Note: Descriptions are shown in the official language in which they were submitted.
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sackground of the Invention
The present invention relates to an improved
asphalt-aggregate paving composition.
Aggregate-con-taining asphalt has been employed
as the paving composition ~or roads or the like for many
years. The asphalt includes bitumens as a predominant
constitutent and is conventionally obtained as a solid
residue from the distillation of crude petroleum. The asphalt
is conver-ted to a fluid state when paving a road. One
fluid form is the suspension or emulsion of the asphalt
in water. After spreading and compressing the aggregate-
containing asphalt, water evaporates and the asphalt hardens
into a continuous mass. Another form of asphalt employed in
road construction is a cut-back, i.e., a liquid petroleum
product produced by fluxing an asphaltic base with a
suitable distillate. A road is formed by layering the cut-back
and evaporating the volatile distillate from the mass. The
` advantage of using the above road construction techniques is
the avoidance of high tempera-ture application. In an
alternative technique, the asphalt and aggregate can be
mixed and applied at elevated temperatures at the fluid
state of the asphalt to form the road. Then, the asphalt
need not be cut-back or emulsified.
It is advantageous to increase the adhesivity of
asphalt, especially in the form of a cut-back of emulsion, to be
employed with aggregate in road construction. One
technique which has been disclosed to increase such adhesivity
is set forth in U.S. patent 2,342,861. The examples of that
patent illustrate the addition of a lead soap, specifically
lead oleate or naphthenate, to asphalt cut-backs or emulsions
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-to incr~ase th~ir adllesivl-ty for aggregate. Although in all
illustrated examples only lead is disclosed as a metal soap to
increase adhesivity, -the patent suggests tha-t other heavy
metal salts of organic acids could be employed including the
following metals: Fe, Al, ~, Zn, Co, Ni, Sn, Ca, Sr, Ba,
and ~Ig. The patent discloses a technique of forming the
lead soap by heating a lead oxide in the presence of the
desired organic acids. Such lead soaps are then added to
the desired asphalt.
Heavy metal salts oE high molecular weiyht organic
acids, such as naphthenates or linoleates, have been employed
to prevent cracking in a blown or oxidized asphalt coatings.
For example, U.S. patent 2,282,703 discloses the use of
heavy metals such as cobalt, manganese, iron, lead, vanadium,
or zinc dispersed into the blown asphalt for this purpose.
Heavy metal soaps have also been disclosed for
use as a dispersant in roofing asphalts to prevent failure
of the asphalt due to "alligatoring". U.S. patent 2,928,753
discloses the polyvalent metal salts of copper, cobalt, or
manganese in combination with high molecular weight
mono-carboxylic acids such as oleic or naphthenic acid. The
final disclosed product is an aggregate-free coating of
0.025 inches thick on an aluminum sheet heated so that
leveling occurs.
Summary of the Invention and Objects
In accordance with the present invention, it has
been found that dispersing certain polyvalent heavy metal
catalysts in asphalt and then mixing the same with aggregate
forms a paving of vastly improved characteristics. In order
of effectiveness, manganese, copper, and cobalt in quantities
as low as 0.05% to 0.59~ by weight o-f the asphalt procluces an enormous in-
crease in comp-ressive, flexural cmcl fatigue strength of the ultimate cured
paved road.
~ he asphalt may be fluidized for me-tal catalyst dispersion by con-
ventional technlques such as emulsification, cutting back, or by heating the
asphalt to a temperature above its mel-ting or softening point. The metal
catalyst-containing asphal-t may -then be mixed in this form directly with the
aggregate for road construction. It has been found that the modified asphalt
may be stored in bulk prior to road formation without hardening.
It is an object of the invention to provide a modified asphalt-
aggregate paving composition of exceptional strength and fatigue resistance
for use in the formation of roads or the like.
It is a particular object of the invention to provide a modified
asphalt which is of suitable viscosity in bulk for paving but which hardens
into a thermosetting polymer of exceptional strength after paving.
It is a further object of the invention to provide an asphalt-
aggregate paving composition of superior Marshall stability.
It is a further object of the invention to provide a paving compo-
sition of the foregoing type which retains a large portion of its strength
at elevated temperatures while forming a flexible pavement possessing self-
healing properties.
The present invention provides a paving composition comprising a
major proportion by weight of aggregate and a minor proportion of substan-
tially unblown asphalt which is present as a coating on the aggregate, the
asphalt having uniformly dispersed or dissolved therein at least one oil-
soluble soap which is a manganese, copper or cobalt salt of a monocarboxylic
acid having not more than 30 carbon atoms, or a mixture of two or more
thereof, and which is present in an amount such that the composition contains
from 0.01 to 0.5%, based on the weight of the asphalt, of manganese, copper
or cobalt ions, or a mixture thereof.
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Detailecl Description of the Preferred Embodiments
l'he present invention relates to a modified
asphalt which, combined with aggregate, forms a paving
composition providing significan-tly improved physical properties.
The asphalt is modified by dispersing a metal catalyst
throughout the asphalt while the asphalt is in a fluid
state. Such fluidity may be accomplished in any of the
known conventional techniques such as by heating -the asphalt
to ahove its softening point, emulsifying the asphalt, or by
forming a cut-back oE the same in a volatile organic solven-t.
The me-tal catalyst of the present inven-tion are formed from
a metal salt in which the metal ion is manganese, copper,
cobalt or mixtures thereof.
As used herein, the term "asphalt" refers to any
of a variety of substantially unblown or unoxidized solid
or semi-solid material at room temperature which gradually
liquifies when heated. Its predominant constituents are
bitumens, which are obtained as the residue of refining
processing.
It is important to disperse the metal catalyst
of the present invention uniformly throughout the asphalt
so that its catalytic effect is imparted to the final product
in a consistent manner. The form of metal catalyst is
important in obtaining such uniformity of dispersion by
thorough penetration of the catalyst throughout the
asphalt. For optimum dispersion, the metal catalyst is in
the form of a metallic organic salt which is soluble in a
significant port-ion of the asphalt. It is known that an
excellent anion for the metallic organic salt of this type
is derived from a high molecular weight monocarboxylic acid.
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Such metallic organic salts are oil-soluble soaps of
monocarboxylic acicls, preferably having from 6 to about
30 carbon atoms in the chain. Preferable anions for ~his
purpose include linoleates, octoates, naphthenates, oleates,
stearates, and laurates.
Significant improvemen-ts in the modified asphalt
are obtained by adding a relatively small quantity o~ the
metal catalyst. Thus, a concentration of metal ion as low
as 0.01% by weight of manganese ion based on the asphalt
yields a paving composition of improved compressive load
strength. It has been found that optimum properties are
obtained at a minimum of 0.05 - 0.5% by weight of metal ion.
Levels of me-tal ion above such concentrations, say at 1%,
produce only marginal improvements. For economy, the optimum
range is from 0.05 to 0.15% by weight of metal based upon
the asphalt.
Other forms of the metal catalyst than -the
foregoing me-tal soaps may be employed in accordance with the
present invention. Thus, for an asphalt containing substantial
naphthenic acid, an inorganic compound of the heavy metal
such as oxide, sulfate, chloride or hydroxide may be added
to asphalt and heated to form a soluble heavy me-tal naphthenate
soap in situ. A technique of this type for oxides is described
in U.S. patent 2,3~2,861.
It may be possible to employ other dispersable
forms of the metal catalysts of the present invention. For
example, the metal may be in a chelatable form suitable
for reaction with the asphalt. If a material of this type
is added in a solid form, it is preferable as a fine powder
to assist dispersion in the asphalt.
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One technique for mixing -the Eoregoiny rnetal
catalysts with the asphalt of the present lnvention is to
heat the asphalt to above its soEtening or melting point
until it is sufficiently fluid to thoroughly disperse the
metal catalyst. This technique is designa-ted "warm mixing"
herein. For this technique, i-t is preferable to employ the
metal catalys-t in the liquid form. For most conventional
asphalts, a temperature on -the order of 110 to 120C is
; sufficient for asphalt fluidizing. At such temperatures,
the viscosity of the asphalt composition is suEficiently
reduced to permit thorough dispersion by manual mixing.
The warm mixing technique may be employed at a
facility remote from the road construction site. This is
possible because, as set forth hereinafter, the catalyst
does not harden the asphalt while it is in bulk form. Thus,
the modified asphalt can be stored in bulk until needed. In
conventional processing, the modified asphalt is maintained in
a fluid state from its time of formation, during normal storage
and transport to the road site, during mixing with aggregate and
until final paving. In an alternative to remote warm mixing,
the metal catalyst could be added to the asphalt at the road
construction site just prior to paving.
The modified asphalt is characterized by a viscosity
in a fluid state at the elevated temperature of road building
comparable to conventional asphalt. However, as set forth
below, the cured paved road has vastly superior strength in
comparison to one formed with conventional asphalt.
Conventionally, the warm mixed modified asphalt in
fluid form is premi.xed with heated aggregate to form a
paving composition, suitably in a mixing tank truck. Then,
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the composition is spread on the road bed and compacted. Af-ter
curiny, the road comprlses agyregate bound by a matxix of
modifie~ asphalt binder.
It is noted tha-t acceptable curing occurs at ambient
temperatures, e.g., 22C. Moderate elevations (e.g., to 50C~
in the temperature of curiny accelerates -the process. However,
very high temperatures such as employed to blow asphalt,
i.e., on -the order of 230C, would be unacceptable for the
present process. As set forth below~ it is is believed -that
this is due to the decomposi-tion of peroxides or hydropero~ides
required for free radical polymerization to form the superior
product of the present invention.
Other conventional techniques for fluidizing
asphalt may be employed to permit thorough dispersion
of the metal catalyst. For example, the asphalt may be
formed into a cut-back by fluxing the asphalt with a suitable
volatile solvent or distillate. Thus, the metal catalyst
of the present invention could be added directly to the
asphalt cut-back. The modified asphalt cut-back could
then be directly mixed with aggregate and applied as a paving
composition.
Another conventional technique for fluidizing the
asphalt to disperse the metal catalyst is to first emulsify
the asphalt by known techniques. Like the cut-back technique,
an advantage of this mode of fluidizing the asphalt is that
dispersion can be accomplished at room temperature. Also,
like the cut-back, the metal catalyst-containing asphalt
emulsion can be mixed in that form with the aggregate to
form the paving composition.
The aggregate of the present invention is suitably
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of a type employ~d in the road building industry. It may
range from Eine particles such as sand to relatively coarse,
ground particles such as crushed stone, gravel or slay.
A major portion by weigh-t of aggregate is mixed
with a minor portion by weight of asphalt. The ratio of
aggregate to modiEied asphalt is -that typical for road
paving applications. Thus, a minimum of about 85% by weight
of aggregate and generally abcut 90 to ~6~o by weiyht of the
total paving composition is employed in the present invention.
As set forth in the background of the invention,
heavy metal soaps have been employed in combination with
asphalt for a number of different purposes. For example,
; they have been used as a catalyst for avoiding cracking in
blown asphalt, and preventing alligatoring in roofing
materials. Also, such metal soaps have been disclosed in
aggregate-containing road building compositions to improve
adhesivity of the asphalt for the aggregate. For use as a
paving composition, there is no disclosure in the prior art that
such heavy metals significantly increase the strength of the
final product. Furthermore, the prior art teaches the
general equivalency of multivalent heavy metal ions for this
purpose. For example, in the aforementioned U.S. 2,342,861,
experiments were performed employing lead soaps to increase
; adhesivity of asphalt for aggregate. In accordance with the
state of the art, the patent asserts that other metals such
-as iron, aluminum, manganese, zinc, cobalt, nickel, tin,
calcium, strontium, barium, or magnesium could also be
employed for the same purpose.
Wlth the above background knowledge, it has
unexpectedly found that only selected heavy metals serve as
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catalysts to enormously increase the strenqth, fatigue
resistance and other properties of an agcJregate-containing
paving composition while the remainder of the heavy metals
have little or no beneficial ef~ect. Thus, it has been
found tha-t manganese, copper and cobalt, in that order, are
vastly superior to the remainder of the heav~ metals ~or
this purpose.
It is believed that extraordinary increases in the
flexural strength and fatigue resistance oE the foregoing
modified asphalt-aggregate cured composition may be explained
in accordance with the following theory. It is believed that
the soluble salts of the manganese, copper, or cobalt metal
ions dispersed in asphalt causes the asphalt to be vinyl
polymerized when mixed with aggregate during curing at
lS either ambient or elevated temperatures. This is to be
contrasted with the oxidation in conventional asphalt which -~
actually degrades the flexural strength and fatigue
properties of the same. There is strong evidence that the
double bond content of the various constituents of the present
modified asphalt are activated to permit cross-linking and
polymerization. A plausible theory as to the effect as
to the metal catalysts of the present invention is that they
generate peroxides or hydroperoxides which are catalyzed by
the metals to yield free radicals which, in turn, are known
to catalyze vinyl polymerization. It is totally unexpected
that manganese, copper, and cobalt, in that order, would be
vastly superior to other heavy metal catalysts for this
purpose.
Support for the above theory of vinyl polymerization
may be found by the following explanation. It is believed
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that the vi~yl unsaturation oE conventional paving
asphalt can be measured by the Woburn Iodine Number Method as
set forth in Von Mikusch, J.D., and Fraizer, Charles, "Woburn
Iodine Absorption Method", Ind. Eng. Chem. Analytical Edition,
1941, 13, 782. A typical paving asphalt has a Woburn iodine
number of about 90. This means -that there is approximately
1 mole of double bond for each 280 grams of asphalt. By the
above test, the starting asphal-t yielded a Woburn iodine value of
91. An asphalt including 0.2% cobalt by weight was mixed
with aggregate and cured. The asphalt was extracted from
this sample and yielded a ~oburn iodine value of 70. The
decrease in iodine number indicates that significant vinyl
polymerization occurred during curing.
Further support for the polymerization theory of
increased strength is found in the ratio of pentane insoluble
materials in the final cured modified asphalt product in
comparison to the starting material. One such test is
; described in a paper by Kleinschmidt, L.R., entitled
"Chromatographic Method for the Fractionation of Asphalt
Into Distinctive Groups of Compounds", Journal of Research
of the National Bureau of Standards, 1955, 54, 163. The
percent of pentane insolubles in the starting aggregate was
12.8% and in the asphalt extracted from aggregate was
26.5%. It is believed that the increase in pentane
insolubles is caused by polymerization as set forth above.
It has been found that the modified asphalt of the
present invention does not harden or cure when in bulk
form. Thus, it remains at a viscosity at elevated temperatures
above its melting point comparable to unmodified asphalt.
Thus, the metal only functions as a catalyst for hardening
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or curing the asphalt after mixing with acJgreyate. It is
believed that this phenomenon may be explained by the requirement
tha-t the modified asphalt be in a relatively -thin film, the
state in which it exists in combina-tion with aggregate.
Thus, the asphalt tends to Eorm a thin coatiny of, 5 - 10 microns
on the surface of sand aggregates which apparently causes
catalytic activity in -the metal catalyst. Although -the
maximum thickness of the -thin film i-or this effect is not
known, it is believed that the film may be as thick as150 rnicrons
or more. An explanation for -the requirement of the asphalt
to be in a thin film form is -that a certain amount of oxygen
is required to penetrate througho~lt the film to permit
catalysis to occur. That is, in accordance with the foregoing
theory, the metal catalyst of the present invention requires
a small quantity of oxygen to form peroxides or hydroperoxides
which yield free radicals for vinyl polymerization.
It has been found that increasing the void ratio
of the modified asphalt-aggregate composition causes a
corresponding increase in the curing rate. This is
consistent with the theory that a certain amount of oxygen
penetration of the asphalt is required to interact with
the metal catalyst to initiate polymerization. Thus, at a
20% void ratio in a sand aggregate composition, significant
curing can occur in a week.
; 25 A further disclosure of -the nature of the present
invention is provided by the following specific
examples of the practice of the present invention. It should
be understood that the data disclosed serve only as
- examples and are not intended to limit the scope of the invention.
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xample 1
Comparative tests were performed with various
transition heavy metals as addi-tives -to the asphalt. In
each instance, sand of the F6-039 (Shayba) type, classified
as a dune sand, was mixed with a modified bitumen asphalt
designated AR-8000 by the Sta-te of California in a ratio of
4% by weight of modified asphalt to 96% by weight of sand.
The modified asphalt in each instance included organo-
metallic compounds (soaps of napthanates or octoates) in a
ratio so that the metal was presen-t at 0.2% by weight of the
asphalt. The soaps, in liquid form, were mixed with the
fluid asphalt at elevated temperatures (about 110-120C)
sufficient to melt the asphalt. Mild manual stirring of the
mixture was employed to thoroughly disperse the metal throughout
the asphalt.
Short minia~ure cores were molded at 154 - 158C
and cured at 50C for seven days. The cores were tested for
compressive strength at both 22C and 50C. The same cores
were re-tested under the same conditions after one and two
weeks. The cores of the second test were slightly larger in
; diameter so the results should be multiplied by approximately
0.97 for correction. The results of the tests are set forth
in the following teble.
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l'he columns designated "enc:Losecl" lndicate that
the compositions were cured in containers to eliminate
mos-t but not all oxygen contact. The compressive strengths
of the enclosed and totally exposed samples are comparable
indicating -that there is no significant effect in starving
the material of oxygen during curing.
It is apparent from Table I -that manganese is the
preferred metal ca-talyst for all tests. However, copper and
cobalt also provided extraordinary increases in s-tructural
streng-th in comparison -to the remainder of the tested
metals.
Example 2
A series of tests were performed on the basic
paving composition of Example 1 but using only manganese
octoate at 0.2% of the total asphalt. The sand aggregate
was loaded at 96~. The results of the above test
are summarized in the below table. All samples were cured
at 50C for one week exposed to the air. Similar results
are obtained at lower ambient -temperatures (e.g., 22C)
at increased curing times.
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TABI,~ Il
_
tJnmodiEied Modified
~sphalt _ Asphalt
- Unconfined Compression Test:
strength at 22C, kg/cm 8.~ 63.2
strength at 22C, kg/cm 0.3 20.3
- Marshall Stabili-ty Test:
stability, lb. 250 1800
flow, 1/100 inch 14 12
- Static Flexural Test:
modulus of elasticity, kg/cm2 780 5175
modulus of rupture, kg/cm 3.4 17.3
ultimate strain (x 10 4) -* 152
! - Dynamic Fatigue Tests:
modulus of elasticity, kg/cm2 -* 60,000
endurance limit, e x 10 ~ -* 80
,, .
* These quantities could not be determined for untreated
; sand-asphalt beams.
It was found that full strength at 22C testing
temperature was obtained in about four weeks, although a longer
period of time was required for full strength at a 50C
test temperature.
The mode of failure was of a plastic nature. The
"failed" specimens could be rested several times within
relatively short periods of time (e.g., one or two days) and
still yield about the same strength. This indicates a
combination of plastic flow and thixotropic behavior, hence,
a retention of strength near the peak point, and a healing
action beyond.
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The Marshall stability test revealed the stability
increased at a decreaslng rate beyond one month.
The static flexure tests were performed by molding
beams rneasuring 25 cm in leng-th, 2 cm x 3 cm in cross-section.
The beams were cured at 22C for about one month, and were
then tested in static flexure in third-point loadiny, over a
clear span of 22 cm. The rate of loading was 0.05 inches per
minute, and the tempera-ture at test was 22C. The results
are set forth in the above table. The ul-timate flexural
strain of the unmodified asphalt-sand beam could not be
obtained because i-t deformed continuously for the duration
of the test. The modified asphalt beam ultimate strength was
approximated by adding the elastic strain near the ultimate
load to its plastic strain at rupture.
. 15 Beams of the foregoing type were tested in a
dynamic fatigue machine supported over a span of 22 cm
loaded repeatedly at their mid-point. A steel leaf was
placed crosswise under the beams to push them back up each time
the load was removed. The rate of loading was three
repetitions per minute, and the temperature at test was 22~C.
In performing the fatigue test, no meaningful
results could be obtained for the unmodified asphalt beams
as they deformed both vertically and laterally under relatively
low levels of load. The results of the fatigue test were
plotted on a log-log scale to yield an equation in the
standard form Nf = K(e)C wherein Nf is the number of load
repetitions to failure, e is the corresponding flexural
strain, and K and c are regression constants. K and c were
found to be 1.82 x 1012 and 3.29, respectively, where e
is expressed in micro units.
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~ i`he clynamic modlllus of elasticity of thc sand-asphalt
beams was found to be on the order of 850,000 p51. At this
modulus, the modi~ied asphalt-sand produc-t was upgraded to
the level of asphaltic concrete in fa-tigue life.
Example 3
Mixes were made of asphalt plus 0.05%, 0.1P6 and
0.2% manganese. Standard Marshall GOreS were molded at 4%
bitumen. Half the cores a-t each level of manyanese were
put into a 50C oven. The other half were left on the
bench. ,At 7 days of cure time, Marshall Stabili-ty Tests
were run. The resul-ts are set forth in Table III below.
TABLE III
% Manganese in Asphalt
Cure and Test 0.05 0.10 0.20
:,
22C cure, Marshall
Stability (lbs.) 370 1030 1140
- 50C cure, Marshall
Stability 1288 2690 3220
CONCLUSION
A graph of this data indicates that the maximum
beneficial effect on stability per unit quantity of manganese
is between 0.08% and 0.12%. Levels of manganese above this
produce only marginal benefits.
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