Note: Descriptions are shown in the official language in which they were submitted.
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IN THE UNITED STATES RECEIVING OFFICE
APPLICATION FOR
IMPROVED POLYMER MODIFIED ASPHALT EMULSIONS
FOR TREATMENT OF ROAD SURFACES
KOICHI TAKAMURA, PH.D.
INVENTOR
PREPARED BY
MANATT, PHELPS & PHILLIPS
The present invention relates to asphalt emulsions for treatment of road
surfaces. More
specifically, the present invention relates to improvements in methods for
treatment of aged,
cracked or otherwise deteriorated road surfaces paved with asphalt. The
improvements provide
stronger, more stable and less costly emulsions than those previously
available.
BACKGROUND OF THE INVENTION
The annual worldwide consumption of asphalt for road surfacing applications
exceeds
90,000,000 tons. Europe and North America are responsible for approximately
two thirds of this
consumption. In the United States more than four million miles of roads are
paved with asphalt.
Asphalt pavement deteriorates with use, due to oxidation of asphalt binder,
high loads and
varying climatic conditions. A recent study demonstrates a statistically
significant relationship
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between a country's economic development and its road infrastructure'1
Accordingly,
maintenance and rejuvenation of asphalt surfaced roads is a matter of some
importance. In
developed countries it is understood that preventative maintenance of existing
roadways is
preferable to replacement2. Accordingly, improvement in the technology for
maintaining
existing roadways is desirable.
Asphalt road surfaces typically consist of asphalt and aggregate. Oxidation of
asphalt
binder during its service time, climate conditions and use of road surfaces,
particularly by heavy
loads, result in deterioration of the road surfaces over time. For example,
repeated contraction of
the road surface during the cold winter nights due to temperature changes
results in formation of
perpendicular cracks in pavement, known as cold fractures. The asphalt binder
becomes too soft
during the hot summer days, resulting in a permanent deformation of the road
surface under
repeated heavy loads, termed "rutting". In addition, as a result of continuous
mechanical stress,
road surfaces become fatigued, resulting in formation of alligator skin-lilce
cracks, known as
fatigue fracture.
One approach to the progressive deterioration of asphalt pavement is to remove
and
replace the existing pavement with either newly prepared or recycled pavement.
However,
removal and replacement is expensive and wasteful3. A preferable approach
involves surface
' C. Queroz, R. Haas, and Y Cai, "National Economic Development and Prosperity
Related to
Paved Road Infrastructure" Transportation Research Record, 1455 (1994).
a M. S. Mamlouk and J. P. Zaniewske, "Pavement Preventive Maintenance:
Description,
Effectiveness, and Treatments", Symposium on Flexible Pavement Rehabilitation
and
Maintenance, ASTM STP 1349, 121-135, 1999.
3 F.L. Roberts, P.S. Kandhal, E.R. Brown, D.Y. Lee, T.W. Kennedy, "Hot Mix
Asphalt
Materials, Mixture Design and Construction", NAPA Research and Education
Foundation
Textboolc, 2"a Edition, 1999.
2
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treatment of the existing pavement to restore the pavement to its condition
when first laid down4.
For example, United States patent 5,180,428 to Richard D. I~oleas discloses a
composition
including asphalt, a recycling agent, a polymer and an emulsifying agent in an
aqueous solution
that when deposited upon aged and cracked asphalt pavement rejuvenates the
pavement by
replenishing solvent oils (maltenes) driven off by wear and exposure to the
elements. The '428
patent is expressly incorporated herein by reference.
The invention of the '428 patent is sold under the mark "PASS." PASS is also
used as a
tack coat, chip seal, scrub seal and fog seal as well as for crack filling. An
advantage of PASS is
that it can be applied in a single step, over existing pavement. Moreover,
PASS rejuvenates and
prevents further oxidation of the underlying pavement. Moreover, PASS can be
applied over a
wide temperature range.
Recent studies of the mechanism by which PASS acts on pavement confirm that it
rejuvenates old asphalt by restoring the aromatic content of the asphalt in
the underlying
pavement, and forms a polymer rich, thin, stress absorbing membrane, which
strongly adheres to
the underlying pavement. Thus PASS prevents reflective craclc formation when
other types of
the surface treatment (i.e, microsurfacing and slurry seal) are applied on the
PASS treated
pavement.
OBJECTS OF THE INVENTION
Although the invention of the '428 patent continues to be a substantial
commercial
success, there continues to be a need for asphalt modifiers with performance
that is superior to
PASS, yet that can be manufactured at a lower cost. Accordingly it is an
object of the invention
4 K. Takamura, K.P.Lok, R. Wittlinger, "Microsurfacing for Preventive
Maintenance: Eco-
Efficient Strategy", ISSA Annual Meeting, March 2001.
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to provide a modifier for asphalt paving that provides improved flexibility,
faster setup time, and
superior performance at low temperatures. These and other advantages of the
present invention
are described in detail below.
SUMMARY OF THE INVENTION
A composition for rejuvenating asphalt pavement according to the present
invention
comprises an asphalt binder, water, a cationic surfactant, a recycling agent,
and a cationic
coagglomerated styrene butadiene rubber latex, which includes sulfur and a
vulcanizing agent.
The composition is also useful as a scrub seal, fog seal, sand seal as well as
for crack filling and
prevention of reflective cracking. The inventive composition may be used in
emulsions with
different setup times. The invention also includes a method for treatment of
aged and cracked
asphalt pavement by application of the disclosed composition.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to an improved asphalt emulsion for restoring
and
rejuvenating aged, cracked and deteriorated asphalt pavement. The invention
reflects an
improvement over United States patent 5,180,428. More specifically, the
disclosed invention
improves on the performance of the modifier of the '428 patent by providing a
stronger, more
flexible surface, useful over a wider range of climatic conditions, yet at a
lower cost.
The following sections describe the preparation of the various components of
the invention.
At the outset, it should be understood that the invention is a mixture of
components that
interact with one another. As a consequence, the concentration of one
component may be
increased if the concentration of another is decreased, without altering the
properties of the
resulting emulsion.
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Asphalt and Recycli~~Agent
A wide variety of asphalts may be used in connection with the invention.
However,
asphalts that are rich in saturates should be avoided. Asphalts ranging from
AC-5 to AC-30 may
be used.
A key aspect of the invention is providing a sufficient quantity of maltenes,
which are the
non-asphaltene fraction of asphalt, and often referred to as the deasphalted
or deasphaltened oil.
The maltene fraction of asphalt consists of polar resins, and aromatic and
saturate solvents.
PASS, as well as the present invention, works best with a recycling agent that
is rich in aromatics
and resins, with small amounts of saturates. The maltene oils may be provided
by the asphalt or
the recycling agent. If the asphalt is low in maltenes, the deficiency may be
made up by
increasing the amount of recycling agent used. It has been discovered that a
sufficient amount of
recycling agent is present when the viscosity of the mixture of recycling
agent and asphalt lies
between 1,000 and 3,000 centipoise at 60°C.
A range of different asphalts will be used depending on the desired time for
setup and
climate, especially maximum and minimum road surface temperature, in summer
and winter,
respectively. For example, an AC-5 asphalt is preferred for a quick break
emulsion, and cold
climate. An AC-10 to 20 asphalt will be used for an intermediate setup, such
as a sand seal, and
an AC-20-30 for a slow setup and/or hotter regions.
The preferred recycling agents are available from Sunoco under their
Hydrolene~ brand
ashpalt oils. Asphalt oils meeting the ASTM standard D4552, and classified as
RA-1 are
preferred for harder asphalt, such as AC-20 and AC-30. RA-5 oils may also be
used with lower
viscosity asphalt, such as AC-5.
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Preparation Of Styrene Butadiene Latex
The styrene-butadiene rubber ("SBR") latex dispersion of the invention is
preferably
prepared using a low temperature method as discussed, e.g., in R.W. Brown et
al., "Sodium
Formaldehyde in GR-S Polymerization", Industrial and Engineering Chemistry,
vol. 46, pp. 1073
(1954) and B.C. Pryor et al., "Reaction Time for Polymerization of Cold GR-S"
Industrial and
Engineering Chemistry, vol. 45, pp. 1311 (1953), both of which are
incorporated by reference
herein in their entirety. In particular, the SBR latex is prepared by
polymerizing styrene and
butadiene monomers at a temperature less than or equal to about 25°C,
and more preferably
between 5°C and 25°C, in an aqueous emulsion polymerization
reaction. The styrene-butadiene
rubber latex dispersion used in the invention is preferred to be non-
functionalized, i.e., is
preferably prepared by polymerizing monomers consisting essentially of
styrene, and butadiene.
In particular, the styrene-butadiene rubber latex dispersion used in the
invention is preferably
substantially free (e.g. less than 1% by weight based on total monomer weight)
of functional
monomers such as hydrophilic monomers (e.g. vinyl carboxylic acids such as
acrylic acid,
methacrylic acid, itaconic acid and fumaric acid), which are used to produce
carboxylated,
polystyrene-butadiene, XSB, latex dispersions. More preferably, the styrene-
butadiene rubber
latex dispersion of the invention is prepared by polymerizing a mix of
monomers that includes
styrene, butadiene and that is free of functional monomers. For example, the
styrene-butadiene
rubber latex dispersion can be prepared by polymerizing monomers consisting
only of styrene,
butadiene or it could be only with butadiene for special cases.
The SBR polymer latex used in the present invention can be produced using
either a
continuous or batch process. In a preferred embodiment, the SBR polymer latex
is produced
using a continuous method by continuously feeding a monomer stream, a soap
stream and an
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activator stream to a series of reactors. The monomers in the emulsion stream
are preferably fed
at a butadiene to styrene weight ratio from about 70:30 to about 7:22.
The soap stream includes a soap, a free radical generator (e.g. organic
peroxide) that is
used in the redox initiator system, and water. The soap in the emulsion stream
is preferably a
natural soap such as sodium or potassium oleate or the sodium or potassium
salt of rosin acid.
The soap is typically present in the emulsion feed in an amount from about 0.5
to about 5 weight
percent, based on total monomer weight.
The free radical generators used in the soap stream generally include organic
peroxygen
compounds such as benzoyl peroxide, hydrogen peroxide, di-t-butyl peroxide,
dicumyl peroxide,
2,4-dichlorobenzoyl peroxide, decanoyl peroxide, lauroyl peroxide,
diisopropylbenzene
hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide, -pinene
hydroperoxide, t-
butyl hydroperoxide, acetyl acetone peroxide, methyl ethyl ketone peroxide,
succinic acid
peroxide, dicetyl peroxydicarbonate, t-butyl peroxyacetate, t-butyl
peroxymaleic acid, t-butyl
peroxybenzoate, and the like, as well as alkyl perketals, such as 2,2-bis-(t-
butylperoxy)butane,
ethyl 3, 3-bis(t-butylperoxy)butyrate, 1,1-di-(t-butylperoxy) cyclohexane, and
the like.
Preferably, the free radical generator includes diisopropylbenzene
hydroperoxide or p-methane
hydroperoxide. The free radical generator is typically present in an amount
between about 0.01
and 1% by weight based on total monomer weight.
The activator stream includes the other components of the redox initiator
system. In
particular, in addition to the free radical generator fed with the soap
stream, the redox initiator
system includes a reducing agent and a water-soluble metal salt of iron,
copper, cobalt, nickel,
tin, titanium, vanadium, manganese, chromium or silver.
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Suitable reducing agents for use in the initiator stream include sulfur
dioxide; alkali metal
disulfites; alkali metal and ammonium hydrogen sulfites; thiosulfate,
dithionite and
formaldehyde sulfoxylates; hydroxylamine hydrochloride; hydrazine sulfate;
glucose and
ascorbic acid. Preferably, the reducing agent is sodium formaldehyde
sulfoxylate dihydrate
(SFS). The reducing agent is typically present in an amount between about 0.01
and 1 % by
weight based on total monomer weight. In addition, the weight ratio of
reducing agent to free
radical generator is preferably between about 0.2:1 and 1:1.
The water-soluble metal salt of iron, copper, cobalt, nickel, tin, titanium,
vanadium,
manganese, chromium or silver can be chosen from a wide variety of water-
soluble metal salts.
Suitable water-soluble metal salts include copper (II) amine nitrate, copper
(II) metaborate,
copper (II) bromate, copper (II) bromide, copper perchlorate, copper (II)
dichromate, copper (II)
nitrate hexahydrate, iron (II) acetate, iron (III) bromide, iron (III) bromide
hexahydrate, iron (II)
perchlorate, iron (III) dichromate, iron (III) formate, iron (III) lactate,
iron (III) malate, iron (III)
nitrate, iron (III) oxalate, iron (II) sulfate pentahydrate, cobalt (II)
acetate, cobalt (II) benzoate,
cobalt (II) bromide hexahydrate, cobalt III chloride, cobalt (II) fluoride
tetrahydride, nickel
hypophosphite, nickel octanoate" tin tartratte, titanieum oxalate, vanadium
tribromide, silver
nitrate and silver fluosilicate. The metal can also be complexed with a
compound such as
ethylene diamine tetracetic acid (EDTA) to increase its solubility in water.
For example,
irouEDTA complexes or cobalt/EDTA complexes can be used. Preferably, the water
soluble
metal salt is used as an iron (II) sulfate EDTA complex. The water-soluble
metal salt is typically
present in an amount less than 0.01 % by weight based on total monomer weight.
The polymerization reaction can be conducted in the presence of C8 to C12
mercaptans,
such as octyl, nonyl, decyl or dodecyl mercaptans, which are used as molecular
weight regulators
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or chain transfer agents to reduce the molecular weight of the SBR polymer.
Typically, either n-
dodecyl or t-dodecyl mercaptan is used and t-dodecyl mercaptan is the most
commonly used.
The amount of t-dodecyl mercaptan used will depend upon the molecular weight
that is desired
for the SBR. Larger quantities of t-dodecyl mercaptan cause greater reductions
in the molecular
weight of the SBR. The amount of t-dodecyl mercaptan is preferably between
about 0.05 and
0.5%.
The monomer feed, soap feed and activator feed are separately fed to a reactor
where
polymerization of the styrene and t-butadiene monomers occurs. The total
amount of water in
the reactors is typically 60-75% by weight based on total monomer weight. The
emulsion
polymerization reaction normally produces between about 60% and about ~0%
conversion of the
styrene and butadiene monomer into polystyrene-butadiene) or SBR particles.
Once the above level or conversion is reached, the polymerization reaction is
terminated
by addition of a shortstop to the last of the reactors in series, which reacts
rapidly with free
radicals and oxidizing agents, thus destroying any remaining initiator and
polymer free radicals
as well as preventing the formation of new free radicals. Exemplary shortstops
include organic
compounds possessing a quinoid structure (e.g., quinone) and organic compounds
that may be
oxidized to quinoid structures (e.g. hydroquionone), optionally combined with
water soluble
sulfides such as hydrogen sulfide, ammonium sulfide or sulfides or
hydrosulfides of alkali or
alkaline earth metals; N-substituted dithiocarbamates; reaction products of
alkylene polyamines,
with sulfur containing presumably sulfides, disulfides, polysulfides and/or
mixtures of these and
other compounds; dialkylhydroxylamines; N,N'-dialkyl-N,N'-methylenebishydioxyl-
amines;
dinitrochlorobenzene; dihydroxydiphenyl sulfide, dinitrophenylbenzothazyl
sulfide and mixtures
thereof. Preferably, the shortstop is hydroquinone or potassium diethyl
dithiocarbamate. The
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short stop is typically added in an amount between about 0.01 and 0.1% by
weight based on total
monomer weight:
As mentioned, the SBR polymer can also be.produced using a batch process. In
the batch
process, the monomers, the soap, the free radical generator and water are all
added to the reactor
a~td agitated. After reaching the desired polymerization temperature, an
activator solution,
including the reducing agent and one of the previously water soluble metal
salts are added to
initiate polymerization. A short stop is added to terminate the polymerization
once the desired
conversion level is reached.
Once polymerization is terminated (in either the continuous or batch process),
the
unreacted monomers are then typically removed from the latex dispersion. For
example, the
butadiene monomers can be removed by flash distillation at atmospheric
pressure and then at
reduced pressure. The resulting styrene monomers can be removed by steam
stripping in a
column. The resulting SBR latex at this point typically has a solids content
of less than 50%.
The SBR latex is then preferably agglomerated, e.g., chemical, freeze or
pressure agglomeration,
and water is removed to increase the total solids content up to about 72%.
When polymerization is terminated, butadiene and styrene mononers removed, the
solids
content is below 50%, and also latex particle size is below 100nm, typically
50-70nm. For these
small particles and very narrow size distribution, the latex viscosity becomes
above 1000cP
(leas) at above 50% solids content. This latex is then agglomerated to produce
larger particles,
with a distribution of particle size ranging from 100nm to between 2 and 3
microns. The result is
to substantially decrease the viscosity of the latex, to about SOmPas or less
at about 50%. Even
after removal of water, leaving the solids content at 70-72%, the viscosity of
the SBR latex is
below 2000cP (2Pas).
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Agglomeration can be carried out by two basic chemical or physical methods.
Agglomeration processes are described in detail in Polymer Latices, Science
and Technology,
Volume 2: Types of Latices by D.C. Blackley, 2°d Edition, Chapman &
Hall. The presently
preferred methods are physical methods. The physical methods include (a)
agglomeration by
subjecting the latex to freezing and thawing, and (b) agglomeration by
subjecting the latex to
mechanical agitation. Freeze agglomeration simply involves freezing the latex
dispersion,
followed by thawing. The result is to produce larger size latex particles,
with a broader
distribution of particle size. Agglomeration by mechanical agitation may be
effected by
pumping the latex through a confined space, which subjects the latex
dispersion to high pressure,
and thus causes agglomeration of the latex particles.
Coagglomeration may be defined as a process in which the particles of two or
more
dissimilar latices are agglomerated to form heterogeneous composite particles
in which the
particles of one type of latex have become embedded in the particles of
another, but otherwise
retain their identity. Coagglomeration has been applied particularly to
mixtures of synthetic
latices of rubbery polymer and glassy polymers. The objective is to produce
lances which
contain composite particles comprising both rigid domains and rubbery domains.
Films dried
down from such latices comprise an intimate mixture of the two types of
particles, and in
consequence exhibit some degree of particulate reinforcement.
United States patent 6,127,461 "Co-agglomeration Of Random Vinyl Substituted
Aromatic/Conjugated Diolefm Polymer With Sulfur To Improve Homogeneity Of
Polymer/asphalt Mixtures," by I~. Takamura et. al, further extends this co-
agglomeration
process to beyond polymer latices. The '461 patent refers to coagglomeration
of SBR latex
and/or polybutadiene particles with organic and inorganic particles including
sulfur and a
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vulcanizing agent as an accelerator. In that invention, co-agglomeration means
that the latex
particles are agglomerated with another solids dispersion, including semi-
micron size organic
and inorganic particles. The result is that the solids dispersions, such as
sulfur and vulcanizing
agent are agglomerated within the latex polymer particles.
With regard to the present invention, more specifically, elemental sulfur is
added at 2%
as a dispersion is preferred. Bostex 410 (68% elemental sulfur as a
dispersion), available from
Akron Dispersions is most preferred. The preferred vulcanizing agent is
diphenylguanidine,
available as Paracure DPG-38 from Parachem Specialties, which is added at
0.2%. Co-
agglomeration may be carried out by either of the methods already discussed.
Freeze
coagglomeration involves a single cycle of freezing and thawing, followed by
removal of water.
For pressure coagglomeration the mixture is subjected to high shear. An
important advantage of
co-agglomeration of the asphalt emulsion of the present invention is that the
sulfur and
accelerator are not diluted, but remain at a relatively high concentration.
Asphalt Emulsion
Asphalt emulsions used in road construction and maintenance are either anionic
or
cationic, based on the electrical charge of the asphalt particles, which is
determined by the type
of the emulsifying agent used. The asphalt contents of these emulsions are, in
most cases, from
55 to 75% and prepared using a high shear mechanical device such as a colloid
mill. The colloid
mill has a high-speed rotor that revolves at 1,000-6,OOOrpm with mill-
clearance settings in the
range of 0.2 to O.Smm. A typical asphalt emulsion has a mean particle size of
2-5 micrometer in
diameter with distribution from 0.3 to 20 micrometer. United States patent
5,180,428 refers to a
non-ionic surfactant for ease of emulsion preparation with non-ionic
chloroprene latex. This
invention employs a cationic emulsifier-cationic latex, or non-ionic
emulsifier-cationic latex
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combination for better asphalt adhesion to aggregate, which results in
enhanced asphalt
antistripping capability.
Cationic emulsifying agents useful in the preparation of asphalt emulsions in
accordance
with the present invention are available from Akzo Nobel under the brand
Redicote, including
Redicote E-4819; E-64R, E4819-3, E-9, E-9A, and E-5. Westvaco cationic
emulsifiers sold
under the marks Imapct SBT, Impact CB1, and CB2, Induline AMS, Qts, Molc-2M
and-1M,
Indulin MQK, W-5 and 2-1. Arosurf brand cationic emulsifiers made by
Goldshmidt for CRS,
CMS and CSS are also useful. The emulsifier level in the asphalt emulsion can
be ranging from
0.2 to 0.5 percent to the asphalt by weight for the rapid setting emulsion, to
as much as 2.0 to 3.0
percent for the slow setting emulsions.
Asphalt emulsions in accordance with the invention may be prepared by mixing
the
emulsifying agent and co-agglomerated latex into water and adjusting this
emulsifier solution to
pH below 3 with an inorganic acid. The emulsifier solution could be adjusted
from slightly
above the room temperature to up to 40°C. Separately, the asphalt is
heated to 130 to 160°C,
depending upon the viscosity of the asphalt used. For example, a low viscosity
asphalt such as
AC-5 could be only heated to 130°C, in contrast, it could be as high as
160°C for AC-20 and
AC-30 asphalts. The emulsifier solution and heated asphalt are injected into
the colloid mill to
produce the asphalt emulsion. The ratio of the asphalt and emulsifier solution
is adjusted to
produce the asphalt emulsion containing a desired amount asphalt contents,
which can be from
55 to 75%.
In the above-described method, the co-agglomerated latex is added into the
aqueous
emulsifier solution. Alternatively, the asphalt emulsion can be produced with
direct injection,
where the emulsifier solution without the latex and asphalt are injected into
the colloid mill
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through a series of pipes, while the latex is directly injected into the
asphalt line just ahead of the
colloid mill. The latex modified asphalt can also be produced by post-
addition, where the
desired amount of the co-agglomerated cationic latex is added into a pre-
manufactured asphalt
emulsion prepared without the latex.
Asphalt emulsions are classified with their charge and on the basis of how
quickly the
asphalt will coalesce, which is commonly referred to as breaking, or setting.
The terms RS, MS
and SS have been adopted to simplify and standardize this classification. They
are relative terms
only and mean rapid-setting, medium-setting and slow setting. A rapid setting,
RS, emulsion has
little or no ability to mix with an aggregate. A medium setting, MS, emulsion
is expected to mix
with coarse but not fme aggregate, and a slow setting, SS, emulsion is
designed to mix with fine
aggregate. The cationic emulsions are denoted with the letter "C" in front of
the emulsion type,
and the absence of the "C" denotes anionic. Thus CRS is a cationic rapid
setting emulsion
typically used for chip seal application. This new invention disclosed herein
utilizes the cationic
latex instead of non-ionic, thus opens new possibilities of preparing the
asphalt emulsions having
different setting characteristics such as CRS, CMS, and CSS to take advantages
of well-practiced
industrial methods for producing the asphalt emulsions for specific
applications, such as chip
seal, slurry seal, microsurfacing, sand seal, fog seal, etc., by choosing
desired types and amount
of cationic emulsifiers to prepare the emulsion.
Example 1
PASS emulsion without latex polymer was obtained from Western Emulsion. This
emulsion was
produced according to their original patent with Oxnad AC-20 asphalt, RA-1 and
non-ionic
surfactant (Indulin XD-70 from Westvaco). Neoprene and cationic co-
agglomerated SBR latex
modified PASS emulsions were prepared by adding desired amount of the latex
dispersion into
this unmodified emulsion. The asphalt emulsion residue was recovered at room
temperature by
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drying the emulsion for 1 day under forced airflow described in (K. Takamura,
Comparison of
emulsion residues recovered by the forced airflow and RTFO drying, AEMA/ISSA
Proceedings,
2000, 1-17). Table 1 lists measured complex modulus of the emulsion binder at
50°C as a
function of the polymer content in the PASS emulsion.
level in the emulsion
Latex t a 1 % 2% 3%
Neoprene 0.70 0.8 0.85
SBR Latex 0.83 1.1 1.2
The complex modulus represents the strength of the emulsion residue under
controlled stress and
strain representing the traffic condition. One day drying under forced airflow
represents initial
strength development of the asphalt emulsion binder after application. Table 1
demonstrates that
the cationic coagglomerated SBR latex develops the strength at lower polymer
level than the
Neoprene latex.
Example 2
The strength development of the PASS emulsion binder for few weeks to months
after
application was tested using the same Dynamic Shear Rheometry. Here, The PASS
emulsions
containing 2% and 3% polymer by weight against asphalt + RA-1 were dried as
example 1. After
1 day forced airflow drying, the emulsion residue was stored in an oven at
60°C for 10 days and
the complex modulus of the residue was measured at 1 day, 3 days, 7 days and
10 days curing in
the oven at 60°C. This temperature represents the maximum road surface
temperature in use.
Table 2 and 3 list measured complex modulus as a function of curing time.
These results clearly
demonstrate early strength development of the PASS emulsion modified with
Cationic co-
a~~lomerated SBR latex against Neoprene modified PASS emulsion.
Table 2 Complex modulus of the cured emulsion residue at 50°C
2% polymer Curin
time
in the
oven
at 60C
0 da 1 da 3 da 7 da 10 da
Neo rene 0.80 1.1 1.1 1.2 1.4
SBR Latex 1.1 1.5 1.8 2.0 2.1
Table 2 Complex modulus of the cured emulsion residue at 50°C
3% Polymer Curin
time
in the
oven
at 60C
0 da 1 da 3 da 7 da 10 da
Neo rene 0.85 1.2 1.6 1.7 2.2
SBR Latex 1.2 2.0 2.3 2.3 2.3
SUBSTITUTE SHEET (RULE 26)
