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Show District Engineer Gives Facts on Oiled Roads i I undertaken. In the meantime the disadvantages of the untreated road have bociome all too apparent and everywhere there is a desire to find the remedy at the earliest possible time. A progress report has been prepared for publication and the essential es-sential poi'.ions of this report ire given here. The study of surface treatments with the asphaltic products and the possibility of utilizing existing gravel grav-el surfaces as bases for bituminous macadam construction are the pu'- poses of this investigation. j Two general methods of treatment have been developed, which may be described respectively, are the method of surface treatment, and the mc'h.id of surface mixing. These are briefly described as follows: Surface treatment method: This treatment is practiced in Oregon and California contemplates the impregnation impreg-nation of 'the upper portion of a compacted com-pacted fine crushed rck or grave! road with light asphaltic oil. The process resembles the ordinary surface sur-face treatment of macadam when light oils or tars are used, but differs dif-fers tvom surface treatments with heavy oils, in "that there is no formation form-ation of a distinct mat of stone, chips, and binder. For practical reasons, some cover material is commonly com-monly used, but the amount is usually us-ually limited, and the light oil so penetrates the road crust, that there is finally little left on the surface to be absorbed by the application of chips. The first step in this process is the thorough sweeping of the existing road surface with a power broom, supplemented by hand brooming if necessary, to remove all loose material mater-ial and scales of fines and expose the compacted rock surface. The light oil is then applied under pressure at the rate of about three-ten". hs of a gallon per square yard and allowed to penetrate, the time required depending de-pending upon the texture of the surface sur-face and the viscosity of the oil. Usually two or three days is sufficient, suffic-ient, during which time the road is closed to traffic if practicable. At this stage in Oregon small imperfections imperfec-tions in the surface are repaired with a lean mixture of oil and ag- Sinee trials at oil rond building in . ' Utah has been given thorough tests and exhaustive study by the state road commission, the state road engineer en-gineer and district engineers, highly gratifying results have been obtained and with a view to impressing upon the public, taxpayers and travelers, the importance in making a monetary mone-tary saving and ns well as splendid reads, R. J. Garn, district, engineer, gives some valuable information that ; is wor:hy of thought in the follow- j ing: j In all states the problem of devel- j oping satisfactory types of surface , for light traffic roads is an important, one because of the large mileage of such roads in the county and local systems, and even in the systems that are set ap3rt for the improve-j ment by the States. In the Western Stai'es the reed for such types of construction is font, perhaps more sharply than in other sections, not only because of the more extensive mileage on which , traffic is now and will remain light, but also because similar forms of construction are needed for the initial in-itial improvements of a ve,ry considerable con-siderable mileage upon which a rapid increase of traffic is expected. On the roads of the latter class "the inexpensive in-expensive surface is regarded as merely a first stage of improvement, to be replaced as traffic demands and funds become available; but for the present the problem is one of improving im-proving the service of such roads at minimum expense in order that the benefit may be quickly and widely , distributed over a large mileage. i To meet this need the States of the West have built in recent years many miles of traffic bound metalled roads, the surfacing material of which is finely crushed rock or gravel. Differing from waterbound macadam in several aspects this type practically practic-ally replaced true macadam, because be-cause it is less expensive in the first and more readily maintained under traffic. And highway officials are becoming seriously concerned at the mounting cost of renewing the road metal. Also the dust nu:s?.nce, and the cost of operating vehicles upon these surfaces is rather high. Recognizing the objectional features feat-ures of the present practices, and convinced of the necessity of developing develop-ing satisfactory types of highway surfacing intermediate between gravel grav-el and the expensive pavement types, and having in mind, especially the need of such types in the Western States, the- U. S. Bureau of Public Roads and ithe Highway Commission of California, in 1926, undertook cooperative co-operative investigation of which the preliminary findings are presented in this article. The particular purpses of the investigations in-vestigations were to determine the service of value that might be expected ex-pected of fine crushed rock and gravel surface to ascertain what methods might be employed to conserve con-serve material and ' increase serviceability service-ability by the use of bituminous material; and to study their value a: basis for higher tyes of less cos: than the plant mixed surfaces. The first effort upon inauguration inaugura-tion of a study was the' accumulatioi of data regarding successful and unsuccessful un-successful examples of the respectivi types, records of processes and ma terials, cost data, wear.her, soil in formation, service history and main tenance methods and costs. Thi examples were found to fall withii three natural groups: 1. Untreated surface, general!; of the fine rock or gravel type. 2. Roadway either natural soi or material, treated with light o fuel asphalitc oil, material whicl can be applied at the atmospheri tempcrture or by gentle warming. 3. Metaled roadways treated wit road oil or with soft grades of as phalt. The multiplicity of 'roadway type within the field of the study eve when limited to the Western State has made clear that much time wi be required to complete the wor gregate. , f ! When the first application of oil has thoroughly penetrated, a second ' is spread at the rate of about two-i two-i tenths of a gallon per square yard, ; and, as before, is allowed to stand for several days without traffic if , ; possible, while the oil is being par-jtially par-jtially absorbed. The treatment is I completed by spreading stone chips j over the surface before the road is j opened to traffic, and, if vehicles can- not longer be kept off, the chips are . j spread immediately after the second , application of oil. The quantity of : cover material usually used ranges 1 1 from 10 to 25 pounds per square . j yard depending upon the viscosity of . ! the oil and whether or not the road . j is to be opened to traffic immediate-. immediate-. I ly. The larger amount is necessary if 3 the road is to be opened immediate- t ly; and oil of higher viscosity require I more cover tha5n the thinner oils. . I There is a tendency in some places , to modify the surface treatment . : method described by substituting ; ; heavy road oil. As before stated, no . recommendations have yet been form-. form-. ulaited on this subject. It should be . pointed out, however, that heavy road e'oil is more costly than "fuel oil," de- mands more equipment and better : technic in application, and requires y from 100 to 200 cubic yards per mile of screenings for cover. Surface mixing method: In the r method of surface mixing, the surface h ! of the previously constructed fine c crushed rock or gravel road is first scarified to a uniform depth of IVi h to 3 inches, according to the thick-ness thick-ness of bituminous surface desired. The light asphaltic residual oil 'is !S then applied in two or three applic-n applic-n ations, each consisting usually of !S about one-half gallon per square 11 k (Continued on last page.) method is to be followed. A layer of loose material between base and mixed top may cause rutting, shoving, shov-ing, or breaking. (e) For surface treatment, repairs re-pairs should be completed and the road compacted well in advance of oiling. Spots escaping attention should be repaired between applications applica-tions of oil. (f) All loose material and scales of fines must be removed before the oil is applied to the surface. Sweeping Sweep-ing must expose clean rock or gravel firmly embedded. (g) The texture of the stone surface sur-face should be uniform. Results of sui"face treatment will be poor if po:tions of the road are porous while cither portins are impervious. Minor irregularities will disappear in the mixing process, but large areas of irregular grading require skilled teatment. The cost of this type of road on an already constructed gravel road : is about $2000 a mile, and federal aid can be secured on it so that the coat to a county would only be about $500 a mile. Engineer Gives Facts on Roads I ir v (Continued from page one.) j c yard; and after each application the-t oil and loose stone are partially mix- i tl with a disk .cultivator or spring- 1 tooth harrow or both; the material is 1 E then bladed repeatedly into windrows I and respread until a uniform color is t attained. It is finally spead to the desired crown and the road is then j j opened and continually dragged or U bladed while it is being compacted ! i by the traffic. j i Roads treated by these methods are of distinctive type and are not to be ' confused with roads treated for dustl palliative purposes. In appearances ! thejy resemble other asphajltic sur- i faces. Skillfully prepared and treat- j , ed, their smoothness shortly after j , completion, as indicated by "rougho-1 , meter" readings, is equal to that of j the best pavements. When well j maintained they appear to rate with 1 ( good bituminous macadam; but, at i their worst, when maintenanre is neglected or when the surfacing ma-1 Serial or its condition at the time of ; treatment is poor, they may become j intolerably rough. There is no dust, and tractive resistance and tire wear are both low. In the progress report which follows fol-lows there re descriptions of whet I appear to be the best methods of ; constructing and maintaining them with light asphaltic residual oil ae-j ae-j cording- to the two general processes I that have been developed. j The principal conclusions are .s ' follows: 1. Light asphaltic risidual treatments treat-ments as practiced in Oregon and California have demonstrated their utility in the preservation of exist- j ing road surfaces and are justified in places where the cost of the oil is not prohibitive. 2. Oil treatment has substantially reduced maintenance and replace- j ment charges on fine crushed rock ; and gravel roads in Oregon and Cal-1 ifornia. The first cost is frequently i less than the value of the metal lost j yearly from the same road before ' tretment. Maintenance after oiling j will probably not exceed the cost of J adequate maintenance of the untreat- j ed surface, exclusive of the replace-! ment of metal. ! 3. Oil treatment improves service' I jerimentaition with heavy asphalts. i However, the most that can be ex-1 1 aected of the ltter is some further j reduction of annual costs, particularly" where the traffic is heavy, and that possibility can not justify failure to accept and use present methods until or unless better are developed. 7. In the matter of new construction construc-tion no conclusions can yet be formulated form-ulated as to the relative merits of building fine crushed rock or gravel surfaces, ito be immediately oil treated, treat-ed, or of adopting some form of bi-tuminus bi-tuminus macadam. 8. Protection of vehicles from freshly applied oil is indispensible; otherwise, damage to traffic may more than offset the benefits resulting result-ing from treatment. 9. Examples of oil-treated natural soil roads furnish impressive figures of good service and low costs. This type has a larger field than has heretofore been realized; where soil, climate, and traffic are favorable. It deserves more scientific study nd consideration. 10. Precautions: The immediate improvement that generally follows oil treatment has sometimes encouraged en-couraged a feeling that almost any road may be successfully treated by almost any method. Subsequent complete or partial failure has discredited dis-credited the process. The facts are that success will be proportionate 'to the suitability of physical conditions, intelligence of supervision, and skillf ulness of -workmanship. The following fol-lowing are important precautions to be observed : (a) Unless there is a maintenance organization accustomed (to giving daily attention to necessary repairs, oiling should be undertaken. Delay and neglect cause rapid destruction and discredit the process with the public, which expects more of an oiled road than of an untreated road. The success in Oregon which has led to renewed interest in the whole subject was due in a large measure to the prior development of an efficient effic-ient maintenance organization. (b) There must be sufficient I thickness of metal ito carry the ex-i ex-i pected traffic. I (c) The width of the stone sur-I sur-I facing should be adequate-rarely less than 18 fec.t. Vehicles turning on ! and off the oiled surfaces tend to crumble the edges. I (d) The metal must be compacted , completely from top to bottom if the method of surface treatment is to be I used, and at least through the un-i un-i (treated base if the surface-mixing and is, therefore, poular with the public. It eliminates dust, decreases tire wear, and lowers fuel consump-1 tion. 4. Any road in Oregon or California Calif-ornia which has justified improvement improve-ment with a fine crushed rock or gravel surface warrants the additional addition-al expense of a light oil treatment, except possibly in rare instances of isolation, extraordinarily cheap material ma-terial supply, or low sendee require- ' mcn'.s. Direct financial justifications will generally follow a comparison of the estimated maintenance after treatment plus a reasonable annual portion of the oiling cost with the , known maintenance cost prior to oil- j ing plus the value of untreated metal destroyed annually. 5. An efficient maintenance or-ganizatiin or-ganizatiin is essential to the success of light oil treatments. Maintenance must be immediate ami continuous, otherwise oiling will be unsuccessful and should not be undertaken. While proper maintenance is stressed as a I prime requisite, the total annual cost is less than that of untreated road:. 0. The recorded success with light oils should not stop continued development devel-opment of present practices or ox- I r : |