US2003888A - Method of constructing asphalt pavement with natural aggregates - Google Patents

Description

June 4, 1935. c, C, JAQHESON 2,003,888

METHOD OF CONSTRUCTING ASRHALT PAVEMENT WITH NATURAL AGGREGATES Filed Oct. 28, 1930 Orff/aff: C Jan/fsa# www@ Patented June 4, 1935 UNITED STATES PATENT OFFICE METHOD OF CONSTRUCTING ASPHALT A PAVEMENT WITH yNATURAL AGGRE- l GATES This invention relates in general to road building and more particularly has reference to the construction of roads using oil with an asphaltic residue for incorporation with the natural aggregate of a roadbed.

It has been common practice, previous to this time, to spray earth roads with oil containing an asphaltic residue so as to form a mat or crust adapted to form a wearing surface for traffic. Oil, with an asphaltic residue has also been mixed with the soil forming a mixed-in-place roadbed to a depth of several inches and'subsequently compacted by various methods to form, in effect, a pavement, usually termed light asphalticv cil roads. This latter construction has proved to afford fairly satisfactory secondary highways, but the. nished road when so constructed has proved to possess certain fundamental disadvantages which I seek to overcome by my present invention.

It is well recognized, that the character of the aggregate of a natural earth road surface, in many instances, changes widely over short distances, that is, in a given stretch of road the natural aggregate may be found to consist over different portions thereofof such materials as loam, sand or shell, or mixtures of these together with other materials and substances.

In the construction of mixed-in-place roads, in the past it has been the'practice to apply the same asphaltic base oil over the entire length of the roadway irrespective of the variation in the aggregate thereof. It will be apparent, that if a road so treated is one in which the character of the aggregate varies widely from section to section, while the blend of asphaltic base oil applied may prove suitable for the aggregate of one section that a second section composed of a different aggregate similarly treated vwill result in a poor 40 or unsatisfactory road.

When the characteristics of the materials which may enter into the composition of the aggregate of the roadbed over even short distances are considered it will be appreciated thatwhere these aggregates are materially different the application of a uniform grade of asphaltic base oil, in. the same quantities cannot result in a road of uniform quality and penetration, but that it will vary in hardness and stability from point to point as the aggregates themselves vary.

In order to'determine the right amount and correct blend of asphaltic base oil to be'applied to the aggregate of the roadway, which is to be treated, it is necessary to take into consideration the size of the particles of the aggregate and the material.

absorptive qualities of the different elements thereof.

If the aggregate is composed wholly of sand or shell or a mixture thereof it is manifest that the yabsorptve qualities of the individual grains will be practically nil, particularly if the sand is of high silica content and that the interstices will be small if the particles of the sand are ne so that a relatively small quantity of asphalt should be applied if flooding is to be avoided, as distinguished from the treatment of an aggregate composed largely of loam, which is much more absorptive, and will require a larger volume of In the case'of shell partly pulverized and mixed with sand, the quantity and thickness of the asphaltic base oil will again differ, due to the non-absorptivequality of the shell. Similarly, the thickness of the blend or the viscosity of the asphaltic cement applied should be controlled according to the character of the material treated, which, if comparatively non-absorptive, with large interstices, Vrequires treatment with a thick viscous blend while if highly absorptive, as in the 'case of loam, the asphaltic blend should be thinn'er and flow with comparative freedom. In stabilizing various aggregates, such as'those described, varying mixtures of the same may be found to compose the aggregate or material of the roadbed and the blend, viscosity and quantity 'of asphaltic cement applied should be controlled and regulated accordingly. l i' Theviinalor proper percentage of asphalt to be appliedisr that necessary to stabilize the particular aggregate. The asphalt should accordingly be applied in'ble'nds'that are iluxed back with 'asplfialtic' oils as a convenient method or means of thoroughly incorporating the asphalt through `out the aggregate. In other words, a primary function of the ilux oil is to thin the asphalt so it Willilo'w freely when heated and act as a vehicle for the purpose of insuring the incorporation of the asphalt throughout the aggregate. lThe blends applied Vmay' vary in asphaltic content andthe number of applications may also vary to Abuild up the proper total asphaltic content to meet the requirements `of the particular aggregate. When constructing a roadway, in the practice of this invention, where the aggregates forming the roadbed are composed of different materials or vary from point to point, the quantity Vof asphalt, the composition of the blends and the -number of applications are regulated so asto produce a pavement of uniform penetration and stability over the entire length of the road regardless of the variation in the aggregates.

An object of this invention is to provide a process of constructing roads from the natural aggregates of the roadbed by a predetermination oi' the size and character of the grains forming the aggregate for the purpose of insuring the use of the correct quantity of asphalt and the proper blends thereof.

Another object of this invention is to provide a process of constructing roads using the natural aggregates of the roadway by determining the density of the aggregates for the purpose of the application of the necessary quantity of asphalt by means of a suitable blend,

Still another object of this invention is to provide a process of constructing roads from the natural aggregates of the roadway by which the neness of the grains of the aggregate and density of the aggregate is determined for the application of the necessary quantity of asphalt of a suitable blend.

n A further object of thisinventionis to provide a process of constructing roads using the natural aggregate of the roadway in which the size of the cation of the right quantity and correct blends thereto..

Still another object of this invention is to provide awprocess for constructing roads using the natural aggregates of the roadway by predetermination of the nneness of the aggregate and the density thereof from point to point or section to section of the roadway in'order that the right quantity of asphalt may be applied in blends of the proper thickness or viscosity and in a desirable number of applications. Y

A stil-l further object of this invention is to provide a processI of constructing roads, using the-roadbed as a source of aggregatey in which a road of uniform penetrationv and stability throughout its length may be built of the naturally varying local types of aggregate present in the said roadbed at the point being worked upon. This is accomplislnzdv byrirst determining the 'neness, density, and other characteristics of the aggregate. Then there is applied the right vquantity oi asphalt insuitable blends in a sufficientl number of applications to properly build up the roadbed.

With these and other objects in view which may be incident to my improvements, the invention consists inY the steps to be hereinafter set forth and claimed with the understanding that the several necessary steps comprising my invention may be varied inorder without departing fromI the spirit and scope of the appended claims. In order to make my invention more clearly understood I havel shown in the'accompanying drawing aI chart illustrating how my invention is vcarried into practical effect without limiting the improvements in their useful applications to the particular steps, which forv the purpose of explanation have been made the subject of illustration. Y g

In the drawing forming a part of this specification, the single figure is illustrative of the steps I follow for determining the composition of a roadoed in order to treat the aggregates composing the same with the necessary quantity of asphalt of suitable stiffness in proper blends and a desirable number of applications for obtaining a iinished roadway of uniform penetration and stability throughout its length over foundations of different character.

I propose to treat the existing natural aggregate of a roadway with asphalt of standard specication and of such penetration that when blended with the proper proportion of asphaltic base oil, a r'oadwayof specied penetration and stability may be produced by a sufficient number of applications.

In practicing my invention, I realize that the aggregate composing a roadbed usually differs in character over various parts thereof, and I have overcome the apparent insurmountable difnculty of constructing a road of uniform penetra-tion and stability from such varying aggregates by incorporation of the right quantity of asphalt in the different' aggregates composing the roadbed by applying varying quantities of g asphalt in suitable proportions differing throughout the length of the roadbed by mear-s of varying blends and numbers of applications thereof according to the neness, density and absorptive quality of the particular aggregates composing the successive portion of the roadbed.

With reference to the accompanying drawing, the letter A is indicative of a roadbed which it is desired toV pave with asphalt in accordance with my invention.

While roads have been previously constructed from the natural aggregate of the roadway by the application of asphaltic base oils, I am not aware that the neness and density of the aggregate have ever heretofore been corr-elated for determining the proper quantity of asphalt necessary in the proper blends with flux oil and the desirable number of applications, or that samples of aggregates from the roadway have ever been selected at fixedv distances, with intermediate samples wherefoun'd desirable, for the purpose of determining the variations in the fineness and density of the aggregates' in' order that the quantity of asphalt,` the blends and the number of applications may bey varied from section to section to obtain uniform results.

In carrying onmy invention the proportionate percentage of asphalt necessary to stabilizev the aggregate is determined according to the iineness and density of the aggregate. mination, asphalt is` mixed with asphal'tic base iiux oil to aiord what are deemed desirable blends, in accordance with' the neness and density of the aggregate, the blending being so determined that with the proper number of applications the desired quantity of asphalt to stabilize the aggregate will* be finally incorporated' therewith. I believe, therefore, the essential feature of my invention to reside in the determination of the character of the aggregate, particularly the fineness and density of the same at short intervals over the length of a roadway, for differentiating between the aggregates' for the purpose of applying diierent quantities of asphalt and Varying blends and numbers ofapplications so that a nal rca-df surface of uniform penetration and stability may be obtained'.

In the construction of an asphalt pavement, I first select samples of the aggregate from the roadway to be treated at various intervals, as in- Withthis deterdicated on the drawing, by the letters B to F, inclusive. The distances may be determined for example by marking off tenth miles on an ordinary speedometer. If marked changes are found to occur intermediate samples may be taken to insure an accurate determination of any changes in the aggregate over shorter distances.

It will of course be appreciated that the intervals of tenth miles indicated for the purpose of illustration are merely arbitrary, and the intervals at which samples are taken can necessarily be determined by the character of foundation of the roadway which is to beworked upon.

When samples of the aggregate are selected for the purpose of identification according to the location where the same are obtained and eXamined to determine the fineness and density, it will, of course, be apparent that this determination may be carried on in any conventional manner. The nneness may be determined by sieve analysis while the density Vmay be computed by the usual displacement method with water or other penetrating liquid. If found desirable, a microscopic examination may be made of the different samples of aggregates to further determine the absorbent qualities of the same. Test samples of the various aggregates may be prepared by the application of the indicated quantity and blends of asphalt and tested by a suitable penetrometer to check the results of using the predetermined quantities before actual construction work on the road begins.

The treatment of aggregates of different sizes, density, and materials will necessarily require different quantities and" blends of asphalt. VIf the aggregate is relatively non-absorbent and fine, a minimum quantity of medium blend asphalt will be required by reason of the small interstices, while if the aggregate is coarse, a greater quantity of relatively viscous or heavy blend of asphalt will be required to fill the interstices. If, on the other hand, the aggregate is of a highly absorbent nature and fine, a greater quantity of the light blend asphalt will be necessary to compensate for the absorption, while if highly absorbent and comparatively coarse a maximum of asphalt content will be required to stabilize the aggregata the viscosity being regulated so as to allow7 absorption by the aggregate and to fill the interstices ofthe compacted aggregate without flooding the finished surface.

As has already been indicated, I determine from the neness and density of the samples of the aggregate collected, the relative measure of asphalt content required to stabilize each aggregate, also determining the most desirable blend of asphalt with iiux oil, and the number of applications deemed most suitable. It will be further noted that I prefer to apply blends to a particular aggregate, increasing in asphalt content in order to obtain the best iinal distribution of the required Vquantity of asphalt throughout the aggregate. The asphalt content of the aggregate treated usually is built up by applying blends increasing in percentage of asphalt inasmuch as it is manifestly impractical to apply a vsingle mix having incorporated therein the total quantity of asphalt on a roadway in a single application, as the asphalt has a tendency to roll into balls and thus prevent uniform distribution throughout the aggregate to the depth of the foundation treated.

Having selected and analyzed samples taken from the roadway to be treated, at suitable intervals, for example, at tenth. miles as shown on the drawing, a chart is plotted to indicate the requirements of the different aggregates in the roadway with respect to the asphalt content necessary to stabilize each, as at G to L inclusive so as to aid in the production of a pavement having a uniform penetration and stability throughout.

As illustrated on the chart, the required amount of asphalt to stabilize each section of the different aggregates is noted. -As shown at G, there is required 23 parts of asphalt for the rst tenth of the mile. That is to saythat out of a hundred parts of asphalt and aggregate, it is necessary to use twenty-three parts of asphalt to stabilize the section. A slight variation. 0f asphalt content is required for the next tenth of the mile as indicated at H. The different amount of asphalt content required'for each section can be shown on the plotted chart for the entire road and this information made available at a glance. Of course, it is to be understood that if there is a marked variation in the different aggregates composing the roadbed, the quantity of asphalt required can be' indicated more frequently than as illustrated. If the reverse is true and there is not a marked variation in the aggregates of the roadbed, the quantity of lasphalt required can be indicated less frequently.

As has been previously pointed out, if the ag# gregate in a particular portionrof the roadway is found to be relatively ne and of such density as to be relatively non-absorbent, a :minimum of asphalt will be necessary to stabilize the aggregate on this particular portion of the road to` be treated. The desirable blends will similarly be determined from the size and densityv of the aggregate and charted as at M to R inclusive. As illustrated in the first tenth mile distance between the letters M and N, there is required a plurality of different blends of asphalt and flux oil. The first treatment requires a blend having a solution of 30% asphalt and 70% flux oil. The subsequent treatments require blends having and respectively, of asphalt with flux oil making up the remaining part. The numerals on the appended chart underthe heading Blends required represent in tenths the asphaltic contents of the solution; In other Words 3.0 represents a 30% solution; 4.5 a 45% solution, etc. If theV aggregate is relatively non-absorbent, a1- though fine a comparatively medium blend may be used, while with an increase in absorbent qualities, as in the caseof a large loam content, the blends applied will necessarily have to be thinned. The number of applications, blends and the quantity of asphalt in each blend to build up the necessary asphalt content is determined by thefcharacter of the aggregate, that is, its nneness and density, in the same way as the blend, and charted as at S to Winclusive. absorbe-nt a greater number of applications will be required to thoroughly incorporate the impregnant, than where the aggregatel is relatively non-absorbent and likewise if fine or coarse.

The relative asphalt content required to stabilize the aggregate found in the roadway at the points where tests are made are thus outlined on the chart for the determination of the changes'n the volume of asphalt applied, the blends deemed suitable and the number of applications to be incorporated the different sectors of the roadway with reference to the chart.

In charting the quantity of asphalt required by the successive changes in the aggregate, in order to produce a uniform road, a graph may be made, as indicated in the drawing by the line X.

If highly Significant points corresponding'to the samples tested are plotted with their abscissas scaled to represent the lineal distance between the points on the road at which the respectiver samples were taken, and their ordinates scaled to represent the calculated quantity in cubic reet of asphalt, orY

pounds of asphalt, per cubic yard of aggregate required to produce a uniform road of the standard desired. This quantity in cubic feet or pounds per cubic yard for each point may be readilycalculated from the respective indicator ligure G, H, I, J, K, or L which states the proportionate parts of asphalt and aggregate necessary as found out by tests.

The signicant points having been plotted, a line X may then be run from point to point. This line is roughly representative of the relative, as well as quantitative, amounts of asphalt necessary, and therefore is approximately inversely a function of the relative stability of the untreated natural local aggregate. The line Z may be divided into sections extending from the midpoint between any two adjacent significant points to the midpoint between one of these points and the next. The ordinates of these sections may then be averaged by adding the ordinates of the two end points with twice'that of the included signiiicant point and ldividing by four. These mean ordinates, representing both relative and absolute volume of asphalt for the respective section of rpad may be multiplied by a fraction having l0 as its numerator and the average of said sections rcspective E5 to W numbers as the denominator to obtain the lines Y which represent volumes, both relative and absolute, of blend to be sprayed on the respective sections of road. Similar methods of calculation may be used without departing from this invention.

The material in which the asphalt adapted tc be incorporated of course, the natural aggregate found in the roadway. All injurious vegetable matter should be removed to the full depth to, be. treated, which may vary from a min'muin thickness of six inches to eight inches or more, depending on local conditions.A The roadway prepared is scaried or harrovved over its entire surface to the required depth, after which the rst application is made, preferably in an amount not to exceed four-tenths of a gallon to a square yard. The irst blend applied upon the roadbed for the particular section will usually be higher in iluxl oil than the successive blends.

The applications on the roadway are preferably made by a positive mechanical pressure distributor combined with equipment to thoroughly mix the asphalt and flux oil therein. The blends are applied at temperatures varying from 21) to 275 F., according to the conditions found, but these temperatures may be higher or lower under particular conditions. i

- After the application of each successive blend, I prefer to immediately mix the same with the aggregate of, the roadway as by harrowing, followedwith a plow and pulverator, such as shown in my copending application, Patent No. 1,902,857, dated March 28, 1933, so that the blend I am applying may be thoroughly incorporated with the aggregate of the roadway to the depth required. I continue the application of the blends followed by the subsequent mixing of the same with the aggregate until the necessary asphalt content for the particular aggregate has been built up. In applying the blends at the proper temperature, I vary the volume applied to each square yard of roadway from a minimum of approximately one and eight-tenths to a maximum of approximately three gallons, for the treatment to the depth of six inches depending upon the particular type of aggregate undergoing treatment. The blends are thus applied in the proper volume until the necessary asphalt content is fully built up by successive applications of the blends followed by mixing in each instance.

In compounding my blend, I employ any asphalt of standard specication and quality and of such penetration that when blended with the correct proportion of asphalt base oil and aggregate, a roadway of specified penetration and stability may be produced. For ordinary purposes l prefer to employ an asphalt of from 50 to G0 penetration, although in some instances as low as from ll0 to 50 may be used and occasionally asphalt of higher penetration. The test used is the A. S. T. M. standard test for penetration of bituminous materials adopted in 1916, serial designation D 5-16. I mix the asphalt with any suitable asphaltic base oil but ordinarily prefer a slow volatilizing flux oil having a content of approximately sixty per cent of asphalt of ono hundred penetration to produce blends, for example, of the character of those indicated on the drawing from S to W, inclusive.

The figures from S to W, inclusive on the drawing indicate the percentage of asphalt in the blend, for example, in the nrst blend a solution 0f 39%.asphalt and 70% flux oil is applied, and subsequently three additional blends containing 45% and 55% asphalt, respectively.

is hereinbefore stated in order to build up the necessary asphalt content, I usually treat the aggregate with'froin one and eight-tenths to 3 gallons total o blend per square yard for treatment of 6 to 8 inches. Each application therefore will be but a fraction or" this voliune while in the first application I deem it preferable not to employ more than from three-tenths to fivetenths of a gallon, dividing up the remainder proportionately among the successive applications of blends in order to build up the necessary asphalt content. The total number of applications may vary from four to ten, and in exceptional cases more, depending upon the blends and the total quantity required. It will be seen, therefore, that I may apply a large volume of blend containing a relatively low percentage of I asphalt to meet the particular requirements of one aggregate or apply a blend having a relatively large asphalt content to meet the requirements of an aggregate of an entirely different characteristic, or may change either the asphalt i..

content or volume to meet the requirements of other aggregates varying between these two extremes.

Thus my treatment is adaptable to aggregates requiring a comparatively large volume of blend carrying a relatively low percentage of asphalt and oppositely, aggregates requiring small volume of high asphalt content to produce a stable pavement having a uniform penetration throughout.

In order to more einciently carry out the operation of applying diiferent blends at various points to meet the particular requirements of aggregates differing in character, I deem it preferable to mix the asphalt and flux oil at the unloading points so that the different blends .may be more easily transported to the particular points where it is intended to apply the saine.

After the necessary asphalt content has been built up in the aggregate by the application and mixing of the required number of blends to build the total percentage of asphalt required, so that the pavement presents a uniform homogeneous appearance, the road may then be shaped to the required cross section and rolled longitudinally from the sides to the center until the entire surface has been covered.

When the pavement has thus been shaped, an application of flux oil may be made on the surface for the purpose of softening any remaining lumps and insuring a uniform distribution of asphalt as well as to color the surface. If a slow volatilizing oil is applied, a thin surface crust adapted to act as a wearing surface will be `formed and the body of the pavement protected.

In this manner the remainder of the cross section is adapted to remain alive so that in subsequent repair work, the pavement may be easily broken up and additional asphalt incorporated in the same manner already described, if found desirable.

A pavement constructed in accordance with my invention will show an average penetration of not more than 15 millimetres as determined by not less than three tests using a penetrometer needle, weighted to a hundred grams, dropped a distance of ten inches upon laboratory samples which have been subjected to a pressure of 130 pounds per square inch. The samples tested shall be representative of the aggregate from the road under construction. The test should be made, as nearly as possible, at a temperature of 77 F.

There is accomplished by this invention a method of constructing asphalt pavement of uniform penetration and stability, using the natural aggregate found in the roadway in which asphalt is mixed with the aggregate in proportions adapted to stabilize the particular aggregate by incorporating the same therein in blends with flux oil in several applications accompanied by mechanical mixing, the distribution blends and volume of asphalt being approximately determined by a selective examination of the characteristics of the different aggregates composing the roadway.

While I have shown and described the preferred embodiment of my invention, I Wish it to be understood that I do not conne myself to the precise details of construction herein set forth, by way of illustration, as it is apparent that many changes and variations may be made therein, by those skilled in the art, without departing from the spirit of the invention, or exceeding the scope of the appended claims.

I claim:

1. A method of constructing a pavement comprising nely breaking up the natural aggregates composing a roadbed intimately mixing therewith by mechanical agitation blends of a binder and a. flux oil in a plurality of applications, each successive application having an increasingly higher percentage of binder, making a sufficient number of applications to incorporate a total amount of binder with the aggregate to stabilize the aggregate without ooding, the proportion of binder in the blends, quantity of blends, number of applications and nal percentage ci binder, being determined by the characteristics of each aggregate.

2. A method of constructing a pavement comprising intimately mixing with the aggregates of a roadbed blends of a binder and a flux oil until the necessary amount of binder has been applied in order to stabilize the aggregate, and then applying suiiicient flux oil to soften any remaining lumps and to insure thorough incorporation and distribution of the blends in the aggregate.

3. A method of constructing a pavement comprising analyzing specied sections of a roadbed to determine the characteristics of the natural aggregates composing the same, determining the amount of binder necessary to stabilize the aggregate of each section, and intimately mixing with the aggregate of each section successive blends of the binder and a flux oil until the necessary amount of binder has been applied to secure the stability of the aggregate, veach application of the blend being made up of an increasing percentage of binder.

4. A method of constructing a pavement comprising analyzing specified sections of a roadbed to determine the characteristics of the natural aggregates composing the same, determining the amount of binder necessary to stabilize the aggregate of each section, and intimately mixing with the aggregate of each section successive blends of the binder and a flux'oil until the necessary amount of binder has been applied to secure the stability of the aggregate, each application of the blend being made up of an increasing percentage of binder, and then applying sufficient ux oil to soften any remaining lumps and to insure thorough incorporation and distribution of the blends in the aggregate.

CHARLES C. JAMIESON.

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