US1975028A - Method of providing roadways with a nonskid surface and product thereof - Google Patents

Description

Sept. 25, 1934. E, c. WALLACE METHOD'OF PROVIDING ROADWAYS WITH A NONSKID SURFACE AND PRODUCT THEREOF Filed April 18, 1933 2 Sheets-Sheet 1 OLD CONCRETE W11H-' DEPRESSION-S FILLED Fig.2

/NVENTOR-' (310M 8w Alla-ATTORNEY Sept. 25, 1934. 5 Q7 WALLACE I 1,975,028

METHOD OF PROVIDING ROADWAYS WITH A NONSKID SURFACE AND PRODUCT THEREOF Filed ,April 18, 1935 2 Sheets-Sheet 2 'GRANULAR Nag-52m: SURFACE ATTORNEY Patented Sept. 25, 1934 METHOD OF PROVIDING ROADWAYS WITH A NONSKID SURFACE AND THEREOF PRODUCT Edwin C. Wallace, Newton, Mass.

Application April 18, 1933, Serial No. 666,721

This invention relates to a method of providing roadways with a non-skid surface and product thereof, and has particularly to do with a bituminous paving structure adapted to prevent or minimize skidding. The invention finds its chief use in resurfacing or the provision of an additional surface upon existing worn or defective pavements, though it is also adapted to be used for wholly new construction.

The change in trafiic conditions which has occurred since the advent of rapidly moving motor vehicles, as compared with slow moving steeltired vehicles, has created a demand for a riding surface upon which the motor vehicles will not 5 slip or skid as upon the smooth surfaced roads and streets so long in general use.

Heretofore efforts have been made to provide a non-skid surface by scattering over pavements of the sheet asphalt type or other smooth surface pavements, stone chips, coarse sand, gravel or the like to provide a gritty surface. Such efforts have proven to be but temporary expedients which within a short time, usually but a few weeks, were completely dissipated through various causes, largely due to the fact that the stone chips were either displaced by traffic or else became so completely embedded in the underlying surface that the non-skid characteristic was entirely lost.

. The herein described construction has for its object the provision of a non-skid pavement which will maintain the integrity of its structure and surface and also maintain the desired nonskid properties of the surface for a long period of time.- Briefly, this improvement consists of a relatively thin, non-skid layer or course, comprising two separate and distinct bituminous mixtures which have entirely different physical properties and which are combined into a single unitary layer in such manner as to utilize to the full the desirable characteristics of each mixture. This layer may be built upon any existing pavement of any desired type as a resurfacing or reconstruction measure, or it may .be used in connection with a new under or body layer to form a wholly new pavement with the non-skid feature built directly into the new structure.

In the drawings:

Fig. 1 is a perspective view illustrating a section of an old, concrete pavement to be resurfaced;

Fig. 2 is a plan view of the same after the chief depressions have been filled;

Fig. 3 is a perspective view (in substantially actual size) of the completed resurfaced section showing to good advantage the coarse, granular texture of the surface; and

Fig. 4 is an additional perspective view (in reduced size) showing a somewhat larger portion of the completed pavement.

(Cl. Sid-23) When applied to an existing pavement or roadway the first step is to correct the contour of the old pavement by filling depressions, removing high spots and strengthening all weak places.

Referring to Figs. 1 and 2 of the drawings,- Fig. 1 illustrates rough, worn concrete and Fig. 2 shows the same after the chief depressions have been filled by the deposit therein of any suitable material, for example, a bituminous concrete mixture, though such depressions may be filled simply by the composition of bituminous cement and fine mineral matter as hereinafter described.

Following such preparatory work, the preferred procedure is as follows,the surface is then cleaned in any suitable manner and given a coat of adhesive, bituminous paint. After the paint has become tacky, there is spread over it to the approximate depth of loose measurement (30-50# per sq. yd.) a composition of bituminous cement and fine mineral matter of such nature that it will readily conform to the old surface, be compressed into shallow depressions and be brought into close contact with and thoroughly united to the old surface,thus to serve as a bonding contacting element into which the coarse particles of the granular, non-skid layer may be partially embedded, as best shown in Fig. 3. As an example of mixture suitable for this purpose, the following is given:

Percent Bitumen 3-13 Passing 8 mesh 55-85 Passing mesh 15-35 Immediately after this fine mixture is spread, it is lightly compressed to bring it into contact with the underlying surface but not sufficient to prevent its uniting with the granular mixture which is applied over it.

The lightly compressed fine mixture may then be straight-edged to ensure good contour and then covered with a granular surface mixture of such nature and to such depth that when compressed into a firmly coherent mass, the two mixtures are combined into a single layer, the upper surface of which presents an open, granular texture with relatively large interstices between the particles. A

As an example of mixture suitable for the It will be noted that' this example of the pre= ferred granular surface mixture includes a sub= stantial percentage of fines. I have discovered that this is a factor of importance for it increases materially both the structural strength of the surface and the bond of the granular particles to each other and to the underlying holding medium or contact layer.

This layer is spread to an approximate depth of loose measurement (35 to per sq. yd.) Immediately after spreading, compression should be applied by means of a heavy roller. The rolling should be'continued until the mass becomes unyielding. Figs. 3 and 4 show the completed construction.

While designed primarily as a renewal or reconstruction measure, when adopted as newsconstruction, the procedure would be similar to that outlined above, except that a new body layer would be substituted for the old pavement and therefore the cleaning, painting, etc. is unnecessary. Preferably the new body layer consists of a coarse-aggregate bituminous composition, well graded from coarse to fine so as to produce low voids and form a dense, stable layer when properly consolidated. This layer which, for convenience, has been called the body layer, should be supported upon a previously prepared foundation of adequate strength.

While the body layer may be of any desired depth, it is usually spread to a depth approxi-,

mating 2" loose measurement.

After light compression the surface is straightedged then covered with a thin layer of fine mixture as described above, which in turn is lightly compressed, straight-edged and then covered with granular surface mixture as described and the entire mass then thoroughly consolidated by means of a heavy roller.

The compression and straight-edging applied to the body layer and the intermediate layer of fine mixture may be omitted if desired, but better results are obtained by compression as described.

By this method there is produced a riding surface of desirable rough texture which is held firmly in place by the fine mixture, the latter forming a holding medium into which the coarse particles are partially but firmly embedded.

To'preserve the granular texture it is important that the fine mixture be spread to sufiicient depth to" act as a conforming and contacting means between the granular surface mixture and the underlying supporting layers, so as to bond them firmly together by forming a holding medium into which the coarse particles may be partially embedded, but not so completely as to cause the 'niixtureto flush up and destroy the granular texture of the surface.

The-depth of the conforming contact layer is controlled by the average size of the coarse particles composing the granular surface mixture. For instance, withgranular surface mixture composed largely of A" particles the conforming contact layer should have an approximate depth of to of an inch. When, however, the granular surface mixture is composed largely of particles, the conforming contact layer (and the granular mixture as well) should have a depth approximating to loose measurement. It is preferable, especially in reconstruction work where the underlying body layer is hard, that the stone particles of the granular surface be spaced or cushioned from saidhard body layer.

Similarly, when the body layer consists of a new but hardened layer of material. Where, however, the intermediate layer is laid upon a body layer while the latter is still plastic, it is of little importance whether the granular particles be vertically spaced from the body layer. When larger sized particles are used, the depth of the contact layer should be increased in proportion.

In this construction the fine mixture serves the dual purpose of (a) Conforming and contacting layer which will readily conform to slight inequalities in the old surface and thus serve as a perfect contact means between it and the more rigid granular layer which could not conform to slight irregularities.

(b) It also serves as a holding medium into which the coarse particles are partially em-' bedded thus reinforcing the granular layer and greatly increasing the resistance to displacement.

By this method the contact and granular layers become, in effect, a single unified layer having at the bottom bonding and cushioning characteristics and at the top the highly desirable and eflicient non-skid granular wearing surface.

The granular mixture prepared with or mesh particles appears most satisfactory for all general purposes for when the mixture is made of $4 particles the texture of the surface is rather too fine to be effectively non-skid. 0n the other hand, however, with particles of 1" and larger in size, the number of points of contact between the particles as well as the number of particles in a given area are so reduced as to cause poor distribution of the weight of loaded vehicles passing over the surface, with the consequent result that individual particles are frequently over-stressed and either shattered under the weight of the load or become dislodged by traflic.

I am aware that it has been the practice for years to clean and paint the surface of an old pavement and then to apply thereover fresh bituminous mixture to rebuild the surface and 115 correct inequalities. I am not aware, however, that it has been the practice to follow the pro cedure described in this application, namely apply a relatively fine bituminous mixture to serve as a conforming contact layer and also to form a 120 holding medium into which a coarser granular surface layer as described may be partiallyembedded to provide a firmly held, coarse granular textured surface which does not fiush up and become smooth under trafilc. Le

Having described my invention what I claim is:

1. The method of renewing pavement surfaces which consists in correcting the contour of the surface, cleaning and applying thereto an adhesive bonding paint, then spreading thereover andcompressing into intimate connection therewith a conforming and contacting medium of relatively fine mineral matter and bituminous cement, and then spreading over said medium and partially embedding therein a. relatively 135 coarse composition of mineral matter and bituminous cement to provide a coarse textured granular surface with relatively large interstices between the particles.

2. The method of renewing old pavement sur- 140 faces which consists in filling the depressions therein, cleaning and applying to the old surface an adhesive paint, then applying thereover to a depth of one quarter inch or more a plastic, conforming and contacting mixture of relatively fine mineral matter and bituminous cement and compressing it into intimate relation with the old surface, and then spreading thereover an open, coarse to fine composition of mineral matter and bituminous cement and consolidating the mass to provide a coarse textured granular surface with relatively large interstices between the particles.

3. The method of reconditioning old pavement surfaces which comprises correcting the contour, cleaning, painting with adhesive paint, then applying a close textured conforming and contacting layer consisting of fine granular mineral matter coated with bituminous cement, then covering it with a layer of granular coarse textured composition of mineral matter coated with bituminous cement and compressing the mass to partially embed the coarse particles of the granular mixture into the fine, close textured conforming and contacting layer to provide a coarse textured granular surface with relatively large interstices between the particles.

4. The method of reconditioning old pavement surfaces which comprises correcting the contour of the old surface and spreading thereover to a depth of one quarter inch or more a plastic mixture of fine mineral particles coated with bituminous cement to provide a close textured conforming and contacting layer, bringing said mixture into intimate connection with the old surface by compression, then spreading thereover and partially embedding therein a relatively coarse textured granular composition of coarse mineral particles coated with bituminous cement to provide a coarse textured granular surface with relatively large interstices between the particles.

5. A pavement comprising a granular coarse textured surface layer consisting of coarse mineral particles and fine mineral particles, all coated with bituminous cement, reinforced and stabilized by being embedded in a fine textured, plastic composition of mineral matter and bituminous cement to such an extent only that the upper portion of the layer remains open and granular.

6. A pavement comprising a granular, coarse textured surface layer consisting of coarse mineral particles and fine mineral particles, all coated with bituminous cement, reinforced and stabilized by being embedded .in a fine textured plastic composition of mineral matter and bituminous cement to not substantially more than A of the depth of the coarse particles.

7. In a pavement, a unified layer of dissimilar bituminous paving mixtures with a comparatively rigid, coarse textured, anti-slip upper surface and a plastic, close textured lower surface which conforms to and contacts with a supporting layer to which it is united by means of an adhesive paint coat.

8. A non-skid paving structure having a body layer, 'an intermediate layer of fine plastic mixture consisting essentially of bitumen and a fine mesh aggregate, and a surface layer of mediumcoarse bituminous -mixture consisting principally of stone larger than the mineral particles in said intermediate layer all coated with bituminous cement and providing a wearing surface of open granular texture with relatively large interstices between the stone of said layer, said intermediate layer of fine plastic mixture providing a holding medium in which the relatively coarse particles of the granular surface layer arebut partially embedded.

9. A non-skid paving structure having a body layer, an intermediate layer of fine plastic mixture consisting essentially of bitumen and a fine mesh aggregate, and a surface layer of mediumcoarse bituminous mixture consisting principally of stone larger than the mineral particles in said intermediate layer all coated with bituminous cement and providing a wearing surface of open granular texture with relatively large interstices between the stone of said layer, said intermediate layer of fine plastic mixture providing a holding medium into which the relatively coarse particles of the granular surface layer extend but partially and are there firmly held but spaced from said body layer.

10. A non-skid paving structure having a body layer with a coating of asphaltic paint adherent thereto, an intermediate layer of fine plastic mixture consisting essentially of fine mesh aggregate coated with bituminous cement, and a surface layer of medium-coarse bituminous mixture consisting principally of substantially uniform size stone larger than the mineral particles in said intermediate layer as well as a small proportion of fines all coated with bituminous cement thus providing a wearing surface of open granular texture with relatively large interstices between the stone of said layer, said intermediate layer of fine plastic mixture providing a holding medium in which the relatively coarse particles of the granular surface layer are but partially embedded.

11. A non-skid paving structure having as a body layer an old pavement, a coating of asphaltic paint adherent thereto, an intermediate layer of fine plastic mixture consisting essentially of fine mesh aggregate coated with bituminous cement, and a surface layer of medium-coarse bituminous mixture consisting principally of mineral particles larger than the stone in said intermediate layer coated with bituminous cement thus providing a wearing surface of open granular texture with relatively large interstices between the stoneof said layer, said intermediate layer of fine plastic mixture providing a holding medium in which the relatively coarse particles of the granular surface layer are but partially embedded.

EDWIN C. WALLACE.

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