CA1114545A - Open-graded asphalt emulsion mixes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
OPEN-GRADED ASPHALT EMULSION MIXES

An open-graded emulsified asphalt paving mix is provided comprising a major portion of open-graded aggregate and a minor portion of cationic or anionic bituminous emulsion, the mix containing a minor portion of a polyelectrolyte having the opposite electric charge from that of the asphalt emulsifier which imparts excellent water resistance properties to pavement prepared from the mix. A method for producing the polyelectrolyte in situ is also provided.

Description

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Field of the Invention This application relates to open-graded, emulsified asphalt pave-.. : .*
ments, compositions suitable for their preparation, and methods for their ~;
preparation.
Open-graded pavements are generally defined in the paving art as :
aggregate blends o~ asphalt mixtures which have high voids content. The ~-pavements may be prepared with either hot-mix asphalt or with asphaltic -emulsions. They possess the characteristics of relatively low cost, and the ability to allow water drainage through the pavement structure. This last feature makes the pavements particularly desirable for overlays on existing high-speed highways to prevent "hydroplaning" vehicle skids caused by a film of water created between a smooth pavement surface and the tire surface. ;~
The open-graded, emulsified asphalt pavements are of particular ~
interest in remote areas far from plants where hot-mix asphalts are avail- -able. With the use of the emulsified asphalts, blending of the emulsions with the aggregates may be performed in blending plants set up easily in the remote areas.
With the use of emulsified asphalts in constructing open-graded -~
pavements, several problems have, however, arisen. Because of the porous nature of the mix, the use of conventional slow setting emulsions (SS type) is not feasible. In such case, substantial amounts of the emulsion will drain from the structure (runoff) before setting occurs, resulting in loss of ~ - ., asphalt. The onset of rain before complete set occurs will result in the -loss of even more asphalt from the pavement (washoff). Both runoff and washoff result in loss of strength in the pavement and possible environmental contamination. Therefore, to reduce these problems, the emulsions used in -~
these applications have been weakly stabilized medium setting (MS type) so designed that they "break" when mixed with the aggregate. However, because of this early break, incomplete coating of the aggregate and poor adhesion -1- ~

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of the asphalt and aggregate often occurs. In most cases, these results have been ameliQrated by the addition of substantial quantities (5-15%, ;
usually 8-10%, by weight relative to the weight of emulsion) of petroleum naphtha to the mixes. This results in softening of the asphalt providing -better coverage and adhesion. -However, with the use of naphtha, new problems have arisen. First, -~
however, with the use of naphtha, the cost is high for the naphtha which is ;
simply lost to the atmosphere by evaporation. Second, evaporation of the naphtha raises possible air pollution problems. Third, the hazard of fire during the operation is enhanced. Fourth, because naphtha softens the asphalt, the pavement requires considerable time to achieve full strength, and the use of heavy vehicles on the pavement before full strength is ~ -achieved may result in rutting of the surface. Therefore, it is desirable to produce open-graded emulsified asphalt paving mixes which display good ~ . . . ,, ;: , , aggregate coating properties and achieve desirable runoff and washoff characteristics without the use of naphtha, and form pavements which develop their full strength rapidly.
Description of the Prior Art Anionic polyelectrolytes such as the salts of synthetic poly-20 carboxylic acids have been discIosed as primary emulsifiers and emulsion stabilizers, although not specifically for bitumens. Rohm and Haas Co. has described the use of neutralized acrylic polyacids marketed as "ACRYSOLS" as emulsifiers and as emulsion stabilizers with emulsions produced with nonionic emulsifiers. -~
Cationic polyelectrolytes, such as the quaternary salts of poly- "~
vinyl pyridine have also been disclosed for use as emulsion stabilizers and emulsifiers (reference: "Cationic Quaternary Polyelectrolytes - A
Literature Review", M. Fred ~oover, a paper presented at the 159 National ACS Meeting, September 9, 1969).
SUMMARY OF THE INVENTION
We have now found that superior open-graded emulsified asphalt pave-

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ment can be prepared from a novel mixture of open-graded aggre-gate, a cationic or anionic (i.e., an ionic) emulsified asphalt, and a minor amount of an ionic polyelectrolyte which has the op-posite charge to that of the asphalt emulsifier. These mixes ~ -~
give excellent aggregate coating, provide pavements which rapidly reach maximum strenght, possess excellent water resistance prop-erties (resistance to washoff and low runof~f) without the pres-ence of petroleum naphtha. Both cationic emulsified asphalt with a minor amount of an anionic polyelectrolyte and an anionic em-ulsified asphalt with a minor amount of a cationic polyelectro-lyte are contemplated.
According to one aspect of the present invention there is prov~ded an ionically charged bituminous emulsion comprising from 40% to 75% by weight of asphalt, from 0.25 to 5.0% by weight of an ionically charged emulsifier, from 0.01 to 3.0% by weight -of a synthetic polyelectrolyte precursor capable of being ionized into a polyelectrolyte having an ionic charge opposite to the -ionic charge of said emulsifier, and water as a continuous phase to make up 100% by weight.
According to another aspect of the present invention there is provided a process for preparing a paving composition by depositing asphalt from an asphalt emulsion onto an aggregate, said process compriSing: mixing an aggregate in any order with water, an ionically charged bituminous emulsion, and a poly-electrolyte having a charge opposite to said emulsion, wherein said ag~regate is about 80 to 97% by weight of said paving compo-sition, said water, said emulsion and said polyelectrolyte are about 3 to 20% by weight of said paving composition and said polyelectrolyte is from 0.01 to 3.0% by weight relative to the emulsion.
In a preferred embodiment, an anionic polyelectrolyte will be produced in situ, i.e., by basification of the emulsion -45~ :

which will contain a minor portion of a polyelectrolyte pre-cursor (PEP), a polymeric polyacid.
The application of these open-graded, emulsified asphalt :~:
mixes may be carried out in several ways, which are as follows: ;
(1~ A polyelectrolyte may be added to the emulsion and the mixture may be stored for a relatively short time, i.e., up to 4 hours. In some specific cases, the mixture may be stored for as long as 100 hours. The emulsion is then mixed with the ag~regate shortly before application to the road bed or road ~;
surface. This method, as well as all of the others, allows sufficient working time of the mix to allow working (screeding, ~ ; -etc.) of the mix before it hardens.
(2~ The aggregate may be pretreated with the poly- ~`
electrolyte, and mixing of the emulsion with the aggregate takes place shortly before application of the mix.

(3) The aggregate, emulsion and polyelectrolyte may be mixed at one time shortly before application.
Three additional methods may also be carried out with ;-cationic emulsions only.
~4) A PEP may be used to pretreat the aggregate, and ~
then the emulsion, in a form sufficiently basic to convert the - -PEP to the polyelectro- -, :,.
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lyte form, may be mixed with the aggregate.
(5) The aggregate, the PEP and the emulsion may be mixed together at one time, and the mix basified by mixing in adequate base to neutr'alize the precursor before use.
(6) A preferred method is to add the PEP to the emulsion, and mix the emulsion with the aggregate and base prior to use. The PEP-containing emulsion in this case may be stored for long periods.
One type of suitable asphalt emulsion is prepared with cationic emulsifiers. Among those are the emulsions described in United States Patents 3,026,266, 3,096,292, 3,220,953, and 3,445,258. Any suitable cationic emulsifier capable of emulsifying bitumen in water may be used including -~
cation active salts of quaternary nitrogen bases, salts of fatty amines, preferably straight-chain primary fatty mono and diamines, amidoamine salts, such as amidoamine hydrochloride of stearic acid, etc., the hydrohalide salts of aminoamides of polyalkylene polyamines such as tetraethylene pentamines and fatty acids, etc. Another class of suitable emulsifiers is that including the salts of ethylene oxide adducts of fatty diamines and of the ethylene oxide adducts of hytrocarbon-substituted imida~olines. This list is, of course, only illustrative, and not inclusive. The use of mix-tures of the various cationic emulsifiers is also contemplated. The pre-ferred cationic emulsifiers are those described as the salts of quaternary nitrogen bases disclosed in United States Patent 3,220,953. These compounds are those materials of the preferred formula - R2 1 +
Rl I R3 X
14 _ n R m in which Rl, R2, R3 and R4 are organic radicals, each having a carbon-nitrogen linkage to the nitrogen atom, X is an anion whose valence does not exceed 2, and m and n are small integers which indicate the molar proportions of the cation and anion required to form the respective salt. Preferred ~4 5;~
'; '', ` , emulsifying salts are those in which the organic radicals Rl, R2, R3 and R4 are alkyl, alkenyl, hydroxyalkyl, arylalkyl or alkylaryl radicals of 1 to 24 carbon atoms or heterocyclic groups of 4 to 10 carbon atoms in which from 2 to 3 of the nitrogen valences are shared by two carbon atoms in a single heterocyclic group. In all of these salts of quaternary nitrogen bases suit-able for use as cationic emulsifiers in the preparation of oil-in-water type emulsions, the aggregate number of carbon atoms in the cationic portion of their molecule should be large enough to impart oil solubility and emulsify-ing properties, and preferably should be equal to and not less than 15 and `~` -not more than 30 carbon atoms. In other words, this class of cationic ' quaternary nitrogen-containing compounds is formed by salts of tetra- -`
substituted ammonium bases and by salts of heterocyclic nitrogen bases, such `
as pyridinium, quinolinium, isoquinilinium, morpholininium, piperidinium, imidazolinium, and other like quaternary nitrogen-containing bases. The anion may be either a halide (X~), a methosulfate (S04CH3-), a nitrate (N03-) or the like ion. Monovalent anions are preferred, particularly the halide anions. `
Numerous cationic quaternary nitrogen-containing emulsifiers may ~;
be employed or the preparation of cationic oil-in-water-type emulsions.
Among them, to mention but a few, are:
N,N-dimethyl-N-benzyl-N-octadecyl ammonium chloride N~N-dimethyl-N-hydroxyethyl-N-dodecyl ammonium chloride N,N-dimethyl-N-benzyl-N-octadecenyl ammonium chloride ' N,N-dimethyl-N-benzyl-N-dodecyl ammonium chloride N,N-dimethyl-N-hydroxyethyl-N-benzyl ammonium chloride ",, !
Hexadecyl pyridinium chloride Hexadecyl triethyl ammonium bromide Octadecylbenzyl trimethyl ammonium methosulfate Isopropylnaphthyl trimethyl ammonium chloride Octadecyl pyridinium bromide `:

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1-(2-hydroxyethyl)-2-heptadecenyl-1-(4-chlorobutyl) imidazolinium chloride i Hexadecyl methyl piperidinium methosulfate Dodecyl hydroxyethyl morpholinium bromide -Among the quaternary nitrogen-containing materials available in -commerce as cationic emulsifiers for the preparation of oil-in-water type emulsions, there are quaternary ammonium salts, such as quaternary ammonium .halide materials sold by General Mills under the trademark "ALIQUAT"; mater- ~ials sold by Armak Company under the several "ARQUAD" trademarks; certain - ~;
quaternized materials developed and sold by the Society of Chemical Industry, ~-in Basel, Switzerland, under the several "SAPAMINE" trademarks, and many others.
The active cationic component of these materials contains the characteristic positively charged quaternary nitrogen configuration ~ R2 +

- R4 - `

in which the aggregate of carbon atoms of Rl, R2, R3 and R4 is sufficient to impart oil solubility and emulsifying properties, and preferably is equal to not less than 15 and not more than 30 carbon atoms.
Best emulsification can be achieved with those among the aforesaid quaternary nitrogen-containing materials in which the active cationic com- ;
ponent contains at least one long aliphatic hydrocarbon chain of not less ~than 12 and not more than 24 carbon atoms, such as an alkyl or an alkenyl ~-chain. This latter chain may be derived from a mixture of organic materials -such as tallow, soybean oil, lard, etc. ~ -The emulsifier material may consist entirely of an active cationic salt of a quaternary nitrogen base, or may also contain some impurities, such as acyl chlorides and amines. It may also be employed in the form of a con- -centrated aqueous solution and may contain auxiliary stabilizers in amounts ~ ~4~

conventionally employed in the trade. -Among the available commercial emulsifier materials of this type, the following may be employed for the preparation of cationic emulsions in accordance with the invention:
(1) HYAMINE 2389. This is the trademark of a product of Rohm and ~ ~
Haas Chemical Company, of Philadelphia, Pennsylvania, for N-alkyl methyl `
benzyl-N,N,N-trimethyl ammonium chloride, which has the following formula :
~ 1 3 f 3 L ~ CU~-3-C33 I Cl wherein R averages about 12 carbon atoms. -. ~:
(2) ARQUAD T. This is the trademark of a product of Armak Company of Chicago, Illinois, for C14-C18 alkyl trimethyl am~onium chloride, which ;
has the following formula~

R - N - CH Cl wherein R i8 a long alkyl chain derived from tallow.
(3) HYAMINE 1622. This is the trademark of a product of Rohm and Haas Chemical Company of Philadelphia, Pennsylvania, for di-isobutyl phenoxy- , ." - ~,.. .
ethoxy ethyl dimethyl benzyl ammonium chloride monohydrate of the formula CCH3'C(CH3)2-CH2(CH3)2 C6H5 OCH2 2 OCH2CH2N (CH3 ) 2~ CH2C6H5~ +Cl- . ~ -,

(4) ARQUAD S. This is the trademark of a product of Armak Company of Chicago, Illinois, for C16-C18 alkyl trimethyl ammonium chloride, which has the formula:

... . . . . .. ...... . , . .. . " . . ~ ~ ,, j ~ L4~5~3~ ~

CH3 +
R - N CH Cl CH
wherein R is a long alkyl chain derived from soybean oil.
It is believed that minor amounts of the starting materials ordinarily are present in the aforementioned emulsifiers as impurities of no -~consequence to their operativeness according to the invention. -~
These and other suitable cationic emulsifiers may be employed in varying amounts, generally from about 0.25 to about 5%, and preferably from about 0.40 to about 2% of the active cationic component, based on the weight ~;
.. .~
of the finished emulsion, although more or less may be employed depending ~ ~-upon factors such as the cost of the emulsifier, its effectiveness as an emulsifying agent, the amount of bitumen dispersed, etc. The asphalt will be present in the emulsion in the amount of from about 40 to 75, preferably 60 to 70, weight percent relative to the emulsion. The balance of the emulsion will be water to make 100%.
Another type of suitable asphalt emulsion is prepared with anionic emulsifiers. Among those are the emulsions described in Canadian Patent 812,658, British Patents 864,102; 1,149,257; and 1,165,517, and United States Patents 2,730,506; 2,436,046; 2,855,319; and 2,512,580. Any suitable anionic emulsifier capable of emulsifying bitumen in water may be used, including the alkali metal salts of sulfonic acids and carboxylic acids.
Carboxylic acid emulsifiers include the salts of fatty acids, ~ ~
naphthenic acids and cresylic acids. These salts are usually made from the ~ 3 alkali metals, and sodium is the preferred metal. The carboxylic acid salts are preferred.
Other carboxylic acid emulsifiers include the salts of tall oil .-acids, rosin acids, fatty acid pitch (residue from fatty acid distillation) and pine chip resin extract. This latter is the preferred carboxylic acid `~emulsifier.

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The sulfonic acids used for forming anionic emulsions include the alkylaryl sulfonates having molecular weights in the range of 400 to 500, `~
e.g., Bis(dodecylphenyl) ether disulfonic acid, octadecylbenzene sulfonic acid, polypropylenebenzene sulfonic acid, dioctylbenzene sulfonic acid, etc.
All of the above acids are utilized as their alkali metal salts, preferably the sodium salt.
Naphthenic acids extracted from petroleum sources are good `
emulsifying agents for this purpose. The acid number of such naphthenic `
acids should be in the range of 75 to 175. -Polyelectrolytes are well-known substances (Encyclopedia of Polymer Science and Technology, Vol. 10, pages 781-854). Electrochemically ~ ~
a polyelectrolyte can be classified as polyacid, polybase or polyampholyte. ~-This application is principally concerned with the polyacid and polybase polyelectrolytes. The polyelectrolyte additives may be described as water soluble high-molecular-weight polymers or copolymers with ionized substituent groups along the backbone chain. These ionized groups may be anionic or cationic in nature. Suitable polyelectrolyte precursors (PEP) are high-molecular-weight polymers or copolymers with anionic ionizable groups along the chain. These ionizable groups, namely acid groups, are readily converted to ionized groups by the addition of an appropriate base. These materials (polyelectrolytes and PEP's) may be either natural or synthetic. Preferably, the polymers used in this application are essentially linear (i.e. non-crosslinked); however, a small amount of crosslinking is acceptable provided that the polymer remains water soluble. The polyelectrolytes and the PEP's will usually be synthetic polymers having average molecular weights (as measured by gel permeation chromatography) of at least about 1,000, prefer-ably 10,000 and as high as 10,000,000.
The anionic substituent ionized groups will be the salts of acidic -groups attached to the polymer backbone, including for example, carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, etc. Such acid _g_ - . . -. . ,. . .. :: : ;: -1~4~5 groups are attached directly to the carbon atoms of the backbone or attached through a connecting atom oratQms such as an oxygen or sulfur atom, an imino group, a polymethylene group or combinations thereof. Examples of this type attachment include monosulfate acid groups, monophosphate acid groups, methylene carboxylic acid groups, and the like. The preferred ionizable and ionized substituents are the carboxylic acid and carboxylic acid salts. There will usually be from 2, preferably 3, to about 30 carbon atoms per ionizable group. That is, the polymer monomers will usually have from 3 to 30 carbon atoms and 1 or more acidic groups.
Synthetic polymers and copolymers having ionizable or ionized groups useful for this purpose are readily prepared by polymerizing or copolymerizing the appropriate monomers. Preferably, the monomers consist of monounsaturated compounds which undergo additional polymerization to form long, linear, polymers or copolymers. The addition of small amounts of di- ~
or poly-unsaturated compounds will effect a small amount of crosslinking.
Non-crosslinked polyelectrolytes are preferred.
It is to be understood that the salt of the ionizable group and the ionizable group itself may be formed after the polymer has been made as, for example, by hydrolyzing an anhydride such as polymaleic anhydride, or by saponifying a polyester, or polyamid, e.g., polymethacrylate, or polyacryl-amide; or by hydrolyzing a nitrile group, e.g., polyacrylonitrile, etc.
Suitable acid or potential acid containing monomers for producing homo- or copolymers for this use include acrylic acid, acrylamide, acrylo-nitrile methyl acrylate, maleic anhydride, maleic acid, methacrylic acid, crotonic acid, allyloxyacetic acid, ethyl vinyl acetate, itaconic acid, citraconic anhydride, dimethyl fumarate, furfurylacrylic acid, 5-norbornene-2-acrylic acid, N-phenylmaleamic acid, vinyladipic acid, p-styrene sulfonic -acid, p-styrene sulfinic acid, ethylene sulfonic acid, allyl hydrogen sulfate, allyl dihydrogen phosphate, allyl methyl hydrogen phosphate, p-vinyl ;~
phosphonic acid, and the like.

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Suitable non-acid containing monomers useful for copolymerizing with one or more acid-containing monomers as, for example, from the above ~-list to form suitable polyelectrolytes include methyl vinyl ether, methyl vinyl ketone, allyl ether, acrylonitrile, vinyl acetate, allyl methyl .. ..,~
orthophthalate, vinyl octyl sulfide, ethylene, propylene, styrene, p-methoxy -styrene, and others.
In addition, polymers with acid sulfate or acid phosphate ionizable groups may also be prepared by sulfating or phosphating polyvinyl alcohol ~ -with sulfuric or phosphoric acid.
Natural anionic polyelectrolytes useful for this process include hydrolyzed yeast or gum arabic, lignin sulfonates, polymerized rosin acids, etc. Protein polyelectrolytes including blood, casein, gelatin and the like are also suitable. ~ -The preferred anionic polyelectrolytes are polyacrylic acid salts.
Suitable cationic substituent ionized groups are amino groups and ~ !.
the salts of quaternlzed amino groups attached to the polymer backbone. Upon , - - . , .
solution in water, amines ionize by forming ammonium compounds with water.
The substituents are attached directly to the polymer backbone or they may be attached through a connecting group such as a polymethylene group, a carbonyl containing group, an ether containing group, and aryl group, and the like. Quaternary amino substituents are made by adding sufficient organic halide or sulfate containing molecules to primary, secondary or tertiary amino groups to convert most of the nitrogens to the four-valent state, such that each nitrogen atom has four groups directly attached to it and also has a net positive charge. Preferably, the quaternizing agents is methyl chloride.
Amino containing polymers may be prepared by homo- or copolymerizing unsaturated amino compounds. Among such compounds are vinylamine, ethylene imine, 4-vinylpyridine, 3-allylpyridine, N-allylpiperidine, allyl diethylamine, N,N-diethylaminoethylacrylamide, N,N-dimethylaminoethylmethacrylic acid, -11- ~;
', ;:
vinylenedipyridine, 2-vinylguanidine, p-diethylaminoethoxyethylmethacrylate, etc.
Amine-containing polymers may also be prepared by aminomethylation, as for example by reacting polyacrylamide with formaldehyde and dimethylamine.
Suitable non-amine monomers useful for copolymerizing with one or more amine-containing compounds to produce amine-containing copolymers include methyl vinyl ether, methyl vinyl ketone, allyl ethyl ether, acrylo-nitrile, vinyl acetate, allyl methyl ortho phthlate, ethylene, propylene, styrene, p-methoxy-styrene, etc.
The polyelectrolytes will be employed in the mixes in a concentra-tion effective to prevent runoff, usually from about 0.01 to 3.0~, preferably 0.05 to 1.0%, by weight relative to the weight of the asphalt emulsion. -~
In a preferred embodiment, the additive will be an anionic poly-electrolyte precursor when the emulsion is formed with a cationic emulsifier.
This precursor will be a polymer corresponding to the polyelectrolytes, but containing unneutralized acid groups. These materials usually are sold in ;~
the form of aqueous emulsions. An example of such a material is Primafloc -A-10*, sold by Rohm and Haas Co., Philadelphia, Pennsylvania. This material is described as an acid-containing polyacrylic acid emulsion polymer. It and ~-other related products have been described as being useful as emulsion stabilizers in combination with non-ionic surfactants (primary emulsifiers).
The asphalt emulsions are prepared in the manner conventional for anionic or cationic bituminous emulsions. Thus, for example, in preparing ;
the cationic emulsions, the cationic emulsifier is first dissolved in water, preferably at a temperature of 100-125F. Then the asphalt, heated at 240- `
280 F is dispersed in the resulting aqueous solution in a colloid mill.
Usually, from 60 to 70 parts of asphalt are thus emulsified with 30 to 40 parts of the water solution containing the cationic emulsifier and optionally other additives. The emulsion may be used immediately thereafter or, alter-natively, stored for use at a later time. The anionic emulsions are prepared *Trademark ... . . . . .. . . . . .. .. . . .....

in the same way using an anionic emulsifier.
In a preferred embodiment, the anionic polyelectrolyte precursor is added in an appropriate amount to the emulsifying water prior to prepara- ~ -tion of the cationic emulsion. In this form, the emulsion may be stored for extended periods of time prior to use; it will remain stable for up to several months. Thus, at the application time, usually a sufficient quantity of base is added to the emulsion to provide a pH to the emulsion of ~;
greater than 7 and usually greater than about 11. In certain cases, suffi-cient basicity is contributed by the aggregate to effect neutralization of the polyelectrolyte without additional base being used. These cases usually ~ -occur with limestone-containing aggregates. Any base is sui.able. Thus, suitable bases include a variety of organic and inorganic bases. The alkali ,-~
metal bases are preferred. Sodium hydroxide is particularly preferred.
Suitable aggregates for use with the emulsions of this invention lnclude a wide variety of siliceous and calcareous materials. As previously ~ ~
mentioned, the so-called "open graded" aggregates are preferred. -~ - -The open-graded asphalt mixes are described in "Design and Con-struction of Emulsified Asphalt Open Graded Mixes and Overlays" by L.D.
Coyne presented at the Twenty-Third Annual Road ~uilders Clinic, University of Idaho, Moscow, Idaho, March 17, 1972. Such a mix is generally defined as an aggregate blend or asphalt mixture which has a high voids content, usually lacking in fine aggregates (sand) and mineral fillers. Federal Highway `
Administration, Region 10, Emory Richardson, W.A. Liddle, "Experience in the Pacific Northwest with Open Graded Emulsified Asphalt Pavements" defines the open-graded asphalt-paving mixes characterized by the use of asphalt emulsion, aggregates as crushed stone or crushed gravel aggrega~e with less than 10 percent passing the No. 10 sieve and 20 to 30 percent air voids in the com-pacted pavement. A consistent aspect of almost all definitions of open-graded aggregate is that less than 2 percent passes a No. 200 screen. The aggregate should preferably be relatively clean, that is, the presence of ~' ~
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': -substantial quantities of dust will require higher quantities of emulsifier -in the mixes. The mixes will contain from about 3 to 20, preferably 5 to 10, percent by weight of emulsion relative to the weight of aggregate.
EXAMPLES
The following examples illustrate this invention. The examples are only illustrative and are nonlimiting.
A specially-developed test was employed for evaluating the coating ability and water resistance of emulsions used in making open-graded aggregate mixes. The test is a variation of ASTM Test Method D-244. The test specifically measures (1) coating, (2) stripping resistance, (3) runoff, ;
(4) washoff, and (5) workability (stiffness) of the mixes. The test pro-,- .
cedure is as follows: ~-(1) 100 g of open-graded aggregate is added to a mixing bowl.
(2) The aggregate is wetted with water which may contain base or polyelectrolyte.
(3) The required amount (7 g.) of emulsion is added to the aggre- - ~i gate.
(4) The mixture is stirred for l5 seconds with a Hobart Mixer (using a "B" blade).

(5) Note is taken whether the emulsion disperses completely over the aggregate, and whether stripping occurs (asphalt being pulled from coated rock).

(6) The mixture is transferred to a pan with an aperture on one ~ ~
side. - -

(7) The pan is tilted and the quantity of emulsion that drains from the aperture i9 collected. Drying the drained material gives the asphalt lost by runoff.

(8) A portion of the mix is removed, and the ease of working is estimated. This sample is washed with cold water until the wash water runs clear.

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(9) The percent of asphalt coating is estimated for the washed and unwashed portions, the difference giving '~ashoff".
Example 1 This example demonstrates the use of anionic polyelectrolytes in combination with a cationic asphalt emulsion. The emulsion was prepared from a 70/80 penetration paving grade asphalt at 65 weight percent relative to the total weight of the emulsion. The emulsifier used was Arquad T-50*, a cationic quaternary previously described, employed at a concentration of 1%
by weight relative to the emulsion.
The polyelectrolytes being tested were added as aqueous solutions to the aggregate before mixing with the emulsions. The total weight of water and polyelectrolyte was 2% by weight relative to the aggregate. The poly- ~ `
electrolytes used were: :
(a) NaOH-neutralized Primafloc-A-10* (previously described);
(b) Dow Chemical Purifloc-A-23*, a neutralized hydrolyzed poly-acrylamide;
(c) Swift Chemical Co. Flocculant X-400*.
The following Table I shows the results of the tests.
The aggregates employed were a variety of types; in each 90% passed a 3/8 screen and is retained on a No. 4 screen and 10% passes a No. 10 screen and is retained on a No. 20 screen, except the dusty limestone which was a gross- `
graded limestone containing about 2% dust passing a 200 screen.

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. . . -These data show that effective coating and workability are attained, ~
the runoff of the emulsions is eliminated, and washoff reduced by use of the ~ -polyelectrolytes in pretreatment of the aggregates.
Example 2 In this example, an anionic PEP was used in combination with a cationic asphalt emulsion.
In the following tests, the emulsion was prepared as in Example l;
to that was added Primafloc A-10* (unneutrali~ed), described above, at 0.3%

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by weight. The aggregate was prewet with 2% by weight of NaOH solutions (at `
different pH) relative to the weight of aggregate. Seven weight percent of the emulsion was employed. The results of the tests are shown in Table II. ~ '~

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These data show the activation of the polyelectrolyte precursor by basic solution, the activation being enhanced with the more basic solution.
Tests S and 6 show that effective activation occurs with certain aggregates with lower pH solutions. Storage at eleyated temperatures, such as 140 F, does not destroy the effectiveness of the method.
Example 3 Tests were performed with open-graded silica aggregate, varying the concentration of the cationic emulsifier (Arquad T-50*), the polyelectro- ~ -~
lyte precursor (Primafloc A-10*), and the pH of the prewetting liquid. The ~

10- polyelectrolyte precursor was added to the water along with the cationic ~ -emulsifier prior to making the emulsion. The asphalt was the same type as that employed in Examples 1 and 2. The results are set forth in Table III, -following. `~ `

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These data show that the emulsions prepared with the PEP present in the emulsifying water, when contacted with aggregate prewet with pH ll.S -prewetting liquid, eliminate runoff and improve water resistance of the coatings. Note that setting occurs with pH 11.5 prewet liquid in this case, whereas with the emulsions of Example 2, in which the PEP was added to the emulsion after its preparation, pH 11.5 liquid failed to cause setting, and pH 12 liquid was required.
Example 4 In this test a cationic polyelectrolyte was used in combination with an anionic asphalt emulsion. The emulsion was prepared as in Example 1, except that 0.3% Vinsol Resin (Hercules Inc.) in dilute sodium hydroxide solution was used as the emulsifier. The test procedure used was that described hereinabove before these examples. -Blends were prepared using the above anionic emulsion to which was `-added Purifloc C-31* (Dow Chemical Co.), a cationic polyelectrolyte. Purifloc ,~ ~
C-31* is a high-molecular-weight, water-soluble synthetic cationic poly- ~ --electrolyte having the following approximate structure~

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TABLE IV
Effect of Addition of Cationic Polyelectrolyte to Anionic Asphalt Emulsion % Coating at Workability 60 min.
Purifloc at 60 Before After Runoff C-31, wt% Aggregate Initial min. wash wash wt % -0 silica Too RM 100 10 15.0 loose 0.1 silica Too RM 100 20 3.0 loose 0.25 silica RM RM 100 90 0 -: . ' Thin coating.
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These data show that without the polyelectrolyte, the emulsion was readily washed off the stones and had high runoff. With the polyelectro- `
lyte the water resistance of the mix was greatly improved, and runoff was -eliminated. --Example 5 :
Numerous other available anionic and cationic polyelectrolytes were tested with asphalt emulsions having the opposite charge. The method of ~ -testing was the same as previously described and the following Table V
indicates the nature of the emulsion and the nature of the commercial poly-electrolyte as well as the results obtained. Although the detailed chemical composition of the polyelectrolytes are not identified by the manufacturers, -~
the results below illustrate the beneficial results obtained when an ionic polyelectrolyte is added to an asphalt emulsion of the opposite charge.
Miscellaneous cationic polyelectrolytes were evaluated in combin-ation with an anionic emulsion made with 0.3% Vinsol Resin emulsifier by the procedure of Example 1. The aggregate employed was an open-graded silica `
aggregate. The data are given in Table V.
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Claims (18)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An ionically charged bituminous emulsion comprising from 40% to 75% by weight of asphalt, from 0.25 to 5.0% by weight of an ionically charged emulsifier, from 0.01 to 3.0%
by weight of a synthetic polyelectrolyte precursor capable of being ionized into a polyelectrolyte having an ionic charge opposite to the ionic charge of said emulsifier, and water as a continuous phase to make up 100% by weight.

2. The emulsion of claim 1 wherein said polyelectrolyte precursor is a polycarboxylic acid having a molecular weight of from about 1,000 to about 10,000,000 and is a polymer of monomer containing from 3 to 30 carbon atoms.

3. The emulsion of claim 1 wherein said polyelectrolyte precursor is a polyacrylic acid.

4. The emulsion of claim 1, 2 or 3, wherein said synthetic polyelectrolyte precursor is present in the emulsion as an ionically charged polyelectrolyte.

5. The emulsion according to claim 1, 2 or 3 wherein the emulsion is a cationic emulsion and the synthetic polyelectrolyte is present in an amount of from 0.01 to 1.0% by weight.

6. The emulsion of claim 1 further incorporating an open-graded aggregate in an amount of about 80% to 97% by weight wherein said emulsion is present in an amount of about 3% to 20%
by weight.

7. The emulsion of claim 6 wherein said synthetic poly-electrolyte precursor is present in the emulsion as an ionically charged polyelectrolyte.

8. A process for preparing a paving composition by depositing asphalt from an asphalt emulsion onto an aggregate, said process comprising:
mixing an aggregate in any order with water, an ionically charged bituminous emulsion, and a polyelectrolyte having a charge opposite to said emulsion, wherein said aggregate is about 80 to 97% by weight of said paving composition, said water, said emulsion and said polyelectrolyte are about 3 to 20% by weight of said paving composition and said polyelectrolyte is from 0.01 to 3.0% by weight relative to the emulsion.

9. The process according to claim 8 wherein the aggregate and the polyelectrolyte are mixed prior to adding the ionically charged bituminous emulsion thereto.

10. The process according to claim 8 wherein the aggregate and the ionically charged bituminous emulsion are mixed prior to adding the polyelectrolyte thereto.

11. The process according to claim 8, 9 or 10, wherein the polyelectrolyte is a cationic polyelectrolyte.

12. The process according to claim 8, 9 or 10 wherein said polyelectrolyte is an anionic polyelectrolyte.

13. The process according to claim 8, 9 or 10, wherein said polyelectrolyte is a polyelectrolyte precursor and sufficient base to neutralize said polyelectrolyte precursor.

14. The process according to claim 8 wherein said aggregate, said ionically charged bituminous emulsion, and said poly-electrolyte are mixed simultaneously.

15. The process according to claim 14 wherein said poly-electrolyte is a polyelectrolyte precursor.

16. The process according to claim 15 wherein sufficient base is added to neutralize said polyelectrolyte precursor.

17. The process according to claim 8 wherein said poly-electrolyte is a polyelectrolyte precursor and said poly-electrolyte precursor is mixed with said ionically charged bituminous emulsion prior to mixing the combination with said aggregate and a base.

18. The process according to claim 8 wherein said poly-electrolyte is a polyelectrolyte precursor and said polyelectrolyte precursor is admixed with said aggregate prior to mixing the combination with said ionically charged bituminous emulsion.