US2134357A - High tractive resistance bituminous - Google Patents

Description

Patented Oct. 25, 1938 UNITED STATES AT T IOFl- ICEff HIGH TRACTIVE nnsrs'ranon nrrommoos scnmcma 2 Claims. (01. 94-23) This invention relatesto a new and novel method of securing a non-skid surface, or high trac-I:

tive resistance, on bituminous road or street S111! faces.

'Iractive resistance, or the ability to resist skid ding, is a much sought for asset in any pavement surfacing. Asphalt pave ents, adhesive and re: silient when being laid, offer more possibilities for the production of a non-skid riding. surface than any other hard-surface type of paving. However, dense, moisture-resisting asphalt. mixtunes-and these are equally important qualities for they increase the life of the resulting pavement-are popularly supposedto offer less tractive resistance than the open type asphalt mixtures. This has resulted in the use-especially among the cold laid types-of bituminous surfaces high in voids, neglecting almost entirely the established and proven principles of bituminous mixture design. Such mixtures, while possibly low in first cost, are expensive because they are open to deterioration from continued attacks of moisture and the elements and also because they are of little protection against moisture to the base on which they are laid.

Asphalt coated stone, slag or gravel, from A" to A" in size, has been used on dense asphalt pavements to increase tractive resistance. On-

hot mix pavements these chips coated with from 3%,to 6% of asphalt have been applied to the surface, after it has been rolled at least once, in the amount of from five to twelve pounds per square yard. When used in these amounts the bituminous coated chips segregate to some extent, for uniform distribution is extremely difficult, and the pockets of chips formed tend to ravel very quickly under trafflc affecting adversely the appearance and often the quality of the pavement. The eflici'ency of the chips in making the pavement more non-skid than it would be without them is also open to question partly because of the size of the chips used and also because in most instances the stone, slag or gravel is of such quality that traffic soon wears it away, or at least wears it down until it makes a smooth surface with the asphalt paving mixture in which it is embedded.

I have found that a fine material, as for instance sand, will when anchored in the surface of a bituminous pavement produce a non-skid surface much more eificient than the asphalt coated chip surface, provided the material is hard enough to withstand the abrasive action of traific. Sand seal coats mixed with asphalt have been used on I asphalt pavements. One instance is the mixed method seal coat used on Warrenite bitulithic pavements. This seal coat contains about 1 1% of asphalt and is used in the amount of about-forty .pounds per square yard. Itisessentially a seal coat and ameans of protecting; and closing the coarseaggregate mixtureon which it is laid, for 5 i the amount of asphalt used in the seal coat mixture tends to either fill or overflll voids, greatly reducing and in some cases entirelyeliminating 1 its non-skid value.

, Crushed stone, slag'or fine gravel, and in some 10 instances sand, have also been used as a blotter or cover on bituminous paint -or squeegee-coats used to seal-old bituminouspavements and in some cases to seal new asphaltic concrete pavement too low in fine aggregate to close up well 15 when rolled. When so used the chips, gravel or sand whip oi! the pavement surface under traflic and only a portion of the total amount used is taken up by the asphalt flush, or squeegeef, coat. This results in an excess of bituminous material 20 on the surface of the pavement and, even though a fine material such as sand is used, this excess bituminous material tends to make the pavement slippe y. 1

My method of increasing the non-skid quality 25 of bituminous pavements relates to the use of a flne hard material, such as silica sand, coated with an amount of bituminous material small enough to allow the coated non-skid agent to be distributed very lightly and evenlyone particle of 30 the agent thick, preferably-over the surface of l either a hot laid or cold laid type of bituminous pavement. The light bituminous coating used is insuflicient to allow the coated non-skid agent to bond together and have sufllcient adhesion to be 35 used in any thickness over the surface on which it is used. The light bituminous coating merely facilitates the anchoring of the sand paper like agent into the surface of the bituminous pavea screen and should contain not more than 30% of particles that would be retained on a 10 mesh sieve, or more than 25% passing a 'mesh sieve. The sandmay be coated in a pug mill mixer, a cylindrical mixer, by hand with shovels, 55

This mate- 45 thesurface bitumen,- the non-skid agent is ap-' plied ina uniform thin coating by means of of pavement. A greater amount may be used,

but is ineffective because it will be whipped ofl by traffic, leaving only the small amount anchored inthe bituminous paving surface. After the non-skid agent has been applied, rolling of the asphalt surface iscompleted in the usual manner. 7 g

The lightly bitumen-coated non-skid agent is also effective on old smooth bituminous paving.

When used on old bituminous paving the old surface would first be painted with a liquefler for the bitumen, such as kerosene. After the liquefier has had sumcient time to slightly soften brooming, lutingyor by mechanical-spreader. It should then be rolled into the surface of the 'old pavement.

I do not wish the materials used to be confined to those described in the foregoing example. In

place of silica sand I might use slag sand, some types of which are dense and hard enough to withstand abrasion, or where commercially'avallable sand made from crushed granite, trap rock, or other extremely hard' rock;- or, if available,

slightly softened iron filings, or other finely ground hard metal could be used. Certain crude oils or road oils might be usedv instead of asphalt emulsion or asphalt cutback; it is also feasible to use heated bituminous cement of either high or low penetration, if the bituminous cement is used in small enough amount so that. the resulting mixture when 0001 will break up readily into its individual bituminous coated particles.

, I claim as my invention:

1. A method of increasing the tractive resistancebf bituminous paving, consisting of coating a finely graded hard mineral aggregate or metal with less than five (5%) per cent of bituminous material, and applying this mixture directly over the surface of bituminous paving during the period of rolling in an amount of not more than two (2) pounds per square yard.

- 2. A method of increasing the tractive resistance of a bituminous pavement; consisting of painting the surface with a solvent, then applying a thin coating of hard mineral aggregate or metal in an amount of approximately-1 to not more than 2 pounds per square yard, so graded that it will all pass a three-eighths (36") inch screen and not more than twenty-five (25%) per cent pass a one hundred (100) mesh sieve, coated with an amount of bituminous material not more than five (5%) per cent small enough so the coated material will not develop sufllcient adhesion to bond together itself after it is mixed or set upafter it is laid.

JOSEPH n conznnmn.