 &gt;1,500 
Stability 
(times/mm) 
______________________________________ 
(2) By controlling the new aggregate feeding temperature in accordance with 
the variations in weight of the base material to be reproduced, it is 
possible to obtain a good quality of asphalt mixture. 
(3) It is possible to cause the internal pressure of the dryer to be kept 
at a specified unvaried level, thus enabling a stable desired and heated 
new aggregate to be fed to the mixer side. By controlling the amount of 
gas exhausted, it is possible to cause a decrease in required electric 
power of the exhausters, to cause a decrease in the amount of dust leaked 
from the dryer, and at the same time, to elongate the service lives of the 
filter, cyclone, etc. 
(4) It is possible to heat the new aggregate uniformly and up to a 
predetermined temperature by providing the interior of the dryer with the 
mentioned blades. 
(5) Effluence of no hot air from the dryer by way of the gaps or clearances 
takes place, so that unnecessary suction of cooling air into the dryer is 
prevented. As a result, it is possible to cause the heating efficiency to 
be kept at the highest level without being affected by the atmospheric 
temperature, weather, or other environmental conditions. And, 
(6) It is possible to prevent the dust, blue smoking, etc. generated when 
the mixer makes its kneading operation, from becoming cuases of the air 
pollution.