US 2507629 A
Description (OCR text may contain errors)
Patented May 16, 1950 STATES PATENT OFFICE.
BITUMINOUS COMPOSITION James F. Gallagher, Thornton, Ill., assignor to Gallagher Asphalt'Company, Inc., Thornton, Ill.', .a corporation of Illinois No Drawing. Application April 24, 1947, Serial No. 743,731
gates, and, to. the use thereof for roads, pave-- merits, air field runways, side-Walks, floor coverings, revetments, drainage ditch, reservoir or tank linings, etc. Its particular use, howevenls for traflicways.
More'specifically; the present invention relates to graded particles composed of a mixture of bituminous material of specific character together with fibrous material and finely-divided mineral fillers, and of a character which permits storage thereof prior to use and subsequent laying, and subsequent compaction and welding of the particles to provide a surface of advantageous character, either by the aid of'h'eat or conventional bituminous binders, fluxes, oil or the like, or both.
All of the bituminous compositions in use at present are composed principally and'mainly of mineral aggregates, for example 85%to 95% by weight cemented or bound together with about 5% to 15% by Weight bitumen; The mineral aggregates are sands, stone'or rocks, either occurring naturally as glacial or eflluvial deposits or as the result of weathering, or artificially produced by-Crushing or grinding. The bituminous binders may be natural or artificial-oils, fluxes, asphalts, tars, pitches, either liquefiedby heat or diluents or emulsification. The mixing or com- I Dining of the ingredients iscarrie'don at-all temperatures from normal to 400F. or higher. In some instances, deposits of sand or rock with a natural impregnation of a bitumen, such as oil or soft or hard asphalt, are used either as occurring in deposits or by crushing and adding either more mineral or bitumen iinecessary.
The use of'mineral aggregates in bituminous pacing-compositions is an old art. Thousands upon thousands of miles have been constructed,
but frequently with only partial success and generally with all too short an existence. Failuses occur very frequently and the-overall lifeaoi even the highest type of roadis comparatively shortl Moreover, excessive thicknesses are required to Withstand the efieots of traffio especial-1y where dense and heavy, and theefiects-of weather "such as'alte'rnate freezing and thawing-arid rainfall. Excessive thicknesses are also; being used and recommended in the building of "airport runways to accommodate ever increasing sizes of airplanes.
Attempts to "use thinner thaniaveragela'yers. of pavements or road coverings have always re 'sulitedi in creeping or early disintegration; Ate
2 tempts have been made to obviate these difficul-ties by incorporating fibrous materials into these compositions but only with partial suc cess. The presence of fibres. is an end. to be. desired and achieved for fibres increase the, toughness and durability of. compositions of this type. if they could be uniformly andevenly dispersed throughout the mixture. So iar, this objective has notbeen attainedbecause lumpspand mats of undispersed fibres, soaked with bitumen, always occur and excessive amounts-of binder have had to be used, resulting in soft, easily displaced and damaged surfaces.
Therefore, it is an object of this invention. to make improvements in the art of introducing or incorporatingfibrous materials into bituminous. pavement compositions whereby all of the known attributes of fibre dispersion in thermoplastic compositions are retained. These attributes are principally increased toughness, malleability, tensile strength, shear strength, compressive strength, greater resistance to abrasionand displacement, less. plastic or cold flow, greater lmpact and shockv resistance, etc. The finer and more intimate the fibre distribution, the greater are allo-f these attributes enhanced. Conversely, coarse fibres give lesser increase to these values just as poor distribution or felting. does.
Another object of this invention is tomake a paving or road composition of the bituminous type in whichv l-ittleor no mineral aggregate, other than finely-divided fillers, is present or necessary.
Among the best times for imparting these values to: thermoplastic compositions are the short-fibered mineral amphibole or chrysotile asbestosor vegetable fibres such as cotton or the haters from the seed, or flax, or animal fibres such-aswool or. the purely. symthetlc extruded or formed fibres; Cotton l-inters are an excellent and reasonably priced fibre, readily available and adaptable to the improvements of this invention.
Themineralfil-ler-used can be from a variety of finely-pulverized minerals, such as dlatomaceous. earth, magnesium carbonate, slate flour, pulverizedsil-ica, talc,phosphates, etc. General y, theflneness is such that all of the material would pass a ZOO-mesh sieve with a; large proportion :passhag the 325-mesh sieve.
The bituminous composition may be composed of a large variety of asphalts. For example, I may employ-a single asphalu acuum. distilled and oxidized to a low penetration and a: highs softening point, such as 2 to -5 penetration-at??? F., 100 grams for five seconds, and about 240 F. to 300 F. or upwards Ring and Ball softening point, although I prefer a melting point of 260 F. to 280 F. Other compositions may contain harder asphalts naturally occurring, such as Gilsonite or manufactured bitumens of equivalent or less hardness, these generally being softened with a higher-penetration, lowersoftening point asphalt, or a semi-liquid fluxing bitumen. The only consistent feature is very low penetration and high-softening point.
The foregoing materials may be employed in the following general proportions:
Per cent Low-penetration, high-softening point asphalt 40 to 50 Fibrous material, such as cotton or asbestos to Balance of finely-divided mineral fillers to I propose to achieve the objects of this inven tion by making a preliminary dispersion of fibre in filler and bitumen, compressing this mixture, cooling and then crushing in an apparatus such as a hammer mill. By regulation and control of both the raw materials and method of crushing, various sizes of pieces or particles can be obtained, from relatively large, such as would be retained upon a one-inch sieve, to very fine sizes, some of which would pass a 325-mesh sieve, and graded in between.
In order to incorporate fibres advantageously into a thermoplastic mixture, it is necessary that they be separated into discrete filaments for otherwise their eifects are minimized or even lost. The nearer the approach to separation into individual fibres, the greater is the strength developed. The separation of mats or tufts of fibres is best accomplished when the medium into which the fibres are being distributed offers a shearing resistance between the mass itself and the mixing or dispersing equipment. In a mixer, it can be accomplished by keeping the mass in a viscous condition by proper adjustment of composition and temperatures. Moreover, in order to minimize actual destruction and breaking down of fibres, the composition should be smooth and coherent.
Heretofore, it has been impossible to obtain satisfactory fibre distribution in a bituminous paving composition, such as a sheet asphalt or asphaltic concrete mixture, because (1) there is not enough bitumen present to make the mixture either smooth or coherent and (2) the sharpness and angularity of the mineral aggregates tend to grind the fibres to destruction and (3) the tendency of the bitumen-soaked fibres to stay matted is not overcome unless, of course, actual destruction of fibre does take place.
The characterizing components, namely finelydivided fibres, finely-divided mineral fillers and low-penetration, high-melting point asphaltic material, may be obtained from any desired source including industrial wastes or reclaims, either individually or two or all of the components in some previous admixture. When obtained from existing mixtures, if not in suitable proportion the composition may be made up by addition of the required component or components and to requisite proportion as previously described.
The following examples are illustrative of my invention, although they are not to be considered a limitation thereof:
. vated conditions of temperature.
Example 1 A mix was prepared composed of 45 parts by weight of blown asphalt having a penetration of 3 at 77 F., 100 grams for five seconds and a Ring and Ball softening point of 275 F., 12 parts by weight of cotton linters and 43 parts by weight of diatomaceous earth passing a ZOO-mesh sieve. The filler was placed in a steam-jacketed mixer and the asphalt, previously heated to 335 F., was added. When the filler-asphalt combination had reached a temperature of 325-350 F., the cotton linters were added slowly and. mixing was continued until a coherent homogeneous composition resulted. This mixture was then formed into rectangular blocks by compression in a mold, and after cooling, were removed. When thoroughly cooled, these blocks were then crushed in a hammer mill to produce an aggregate material having the following average mesh composition:
. Per cent Passing 200-mesh sieve 26.5 Passing SO-mesh sieve retained on 200 2.9 Passing LO-mesh sieve retained on 80 4.5
i Passing 10-mesh sieve retained on 40"-.. 32.6 Passing 4-mesh sieve retained on l0 33.5
In the alternative, the plastic mass may be compacted by extruding it from suitably shaped dies under pressure, or it may be cast in the form of sheets and compressed by means of a roller. This grading may be varied to suit by adjusting the setting of the hammer mill or controlling its speed, or by separating the crushed material on various sized screens and re-combining as desired. This crushed synthetic aggregate can be stored for any length of time under any ordinary atmospheric conditions without setting up or losing its usefulness due to the characteristics of the bituminous component. Thereafter the synthetic' aggregate may be withdrawn from the stockpile for use as desired for the laying of trafficways or other surfaces.
Laying of surfaces may be accomplished by employing from to parts by weight of the synthetic aggregate in combination with about 5 to 15 parts by weight of various surface-softening or fiuxing-agent bituminous materials, such as slow-curing oils, rapid-curing cut-backs, emulsions and soft asphaltic cements for the purpose of rendering the surfaces of the synthetic aggregate cohesive under pressure. The combination of the synthetic aggregate with these materials may be done at either atmospheric or ele- This mixture may then be layed to desired thickness and the particles of synthetic aggregate amalgamated by rolling pressure load of about 5,000 pounds per square inch, such as provided by compaction rollers conventionally employed in paving.
Example 2 As a further specific example, previously prepared slabs composed of 50 parts by weight of low-penetration, high-softening point asphalt, 15 parts by weight of cotton fibres and 35 parts by weight of minus 200-mesh pulverized silica were crushed in a hammer mill to provide a graded mixture of which all passed a #4 sieve with intermediate particles passing sieves up to ZOO-mesh. Ninety parts by Weight of this synthetic aggregate was then mixed at atmospheric temperature with 10' parts by weight of a s'low-curing'road oil. known as SC-l. This mixture was then spread out to one-inch thickness, compacted with a 10- ton roller, and immediately opened to road trafllc. This roadway was a dense, well-compacted bituminous mixture, showing a density of 1.41 with a minimum of air voids.
Example 3 Ninety parts by weight of the same aggregate employed in a previous example was heated to a temperature of 175 F., mixed with parts by weight of a previously liquefied 150-200 penetration asphalt and was then spread and immediately rolled while hot. This made a very satisfactory bituminous pavement structure of high density and low porosity.
Example 4 Ninety per cent of synthetic aggregate, such as in Example 2, was made into a cold-lay mixture as follows: 90 parts by weight of this aggregate was mixed with 10 parts by weight of a standard MC-2 cut-back asphalt. This mixture was then stored in stockpiles and after several months was found to be still loose and uncompacted, but readily compacted when placed on the road and compressed with heavy rollers.
Due to the lightness in weight of surfaces of the foregoing class of compositions, they may be advantageously employed for paving surfaces where weight is a factor, such as for upper-story garages or other floors where high dead weight is disadvantageous, such as bridge floors.
Small sections of actual pavement construction has shown that pavements composed principally of my synthetic aggregate perform excellently and are able to withstand extremely heavy trafiic even when laid less than one inch in thickness, whereas the conventional present day type of pavement, composed wholly of mineral aggregate, must be considerably over one inch in thickness to withstand the same traflic.
For certain uses, it may be desirable to add ordinary mineral aggregate, such as sand or graded stone, to a minor extent, such as not more than about without departing from the spirit of my invention. While the addition of such small percentages of mineral aggregates shows relatively satisfactory shear tests compared with the prior practice, their incorporation results in somewhat lower strength than when using substantially 100% of my synthetic aggregate. This evidences the fact that if I employ my synthetic aggregate alone, I can produce paving mixtures of superior strength and, therefore, durability.
I claim as my invention:
A bituminous pavement composed of from to parts by weight of synthetic aggregate composed of graded size, irregular particles of a compact and solid homogeneous mixture of 40 to 50 parts by weight of bituminous material having a penetration of from 2 to 5 at 77 F. grams for 5 seconds and a Ring and Ball softening point of from 240 F. to 300 F., 10 to 15 parts by weight of fibrous material, and 35 to 50 parts by weight of minus 200-mesh mineral filler coated with from 5 to 15 parts by weight of bituminous fluxing agent, and the particles cohered in the form of a dense sheet.
JAMES F. GALLAGHER.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 1,752,917 Lukens Apr. 1, 1930 2,051,532 Rogers Aug. 18, 1936 2,082,259 Peden June 1, 1937 2,087,088 Greider et a1 July 13, 1937 2,109,020 Abernathy Feb. 22, 1938 2,158,772 Beckwith May 16, 1939 2,368,371 Minge et a1. Jan. 30, 1945 2,455,709 Spelshouse et al Dec. 7, 1948 FOREIGN PATENTS Number Country Date 515,146 Great Britain Nov. 28, 1939