US1007833A - Manufacture of compressed asphalt paving-blocks. - Google Patents

Description

WALTER S. WILKINSON, 0F

(srArns rarnnrrnnnonl MANUFACTURE OF COMPRESSED ASPHALT PAVING-BLOCKS,

No Drawing.

To all whom it may concern:

Be it known that I, WALTER S. WILKIN- SON, a citizen of the United States, and a resident of Wytheville, county of Wythe, State of Virginia, have invented an Improvement in Manufacture of Compressed Asphalt-Paving-Blocks, of which the following is a specification.

This invention relates to the manufacture of asphalt paving blocks which comprise stony ingredients concorporated with a bituminous binder, commonly an asphaltic cement, and formed in a mold under great pressure, as distinguished from the so-called sheet pavements, which comprise stony and binding constituents mixed and'spread upon aroadway in a more or less plastic v condition, with only enough pressure to roll the .materials into a substantially smooth and continuous sheet. 7

More particularly, the' invention is intended to obviate certain deficiencies in asphalt blocks, which have been considered, prior to this invention, to bethe practically unavoidable accompaniment of those distinctive characteristics of asphalt paving blocks which differentiate them from sheet asphalt pavingand commend their use in lieu of the latter.

Hitherto, asphalt paving blocks have proven particularly satisfactory for residential streets or the like where the traflic conditions are not heavy or severe; but they have not always been as satisfactory under heavy traflic conditions, especially during low winter temperatures. One of the dis tinctive characteristics of paving blocks,

which, as they have heretofore been made, has sometimes rendered them not wholly satisfactory under heavy traffic conditions, especially at low temperature, is the quality of substantial hardness which must exist in block compositions to enable the blocks to maintain their form, shape and integrity as separate blocks. This quality of hardness has hitherto given rise to. a frequently undesirable brittleness and sometimes friability in the fin'ished blocks, more especially in cold weather. The importance of and reasons for this characteristic stiffness, or comparative hardness, will readily appear upon comparison of some of the'essential differences between the block and sheet pavements.

- It is well recognized in the. art that as Specification of Letters Patent.

Patented Nov, 7, 1911.

Application filed March 11, 1910. Serial No. 548,673.

phalt paving block compositions employed prior to th1s invention, difi'er essentially from sheet asphalt paving compositions not only in respect to the character of the stony or body material employed, but also in respect to the physical character of the cementitious binding materials used. This essential difference in character of binding material arises from the necessarily dissimilar conditions of manufacture and laying of the two varieties of pavement, and also from the different qualities which the respective pavements are preferred tohave when laid, in order that each, according to its peculiarithe impact and wear of traflic. For instance, a block composition must have a sufficiently coherent consistency, even at high temperatures, both" during the course of manufacture and during subsequent handling, transportation, storage for perhaps indefinite able the blocks to preserve substantially blocks.

As' at present manufactured, in the later stages of the process, that. is to say, after the blocks have been compressed into shape in a mold, it. isindispensable that. they be sufficiently stiff, stable and coherent to retain mold and removed to the cooling bath, although still, in a highly heated condition, for as at present made it would be commercially impracticable to permit the blocks to remaln for a suflicient length of time in the mold to cool therein. They are, as a matter "of practice, ejected from the mold in a very short period after they are given final compression. It is manifest therefore that under such conditions the ceme'ntitious coherent, and stable blocks even while very hot, otherwise the blocks 'will not hold their proper shape and dimensions when ejected from the mold and while being removed to and in the cooling bath in which they are commonly immersed as soon as practicable after leaving the press in order to set them, and preserve their shape. It is preferred also, that the finished blocks be stable during actual use when subjected to the combined influences of summer heat and the imties of structure, may be able to Withstandtheir shape while being ejected fromi the binder must be such as to produce suflicientty enough to maintain their separate integrity pact and pressure of traflic. To contribute,

periods and preferably after laying, to entheir form, shape and integrity as separate to these ends, a block composition must be susceptible of being formed in a mold under tremendous pressure and'otherwise treated as hereafter described. Sheet asphalt paving surface mixtures, being required merely to be spread upon a roadway and then progressively rolledunder a pressure light in comparison with the mold pressure used in block'manufactureinto a mobile integral sheet, and being requiredalways to possess suflicient ductility to accommodate expansion and contraction throughout extended areas under varying temperatures, are not such as could be used commercially in the formation of compressed asphalt blocks formed in a mold.

As usually laid, asphalt paving blocks merely rest as separate disconnected units upon a cement-mortar or other suitable bed, much after the manner in which the ordinary granite or Belgian paving blocks are laid and ordinarily with spaces'of to k of ,an inch between them, and are therefore preferred to be substantially self sustaining, and while their. upper traffic receiving surfaces in time may iron out so as to partially or wholly close the intervening spaces at the joints of the wearing surfaces, the blocks nevertheless preferably remain essentially separate and distinct, so that when taken up they may be separated as they were originally'without substantial breakage or injury saveonly that wear due-to use. On the other hand, a sheet pavement presents an integral body, having no corners or edges,-

all parts of which receive integral lateral support, and are further tenaciously held against lateral displacement or wave-like formation by a strong binder, so-called,

which unites the sheet surface to its "anchoring foundation.

The necessary and distinctive quality of strong coherence and comparative hardness in asphalt paving blocks is ordinar ly obtained by the use of a large PIOPOICIOII. of comparatively coarse grades of'mineral aggregate comprising, preferably hard substantially non-porous stony particles, combined with a proper proportion of fines and a comparatively hard bituminous cement, united, compacted and compressed under tremendous pressure in a. mold while such ingredients are necessarily heated to a high temperature. While this quality .of comarative hardness has been recognized as indispensible to those characteristics of asphalt paving blocks which diflerentiate them from sheet asphalt pavements, it has heretofore been considered practically impossible to obtain a suflicient degree of coherence and stability to have the blocks stand up and hold their shape without lateral support 1n the final processes of manufacture, as heretofore descrlbed, and to avoid an undesirable degree of brittleness or friability in the finished blocks, especially at low winter temperatures, which brittleness or friability has been understood to be a necessary incident to sufficient hardness in the finished blocks to enable them to sufiicientlymaintain their shape. Attempts to employ such mixtures as would not be unduly friable in cold weather have been heretofore accompanied at the very outset by the liability of the blocks, when ejected from the mold or press and before becoming set, to lose their shape or become distorted and thus rendered unfit or undesirable for use. It is obvious that unless the blocks are accurately shaped and of substantially uniform dimensions they cannot be laid with uniformity and minimum clearance or spaces between them, which'is essential to secure the best results.

In accordance with this invention, I have found it practicable to make blocks of all necessary stability, coherence and hardness, and to preserve these important and distinctive characteristics differentiating the asphalt blocks from sheet asphalt paving, while at the same time avoiding that degree of friability which has hitherto constituted a defect in paving blocks of this kind.

It has been attempted heretofore to avoid friability of asphalt blocks, especially in cold weather, by modifying the mineral aggregate, but such attempts have met with no practical success; also by using a binding cement of a softer consistency than those generally used, and while this has sometimesyielded more or less favorable results, it has nevertheless remained the general belief in the art that an undesirable degree of friability could not be practically avoided in blocks capable of maintaining their integrity and preserving substantially their original form.

In the practice of this invention I aim to retain the same mineral aggregate and the same stiff and coherent cementitious binding material which give to blocks their distinctive characteristics previously described.

The character of the invention may be readily understood by reference to an illustrative course of manufacture which I have practiced with highly satisfactory results and in which I have modified former practices by introducing a new ingredient, or, it may be, by introducing at another time, in another way and with another effect a suitable quantity of an ingredient already present, and applying the same in such a manner as to preserve the necessary and distinctive characteristics of firm coherence or stability and comparative hardness and at the same time to obtain an entirely new quality which I designate structural-malleability, that is to say, that quality of the mass made up, in by far the larger part, of non malleable stony particles, and a cement which, at low temperatures, is somewhat friable, which permits of and results ina malleable action under traffic while retaining at the same time the structural formation of the block. This structuralmalleability enables the blocks to sustain the impacts of traflic, even during low winter temperatures and under heavy traflic. conditions, with such reduced or eliminated tendency to friability as has been impracticable to procure on a commercial scale by any method heretofore employed in the art of manufacturing asphalt paving blocks. For illustration, this invention may be practiced as follows. A large quantity of preferably hard and substantially non-porous or non-absorbent stony material, as for instance 850 lbs. more or less of crushed trap rock or other hard, substantially non-absorbent crushed stone, properly graded, is heated to a temperature, for instance of about 370 F. To this body material which constitutes the important wear resisting element of the blocks is added the so-called fines, in such quantity as may be desired which may conveniently comprise finely pulverized limestone in the form of an impalpable dust' and ordinarily in quantity say about 175 lbs. The fines so added enter the interstices between the larger particles of the body material, and also lend body to the binding material when the latter is subsequently added. The hard, coarser, stony particles constituting the body material, are

preferably thoroughly commingled with the fines in a suitable mixer. The fines may be mixed with the body material before the cement, or may be first incorporated, in part at least, with the cement before adding the latter to the body material. Before the commingled mass of stony material is incorporated with the cement, it, or so much thereof as may be necessary to obtain. the substantial results desired, is treated according to the practice of my present invention with a suitable oil including in the term suitable oil equivalent substances, as for instance, a blown oil flux, or a petroleum residuum, at such temperature as will render the latter properly mixable with the body material and the fines, the quantity thereof being sufiicient to coat the particles of the,

preferably non-porous body material with a thin oil or flux film or surfacing and to permeate the fines. Whatever the character of the body material, it is desired that the oil, flux or the like with which the nonporous particles are treated shall remain preferably as a surface coating thereon. The .fines may be treated by oil flux or the like, either separate or together with the body material, and to the extent that the preferably small proportion of fines is or may be porous or otherwise capable of absorbing the cement or its constituents, or extracting any constituent thereof, the

treatment of such fines with oil, flux or the like, as above described, may by more or less permeation or impregnation of the fines prevent to a corresponding extent their subsequent permeation or impregnation by absorption or otherwise from the ingredients of the cement and the resultant loss to and deterioration of the cement.

The body material treated as above described and the fines preferably also so treated, are thoroughly mixed, either separately or preferably together, with the cementitious binding material, which may be of the samecharacter which has been used heretofore for similar purposes, viz: preferably the usual and well known mixture of dried or refined asphalt with the usual flux, preferably a blown oil flux. As much of this cementitious binding material should be put into the mixture as can be used and still have the blocks capable of preserving their structural form and shape when and after they are ejected from the mold. Since the oil or flux used for treating the stony material in the manner hereinbefore described may contain a very large percentage of bitumen and is commonly practically .pure bitumen, the amount of said cementitious binding material may be somewhat less than the proportion heretofore used, although the total amount. of bitumen in the block for a given grading of the'stony materials may be increased by the process embodied in this invention. When so mixed relatively small batch is segregated from the mass of the composition and is introduced to a block mold preferably to produce a block of about 12x5x3 inches or 12x5x2 inches and is therein, while preferably at a temperature of about 280 to 290 F., heavily compressed preferably under a pressure of about 200 tons or about 6666 pounds per square inchof surface. During this eavy compressing action, the stony ingredients are caused to readjust themselves and to enter into a final compact concorporation with the binding cement whereby the whole becomes a stable, strongly coherent and structurally-malleable unit. After the heavy compression in the mold, the block while still at a high temperature is preferably immediately ejected and conveyed away to set preferably in a water bath. During the movement betweenthe mold and setting bath, the block retains the high temperature preferably used in molding and even at such high temperature must be sufli ciently self-supporting to retain its form and shape. This self-supporting quality is provided by the block supporting bituminous or asphaltic cement; without it the other materials constituting the composition would not retain'their molded formeven during ejection from the mold.

A block made by the above described course of manufacture is found to'retain its form, shape and separate integrity to the fullest extent necessary or desirable and it has been amply demonstrated to possess the highly advantageous quality of structural malleability, so that, for instance, in the well-known rattler tests and in actual use under heavy traflic conditions, the block is sufliciently coherent and malleable to sustain heavy and repeated impact with re-- markably little tendency to friability even at low temperatures.

I at present believe that by the use of the process herein described more bitumen, for a given grading of the stony materials, can be incorporated in the blocks and still have them capable of retaining substantially their molded shape, than by any process heretofore known.

It is, of course, difiicult to ascertain the exact behavior of the constituents of an asphalt paving block during and following compression in a mold. It can, however, be stated that the introduction of the oil orflux in the manner herein described, which I believe to be entirely new in the art, appears to soften the fines and'render the entire block composition and the particles thereof. more mobile while under heavy compression in the mold, also more malleable when subjected to trafiic on the streets, while retaining all necessary stiffness and stability to enable the block to maintain its form and shape throughout manufacture, storage, transportation and use. It appears also to render the cementitious union between the adjacent stony particles more flexible, also to serve ,in effect as a lubricator during the application of the tremendous pressure, and to thus facilitate the distribution and readjustment of the stony particles and the cement while entering into their final compacted relations in the mold.

I have found in practice that by treating the stony material especially the fines, in the manner hereinbefore described, the fines thus lubricated have less tendency to segregate or ball up and are more thoroughly disseminated throughout the block than when incorporated in the mixture without such treatment. This is important because, for

instance, it has-been found that the adhesive quality of asphaltic cement isfar greater than its cohesive quality and with reference to these qualities, as well as in other respects, the fines 1n the block composition and in the finished block perform very important-functions. It .is manifest that the multitude of surfaces presented by the fines, even though individually very small, aggregate an extensive surface area to be coated by the cement and to which the latter strongly adheres and that the presence of the fines thus affords an extensive opportunity for the exercise of the adhesive quality of the cement.

Obviously, as will appear to those skilled in the art, the fines must be thoroughly and evenly disseminated throughout the mass of the block composition in order to secure the best results; and this desirable end is contributed to very effectively by the treatment of the fines in accordance with the process embodying this invention.

. Whatever may be the correct theory upon which this improvement in the art is based, it is true that the flexibility of the union between the particles of the body material appears to be largely increased by the addition of oil or flux in the manner set forth, and that the composition appears to form a more malleable block by reason of the prior treatment of the stony materials with said oil or flux, as herein set forth.

It is to be understood that the invention is not limited to the specific ingredients, proportions or sequence of operations hereinbefore described for illustration; on the contrary, the invention may be variously practiced as will appear to those skilled in the art of asphalt paving blocks.

Claims:

1. That improvement in the art of manufacturing compressed asphalt paving blocks which consists in crushing and heating a comparatively non-absorbent stony ingredientv to form a part of the mineral aggregate; pulverizing a comparatively absorbent stony ingredient to provide fines for the remainder of the mineral aggregate mixing the stony ingredient and fines; and uniting the particles of the mixed" non-absorbent and absorbent aggregate by forming between them a permanently structurally-malleable cementitious union by first treating the stony particles to a suitable oil coating which remains substantially as an 'oil coating on the non-absorbent particles and permeates more or less the absorbent fines of the aggregate, and then mixing the hot coated and permeated stony particles with a heat softened block supporting asphaltic cement, segregating the mass into relatively small batches and separately compressing, compacting and readjusting said small batches of hot stony ingredients and hot cement into unitary block form by heavy pressure in a closed mold and cooling the compressed block to produce the structurally-malleable block for use.

2. That improvement in the art of manufacturing compressed asphalt paving blocks which consists in crushing and heating a stony ingredient for part of the mineral aggregate; pulverizing a stony ingredient to provide fines for the remainder of the mineral aggregate; and uniting the particles of the mineral aggregate by forming between them a permanently structurallymalleable cementitious union by first treating particles of the stony material to a suitable oil coating and then mixing the hot coating-treated particles with a heat softened block supporting asphaltic cement, segregating the mass into relatively small batches, and separately compressing, compacting and readjusting said small batches of hot stony ingredients and heat softened cement into unitary block form by heavy pressure in a closed mold and cooling the compressed block to produce the commercial malleable block for use.

3. That improvement in the art of manufacturing compressed asphalt paving blocks which is characterized by treating suitable hot stony material destined therefor, with a lubricating substance; mixing said hot stony material so treated with a heat softened asphaltic cement; segregating from a mass comprising said mixture batches from which to produce blocks; compacting the segregated batches while hot in a closed mold under heavy pressure to form a structurallymalleable unitary block; and then cooling said block inwater to set and preserve its shape.

In testimony whereof, I have signed my name to this specification, in the presence of two subscribing witnesses.

WALTER S. YVILKINSON.

Witnesses:

EVERETT S. EMERY, ROBERT H. KAMMLER.