DETROIT, MICH., JANUARY, 1911. 



Michigan State Good Roads Association 



P. T. COLGROVE, Hastings, President. N. P. HULL, Diamondale, Vice-President. 

 THOMAS SATTLER. Jackson. Secretary and Treasurer. 



TOWN ROADS NEED 



HEAVIER CONSTRUCTION 



Paper presented at Second International 

 Road Congress, Brussels, Belgium, July 31 to 

 August 7, 1910, by R. O. Wynne-Roberts M. 

 Inst. C. E., London, Eng. 



The materials usually employed and the 

 .Miiditions to be fulfilled in the construction 

 and maintenance of roads in large towns, dif- 

 fer considerably from those found on rural 

 and suburban roads, for the financial re- 

 sources at the dispn^l of the municipal au- 

 thorities of large towns enable them to use 

 materials which are quite beyond the means 

 "f rural and suburban road authorities. In 

 view of the extraordinary growth of rapid 

 transit locomotion and the difficulties created 

 thereby, the f Hi wing observations will be 

 confined to roads of the latter category. 



In the first place, the satisfactory construc- 

 tion and maintenance of roads on wet sub- 

 is admittedly difficult and expensive; effi- 

 ciency and economy, therefore, require that 

 unto drainage should be provided, for 

 which purpose stoneware or concrete pipes 

 are suitable. The former should be thorough- 

 ly vitrified, strong and of good form, the lat- 

 ter should be made of high grade air slaked 

 Portland cement and lean hard aggregate, in 

 rtions and well mixed. Reticu- 

 lating drains of -trong agricultural pipes or 

 stonework should be laid to remove water 

 from all parts of the subsoil to the main con- 

 duits. 



The foundation of the road constitutes the 

 main strength of the structure and should be 

 built of durable stone, handpacked and well 

 bedded. Inasmuch as the bulk of the traffic 

 traverses the crown of the road the foundation 

 should be stronger there than at the sides. 

 If heavy traction engines use the road, the 

 thickness of the foundations should be from 

 nine to twelve inches at the crown, and for 

 a width of about 12 feet to 18 feet along the 

 center, thinness will, of course, depend largely 

 "ii the nature, the composition and the weight 

 bearing capacity c f the subsoil, and the char- 

 acter and magnitude of the traffic which it 

 lias to sustain. 



The surface material should consist of the 

 most durable macadam obtainable, and in this 

 connection it may be stated that there is am- 

 ple room for standardizing, for at present 

 there is no satisfactory methrcl of correlating 

 the value of different kinds of macadam. At- 

 trition tests, etc., do not always conform with 



the results obtained in practice. The mini- 

 mum thickness of macadam on the center of 

 the road should be about six inches and at 

 the sides about four inches. The macadam 

 should be spread in thin layers and rolled 

 dry, the interstices being well filled with small 

 graded stones, so as to reduce the voids as 

 much as possible; a minimum of hard grit 

 shculd be thrown on to bind the whole mass. 



Taking into account the disintegrating ef- 

 fect of high speed traffic on the roads, it is 

 necessary to employ a bituminous binder, such 

 as coal tar, so as to keep the macadam to- 

 gether, to form a coherent and resilient sur- 

 face, to prevent rain percolating into the 

 fabric of the road, and to reduce the quantity 

 of dust produced by the traffic. Tar is one 

 of the by-products of gas manufacture, but it 

 is also produced in connection with coking 

 ovens, blast furnaces, etc.; this communica- 

 tion, however, will in the main only deal with 

 that produced from coal at gas works. 



The writer having also had some experience 

 as a gas engineer is therefore acquainted with 

 the methods of gas manufacture. The quality 

 of the tar depends on the composition of the 

 coals carbonized, the quantity distilled in each 

 retort, the class of retort installed, the heat 

 employed, methods of dehydration, etc. The 

 constituent parts of the tar are differently 

 grouped in each case, and it is therefore not 

 surprising that the results obtained on road 

 works differ so much under apparently similar 

 circumstances. The space and time at the 

 writer's disposal do not permit a description 

 cf the process of tar production, in detail; 

 suffice it to state that water, light oils, and 

 an excess of free carbon contained in crude 

 tar have a deteriorating influence on the dur- 

 ability and effectiveness of its application on 

 roads. 



All crude tars retain a quantity of water in 

 intimate admixture, and the latter increases, 

 in most cases, in proportion as the tempera- 

 ture employed at the gas works is raised, and 

 no extended period of rest will cause the same 

 to be entirely eliminated. If therefore crude 

 tar is used, it should be carefully boiled, which 

 work entails some risk, as owing to the pres- 

 ence of water and free carbon, it is liable to 

 froth over and cause trouble. When crude 

 tar is used on roads, it is, owing to the emul- 

 sifying actirn of the light oils have been ex- 

 tr.-'-ted by effective distillation. Given a period 

 of dry, hot weather, the oils will vola- 

 tilise on the TI. ad surface. Some engineers 

 maintain thai these oils are driven off by boil- 

 ing in portable boilers, or kettles, but the 



Continued on Page 6 



DUST PREVENTION AND 



ROAD PRESERVATION 



During the last year the United States 

 Office of Public Roads conducted a number 

 of experiments in dust prevention and road 

 preservation in various parts of the country. 

 A recently issued publication, Circular No. 92, 

 entitled "Progress Reports of Experiments in 

 Dust Prevention and Road Preservation," des- 

 cribes the work and summarizes the results 

 obtained and the conclusions reached. 



The first work with which the report deals 

 consisted of five experiments with waste sul- 

 phite liquor carried out in the grounds of the 

 Agricultural department at Washington, D. C. 

 In the first experiment a 615-ft. section of 

 road built of trap rock macadam with a lime- 

 stone binder was treated with a sulphite liquor 

 of a specific gravity of from 1,267 to 1,270 at 

 25 C., mixed with an equal amount of water. 



The solution was applied by means of a 

 300-gal. sprinkling cart at the rate of 0.54 gal. 

 of the mixture or 0.27 gal. of the liquor per 

 sq. yd. The first application was made on 

 Mar. 17, 1909; about the middle of May the 

 road became somewhat dusty and was water- 

 ed several times. On June 1, another appli- 

 cation of the sulphite liquor in a mixture con- 

 taining 80 per cent, of water was made at the 

 rate of 0.366 gal. per sq. yd. In making the 

 first application 1,093 sq. yds. of road were 

 covered and 820 sq. yds. were covered by the 

 second application. The road was one sub- 

 jected to a rather light traffic, but became 

 quite dusty in dry weather. The results ob- 

 tained by the first application were satisfac- 

 tory until the middle of May at the time the 

 road was watered. 



Experiments Nos. 2, 3, 4 and 5 were carried 

 out on a branch of the road used for the 

 first experiment. It was of a similar con- 

 struction and carried less traffic. The portion 

 employed for experiment No. 2 comprised an 

 area of 90 sq. yds. and was treated with a sul- 

 phite liquor at the rate of 0.5 gal. per sq. yd., 

 the material being sprinkled by common gar- 

 den watering pots and then broomed into the 

 surface. The material was readily absorbed 

 but was apparently a less satisfactory binder 

 than that used en the first section. 



Eperiment No. 3 was practically a duplica- 

 tion of No. 2 with a sulphite liquor obtained 

 from a different source. The results seemed 

 less satisfactory than those obtained in the 

 preceding eperiment. 



In experiment No. 4 a concentrated liquor 



