U.S. patent application number 10/146293 was filed with the patent office on 2003-11-20 for polymer modified asphalt emulsions for treatment of road surfaces.
Invention is credited to Takamura, Koichi.
Application Number | 20030215286 10/146293 |
Document ID | / |
Family ID | 29418790 |
Filed Date | 2003-11-20 |
United States Patent
Application |
20030215286 |
Kind Code |
A1 |
Takamura, Koichi |
November 20, 2003 |
Polymer modified asphalt emulsions for treatment of road
surfaces
Abstract
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, co-agglomerated
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 the 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 by application of
the disclosed compositions.
Inventors: |
Takamura, Koichi;
(Charlotte, NC) |
Correspondence
Address: |
MANATT, PHELPS & PHILLIPS, LLP
11355 West Olympic Boulevard
Los Angeles
CA
90064
US
|
Family ID: |
29418790 |
Appl. No.: |
10/146293 |
Filed: |
May 14, 2002 |
Current U.S.
Class: |
404/17 |
Current CPC
Class: |
E01C 7/187 20130101;
C08L 53/02 20130101; C08L 9/06 20130101; C08L 95/005 20130101; C08L
95/005 20130101; C08L 95/005 20130101; C08L 53/00 20130101; C08L
2666/08 20130101 |
Class at
Publication: |
404/17 |
International
Class: |
E01C 007/00 |
Claims
I claim:
1. A composition for rejuvenating asphalt pavement comprising, a.
asphalt, b. a cationic surfactant, c. a recycling agent, and d. a
co-agglomerated styrene butadiene rubber latex.
2. The composition for rejuvenating asphalt paving of claim 1
further comprising sulfur.
3. The composition for rejuvenating asphalt paving of claim 1
further comprising a vulcanizing agent.
4. The composition for rejuvenating asphalt pavement of claim 1,
wherein the viscosity of a mixture of the recycling agent and
asphalt is between 1,000 and 3,000 centipoise.
5. An asphalt emulsion comprising a co-agglomerated styrene
butadiene rubber latex.
6. The asphalt emulsion of claim 5 further comprising a cationic
surfactant.
7. The asphalt emulsion of claim 5 further comprising a vulcanizing
agent.
8. The asphalt emulsion of claim 7 wherein the vulcanizing agent is
diphenylguanidine.
9. The asphalt emulsion of claim 5 further comprising a dispersion
of elemental sulfur.
10. An asphalt emulsion for treatment of aged and cracked asphalt
prepared by a method comprising a. generating free radicals in a
stream of soap b. and activating a redox initiator system.
11. The asphalt emulsion of claim 10, further comprising a redox
initiator system comprising a reducing agent, and a water soluble
metal salt.
12. The asphalt emulsion of claim 11 wherein the water soluble
metal salt is selected from the group consisting of iron, copper,
cobalt, nickel, tin, titanium, vanadium, manganese, chromium and
silver.
13. The asphalt emulsion of claim 12 wherein the reducing agent is
sodium formaldehyde sulfoxylate dihydrate.
14. A method for producing latices which contain both rigid domains
and rubbery domains by agglomerating latex particles with another
solids dispersion.
15. A method for preparing a polymer modified asphalt emulsion
comprising by agglomerating a first dispersion of SBR latex with a
second dispersion that includes sulfur and a vulcanizing agent.
16. The method of claim 15, wherein the second dispersion comprises
diphenylguanidine and elemental sulfur.
17. A method for preventing reflective cracking comprising the
application of a thin film of the composition of claim 1
hereof.
18. A method for the rejuvenation of aged and cracked asphalt
surfaces comprising application of the composition of claim 1.
Description
[0001] 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
[0002] 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 between a country's economic development
and its road infrastructure.sup.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
replacement.sup.2. Accordingly, improvement in the technology for
maintaining existing roadways is desirable. .sup.1 C. Queroz, R.
Haas, and Y Cai, "National Economic Development and Prosperity
Related to Paved Road Infrastructure" Transportation Research
Record, 1455 (1994). .sup.2 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.
[0003] 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-like cracks, known as
fatigue fracture.
[0004] 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 wasteful.sup.3. A preferable approach
involves surface treatment of the existing pavement to restore the
pavement to its condition when first laid down.sup.4. For example,
U.S. Pat. No. 5,180,428 to Richard D. Koleas 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. .sup.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 Textbook, 2.sup.nd Edition, 1999. .sup.4 K. Takamura, K.
P. Lok, R. Wittlinger, "Microsurfacing for Preventive Maintenance:
Eco-Efficient Strategy", ISSA Annual Meeting, March 2001.
[0005] 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.
[0006] 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 crack 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
[0007] 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 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
[0008] 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
[0009] 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 U.S. Pat. No. 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.
[0010] 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.
[0011] Asphalt and Recycling Agent
[0012] 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.
[0013] 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.degree. C.
[0014] 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.
[0015] The preferred recycling agents are available from Sunoco
under their Hydrolene.RTM. 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.
[0016] Preparation of Styrene Butadiene Latex
[0017] 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.degree. C., and more
preferably between 5.degree. C. and 25.degree. 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-butadienie 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.
[0018] 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 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 78:22.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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, iron/EDTA 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.
[0024] 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 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%.
[0025] 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 80% conversion of tile styrene and
butadiene monomer into poly(styrene-butadiene) or SBR
particles.
[0026] 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'-methylenebishydroxyl-amines;
dinitrochlorobenzene; dihydroxydiphenyl sulfide,
dinitrophenylbenzothazyl sulfide and mixtures thereof. Preferably,
the shortstop is hydroquinone or potassium diethyl dithiocarbamate.
The short stop is typically added in an amount between about 0.01
and 0.1% by weight based on total monomer weight.
[0027] 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 and
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.
[0028] 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%.
[0029] When polymerization is terminated, butadiene and styrene
mononers removed, the solids content is below 50%, and also latex
particle size is below 100nm, typically 50-70 nm. For these small
particles and very narrow size distribution, the latex viscosity
becomes above 1000 cP (1 Pas) at above 50% solids content. This
latex is then agglomerated to produce larger particles, with a
distribution of particle size ranging from 1 00nm to between 2 and
3 microns. The result is to substantially decrease the viscosity of
the latex, to about 50 mPas 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 2000 cP (2 Pas).
[0030] 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.sup.nd 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.
[0031] 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 latices
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.
[0032] U.S. Pat. No. 6,127,461 "Co-agglomeration Of Random Vinyl
Substituted Aromatic/Conjugated Diolefin Polymer With Sulfur To
Improve Homogeneity Of Polymer/asphalt Mixtures," by K. Takamura
et. al, further extends this co-agglomeration process to beyond
polymer latices. The '461 patent refers to coagglomeration at SBR
latex and/or polybutadiene particles with organic and inorganic
particles including sulfur and a 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.
[0033] 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 fromn
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.
[0034] Asphalt Emulsion
[0035] 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 1,000-6,000 rpm with
mill-clearance settings in the range of 0.2 to 0.5 mm. A typical
asphalt emulsion has a mean particle size of 2-5 micrometer in
diameter with distribution from 0.3 to 20 micrometer. U.S. Pat. No.
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 combination for better asphalt adhesion
to aggregate, which results in enhanced asphalt antistripping
capability.
[0036] 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 Impact SBT, Impact CB1,
and CB2, Induline AMS, Qts, Mok-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.
[0037] 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.degree. C.
Separately, the asphalt is heated to 130 to 160.degree. 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.degree. C., in contrast, it could be as high as 160.degree. 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%.
[0038] 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 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-mantifactured asphalt emulsion
prepared without the latex.
[0039] 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
fine 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
[0040] 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 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.degree. C. as a function of the polymer
content in the PASS emulsion.
1TABLE 1 Measured complex modilus of the emulsion residue at
50.degree. C. Polymer level in the emulsion Latex type 1% 2% 3%
Neoprene 0.70 0.8 0.85 SBR Latex 0.83 1.1 1.2
[0041] 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
[0042] 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.degree. 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.degree. 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-agglomerated SBR latex against
Neoprene modified PASS emulsion.
2TABLE 2 Complex modulus of the cured emulsion residue at
50.degree. C. Curing time in the oven at 60.degree. C. 0 day 1 day
3 day 7 day 10 day % polymer Neoprene 0.80 1.1 1.1 1.2 1.4 SBR
Latex 1.1 1.5 1.8 2.0 2.1 3% Polymer Neoprene 0.85 1.2 1.6 1.7 2.2
SBR Latex 1.2 2.0 2.3 2.3 2.3
[0043] The invention has been disclosed in terms of various
embodiments. Those embodiments are merely illustrative, and should
not be understood as limiting the scope of the invention, which is
instead defined by the claims appended hereto.
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