U.S. patent application number 09/788982 was filed with the patent office on 2001-07-19 for microwave apparatus and method for analysis of asphalt-aggregate compositions.
Invention is credited to Barclay, David Allan, Regimand, Ali.
Application Number | 20010008773 09/788982 |
Document ID | / |
Family ID | 26722711 |
Filed Date | 2001-07-19 |
United States Patent
Application |
20010008773 |
Kind Code |
A1 |
Barclay, David Allan ; et
al. |
July 19, 2001 |
Microwave apparatus and method for analysis of asphalt-aggregate
compositions
Abstract
A method and apparatus are disclosed for analyzing the aggregate
content of asphalt-aggregate compositions. The method includes
placing a preheated, preweighed container carrying a sample of an
asphalt-aggregate composition into a preheated furnace with the
preheated furnace being warmer than the preheated sample,
continuing to heat the furnace while drawing air through the
furnace at a rate that avoids impeding the heating of the furnace
or the sample until the sample in the container reaches its
combustion temperature and the combustion of the sample becomes
exothermic, initiating a second draw of air around rather than
through the furnace to moderate the exterior temperature of the
furnace, accelerating the draw through the furnace to increase the
rate of combustion of the exothermic reaction, and reweighing the
container and sample after combustion is complete. The apparatus
includes a furnace, a housing around the furnace, a furnace exhaust
in communication with the furnace, a housing exhaust in
communication with the housing, means for drawing an airflow though
the furnace and into the furnace exhaust, means for drawing a
separate airflow though the housing and into the housing exhaust,
and a junction between the exhausts that forms a common exhaust
from the housing and the furnace.
Inventors: |
Barclay, David Allan;
(Charlotte, NC) ; Regimand, Ali; (Raleigh,
NC) |
Correspondence
Address: |
PHILIP SUMMA PATENT ATTORNEY
SUITE 315
13777 BALLANTYNE CORPORATE PLACE
CHARLOTTE
NC
28277
|
Family ID: |
26722711 |
Appl. No.: |
09/788982 |
Filed: |
February 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09788982 |
Feb 20, 2001 |
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09187854 |
Nov 6, 1998 |
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6207462 |
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09187854 |
Nov 6, 1998 |
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09045392 |
Mar 20, 1998 |
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6190917 |
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Current U.S.
Class: |
436/155 ; 422/51;
422/78; 436/139; 436/143; 436/147; 436/160 |
Current CPC
Class: |
Y10T 436/214 20150115;
Y10T 436/25875 20150115; Y10T 436/212 20150115; G01N 33/42
20130101; Y10T 436/21 20150115; G01N 5/04 20130101; Y10T 436/216
20150115; Y10T 436/218 20150115; G01N 1/44 20130101; G01N 31/12
20130101; Y10T 436/12 20150115; Y10T 436/23 20150115 |
Class at
Publication: |
436/155 ;
436/147; 422/51; 422/78; 436/160; 436/139; 436/143 |
International
Class: |
G01N 025/00 |
Claims
That which is claimed is:
1. A method of analyzing the aggregate content of asphalt-aggregate
compositions, the method comprising: heating a furnace with a
preweighed container carrying a sample of an asphalt-aggregate
composition therein while drawing air through the furnace at a rate
that avoids impeding the heating of the furnace or the sample until
the sample in the container reaches combustion and the combustion
of the sample becomes exothermic; accelerating the draw through the
furnace to increase the rate of combustion of the exothermic
reaction until the exothermic reaction is complete; and reweighing
the container and sample after combustion is complete.
2. An analysis method according to claim 1 and further comprising
initiating a second draw of air around rather than through the
furnace to moderate the exterior temperature of the furnace.
3. An analysis method according to claim 1 comprising weighing the
container and sample and thereafter placing the container and
sample in the furnace.
4. An analysis method according to claim 3 comprising preheating
the container and sample prior to placing the container and sample
in the furnace.
5. An analysis method according to claim 4 comprising preheating
the furnace prior to placing the container and sample in the
furnace.
6. An analysis method according to claim 5 comprising preheating
the furnace to a temperature higher than the preheated temperature
of the container and sample.
7. An analysis method according to claim 1 wherein the step of
heating the furnace comprises directing microwave radiation at
microwave-absorbent materials in the furnace that convert the
microwave energy into heat.
8. An analysis method according to claim 1 comprising weighing the
container and sample while the container and sample are in the
furnace and while the furnace is being heated.
9. An analysis method according to claim 1 comprising continuously
weighing the container and sample.
10. An analysis method according to claim 1 and further comprising
sizing the aggregate after combustion of the asphalt.
11. A method of analyzing the aggregate content of
asphalt-aggregate compositions, the method comprising: placing a
preheated, preweighed container carrying a sample of an
asphalt-aggregate composition into a preheated furnace with the
preheated furnace being warmer than the preheated sample;
continuing to heat the furnace while drawing air through the
furnace at a rate that avoids impeding the heating of the furnace
or the sample until the sample in the container reaches its
combustion temperature and the combustion of the sample becomes
exothermic; initiating a second draw of air around rather than
through the furnace to moderate the exterior temperature of the
furnace; accelerating the draw through the furnace to increase the
rate of combustion of the exothermic reaction; and reweighing the
container and sample after combustion is complete.
12. An analysis method according to claim 11 comprising weighing
the container and sample prior to placing the container and sample
in the furnace.
13. An analysis method according to claim 11 comprising preheating
the container and sample to a temperature of about 150.degree. C.
prior to placing the container and sample in the furnace.
14. An analysis method according to claim 13 comprising preheating
the furnace to a temperature above about 540.degree. C. prior to
placing the container and sample in the furnace.
15. An analysis method according to claim 11 wherein the step of
heating the furnace comprises directing microwave radiation at
microwave-absorbent materials in the furnace that convert the
microwave energy into heat.
16. An analysis method according to claim 11 comprising weighing
the container and sample while the container and sample are in the
furnace and while the furnace is being heated.
17. An analysis method according to claim 16 comprising
continuously weighing the container and sample.
18. An analysis method according to claim 11 and further comprising
sizing the aggregate after combustion of the asphalt.
19. A method of analyzing the aggregate content of
asphalt-aggregate compositions, the method comprising: placing a
preheated, preweighed container carrying a sample of an
asphalt-aggregate composition into a preheated furnace; monitoring
the temperature of the furnace; continuing to heat the furnace
while drawing air through the furnace at a rate that avoids
impeding the heating of the furnace or the sample until the sample
in the container reaches a first predetermined setpoint
temperature; accelerating the draw through the furnace to increase
the rate of combustion of the sample; and reweighing the container
and sample after combustion is complete.
20. An analysis method according to claim 19 comprising initiating
a second draw of air around rather than through the furnace to
moderate the exterior temperature of the furnace when the
temperature reaches a second predetermined setpoint.
21. An analysis method according to claim 20 wherein the second
predetermined setpoint temperature s lower than the first
predetermined setpoint temperature so that the second draw of air
around the furnace is initiated prior to the acceleration of the
draw through the furnace.
22. An analysis method according to claim 19 comprising weighing
the container and sample while the container and sample are in the
furnace and while the furnace is being heated.
23. An analysis method according to claim 22 comprising
continuously weighing the container and sample.
24. An analysis method according to claim 19 comprising preheating
the furnace to a temperature warmer than the preheated sample.
25. An analysis method according to claim 19 wherein the step of
heating the furnace comprises directing microwave radiation at a
susceptor in the furnace that absorbs the microwave radiation and
converts it into heat.
26. An analysis method according to claim 19 and further comprising
sizing the aggregate after combustion of the asphalt.
27. An apparatus for analyzing the aggregate content of
asphalt-aggregate compositions and comprising: a cavity for holding
an asphalt-aggregate sample; means for introducing microwave
radiation into said cavity; materials in said cavity for absorbing
microwave radiation and converting the microwave radiation into
heat; an afterburner in gas flow communication with said cavity; a
first fan for drawing air through said cavity and through said
afterburner; and a second fan for drawing air around said cavity to
moderate the external temperature of said cavity and its immediate
environment.
28. An analysis apparatus according to claim 27 and further
comprising a scale in said cavity for continuously monitoring the
weight of a sample in said cavity.
29. An analysis apparatus according to claim 27 and further
comprising a temperature sensor in said cavity for monitoring the
temperature of the sample.
30. An analysis apparatus according to claim 29 wherein said first
and second fans are controllable variable speed fans.
31. An analysis apparatus according to claim 30 and further
comprising a controller that moderates the draw of said first fan
based upon the sample temperature measured by said temperature
sensor.
32. An analysis apparatus according to claim 30 and further
comprising a controller that moderates the draw of said second fan
based upon the sample temperature measured by said temperature
sensor.
33. An analysis apparatus according to claim 27 comprising a
housing surrounding said cavity.
34. An analysis apparatus according to claim 33 wherein said second
fan is positioned to draw an airflow between said cavity and said
housing.
35. An analysis apparatus according to claim 27 wherein said cavity
is formed of a material that is insulating with respect to
conductive heat transfer and substantially transparent to microwave
radiation.
36. An analysis apparatus according to claim 35 wherein said cavity
is formed of a glass ceramic fibrous material.
37. An analysis apparatus according to claim 27 wherein said
microwave introducing means comprises a source and a waveguide.
38. An analysis apparatus according to claim 27 comprising a
susceptor in said furnace for absorbing microwave radiation and
converting it into heat.
39. An asphalt analysis furnace system that enhances the airflow
and combustion of asphalt-aggregate compositions, said furnace
system comprising: a furnace; a housing around said furnace; a
furnace exhaust in communication with said furnace; a housing
exhaust in communication with said housing; means for drawing an
airflow though said furnace and into said furnace exhaust; means
for drawing a separate airflow though said housing and into said
housing exhaust; and a junction between said exhausts that forms a
common exhaust from said housing and said furnace.
40. An analysis system according to claim 39 wherein said furnace
drawing means and said housing drawing means comprises a single fan
downstream from said junction.
41. An analysis system according to claim 39 wherein said furnace
drawing means comprises a first fan in communication with said
furnace exhaust upstream from said junction and said housing
drawing means comprises a second fan in communication with said
housing exhaust upstream from said junction.
42. An analysis system according to claim 39 wherein said furnace
comprises a source of microwave radiation and a susceptor for
absorbing the microwave radiation and converting it into heat.
43. An analysis system according to claim 39 and further comprising
an afterburner between said furnace and said furnace exhaust.
44. An asphalt analysis furnace system that enhances the airflow
and combustion of asphalt-aggregate compositions, said furnace
system comprising: a furnace; a housing around said furnace; a
first fan that pulls air though said furnace; a second fan that
pulls air between said furnace and said housing, but not through
said furnace; a furnace exhaust pipe in communication with said
first fan; a housing exhaust pipe in communication with said second
fan; and a junction between said exhaust pipes that forms a common
exhaust for both of said fans.
45. A furnace system according to claim 44 wherein said furnace
comprises a source of microwave radiation and a susceptor that
absorbs microwave radiation and converts it into heat.
46. A furnace system according to claim 44 comprising an ambient
air stem in communication with said furnace exhaust pipe.
47. A furnace system according to claim 44 and further comprising
an afterburner between said furnace and said furnace exhaust
pipe.
48. A method of analyzing the aggregate content of
asphalt-aggregate compositions, the method comprising: heating a
sample of an asphalt-aggregate composition to combustion in a
furnace; drawing an airflow into, through, and out of the furnace
to promote the combustion of the asphalt in the composition;
drawing a separate airflow around and past but not through the
furnace to help moderate the exterior temperature of the furnace
without interfering with the combustion therein; and blending
airflow that has exited the furnace with the airflow that has
passed the exterior to thereby moderate the temperature of the
furnace-exited airflow.
49. An analysis method according to claim 48 and further comprising
blending an ambient airflow with the furnace-exited airflow.
50. An analysis method according to claim 49 comprising blending
the ambient and furnace-exited airflows, and thereafter blending
with the exterior-passed airflow.
51. An analysis method according to claim 48 wherein the step of
drawing the airflow out of the furnace comprises drawing the
airflow and gaseous combustion products into an afterburner prior
to blending with the exterior airflow.
52. An analysis method according to claim 48 wherein the step of
heating the sample comprises directing microwave radiation into the
furnace.
53. An analysis method according to claim 52 wherein the step of
directing the microwave radiation into the furnace comprises
directing the radiation to a susceptor that absorbs the microwave
radiation and converts it into heat.
54. An analysis method according to claim 48 and further comprising
sizing the aggregate after combustion of the asphalt.
Description
[0001] This application is a continuation-in-part of Ser. No.
09/045,392 filed Mar. 20, 1998. The present invention relates to
the analysis of compositions formed of asphalt and aggregates such
as crushed rock and sand.
FIELD OF THE INVENTION
[0002] In particular, the invention relates to a method and
apparatus for analyzing the percentage composition of asphalt in
such compositions.
BACKGROUND OF THE INVENTION
[0003] Compositions formed of mixtures of asphalt and aggregates
materials are one of the most widely used materials for paving
roads and highways. Although the term "asphalt" is commonly used to
refer to the road material, it more properly applies to the "tar"
portion of a mixed composition of tar and aggregate. Thus, the
asphalt is a dark brown or black cementitious material, which is
solid or semi-solid in consistency, in which the predominating
constituents are bitumens which occur in nature or are obtained as
byproducts from petroleum refining. Asphalt is a mixture of
paraffinic and aromatic hydrocarbons and heterocyclic compounds
containing sulfur, nitrogen and oxygen. Asphalt is also referred to
as "petroleum asphalt," "Trinidad pitch," or "mineral pitch."
Asphalt is a black solid or viscous liquid that has a flash point
of about 450.degree. F. (232.degree. C.), an auto-ignition
temperature of about 900.degree. F. (482.degree. C.), and softens
from its solid or semi-solid state to a viscous liquid at
approximately 93.degree. C. Other typical uses of asphalt include
roofing, joint filling, special paints, adhesive and electrical
laminates, and hot belt compositions, a dilutent in low-grade
rubber products and a number of other applications. These and other
properties and uses of asphalt are generally well known in the art
and can be found, for example, in Lewis, Hawley's Condensed
Chemical Dictionary, 12th Edition (1993).
[0004] In paving compositions, asphalt is typically present in an
amount of about 5% by weight. With respect to such compositions,
the percentage of asphalt and the nature and size of the aggregate
material (typically rocks and sand) used to make the composition
are important for the proper structure and characteristics of the
final road structure. For example, typical roads are formed of
three layers of asphalt and aggregate compositions. The bottom most
layer includes rocks of one inch or greater average size, sand, and
the asphalt. An intermediate layer generally includes a composition
formed of somewhat smaller rocks, typically 0.5-1 inch in diameter,
again with sand and asphalt. Finally, a top layer is usually
applied which has the smallest rocks, typically 0.5 inches or less
in diameter plus sand and tar.
[0005] Because the aggregate generally represents more than 90% of
a hot asphalt mix, aggregate gradation (i.e., the different
particle sizes that are present in the blend) profoundly influences
the properties of the hot mix (such as air voids, workability, and
the amount of asphalt binder required) and the resulting properties
of the pavement (such as stiffness, stability, and durability)
(e.g., Aljassar et al., Toward Automating Size-Gradation Analysis
of Mineral Aggregate, Transportation Research Record, Issue Number:
1437, pp. 35-42 (1994)). In this regard, research on
asphalt-aggregate compositions has become quite detailed, including
for example quantifying the influence on resistance to ruffing when
rounded, smooth, sand-sized aggregate particles are replaced by
rough, angular, porous particles while other aggregates and the
total gradation remain unchanged (e.g., Perdomo, D. and Button, J.
W., Identifying and Correcting Rut-Susceptible Asphalt Mixtures,
Final Report, Texas Transportation Institute, Texas A&M
University, Texas State Department of Highways & Public Transp,
Federal Highway Administration, Report Number:
Fhwa/Tx-91/1121-2F;Res Rept 1121-2F;TTI: 2-8-87/91-1121,Pag: 164
p), or evaluating the effect of the amount of soil binder (i.e.,
the smallest aggregate particles) on the engineering properties of
asphalt-treated paving materials (Ping, and Kennedy, The Effects of
Soil Binder and Moisture on Black Base Mixtures, Texas University,
Center for Highway Research, Austin, Texas State Department of
Highways & Public Transp Report Number: FHWA/TX-79/08+183-12
Intrm Rpt.;FCP 45C2-352 Pag: 127 p (1997)). Aggregate gradation is
frequently determined by the well-known and widely used sieve
analysis method.
[0006] Accordingly, as these exemplary references indicate,
depending upon the conditions under which a road is used (e.g.,
traffic patterns and weather conditions), the composition of any
one or more of the asphalt layers must be carefully designed and
monitored. Additionally, because the aggregate materials are
typically taken from local quarries, and the manufacture of the
composition is not an exact science, the asphalt and aggregate
compositions must be frequently tested, both as they are being made
and after they have been applied to a roadway, to make sure that
they meet the appropriate requirements.
[0007] Thus, there exists a need for determining: (1) the weight
percentage of asphalt; and (2) the aggregate size distribution in a
given sample of an asphalt-aggregate composition. In one
conventional method of analysis, the percentage of asphalt is
determined by a solvent extraction technique which uses chlorinated
hydrocarbons to separate the asphalt from the aggregate materials.
Because the solvents are generally considered to raise a hazard to
persons who are exposed to their vapors, the solvent testing is
becoming more and more disfavored, and indeed is expected to
eventually become prohibited under appropriate environmental
regulation.
[0008] In a second conventional method, a weighed sample of the
composition is placed into a furnace which is then heated until the
asphalt in the composition ignites. The asphalt is then allowed to
burn until it is entirely consumed after which the remaining
aggregate is weighed. The difference between the starting and
ending weight is a measure of the composition of asphalt in the
composition.
[0009] There are, however, at least two problems with this
conventional ignition technique. First, in conventional conduction
and convection heating, the burning asphalt can carry the
combustion to temperatures of up to 900.degree. C., i.e., a state
which is somewhat out of control. These extreme temperatures can
cause particular problems in the equipment or in handling the hot
material or even confining the resulting fire.
[0010] Second, and perhaps just as important, the extreme
temperatures tend to degrade the physical characteristics of the
aggregate in the mixture, including its size. Thus, because the
aggregate remaining after the asphalt has been burned off is
typically measured to determine whether it is of the proper size,
the size degradation resulting from the conventional ignition test
leads to a certain inaccuracy in measuring the sizes of aggregate
in any given sample.
[0011] As another problem, if the aggregate contains carbonate
compounds, the excessive heat can drive off carbon dioxide, thus
changing both the chemical and physical characteristics of the
aggregate. Finally, the conventional ignition techniques tend to
cause a loss of "fine" aggregates--literally blowing them away--so
that such fines are neither sized nor weighed, further acerbating
the accuracy problem.
[0012] Accordingly, the need exists for a method of determining the
amount of asphalt in an asphalt-aggregate combination which avoids
the use of environmentally disfavored solvents, which more
carefully controls the combustion and which avoids the breakdown in
the aggregate materials that tends to result in improper sizing
following such testing.
[0013] In co-pending parent application Ser. No. 09/045,392 an
improved technique for asphalt-aggregate analysis is disclosed that
takes advantage of the properties of microwave radiation to provide
improved methods and apparatus for the combustion-based analysis of
asphalt-aggregate mixtures. It has now been discovered that such
apparatus and methods can be enhanced--and the time required for
analysis greatly reduced--by additional control of the appropriate
airflows, and by incorporating improved structural elements.
OBJECT AND SUMMARY OF THE INVENTION
[0014] Therefore, it is an object of the present invention to
provide a method and apparatus for analyzing asphalt aggregate
compositions that has the potential to be generally faster, more
efficient, and more accurate than prior techniques.
[0015] The invention meets this object with a method of analyzing
the aggregate content of asphalt-aggregate compositions, in which
the method comprises heating a furnace with a preweighed container
carrying a sample of an asphalt aggregate composition therein while
drawing air through the furnace at a rate that avoids impeding the
heating of the furnace or the sample until the sample in the
container reaches its combustion temperature and the combustion of
the sample becomes exothermic. At that point the method comprises
accelerating the draw through the furnace to increase the rate of
combustion of the exothermic reaction until the exothermic reaction
is complete, and thereafter re-weighing the container and
sample.
[0016] In another aspect, the step of heating the furnace comprises
heating the furnace while drawing air through it at the rate that
avoids impeding the heating of the furnace or the sample until the
sample reaches a first predetermined steeping temperature, a which
point the draw through the furnace is accelerated to increase the
rate of combustion of the sample.
[0017] In another aspect, the method comprises heating a sample of
an asphalt-aggregate composition to combustion in a furnace,
drawing an airflow into, through and out of the furnace to promote
the combustion of the asphalt in the composition; drawing a
separate airflow past, but not through, the furnace to help
moderate the exterior temperature of the furnace without
interfering with the combustion therein, and blending airflow that
has exited the furnace with the airflow that has passed to the
exterior to thereby moderate the temperature of the furnace exited
airflow.
[0018] In its apparatus aspects, the invention comprises a cavity
for holding an asphalt-aggregate sample, means for introducing
microwave radiation into the cavity, materials in the cavity for
absorbing microwave radiation in converting the microwave radiation
into heat, an afterburner in gasflow communication with the cavity,
a first fan for drawing air through the cavity and through the
afterburner, and a second fan for drawing air around the cavity to
moderate the external temperature of the cavity and its immediate
environment. In another aspect, the furnace system comprises a
furnace, a housing around the furnace, a furnace exhaust in
communication with the furnace, a housing exhaust in communication
with the housing, means for drawing an airflow through the furnace
and into the furnace exhaust, means for drawing a separate airflow
through the housing and into the housing exhaust, and a junction
between the two exhausts that forms a common exhaust from the
housing and the furnace.
[0019] The foregoing and other objects and advantages of the
invention and the manner in which the same are accomplished will
become clearer based on the following detailed description taken in
conjunction with the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a cross-sectional schematic view of the
invention;
[0021] FIG. 2 is a front perspective view of a commercial
embodiment of the invention; and
[0022] FIG. 3 is a rear perspective view of the embodiment
illustrated in FIG. 2.
DETAILED DESCRIPTION
[0023] The present invention is a method and associated apparatus
for analyzing the aggregate content of asphalt-aggregate
compositions. FIG. 1 is a cross-sectional schematic diagram that
illustrates many of the method and apparatus aspects of the
invention. The overall apparatus is broadly designated at 10 and
includes a cavity 11 which is generally defined by the surrounding
ceramic fibrous material 18 that is insulating with respect to
conductive heat transfer and substantially transparent to microwave
radiation. Although the term "furnace" can be applied to the entire
apparatus 10, the term "furnace" is also used to describe the
ceramic fibrous material 18. The particular use will be evident
herein based on the context. The ceramic fibrous material 18 and
the furnace structure it produces are quite similar to those
referred to as "muffle" furnaces (e.g., U.S. Pat. No. 5,318,754
which is commonly assigned with the present invention) and will not
otherwise be described in detail herein.
[0024] The cavity 11 holds an asphalt aggregate sample 12 which in
preferred embodiments is maintained in a container 13. Means
illustrated as the magnetron 14 and the waveguide 15 introduce
microwave radiation into the cavity 11. Although microwave energy
can be used to heat the sample 12 directly, in preferred
embodiments, other materials illustrated as the susceptors 16,
typically formed of a material such as silicon carbide, are placed
in the furnace to absorb microwave radiation and convert it into
heat energy which in turn heats the sample 12.
[0025] The apparatus 10 further comprises an afterburner 17 which
in preferred embodiments comprises a tubular furnace, the nature
and operation of which are generally well understood and will not
be otherwise described in detail herein. The afterburner serves to
complete the combustion of certain of the byproducts of the initial
combustion of the sample 12 in the cavity 11. A first fan 20 draws
air through the cavity 11, into a microwave choke 19, and through
the afterburner 17. A second fan 21 draws air around, but not
through the cavity 11 to moderate the external temperature of the
cavity 11 and its immediate environment. The choke 19 is formed of
a material that blocks microwave radiation (usually a metal) and
has a length to diameter ratio that prevents microwaves from
escaping into or through the afterburner. The length and diameter
of the choke are selected based upon the wavelength of the
microwaves produced by the source, using relationships that are
well understood in this art.
[0026] Because the asphalt-content aspects of an the
asphalt-aggregate analysis is generally based on weight loss, in
preferred embodiments, the apparatus 10 further comprises a scale
22 in the cavity 11 for monitoring (preferably continuously) the
weight of a sample 12 in the cavity 11. In preferred embodiments,
and as illustrated in FIG. 1, the scale has a pan portion 23 in the
cavity 11, and a series of supports 24 that extend downwardly from
the pan through openings 25 in the furnace material 18. In this
arrangement, many of the mechanical and electrical components of
the scale can be positioned outside of the cavity 18 thus
protecting them from the relatively harsh conditions, both of
temperature and materials, that are generated in the cavity 11
during operation of the furnace. In the preferred embodiments, the
support openings 25 also provide the entry point for airflow from
the external surroundings into the cavity 11 and then to the
afterburner as just described.
[0027] In preferred embodiments, the apparatus further comprises a
temperature sensor 26 in the cavity 11 for monitoring the
temperature of the sample. In these preferred embodiments, the
first and second fans 20,21 are controllable variable speed fans.
In these embodiments, the apparatus further comprises a controller
27 that moderates the draw of the first fan 20, the second fan 21,
or both, based upon the sample temperature measured by the
temperature sensor 26. As will be described herein with respect to
the method aspects of the invention the ability to control the
airflow based upon the particular stage of heating, combustion, or
cooling, can speed the analysis considerably. The temperature
sensor can be selected as desired based on a number of engineering
criteria, but will typically comprise a thermometer, a thermocouple
or an optical temperature measuring device. It will be understood
that the particular device used to measure the temperature is in no
manner limiting of either the apparatus or method of the present
invention.
[0028] Controllers and their method of operation are generally
well-understood in this art and will not be described in detail
herein. Exemplary devices and techniques are set forth, for
example, in Dorf, The Electrical Engineering Handbook, Second
Edition, CRC Press (1997).
[0029] Because this particular embodiment of the invention uses
microwave heating, it further comprises the housing 30 shown in
FIG. 1 that is formed of a material, typically metal, that
surrounds the cavity 11 and the ceramic furnace material 18 to
shield the external surroundings from the microwaves that are
propagated into the cavity 11 by the magnetron 14 and the waveguide
15. Any materials that will suitably shield microwaves are
appropriate for the housing 30, but metal is typically used under
most circumstances. The housing 30 also defines a ventilation
opening 31 through which air can flow into the space between the
housing 30 and the furnace ceramic material 18. In this embodiment,
the second fan 21 is positioned to draw an airflow into the space
between the housing 30 and the cavity 21. Because this airflow
starts from an ambient source, and does not pass through the
combustion chamber, it generally serves to moderate the high
temperatures on the exterior of the cavity generated by the
combustion taking place inside. As in the case of the choke 19, the
opening 31 (which is not drawn to scale) is either of a size that
prevents microwaves from escaping therethrough, or includes an
appropriately sized choke of its own.
[0030] FIG. 1 further illustrates a furnace exhaust pipe 32 that is
in communication with the afterburner 17 and the first fan 20, and
a housing exhaust pipe 33 that is in communication with the housing
30 and the second fan 21. The exhaust pipes 32 and 33 merge at a
junction 34 to form a common exhaust designated by the arrows 35
for both of the fans. In preferred embodiments, the apparatus 10
includes an ambient air stem 36 in communication with the furnace
exhaust pipe 32 which helps draw additional ambient air that blends
with the furnace exhaust to help reduce its temperature.
[0031] FIG. 1 also illustrates that in the preferred embodiment,
the housing exhaust pipe 33 has portions that are large enough for
a smaller portion of the furnace exhaust pipe 32 to be positioned
therein in generally concentric fashion (when the pipes are
circular). In this manner, the generally cooler air that the second
fan 21 draws into the housing 30 and through the housing exhaust
pipe 33, cools the generally much hotter gaseous byproducts from
the furnace 18 and the afterburner 17 that travel through the
furnace exhaust pipe 32. Thus, the invention provides an apparatus
and method for drawing one airflow through the furnace 18 and into
the furnace exhaust 32 while concurrently drawing another, separate
airflow through the housing 30 and into the housing exhaust 33, and
then joining the exhausts to form a common exhaust from both the
housing 30 and the furnace 18.
[0032] It will be understood that a single fan, if positioned
appropriately downstream, can draw the separate airflows, but in
preferred embodiments the two separate fans 20 and 21 are
incorporated. In the preferred embodiments, the fans 20 and 21 are
each located upstream from the junction 34 (with downstream
referring to the exit portions of the exhaust) although other
arrangements in the positioning of the fans are appropriate
provided the airflows are drawn in the manner of the invention.
[0033] FIGS. 2 and 3 show some of these same elements in a more
realistic and less schematic illustration. In FIG. 2 the apparatus
10 includes the overall housing 30, the housing for the scale 22,
the afterburner 17, the furnace exhaust pipe 32, and the common
exhaust 35.
[0034] FIG. 2 also illustrates a control panel 37, the first fan
20, and a third fan 40 which is used to cool the electronic
portions of the device rather than the airflow from the furnace or
the housing.
[0035] As in many microwave devices, the housing 30 includes a door
40 for providing access to the furnace therein, as well as a window
41 that permits portions of the interior to be visible from the
exterior of the housing 30. FIG. 2 also illustrates a basic power
switch 42 and connections for exchanging data (e.g. parallel and
serial connectors) 43.
[0036] FIG. 3 illustrates many of the same elements as 1 and 2, but
from a rear perspective view. In addition to those elements already
recited with respect to FIG. 2, FIG. 3 shows the ambient air stem
36 and the housing exhaust pipe 33. The second fan 21 is generally
interior to the housing in these embodiments, and thus not visible
in FIG. 2 or 3. FIG. 3 also shows a power connector 44 for
providing current to the device from a typical commercial or
industrial line.
[0037] The apparatus aspects of the invention compliment the
method. In its basic aspects, the method of the invention comprises
heating a furnace with a preweighed container carrying a sample of
an asphalt-aggregate composition therein while drawing air through
the furnace at a rate that avoids impeding the heating of the
furnace or the sample until the sample in the container reaches its
combustion point and the combustion of the sample becomes
exothermic. At that point, the draw of airflow through the furnace
is accelerated to increase the rate of combustion of the exothermic
reaction until the exothermic reaction is complete. Thereafter, the
container and sample are re-weighed.
[0038] With respect to weighing the sample, it will be understood
both from the apparatus aspects of the invention and from the
techniques described in parent application Ser. No. 09/045,392 that
in preferred embodiments, the container and sample are continuously
weighed during the heating and combustion processes. As further set
forth in the parent application, after the aggregate has been
cooled, it is preferably sized to provide the useful information
about the aggregate that is the desired end product of the overall
analysis.
[0039] As described with respect to the apparatus aspects, the
method preferably further comprises initiating a second draw of air
around rather than through the furnace to moderate the exterior of
the furnace. In typical operation, the method comprises weighing
the sample and its container before placing it in the furnace and
also preheating the sample and container prior to placing them in
the furnace. In the preferred embodiments, the furnace is preheated
to a temperature higher than the preheated temperature of the
container and sample. In typical embodiments, the container and
sample are heated to a temperature of about 150.degree. C. prior to
placing them in the furnace, while the furnace is typically heated
to a temperature above about 540.degree. C. prior to placing the
container and sample therein.
[0040] As in the apparatus aspects of the invention, the step of
heating the furnace preferably comprises directing microwave
radiation at microwave absorbent materials in the furnace that
convert the microwave energy into heat.
[0041] In another aspect, the step of heating the furnace while
drawing air therethrough can comprise heating the sample until it
reaches a first predetermined setpoint temperature and then
accelerating the draw through the furnace to increase the rate of
combustion of the sample. In this embodiment, the method preferably
also comprises initiating the second draw of air around rather than
through the furnace when the temperature reaches a second
predetermined setpoint. In the most preferred embodiments, the
second predetermined setpoint temperature is lower than the first
predetermined setpoint temperature so that the second draw of air
around the furnace is typically initiated prior to the acceleration
of the draw through the furnace. As exemplary, but not limiting
temperatures, the external draw of air through the housing is
initiated when the temperature of the sample and container reach
about 480.degree. C., and the furnace draw is accelerated when the
temperature reaches about 500.degree. C. The temperature is
monitored throughout the process, and preferably continuously.
[0042] In another aspect, the method comprises heating a sample of
the asphalt-aggregate composition in the furnace, drawing an
airflow into, through, and out of the furnace to promote the
combustion of the asphalt in the composition, drawing a separate
airflow around and past, but not through, the furnace to help
moderate the exterior temperature of the furnace without
interfering with the combustion therein, and blending the airflow
that has exited the furnace with the airflow that has passed the
exterior to thereby moderate the temperate of the furnace exited
airflow.
[0043] In this embodiment, the method preferably further comprises
blending an ambient airflow with the furnace-exited airflow, and
thereafter blending again with the exterior airflow. As in the
prior embodiments, the step of drawing the airflow out of the
furnace preferably comprises drawing the airflow and gaseous
combustion products from the furnace into the afterburner prior to
blending it with the exterior airflow.
[0044] In operation to date, the apparatus and method of the
invention appear to reduce the time required to conduct the
combustion portion of an asphalt-aggregate analysis by at least
about 40%. As set forth in the parent application, one of the
advantages of faster analysis of asphalt-aggregate compositions is
the ability to get information about the composition as soon as
possible after the composition has been sampled. In that manner,
any changes required in the aggregate mix or the aggregate asphalt
composition can be made as quickly as possible.
[0045] As noted above, one of the most important characteristics of
an asphalt-aggregate composition is the particle size distribution
of the aggregate materials. Thus, the method of the invention
further comprises sizing the aggregate after combustion of the
asphalt. In particular, the nature of the combustion process
according to the invention provides a less distorted and frequently
undistorted aggregate for which the sizes and size distribution can
be more accurately determined.
[0046] In typical embodiments, the step of sizing the aggregate
comprises sieve analysis (e.g., U.S. standard sieve sizes), but it
will be understood that any appropriate sizing technique can be
used with the present invention and that the invention provides the
advantage of maintaining the aggregate in its original size
following combustion much more successfully than have prior
ignition techniques.
[0047] Because asphalt-aggregate compositions can vary so widely
depending on a variety of factors, objective determinations of
post-combustion aggregate quality can be difficult. Nevertheless,
the appearance of the post-combustion aggregate can provide a
qualitative measure of the success of the method in preserving the
aggregate as closely as possible to its pre-combustion condition.
In this regard, the post-combustion samples from asphalt-aggregate
compositions analyzed according to the present invention give every
indication of being in better--i.e. close or identical to
pre-combustion--condition that samples analyzed using more
conventional ignition techniques. It is thus expected that any
objective evaluation of such post-combustion samples will similarly
demonstrate the advantages of the present invention in properly
preserving the aggregate.
[0048] In summary, the invention provides a more controllable
method of carrying out an ignition and combustion analysis of
asphalt-aggregate compositions and does so in a manner that
minimizes or avoids the degradation of the aggregate that is
commonly observed in conventional ignition and combustion
testing.
[0049] In the drawings and specification, there have been disclosed
typical embodiments of the invention, and, although specific terms
have been employed, they have been used in a generic and
descriptive sense only and not for purposes of limitation, the
scope of the invention being set forth in the following claims.
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