U.S. patent application number 11/934613 was filed with the patent office on 2008-09-04 for antioxidant treatment of asphalt binders.
Invention is credited to Alex K. Apeagyei, William G. Buttlar, Barry J. Dempsey.
Application Number | 20080210126 11/934613 |
Document ID | / |
Family ID | 39365258 |
Filed Date | 2008-09-04 |
United States Patent
Application |
20080210126 |
Kind Code |
A1 |
Apeagyei; Alex K. ; et
al. |
September 4, 2008 |
Antioxidant treatment of asphalt binders
Abstract
A combination of antioxidants and method of incorporating the
antioxidants into an asphalt binder to make a modified asphalt
binder are described. The antioxidants comprise a thioester and an
aldehyde. The aldehyde and thioester, in a ratio between about
1:100 and about 100:1, are added to an asphalt binder. An acidic
catalyst is also added in a concentration between about 0.1 wt %
and about 18 wt % of the asphalt binder. The antioxidants, asphalt
binder, and catalyst are mixed at a temperature between about
85.degree. C. and about 135.degree. C. for a time between about 30
minutes and about 6 hours. The antioxidants are capable of
improving the performance grade of the asphalt binder. The modified
asphalt binder possesses superior resistance to oxidative age
hardening compared to other modified asphalt binder compositions
that incorporate various antioxidants.
Inventors: |
Apeagyei; Alex K.; (Urbana,
IL) ; Buttlar; William G.; (Savoy, IL) ;
Dempsey; Barry J.; (White Heath, IL) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Family ID: |
39365258 |
Appl. No.: |
11/934613 |
Filed: |
November 2, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60856571 |
Nov 3, 2006 |
|
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Current U.S.
Class: |
106/273.1 ;
252/182.29 |
Current CPC
Class: |
C08G 16/0293 20130101;
C08G 16/0237 20130101; C08L 61/00 20130101 |
Class at
Publication: |
106/273.1 ;
252/182.29 |
International
Class: |
C09D 195/00 20060101
C09D195/00 |
Claims
1. An antioxidant composition comprising: an aldehyde; and a
thioester, wherein the thioester and the aldehyde are present in an
effective amount capable of lowering oxidative aging of an asphalt
or polymeric materials.
2. The antioxidant composition of claim 1, wherein the thioester is
selected from the group consisting of dilauryl thiodipropionate,
distearylthiodipropionate, and dimethyl 3,3'-thiodipropionate, and
other esters of thiodipropionic acid.
3. The antioxidant composition of claim 2, wherein the aldehyde is
selected from the group consisting of formaldehyde, acetaldehyde,
propionaldehydes, butyraldehyde, acrolein, crotonaldehyde,
tiglaldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde,
furfural alcohol, paraformaldehyde, and furfural.
4. The antioxidant composition of claim 1, wherein the ratio of the
aldehyde to the thioester is between about 1:50 and about 50:1.
5. The antioxidant composition of claim 1, wherein the aldehyde is
furfural and the thioester is dilauryl thiodipropionate.
6. A modified asphalt binder composition made by the process
comprising mixing an asphalt binder, the antioxidant composition of
claim 4, and an acidic catalyst to create a modified asphalt binder
characterized by an aging index that is lower than that of an
untreated asphalt binder.
7. The modified asphalt binder composition of claim 6, wherein the
aldehyde reacts with phenols in the asphalt binder to form phenolic
resins, the phenolic resins comprising novolacs, resoles, or
combinations thereof.
8. The modified asphalt binder composition of claim 6, wherein the
thioester is bounded to the asphalt binder to allow stabilization
of the thioester.
9. The modified asphalt binder composition of claim 6, wherein the
thioester and the aldehyde are provided in enhanced effective
amounts for the reduction of the oxidative aging of the asphalt
binder.
10. The modified asphalt binder composition of claim 6, wherein the
modified asphalt binder possesses at least about 50% lower flexural
stiffness relative to an unmodified asphalt binder at a low
temperature, the low temperature ranging from about -4.degree. C.
to about -58.degree. C.
11. The antioxidant composition of claim 6, wherein the modified
asphalt binder possesses at least about 18% higher stiffness
relative to an unmodified asphalt binder at a high temperature, the
high temperature ranging from about 46.degree. C. to about
82.degree. C.
12. The modified asphalt binder composition of claim 6, further
comprising an antistripping agent that promotes adhesion of the
modified asphalt binder with a mineral aggregate.
13. The modified asphalt binder composition of claim 6, wherein the
aldehyde is furfural and the thioester is dilauryl
thiodipropionate.
14. An antioxidant modified asphalt binder prepared by the process
comprising: (a) heating an asphalt binder in an oxidation rich
environment to a first temperature sufficient to liquefy the
asphalt binder; (b) adding an antioxidant mixture to the asphalt
binder in the presence of an acidic catalyst to form the
antioxidant modified asphalt binder, wherein the antioxidant
mixture comprises an aldehyde and a thioester, and further wherein
the thioester is added in a ratio of the aldehyde to the thioester
that ranges between about 1:100 and about 100:1; and (c) mixing the
modified asphalt binder at a second temperature between about
85.degree. C. and about 135.degree. C. blend until a predetermined
stiffness of the binder has been attained.
15. The antioxidant modified asphalt binder of claim 14, further
prepared by the process of: (d) adding an antistripping agent to
the modified asphalt binder, wherein the antistripping agent
promotes adhesion of the modified asphalt binder with a mineral
aggregate.
16. The antioxidant modified asphalt binder of claim 14, wherein
the first temperature is between about 80.degree. C. and about
200.degree. C.
17. The antioxidant modified asphalt binder of claim 14, wherein
the antioxidant mixture comprises up to about 30 wt % based on the
total weight of the unmodified asphalt binder.
18. The antioxidant modified asphalt binder of claim 14, wherein
the aldehyde is selected from the group consisting of formaldehyde,
acetaldehyde, propionaldehydes, butyraldehyde, acrolein,
crotonaldehyde, tiglaldehyde, benzaldehyde, salicylaldehyde,
cinnamaldehyde, furfuryl alcohol, paraformaldehyde and
furfural.
19. The antioxidant modified asphalt binder of claim 18, wherein
the thioester is selected from the group consisting of dilauryl
thiodipropionate, distearylthiodipropionate, dimethyl
3,3'-thiodipropionate, and other esters of thiodipropionic
acid.
20. The antioxidant modified asphalt binder of claim 19, wherein
the antioxidant mixture comprises from about 0.1 wt % to about 30
wt % furfural and from about 0.1 wt % to about 22.5 wt % dilauryl
thiodipropionate based on the total weight of the unmodified
asphalt binder.
21. The antioxidant modified asphalt binder of claim 20, wherein
the acidic catalyst is selected from the group consisting of
sulfuric acid, toluene sulfonic acid, paratoluene sulfonic acid,
ascorbic acid, phosphoric acid, and hydrochloric acid.
22. The antioxidant modified asphalt binder of claim 20, wherein
the antioxidant modified asphalt binder is characterized by an
aging index that is lower than that of an untreated asphalt
binder.
23. The antioxidant modified asphalt binder of claim 20, wherein
the dilauryl thiodipropionate and the furfural are provided in an
enhanced effective amount for lowering of oxidative aging of the
modified asphalt binder.
24. The antioxidant modified asphalt binder of claim 20, wherein
the modified asphalt binder possesses a reduction in flexural
stiffness relative to that of an unmodified asphalt binder.
25. The antioxidant modified asphalt binder of claim 20, wherein
the modified asphalt binder possesses a higher complex shear
modulus relative to that of an unmodified asphalt binder.
26. The antioxidant modified asphalt binder of claim 14, wherein
the asphalt binder is selected from the group consisting of a joint
sealant, recycled asphalt pavement, emulsion, cut-back, and
naturally occurring asphalt.
27. The antioxidant modified asphalt binder of claim 14, wherein
the antioxidant mixture is capable of improving the performance
grade of the asphalt binder by extending the temperature range that
the binder can be used within.
28. The binder of claim 14, wherein the process further comprises:
(d) coating the modified asphalt binder of claim 14 onto a surface
of the mineral aggregate.
29. A method of making a modified asphalt binder, comprising the
steps of: (a) heating an asphalt binder to liquefy the binder; and
(b) mixing an aldehyde and a thioester with the asphalt binder at a
first temperature between about 100.degree. C. to about 135.degree.
C. in the presence of an acidic catalyst, wherein the ratio of the
aldehyde to the thioester is between about 1:100 and about 100:1,
and wherein the mixing occurs until a predetermined stiffness of
the modified asphalt binder has been attained.
30. The method of claim 29, wherein the aldehyde is selected from
the group consisting of formaldehyde, acetaldehyde,
propionaldehydes, butyraldehyde, acrolein, crotonaldehyde,
tiglaldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde,
paraformaldehyde, furfuryl alcohol, and furfural, and wherein the
thioester is selected from the group consisting of dilauryl
thiodipropionate, distearylthiodipropionate, and other esters of
thiodipropionic acid.
31. The method of claim 29, wherein the ratio of the aldehyde to
the thioester is in a ratio from about 1:50 to about 50:1.
32. The method of claim 29, further comprising the steps of: (c)
mixing the modified asphalt binder with an antistripping agent.
33. The method of claim 32, further comprising the steps of: (d)
mixing the modified asphalt binder with an unmodified bulk asphalt
binder to form an end product asphalt, the end product asphalt
comprising up to about 20 wt % of the modified asphalt binder based
on the weight of the end product.
34. The method of claim 33, further comprising the steps of: (e)
coating the end product asphalt onto a surface of a mineral
aggregate at a second temperature between about 125.degree. C. and
about 200.degree. C.; and (f) compacting the coated mineral
aggregate to produce a laydown of asphalt concrete at a third
temperature between about 120.degree. C. and about 150.degree.
C.
35. The method of claim 29, wherein the acidic catalyst is present
in an amount between about 0.1 and about 0.8 parts by weight, the
aldehyde is present in an amount between about 1 and about 2 parts
by weight, and the thioester is present in an amount of about 1
part by weight.
36. The method of claim 31, wherein the aldehyde is furfural and
the thioester is dilauryl thiodipropionate.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of priority from U.S.
Provisional Application No. 60/856,571, filed Nov. 3, 2006, which
is incorporated herein by reference.
BACKGROUND
[0002] The present invention relates to the modification of various
materials, and more particularly to incorporation of antioxidants
in asphalt binders to lower their oxidative aging.
[0003] Asphalt concrete is a composite material that is commonly
used for construction of pavement. More than 95% of all pavements
in service today incorporate asphalt concrete. Asphalt concrete
includes an asphalt binder and mineral aggregate. The binder and
aggregate are mixed together and then layered down and
compacted.
[0004] The asphalt binder deteriorates during hot-mix production
and service because of oxidative hardening. Oxidative hardening
occurs as a result of the asphalt binder readily undergoing
oxidation when it reacts with atmospheric oxygen at elevated
temperatures. Asphalt binder is a hydrocarbon which generally
consists of about 85% carbon, 10% hydrogen, 5% heteroatoms, and
trace elemental atoms. The heteroatoms, which include sulfur,
oxygen, and nitrogen, can form reactive functional groups that
accelerate the oxidation process. The trace metals, which include
vanadium, nickel, and iron, can act as catalysts for the oxidation
reaction.
[0005] Furthermore, oxidation is an irreversible chemical reaction
that can occur throughout the life of an asphalt pavement such as
during mixing, field placement, and during service. Excessive
oxidation of the asphalt may potentially cause the asphalt to
harden, become brittle, and ultimately crack over time. This
stiffening mechanism of the asphalt is also commonly termed "age
hardening."
[0006] Currently, no effective treatments exist to control the
excessive age hardening of the asphalt binder. Accordingly, there
remains a need to increase the durability of the asphalt binder by
reducing its oxidative age hardening.
SUMMARY
[0007] In one aspect, an antioxidant composition is provided that
includes an aldehyde and a thioester. The ratio of the aldehyde to
the thioester is between about 1:100 and about 100:1. The thioester
and the aldehyde are capable of lowering oxidative aging of various
materials.
[0008] In another aspect, a modified asphalt binder composition is
made by the process comprising mixing an antioxidant composition
comprising an acidic catalyst, an aldehyde and a thioester. The
ratio of the aldehyde to the thioester is between about 1:50 and
about 50:1. The mixing of the aldehyde and the thioester create a
modified asphalt binder characterized by an aging index that is
lower than that of an unmodified asphalt binder.
[0009] In another aspect, an antioxidant modified asphalt binder is
prepared by the following process. The asphalt binder is heated in
an oxidation rich environment to a temperature sufficient to
liquefy the asphalt binder. An antioxidant is added to the asphalt
binder in the presence of an acidic catalyst to form an
antioxidant-asphalt binder blend. The antioxidant comprises an
aldehyde. Water is formed in the first antioxidant-asphalt binder
blend from a condensation reaction of the aldehyde with the asphalt
binder. The water vaporizes off. Another antioxidant is added to
the antioxidant-asphalt binder blend to form the antioxidant
modified asphalt binder. The added antioxidant is a thioester that
is added to the antioxidant-asphalt binder blend in a ratio of the
aldehyde to the thioester that is between about 1:100 to about
100:1. The antioxidant modified asphalt binder is mixed until a
sufficient stiffness of the binder has been attained.
[0010] In another aspect, a method of making a modified asphalt
binder is described. A first antioxidant comprising an aldehyde is
mixed with an asphalt binder at a temperature between about
100.degree. C. to about 150.degree. C. in the presence of an acidic
catalyst to form a liquefied asphalt blend. Water is formed as a
by-product of the condensation reaction and thereafter vaporizes
off. A second antioxidant comprising a thioester is added to the
liquefied asphalt blend to form the antioxidant modified asphalt
binder. The contents are mixed until a sufficient stiffness of the
modified asphalt binder has been attained.
[0011] The foregoing paragraphs have been provided by way of
general introduction, and are not intended to limit the scope of
the following claims. The presently preferred embodiments, together
with further advantages, will be best understood by reference to
the following detailed description.
DETAILED DESCRIPTION
[0012] The relationship and functioning of the various elements of
this invention are better understood by the following detailed
description. However, the embodiments of this invention as
described below are by way of example only.
[0013] An asphalt binder may be modified by incorporating an
antioxidant mixture therein to produce a modified asphalt binder
that exhibits reduced age hardening. The modified asphalt binder
possesses increased resistance to oxidation, thereby increasing the
durability of the asphalt binder. For the purpose of this
application, the antioxidant mixture used in a modified binder in
accordance with the invention may be referred to as AOXADUR, which
stands for Antioxidant Asphalt Durability Treatment.
[0014] The antioxidant mixture includes a combination of an
aldehyde, a thioester, and an acidic catalyst. Aldehydes that may
be used include, but are not limited to, aliphatic aldehydes and
aromatic aldehydes, including heterocylic aldehydes. Examples of
suitable aldehydes include formaldehyde, acetaldehyde,
propionaldehydes, butyraldehyde, acrolein, crotonaldehyde,
tiglaldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde,
furfuryl alcohol, and furfural. Additionally, aldehydes in their
polymeric forms such as paraformaldehyde may be utilized. The
aldehydes may also comprise mixtures of aldehydes and aldehyde
polymers.
[0015] Preferably, the aldehyde is furfural. Furfural, which is
also known as furan-2-carboxaldehyde, is an aromatic aldehyde
having the chemical formula C.sub.5H.sub.4O.sub.2. Furfural readily
dissolves in most polar organic solvents, but is only slightly
soluble in water and alkanes. When heated above 250.degree. C.,
furfural decomposes into furan and carbon monoxide. Without being
bound by any theory, it is believed that furfural undergoes a
chemical condensation reaction with aromatic phenols that are
naturally contained in the asphalt binder in the presence of a
mineral acid to form two major types of resins known as novolacs
and resoles. The amount of novolacs or resoles formed during the
condensation reaction may depend on the concentration of phenol to
aldehyde ratio. Phenol to aldehyde ratios less than unity may
result in the formation of resoles, which is a thermosetting resin.
Phenol to aldehyde ratios greater than unity may result in the
formation of novolacs, which is a thermoplastic resin. Preferably,
for paving applications, the formation of resoles may be minimized
while the formation of novolacs may be maximized because the
novolacs may liquefy more readily than the resoles and the novolac
resins may act as antioxidants. Because there are typically more
aromatic phenols than the furfural additive levels, substantially
all of the furfural reacts in the condensation reaction to form
novolac resins. Polar aromatics, including the aromatic phenols,
are contained in the asphalt binder and have been identified as one
of the major aging fractions in the asphalt binders. Because
furfural can readily react with the polar aromatics, furfural can
assist with lowering the oxidation of the asphalt binder.
[0016] Furfural can be obtained commercially from many sources
including Fisher Scientific. Furfural can also be produced by
hydrolyzing the polysaccharide hemicellulose, which is a polymer of
sugars found in plant materials. When heated with sulfuric acid,
the hemicellulose hydrolyzes into xylose. Further hydrolysis of the
xylose yields furfural:
C.sub.5H.sub.10O.sub.5.fwdarw.C.sub.5H.sub.4O.sub.2+3H.sub.2O
[0017] As mentioned, the condensation reaction that furfural
undergoes with the phenols in the asphalt binder requires the
presence of an acidic catalyst. The acidic catalyst may include any
strong acid, including sulfuric acid, toluene sulfonic acid,
paratoluene sulfonic acid, ascorbic acid, phosphoric acid, and
hydrochloric acid. Preferably, the acid catalyst is hydrochloric
acid.
[0018] The antioxidant mixture also includes a thioester.
Thioesters are organo-sulfur compounds formed by the bonding of
sulfur and an alkyl group (R) that is attached to a carbon-oxygen
double bond. A thioester has the general formula R--S--CO--R' and
forms from the reaction of a thiol (R--SH) and a carboxylic acid
(R'--COOH). Thioesters can act as both a primary antioxidant and a
secondary antioxidant. Thioesters act as a primary antioxidant by
donating hydrogen atoms to the asphalt peroxy free radical, ROO.,
to form a stable compound that breaks the oxidation chain of
reactions. The asphalt peroxy free radical is formed when the
asphalt molecule (RH) is converted via heat to a free radical (R.),
which subsequently reacts with oxygen to form the peroxy free
radical ROO..
[0019] Thioesters can also act as a secondary antioxidant. In the
absence of enough primary antioxidant molecules, the peroxy free
radicals ROO will react with other asphalt molecules (RH) to form
new asphalt free radicals (R.) and hydroperoxide (ROOH).
Hydroperoxide is unstable and will react with new asphalt molecules
to propagate the oxidative degradation process in the absence of
secondary antioxidants. However, the thioester can react with
hydroperoxide to be reduced to an alcohol (ROH), thereby ending the
chain of oxidative degradation reactions.
[0020] Any type of thioester is contemplated. Examples of other
types of thioesters include dilauryl thiodipropionate,
distearylthiodipropionate, dimethyl 3,3'-thiodipropionate, and
other esters of thiodipropionic acid. Preferably, the thioester is
dilaurylthiodipropionate (DLTDP). DLTDP can be obtained
commercially from the Struktol Company of America as CARSTAB DLTDP.
DLTDP can also be obtained commercially from many other chemical
producers. DLTDP may be bound to the asphalt binder during mixing
of the asphalt binder under high shear rates. Binding the DLTDP to
the asphalt binder results in a stabilized antioxidant which will
not leach out over time. Volatization/leaching out of lead-based
and other types of antioxidants has been a problem that lowers the
effectiveness of the modified asphalt binder to resist oxidation.
It has been observed that asphalt binders incorporating lead-based
antioxidants have a tendency to lose their resistance to oxidative
age hardening after about five years because the lead-based
antioxidants have been found to leach out over time, thereby
rendering them ineffective as an antioxidant for the asphalt
binder. It is believed that the ability of the thioester to be
stabilized onto the asphalt binder by binding it thereto ensures
that the modified asphalt binder continues to maintain its
resistance to oxidative age hardening over time. Another problem
with prior antioxidant use in paving asphalt is the tendency for
the antioxidants to excessively soften the modified asphalt,
thereby rendering them prone to rutting and/or limiting their use
to only colder temperatures. The invention disclosed here may not
only prevent softening of the asphalt, but may actually expand both
the high and low temperature ranges at which the modified asphalt
can be used, as will be discussed in greater detail with respect to
Table 5 and Examples 32-34.
[0021] Any type of asphalt binder may be used. Examples of paving
grade asphalt binders include the Penetration Grade such as 40-50,
60-70, 85-100, 120-150, and 200-300; the Viscosity Grade such as
AC-2.5, AC-5, AC-10, AC-20, AC30, AC-40, AR-1000, AR-4000, AR-8000,
and AR-16000; and all of the Performance Grade ranging from PG
46-46 to 82-34. Asphalt of all SUPERPAVE codes and crude sources
could be used. Examples include AAO from Mid-East; AAA-1 from
Lloydminster; AAB-1 from Wyoming; AAC-1 from Redwater; AAD-1 from
California Coastal; AAF-1 from West Texas Sour; AAG-1 from
California Valley; AAK-1 from Boscan, Venezuela; AAT from Maya
Blend; AAV from Alaska North Slope; AAW from West Texas-Maya Blend;
etc. Additional examples include asphalts used for Tack Coat, prime
coat, seal coat, recycled asphalt, surface treatment, joint
sealants, landfill liners, recreational facilities, warm mix and
cold mix including cut-back and emulsions, natural asphalt, rock
asphalt, and Trinidad Lake asphalt. Roofing Grade Asphalts may also
be used. PG 64-22 binders from Illinois and Wisconsin refineries as
well as an AAD-1 asphalt sample from the SHRP Materials Reference
Laboratory were used in the examples discussed below to illustrate
the invention. The asphalt samples were selected to demonstrate the
effectiveness of the invention in asphalts of different grades and
crude source. The PG 64-22 binder from Illinois was obtained from
Emulsicoat, Inc. of Urbana, Ill.
[0022] Preferably, the antioxidant modified asphalt binder may be
prepared as follows. The asphalt binder is heated at atmospheric
pressure in an oxidation rich environment to a temperature
sufficient to liquefy the asphalt binder. This temperature ranges
from about 80.degree. C. to about 150.degree. C. Each of the
antioxidant additives are then added to the asphalt binder.
Hydrochloric acid and furfural are added to the liquefied asphalt
binder. They generally comprise about 0.1 wt % to about 18 wt % HCl
and about 0.1 wt % to about 30 wt % furfural based on the weight of
the asphalt binder. Preferably, the HCL and furfural each comprise
about 0.1 wt % to about 10 wt %. More preferably, the HCl and
furfural each comprise about 0.1 wt % to about 3 wt %. The contents
are contained in a reactor vessel with a mixer. The contents are
continuously mixed within the reactor vessel. The furfural in the
presence of the hydrochloric acid catalyst reacts with the polar
aromatics of the asphalt binder in a condensation reaction. The
reaction is carried out at a temperature that is sufficiently high
to effectuate condensation between the furfural and the asphalt
binder in the presence of the hydrochloric acid but yet not
sufficiently high to significantly oxidize and age the asphalt.
This temperature generally ranges from about 100.degree. C. to
about 135.degree. C. Water is formed as a by-product and vaporizes
off. The time of the reaction will vary inversely with the
temperature and may be carried out over a period varying from about
5 minutes to as high as about 6 hours.
[0023] The DLTDP is added to the furfural-catalyst-asphalt binder
mixture. DLTDP generally comprises about 0.1 wt % to about 22.5 wt
% based on the weight of the asphalt binder. Preferably, DLTDP
comprises about 0.1 wt % to about 10 wt %. More preferably, DLTDP
comprises about 0.1 wt % to about 3 wt %. The ratio of the furfural
to the DLTDP may range between about 1:100 to about 100:1 and
preferably about 1:50 to about 50:1, and more preferably about 1:5
to 5:1. The contents are continuously mixed within the reactor
vessel for a time sufficient for the modified asphalt binder to
attain a desired stiffness. The temperature of the mixture may
range from about 85.degree. C. to about 135.degree. C. Because the
time of the reaction varies inversely with the temperature of the
mixture, about 30 minutes is sufficient to prepare the modified
binder when the mixture is at about 135.degree. C. and about 6
hours is sufficient to prepare the modified binder when the mixture
is at about 85.degree. C. However, mixing is stopped before the
modified asphalt binder becomes too stiff to coat or spray onto a
mineral aggregate. The still free-flowing modified asphalt binder
is removed from the mixer and is ready to be coated or sprayed onto
a mineral aggregate.
[0024] Preferably, continuous mixing of the furfural, hydrochloric
acid and asphalt binder occurs for a time sufficient to generate
high shear mixing that enables subsequent addition of the DLTDP to
bind to the asphalt binder. Previous studies indicate that under
extensive mixing conditions, DLTDP is capable of binding to its
substrate. Although a bounded DLTDP can decrease its loss from the
modified asphalt binder, it is not necessary for the DLTDP to be
bounded. The DLTDP may still function as an antioxidant without
being bounded to the modified asphalt binder. Incorporating an
unbounded DLTDP into the asphalt binder allows the DLTDP to be
added to the asphalt binder shortly after the furfural and
hydrochloric acid are added, or even at the same time that the
furfural and the hydrochloric acid are added, thereby reducing the
preparation time of the modified asphalt binder.
[0025] Additionally, an antistripping agent may be added to the
modified asphalt binder to increase the adhesion of the asphalt
binder with the mineral aggregate. Stripping may occur when there
is a loss of a bond between the asphalt binder and the mineral
aggregate in the presence of water. A variety of antistripping
agents may be used to increase the stripping resistance of the
asphalt-coated mineral aggregate. These include lime, amines,
phenol, furfural, a phenol-furfural mixture and/or its resinous
derivatives, and an aniline-furfural mixture and/or its resinous
derivatives. Conventional antistripping additives may also be used,
as are known to one of ordinary skill in the art.
[0026] After the modified asphalt binder is formed, it is sprayed
or coated onto a mineral aggregate. The temperature of the
binder-aggregate mixture during this spraying/coating process is
generally higher than the temperature during addition of the
antioxidants to the asphalt binder to form the modified asphalt
binder. The binder-aggregate mixture ranges from about 125.degree.
C. to about 200.degree. C. The particular temperature varies with
the type of asphalt grade. After the aggregate has been sprayed or
coated with the modified asphalt binder, compaction of the coated
aggregate occurs to produce a laydown of asphalt concrete. The
compaction of the coated aggregate occurs at a temperature ranging
from about 120.degree. C. to about 150.degree. C.
[0027] Although incorporation of the antioxidants has been
described as occurring in the molten asphalt stage as a batch
preparation, other alternatives are contemplated. For example, the
antioxidants can be added in a continuous process to the asphalt
binder before it is mixed with the mineral aggregate by metering
the antioxidants to the asphalt binder while the binder is flowing
through a line such as a feed line to a mixing plant or a
truck-loading line. Alternatively, rather than prepare batch
quantities in a reactor mixing vessel, the antioxidants may be
incorporated as batch additions into a fixed quantity of asphalt in
the asphalt supplier's tank, or in the tank of the truck delivering
the asphalt to the mixing plant. Heating and storage temperatures
of the AOXADUR modified asphalt binders may be the same as
conventional binders.
[0028] As an alternative to preparing the modified asphalt binder
as described above, a highly concentrated master batch of a
modified asphalt binder may be produced. The highly concentrated
master batch may contain up to 30 wt % of hydrochloric acid and 30
wt % of each of the antioxidants based on the weight of the master
batch. The modified asphalt binder could then be mixed with a
portion of the master batch to produce a binder that could then be
sprayed or coated onto the mineral aggregate. For example, a
relatively small portion of the concentrated master batch of
modified asphalt may be mixed with a relatively large portion of an
unmodified asphalt binder to form a resultant binder having a range
from about 10 wt % to about 20 wt % of the concentrated modified
asphalt. A highly concentrated master batch of the modified asphalt
is advantageous because it eliminates handling of the antioxidants
and the corrosive acid catalyst by the end user, thereby making use
of the modified asphalt binder safer. Additionally, the end user
does not have to deal with mixing the antioxidants in the
predetermined ratios, thereby simplifying the process for the
asphalt end user.
EXAMPLES 1-4
[0029] A general procedure for preparing a modified asphalt binder
is as follows. The preparation of the modified asphalt binder may
occur as a batch or a continuous process. An asphalt binder feeds
into a reactor vessel and is heated to a temperature sufficient to
liquefy the asphalt binder. This temperature varies with the
specific type of asphalt binder used, but typically ranges from
about 80.degree. C. to about 150.degree. C. After the asphalt
binder has liquefied, a combination of antioxidants is added to the
reactor vessel. An acidic catalyst and aldehyde antioxidant are
added to the liquefied asphalt binder. The asphalt binder, aldehyde
antioxidant, and acidic catalyst are mixed in the reactor vessel.
The aldehyde antioxidant in the presence of the acidic catalyst
reacts with the polar aromatics of the asphalt binder in a
condensation reaction. The reaction is carried out at a temperature
that is sufficiently high to effectuate condensation between the
aldehyde antioxidant and the asphalt binder in the presence of the
acidic catalyst. This temperature generally ranges from about
100.degree. C. to about 135.degree. C. Water is formed as a
by-product and vaporizes off. The time of the reaction will vary
inversely with the temperature and may be carried out over a period
varying from about 5 minutes to as high as about 6 hours.
[0030] A second antioxidant is then added to the aldehyde-acidic
catalyst-asphalt binder mixture. The second antioxidant is a
thioester. All of the contents are continuously mixed within the
reactor vessel for a time sufficient for the modified asphalt
binder to attain a desired stiffness. The temperature of the
mixture may range from about 85.degree. C. to about 135.degree. C.
Because the time of the reaction varies inversely with the
temperature of the mixture, about 30 minutes is sufficient to
prepare the modified binder when the mixture is at about
135.degree. C. and about 4 hours is sufficient to prepare the
modified binder when the mixture is at about 85.degree. C. However,
mixing is stopped before the modified asphalt binder becomes too
stiff to coat or spray onto a mineral aggregate. The still
free-flowing modified asphalt binder is removed from the mixer and
is ready to be coated or sprayed onto a mineral aggregate.
[0031] Table 1 indicates that various amounts of the
aldehyde-thioester antioxidant combination can be added to the
asphalt binder. The weight percentages are based on unmodified
asphalt binder. Additionally, Table 1 indicates that various types
of aldehydes and thioester can be used to form the modified asphalt
binder. Example numbers 1 and 2 show the amounts of furfural and
DLTDP that may be used in a batch, continuous, or semi-continuous
process. Example numbers 3 and 4 show the amounts of a concentrated
masterbatch comprising furfural and DLTDP. A relatively small
portion of the concentrated masterbatch of example 3 or 4 could be
mixed with a relatively large portion of an unmodified asphalt
binder to form a resultant binder having a predetermined
concentration range. Other types of aldehydes and thioesters could
be formulated using additives levels shown in Table 1.
TABLE-US-00001 TABLE 1 Antioxidant Compositions Acidic Exam- Alde-
Acidic Aldehyde Thioester Catalyst ple No. hyde Thioester Catalyst
Weight % Weight % % 1 Furfural DLTDP HCl 2.0 1.5 1.2 2 Furfural
DLTDP HCl 14.8 9.2 12.1 3 Furfural DLTDP HCl 20.0 12.0 15.0 4
Furfural DLTDP HCl 30.0 18.0 22.0
EXAMPLES 5-17
[0032] PG 64-22 base asphalt (commercially available from
Emulsicoat, Inc.) is modified by incorporating 1.2 wt % HCl
(commercially available from Fisher Scientific), 2.0 wt % furfural
(obtained commercially from Fisher Scientific and Sigma-Aldrich),
and 1.5 wt % DLTDP (commercially available from Struktol Company of
America as CARSTAB DLTDP). Weight percentages are based on the
weight of the base asphalt. The heating and mixing of the mixtures
are accomplished using a convection oven fitted with a Bamant
Mixer. Mixing of all the modified asphalt is done in quartz-size
paint cans using about 350 g of asphalt per batch. The ratio of the
polar aromatics (e.g., phenols) contained in the asphalt to the
furfural is greater than 1. HCl and furfural are added to the
asphalt, followed by DLTDP. The total mixing time is four hours.
Mixing temperature is kept constant at about 115.degree. C. The
DLTDP is added after the second hour in three divided portions. The
purpose of delaying additions of DLTDP is (i) to allow the furfural
to completely react with all of the aromatics and (ii) to create a
high shear mixing to allow the DLTDP to "bind" to the asphalt.
[0033] The effectiveness of the antioxidants in reducing
age-hardening is evaluated using the Aging Index (AI) parameter. AI
is based on binder stiffness at multiple temperatures. AI is
defined as the ratio of the value of a rheological parameter after
aging to the value of the rheological parameter before aging. The
specific theological parameter used depends on whether oxidative
aging is simulated under high pavement temperatures (the high
temperatures defined in SUPERPAVE) or low pavement temperatures
(the low temperatures defined in SUPERPRAVE). The AI shown in Table
2 is computed at high temperatures and is based on a rutting
parameter, which is calculated as G*/Sin .delta.. G* is the
stiffness of the tested binder and .delta. is the phase lag of the
tested binder as it responds to a load. The rutting parameter is a
typical way of characterizing the extent of deformation the binder
undergoes at high pavement temperatures in accordance with
SUPERPAVE protocol. Incorporation of the antioxidant combination of
2.0 wt % furfural, 1.5 wt % DLTDP, and 1.2 wt % HCl to the binder
produces a modified asphalt binder (AOXADUR) having the lowest
aging index value, as indicated in Table 2. The effects of several
other antioxidants including Irganox 1010, Carbon Black, Vitamin E
on Asphalt A are also compared. The lower the aging index, the
higher the resistance of the asphalt binder to oxidative aging,
thereby increasing the durability and life of the modified asphalt
binder. Example No. 5 indicates that additions of the antioxidant
mixture of 2% Furfural+1.5% DLTDP+1.2% HCl incurs the least amount
of age hardening, as denoted by the low aging index (AI=1.44).
Additions of the test antioxidant mixtures in example nos. 6-17
show higher levels of age hardening, as indicated by the higher AI
values.
TABLE-US-00002 TABLE 2 Screening of Various Antioxidant AI based
Example on rutting No. parameter Antioxidant Concentration 5 1.44
2% Furfural + 1.5% DLTDP + 1.2% HCl 6 1.46 2% Furfural + 1.2% HCl 7
1.63 2% Furfural + 1.5% Irganox 1010 + 1.2% HCl 8 1.72 2% Furfural
+ 2% Vitamin E + 1.2% HCl 9 1.73 1.5% DLTDP + 5% Carbon Black 10
1.73 2% Furfural + 2% Vitamin E + Catalyst 11 1.86 2% Furfural 12
1.94 1.5% DLTDP mix for 4 hours 13 1.96 1.5% DLTDP mix for 1 hour
14 2.01 2% Vitamin E 15 2.01 5% Irganox 1010 16 2.02 0.5% DLTDP 17
2.32 Control PG 64-22 (Asphalt A)
[0034] Table 2 indicates that the combination of the DLTDP with the
furfural creates a synergistic effect in the reduction of the
oxidative aging of the asphalt binder. Accordingly, the most
effective antioxidant treatment is determined to be 2%
Furfural+1.5% DLTDP+1.2% HCl based on the fact that it has the
lowest aging index.
EXAMPLES 18-29
[0035] Having identified the most effective antioxidant mixture in
Table 2, further effects of this antioxidant mixture may be
described for various asphalt binders. Tables 3a-3c shows the
results of the most effective additive levels of the antioxidant
mixture (2% Furfural+1.5% DLTDP+1.2% HCl) on four asphalt binders.
PG 64-22 base asphalt binders A and B are commercially available
from Emulsicoat, Inc. of Urbana. Asphalt C is also a PG 64-22
binder that is available from Seneca Petroleum Company and was
obtained from a Wisconsin source. Asphalt D is an AAD-1 binder
available from SHRP MRL. Furfural samples for modifying Asphalt A
are available from Fisher Scientific. Furfural samples for
modifying Asphalt B, C, and D are available from Sigma-Aldrich. All
of the asphalts used HCl available from Fisher Scientific, and
DLTDP available from Struktol Company of America as CARSTAB
DLTDP.
[0036] AI is evaluated under short-term aging conditions at
64.degree. C. (Table 3a), in accordance with SUPERPAVE protocol.
The short-term agings are simulated using a Rolling Thin Film Oven
(RTFO), as is known to one of ordinary skill in the art. A Dynamic
Shear Rheometer (DSR) is used to compute a SUPERPAVE rutting
parameter G*/Sin .delta. at high pavement temperatures (FIG. 3a)
and a SUPERPAVE fatigue parameter at intermediate temperatures
(FIG. 3b).
[0037] Table 3a indicates that the modified binders have relatively
lower aging indices (AI) compared to the control asphalt binders.
The AI is based on short-term aging at a high temperature. The AI
is computed as the ratio of the rutting parameter of the material
after short term aging to the rutting parameter unaged. Example
Nos. 18-21 indicate that the unmodified asphalt binders A, B, C,
and D incur higher stiffness after the short-term aging as compared
to the modified binders A, B, C, and D. For example, short-term
aging results in more than a two fold increase in stiffness due to
oxidative aging of the unmodified binder A (AI of 2.32) but only a
44% increase in modified binder A (AI of 1.44). Additionally,
unmodified binder D incurs about a two fold increase in stiffness
(AI of 2.02) but the modified binder D incurs virtually no increase
in stiffness (AI of 1.04). Additionally, unlike antioxidant
treatments of the prior art, the current antioxidant treatment does
not result in excessive softening of the modified asphalt. This is
especially a desirable property for paving grade asphalt where
adequate structural rigidity is required.
TABLE-US-00003 TABLE 3a Short-term aging at high temperature
Rutting parameter G*/Sin.delta. at Example 64.degree. C. (kPa)
Number Sample Tank RTFO Aging Index 18 A 1.2446 2.8892 2.32 A +
AOXADUR 1.9019 2.7480 1.44 19 B 1.3099 3.3823 2.58 B + AOXADUR
3.4964 4.6302 1.32 20 C 1.2338 3.3174 2.69 C + AOXADUR 3.1124
6.7150 2.16 21 D 1.3643 2.7620 2.02 D + AOXADUR 14.2070 14.7960
1.04
[0038] Table 3b indicates that AI is evaluated under long-term
aging conditions at an intermediate temperature of 25.degree. C. in
accordance with SUPERPAVE protocol. The long-term aging conditions
at 25.degree. C. are simulated using a Pressure Aging Vessel (PAV),
as is known to one of ordinary skill in the art. The AI is computed
as the ratio of the fatigue parameter of the material after
long-term aging to the fatigue parameter of the unaged material.
The fatigue parameter is a standard way as known to one of ordinary
skill in the art for characterizing long-term aging of test
material at intermediate temperature. Example Nos. 22-25 indicate
that the unmodified asphalt binders A, B, C, and D incur higher
stiffness after the long-term aging as compared to the modified
binders A, B, C, and D. For example, long-term aging results in
more than a five-fold increase in the stiffness of unmodified
binder A (AI of 5.24) but slightly over a three fold increase in
the stiffness of modified binder A (AI of 3.17). Additionally,
although the unmodified binder D incurs over a five-fold increase
in stiffness (AI of 5.55), the modified binder D incurs about a
three-fold increase in stiffness (AI of 2.88).
TABLE-US-00004 TABLE 3b Long-term aging at intermediate temperature
Fatigue parameter Example G*Sin.delta. at 25.degree. C. (kPa)
Number Sample Tank PAV Aging Index 22 A 917 4807 5.24 A + AOXADUR
853 2703 3.17 23 B 890 4629 5.20 B + AOXADUR 1121 3604 3.22 24 C
647 3322 5.13 C + AOXADUR 687 2306 3.36 25 D 404 2240 5.55 D +
AOXADUR 875 2520 2.88
[0039] Table 3c indicates that AI is evaluated under long-term
aging conditions at a low temperature of -12.degree. C. in
accordance with SUPERPAVE protocol. The long-term aging conditions
at low temperature are simulated by using a Pressure Aging Vessel
(PAV) to subject the test binder material to a load associated at
-12.degree. C. for 60 seconds, in accordance with SUPERPAVE. The
long-term aging at low temperature is designed to evaluate the
extent to which unmodified binder and modified binder material
thermally crack as the material shrinks due to the residual stress
within the material. A Bending Beam Rheometer (BBR) was used to
evaluate the performance of the modified binders at the low
pavement temperatures.
[0040] The extent to which the material thermally cracks at low
temperature can be described by the material's flexural stiffness,
S(t), and its m-value, which is defined as the rate at which the
thermally-induced stress is relieved in the material. A high
m-value corresponds to the ability of the material to flow faster
and thereby relieve the thermally-induced stress. A low m-value
corresponds to a slower rate at which the stress in the material is
relieved. Example Nos. 26-29 indicate that the unmodified asphalt
binders A, B, C, and D incur higher flexural stiffness after the
long-term aging as compared to the modified binders A, B, C, and D.
Additionally, modified binders A, B, and C exhibited relatively
higher m-values as compared to their respective unmodified binders.
This indicates that the modified binders have the ability to
relieve the thermally-induced stress faster than the unmodified
material.
TABLE-US-00005 TABLE 3c Long-term aging at low temperature Flexural
stiffness at Example -12 C., 60 seconds Number Sample S(t) m-value
26 A 146 0.42 A + AOXADUR 86 0.46 27 B 207 0.31 B + AOXADUR 131
0.32 28 C 111 0.31 C + AOXADUR 76 0.33 29 D 74 0.38 D + AOXADUR 64
0.35
EXAMPLES 30-31
[0041] Table 4 shows that the addition of DLTDP results in lowering
the stiffness of the base asphalt while the addition of furfural
with the HCl catalyst results in significant increase in binder
stiffness. The combination of the DLTDP and the furfural produces
the desirable property of exhibiting relatively lower stiffness
than unmodified asphalt binders at lower temperatures while
exhibiting relatively higher stiffness than unmodified asphalt
binders at higher temperatures, as shown in Table 4 for Asphalt A.
The low temperature at which stiffness is tested is -12.degree. C.
in accordance with the SUPERPAVE specification for PG 64-22 asphalt
binder. The high temperature at which stiffness is tested is
64.degree. C., which is also in accordance with the SUPERPAVE
specification, and is incorporated in its entirety herein by
reference. It can be seen from Table 4 that at low temperatures
binder A is 70% stiffer than the antioxidant modified binder, which
indicates a higher potential for thermal cracking of the unmodified
asphalt binder A. At high temperatures where higher stiffness is
desirable, the unmodified binder is 18% softer than the modified
binder.
TABLE-US-00006 TABLE 4 Comparison of Binder Stiffness For Asphalt
Binder A Example Stiffness at Stiffness at 64.degree. C. Nos.
-12.degree. C. (MPa) (MPa) Description 30 85.7 0.0152 Antioxidant-
modified 31 145.6 0.0125 Unmodified Asphalt Binder (A)
[0042] This is a desirable property for asphalt binders to possess.
At lower temperatures, pavements shrink, thereby causing the
asphalt in the pavement to be put in tension. If the asphalt binder
is unable to elongate through ductile flow and the tensile strength
of the asphalt is exceeded, it breaks in brittle fracture. Because
the asphalt binder becomes relatively less stiff at the lower
temperatures, it can release the tensile stresses by ductile flow,
thereby preventing cracking from occurring. At higher temperatures,
the pavement expands and becomes pseudo-viscoelastic. Because the
modified asphalt binder becomes relatively stiffer at higher
temperatures, it may reduce rutting susceptibility (i.e., the
extent to which the binder undergoes deformation). Accordingly, it
is desirable for the asphalt binder to be relatively stiffer
because the asphalt binder has a tendency to rut or deform at the
higher temperatures.
EXAMPLES 32-34
[0043] In addition to reducing oxidative aging and reducing rutting
susceptibility, the antioxidant mixtures disclosed herein may
extend the temperature range that the binder may be used within. A
performance grade designation is used to quantify the temperature
range. For example, a performance grade of PG 64-22 indicates that
the binder can withstand the load specifications set forth in
SUPERPAVE at temperatures as high as 64.degree. C. and temperatures
as low as -22.degree. C. Stiffness is a desirable property for
asphalt to have at the higher temperatures because the asphalt
tends to soften at such high temperatures. Flowability and the
ability to relieve thermally-induced stress is a desirable property
for asphalt to have at the lower temperatures because the asphalt
tends to thermally crack at the lower temperatures.
[0044] The results of Table 5 show that addition of the antioxidant
mixture imparts stiffness to the binder at the higher temperatures
and imparts ductility at the low temperatures. Specifically, Table
5 shows that incorporation of the antioxidant mixture of 2%
Furfural+1.5% DLTDP+1.2% HCl to binder C improves its grade from PG
64-22 to PG 70-28. In other words, binder C expands by two grades,
each grade being defined in increments of 6.degree. C. Similarly,
using the same antioxidant mixture improves the grade of binder D
from PG 64-22 to PG 76-28, which is an expansion of three grades.
The grade of binder B improves from PG 64-22 to PG 70-22, which is
an expansion of one grade.
[0045] As shown in Table 5, in order for a binder to be graded at a
particular level, it must pass four tests. They are the unaged
test, short-term aging test, long-term aging test, and creep
stiffness test. These tests are in accordance with SUPERPAVE
requirements. Essentially, in accordance with SUPERPAVE, a
predetermined level of stiffness is required at high, intermediate,
and low temperatures for the binder to maintain adequate structural
rigidity for pavement applications. If the binder passes each of
the four tests, then it is considered suitable for application at
that particular grade.
[0046] The requirements of each test will now be discussed. The
unaged test evaluates rutting susceptibility (i.e., the tendency to
deform which is computed as G*/Sin .delta.) of unmodified and
modified binders C, D, and B at the high temperatures of 64.degree.
C., 70.degree. C., 76.degree. C., and 82.degree. C. In accordance
with SUPERPAVE, in order for the binder to pass the unaged test at
each of the high temperatures, it must exhibit a stiffness greater
than 1.0 kPa. The short-term aging test evaluates rutting
susceptibility of the unmodified and modified binders at 64.degree.
C., 70.degree. C., 76.degree. C., and 82.degree. C. for a
predetermined short period of time as defined in SUPERPAVE. In
accordance with SUPERPAVE, in order for the binder to pass the
short-term aging test at each of the high temperatures, it must
exhibit a stiffness greater than 2.2 kPa. The long-term aging test
evaluates fatigue cracking, which is computed as G*Sin .delta., at
the intermediate temperatures of 22.degree. C. and 25.degree. C.
for a predetermined long period of time as defined in SUPERPAVE. In
accordance with SUPERPAVE, in order for the binder to pass the
long-term aging test at each of the intermediate temperatures, it
must exhibit a stiffness less than 5.0 MPa. For the unaged,
short-term aging, and long-term aging tests, a dynamic shear force
was applied by a test machine.
[0047] The creep stiffness test evaluates thermal cracking at
-22.degree. C. Pursuant to SUPERPAVE, in order for the binder to
pass the creep stiffness test it must exhibit a creep stiffness
less than 300 MPa and a m-value greater than 0.3, where the m-value
is defined as the rate at which stress is relaxed. In other words,
the slope of the curve of logarithm of stiffness versus logarithm
of time at a given time (60 seconds as specified in SUPERPAVE) is
the m-value.
[0048] Table 5 demonstrates that modification of each of the
binders with the antioxidant mixture of 2% Furfural+1.5% DLTDP+1.2%
HCl expands the grade of the material, thereby increasing the high
and/or low temperature ranges of the binders. Referring to the
unaged test, each of the modified binders increases in stiffness at
64.degree. C. For example, modified binder C increases in stiffness
from 1.2338 (unmodified binder C) to 3.1124. Notably, binder D
increases in stiffness by about 14 fold compared to unmodified
binder D. Additionally, the unaged test indicates that modified
binder D passes the requirements for the unaged tests (i.e.,
exhibiting a stiffness greater than 1.0 kPa) for the highest tested
temperature of 82.degree. C., which represents an improvement of
three grades at the higher temperature (from PG-64 to PG-82).
Binders C and B passes the requirements for the unaged tests at
70.degree. C., which represents an improvement of one grade. These
are desirable results because the binder materials tend to flow at
the higher temperatures due to their viscoelastic properties. To
counteract this tendency, a predetermined level of stiffness is
required to maintain structural rigidity.
[0049] Referring to the short-term aging test, each of the modified
binders increases in stiffness at 64.degree. C., which is desirable
because the increased stiffness imparted by the antioxidant mixture
counteracts the tendency of the binder to viscoelastically flow at
the high temperature. Additionally, modified binder D improves two
grades by exhibiting a stiffness above the required 2.2 kPa at
76.degree. C. Modified binders C and B improve one grade by
exhibiting stiffness levels above the required 2.2 kPa at
70.degree. C.
[0050] Referring to the long-term aging tests, modification of
binders C and B result in lower G*Sin .delta. values at 25.degree.
C. Lower G*Sin .delta. values translates into softer materials.
Because this test evaluates fatigue cracking, at 25.degree. C.,
softer materials are desirable to counteract the tendency to
fatigue crack. Although modified binder D does not become softer
upon addition of the antioxidant mixture, it remains at the same
grade, PG-28 grade, with respect to the low temperature.
[0051] Creep stiffness values are obtained at -12.degree. C. and
-18.degree. C. to assess thermal cracking. The creep stiffness
values at -12.degree. C. and -18.degree. C. are equivalent to the
values that would have been obtained at -22.degree. C. and
-28.degree. C. Because testing at about -22.degree. C. and about
-28.degree. C. would have required substantially longer testing
times, asphalt's time-temperature superposition principle is
utilized so that the binder incurs the same stiffness from a load
applied at -12.degree. C. and 2 minutes as it would incur from a
load applied at -22.degree. C. and 2 hours. Lower stiffness values
are obtained for each modified binder C, D, B at -12.degree. C.
(equivalent to -22.degree. C.) and -18.degree. C. (equivalent to
-28.degree. C.). These results indicate that the modified material
is better able to flow and dissipate thermally-induced stress at
the lower temperatures as compared to the unmodified binders.
Additionally, the higher m-values for modified binder C and
modified binder B indicate that the rate at which stress is relaxed
is higher in the modified binders C and B.
[0052] The overall results of the tests are given in the last row.
The last row of Table 5 indicates the improved grades for modified
binders C, D, and B. For example, modified binder C improves from
PG 64-22 to PG 70-28. In other words, modified binder C is suitable
for pavement applications as high as 70.degree. C. and as low as
-28.degree. C. Modified binder D improves from PG 64-28 to PG
76-28, and modified binder B improves from PG 64-22 to PG
70-22.
[0053] Typically, polymers and other additives are frequently used
to increase the useful temperature range of binders. However, such
additives tend to increase the price of the binder by as much as
about 200%. Incorporation of the antioxidant mixture disclosed
herein offers a more economical alternative for achieving the same
result. Additionally, prior antioxidant use in paving asphalt has
tended to excessively soften the modified asphalt, thereby
rendering them prone to rutting and/or limiting their use to only
colder temperatures. The antioxidant mixture disclosed herein was
not observed to excessively soften the asphalt binder.
TABLE-US-00007 TABLE 5 SUPERPAVE performance grade of
antioxidant-modified asphalt binder Asphalt Asphalt Asphalt Asphalt
Binder D Asphalt Binder B Asphalt Binder C Binder Example Binder
Example Binder Properties Example 32 C + AOX 33 D + AOX 34 B + AOX
Unaged Dynamic Shear (kPa) > 1.0 G*/Sin.delta. at 64.degree. C.
1.2338 3.1124 1.3643 14.207 1.3099 3.4963 G*/Sin.delta. at
70.degree. C. <1(fail) 1.6456 <1(fail) <1(fail)
<1(fail) 1.7377 G*/Sin.delta. at 76.degree. C. <1(fail)
<1(fail) <1(fail) 3.3329 <1(fail) <1(fail)
G*/Sin.delta. at 82.degree. C. <1(fail) <1(fail) <1(fail)
1.4975 <1(fail) <1(fail) Short-Term Aging Dynamic Shear (kPa)
> 2.2 G*/Sin.delta. at 64.degree. C. 3.3174 6.715 2.762 14.796
3.3402 4.6302 G*/Sin.delta. at 70.degree. C. <2.2(fail) 2.9461
<2.2(fail) <2.2(fail) 2.241 G*/Sin.delta. at 76.degree. C.
<2.2(fail) <2.2(fail) <2.2(fail) 3.9439 <2.2(fail)
<2.2(fail) G*/Sin.delta. at 82.degree. C. <2.2(fail)
<2.2(fail) <2.2(fail) <2.2*(fail) <2.2(fail)
<2.2(fail) Long-Term Aging Dynamic Shear (MPa) < 5.0
G*Sin.delta. at 22.degree. C. 3.3285 3.4052 3.3486 5.0178
G*Sin.delta. at 25.degree. C. 3.3223 2.3061 2.2402 2.5204 4.6965
3.6043 Creep Stiffness (MPa) < 300 Stiffness at -12.degree. C.
111 76 74 64 207 131 Stiffness at -18.degree. C. 227 149 141 266
m-value > 0.3 m-value at -12.degree. C. 0.31 0.33 0.38 0.35
0.3121 0.32 m-value at -18.degree. C. 0.29 0.3 0.33 0.28 Possible
PG grade PG 64-22 PG 70-28 PG 64-28 PG 76-28 PG 64-22 PG 70-22
EXAMPLE 35
[0054] The modified asphalt binder batches incorporating the 2.0 wt
% furfural, 1.5 wt % DLTDP, and 1.2 wt % HCl are mixed with mineral
aggregate batches to produce asphalt concrete. The aggregates used
are typical Illinois limestone of 9.5 mm nominal maximum size. The
aggregates are blended using SUPERPAVE procedures. The batch weight
of each aggregate batch is 4700 grams. The batch weight of each
modified asphalt binder is about 5% by weight of the total mix.
[0055] The modified asphalt binders are heated in a forced draft
oven at a temperature of 150.degree. C. The batch aggregates are
also kept in the forced draft oven which is maintained at a
temperature of 150.degree. C. for a minimum of three hours before
mixing. The batches of aggregates and modified asphalt binders are
mixed at 150.degree. C. using a 16 liter mechanical mixing bowl.
The mixing continues until the aggregates are completely coated
with the modified asphalt binder. The loose mixtures are aged in a
forced draft oven maintained at about 135.degree. C. for about 2
hours to simulate short-term aging and about 8 hours to simulate
long-term aging. The mixtures are compacted after aging.
[0056] Compaction of the mixtures is done using a SUPERPAVE
gyratory compactor. The compactor operated at 30 rpm. All of the
samples are compacted to a height of 120 mm. Two 150 mm diameter
compaction molds are used. The target compaction temperature is
135.degree. C. After compaction, the samples are extruded from the
compaction mold.
[0057] The aggregate-modified asphalt binder mixtures exhibit a
higher resistance to aging compared to the aggregate-unmodified
asphalt binder mixtures (i.e., control) under aging conditions that
are simulated using the aging procedures described above.
Mechanical tests are performed on the finished aggregate-asphalt
mixtures to evaluate the resistance to aging. The mechanical tests
include tensile strength, creep compliance, fracture test, and
moisture damage. The tests show that the antioxidant treatment has
superior resistance to aging compared to conventional antioxidant
treatments and is effective in controlling age-hardening.
[0058] Although the antioxidant additives have been described above
for use in asphalt binders, other uses of the antioxidant mixture
are contemplated. For example, the combination of a thioester and
aldehyde may be incorporated into polymeric materials to reduce
oxidation of the polymeric materials.
[0059] It should be appreciated that the above described methods
and compositions are capable of being incorporated in the form of a
variety of embodiments, only a few of which have been illustrated
and described above. The invention may be embodied in other forms
without departing from its spirit or essential characteristics.
However, the described embodiments are to be considered in all
respects only as illustrative and not restrictive, and the scope of
the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
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