THE IMPORTANCE OF CARE IN MECHANICAL HANDLING OF BITUMINOUS MATERIALS FOR PENETRATION MACADAM AND SURFACE TREATMENTS By William E. Worcester, Manager, Philadelphia District, Kinney Manufacturing Co. At the Detroit meeting of the Asphalt Association in October, 1925 and again at the meeting of this Association in Des Moines the same month, an interesting and highly instructive paper was presented by Messrs. Prevost Hubbard and F. C. Field on the stability of Asphalt pavements. Pages 26 and 27 of the proceedings of this Association for 1925 record tests made at Atlanta, Georgia, on the actual street samples on a hot mix pavement showing a variation in stability values of from 1629 to 983-or 166%. The work in question was performed by a reputable and experienced contractor under careful supervision. Tables presented in this same paper show clearly the great variation in stability with a comparatively small variation in asphaltic content with all other factors remaining constant. If such results are obtained with hot mix types of pavements where conditions are relatively easy to control, it is perfectly obvious that much more care should be given to surface treatment and penetration type construction where laboratory and engineering supervision are not usually readily available and where the mineral aggregate varies much more than in hot mix types. Mr. B. E. Gray of West Virginia State Department and Mr. Wm. Catchings of North Carolina, at the Detroit meeting, and recent papers by J. N. Mackall of Maryland and F. L. Betts of Michigan, all emphasize the fact known to all of us that for many years to come the cheaper types of road surface must be of interest, since it is financially impossible to build concrete or sheet asphalt roads for all our traffic; and even if it were possible, it would be uneconomic, since frequently traffic conditions do not warrant such roads, as was ably proved in various addresses by Wm. H. Connell of Pennsylvania State Highway Department and others. A study of these papers, however, together with the article on maintenance equipment by H. J. Kirk, Ohio State Highway, printed in the June 1926 "American City," and the specifications of some twenty cities and state departments for the application of bituminous materials, indicate that the importance of uniform application of the bitumen is receiving little or no consideration and its importance. is apparently not recognized. The specifications for bituminous macadam recently adopted by this society and printed on pages 465-471 of the 1925 proceedings, is one of the first recognitions in print that this problem is important. A few months ago the writer was informed by the maintenance engineer of a state highway department, that many of their surface treated roads had pushed under traffic and were classed as failures. Inquiry developed that the covering material was placed in piles beside the road at regular intervals and the piles were of uniform size so the mineral matter varied little in quantity, but that there was no mechanical relation between the output of bitumen from their distributors and the yardage covered and that the check up showed a maximum variation in the actual application of 40%. Reference made to the Hubbard and Field tests afford easy explanation of the causes, yet the remedy in many cities, counties and states has not been to study the methods and results; but instead the engineers have jumped to the conclusion that all the cheaper types of surface were unsatisfactory, and the taxpayers have been increasingly burdened with exceedingly expensive surfaces for light traffic residence streets and country roads which have little or no heavy or through traffic. The time has now come when the problem of the light traffic street must receive some attention from the first class engineers, and not be left entirely to chance and rule of thumb methods; when the same care must be given to penetration and surface treatment work that is given to concrete, sheet asphalt, bitulithic, and brick. With this in mind, let us note the following points which vitally affect the final results: 1. Bituminous material is readily burned or coked, and light oils can be readily driven off by too much heat, therefore (a) you must agitate when heating to get uniform tempera- (b) draw fires or turn off steam when hot enough to use. 2. Since variation in bitumen content makes for unstable surface, it is necessary— (a) to measure the material on to the road and this can only 3. Operators and inspectors should understand the mechanical equipment and have at least an elementary knowledge of the properties of the materials they are handling as affected by (a) temperature at which it will bond to the minerals in the road. (b) temperature at which it will burn. (c) quantity of bitumen which is required to bond a given quantity of various types of stone, sand or slag. 4. All the care and training that can be applied to teaching laborers to spread stone evenly from shovels, is well repaid; mechanical stone or chip spreaders that are mechanically accurate and which will operate without passing over fresh bituminous surfaces, are needed and well worth the research necessary to produce such equipment. It is obviously recognized that the difference between careful handling either the bituminous material or the mineral aggregate, will cost more than the thoughtless methods too frequently employed. The difference in cost, however, is only a small fraction of the additional expense of going to expensive surfaces where cheaper types would carry the traffic if a little care in construction were used. Many engineers have proved that good results can be obtained-many have given up in disgust, simply because they neglected the fundamentals. To these I recommend a thoughtful study and rigid enforcement of paragraph (c) of the specification for bituminous macadam adopted by this society in 1925. ROCK ASPHALT, KYROCK AND ITS PLACE AMONG PAVING MATERIALS OF TODAY By W. A. Brownfield, Chief Engineer of the Kentucky Rock Asphalt Company, Louisville, Ky. The use of Rock asphalt dates back to the year 1710 when the Greek physician, Eirinis discovered a large deposit at Val de Travers in the canton of Neufchatel. Prior to this time asphalt had been from time immemorial known and used as a natural cement, even unto the days of Noah when he "Pitched the Ark within and without," and later it was referred to as "Miracular Oils," "Healing Balm" and other medicinal terms. Again in 1802 another large deposit was discovered in the vicinity of Seyssel (Aine) near the river Rhone; but prior to this discovery, Rock Asphalt had for some time been extensively used for building stone foundations, fortifications, sea walls, and for many other purposes wherein the structures were designed to withstand the ravages of the elements for all time to come. While carting the Rock Asphalt for this purpose, from these several mines, it was found that the small pieces which fell from the carts, after being run over, made a very excellent road-bed. Eirinis' dream of an asphalt pavement in 1712 has been realized in our modern day construction. Much difficulty was experienced in those days by the early promoters of Rock Asphalt as a paving material, in reducing the rock formation to a proper consistency and uniformity so that it could be laid as a wearing surface. Two methods of preparation were employed, viz: the slow crude method of pulverizing by hand, and the warming of the boulders until they dissolved and applying the material before it cooled. The latter seemed to be the most economical at that time and was the method most generally used. Through the efforts of Count Sassenay, Rock Asphalt sidewalks were laid in Paris in 1832. In 1838 a section of Oxford Street in London was paved with Rock Asphalt, as were many other experimental sections throughout the European continent. Some of these experiments were wholly without merit, while others were very satisfactory. Probably the first roadways of any prominence successfully paved with pulverized and cold compressed Val de Travers Rock Asphalt and of which we have any accurate information concerning the methods of laying and the results obtained, were the Rue Bergere in Paris in 1854 and Threadneedle Street in London in 1869. However, the application of cold compressed Rock Asphalt in its natural state had long been advocated by M. Darcy, Inspector General of Bridges and Roads, in France, who had prior to this time made many experiments with Rock Asphalt, as reported in the, "Annales" in 1850, along with other valuable information about Rock Asphalt by M. Leon Malo, graduate of Ecole Centrale, and former Engineer of the Midi Railroad. And, in those days as well as now, it was known by those who were most familiar with Rock Asphalt that all of the deposits were not suitable for roadway paving; but there was a necessity for asphalt paving and an industry had been created. On July 10th, 1885, the first quarry of Rock Asphalt was opened in Edmonson County, in the State of Kentucky. Soon thereafter many quarries were in operation within the State and not many years later quarries were opened in many other states for producing Rock Asphalt. The action of the materials furnished by these many quarries have been as varied as the number of the quarries opened plus the number of those who have experimented with the construction of the pavement. A discussion in detail of these various deposits is not here intended, but, a mention of Uvalde, a limestone Rock Asphalt produced in Texas by the Uvalde Rock Asphalt Company, and Kyrock, a sandstone Rock Asphalt produced in Kentucky by the Kentucky Rock Asphalt Company includes the two largest producers of Rock Asphalt in America. Many other deposits of Rock Asphalt are found from Canada to Cuba and from the Atlantic to the Pacific, each varying in its composition, quality and usefulness. In Kentucky alone, where the largest production of sandstone rock asphalt in the world is found, there are no less than three known and distinct Rock Asphalt horizons. And, within the same geological formation we know the characteristics of the several deposits are sharply differentiated, both as to the physical character of the aggregate and as to the chemical composition of the asphalt. Kyrock, the material here selected for discussion, is a clean sharp quartz sand about 95% silica (Si02) which is thoroughly impreg nated with a natural asphalt which contains about 90% pure bitumen. The proportion of the two materials in commercial Kyrock is 6.5 to 7.5 per cent natural asphalt and 92.5 to 93.5 per cent of sand, and nothing else. This material is found in this proportion in sandstone rock formation overburdened with about twenty feet of white sand and earth. Its geographical location is along Nolin River, which is a tributary to Green River, in the cavernous sections of West Central Kentucky, or near the famous Mammoth Cave. Its geological location is above the conglomerate in the Pottsville sands of the Pennsylvania Series. |