Solid sulfur-extended asphalt composition and method and apparatus therefor

An improved sulfur-extended asphalt composition and method for use in making compacted bituminous concrete, whereby solid sulfur, preferably in powdered form, is added to liquid asphalt on substantially a 1:1 weight basis, the asphalt comprising less than 3.1% of the weight of the total bituminous concrete mixture. The solid sulfur is melted by the heat present in the molten asphalt thereby lessening the overall energy consumption and eliminating the need for any liquid sulfur-related heating equipment. The overall binder content of the resultant bituminous concrete is varied so as to both maintain the 1:1 sulfur-replacement-of-asphalt relationship utilized with this invention, and to reduce the occurrence of air voids. Such a 1:1 replacement relationship provides economic efficiencies in bituminous concrete production not previously obtainable. The resultant sulfur-extended bituminous concrete when compacted provides substantially increased mechanical strengths over conventional asphalt mix designs. A solid sulfur mixing and blending apparatus is disclosed for use with asphalt batch plants to accommodate the present sulfur-extended asphalt composition and method.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to bituminous concrete and the methods of making 
same, and more specifically to sulfur-extended asphalt mix designs, 
processes, and apparatus for use with the same. 
2. Description of Prior Art 
Preliminarily, as used herein, the terms "asphalt" or "asphalt cement" 
shall mean any of the heavy petroleum oils or tar or pitch; "bituminous 
contrete" shall mean a composition of asphalt cement and aggregate (such 
as gravel, sand, mineral fillers, etc.); and "sulfer-extended asphalt" 
shall mean a mixture of sulfur and asphalt cement. Additionally, the term 
"binder content" shall mean, depending upon the context, either the weight 
of the asphalt cement alone or the weight of the sulfur-extended asphalt 
mixture, expressed as a weight percentage of the total weight of the 
bituminous concrete mixture. The units of measurement for the results of 
the well-known Marshall Flow test noted herein are in one one-hundreths of 
an inch. For example, if a bituminous concrete test specimen deforms 0.15 
inch, the Marshall Flow value is noted as 15. 
There have been various prior attempts to eliminate dependence upon 
petroleum in the manufacture of compacted bituminous concrete or so-called 
blacktop by using sulfur-extended asphalt compositions. The majority of 
such teachings require that molten sulfur be utilized in making the 
sulfur-extended asphalt. However, such prior art liquid sulfur-extended 
asphalt methods require costly and specialized equipment to maintain the 
elevated temperature of the molten sulfur (at 246.degree. F. or more) and 
also to properly blend it with the liquid asphalt cement. In a typical 
asphalt batch plant, the use of liquid sulfur would require heated liquid 
sulfur storage tanks, supplemental burners, and associated heated valves, 
pumps and piping equipment. Additionally, since the molten sulfur and 
asphalt are preblended before being introduced into the asphalt weigh 
bucket and finally into the the heated aggregate to form the bituminous 
concrete, costly high shear energy-type blending units must be used due to 
liquid sulfur's relatively high viscosity. These include colloid mills, 
gear pumps, high speed stirrers, propeller mixers, static mixers, or other 
such devices. 
Additionally, the known prior art mix designs for liquid sulfur-extended 
asphalt typically require that the asphalt be replaced by liquid sulfur on 
an equal volume basis. This means then that, since sulfur is twice the 
weight of asphalt, two weight units of sulfur must be included for every 
asphalt unit being replaced. Such a 2:1 weight ratio replacement was 
primarily used to minimize the high air void contents found in many 
sulfur-extended bituminous concrete mixtures of the prior art. Due to the 
typically prevailing market prices for liquid sulfur and asphalt cement, 
such prior art liquid sulfur-extended mix designs were not satisfactory 
from a cost savings standpoint. Thus, they were not widely utilized. The 
latter is also true because the supply of liquid sulfur has not 
historically been reliable. Consequently, until the present invention the 
manufacture of bituminous concrete has remained highly petroleum 
dependent. Moreover, from an energy consumption standpoint, the extra 
energy required to maintain molten sulfur at useable liquid states with 
such prior art mix designs is highly disadvantageous. 
There have been prior art attempts to replace liquid asphalt cement by 
solid sulfur. Such prior art mix designs were also typically produced on 
an equal volume basis, i.e., a sulfur-to-asphalt weight ratio of 1.75:1, 
2:1, or even higher. At such high sulfur concentrations, the resulting 
pavement product was difficult to compact using conventional rolling 
techniques. Thus, such prior art designs that were used in relation to 
highway paving were primarily for repair work. That is, individual 
segments of asphalt were cast without subsequently being compacted, such 
as for repairing potholes, for example. 
Examples typifying such prior art sulfur-extended asphalt compositions for 
use in bituminous concrete are disclosed in U.S. Pat. Nos. 2,182,837, 
3,738,853, and 3,960,583, British Pat. No. 1,363,706, and Canadian Pat. 
Nos. 755,999, 945,416 and 1,042,610. 
SUMMARY OF THE INVENTION 
The present invention overcomes these and other problems of the prior art 
by providing an improved sulfur-extended asphalt composition for use in 
making compacted bituminous concrete in which the asphalt cement is 
replaced by solid sulfur on a 1:1 weight basis and the heat present in the 
molten asphalt is used to melt the solid sulfur. With the present 
invention the asphalt comprises less than 3.1% of the total weight of the 
bituminous concrete mixture. The overall binder content of the bituminous 
concrete mixture is selectively varied to assure both use of the desired 
1:1 replacement ratio and maintenance of proper paving design criteria. 
Through use of solid sulfur, preferably in powdered or crushed form, the 
expensive liquid sulfur handling equipment and high shear energy 
pre-blending equipment of the prior art mix designs are eliminated. The 
present invention's replacement of liquid asphalt by solid sulfur on a 1:1 
weight basis, rather than the prevailing 2:1 or more weight basis of the 
prior art mix designs, makes use of sulfur-extended asphalt compositions 
highly attractive from a cost standpoint. This is because solid sulfur is 
substantially less expensive than heated liquid sulfur on a delivered-ton 
basis. Further, the present invention assures that no extra energy is 
required to heat the solid sulfur since it is melted on-site at the 
asphalt batch plant by pre-blending it with the heated liquid asphalt 
directly in the heated asphalt weigh bucket. This is contrary to the prior 
art liquid sulfur mix designs where the elemental sulfur was first 
separately melted to a liquid state and then maintained at an elevated 
temperature, all requiring additional energy. In addition to reduced heat 
energy consumption, the present invention also provides an economical 
sulfur-extended asphalt composition by which petroleum dependence is 
substantially reduced, i.e., almost in half. 
A specialized mixing apparatus for use with the conventional heated asphalt 
cement weigh bucket of a typical asphalt batch plant is also disclosed. 
This mixing apparatus can be incorporated as an inexpensive modification 
to an existing asphalt plant or built integrally with new asphalt weigh 
buckets so as to accommodate the present solid sulfur-extended asphalt 
process. 
Thus, it is a primary object of the present invention to provide a 
sulfur-extended asphalt composition in which the asphalt is replaced by 
solid sulfur on a cost-efficient, substantially 1:1 weight basis. 
It is another object of the present invention to provide special mixing 
apparatus for use with a conventional asphalt batch plant to accommodate 
the blending of solid powdered sulfur with liquid asphalt cement in a 
heated asphalt weigh bucket. 
It is still another object to provide a sulfur-extended asphalt blending 
process whereby the total energy consumed is substantially reduced from 
that of conventional methods. 
It is a further object to provide a solid sulfur-extended asphalt mix 
design which eliminates costly liquid sulfur-related equipment required by 
prior art methods. 
It is yet another object to provide a method for making sulfur-extended 
bituminous concrete whereby a substantially 1:1 sulfur-to-asphalt 
replacement ratio may be regularly utilized by adjusting the overall 
binder content. 
It is a still further object to reduce harmful sulfur emissions from a 
sulfur-extended asphalt process.

EXAMPLE 1 
Preliminarily, it should be understood that a conventional process for 
making bituminous concrete typically includes the following steps as 
listed. Asphalt cement is heated to a liquid and maintained at 
approximately 300.degree. F. A quantity of aggregate in the form of sand, 
limestone, gravel, or slag is heated to a temperature of approximately 
350.degree. F. for a period of time long enough to be completely dried. 
The dried aggregate is then screened, weighed, and proportioned in a 
conventional aggregate weigh hopper and mixed with the heated asphalt 
cement in a blending apparatus such as a pugmill. The resulting bituminous 
concrete mixture made by such a conventional process generally has a 
temperature in the range of from 280.degree. F. to 290.degree. F. when 
leaving the batch plant site. In using this conventional process, the heat 
energy required to produce one ton of hot mix bituminous concrete is on 
the order of 350,000 BTU's. 
The pavement laying characteristics or so-called "lay down" criteria for a 
conventional bituminous concrete mix utilizing 100% asphalt cement, i.e., 
one not extended by sulfur, and listed as Example 1 in the Chart 1 below. 
As shown there, with an optimum 5% binder content as used in a typical 
conventional mix and due to the particular aggregate used, and with the 
binder being 100% asphalt cement, the finished bituminous concrete mix had 
the following characteristics: a 4.78% air void content, a bulk specific 
gravity of 2.39, a Marshall Flow of 12.5, and relatively low Marshall 
Stability rates of 1,400 lbs./in..sup.2 @ 24 hours and 1,450 
lbs./in..sup.2 @ seven days. 
EXAMPLE 2 
Further, the usual process for making a typical prior art bituminous 
concrete mix utilizing liquid sulfur-extended asphalt includes the 
following steps as listed. The liquid asphalt cement is heated to a 
temperature of 300.degree. F. and is introduced into a special high shear 
energy-type preblending unit, such as a colloid mill, for example. At the 
same time, liquid sulfur maintained at a temperature of at least 
280.degree. F. is introduced into the colloid mill through special 
heat-jacketed delivery lines and blended with the asphalt. This liquid 
asphalt extension, i.e., replacement, by liquid sulfur is done on 
essentially an equal volume basis. Thus, two weight units of sulfur are 
substituted for one weight unit of liquid asphalt cement. Meanwhile, the 
aggregate is heated and dried to a temperature of approximately 
350.degree. F. The total liquid sulfur-extended asphalt blend is 
proportionately weighed and introduced into the pugmill where the heated 
aggregate and sulfur-extended asphalt are then mixed. 
The final mixture of bituminous concrete made by such a liquid 
sulfur-extended asphalt process of the prior art is typically at a 
temperature of 280.degree.-290.degree. F. when leaving the plant site. The 
heat energy necessary to maintain sulfur in liquid form for subsequent use 
with liquid asphalt is on the order of 570,920 BTU's per ton of sulfur. 
This, of course, does not include any heat energy required when the solid 
sulfur is melted off-site and subsequently transported and stored in 
heated liquid form at the asphalt batch plant until needed. 
The lay down characteristics for such a bituminous concrete mixture 
utilizing the typical liquid sulfur-extended asphalt technology of the 
prior art are listed as Example 2 in Chart 1. A test sample was made 
according to the prior art's equal volume substitution ratio of liquid 
sulfur to liquid asphalt, i.e., a 2:1 weight ratio substitution. It will 
be noted that the total sulfur-extended binder content of this test sample 
was raised to 6.3% which relates to the 5% binder of the conventional mix 
of Example 1. This is because under existing sulfur-extended asphalt 
technology, binder content requirements for sulfur-extended asphalt paving 
are greater than for conventional paving. These higher binder 
requirements, in turn, result primarily because of the approximately 2:1 
weight and specific gravity ratio between the sulfur and asphalt. 
More specifically, the Sulphur Development Institute of Canada specifies 
that the optimum sulfur-extended asphalt binder may be determined from a 
conventional asphalt cement mix design by using the following formula: 
##EQU1## 
where, (with the values for Example 2 of Chart 1 shown in parenthesis): 
A=Weight percentage of Asphalt Cement in a Conventional Mix (5.0) 
R=Sulfur to Asphalt Binder Ratio (2.0) 
S=Weight percentage of Sulfur in the Sulfur-Extended Asphalt Binder (42.0) 
G=Specific Gravity of the Asphalt (1.013). 
The resulting sulfur-extended binder content for Example 2 then is 6.3%. In 
any event, the results for such a liquid sulfur-extended mix with a 6.3% 
binder content are a 2.6% air void content, a 24 hour Marshall Stability 
rate of 2120 lbs./in..sup.2, and a Marshall Flow of 12.5. 
DESCRIPTION OF PREFERRED EMBODIMENT 
In contrast, the improved sulfur-extended asphalt mix design of the present 
invention utilizes solid sulfur. The preferred process by which bituminous 
concrete is made from the present invention includes the following steps. 
The asphalt cement is heated to a temperature of 300.degree. F. and 
maintained there. The aggregate is heated and dried at a temperature 
preferably no greater than 305.degree. F. The purpose for this maximum 
aggregate drying temperature will be explained later herein. Elemental 
solid sulfur in bulk form is first pulverized and then introduced in a 
substantially crushed form into the heated liquid asphalt cement weigh 
bucket. 
The present invention's solid sulfur extension of asphalt cement is 
accomplished on substantially a 1:1 weight basis, the latter being assured 
through use of a variable binder content. That is, one weight unit of 
solid sulfur is added to one weight unit of liquid asphalt cement as 
weighed in the asphalt weigh bucket. The heat energy present in the liquid 
asphalt cement held in the asphalt weigh bucket supplies a major part of 
the heat required to melt the powdered solid sulfur. Only a minor portion 
of the energy needed for heating of the liquid asphalt, the sulfur, or the 
mixture of solid sulfur and liquid asphalt is required to be supplied by 
the heated oil chamber 52 in the asphalt weigh bucket 38. 
As the powdered sulfur is introduced into the heated asphalt weigh bucket 
it is simultaneously mixed with the liquid asphalt and dispersed 
throughout the same. At this stage, the now completely liquid mixture of 
heated sulfur and asphalt cement will have a temperature of approximately 
270.degree. F. The blended liquid mixture of sulfur and asphalt cement is 
then introduced into and blended with the heated aggregate in the asphalt 
batch plant's pugmill. So as to obtain desirable laydown criteria, the 
binder content (weight percentage of sulfur and asphalt blend) is 
selected, i.e., varied, so that the asphalt remains less than 3.1% of the 
total weight of the bituminous concrete mix and so that the desirable 1:1 
replacement ratio may be used. The aggregate comprises from 93-95% by 
weight of the total mix. 
The final mixture of bituminous concrete made by the improved process of 
the present invention will be at a temperature of approximately 
280.degree. F. to 285.degree. F. when leaving the plant site. It has been 
found that bituminous concrete made according to the process of the 
present invention is no more difficult to compact into pavement than 
conventional non-extended asphalt mix designs. Contrary to prior art 
sulfur-extended mix designs, no casting procedures are required with the 
present invention. Due to the fact that the heated aggregate of the 
present invention is dried to a lower than usual temperature, the heat 
energy required to produce one ton of the present invention's bituminous 
concrete is on the order of only 300,000 BTU's. 
Any harmful gases such as H.sub.2 S (hydrogen sulfide) and SO.sub.2 (sulfur 
dioxide) that may be emitted at the plant site due to the mixing of solid 
sulfur and liquid asphalt are substantially minimized for two reasons. 
First, the ambient temperature of the powdered sulfur slightly lowers 
rather than raises the temperature of the heated asphalt which is held at 
300.degree. F. prior to blending. Second, when the lower-temperature blend 
of liquid sulfur and asphalt is mixed with the higher temperature dried 
aggregate, the final mix temperature does not rise above that of the 
aggregate, i.e., approximately 300.degree. F. Thus, at all times the 
temperature of the resultant bituminous concrete mix is sufficiently below 
the critical temperature of 309.degree. F., above which H.sub.2 S and 
SO.sub.2 may be emitted. Accordingly, no harmful emissions other than a 
slight sulfur odor will result with use of the present invention. 
EXAMPLE 3 
A sample of bituminous concrete utilizing the solid sulfur-extended asphalt 
cement process of the present invention is shown as Example 3 in Chart 1. 
With this test sample, the conventional 5% binder content was maintained 
as with Example 1. However, the preferred 1:1 sulfur-to-asphalt 
substitution ratio was utilized. On a weight basis, 42% of the binder 
content was sulfur, 58% of the binder content was asphalt, while only 
2.90% of the total weight of the total bituminous concrete mix was 
asphalt. 
The test sample for this Example 3 was made by first preheating a 
convection oven to 300.degree. F. and by maintaining this temperature 
constant throughout the test. A container having a volume of 0.07 ft. was 
placed in the oven. A quantity of 1.45 lbs. of liquid asphalt was placed 
in the container and allowed to reach a temperature of 300.degree. F. A 
quantity of 1.05 lbs. of powdered solid sulfur was added to the heated 
asphalt cement and mixed into it for one minute by a propeller-type 
stirrer operated at 1,000 RPM. The sulfur dissolved completely in 30 
seconds and mixing and blending were accomplished in one minute. The 
blended mixture's temperature dropped to 294.degree. F., evidencing that 
the heat contained in the liquid asphalt cement can be utilized to melt 
the solid sulfur with only a minor temperature drop. This solid 
sulfur-extended asphalt blend was then mixed with aggregate heated to 
300.degree. F. The resulting bituminous concrete composition of this 
Example 3 had a 5.5% air void content, a bulk density of 149.1 
lbs./ft..sup.3, a Marshall Stability rate of 3,510 @ 24 hours, and a 
Marshall Flow rating of 9.0. 
More specifically, it is to be noted that the specific heats of sulfur 
range from 0.167 BTU's/.degree.F./lb. to 0.250 BTU's/.degree.F./lb., while 
the specific heats for asphalt, stone, and sand are approximately 0.5, 
0.5, and 0.4 BTU's/.degree.F./lb. respectively. (The term "specific heat" 
as used here is defined as heat in BTU's required to raise the temperature 
of a material one degree Fahrenheit, per pound of material.) Based upon 
these specific heats, and if the temperature of the asphalt cement is 
maintained at 300.degree. F., the final temperature of the liquified solid 
sulfur-extended asphalt cement blend in bulk quantities will have a 
temperature of approximately 270.degree. F. when ready to be introduced 
into the heated aggregate. Thus, when mixed with the aggregate heated to 
305.degree. F., the temperature for the resultant bituminous concrete mix 
as it is ready to leave the plant site will be on the order of 280.degree. 
F. to 285.degree. F. In view of the above, no additional energy source is 
required to melt the solid sulfur when using the improved process of the 
present invention. 
CHART #1 
__________________________________________________________________________ 
Example 
Sulphur %- 
Substitution 
Binder 
Sulphur-Asphalt 24 Hour Marshall 
No. Asphalt % 
Ratio Content 
(as % of total mix) 
% Air Voids 
Bulk Density 
Stability 
Marshall 
__________________________________________________________________________ 
Flow 
1 0-100 
N.A. 5.0 0-5.0 4.78 148.6 1400 12.5 
2 42-58 2:1 6.3 2.65-3.65 2.60 152.8 2120 12.5 
3 42-58 1:1 5.0 2.10-2.90 5.5 148.0 3510 9.0 
4 45-55 1:1 5.4 2.43-2.97 4.8 149.1 2660 10.0 
__________________________________________________________________________ 
EXAMPLE 4 
A second sample made according to the present invention is depicted as 
Example 4 in Chart 1. In this case, the binder content was raised from 5% 
as with previous Examples 1 and 3 to 5.4%. Again the 1:1 sulfur-to-asphalt 
substitution ratio was used. This heavier binder content on a weight basis 
comprised 45% sulfur and 55% asphalt cement. In this instance the asphalt 
was only 2.97% by weight of the total bituminous concrete mix. Utilizing 
the same test procedures and equipment as explained in relation to Example 
3 above, the resulting bituminous concrete composition had a 4.8% air void 
content, a bulk density of 149.1 lbs./ft..sup.3, a 24 hour Marshall 
Stability rate of 2660 lbs./in..sup.2, and a Marshall Flow rating of 10.0. 
It will be understood that, for the four Examples described above, the 
following aggregate comprising a conventional CA-16 crushed limestone 
surface mixture was used: 
______________________________________ 
% 
Specifi- 
cations* 
% 
Passing Retained of Exam- 
Specifications* 
Item Through By ples 1-3 
For Example 4 
______________________________________ 
Crushed Lime- 
stone Rock 
1/2" #10 sieve 
60.3% 60.3% 
Coarse Sand 
#10 sieve 
#80 sieve 
20.5% 20.5% 
#200 
Fine Sand #80 sieve 
sieve 11.0% 11.0% 
minus 
#200 
Mineral Filler sieve 3.2% 2.8% 
Binder Content 5.0% 5.4% 
100.0% 100.0% 
______________________________________ 
*Percentage of total bituminous concrete mix by weight. 
Also, an AC-10 asphalt cement from Shell Oil Company was used throughout. 
Other test specimens and their test results using the solid sulfur-extended 
process of the present invention and having varying binder contents are 
shown as Examples 5 through 10 in Chart 2 below. It will be understood 
that any increase in binder content and hence weight of the respective 
binder content and hence weight of the respective binder was compensated 
for by reducing the weight percentage of the coarse sand or mineral filler 
in the aggregate. 
CHART 2 
__________________________________________________________________________ 
Example 
Sulphur %- 
Substitution 
Binder 
Sulphur-Asphalt 24 Hour Marshall 
No. Asphalt % 
Ratio Content 
(as % of total mix) 
% Air Voids 
Bulk Density 
Stability 
Marshall 
__________________________________________________________________________ 
Flow 
5 42-58 1:1 5.20 2.18-3.01 5.0 148.8 1260 6.0 
6 42-58 1:1 5.20 2.18-3.01 4.4 149.6 2413 6.5 
7 42-58 1:1 5.20 2.18-3.02 5.60 147.8 2340 6.7 
8 42-58 1:1 5.20 2.18-3.02 5.5 151.7 2180 9.0 
9 45-55 1:1 5.20 2.34-2.86 5.8 147.5 2580 7.0 
10 45-55 1:1 5.60 2.52-3.08 5.7 147.7 2340 10.0 
__________________________________________________________________________ 
As can be seen from Charts 1 and 2, solid sulfur-extended asphalt mix 
designs made according to the present invention exhibit similar properties 
as compared to both conventional (100% asphalt) and liquid sulfur-extended 
mix designs. In fact, in some instances, these solid sulfur-extended mixes 
are even superior. Accordingly, depending upon the specific lay down 
characteristics as dictated by field conditions, the air void content and 
bulk density of a particular mix design are believed to be a function of 
the amount of binder content in a bituminous concrete mix. It will be 
understood that with an optimum paving mix, the bulk denisty is preferably 
within the range from 147-155 lbs./ft/.sup.3, and the air void content is 
preferably no greater than 5.8%. Where a heavier binder content (greater 
than the conventional 5%) is required with the present invention to 
accommodate particular road design criteria, the present solid 
sulfur-extended asphalt mix may still be satisfactorily used such that 
asphalt can be replaced with sulfur on substantially a 1:1 weight basis. 
Further, the asphalt is typically less than 3.1% by weight of the total 
bituminous concrete mix. Thus, by selectively varying the binder content 
as required and by assuring that the compaction of the bituminous concrete 
into pavement is accomplished within the conventional temperature range, 
i.e., 240.degree. F. to 265.degree. F., a satisfactory pavement product 
can be economically produced according to the present invention. 
It is thus apparent that use of the present invention can result in savings 
of the amount of purchased liquid asphalt of up to 45 percent, yet without 
any increase in heat energy consumption beyond that required for a 
conventional bituminous concrete mix. In fact, due to the fact that the 
aggregate in the present invention is dried at a lower temperature, the 
total energy utilized for finished product on a per-ton basis is somewhat 
less than that for a conventional mix. Also, the present invention 
overcomes the high cost of energy inherent in prior art liquid 
sulfur-extended asphalt mix designs by avoiding the extra energy needed to 
melt, transfer, blend, or store the liquid sulfur. 
Turning now to a description of the apparatus necessary to perform the 
process of the present invention, there is shown in FIG. 1 a 
schematic-type plan view of the well-known asphalt batch plant, generally 
denoted by reference numeral 20. The asphalt plant 20 includes aggregate 
stockpiles 22, an aggregate feed mechanism 24, an aggregate dryer 26 
having a combustion chamber (not shown), a heated asphalt storage tank 28 
having supplemental burners (not shown), a tower support structure 30, a 
pugmill apparatus 32 mounted on the tower 30 and used to mix the various 
constituent materials, a silo 34 for storing mineral filler, a hot 
elevator mechanism 36 for transferring the dried aggregate from the dryer 
to a series of screens 37 which size it, an aggregate weigh hopper 39 for 
weighing the sized and heated aggregate, and a heated asphalt weigh bucket 
38 supported off the tower 30 by scales (not shown) adjacent the pugmill 
32. The batch plant 20 also includes a solid sulfur bulk storage bin 40 
and a screw auger or vane feeder type mechanism 42. The auger 42 is 
utilized to transfer the solid sulfur from a sulfur crusher device 50 to 
the asphalt weigh bucket 38. The asphalt plant's usual pollution control 
mechanism, such as a bag collector, for example, has been omitted in FIGS. 
1 and 2 for purposes of better viewing. 
As best seen in FIG. 2, the tower 30 also includes elevated aggregate 
storage containers 44 which transfer sized, heated aggregate into the 
aggregate weigh hopper 39. The asphalt storage tank 28 has a pump 46 for 
transferring liquid asphalt 29 from tank 28 through a delivery line 48 
into the asphalt weigh bucket 38. Since the asphalt weigh bucket 38 is 
connected to a scale (not shown) in a wellknown manner, it is capable of 
weighing any ingredients placed therein. In this manner, the 
scale-connected asphalt weigh bucket 38 can be used to proportion and mix 
the solid sulfur 41 and the liquid asphalt 29. It will be understood that 
both the aggregate weigh hopper 39 and asphalt weigh bucket 38 feed into 
the pugmill 32. 
As seen in FIG. 4, the asphalt weigh bucket 38 is hot-oil jacketed in a 
well-known manner. That is, it is surrounded by heated oil chambers 52 
which maintain the desired temperature within the asphalt weigh bucket 38, 
preferably at 300.degree. F. with the present invention. The sulfur feeder 
42 and asphalt delivery line 48 are respectively connected to the top 
cover panel 49 of the weigh bucket 38. The latter is outfitted with a 
special mixing apparatus, generally denoted by reference numeral 54. This 
mixing apparatus 54 includes a shaft 56 which is journalled within 
bearings 58 on each end wall of bucket 38. The shaft 56 is rotatably 
driven by a motor 60 mounted exteriorly of the weigh bucket 38. A series 
of paddle members 62 are mounted along the shaft 56. A plurality of paddle 
holes 64 are formed on the paddles 62 to effect the proper mixing action 
within the weigh bucket 38 when the paddle shaft 56 is rotated by motor 
60. 
FIG. 3 depicts in block diagram form the special equipment needed then to 
modify an existing asphalt batch plant, such as that of FIGS. 1 and 2, so 
as to accommodate the solid sulfur-extended asphalt process of the present 
invention. As shown there, the liquid asphalt 29 is pumped from the 
asphalt storage tank 28 by a pump 46 into the plant's heated asphalt weigh 
bucket 38. There, due to the hot-oil jacket heating of the weigh bucket 
38, the liquid asphalt 29 is brought up to a temperature of approximately 
300.degree. F. Further, solid sulfur 41 from the sulfur storage bin 40 is 
first pulverized by the crusher 50 and then transported by the auger 
feeder 42 into the plant's asphalt weigh bucket 38. Operation of the 
mixing apparatus 54 within the weigh bucket 38 causes the crushed solid 
sulfur to be quickly melted and uniformly dispersed throughout the liquid 
asphalt. A uniform blend of sulfur-extended asphalt is then obtained. This 
blend of sulfur-extended asphalt is then placed into the pugmill 32. In a 
well known fashion, the aggregate weigh hopper 39 is similarly filled with 
appropriate amounts of the various aggregate materials. These materials 
are each proportioned, weighed, and then placed into the pugmill 32. After 
mixing all ingredients in the pugmill, the finished solid sulfur-extended 
asphalt mix is delivered to the laydown site and compacted into pavement. 
It will be understood that, in relation to FIG. 4, the preferred embodiment 
of mixing apparatus 54 (stirrer mechanism comprising shaft 56, motor 60, 
and paddles 62) can be replaced by any other well-known type of mixing 
apparatus. The only requirement is that some form of mixing action occur 
within the heated asphalt weigh bucket 38 so as to promote melting and 
pre-blending of the solid sulfur within the asphalt prior to mixing with 
heated aggregate in the pugmill 32. Further, it will be understood that 
conventional heated weigh buckets of existing asphalt batch plants can be 
readily retrofitted with the mixing apparatus 54 and auger feeder 
mechanism 42. 
From the foregoing, it is believed that those skilled in the art will 
readily appreciate the unique features and advantages of the present 
invention over previous bituminous concrete compositions made with 
sulfur-extended asphalt and the methods and apparatus for making the same. 
Further, it is to be understood that while the present invention has been 
described in relation to a particular preferred embodiment as set forth in 
the accompanying drawings and as above described, the same nevertheless is 
susceptible to change, variation and substitution of equivalents without 
departure from the spirit and scope of this invention. It is therefore 
intended that the present invention be unrestricted by the foregoing 
description and drawings, except as may appear in the following appended 
claims.