Many other Rock Asphalt deposits in Kentucky are found in the Chester sands of the Mississippi Series, and some are found in the limestones and shales of the state, but their commercial value is questionable.

These deposits are all different. Geologists do not agree as to their formation. Some believe them to have been oil bearing sands; some believe the asphalt and sands were washed in from the seas and deposited simultaneously by the receding waters; but we do know that the different deposits show different geological ages and have different characteristics.

With the fact of known differences existing in the different Rock Asphalt deposits, it would seem the next point of interest then to the producer and the user of Rock Asphalt would be, how to determine which of these deposits are commercial Rock Asphalt for roadway paving and which are partially or wholly unfit for any type of paving.

This question can only be answered by a careful study of the performances of a material from a known site. No laboratory test, within the author's knowledge, can determine this before the service test has proven the fact.

After this point has been determined by the producer over a satisfactory period of years, it is safe then and then only, to specify an identical quality for Rock Asphalt.

To simply specify "Rock Asphalt" or to identify it as "Kentucky Rock Asphalt" means nothing in regard to the results which may be expected. The material must have had the acid test of use.

When through service, a material has proven its worth, it is very essential that the same uniform product is furnished on any future work. This depends upon the representation, equipment and the ability of the producing company to furnish the same quality of material at all times. It is worth while here to mention the method employed by the Kentucky Rock Asphalt Company, the producers of "Kyrock" which is about 90% of all the sand Rock Asphalt produced in Kentucky, to establish and control the uniformity of its product.

After many years of very careful study of the geological formations and the behavior of the materials produced from the many different deposits, it was easy to determine which formation and deposits would produce a "real" pavement.

This deposit was then systematically diamond core drilled every fifty feet square, to accurately determine the extent, quantity, and uniformity of the unexposed asphalt rock. These cores were analyzed for every inch and the results of the analysis and extent of the area was plotted so that an accurate record was made of the quality and quantity of the asphalt rock before real production was begun.

From the quarry face, which is more than five thousand feet in length, the day's production is secured. This material is all hand picked, thus preventing any dirt or other foreign matter from getting mixed with the Rock Asphalt.

Trains loaded with these asphalt boulders move from all parts of the quarry to the primary 48"x64" jaw crusher. The crushed material then passes by belt conveyor to a long reserve storage bin, and from this bin, by more conveyors, to the secondary jaw crusher. When leaving the last crusher the asphalt rock is broken down to about a two inch size stone and this is distributed to the roller mills which finally break the material down to the individual sand grains, or about the consistency of coarse meal.

This ground Kyrock is then loaded through chutes into river barges and while the barges are being loaded, they are slowly moved by power forward and backward, so as to result in another mixing of the material.

These barges are then towed to Bowling Green or Rockport, the railroad shipping points, and there unloaded by clam shell buckets into a storage pile for future shipments.

The Kyrock is loaded into open top railroad cars by steam shovel from this storage pile and shipped ready to be used by the purchaser.

At no time during the process of production, preparation, or laying, is there anything mixed with, added to, or taken from the Rock Asphalt; it is produced in its natural state and is laid cold.

From its original formation in the quarry to the finished product, Kyrock encounters eight conditions which produce a thorough mixing of the material and is subjected to six laboratory tests before being shipped. Each one half ton is tested when it is produced and every car is carefully analyzed before it is shipped.

This thorough process of mixing and the careful method of systematic testing assures the absolute uniformity of Kyrock.

Service results have, after a period of forty years use, proven that the uniformity of the material is of vital importance to the success. of the pavement.

After the Kyrock has been produced as above described, it is ready to be laid on any type of base which is sufficiently stable to carry the traffic. The standard thickness for the heaviest traffic is one and one-half (12) inches compacted, which requires that the material be laid loose to a thickness of two and one-quarter (214) inches, as Kyrock will uniformily compress one-third of the loose depth.

The weight of Kyrock is calculated at 2,160 pounds per cubic yard loose, or 133.3 pounds per square yard for a one and one-half (1) inch compacted surface, one ton covering fifteen square yards of surface.

Kyrock is unloaded from the railroad cars by clam shell or by asphalt forks and hauled to the roadway in any type of vehicle.

There it is dumped upon shoveling boards, platform, or directly upon the base, if it is smooth enough to shovel from.

The material is them shoveled directly onto the base to be surfaced. It should be deposited by the shovelers about twice the thickness desired for the loose material. As the material is deposited by the shovelers, the rakers with a combing motion, break up all lumps and rake it to the required thickness loose.

Not more than two shovelers should be used to one raker, or, five shovelers to two rakers. The shoveling and raking should be a continuous operation and no walking should be done on the material while it is being spread, before it is rolled.

During the raking all small lumps should be raked from the surface and broken down to one inch or less in size. The surface should be uniform in texture and density. This is easily accomplished by using the back of the rake to finish the surface to grade.

The Kyrock should then lay exposed to the warm atmosphere and sunshine until the whole surface has become warm and any moisture that may have been in it, has dried out before it is rolled.

The edges along the curb or gutter line should be left standing as vertical as possible and slightly higher than the rest of the loose material. This assures good compaction in the corner formed between the gutter and the base and protects the edges of the curb or gutter from the roller wheels.

The first rolling should be done with a roller weighing not over 6 to 8 tons and should be run parallel to the center line of the roadway at all times. After once over the surface with the usual lapping of the roller wheels the material should be allowed to lay for several hours, or until the next day, before it is rolled again.

Usually two, and never more than three rollings are sufficient before the surface is opened to traffic.

At any time after the first rolling and before the roadway is opened to traffic, all irregularities in the surface may be corrected by the addition of fine material sifted through a one-quarter inch mesh sieve directly upon the low place and rolled without any other preparation whatsoever.

In preparing bases for new construction if it is macadam, the usual method shall be employed as used for regular waterbound macadam, but no course of stone should be thicker than four inches without being thoroughly bound with screenings and rolled. The last or top course after it is water bound with screenings, should be swept with power broom or hand broom until all excess screenings and dust have been removed to a point where the coarse stone are exposed about one-quarter of an inch before the Kyrock surface is laid.

For Black Base construction not over one and one-half (1) gallons of asphalt or tar penetration should be used in the top course if a two inch course of stone is laid, and if the voids in the stone are

small, there need not be a course of chips spread on the penetration before Kyrock is laid; but if the voids are large, a layer of chips may be used for the purpose of filling the large void. This course should be rolled before the Kyrock surface is laid.

For new concrete base the concrete surface should be finished to true grade and should be painted with a very thin application of asphaltic cement paint.

For resurfacing old roadways such as old concrete, brick, and all types of bituminous top, the surface should be cleaned and painted. All depressions should first be filled with Kyrock and compacted before the main surface is laid.

The paint used should be an asphaltic cement of approximately 55 penetration cut back with approximately 50% of naphtha or gasoline, which should be applied with hand sprays and allowed to become dry before the Kyrock is applied.

No Kyrock should be laid or rolled when the temperature is below 40 degrees F. nor when the base or the material is damp.

A very careful study of the standard specifications prepared by the Kentucky Rock Asphalt Company should be made before laying Kyrock. These specifications are free, and if followed, satisfactory results are assured.

The ease of maintenance with Kyrock of all types of streets is well worth the attention of all City officials as it can be stored ready for use without any preparation for an indefinite period, and can be applied by unskilled labor in any type of maintenance work, without the use of expensive equipment.

Its growth from a few tons production in 1885 to the enormous production today speaks of its popularity and successful use. One producing concern alone, the Kentucky Rock Asphalt Company at Louisville, Ky., produced in the calendar year 1924, more than 2,000,000 square yards; in the calendar year 1925 more than 4,000,000 square yards, and in the calendar year 1926 it will have produced more than 5,000,000 square yards of Kyrock paving material, or the equivalent of more than 16,000 square yards of Kyrock per day, which has been distributed into over thirty states of the union and into three foreign countries.

The figures from the Uvalde Rock Asphalt Company of Texas are not available but we are informed that they compare very favorably with these.

The production figures of the other companies who have recently gone into business are also not available at this time.

The object of this paper has been primarily to place before this organization and the public through this Society, some facts worthy of consideration by its members, relative to a material which once was the only asphalt paving material known and used and which today in America is becoming again a very popular, and one of the most talked of asphalt paving materials of the day.

"BLACK BASE" AND ITS PLACE IN STANDARD

SPECIFICATIONS

By Hugh W. Skidmore, President, Chicago Paving Laboratory

"Black Base" has acquired widespread recognition as a standard type of pavement foundation by reason of its long and honorable service record. There has been very little experimentation connected with the development of this type of foundation, especially for use under all types of asphaltic surfacing. Its use in this country dates back to the earliest days of asphalt pavement of the hot mix type, and its service record covers the same span of years. I do not believe anyone dare attempt to predict the probable expectancy of a well-built asphaltic concrete base. If it is allowed to function undisturbed by excavations, etc., it appears to possess almost interminable life.

Frequently you will see reference to a very old piece of "Black Base that has been opened for some reason or other, and invariably you will note that its condition is excellent, showing no ill results from contact with earth moisture, frost and similar destructive elements.

The present extensive popularity of bituminous foundation is in no small measure due to its adaptability to almost any conceivable local condition which may offer real difficulties toward the employment of any other distinctly different type. Witness its use in widening and resurfacing old roads and pavements of all kinds, gravel, broken stone, waterbound and bituminous macadam, brick, block and Portland cement concrete. Likewise, by virtue of this great latitude of application, "Black Base" construction is rapidly increasing—indeed, much more rapidly than most of us realize until we have looked into the matter to some extent. In short, engineers have not been slow to recognize its high merit once their attention has been directed to it.

Notwithstanding the efforts of a few of us to extol its virtues, "Black Base" construction has not received the publicity it deserves, and that much less meritorious types have received. There are hundreds of most admirable examples of this type of foundation which are practically unknown except to those who actually attend their construction possibly even forgotten by them. But in spite of lack of advertising of this most excellent form of pavement construction, it is showing a remarkable yearly increase throughout the country. There are very few, if any states, which do not have at least a few excellent examples, and in some localities the yardage is very extensive indeed. Perhaps it is best that its development has resulted from the sheer merit of the product. It will be all the more secure, having so evolved.