US2349445A

US2349445A - Method of making bituminous paving compositions and pavements

Info

Publication number: US2349445A
Application number: US333935A
Authority: US
Inventors: Frank B Mcgrane
Original assignee: Colprovia Roads Inc
Current assignee: Colprovia Roads Inc
Priority date: 1940-05-08
Filing date: 1940-05-08
Publication date: 1944-05-23
Anticipated expiration: 1961-05-23

Description

UNITED STATES PATENT OFFICE METHOD OF MAKING BITUMINOUS PAVING COMPOSITIONS AND PAVEMENTS Frank B. McGrane, Quincy, Masa, assignor to '(lolprovia Roads, Inc., Rochester, N. Y., a cornotation of New York No Drawing. Application at, a, 1940, sci-n1 No. 333,935

7 Claims. (Cl. 106-280) This invention relates to paving compositions be a substantially non-volatile flux oil that is employing bituminous material as a binder for liquid at ordinary temperatures and the other aggregate particles. More particularly it relates component may be a powdered asphalt adapted to the manufacture of pavements and paving to gradually blend or amalgamate with the flux compositions which remain friable after mixing oil to produce a permanent binder having a melteven though the temperature of the composition ing point and penetration required in the ultiis below that at which the bituminous binder in 'mate pavement. Usually the flux oil is first apthe ultimate pavement is quite stiff and which plied to the aggregate until the aggregate is after mixing can therefore betransported to the coated and then the powdered asphalt is mixed point of use and laid without requiring the, appli- 10 for a brief interval of time to distribute it through cation of heat to keep the composition in a workthe mass. Sometimes with a heavy flux oil it is able condition. heated somewhat to make it flow more readily,

A bituminous binder in a completed pavement especially in cold weather and the aggregate may should be sufllciently hard at atmospheric tembe supplied quite warm if it has just come from perature to impart stability to the road sufflcient a drier; but it is also possible to carry out the to withstand the demands of tramc. It is reentire process at atmospheric temperature or subgarded as good practice to use in the completed stantially 50. While this coldmix method has pavement a bituminous binder having a softening many advantages, the pavement immediately point (ball and ring) of about 95 F. to about after laying does not have as great stability as 60 F. and having a penetration of about 35 to desired and has considerably less stability imabout 150 at 77 F. For a greatmany years mediately after laying than a pavement of the bituminous binders of this character have been hot mix type. In addition even after the comapplied to aggregate such as stone by first reponents of the bituminous binder after a, time ducing it to a molten condition, e. g. at a tembecome sufliciently amalgamated to afford a perature of about 225 to about 350 F. and applypavement of desired stability, the binder usually ing it to aggregate that has previously been has less durability and wearing capacity than an heated. The resulting mixture tends to cool and asphalt cement of the same penetration applied become set up quite rapidly, however, which by the hot mix method. places great limitation on the transportation and Another cold mix method of road construction laying of the material. This hot mix method has been based upon the use of suflicient volatile has the advantage, however, of great pavement solvents to render a paving asphalt cement of the stability immediately upon laying. type ordinarily used in the hot mix method sufil- Because of the disadvantages of the hot mix" ciently fluid at relatively low temperatures to method of road making, many cold mix proallow the aggregate to be coated and laid without posals have, been made for mixing the paving resort to the high temperatures required for the composition or. laying the paving composition or hot mix method. After a paving composition both at a temperature substantially below that including a volatile solvent is laid it is expected which is required using the hot mix method. that the solvent will evaporate leaving only the One form of cold mix that has been used extenstable asphalt cement. But the disadvantages of sively in the manufacture of pavements involves such compositions are well hown. In order to the admixturewith aggregate of a bituminous permit evaporation of the volatile solvent the binder divided into two component parts, one pavement must be left open, that is with a too soft at atmospheric temperature to form a multiplicity of open passages therein through stable pavement and the other too hard to be which the solvent may evaporate; but a paveproperly adhesive. Upon mixing the aggregate ment containing such a high percentage of voids with the two component parts of the binder they is not desirable. Also in such pavements, espedo not blend or amalgamate with each other imcially where it is attempted to make them more mediately and the bituminized aggregate remains dense, a substantial proportion of the volatile friable so as to permit shipment or storage and solvent becomes entrapped and cannot evaporate laying of the composition without application of with the result that the asphalt cement remains heat. After laying and under the pressure of a soft and tends to bleed or flush to the surface roller or trailic the two bitumens blend or amalexcessively. Such a pavement is deficient in regamate to form a binder of desired stability. sistance to excessive internal movement and tends For example, in carrying out this type of cold to rut and shove under traflic. This type of mix method one of the binder components may cold mix pavement also has th disadver-iwe not having requisite stability immediatelyaiter laying.

It is a purpose of this invention to afford a cold mix type of pavement which avoids the defects of cold mix pavements heretofore proposed. It is a further purpose of this invention to aiIord a cold mix paving method which has the advantages of good stability immediately after laying and of durability and denseness of the order of hot mix pavements and which at the same time has the advantages of easy handling and storing of cold mix types of pavements.

It is a feature of this invention that in a process wherein a binder is applied to the aggregate in the form of two component parts, one component being a flux oil and the other component a powdered hard bitumen adapted to amalgamate gradually with the flux oil, a paving bituminous cement is also used, the paving bituminous cement being commingled with the flux oil, to form a friable composition comprising aggregate particles carrying unamalgamated powQered hard bitumen and flux oil together with paving bituminous cement commingled with the flux oil. I have found that a bituminous cement can be used for example when heated above its softening point in the manner mentioned and notwithstanding that the cement tends to become hardened at ordinary atmospheric temperature themixture retains the advantages of good workability at relatively low temperatures that are incident to cold mix methods oi pavement construction. At the same time the paver entis greatly improved as to stability immediately after laying and compaction. Moreover this method makes available in coil mix pavements high duc-' tility paving asphalt cements and enables cold mix pavements to be manufactured that are of improved ductility and wearing qualities.

By referring to paving bituminous cement reference is made to those adhesive bituminous aaeacas adhesive at ordinary temperatures that it can be reduced to a powdered form.- This material has a low penetration ranging from 0 to about 5.

In carrying out this invention it is not neoessary that the paving bituminous cement be adapted to blend or amalgamate with either the powdered hard bitumen or the flux oil and in the practice of some of the modification of this invention it is preferable that the paving bituminous cement amalgamates only slightly with the flux oil at least before the flux oil .amalgamates with the powdered hard'bitumen.

For this reason one can select a paving bituminous cement to obtain optimum properties of binders which are quite hard at ordinary temperatures and which are generally used in the manufacture of pavements by the hot mix methods wherein the bituminous cement is applied to aggregate in a heat liquefledcondition. Such paving bituminous cements are commonly supplied in various ranges of penetration, the more usual ranges being between about 50 to about 120 penetration. (The A. S. T. M. penetration test using 100 grams, 5 secs. at 77 F. is referred to throughout this specification.) The penetration of paving bituminous cement does not run lower than about 20 or above about 300. The term paving bituminous cement includes the ordinary asphalt paving cement and other bituminous materials having corresponding softening point or penetration.

By non-volatile flux oil reference is made to those oils, generally derived from petroleum, that are characterized by being of fluid character (as distinguished from a bituminous cement solid at atmospheric temperatures) and that have the capacity "to flux or blend with harder bituminous materials used in the present process such as, for example, powdered hard asphalt. Flux oils vary from oils that are quite fluid at ordinary temperatures to those which flow quite slowly at ordinary temperatures and which, if desired, can

.be heated somewhat to make them flow more mately 50% ductility and toughness. The flux oil and powdered bitumen that are used should be selected so that they will amalgamate with each other to form a stable bituminous binder upon laying and consolidation in place. As to the selection of complementary pairs of flux oil and powdered bitumen appropriate for proper amalgamation with each other reference is made to the patents of Alfred R. Ebberts No. 1,937,749 and 2,067,264.

In order that this invention andthe practice thereof may be better understood it will be described in connection with a specific example that has proved to be satisfactory in practice. According to this example mineral aggregate of desired size was mixed in a mechanical mixer so I p as to receive a total of about 8% of bituminous material and after mixing the mixture was talren to the point of use and laid and was rolled or thrown open to trailic to consolidate it in place. The paving asphalt cement consisted of 92 penetration asphalt derived from petroleum and constituted 4% of the final mixture or 50% of the total bituminous binder. The asphalt cement was reduced to a molten condition by heatin to about 325 F. To the molten asphalt cement the "flux oil was added at a temperature of about 125 F., the mixing being only suilicient to distribute the flux oil in the molten paving asphalt. In the resultant mixture the paving asphalt and flux oil formed a rather stringy mixture without complete mutual solution or amalgamation tween these two components of the binder. The flux oil constituted about 2.2% oi the entire mix or about 27% of the total bituminous binder and consisted of flux oil having a .viscosity Furol of about 600 to 800 seconds at 122 F. and exhibiting a loss of less than 5% on heating 50 grams for 5 hours at 325" F.

As soon as the paving asphalt cement and flux oil were admixed in the manner aforesaid, the admixture was applied to the previously dried aggregate at a temperature of about F. while the aggregate was in the mixer and mixing was continued until the aggregate was coated. Thereafter the powdered asphalt at atmospheric temperature e. g., about 70 F. was mixed in. the powdered asphalt being composition or about 23% of the total bituminous binder. The powdered asphalt had a penetration of approximately 1 and the mixing was continued only for a short time, e. g. 10 to 20 seconds. The flux oil and powdered asphalt in the .quantities used were adapted upon amalgamation to form a bituminous cement having a penetration in the neighborhood 01' 100. It may be noted that the bituminous cement resulting from the amalgamation-of the flux oil and powdered hard bitumen constituted approxiof the total bituminous binder in the finished pavement and that the paving bituminous cement added to the flux oil also conabout 1.8% oi. the

stituted approximately 50% of the total bituminous binder in the finished pavement.

The composition prepared as above described was easily workable and could be satisfactorily transported and laid. Upon application of pressure by a roller or by traflic the pavement exhibited pronounced stability, both initially because of the intially stable bituminous binder present in the form of paving asphalt, and permanently because of the binder formed by the amalgamation of the flux and powdered hard asphalt. The stability was of the order of that obtained upon cooling a hot mix type of road composition and was a great improvement upon cold mix compositions using flux oil and powdered asphalt alone or using paving asphalt cement cut back with volatiles.

While the foregoing constitutes a preferred illustration of the practice of this invention it is apparent that the process of the specific example above given can be varied without departing from the scope of the invention. Thus the amount and penetration of the paving bituminous cement may be varied considerably to control during mixing and laying the stiffness of the mix and the rapidity of the setup of the mix after laying. One of the advantages of this invention is the control that is possible over conditions of mixing and laying and over the characteristics of the finished pavement. One of these controls can be exercised merely by varying the relative proportion of paving bituminous cement used in the binder. In general the greater the amount of the paving bituminous cement the greater will be the stiffness of the composition in the mixer and the quicker-will be the setup and pavement stability after the composition has been laid. The advantage of the quick setup after laying has been commented upon above. The control of the stiffness during mixing is likewise advantageous. When a flux oil and powdered asphalt are used alone the flux oil sometimes tends to scrub off the aggregate, particularly off the coarser part of the aggregate, so that non-uniformity of coating results. By use of the pav ng bituminous cement the consistency of the material applied to the aggregate can be controlled while still retaining friability and more uniform coating of the aggregate secured. Especially when the total amount of bituminous binder is relatively high in proportion to the aggregate the improved consistency obtained by incorporating the paving asphalt mixed but not completely amalgamated with the flux oil is ad vantageous in obtaining uniform coating of the aggregate particles.

Referring to the foregoing example, the bituminous binder in the completed pavement, which was a combination of thepaving cement resulting from substantially complete amalgamation of the flux oil and powdered hard bitumen together with the added paving bituminous cement mixed with the flux oil, had a penetration of the same order as the penetration of these two bituminous cements, namely, slightly under 100. If it is desired to vary the penetration of the composite binder in the completed pavement this can be readily accomplished by varying the relative proportions of the flux oil and powdered asphalt. Thus to decrease the penetration of the composite binder more of the powdered asphalt and less of the flux oil are used and conversely to increase the penetration of the composite binder more of the flux oil and less of the powdered asphalt are used.' This control of the characteristics of penetration of the ultimate composite binder in the aggregate is V4" the finished pavement can be varied independentlyof the variations in the stiffness of the composition during mixing and the rapidity of setup.

So far as I am aware such relative control has not been possible in connection with paving methods heretofore known.

In good practice the amount of paving bituminous cement that is used varies from about 20% to about 60% of the total bituminous binder and in preferred practice from about 30% to about 50% when relatively coarse aggregate is used, such as when, for instance, about 30% of stone or larger. When "sheet aggregates, or those consisting largely of particles passing a 10 mesh screen are used, the amount of paving bituminous cement used varies from about 10% to 50% of the total bituminous binder, preferably not being over about 40%.

The penetration of the paving bituminous cement that is used may vary considerably, i. e. from about 20 to as high as 300 depending upon the type of pavement being manufactured and the amounts'and characteristics of the flux oil and powdered bitumen that are also used. For the usual types of road pavements I prefer to use paving bituminous cements having a penetration of about 40 to about 120. When the penetration of the paving bituminous cement is in the lower part of the range indicated above it is usually preferable to employ somewhat less of the paving bituminous cement in proportion to the amount of the binder that is added in the divided form of flux oil and powdered hard bitumen. I prefer to' employ paving bituminous cement produced in the refining of petroleum. However, other bituminous materials or asphalts may be used such as tar, pitch, natural asphaltic materials and the like.

Any good grade of flux oil may be used in the practice of this invention. Preferably non-volatile flux oils produced by petroleum refining from any good asphaltic base crudes are used, although other bituminous flux oils such as those derived from mixed base crudes or tars may be employed. The viscosity range of oils that may be selected vary quite widely between about and 2500 seconds Furol at 122 F. In preferred practice the viscosity of the oil used usually varies from about 200 to 1600 "seconds Furol at 122 F.

r Usually it is desirable that the flux oil constitutes at least about 20% of binder in order to get good workability of the mixture during mixing and good coating of the aggregate. The amount of powdered bitumen that is used is sumcient to amalgamate with the flux oil to form a bituminous cement of the paving grade. The amount of powdered bitumen has been varied from about half to twice the amount of flux oil used. In general it is desirable to use a mixture of flux oil and powdered bitumen that will amalgamate with each other and that will when substantially completely amalgamated form a binder cement with a penetration test of about 50 to about 120, although a wider range is permitted under certain circumstances, e. g. about 20 to 200. A test for determining the capacity of the flux oil and powdered bitumen to amalgamate'with each other is described on page 4 of the Ebberts Patent No. 1,937,749 above referred to. In order that the amalgamation may take place at proper rate the powdered hard bitumen is preferably screen although coarser 95% shall pass a 20 mesh mesh screen may be material, e. g. passing a used.

-As aforesaid the binder derived from,the flux oil and powderedbitumen constitutes for good practice at least 40% of the total bituminous binder and preferably constitutes about 50% to 60% of the total bituminous binder.

It is not essential that the penetration of the binder resulting from the amalgamation of the flux oil and powdered hard bitumen correspond with the penetration. of the paving bituminous cement component of the binder. It is usually preferable however to use a paving bituminous cement that has a penetration approximating that desired in the ultimate pavement and to use a flux oil and powdered bitumen mixture which yields a bituminous material that has approximately the same penetration or differs by about 10 to 20 points therefrom. However, if one is limited as to the type of paving bituminous cement that is available and one must use a paving bituminous cement that has either a higher or lower penetration than the required penetration of the total binder in th finished pavement, it is advantageous that the presence of a bituminous cement of too low penetration can be compensated for by using a flux oil and powdered asphalt binder the penetration of which when amalgamated is higher than desired for the total binder in the pavement and compensates for the too low penetration of the bituminous paving cement so as to obtain the desired penetration in the finished pavement; and the converse is also true.

While it is to be preferred, it is not essential that the flux oil and paving bituminous cement be premixed previous to application of the paving bituminous cement to the aggregate. Thus substantially the same effect but to a lesser degree can be produced by mixing the flux oil and paving bituminous cement on the aggregate particles. To illustrate, the flux oil and paving bituminous cement may be added separately to the aggregate in the mixer, the powdered hard bitumen preferably being added after the incorporation of one or the other or both of the other bituminous ingredients. While in such case it is preferable that the paving bituminous cement be applied to the aggregate either substantially simultaneously with flux oil or after flux oil has been applied to the aggregate, the paving bituminous cement in a heat liquefied condition may be satisfa'ctorily added at any stage of the mixing operation under certain conditions. In the first place, sufficient mixing time should be allowed, if the flux oil and pavin bituminous cement are added separately, to permit good commingling of these materials on the aggregate, preferably while the paving bituminous cement is still in a heat liquefled condition. In the second place, sufllcient of the flux oil unamalgamated with powdered hard bitumen should be present during the mixing so that the mass remains in a friable condition because of the occurrence of the paving bituminous cement in a commingled state with flux oil and because of the presence of a substantial amount of the powdered hard bitumen in an unamalgamated and non-adhesive condition. However, while it is possible to add the paving bituminous cement and the flux oil separately and commingle them on the aggregate as aforesaid, the procedure is less desirable than premixing these materials before application to the aggregate because the bituminous coating for the aggregate is usually less uniform than when the flux oiland paving bituminous cement are premixed and because the paving bituminous cement frequently tends to ball up and form small lumps throughout the aggregate; It is also possible to apply paving bituminous cement in an emulsified condition and remove excess water and commingle it as thus added with flux oil and powdered hard bitumen but this method is much less desirable than the other methods described herein.

The temperature during mixing should as aforesaid preferably be below that which tends to prematurely cause a melting of the bituminous components together prior to laying. For this reason customary hot mix temperatures, e. g. 225' F. to 375 F. are avoided. when the flux oil and powdered asphalt blend quite gradually mixing temperatures as high as about 200 F. may be used in the practice of this invention; and especially in cold weather or when an abnormally viscous flux oil is used fairly high temperatures below about 200 F. may be employed. In preferred practice, however, temperatures which are usually below the softening point of the paving bituminous cement, e. g. ranging from normal summer temperatures to about 140 F. are employed during mixing thereby taking full advantage in mixing the materials of avoiding the expense and inconvenience of working at higher temperatures while still retaining workability and friability of the composition. To produce uniform coating of the aggregate the aggregate is preferably at approximately the same temperature throughout.

The aggregate that is used is generally a graded mineral aggregate consisting of sand, crushed size ranging from sand and the like to relatively coarse store, e. g. about 1 inch may be included. When the aggregate contains a high percentage of fines, e. g. sand or screenings, it is preferable to select a paving asphalt cement of relatively high penetration, e. g. from overto about 200. When filler is used such as powdered limestone, fine sand or the like, the filler may be present during mixing although it is usually preferable to add the filler after the flux oil and paving bituminous cement have been applied to the aggregate. If desired, any filler that is used can be added with the powdered hard bitumen. In carrying out the processes above described the aggregate becomes coated substantially uniformly throughout so that in preferred practice each of the aggregate particles carries a similar coating of powdered hard bitumen unamalgamated with flux oil and paving bituminous cement commingled with fiux oil.

Other examples of the practice of this invention are as follows:

An amount of coarse aggregate, consisting of quarter inch stone and comprising 50% of a total aggregate, was placed in a mixer at a temperature of 125 F. To the stone 9, quantity of flux oil at a temperature'of 125 F. was added, and mixing was continued for a short time, where'- upon paving asphalt of penetration liquefied by heating to a temperature of 325 F. was added and was commingled with the flux oil on the coarse aggregate by mixing, the paving asphalt cement by this operation being commingled with the flux oil during the application of the paving asphalt cement to the aggregate. The remainder of the aggregate, consisting of sand and filler,

was then added and mixing was continued until all was thoroughly coated, when powdered asphalt was mixed in. The fiux oil, which was about 800 sec. viscosity Furol at 122 F. comprised 3.0% of the total mixture or 37% of the binder material, the asphalt cement comprised 2.7% of the total mixture or 33% of the binder material and the powdered asphalt comprised 2.4% of the mixture or 30% of the binder. It was found that by virtue of the paving asphalt cement being mixed with relatively liquid fiux oil on the coarse aggregate, it was possible to coat the total aggregate, including the fines, easily and at a low temperature. In this example and in the following two, the fiux and powdered asphalt were used in such proportions as to give upon substantialh; complete amalgamation a bituminous cement having a penetration of about 80. The paving composition was friable until compacted, and then formed a firm mass bound by .both the paving asphalt cement and the cement formed by the amalgamation of the flux and powdered asphalt.

As another example, an amount of flux oil at a temperature of 125 F. was added to paving asphalt cement at a temperature of about 300 F.,

and the resulting mixture was immediately added, after very little stirring, to aggregate in a mixer. When the aggregate particles were thoroughly coated with the mixture, powdered asphalt was added and mixed with the coated aggregate. The paving asphalt cement comprised 3.3% of the total mixture or 30% f the hinder, the flux oil comprised 4.2% of the mixture or 38% of the binder, and the powdered asphalt comprised 3.5% of the mixture or 32% of the binder. When it was desired to prepare a mixture in which only fine aggregate, consisting of sand and filler should be used, but which should have more stability than most cold mixes and yet should handle easily and store well, a mixture was made in the example above, but in which the asphalt cement comprised 1% of the total mixture or 13% of the binder, the flux comprised 3.7% of the mixture or 48% of the total binder, and the powdered asphalt comprised 3% of the mixture or 39% of the binder. The ggregate in this mixture was not as firmly vor heavily coated with bituminous materials as that in the preceding examples, but the mixture was much more stable immediately after compaction than a similar mixture in which no paving asphalt cement was employed.

In the practice of this invention and as exemplified bythe foregoing examples the paving bituminous cement is commingled with the fiux oil as applied to the aggregate particles and notwithstanding the fact that the paving bituminous cement would be quite still at the temperature occurring during mixing, the commingled materials together with the powdered hard bitumen satisfactorily and readily coat the aggregate at such temperatures. In fact the coating that is obtainable is more complete and more uniform than when fiux oil and powdered asphalt are used by themselves and forms thicker films than when paving asphalt cement is applied by itself under not mix conditions:

Maximum workability at any given temperature is obtained when the fiux oil and paving asphalt are commingled on the aggregate or are applied to the aggregate promptly after having become commingled. This is because the fiux oil and paving asphalt cement do not immediately blend or amalgamate with each other but are merely commingled with retention in large degree of the the paving bituminous cement have little solu cause it is injurious in the oiilty either with the flux oil or with the powdered hard bitumen as under these conditions optimum workability during mixing and laying is obtained since many of the paving bituminous cements which have very high ductility e. g. plus at 77 F. A. S. 'I'. M. test and which navesuperior wearing properties in the finished road have little it any solvent power for powdered hard bitumen at low temperatures, it is preferable in the practlce of this invention to select such materials both from the point of view of workability during mixing and laying and from the point of view of obtaining'desired characteristics in the ultimate pavement. since, however, the paving bituminous cements have very little solvent power for powdered hard bitumen, the flux oil that is used should be of such character and quantity as to blend with the powdered hard bitumen to produce a bituminous cement of desired penetration.

In the practice or this invention the presence of volatile solvent for the powdered bitumen or paving bituminous cement is undesirable. vIt has been mentioned above that any volatile solvent that is present during laying is undesirable bepavement and cannot be driven ofl from a pavement of desirable density. It is one of the advantages of the present invention that pavements of high density can be manufactured which are resistant to internal movement after the laying and consolidation. The presence of volatile solvent during the mix-. ing of the materials is also undesirable because the presence of the solvent promotes mutual solubility of the flux oil and powdered hard bitumen and while the volatile solvent has a somewhat thinning action on the bituminous material this is counteracted by the premature setting up effect that results from of the intermingled components of the bituminous binder. While substantially complete absence of constituents volatile at ordinary temperatures is much to be preferred some of the advantages of this invention can be achieved even though a small amount of volatile material such as kerosene, naphtha or the like is present, e. g. about 5 of the total binder material and preferably less than 3%. In such case premature solvent action is not excessive and the presence of the'small amount of solvent in the finished pavement, even if the pavement is dense, will not result in excessive bleeding of the pavement, or excessive rutting. If any volatile matter is present during harmful when presentgin the cement upon application of the paving bituminous cement to the aggregate.

premature amalgamation trapped in the-finished pavement tor a considerable period of time.

While it is ordinarily preferable to mix 'the materials in a mechanical mixer such as the ordinary pug mill mixer, the pavement can be mixed in place on the road foundation. In such case it is usually desirable to preliminarily dry the aggregate and the drying may be assisted by the use of a drag or blader. When the paving composition is mixed ditions be such as by using a has a somewhat It is an advantage of this invention that no expensive or special apparatus is required, that the method of mixing is economical, and that the materials used are readily available.

While mention has been made of the manufacture of a composition suitable for the manufacture of road pavements, it is apparent that the method described herein can be used in the manufacture of other pavements (the term being used broadly) including but without limitation such pavements as sidewalks, levee linings, roofs, asphalt blocks, and the like.

While this invention has been described in connection with certain exempliilcations of the practice thereof this has been done for the purpose of affording a better understanding thereof, it being understood that variations in the practice thereof may be made without departing from the scope of the invention. In fact it is one of the advantages of this invention that the paving method can be varied so as to achieve control of the mixing consistency and the coating of the aggregate as well as the penetration and initial stability of the completed pavement while retaining the mass in a physical state such that the composition, notwithstanding the presence therein of substantial quantities of paving bituminous cement, can be readily mixed, stored, transported and laid at relatively low temperatures. ,The scope of my invention is therefore to be governed by the language of the following claims construed in the light of the foregoing description of my invention.

I claim:

1. In a method of making a paving composition. the steps comprising utilizing a normally solid paving bituminous cement, powdered hard bitumen and a substantially non-volatile flux oil having a viscosity Furol at 122 F. between 100 and 2500 seconds and constituting at least about 20% of the bituminous binder materialin the composition, commingling said paving bituminous cement in a heat-liquefied condition with said flux oil, coating the aggregate particles with the flux oil and paving asphalt cement while the flux oil acts as a carrier for paving bituminous cement unamalgamated therewith, and then incorporating the powdered hard bitumen and distributing it throughout the mass, thereby forming a paving composition wherein the aggregate particles substantially uniformly throughout the mass are coated with the flux oil containing paving bituminous cement unamalgamated with the flux oil and containing P wdered hard bitumen that is unamalgamated with the flux oil and paving bituminous cement, said composition being adapted upon consolidation in place and upon amalgamation of the flux oil and powdered hard bitumen to produce a pavement resistant to internal movement in which aggregate particles are bonded both by the paving bituminous cement and by the cement resulting from the amalgamation of the flux oil and the powdered bitumen.

2. In a method of making pavements or the like, the steps comprising utilizing a normally solid paving bituminous cement having approximately the penetration desired for thebinder in the completed pavement together with a substantially non-volatile bituminous flux oil and powdered hard bitumen, the said bituminous flux oil and powdered hard bitumen being adapted to' mixture of commingled flux oil and paving asphalt cement, and adding said powdered hard bitumen, thereby forming a friable composition containing the aggregate particles coated substantially uniformly with the commingled and incompletely amalgamated flux oil and paving bituminous cement together with particles of powdered hard bitumen unamalgamated with either the flux oil or paving bituminous cement,

said flux oil plus said powered hard bitumen constituting at least about 40% of the total bituminous material in the composition and said paving asphalt cement constituting at least 20% of the total bituminous material.

3. A method comprising the steps according to claim 2 wherein the amount of said powdered hard bitumen is about half to about twice the amount of said flux oil.

4. In a method of making pavements or the flux oil, coating the aggregate particles with the,

. admixture of commingled flux oil and paving bituminous cement and adding said powdered hard bitumen, thereby forming a paving composition that is friable at temperatures below the softening point of the paving bituminous cement and that contains said commingled flux oil and having bituminous cement together with powdered hard bitumen unamalgamated with either the flux oil or paving bituminous cement; said unamalgamated flux oil and powdered hard bitumen upon laying and consolidating the friable composition in place being adapted to amalgamate with each other in situ to solidify the composition in the form of a pavement wherein the aggregate particles are bound in conjoined relationship by a bituminous binder comprising the said paving bituminous cement together with the bituminous cement resulting from the amalgamation of the flux oil with the powdered hard bitumen.

5. A method according 'to claim 4 wherein said paving bituminous cement has a penetration between about 40 and about 120 and wherein said 'substantially non-volatile bituminous flux oil and powdered hard asphalt are adapted to amalgamate to form a bituminous cement having a penetration between about 50 to about 120, the powdered hard bitumen being about one-half to twice the amount of said flux oil, and said flux oil having a viscosity Furol at 122 F. between 200 and 1200 seconds.

6. A method according to claim 4 wherein the powdered hard bitumen is about one-half to twice the amount of the substantially non-volatile bituminous flux oil, said flux oil has a viscosity Furol at 122 F. between 200 and 1200 seconds, the bituminous cement formed by amalgamation of the flux oil and powdered hard bitumen constitutes at least about 40% of the total bituminous cement in the completed pavement, and said paving asphalt cement constitutes at least 20% of the bituminous cement in the completed pavement.

7. In a method of making pavements or the like, the steps comprising utilizing paving bituto about twice the amount 01 flux oil and being adapted to gradually amalgamate with the flux oil to produce a bituminous binder cement which has a penetration of about 40 to 200 and which constitutes at least about 40% of the total bituminous material in the pavement; and mixing the paving bituminous cement in heat-liquefied condition with the flux oil to commingle said paving bituminous cement with said flux oil, coating aggregate particles while the aggregate is at a temperature below 200 F, with the admixture of commingled flux oil and paving bituminous cement, and adding said powdered hard bitumen, thereby forming a paving composition that is friable and that contains said commingled flux oil and paving bituminous cement together with powdered hard bitumen unamalgamated with either the flux oil or paving bituminous cement; said unamalgamated flux oil and powdered hard biminous cement having a penetration of about 20 tumen, upon laying and consolidating the friable composition in place, being adapted to amalgamate with each other in situ to solidify the composition in the form of a pavement wherein the aggregate particles are bound in conjoined relationship by a bituminous binder comprising the said paving bituminous cement together with the bituminous cement resulting from the amalgamation of the flux oil with the powdered hard bitumen, and any component of the bituminous binder materials that .is volatile at ordinary temperatures being not more than 5% of the total of said bituminous binder materials.

FRANK B. McGRANE.