US3074807A - Cold-laid bituminous paving materials - Google Patents

Description

United States Patent 3,074,807 (ZULU-LAID BETUMENQUS PAVING MATERIALS Qarl B. Darius, Salt Lake Qity, George Mi. Jones, Salt Lake County, and Part: L. Morse, Sait Lake City, Utah, assignors to American Giisonite Company, Sait Lake City, Utah, a corporation oi Delaware No Drawing. Filed May 5, 1959, Ser. No. 811,010 13 Claims. (Ql. 106--2'73) This invention relates to bituminous paving compositions and, more particularly, to bituminous paving compositions which, in admixture with paving aggregates, can be formed into dense, stable pavements by application of pressure but without the application of heat.

The adhesive qualities of bituminous materials, coupled with their wear characteristics, commend these materials for the construction of road surfaces and the like. While dense, stable road surfaces can be constructed utilizing heat-liquefied high penetration bituminous materials and aggregate, the sometimes more economically attractive cold-laying methods utilizing delayed amalgamation of a powdered bitumen and liquid bitumen have presented a number of difficult problems.

Since economy dictates that the stone aggregate and bituminous binder be premixed at a plant in bulk quantities and requisite amounts of cold-laid paving materials be shipped to the individual job site for use at the appropriate time, cold-laid paving materials must be capable of retaining their workability for considerable storage periods regardless of seasonal temperature changes encountered, such as relatively high summer storage temperatures. The aggregate and associated binder must not coalesce into an unworkable mass with an increase in ambient temperature, nor may the aggregate and binder be converted to granules which are incapable of being compacted into a stable pavement because the weather turns cold.

While a retarded amalgamation rate is essential to insure extended stockpiling, once the pavement is formed the retarded amalgamation rate of the powdered bitumen can become a troublesome handicap. Since the powdered bitumen in the newly formed pavement is not amalgamated, the binder of the pavement has not attained its ultimate hardness and stability. Yet the pavement must exhibit immediate, i.e. early, stability even when elevated pavement temperatures are experienced due to solar radiation. Inasmuch as increasing temperatures decrease the viscosity of the fluid portion of the binder, elevated temperatures aggravate further the problem of achieving immediate pavement stability.

Consequently, practical cold-laid paving formulations functioning on a delayed amalgamation principle must attempt to reconcile conflicting requirements. In order to achieve extended stockpile periods for the coated aggregate it is desirable that the powdered bitumen exhibit a very slow rate of amalgamation with the liquid bitumen. in order to achieve high immediate stability upon laying the pavement, however, it is desirable that the powdered bitumen exhibit a rapid rate of amalgamation. Each apparently is the antithesis of the other.

Prior art attempts to formulate practical cold-laid paving materials utilizing delayed amalgamation of powdered bitumen with a liquid bitumen to enable a mixture to be formed into a pavement before complete amalgamation takes place to provide a high penetration binder are exemplified, inter alia, by US. Patents 1,937,749, 2,049,- 985, 2,067,264, 2,083,900, 2,104,411, 2,229,872, 2,340,- 779, 2,349,445 and 2,346,446. While the prior art is replete with examples of powdered bitumens associated with liquid bitumens the art has failed to provide a guide for the formulation of cold-laid paving materials which may be stored for extended periods of time and subsequently formed readily into pavements that exhibit both a high early stability and a continuing stability when subjected to elevated pavement temperatures.

Accordingly, it is a primary object of this invention to provide bituminous paving materials which can be formed into stable pavements without the application of heat.

It is an additional object of this invention to provide bituminous paving materials which can he cold-compacted into pavements that exhibit both a high initial stability and continuing stability when subjected to high pavement temperatures.

It is a further object of this invention to provide bituminuous paving materials which can be formed into stable pavements without the application of heat after extended periods of storage.

It is a still further object of this invention to provide a bituminous binder for coating aggregate to form paving materials which can be cold-compacted into stable pavements after extended periods of storage.

It is another object of this invention to provide a meth- 0d of producing bitumen coated aggregate to form paving materials which can be cold-compacted into stable pavements after extended periods of storage.

It is yet another object of this invention to provide a method of cold-forming a stable bituminous pavement.

According to the present invention there is provided a paving material suitable for stockpiling and cold-laying to form pavements which have high early stability and high heat stability as measured by the Marshall stability test, which comprises aggregate coated with (l) a bituminous binder liquid at ambient temperatures; (2) a substantially unamalgamated powdered natural asphaltite having a softening point of at least about 330 F. dispersed throughout said liquid binder;

said liquid binder having a viscosity of at least 7,000 cps. at the critical amalgamation temperature of said powdered natural asphaltite in said liquid binder, the critical amalgamation temperature being that temperature at which the amalgamation rate of said natural asphaltite in said liquid binder at hours is between about 0.1 and about 0.3, said critical amalgamation temperature being substantially higher than any sustained temperature anticipated during the stockpiling period, the viscosity of said liquid component of the binder being not greater than about 200,000 cps. at any temperature anticipated for the working of aggregate coated with the binder.

The present invention additionally embraces methods of coating aggregate with the formulation and methods of forming pavements utilizing aggregate coated with the above binder formulation.

The present invention is premised upon the discovery that specific powdered bitumens possess characteristics which ideally suit them for use in cold-laid paving formulations. The invention further is premised upon the recognition of several critical requirements which must be observed when these powdered bitumens are employed to obtain paving materials which can be stored for extended lengths of time and after storage economically can be formed without the application of heat into dense pavements which have high early and continuing stability regardless of changes in ambient temperature that may be encountered.

Aggregate compositions can be formulated or designed in accordance with this invention so as to be best adapted for storage and use under local conditions likely to be encountered between the time the mixture is made and the time when it is formed into a pavement. Take, for example, a locality with fairly well defined seasons ranging from moderate spring and fall temperatures to comparatively hot summers andcold winters. The manufacturer can anticipate, within reasonable limits, the minimum and maximum temperature conditions likely to be encountered, both for stockpiling the composition and for laying the pavement within a given period of weeks or months. A sutlicient safety factor can be allowed to achieve the necessary immediate stability and still attain good workability at the minimum anticipated laying temperatures. The paving materials will yielda pavement of high early strength which will remain stable continuously until complete amalgamation has occurred. As seasonal changes occur, the design can be changed accordingly.

Take the case of an ,rnanufacturer located in the Great Lakes region. Between November and April temperatures seldom, if ever, rise above'60-5f F,, but circumstances dictate thatpavements frequentlyinust be laid or patched at temperatures close .to freezing. A t the lower temperatures the viscosity of the liquid binder increases and consequently the pavement is more difiicult to lay. Thus, a composition designed to be laid in midsummer at a temperatureof 8590 Fl mightbe practically unworkable at say 35 F. Since at'the'beginning of this period it is'known'that temperatures above'60-65 P. will not be encountered for several'months; a'composition can be designed which can be safely stockpiled for an'extended periodand which is readily laid over the entire anticipated temperature range to produce high density and high early stability.

After the aggregate and associated binder have been formed into a pavement the powdered hard bitumenin thecompo'sition slowly undergoes amalgamation with the liquid binder due to the combined effect of time, heat from the sun, and pressure of vehicles passing over it so that after several months, even at moderate temperatures,- enough hard bitumen has become amalgamated to compensate the stability of the pavement against increasing temperatures. Moreover, the more or less gradual seasonal temperature rise results in increased amalgamation rates so that bythe time hot weather arrives the pavement will have reached a high stability.

With-the approach of the milderweather, the problem of workability at low temperatures becomes less acute, but the problem of stability at higher temperatures soon to be encountered becomes more important. Anticipating this, the manufacturer can adjust the formulation to provide good stockpiling characteristics, good workability and high early stability without losing stability at the tempera tures soon to' be expected,

Thus, in accordance with this invention the manufacturer can design for any seasonal change, as Well as for use under any climatic conditions where it is practical to cold-lay pavement. The fa'ctors governing the formulation of these compositions for stockpiling and use under widely diflering conditions are not so sharply defined but what a safety factor can be introduced.

The present invention utilizes a high softening point natural as'phaltite in conjunction with a liquid binder so that the powdered asphaltite remains substantially unamalgamated with the liquid binder at anticipated storage temperatures for extended periods of time. While in a finished pavement: this mixture will amalgamate to some degree under the influence of pressure even at moderate temperatures, it is apparent that stability could not be assured if aslow pressure amalgamation were relied upon. If the temperature of the pavement increased shortly after the pavement was laid, the traffic would displace the pavement and cause ruts or raveling. Accordingly, the liquid binder employed in this invention exhibits at least a critical minimum adhesivity necessary to impart the requisite cohesion and stability to the finished pavement at temperatures below the critical amalgamation temperature. Consequently, at temperatures below the critical amalgamation temperature of the powdered natural asphaltite, the liquid constituents of the binder assure the requisite early stability and cohesion and as an increase in temperature above the critical amalgamation temperature tends to lower the viscosity of the liquid binder below the requisite level, the powdered asphaltite amalgamates with the liquid portion of the binder and elfectively offsets the decrease in viscosity due to temperature rise.

in order to achieve the'excellent storage characteristics or" the composition of the invention it is necessary to employ a powdered asphaltite having a softening point (S.P.) above about 330 F. Asphaltites having a softening point below about 330 R, such as for example 285 F. softening point gilsonite, amalgamate too rapidly with liquid binders at normal stockpile temperatures to provide an assured extended stockpile life.

The present invention contemplates theutilization of powdered naturalasphaltites generally which exhibit a softening point above 330 F. includingtor example, gilsonites, glance pitch, grahamite', and the like. Preferred natural asphaltites constitute thosehavin'g a softening point from about 330? F. to about 400 F. Gilsonite from the Eureka mine having a softening point range from 330'to 350 F. (hereinafter referred to as 340 F. 5.1 gilsonite) and gilsonite from the Little Emma Mine having a softening point range from 365 to 385 F. (hereinafter referred to as 380 ESP. gil'sonitefare' particularly preferred and will be employed to describe and illustrate the practice of this invention.

The natural asphaltites employed inthe practive of the present invention are ground to 30" mesh with at least of the powdered asphaltite passing an 80' mesh screen. The substantially "80 mesh material provides the proper rate of amalgamation and yields a homogeneous finally cured binder.

To determine the critical amalgamation temperature of the high softening point gilso'nite with a liquid binder, or that temperature at which amalgamation proceeds sufficiently rapidly to prevent pavement instability due to a still further increase in temperature, the powdered high softening point g i'lsonite is admixed with a liquid bituminous binder in requisite proportions to provide the desired final penetration and the mixture is held at a constant temperature. 4 The viscosity of the liquid binder is recorded periodically and is plotted on a graph having the logarithm of the binder viscosity (v) as the Y-axis and the logarithm of time (t) as the X-axis. A series of cu'rves m'ay be plotted with temperature as the parameter, each reflecting the viscosity data obtained when the powdered gil sonit'e and liquid binder are permitted to amalgamate ata series of constant temperatures. The critical amalgamation temperature is that temperature which at hours provides a slope (d In v/d In t) of about 0.1. It has been found, however, that tempera tures which provide slopes from about 0.1 to about 0.3 after 100 hours may be regarded as the critical temperature, for the purpose of this invention. At temperatures below the critical amalgamation temperature the vis-- cosity-time curve presents a substantially flat profile with no material increase in the viscosity of the liquid binder for a period of several hundred hours or more. At temperatures above the critical amalgamation temperature, however, the amalgamation rate accelerates appreciably and a very material increase in viscosity occurs in a very short period of time. Consequently, at temperatures be low the critical amalgamation temperature the paving materials will exhibit maximum stockpileability, whereas at temperatures above the critical amalgamation temperature, amalgamation will proceed sutficiently rapidly, substantially to otfset any decrease in viscosity of the liquid portion of the binder.

It is essential that the liquid bituminous binder employed in conjunction with the high softening point gilsonite of this invention exhibit a viscosity of at least about 7,000 centipoises (cps) at and below the critical amalgamation temperature of the asphaltite to impart the requisite cohesion and stability to the paving materials. While a viscosity of 3,000 cps. will provide the necessary stability under ideal laboratory conditions, to achieve the necessary cohesion a viscosity of 7,000 cps. is required. At liquid binder viscosities below 7,000 cps. the coated aggregate tends to ravel and normal compacting procedures will not assure a stable pavement. The minimum viscosity of 7,000 ops. must apply up to the critical amalgamation temperature.

So that the binder will be as fluid as possible at working temperatures, it is preferred to employ a liquid binder which exhibits a viscosity of from about 7,000 to about 20,000 cps. at the critical amalgamation temperature. A viscosity of from about 10,000 to about 15,000 is especially preferred for the practice of this invention. Liquid binders which exhibit a viscosity higher than 20,000 cps. at the critical amalgamation temperature also are within the contemplation of this invention but, in any event, the liquid binder must exhibit a viscosity of less than about 200,000 cps. at the lowest contemplated working temperature to provide workability. Preferably, the liquid binder will exhibit a viscosity of less than about 100,000 cps. at the lowest contemplated working temperature.

The liquid binder may be a mineral oil which has been subjected to sufiicient distillation to provide the requisite viscosity. Alternatively, a soft asphalt may be cut-back with a more fluid hydrocarbon, or a hydrocarbon oil which exhibits too low a viscosity may be amalgamated with minor proportions of a low softening point powdered bitumen having a softening point below about 300 F. to provide a liquid bituminous binder of the requisite viscosity. In all cases, however, the viscosity and amalgamation rate requirements must be observed.

Since a major portion of the liquid constituents of the binder which have a boiling point below about 680 F. will ultimately volatilize from the pavement it is desirable that at least about 50% of the constituents of the liquid binder be characterized by boiling point above 680 F. Since the proportion of binder required per unit weight of aggregate must be based only on that part of the binder which will not volatilize, the utilization of large quantities of lower boiling components will require a greater proportion of initial binder to produce the desired amount of finally cured binder. In order to provide a dense pavement it is preferred that the liquid binder contain less than about 30% volatiles when subjected to the ASTM D-402 Distillation at 680 F.

Hydrocarbon oils having a Flash point of at least 150 F., a viscosity of from about 40 to about 350 S.S.F. at 122 F., and less than 25% volatiles when subjected to ASTM D402 distillation at 680 F. are well suited for use in obtaining the liquid binder of the present invention.

Slow curing bitumens containing less than 25% volatiles when subjected to ASTM 13-402 distillation at 680 F. and known to the art as SC2 oils appropriately may be employed as a constituent of the liquid binder in the practice of this invention. A number six fuei oil also may be employed as a constituent of the liquid binder. It is similar in nature to an SC-Z and is specified as having a viscosity of 45300 S.S.F./122 F. Ordinarily the material has a 13-402 volatile (680 F. liquid cut point) content of less than 25%.

The viscosity of the liquid bitumen may be increased by blending therewith 285 F. S.P. gilsonite or, alternatively, the viscosity of the SC-Z oil may be decreased by incorporating a mineral oil having, for example, a distillation range in the broad range of 300 to 680 F. when subjected to an ASTM D-l58 distillation. Oils known to the art as MC cutter stocks having a distillation range of approximately 300-500 F. have proved most useful for this purpose. Lighter stocks having a distirlation range extending down to about 200 R, such as naphtha or the like, with a distillation range of 220420 F, may also be employed to reduce the viscosity of heavier bitumens. Generally, the more volatile oils with a distillation range below 350 F. are used in amounts of less than about 10% of the liquid binder although, in the event very low working temperatures are contemplated, these oils may be employed up to about 20% of the liquid bitumen. The more volatile oils are often used for the reduction of viscosity of the binder during mixing. When stockpiling occurs such materials are considered to be evaporated within a short time unless temperatures are at 45 F. and lower. The nonvolatile oils such as an MC cutter stock will remain in stockpiles for long periods.

Since the lighter oils volatilize more rapidly from the 'binder, small additions of naphtha or the like may be more desirable than equivalent additions of higher boiling oils such as MC cutter stocks which more slowly volatilize from the binder.

In view of the rapid evaporation of oils, such as naph-.

that or the like, boiling below about 400 F., the specified minimum liquid viscosity of 7,000 cps. at the critical amalgamation temperature is calculated on a volatile free basis. Consequently, the viscosity which is critical is the viscosity of that portion of the liquid binder which has a boiling point above about 350 F.

The aromatic or aliphatic content of the liquid binder will affect the amalgamation to some extent, aromatics tending to cause more rapid amalgamation. Likewise, the viscosity of the liquid binder will affect the amalgamation rate, particularly if the binder contains appreciable amounts of light components such as naphtha or the like. When a viscous, substantially nonvolatile liquid bitumen is employed, however, the amalgamation rate has been found to be primarily a function of the softening point of the powdered gilsonite and of the temperature. For a given powdered, high softening point gilsonite, the amalgamation rate will not be substantially affected by aromatic content or by minor changes in viscosity. Accordingly, a liquid bitumen and powdered gilsonite may be elected and the critical amalgamation temperature determined prior to adjusting the viscosity of the liquid bitumen to meet the requirements of this invention. Minor additions of slightly less viscous hydrocarbon oils or of more viscous hydrocarbon oils or solids to amalgamate with the liquid bitumen will not aifect significantly the critical amalgamation temperature of the powdered gilsonite with the base liquid bitumen.

A powdered 340 F. S.P. gilsonite and liquid binder may be combined in accordance with the present invention to provide binder formulations which exhibit a critical amalgamation temperature of F. and which provide paving materials that are storable and workable from about 20- F. to about 85- F. By employing 380- F. S.P. gilsonite, formulations may be obtained which exhibit a critical amalgamation temperature of F. and which provide paving materials that are storable and workable at any temperature within the range of from about 30 F. to about 100 F. For these formulations liquid binders are employed which exhibit a viscosity of at least about 7,000 cps. at 85 and 100 F. respectively. Critical amal' gamation temperatures of at least about 85 F. will provide year-round stockpileability in the cooler regions of the United States whereas a critical temperature of at least about 100 F. will provide year-around stockpileability in the Warmer regions of the United States. Good economic practice dictates that formulations will be used that have the lowest possible critical amalgamation temperature. In this way the lowest solvent dosage will be made possible. The term year-round stockpilea ability as employed herein signifies that the material may be stockpiled for extended periods at any season of the year.

In order to obtain this assured stockpileability it is essential that a high softening point gilsonite be employed. Formulations containing only powdered low softening point gilsonites such as 285 F. 8.15. gilsonite exhibit a critical amalgamation temperature within the range of temperatures which will be experienced in storage and, consequently, formulations containing 285 F. S.P. gilson- 7. ite may amalgamate at an advanced rate during storage to produce an unworkable mass.

Generally, to assure extended stockpile life, the critical amalgamation temperature should be at least about F. and preferably at least about F. higher than the maximum contemplated sustained storage temperature although critical amalgamation temperatures may be as high as 110 F. Storage temperature as employed herein refers to the temperature of stockpiles which, in accordance with art-recognized practice, are shielded from the direct rays of the sun. The temperature of a stockpile a short distance inside the outer surface meets this definition.

The ultimate penetration of the totally amalgamated nonvolatile portion of the liquid bitumen and powdered gilsonite may be varied according to the demands of the particular situation. Generally, however, pavements in the colder areas of the United States desirably have penetrations of from 100 to 150; more temperate areas within the United States utilize pavements which exhibit a penetration of from 80 to 100, while the warmer portions of the United States may require pavements with a penetration of 50 to 80; Additionally, paving for mulations which exhibit a pentration of about 60 or lower may be employed for curbs or the like. The above penetrations are determined by ASTM D -S at 77 F.,-

Weight Ingredient: percent Liquid btiumen 50-70 Low S.P. bitumen 0-15 High S.P. bitumen -35 Volatile Oils (300-500 F.) 0-6 Volatile Oils 300 F.) 0-20 The binder formulations of this invention may be employed in conjunction with any aggregate known to the art such as sand, gravel, stone, granite or the like While the invention contemplates the utilization of aggregate of any size, it is preferred to employ a densely graded aggregate, since densely graded aggregate enhances the stability of a pavement. A suitably graded aggregate may be characterized, for example, by the following sizing specification:

Percent Screen size: passing Other size distributions for graded aggregate are wellknown to the art and may be used in conjunction with the present invention.

The binder may be associated with the aggregate in any desired amount depending again upon the particular application. Generally, however, paving materials will contain from about 4.0 to about 10 parts by weight of binder on a volatile free basis per 100 parts by weight of dry aggregate.

The binder and aggregate may be combined in any apparatus known to the art such as, for example, a pug mill, blade mixer or the like. Pug mills generally are effective when the paste viscosity (the viscosity of the '1 liquid and solid hydrocarbons) is below about 200,000 cps. Mixing at paste viscosities below 100,000 cps., how-- ever, is more economical and therefore generally preferred. Blade mixers are generally effective at paste viscosities belowd about 30,000'cps.

The unheated liquid binder and powdered gilsonite may be pre-mixed and subsequently admixed with the aggro gate, or, alternatively, the powdered asphaltite may beadmixed with the aggregate and the liquid binder thereafter added to the mixture. Should it be desired to de-- crease the viscosity of aliquid bitumen so that mixingi may be facilitated, a volatile oil may be added at any point in the process. Similarly, a more viscous liquid bitumen or powdered low softening point gilsonite that'- readily amalgamates with the liquid bitumen may be added'at any point in the process to increase the viscosity of a liquid bitumen. The powdered low softening point gilsonite'may be totally amalgamated with the liquid bitu men before furtherprocessing is effected, or the powdered low and high softening point gilsonites may be admixed with the aggregate before the liquid bitumen is added. The low softening point gilsonite will subsequently amalgamate to provide a liquid binder with the requisite viscosity while the high softening point gilsonite will remain substantially unamalgamated until time, temperature and pressure are favorable.

Generally viscous hydrocarbons are delivered in a heated condition and may have a temperature, for example, of about 200 F. or more. In the event a heated liquid binder is employed, the high softening point gilsonite may be premixed with the aggregate and the heated liquid binder advantageously may be addedto the solid materials. In this manner the viscosity at the time of mixing is low yet the cold aggregate will reduce the tem perature of the heated liquid binder in a sufiiciently short time to prevent appreciable amalgamation between the powdered asphaltite and the heated liquid binder.

In the event that the viscosity of the heated liquid bitumen must be increased to meet the requirements of this invention, a low softening point 285 F. S.P. gilsonite may be amalgamated therewith prior to adding the heated liquid to the aggregate. If a heated liquid bitumen is employed, both the low softening point gilsonite and the high softening point gilsonite appropriately may be premixed with the aggregate prior to the addition of the heated liquid to obtain as low a viscosity as possible at the time of mixing. While the cold stone will reduce the temperature of the liquid bitumen sufliciently to prevent amalgamation of the high softening point gilsonite, the amalgamation of the 285 F. S.P. gilsonite nevertheless will take place to provide a liquid binder with the requisite viscosity. Normally, hot flux oil and low softening point gilsonite are premixed and added to an admix of high softening point gilsonite and aggregate. Other low softening point powdered bitumens having a softening point below about 300 P. such as reduced asphalts and the like may be employed to replace part or all of the 285 F. S.P. gilsonite.

As noted earlier, volatile oils may also be added to the binder. These oils normally may be added at any stage of the mixing. At high liquid temperatures, however, it is preferred to add RC cutter stocks to the aggregate admix. If fluid handling problems exist, these may be overcome by adding an MC cutter stock to the heated liquid bitumen.

When the viscosity of a liquid bitumen is adjusted by the addition of low softening point powdered bitumen the amount of high softening point powdered gilsonite required to provide the desired penetration readily may be calculated. The necessary data may be obtained by performing the following routine tests.

The liquid bitumen such as an SC-Z oil is subjected to an ASTM D-402 distillation to a 680 F. liquid temperature and the weight fraction of volatiles to 680 F. is recorded as W,. A portion of the residuum from the distillation is then fluxed hot with 285 F. S? gilsonite and an additional portion of the residuum is iluxed hot with 340 'F. S.P. gilsonite. A separate binder with the desired final cured out penetration of the pavement binder is made from each portion of the residuum and the weights of 285 '5. and 340 F. SP. gilsonites (per unit weight of residuum) required are recorded as P and P respectively. Powdered 285 F. 8.19. gilsonite then is amalgamated with the SC-Z oil as received until a liquid binder with desired viscosity is obtained and this amount per unit weight of the SC-Z oil is recorded as Wg.

The amount of high softening point gilsonite per unit weight of SC-2 oil to be employed in conjunction with the powdered 285 F. 8.1. gilsonite may be calculated from the expression,

wherein Z=weight of high softening point powdered 'gilsonite per unit weight of liquid bitumen.

P =weight of low softening point powdered gilsonite per unit weight of the nonvolatile portion of the liquid bitumen required to provide desired penetration. The nonvolatile portion of the liquid bitumen is the residue from an ASTM D-402 distillation at 680 F.

P =weight of high softening point powdered gilsonite per unit weight of the nonvolatile portion of the liquid bitumen required to provide desired penetration.

Wg=weight of low softening point powdered bitumen per unit weight of the liquid bitumen to provide desired viscosity.

W.,=volatile weight fraction of the liquid bitumen as determined by ASTM 13-402 distillation at 680 F.

Should the liquid binder contain volatiles, these ultimately will pass out of the pavement. The amount of binder added to the aggregate then must be in excess of the final amount of binder desired. The amount of liquid bitumen required to produce a given amount of cured binder may be determined by the expression,

e (2) Wg+(1Wv)+Z wherein:

S=amount of liquid bitumen.

B amount of cured binder.

Wg, W Z=as indicated in expression (1) above.

In the above expression liquid bitumen includes liquid bitumen constituents exclusive of 285 F. SP. gilsonite. The amalgamated 285 F. S1. gilsonite and liquid bitumen are considered to constitute the liquid binder.

The paving materials of this invention may be formed into pavements by any of the cold-compacting methods known to the art. Generally, coated aggregate is positioned to proper depth on a base coarse of aggregate by means of a shovel, rake, road-laying machine, or the like. The coated aggregate is then cold-compacted by hand tamping or by machines. These methods are wellknown to the art and will not be further described here. While paving materials of this invention are ideally suited for cold compaction, it will be apparent that the paving materials also may by formed into stable pavements by compaction methods which utilize heat as Well as pressure.

The Marshall stability test referred to herein is wellknown to the art and is described, inter alia, in Mix Design Methods for Hot-Mix Asphalt Paving, The Asphalt Institute, Manual Series No. 2, 1956. The outlined test procedure is applied to specimens formed by cold-compacting the coated aggregate of this invention.

The following specific embodiments are included to describe more fully the present invention. These embodi ments are included for illustrative purposes only and in no way are intended to limit the scope of the present invention.

His P1 10 EXAMPLES r-rv The binder formulations shown in Table 1 illustrate the practice of this invention utilizing 340 F. S.P. gilsonite. Oil A was a Utah Oil Co. SC-2 oil which was chaacterized by a viscosity of 180 SSF at 140 F., a D402680 F. volatile content of 9.1% and a D-402- 680 F. residuum viscosity of 106 SSF at 180 F. Oil B was a Phillips Petrolium Co. SC-2 oil which was characterized by a viscosity of 116 SSF at 140 F., a D402- 680 F. volatile content of 7.2% and a D-402-680 F. residuum viscosity of 128 SSF at 180 Table l Ingredient Ex. I Ex. II Er. III Ex. IV

Oil A, Percent 72 Oil B, percent 285 F. 8.1.. gilsonito, percent 340 F. S.P. Gilsonite, percent 28.0

Autistrip age-i percent Styrencl3utadrene Latex, percent Cri gical amalgamation temperature 85 85 Liquid viscosity (cps.) at Tc 7, 400 7, 400 9, 600 15, 000 Paste viscosity art To 500 20, 600 21, 500 44, 000 Cured penetration 88 9;. 75

1 Amalgamated into oil.

EXAMPLES V-VIII The practice of the invention utilizing 380 F. S.P. gilsonite is illustrated by the binder formulations set forth in Table II. The oil is identified above.

Table II Ingredient Ex. V Ex. VII

Oil A, percent Oil B, percent 285 F. 8.1. gilsonite, percen 380 F. ST. gilsonite, pcrcent Antistrip agent, percent Critical amalgamation temperature (Tc) F 100 100 100 100 Liquid viscosity (cps) at Tc 9, 700 9,700 14, 000 7, 200 Paste viscosity at; Tom. 22, 000 22,000 40, 000 22, 500 Cured penetration 96 92 100 1 Amalgamated into oil.

Each of the above formulations is excellently suited to be incorporated with aggregate to form paving materials adapted for year-round stockpiling even in the warmer portions of the United States. Pavements exhibited immediate stability and remained stable even when subjected to elevated temperatures.

It will be noted that the viscosity of the oil in the above formulations was adjusted by a minor addition of 285 F. SP. gilsonite. Such addition did not significantly effeet the critical amalgamation temperature of the 380 F. S.P. gilsonite in the oil.

EXAMPLE IX The composition of Example VI was altered by add- 1T ing 0.1 pound of RC cutter stock per pound of oil A to provide .the following formulation:

While the composition of Example VI can be mixed with aggregate in a pug mill at temperatures of 90 F. and above to provide a coated aggregate which can be laid at temperatures down to about 58 F., the above composition may be mixed with aggregate at temperatures above 55 F. and the coated aggregate may be laid at temperatures down to about 55 F. If the stockpile of the mix is not subjected to sustained temperatures above about 45 F. the RC cutter stock will not evaporate from the stockpile. and the coated aggregate may be laid at temperatures as low as about 25 F.

EXAMPLE X Marshall stability tests were conducted employing sized aggregate coated with the binder formulations of Examples I and V. The results of the tests are reflected in Table III below.

In order to. demonstrate the stockpile life of binder formulations utilizing 340 F. S.P. gilsonite, aggregate was coated with a formulation similar to that of Example III and separate portions of the coated aggregate were subjected to constant temperatures of 60, 70, 75 and 85 F. The results are shown in Table IV.

Table IV Minimum stockpile Temperature; life, months 60 F +6 70 F 2 75 F 1 85 F Consequently, it is apparent that the above formulation is excellently suited for a fall-winter stockpile. Even when continuously subjected to its critical amalgamation temperature of 85 F., the coated aggregate had a stockpile life of /2 month.

EXAMPLE XII Example Xlwasrepeated utilizing an aggregate coated with a binder containing 380 F. S.P. gilsonite similar to the binder of Example VI. The results are tabulated below.

Table V Minimum stockpile Temperature: life, months 70 F +6 75 F 4 85 F 1 Again Ill: should be noted that the above results were obtained when the sample was continuously subjected to the indicated temperature.

l 2 EXAMPLE xrn For purposes of comparison, the following binders were formulated:

Oil B, percent 63.1 65. 5 285 F. S.P. gilsonite, percent. 3. 2 25. 4 340 F. S.P. gilsonite, percent- 24. 6 Cutter stock, percent 9.1 9. 1

Binder (1)- represents the practice of this invention whereas binder (2) represents the prior art practice of employing low S.P. gilsonites.

When binder (1) was subjected to a constant temperature of F. for 100 hours, the viscosity increased only about 3,500 cps. in 100 hours. Binder (2) experienced a viscosity increase of about 850,000 cps. in 20 hours at 40 F.

This invention further contemplates the incorporation into the binder of adhesion improving, agents, rubber latex, crumb rubber, depolymerized rubber or other additives which improve the characteristics of bituminous binders. Such materials are well-known to the art and will not be described in detail here.

Since variations of this invention will be apparent to those skilled in the art, it is intended that the invention be limited only by the scope of the appended claims;

We claim:

:1. A paving material suitable for stockpiling and coldlaying to form pavements which have high early stability and high heat stability as measured by the Marshall stability test, consisting essentially of aggregate coated with (1) a bituminous binder liquid at ambient temperatures;

(2) a substantially unamalgamated powdered natural :asphaltite having a softening point of,- at least about 330 F. dispersed throughout said liquid binder;

said liquid binder having, a viscosity of at least 7,000 cps. at the critical amalgamation temperature of said powdered natural asphaltite in said liquid hinder, the critical amalgamation temperature being that temperature at which the amalgamation rate (d In viscosity/d ln temperature) of said natural asphaltite in said liquid binder after 100 hours is between about 0.1 and about 0.3, said criticalamalgamation temperature being at least about 5 F. higher than the maximum temperature anticipated during the stockpiling period, the viscosity of said liquid component of the binder being not greater than about 200,000 cps. at any temperature anticipated for the working of said coated aggregate.

2. The paving material of claim 1 wherein the liquid binder exhibits a viscosity of from about 7,000 to about 20,000 cps. at the critical amalgamation temperature.

3. The paving material of claim 1 wherein the critical amalgamation temperature of the powdered natural asphaltite is'from about to about F.

4. The paving materialofi claim 1 wherein the powdered natural asphaltite is characterized by a softening point of from about 330 F. to about 400 F.

5. The paving material of claim 1 wherein the aggregate is coated with from about 4 to about 10% by weight of binder based on the dry weight of the aggregate.

6. A paying material suitable for stockpiling and coldlaying to form pavements which have high early stability and high heat stability as measured by the Marshall stability test, consisting essentially of aggregate coated with (l) a bituminous binder liquid at ambienttemp eratu-res;

(2) a substantially unamalgamated powdered gilsonite having a softening point of at least about 330 F. dispersedthroughout said liquid binder;

said liquid binder having a viscosity of at least 7,000 cps. at the critical amalgamation temperature of said powdered gilsonite in said liquid binder, the critical amalgamation temperature being that temperature at which the amalgamation rate (d ln viscosity/ d In temperature) of said gilsonite in said liquid bind after 100 hours is between about 0.1 and about 0.3, said critical amalgamation temperature being at least about F. higher than the maximum temperature anticipated during the stockpiling period, the viscosity of said liquid component of the binder being not greater than about 200,000 cps. at any temperature anticipated for the working of said coated aggregate.

7. The paving material of claim 6 wherein the liquid binder exhibits a viscosity of from about 7,000 to about 20,000 cps. at the critical amalgamation temperature.

8. The paving material of claim 6 wherein the critical amalgamation temperature of the powdered gilsonite is from about 85 to about 100 F.

9. The paving material of claim 6 wherein the powdered gilsonite is characterized by a softening point of from about 330 F. to about 400 F.

10. The paving material of claim 6 wherein the aggregate is coated With from about 4 to about by Weight of binder based on the dry weight of the aggregate.

11. A bituminous binder formulation for coating aggregate to form paving materials suitable for stockpiling and cold-laying to form pavements which have high early stability and high heat stability as measured by the Marshall stability test, consisting essentially of (1) a bituminous binder liquid at ambient temperatures;

(2) a substantially unamalgamated powdered gilsonite having a softening point of from about 330 F. to about 400 'F. dispersed throughout said liquid binder;

said liquid binder having a viscosity of from about 7,000 to about 20,000 cps. at the critical amalgamation temperature of said powdered gilsonite in said liquid hinder, the critical amalgamation temperature being that temperature at which the amalgamation rate (d In viscosity/d 1n temperature) of said gilsonite in said liquid binder after 100 hours is between about 0.1 and about 0.3, said critical amalgamation temperature being at lea-st 5 F. higher than the maximum temperature anticipated during the stockpiling period, the viscosity of said liquid component of the binder being not greater than about 200,000 cps. at any temperature anticipated for the working of aggregate coated with the binder.

12. The method of producing a coated aggregate suitable for stockpiling and cold-laying to form pavements which have high early stability and high heat stability as measured by the Marshall stability test consisting essentially of (1) admixing with aggregate (a) a powdered bitumen having a softening point below about 300 F.; and

(b) a powdered natural asphaltite having a softening point of at least about 330 F.;

(2) admixing with said aggregate and said powdered bitumen and asphaltite a heated liquid bitumen liquid at ambient temperatures, said liquid bitumen and said powdered natural asphaltite having a critical amalgamation temperature of at least about 85 F., said critical amalgamation temperature be- 14 ing that temperature at which the amalgamation rate (d In viscosity/ d ln temperature) of said natural asphaltite with said liquid bitumen after 100 hours is between about 0.1 and 0.3;

whereby said powdered bitumen having a softening point below about 300 F. amalgamates with said liquid bitumen to form a liquid binder which exhibits a viscosity of at least 7,000 cps. at the critical amalgamation temperature, the viscosity of said liquid binder being less than about 200,000 cps. at any temperature anticipated for working said coated aggregate, said powdered natural asphaltite remaining unamalgamated with said liquid bitumen.

13. The method of claim 12 wherein said liquid bitumen and said solid bitumen amalgamate to form a liquid binder having a viscosity of from about 7,000 to about 20,000 cps. at the critical amalgamation tempera ture.

14. The method of claim 12 wherein the critical amalgamation temperature is from about F. to about F.

15. The method of claim 12 wherein the powdered natural asphaltite i-s gilsonite.

16. The method of forming a pavement which exhibits high early stability and high heat stability as measured by the Marshall stability test which comprises cold compacting to an adherent mass an aggregate having a coating consisting essentially of (1) a bituminous binder liquid at ambient temperatures;

(2) a substantially unamalgamated powdered natural asphaltite having a softening point of at least about 330 F. dispersed throughout said liquid binder;

said liquid binder having a viscosity of at least 7,000 cps. at the critical amalgamation temperature of said powdered natural asphaltite in said liquid binder, the critical amalgamation temperature being that temperature at which the amalgamation rate (d In viscosity/d 1n temperature) of said natural asphaltite in said liquid binder after 100 hours is between about 0.1 and about 0.3, said critical amalgamation temperature being at least about 5 F. higher than the maximum temperature anticipated during the stockpiling period, the viscosity of said liquid component of the binder being not greater than about 200,000 cps. at any temperature anticipated for the working of said coated aggregate.

17. The method of claim 16 wherein the powdered natural asphaltite has a softening point of from about 330 F. to about 400 F.

18. The method of claim 17 wherein the powdered natural asphaltite is gilsonite.

References Cited in the file of this patent UNITED STATES PATENTS 1,672,361 Berger June 5, 1928 1,685,304 Berger Sept. 25, 1928 1,776,379 Berger Sept. 23, 1930 1,776,763 Berger Sept. 23, 1930 1,937,749 Ebberts Dec. 5, 1933 1,940,645 Fletcher Dec. 19, 1933 1,999,178 Baskin Apr. 30, 1935 2,340,779 Talbot Feb. 1, 1944 2,783,163 Mollring Feb. 26, 1957 2,939,800 Fox et al. June 7, 19-60

Claims (1)

1. A PAVING MATERIAL SUITAVLE FOR STOCKPILING AND COLDLAYING TO FORM PAVEMENTS WHICH HAVE HIGH EARLY STABILITY AND HIGH HEAT STABILITY AS MEASURED BY THE MARSHALL STABILITY TEST, CONSISTING ESSENTIALLY OF AGGREGATE COATED WITH (1) A BITUMINOUS BINDER LIQUID AT AMBIENT TEMPERATURES; (2) A SUBSTANTIALLY UNAMALGAMATED POWEDERED NATURAL ASPHALTITE HAVING A SOFTENING POINT OF AT LEAST ABOUT 33* F. DISSOLVED THROUGHOUT SAID LIQUID BINDER SAID LIQUID BINDER HAVING A VISCOSITY OF AT LEAST 7,000 CPS. AT THE CRITICAL AMALGAMATION TEMPERATURE OF SAID POWDERED NATURAL ASPHALITE IN SAID LIQUID BINDER, THE CRITICAL AMALGAMATION TEMPERATURE BEING THAT TEMPERATURE AT WHICH THE AMALGAMATION RATE (D) IN VISCOSITY /D IN TEMPERATURE) OF SAID NATURAL ASPHALITE IN SAID LIQUID BINDER AFTER 100 HOURS IS BETWEEN ABOUT 0.1 AND ABOUT 0.3, SAID CRITICAL AMALGAMATION TEMPERATURE BEING AT LEAST AOUT 5* F. HIGHER THAN THE MAXIMUM TEMPERATURE ANTICIPATED DURING THE STOCKPILING PERIOD, THE VISCOSITY OF SAID LIQUID COMPONENT OF THE BINDER BEING NOT GREATER THAN ABOUT 200,000 CPS. AT ANY TEMPERATURE ANTICIPATED FOR THE WORKING OF SAID COATED AGGREGATE.