The development of modern road surfaces

FRANKLIN INSTITUTE ( S t a t e d meeting, held [Fedncsday, June z6, z9o9.

THE D E V E L O P M E N T OF M O D E R N ROAD SURFACES. BY

W. H. FULWEILER. ( C o n c l u d e d f r o m S e p t e m b e r , page x 8 3 . ) SURFACE

COATING

WITH

TARS.

T h e n l o s t g e n e r a l process, h o w e v e r , f o r t h e suppression o f t h e d u s t n u i s a n c e is t h e use o f a s u r f a c e c o a t i n g o f t a r . From t h e c h r o n o l o g i c a l t a b l e o f its d e v e l o p m e n t , we s h a l l see t h a t a l t h o u g h its g e n e r a l use c a m e a b o u t t h e same t i m e as t h e use o f o i l , e x p e r i m e n t s h a d been m a d e w i t h it in F r a n c e t w e n t y y e a r s e a r l i e r , y e t o n a c c o u n t o f t h e universal use o f gas t h e e c o n o m i c a l s u p p l y o f t a r w a s n o t l i m i t e d by geographical c o n s i d e r a t i o n s , so t h a t it a t o n c e s e c u r e d a w i d e field o f u s e f u l n e s s . T h e f o l l o w i n g t a b l e g i v e s t h e g e n e r a l d e v e l o p m e n t o f its use: DEVELOPMENT

OF T A R

COATING.

'1867. Chas. Tellier, in France, first proposed the use of tar as a surface treatment on roads. I87I. A. M. Francon, at Auch, applied a coating of cold tar, and then fired it to secure a better penetration. 188o. Cristople, at St. Foy le Grande, and Lavinge, at St. Gaudens, made some experiments with cold tar. 1886. Experiments were made at Melbourne, Australia, with considerable success. I888-I892. F u r t h e r work was done at St. Gaudens by Cristople. ~894. A s h o r t piece of road at Montclair, N. J., was treated with coal tar, and screenings were rolled in. The first use of this method. I895. The first general experiments, where all conditions were noted and considered by Guardeau in France. He used both hot and cold tar, and noted the better effect with hot tar. 19oo. Rimini, an Italian road engineer, patented the use of coal tar mixed with a drying oil. This gave a quick, smooth finish, but did not last very well. I9Ol. Drs. Schottelius and Guglieminetti made their classical experiments at Monte Carlo and Nice, and determined the essentials for successful results. 19o2. The League for the Suppression of Road Dust was formed with headquarters in Paris. They succeeded in interesting the F r e n c h Government, so that systematic experiments were undertaken in the Department of Seine, Seine et M a r n e and Seine et Oise. This same year the success attained at Monte Carlo and Nice led to the tarring of the whole road from Cannes to Mentone. 260

DEVELOPMENT I9o3. 19o4. ~9o5. I9O6.

OF M O D E R N

ROAD S U R F A C E S .

26I

T h e work was now undertaken on some of the suburban roads that were largely used by m o t o r s abont P a r i s ; at St. Cyr and i n and a r o u n d Versailles. T h e r o a d s i n the Bois de B o l o g n e were tarred, and the Boulevard M a i l l o t and Avenue de la G r a n d Armfie. T h e use of tar mixed w i t h tar oils s o that heating was avoided, was widely tried i n France. T h e u s e of tar became q u i t e general in France, E n g l a n d , and was connnenced i n America.

There are several reasons wh the use o f tar was more general t h a n that of oil. As mentioned before, it couhl be more easily procured, it was cheaper, and it was more widely applicable to different kinds of road surfaces, particularly to the brokenstone r o a d s of Continental Europe, and it gave much better results t h a n the paraffin base oils first used on the Continent. Again, the object o f Dr. Guglieminetti's experiments were, primarily, to better the hygienic conditions that resulted from the dust clouds raised by traffic. T h e y f o u n d t h a t there was a great increase in the number of microbes per cubic centimeter in the air near r o a d s t h a t were frequented by automobiles, and that while the use o f petroleum oils that were first experimentally used decreased the number o f microbes when first applied, yet their value as antiseptic agents soon diminished almost t o zero. So that they were searching for some antiseptic a g e n t t h a t would have a more permanent value. The value of t a r in this connection was well known, as it had been used for many years in treating various plant diseases, a n d this led t o its trial at M o n t e Carlo, with surprisingly successful results. W h e n we consider the methods o f applying the tar, we find that they may be divided into three general heads. I. Painting the road surface by b r u s h i n g with a hot coating of coal t a r and dusting it lightly with sand. In general use in France. 2. Painting the surface by machine or with a very light coating o f oil t a r o r thinned coal tar, and d u s t i n g with sand. This is generally used in England. 3. Coating the surface with a fairly h e a v y coating o f hot t a r o r t a r compounds, and th~en covering with a light coat o f screening and rolling. This is the general system used in America. In reviewing these methods, we should bear in mind the objects to be attained. In the first place, we wish to hold the

2(J2

\V. H. I~'ULWEILER.

surface dust iu place so that it may perform its function of retaining the stones composing the w e a r i n g surface ill t h e i r proper position to reinforce this m a t r i x against the shearing strain put Oll the surface by tile passage of m o t o r cars, and to form a waterp r o o f coating on the road surface protecting it from the action of the almOsl)here, m'Jd thus minimizine, the formation of nmd. \Ve cannot, of course, prevent the formation of dust from detritus dropped oil the road by traffic, but when first applied the tar will absorb a consideral)le quantity of it, and in this action is surpassed by the h e a v v oils. T h e r e have been an innumerable n u m b e r of variations proposed and tried, so that it would be almost ilnpossible t o even review them all, so that only the most successful methods c o m i n g u n d e r the t h r e e f o r e g o i n g h e a d s will be gone into. The first m e t h o d was the-ontgroxx:th of the experimental work done by the F r e n c h engineers, and the general conclusions laid down by Dr. Guglieminetti seem to c o v e r the subject so thoroughly that they will be repeated here. The w e a t h e r should be c l e a r and dry with an air temperature not l o w e r than 70 F., and preferably l'ligher. The road should have been resurfaced d u r i nK the past four to six months. The surface should be thoroughly dry, and tar should not be applied ' b e f o r e ten ()'clock in the morning. The surface should be free froln (lust and dirt, and w h e r e possible the surface should be lightly washed with a hose anti w a t e r u n d e r pressure, and the road allowed to dry with traffic excluded for two or t h r e e days. The tar should be h e a t e d to I4 o:' F. and spread very evenly, avoiding excess, and well brushed into tile surface voids. Two or t h r e e h o u r s should be allowed for lhe tar to be absorbed, and then a light even coating of s h a r p sand should be spread over it. The quantity of tar should be regulated according to the capacity of tile road for absorption, and should not be less than .25 g a l l o n s or over .5 gallons per square yard. Two light coats are recommended as more efficient than one h e a v v coat. No essential modification has resulted in seven years work with this method. The most important specification is that of the choice of the day for d o i n g the work. It is ahsolutely essential that the w e a t h e r should be c l e a r and warm, and that the road should t~e thoroughly dry. not only on the surface but down into the body

I)F.V;~.hOP_~rENT <~F ~\[~ln~.Rx l{~),\lJ ~tRF.\C~:;S.

263

for several inches. This means that at least two days of dry, clear weather shouhl have elapsed since the last rain, and that June in this latitude is a b o u t the first month t h a t successful resuhs may be expected, due to the excess o f moisture absorbed during the winter and spring rains, and September is l~robably the latest. The necessity of observing the proper weather conditions, and the shortness of the season, naturally increases llle cost of work when done by contract, as the men and plant are idle so mtu:h o f the time, but with highway COlllnlissions the nlen can generally be utilized in o t h e r work. so that it is not so important. El{;. ~3.

F r e n c h tar distributing machine.

Considering the practical apl)lication of this method, we find here that freeing the road from dust is the most difficult and expensive part of the process; but this is due to the fact that in France. and, to a very considerable extent in England, they keel) the surface of their r o a d s free from mud and dirt by frequent scrapings and brushings, so that the preparation for ti~e application of far is not so difficult, while here only in the case of a' few turnpikes, parks, or closely settled subu1"ba11 villages, is such a thing ever thought of, so that it requires it great deal more labor on ,mr r o a d s to remove llle accumulated dust. .\gain,

264

W . H . FULWEILER.

owing to the fact that our horses are nearly all shod with caulks, the surface is continually kept rough, and thus affords lodgment for the road and traffic dust, while abroad the horses are smooth shod, or when caulks are used a t all it is only in cities, so that the road surface is smoother and easier cleaned by brushing, which would ravel an American road. The preliminary sweeping is usually done by hand in France, and by horse sweepers in England and America, reinforced by a hand g a n g who clean o.ut any hollows o r depressions not reached bv the larger and stiffer revolving broom. F~G. I 4 .

Lassailly tarring machine.

This sweeping is of the greatest importance, and lack o f care with it is responsible for the majority o f the failures, even where the o t h e r conditions have been carefully observed. T h e r e are two main reasons: W h e n the surface voids are filled with dust, the t a r collects in little globules and does not penetrate the road metal a t all, just as water assumes the spheroidal state on a hot iron plate, and is readily w a s h e d away at the first rain. Again, when a quantity of dust is allowed to remain in the bottom o f any little hollow o r chuck hole, the "excess o f t a r that will nearly always collect there f o r m s a cake with an apt~rently smooth surface, but u n d e r the action o f the weather and the traffic this soon disintegrates and is licked out bv passing wheels, leaving the metal unprotected, so that moisture penetrating u n d e r the tar surface soon destroys it for a considerable distance a r o u n d

DEVELOPMENT

OF MODERN ROAD SURFACES.

265

the original hollow, giving the road a very bad appearance and soon forming deep chuck holes. The t a r has been applied in a number o f different ways. At first and in small jobs it was heated in kettles on the roadside, and applied from hand sprinkling cans provided with wide flaring nozzles. A small tank holding a b o u t fifty gallons, on wheels, that could be pulled by two men, was then used in France. Nozzles were provided, so that an even distribution was secured. This was succeeded by portable horse-drawn boilers that would hold a number of gallons, but the actual sprinkling was done bv hand Fro. I 5.

Distributing

and brooming-in tar

with a fiat nozzle connected by a flexible hose so that the quantity of t a r used could be more accurately apportioned to the requirements of the surface. A b o u t i9o6 the Lassailly machine was invented, which sprinkled the tar a t a predetermined rate, a n d made use of a set o f automatic brushes to secure a more uniform distribution. In the United States the usual form of s t r e e t sprinkler has been provided with an iron tank (that would remain tight u n d e r the influence of the hot tar) and the sprinkler has been modified to handle the thicker substance, while the White oilinK machine has been adopted to some extent.

26(~

\V. H.

lgUL\VEILER.

l'robably the very best work has been done by a skilled man distributing the tar from a nozzle, as he can g a u g e precisely just how nmch tar each s e p a r a t e section requires, but, of course, at nmch g r e a t e r expense than w i t h the machines, w h e r e the flow must be more or less u n i f o r m regardless of requirements. Following the actual spreading of the tar come men who follow the sprinklers with 1)rooms and brush it thoroughly into the road metal. They see that it is spread evenly and r e m o v e any excess and c o v e r the thin places. T h e i r work is very imp o r t a n t , as it is diflScull when the d u s t has not been completely F I ( ; . l (~.

R o a d t r e a l e d b y f i r s t m u t h o d , S a v a n n a h , Ga.

r e m o v e d to make the tar " take " on the surface, that is lo b r e a k down the surface film that is f o r m e d and really p e n e t r a t e the interstices of the metal. It was to overcome this difficulty that the u s e of w a t e r as a preliminary washing was recommended: but, of course, this is not a h v a y s practicable as the road must be closed to traffic while it is drying. The w a t e r removes the surface d u s t film and leaves the stone in very good condition to receive the tar. It is essential also, for the reasons g i v e n above. that no excess of tar should be allowed to collect in puddles in hollows in the road surface. Stable b r o o m s are g e n e r a l l y used, and al)out one man fl~r each 3 feet of w i ( l t h of r o a d . w i t h an

[)I~2VEImPMEX;r

()F MOnERX ROAD Svm:.xCES.

--'67

extra man ~)r two bringing up the rear to remove any puddles, etc., that have escaped the regular gang. The men here frequently work so that they b r u s h towards the l~ody, 1)\ s t a n d i n g on the untreated road, but in France they are provided with wooden shoes and b r u s h away from the body, walking in the tarred surface. The latter seems much the better method, except from the nuisance to the men. ()n the smoother road surfaces of I:rance they fl'equently use a r u b b e r s~'iuegee to spread the tar after spril~kLing: this seems to give very good results there, but does not seem adapted to the r o u g h e r surface <,f ollr roads. F I ¢ ; . ~ 7-

Horse-drawn far-spraying machine

This 1)roonlin K or sweeping in is a very disagreeable and hard work if it is done properly, as the tar nlust 1)e thoroughly brushed and rul)l)ed into the road metal to secure the best results. It seems to take weight to do this, and the 1hen can't keep it tip prol)erly for very long a t a time. T h e y frequently arrange the work so that the g a n g s change places about every hour. The surface should remain undisturbed for several hours to allow the absorption of the tar, and then be liKhtly covered with a clean, sharp sand just sufficient to absorb any of the tar remaining on the surface and t o t511 the voids which were opened by the sweeping.

268

\V. H. FULWEILER.

This method has been widely used in France, and has proven very successful with their smooth surfaces, but it is necessarily slow and expensive at the higher rates o f labor in England a n d America. t n o r d e r to obviate the labor cost, and to avoid the necessity o f heating the tar, some modifications have been made to it. About 19o5 they commenced applying the tar cold after thinning it with t a r oils, and in o r d e r to avoid the labor necessary for sweeping and spreading, a number o f machines' have been invented t o s p r a y the t a r on the road u n d e r pressure. These methFIG.

18.

Power tar-spraying machine.

ods come u n d e r the second heading, and are known in general as t a r painting." The preliminary sweeping need only renlove the larger particles of debris as the pressure of the t a r forces it t h r o u g h the dust. The uniforlnitv o f the machine's action allows a very lnuch smaller quantity of t a r to be used and yet secure a continuous coating, while the brooming afterwards is entirely done away with; moreover, the work is done a b o u t twenty to thirty times as rapidly, thus enabling more work to be done during the most suitable season. This method has been widely used in England with both coal gas tar, and almost en"

DEVELOPMENT OF ~/~ODERN ROAD SURFACES.

z69

tirely now with water gas tar, and has given generally satisfactory results. The machines in use a r e - Aitkens Pneumatic T a r Sprayer is the inventon of Mr. T. Aitken, County Surveyor of Cupar-Fife in Scotland. It is ma.de in two forms, one with steam drive and the o t h e r for horsepower. Pumps geared to the wheels compress the t a r to a pressure o f IOO to 150 lmunds when it is atomized with air u n d e r a pressure FIG.

IQ.

Spreading and rolling screenings.

Of IOO to I50 pounds in nozzles, into the road surface. The p o w e r machine has steam coils so t h a t the t a r may be heated, but with the horse-drawn vehicle the t a r must be used cold o r h e a t e d before being put into the tank. The Tarspra discharges the tar u n d e r a pressure of 2oo pounds, and has pumps t o keep up this pressure and the deliverv of the t a r constant. These machines are now made bv the ;Faroads Syndicate o f L o n d o n , England. There are. of course, a number of other machines, but these seem to be the most important. The introduction o f these machines has enormously increased

270

\\*.

H.

IVt'IA\'EIIA£P,.

the nse of tar for road t1eatme13t in ]~ngland, and I believe t h a t it would be of equal benefit here, as it does away with a great deal of labor and applies the tar quickly and economically. To better adal)t the application of t a r to the r o u g h e r surfaces of our American roads, the third method has been evolved and which seems to give the best results u n d e r our conditions. Tke work is all done exactly as u n d e r the first method, except that a considerabh, heavier refined grade of t a r is used, that has more body and greater binding properties, and it is applied a b o u t twice as heavily. T h e n , instead of sand. a light coating of clean gravel or fine stone chips is put on, and the whole surface is rolled with a road roller. This treatment renews the wearing surface and fills the voids made by sweeping very much better than the sanding, while it also ( f r o m the heavier t a r used and greater quantity) seems to penetrate more deeply, and its effect is more lasting. It succeeds best on Macadam roads. It is practically mud-proof; absolutely free froIn road d u s t ; apparently p r o o f against very heavv motor traffic, and u n d e r American condit i o n s is bv far the most satisfactory surface treatment. Its cost. however," is very much higher than either of the two o t h e r methods. In lllis connection it will be considered later with respect to o t h e r methods. Considering now some o f the details regarding the I)roper quantities o f materials necessary, we find that they are dependent almost entirely on lhe condition of the surface to be treated, a n d - t h e y may he tabulated as follows: M A T E RI A L S . Tar gals.

M e t h o d No. i, S m o o t h r o a d s . R o u g h r o a d s. . M e t h o d N o . 2, S m o o t h r ~ a d s . R o u g h r o a d s. . M e t h o d No. 3, S m o o t h r o a d s . R o u g h r o a d s. . Gravel r o a d s. .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

P e r sq. yd. . 2 0 - - .3° . 3 ° _ • 40 . 1 2 - - . 15 . 1 5 - - . 25 . 33 .45 . 45 .65 . 6 0 - . 70

Sand tons.

Screenings.

P e r s q . yd. T o n s p e r s q . y d . .006 • 009 • oo 3 .oo~

.OIO---.OI 5 .OI5--.O25 .o25--.o3o

In general, a road when slightly dalnp will not absorb onehalf the t a r that it will when thoroughly dry, and the same h o l d s with a badly swept road. Gravel will take more t a r than Iacadam.

DEVELOPMENT (IF ~IODERN ROAD ~URFACES.

27[

Ill the selection of tile tar for use as a surface coatiug, we nmst consider the conditions and the results that are desired. The first lnethod was developed to utilize a dehydrated coal tar, and this seems to serve the lmrpose quite well, as it is intended not only to lay" the dust but to serve as a waterproof coating for the r o a d , but it was not expected that it should last more than one season, and the plan now seems tgo be to give two treatments a year. The tar should then have a fair body, and be free from ammoni~cal liquor, as this prevents a proper penetration and has a disintegrating effect on the coating a f t e r b e i n g apl)lied. F r e e dom f r o n t carbon is a n o t h e r advantageous characteristic, as it is the excess of free c a r b o n that undoubtedh" causes the black mud formation in winter. In the second m e t h o d coal tar thinned with tar oils, creosote oil or mixed with resin, or, best of all, w a t e r gas tar, seems to have given the best results. Here the principal effect desired is the (lust laying, and as a n u m b e r of coats are applied per season the tar does not r e q u i r e much 1/o(13. For the t h i r d process, w h i c h is expected t o be very much more permanent, and which, moreover, is required to act as a )natrix )tot only for the road m e t a l proper but also for the surface l a v e r of screeniltg, a l n u c h h e a v i e r bodied tar is required. The material generally used for this purpose has been a dehydrated coal tar with n e a r l y all the light oils ( t h a t is, up to 392o F.) removed, and sold u n d e r the t r a d e name of T a r v i a in this country, and Claires' Tar Comp. in E n g l a n d . D u r i n g the past year compounds n l a d e f r o l n water-gas tar have been successf u l l y used. T h e r e are several patented foreign preparations for use in t a r r i n g roads. A m o n g t h e m . and probably the most widely used, is Claire's Tar Comp., a dehvdrated coal tar preparation very similar to the American T a r v i a : Solidified Tar, made by Tar Pateuts Co., of London. is simply coal tar dehydrated and treated with 4 to 5 per cent. of HIs SO4: Marbit, prepared by T. E. Marriott, of Glasgow, is c r u d e coal tar and a specially prepared n a t u r a l bitmnen which are mixed and immediately applied. The advantages of the surface treatment with tar preparations are, in general, as follows: ( I ) F r e e d o m from dust. (2) Protection of the road surface from m o t o r traffic. (3)

272

\V. H. IrULWEmEI<

Lengthening o f life of surface by waterproofing effect o f tar. (4) More resilient surface for horses. (5) Freedom from surface wash, and less clogging o f drains. There are, however, a number of objections that have been urged against its application, particularly by the first two methods; this is u s i n g crude coal t a r o r t a r painting with water or coal t a r with lnachines. W h e n a h e a v y rain follows an application of crude coal t a r or t a r painting, it has been f o u n d in some cases t h a t fish in neighboring streams have been killed by" the tar oils. T h i s , o f course, does not apply t o the heavier tars used in the third method. The tarred r o a d s have in some cases c h u r n e d badly in winter, forming a very disagreeable black slimy mud. This dries out and the road regains its fornler appearance with dry weather. This is not so noticeable when water-gas t a r has been used, which is low in free carbon and is less noticeable on road. surfaces t h a t are kept free from traffic debris; this does not apply t o the third method. It has been f o u n d that with " t a r painting " the surface does not stand skidding on curves. The most important objection, however, is that lately b r o u g h t u p in Paris, where it was claimed that a number o f trees h a d been killed by the tar used on the r o a d s in the Bois de Boulogne, a n d that o n this account they were going t o discontinue its use. In fact,a n article appeared in the September Engineering Record, which said that it had been decided n o t t o t a r on this account during the next season the seven main suburban r o a d s leading out o f Paris. A considerable amount o f discussion has resulted from these statements, and the English Surveyor and Municipal Engineer sent out a circular letter to all the county surveyors in England who had tarred roads, asking for their experiences. In general, there was not a single instance where a n y damage t o trees o r to shrubs could be directly charged to tarring the roads. Dr. Guglieminetti, who is probably the foremost authority, ridiculed lhe whole affair. H e admitted, however, t h a t there were several delicate plants that did not seem to bloom when planted close to r o a d s used for fast motor traffic, that had been tarred. H e advised that hardier flowers be used, and this has been done. The question was b r o u g h t u p at the International Road Congress, and the authorities in charge of the Bois de Boulogne denied that any trees had been direetlv injured by the tar, but

DEVELOPMENT OF ~[ODERN ROAD SURFACES.

273

they did have trouble with some flowers. Moreover, the Cong r e s s went on record as f a v o r i n g the use oi tar. It should also be remembered in this connection that tax has been used for years in treating parasitic diseases of plants and trees, without any evil effects resulting from its use. A g a i n , we know that c r u d e water-gas tar is very successful, according to Mr. Waring, of Omaha, in preventing the g r o w t h of g r a s s and weeds in r o a d s w h e r e it has been applied. I feel,-, that with both c r u d e coal and w a t e r - g a s tar t h e r e may be some danger if they are used in excess by the first two methods but I do not believe that there is anything to be f e a r e d from the use of the heavier grades of refined tars used in the t h i r d method, as no damage by this m e t h o d has been repo.rted publicly, nor has considerable inquiry revealed any existing. The use of tar as a surface treatment is by far the most effective m e t h o d for controlling the dust and preserving the road surface from motors, particularly when a h e a v y refined tar is used and a sufficiency of screening is rolled in, thus obviating the objections which have been raised to the first two methods mentioned. It seems to give good results with v a r y i n g road surfaces, but succeeds best with M a c a d a m in good original condition. However, any surface treatment must be looked upon as m e r e l y a palliative, and it is not a preventative in the true sense of the w o r d , so that some more permanent treatment or m e t h o d of construction is required. INCORPORATING TARS IN THE MATERIAL OF THE ROAD. The f a i l u r e of the s u r f a c e treatment to stand the strain of h e a v y m o t o r traffic, especially on curves, and the desire for a more permanent road construction, led to the revival of the use of the so-called tar M a c a d a m , w h i c h is a M a c a d a m construction with the upper two to four inches of the stone embedded in a m a t r i x of tar r a t h e r than the usual one of cementing rock powder. This is laid by coating the stone with tar b e f o r e spreading and rolling. It was apparently used at Nottingham, E n g . , a b o u t 184o, and at Sheffield in 1845. It was introduced in P a r i s a b o u t 1854, Knoxville, Tenn., a b o u t 1866. The important use of it in street p a v i n g came a b o u t 1871. when the Snow and D a v i s patents

0-74

\\;. H.

tCt'LWWH.ER.

were g r a n t e d . T h e s e required tile use of H.,,SO4 to h a r d e n the tar used. The Filbert Vulcanite Paving also used a h a r d e n ing material. Front x87r to I878 about 75o,ooo square yards o f this form o f paving was laid in \Vashington, with the following" results : 2o p e r c e n t . f a i l e d w i t h i n .~ t o .3 y e a r s .

3o per cent. lasted 7 years. 41 per cent. lasted I5 years. 4.9 p e r c e n t . l a s t e d 20 y e a r s . 1.2 p e r c e n t . l a s t e d 3o y e a r s . G i v i n g a n a v e r a g e life o f I 2 y e a r s .

i n I,~77 machine m i x i n g was introduced with improved results, and the same year it b e g a n to be used at Stratford, Ont., ~c~ 8t Hamilton, Ont.. used it with conspicuous success I886 the influence of the asphalt conapanies caused its abandomnent in \Vashington. In I~ 87 it was used at Aim Arbor, Springfield. and Topeka. From r89o to ~894 a great deal was laid a t Barre, Vt., Pawtucket, R. l., St. Johnsbury, Vt.. and Littleton, Vt. In I898 \\:oodsville. \Tt., used it successfully. In I9Ot the \Varren Bitulithic paving was patented, and was widely used. The ~fl)ject now assumed more ilnportance f r o l n the advent o f the motor car a n d the necessity o f more durable road treatment, and various modifications of the use o f tars or oils in impregnating the ul~per wearing surfaces of roads, were evoh-ed. The California method of constructing dirt roads was used a b o u t I9O 3, and was 1)atented 1)v the Petrolithic Co. The \\:afsworth system, using rock asphalt, was 1)rought out in I9o5 . The Gladwell system was first used in t9o6, and the Imperial road was patented the salne vear. In ~9o7 crude residue molasses was used a t Newton, Mass. There have been so many variations introduced into the construction of roads, with this general principle, that we will' include all constrttctioll where the u p p e r layers of the surfacing are saturated or coated with a 1)ituminous substance, u11der this heading, and divide them into four classes: ( I ) \Vhere the material is first coated, then spread on the surface and rolled. hmluding Bitulithic, Tarlnac, Gladwell system. (25 \Vhere the materials are coated in layers in situ, so-called penetration system. (3) \Vhere the upper surface is harrowed, the oils worked ill by m i x i n g in the surface. The California system including Petrolithic and Imperial systems. (4"1 The use of rock asphalts.

•

DEVELOPMENT

OF

MODERN

RoAn

SURVACES.

0_75

In general, t a r Macadam is laid as a wearing surface on any well drained a n d compacted foundation; an old road surface may be used, but usually a Telford, o r preferably, a regular Macadam foundation is built up and the top 2 to 3 inches, o r wearing surface, is made o f the bituminous mixture. The first method by m i x i n g is the earliest, and still seems t o give the best results, but a t a considerably higher cost. The principal object is to insure that each particle of stone shall be FIr;,

20.

Mixing tar Macadam.

evenly and completely covered with the bituminous compound. This requires that the stone shall be dry and warm and well turned in contact with the t a r mixture. The earlier engineers heaped the stone on alternative layers with coke and breeze, and fired them after the manner of a lime kiln, then spread t a r over the whole mass and turned it like, concrete. This resulted in overheating some of the stone and burning the tar. Later the stone and tar were heated separately and m i x e d in hot iron plates, by h a n d , but machine m i x i n g is now VOL. CLXVIII, No. 1oo6-- 2~

276

W . H . FULWEILER.

used in all large pieces o f work with the constituents separately heated. The method in use a t Sheffield, Eng., where t a r Macadam has been in use over 4o years, is as follows: On a Macadam foundation they put a one-stone layer of 2I~ inches limestone, and a one-stone layer o f I 3~ inches slag, both tarred with a m i x t u r e o f I IO gallons o f t a r boiled 2 hours, with 125 pounds pitch, used a t the rate of 13 gallons per ton of PIG,

2 1.

Spreading and rolling tar M a c a d a m .

aggregate. A top coat 3/4 inch of a m i x t u r e of ~ inch fine stone and i~ inch slag, tarred with I7. 5 gallons o f the m i x t u r e p e r cubic yard is put on, and the whole rolled until it is 4 inches thick. A light coating o f clean ~ inch limestone chips is spread o n .the surface and rolled in. The method used successfully a t Hamilton, Ont., requires a 6-inch Telford foundation with 6-inch chamber, voids filled with smaller stones and well rolled. A layer of tarred 2 ½ inches stone is put on, and voids filled with tarred gravel: then a laver o f

"

DEVELOPMENT

OF ~IODERN

ROAD S U R F A C E S .

277

tarred 2 inches stone is rolled in. The top dressing is composed of two-thirds sharp fine gravel a n d one-third stone dust, m i x e d with 25 gallons o f t a r per cubic y a r d . This is put on about inch deep, and after t h o r o u g h rolling, is covered with fine dry stone dust and rolled again. A t Newton, Mass., during 19o8, the Office o f Public R o ad s put on a surface coating that seemedoto give very good results, and which withstood the past winter very successfullv. The FIG. 22.

i

Finished surface, Newton, Mass.

old surface was picked up with a road roller and b r o u g h t up to crown with No. 2 stone, a n d carefully rolled. A one-stone layer of No. 1 stone was then spread on the surface and rolled carefully with a 2o-ton roller. A b o u t 2 ~ inches of a tarred aggregate composed o f 960 pounds of I ~ t o ~ inch stone, 35 ° po'unds of ~ inch dust stone, and 6 gallons of the bituminous binder; on one portion o f this work. a water-gas tar compound made by my company, was used. This aggregate was m i x e d hot like concrete, and after spreading was lightly rolled once. A f t e r 5

278

\V. H. I:tTLXVEH.ER.

t o 6 hours it was given two trips of tile roller, and the next clay enough crushed grit o r tarred sand was put on to fill the surface voids, and the whole surface thoroughly rolled with a 2o-ton roller. The road has the appearance o f sheet asphalt, especially on the section where tarred sand was used as a top dressing: but it gives a better footing and does not cause skidding in wet weather. In 19Ol F. Warren patented a combination of graded broken stone and dust o f different sizes, m i x e d with a bituminous cement, so that the stone m i x t u r e should have a very low percentage of voids. His original patent used six sizes o f stone in varying proportions. 7° 20 4 3 3

per c e n t . per c e n t . per cent. per c e n t . per cent. per cent.

of of of of of of

s t o n e passing 3 i n c h e s s t o n e passing 2 inch s t o n e passing ~,; inch s t o n e passing ~1,~ inch d u s t passing inch. d u s t passing 2 616 i n c h .

and and and and

on on on on

_~ i n c h . 110 i n c h • ~¢, i n c h . ~,, i n c h .

One h u n d r e d parts of this m i x t u r e heated and m i x e d with six parts of bituminous cement. His argument was that such a m i x t u r e ~required the m i n i n m m amount of cementhlg material, which could, therefore, be made quite soft and have a longer life. H e has since reduced t h e number of sizes of stones required and made some o t h e r improvements. Owing to the care used ill selecting, mixing, and laying, and in the uniform quantity d f the bituminous cement, the work doue by the \Varren o r affiliated companies has given excellent satisfaction. The extended use of tar Macadam in England has b r o u g h t out a number of patented preparations. Tarmac was the earliest, and was invented, if it can be so called, by E. P. Hooley, Sur¢eyor o f Nottingham. It is now supplied by the T a r m a c Co., o f Ettingshall, near Birmingham. This is blast-furnace slag boiled in a tar pitch m i x t u r e and seasoned. It is prepared ready for rolling, and has been very w[delv used throughout England. The slag is carefully selected and graded so that the best results may be obtained. Tarfaat is a top dressiug made of tarred powdered slag. Tarlithic and Granite are prepared mixtures of granite tarred and ready for spreading. In this country the Sarco Road Compound (apparently a " blown oil " mixture) has been exploited for this lmrpose, and a n extended trial was made on one o f the Chicago Boulevards durino i 9o.q.

"

1)EVELOPMENT

OF ~[ODERN

ROAD

SURFACI£S.

279

Another patented componnd which gives promise of success is a prepared top dressing known as " Amiesite." This consists of crushed stone coated cold a t the quarry with a hot m i x t u r e o f 6o per cent. solid asphalt and 4 ° per cent. of a heavy asphalt oil. The m i x i n g is done in a concrete m i x e r and after the stones are coated about half a bnshel of slacked lime is a d d e d to each cubic yard. Wheli this is worked in half a-peck of damw,ned sand is added. The addition of the dampened sand prevents the particles of~tone from adhering a n d enables it to be handled very easih,. F r o . 23.

Bitulithic pavement, Wilmington, Del.

The prepared m i x t u r e is spread on the clean Macadam foundation about 4 inches in d e p t h and after a t h o r o u g h rolling is ready for travel. Several, experimental pieces o f this road have been laid near Camden, N. J. In general, it seems to cost from 25 to 33 per cent. more t o lay t a r Macadam by the m i x i n g method than ordinary Macadam. but it should have fronl two to five times as long a life. A variation of this general method is the Gladwell system, b r o u g h t out by Mr. A. Gladwell, Eaton, Eng. It was first used during 19o6 at Stoke Poges. The old surface is carefully swept clean, and a ~ - i n c h layer of ~ - i n c h tarred granite chips are carefully and evenly spread

280

\V. H. F~_'LWEILER.

on. It is then covered with a two-stone layer of 2 ~ - i n c h dry crushed stone, free from dust and chips. A light s t e a m roller is now very slowly run over the surface t o press the stones down into the tarred m a t r i x and to draw the latter up to surface. FIG.

24.

L a y i n g A m i e s i t e , C a m d e n Co., N . J .

W h e n the binder is seen working up to the surface a light layer of t h e tarred chips is spread over the top and b r u s h e d into the voids, the rolling is continued until t h e finished thickness is 23~ t o 3 inches thick, and the surface is compact. A b o u t one-sixth o f a gallon o f hot tar compound is sprayed o r brushed over the

DEVELOPMENT

OF MODERN ROAD SURFACES.

28I

surface, and covered with ~ of an inch of clean dry granite or trap screenings, f o l l o w e d by a roller. It is estimated that this method w o u l d cost 20 per cent. more than the o r d i n a r y M a c a d a m in the U n i t e d S t a t e s . In an e n d e a v o r to find a c h e a p e r m e t h o d of b u i l d i n g a s u r f a c e resembling that m a d e by the m i x i n g process, the so-called penetration process was used. This consists of saturating the diff e r e n t layers of stone composing the~wearing s u r f a c e a f t e r they FIG. 2 5'

Amiesite, Magnolia, N. J.

have been p l a c e d on the r o a d , by s p r a y i n g or sprinkling the b i n d e r on them. This m e t h o d was used as e a r l y as I 8 5 6 - 6 o at W e s t o n s u p e r - M 6 r e in E n g l a n d , but it did not attain much importance u n t i l it was b r o u g h t out by Mr. T h o s . A i t k e n in connection with his pneumatic s p r a y i n g machine, for w h i c h p u r p o s e it is said to be eminently a d a p t e d . The g e n e r a l m e t h o d is to b u i l d up the road in the u s u a l manher, e x c e p t that no w a t e r is used in r o l l i n g ; then just b e f o r e the

282

\V. I~I. FULWEILER.

binder course o f fine gravel or screenings is applied, the surface is sprayed with the hot t a r compound from a machine. The pressure used secures a penetration of from 2 to 3 inches. The layer o f gravel is now rolled in, and the surface pores are filled with another light coat o f tar, followed by dry screenings and rolling. The m a x i m u m binding value from the smallest quantity o f tar is obtained at a minimum labor cost. The quantity of t a r used per square yard o f course varies according to the stone used and the traffic expected, but is usually at the rate of from F I G . 26.

Tar Macadam by penetration, Wilmington, Del.

•7 to I.o gallons per square y a r d . In England it costs from 2 to 4 cents per square yard for this method over the ordinary Macadam, while here it would probably run from 6 to 8 cents. A nnmber of experimental pieces of road have been laid by the penetration method a r o u n d Boston. At Newton, Mass., they pick up the surface to a depth o f from 2 to 3 inches, harrow ii, dress up to crown with No. t and No. 2 stone, and roll. SprinkIe I to 1.3 gallons of hot tar compound, and tilen spread o11 a light coat of screening and roll. The Metropolitan Park Commission

])EVELOPMENT

OF ~IODERN

ROAD SURFACES.

283

built a stretch o f road especially for motor traffic, as follows: 011 a regular Macadam foundation, 4 inches o f No. I stone, with a little fine gravel as a binder, is rolled in. F o u r inches of gravel is then s p r e a d oll and I.3 gallons of asphaltunl base oil is sprinkled on it; a light coat of gravel is put on to absorb t h e surplus oil, and the whole is thoroughly rolled. Mr. Blanchard, of Rhode Island, made some experiments with this method, but he (lid not have the p r o p e r facilities for sprea(hng the tar, so that his results w~re not satisfactory owing to the necessity o f u s i n g too much tar. Fro. 27.

Liquid asphalt. Blackwood, N. J.

Considerable work has been done in New Jersey with a socalled " Liquid Asphalt," a heavy asphaltic base oil containing 82 per cent. of asphalt oils. The oil was applied to the compacted I ~ - i n c h course before the binder was applied. The ~ - i n e h binder and screening were then put on and rolled in. This road gave great promise up to the early part of this spring when with the coming o f the warm weather the surface ravelled considerably and they are now applying a t o p d r e s s i n g o f gravel.

284

W . H . FULWEILER. INCORPORATING

OILS I N T O T I l E ROAD S U R F A C E .

The peculiar climatic and soil conditions o f California have developed methods for the construction o f both earth a n d stone r o a d s that are, in general, somewhat" similar to a tarred Macadam, in t h a t they s u r r o u n d t h e particles with a binder. W h e n oil was FIG. 28.

Petrolithic rolling tamper.

first used, they f o u n d that the surface application did not secure sufficient penetration for the best results, so o t h e r methods o f incorporating the oil were devised. In Yolo County the road surface is cut out to-the desired cross section with an 8-inch crown, and a hard even base is secured free from weak spots,

DEVELOPMENT

OF

MODERN

ROAD S U R F A C E S .

285

A b o u t I gallon of oil per square yard is now put on, a n d the earth that was cut out is returned to a d e p t h of 4 to 5 inches. This is then rolled and travel is permitted. As t h e oil works t o the top, a grader a n d drag are run over the surface, and more soil is b r o u g h t on. This is repeated until the oil fails to work out, and results in a very c h e a p construction, costing only $I5 ° per mile. ,0 PIG. 29.

Tamping--Imperial

construction.

The Petrolithic system o f building r o a d s was started a b o u t 19o 3, a n d was a development o f the earlier systems. In Santa Monica, Cal., the system is as follows: A f t e r grading, t h e surface is plowed 4 inches deep with a turning plow, clods are pulverized and the surface is cultivated a n d harrowed until it is o f a uniform consistency. A b o u t I gallon per square yard o f h o t asphalt base oil o f I2 t o 15 ° B., and containing not less than 7o per cent. of D grade asphalt, is put on. If the soil is light o r sandy, .15 gallon more is put on. This is thoroughly cultivated and harrowed in, and a n o t h e r coat a t the same rate is pnt on.

286

\V. H. FULWEILER.

The s u r f a c e is then t u r n e d u n d e r with a 4-inch plow and thoro u g h l y h a r r o w e d a l o n g the length and diagonally. It is then cultivated to an even g r a d e and sprinkled. A r o l l i n g t a m p e r is then a p p l i e d ; this w e i g h s a b o u t I 5oo p o u n d s , and has iron pins set in its s u r f a c e a b o u t 7 inches long with h e a d s a b o u t 2 x 3 inches. T h e r e are fifteen pins a r r a n g e d in 12 r i n g s , or 18o in all. This is r u n over the road u n t i l it is thoroughly compacted to w i t h i n an inch of the s u r f a c e . A b o u t I ~ to 2 inches of FIG.

,30.

I m p e r i a l - - p u t t i n g o n s t o n e s u r f a c e , Westville, N. J .

g r a v e l is s p r e a d on the road and m i x e d carefully with the s u r f a c e soil, and from I tO 1. 5 g a l l o n s of hot oil are sprinkled on. The s u r f a c e is a g a i n h a r r o w e d and then t a m p e d u n t i l it is solid. A very l i g h t l a y e r of fine g r a v e l is put on, and the s u r f a c e is smoothed with an o r d i n a r y s t e a m roller. A very s i m i l a r type of road is b e i n g exploited u n d e r the name of Imperial P a v i n g ; this is laid u n d e r the patent No. 833,551, g r a n t e d in i9o6,and in g e n e r a l thev plow up the o r i g i n a l

DEVELOPMENT

OF ~ ' I O D E R N ROAD S U R F A C E S .

287

surface, stones or dirt, harrow it, apply the binder, a n asphalt o i l u n d e r 4o pounds pressure, harrow again and compact with a rolllng tamper, which consists of a number o~ toothed disks in a shaft, the t e e t h being a b o u t 4 inches deep. The roller weighs 3 tons. This tamping is continued until the whole surface is hard. Gravel or stone chips are put on, and the surface smoothed with a ten-ton s t e a m roller. Some of.,'these r o a d s in Kansas FiG. 3 1.

White road-oiling machine.

City, Mo., have been very satisfactory, but generally this type o f construction has not been very successful u n d e r our Eastern climatic conditions. Several useful f o r m s o f machinery have been developed m connection with the use o f oil in road building that might serve a u s e f u l purpose with tar. The White oiling machine has alreadv been mentioned. This has a large number o f openings t h a t are controlled by levers in sections I8 inches long, so that I8 inches o r any nmltiple o f this width can be treated or cut off b v the operator. The D e C a m p machine is adapted for oiling

288

W . H . FULWEILER.

dusty roads. It has three sets o f plungers similar to a corn planter. It opens a furrow, puts the oil a t its base, covers it t~p and then stirs it. The White Sanding machine distributes an'even layer o f sand in a road surface. It uses an apron feed geared with the wheels, the depth of sand o n which can be acct~ately regulated. Related to this construction is the use o f oil in consolidating sand roads. This was successfully tried i n Massachusetts in 19o5-6. The surface was dressed up a n d .75 gallon per square yard was put on a t 18o° F. and allowed two weeks t o be absorbed ; •75 gallon more were put on and t h e surface was harrowed, rolled, and sprinkled lightly with sand. The next year .76 gallon per square yard was put on, and a b o u t .0024 ton per square yard o f stone screening was rolled in. The surface is said to b e very good, a n d the cost was 27.76 cents per square y a r d . During I9o8 the Office of Public Roads made a n experiment on a Gumbo clay road a t Independence, Kan., u s i n g a n artificial asphalt. It was f o u n d difficult, however, t o make the soil absorb the asphalt satisfactorily, but this might have been avoided possibly to some extent by cutting back t h e preparation with a crude oil to reduce its viscosity. In general, I do not believe from the results so far obtained, t h a t the methods u s i n g the asphaltic base oils will ever achieve complete success in this latitude, owing to the fact t h a t the binder in.the surface course seems to lose its life after a winter's exposure t o the alternate hail, snow, heat, and cold o f the climate in this latitude. A method accomplishing much the same results as, t a r Macadam, is the use of natural asphalt rock from Kentucky, and applied u n d e r the trade name o f W a d s w o r t h Macadam. This was first used commercially in Kentucky in 19o5. The specifications recommended by the distributors o f the asphalt rock are as follows: " Shape and roll t h e dirt bed thoroughly as if a regular Macadam or asphalt pavement were t o be constructed. Next, place and roll a 6-inch layer o f good crushed stone, a b o u t 2 ~ - i n c h size. T h e n spread a 2-inch layer o f 2-inch stone, and on this second layer o f stone, before same is rolled, spread an inch of Kentucky rock asphalt, and after again thoroughly rolling, the road is ready for traffic." The Office o f Public Roads in i9o 7 made an experiment with

DEVELOPMENT OF ~IODERN I~.OAD SURFACES.

289

t h i s m a t e r i a l at Bowling Green, Ky. The road had an 8-inch gravel surface over a T e l f o r d foundation ; t.his s u r f a c e was spiked up to a depth of 4 inches, and b r o u g h t to a camber of ~ inch to the foot by removing the excess gravel. This s u b g r a d e was c a r e fully rolled. Four inches of I ~ - and 1-inch stone was spread evenly over the surface, and rolled once t o turn down the s h a r p edges and leave an even surface. OIle and one-half inch of the asphalt rock was then spread on, b r e a k i n g up the lumps and filling a14 the voids as mttch as possible. The r o l l e r was then kept m o v i n g parallel to the axis of the roadway, r u n n i n g off occasionally t o dust the roller t o keep it from sticking. A f t e r about the fifth rolling the surface begma t o compact as the rock came t o a firm bearing. It was f o u n d that the rock c o u l d not be w o r k e d b e l o w 7 ° to 75 ° F., and w o r k e d better as the temperature increased. The road rutted quite b a d l y when traffic was first allowed on it, but by the end of a week these all disappeared and the surface had become smooth and compact. The surface was elastic, yet self-healing from any, ruts or dents. While it is admitted that with a proper tar Macadmn construction we secure a w e a r i n g surface that is dustless, resilient, p r o o f a g a i n s t m o t o r traffic, easy t o clean, t h o u g h expensive, yet t h e r e are several objections that must be considered. The most important one is that of grade. In general, it has not been f o u n d wise to use it on grades g r e a t e r than 3 to 4 i n a hundred, o w i n g to the fact that h o r s e s seem to have trouble with footing. "]'his is especially apparent d u r i n g frosty weather in the e a r l y morning. On c u r v e s in wet weather it has been found to increase the tendency to side-slip with motors. It seems that these effects are caused by an excess of tar on the surface when an insufficient quantity of dry screenings were applied, or they were not rolled in properly and were then picked out by the traffic. T h e most important points in f a v o r of this type of construc.lion are the facts that it is absolutely waterproof, and is, theref o r e , free from frost action, and that all the stone particles are held rigidly in position so that there can be no internal attrition. SELECTION" OF MATERIALS.

In considering the selection of materials for use in m a k i n g tar M a c a d a m , t h e i r availability is. of course, the primal consid-

290

\¥. H. FULWEILER.

eration, but w h e r e several g r a d e s of stone are near at h a n d , it has been f o u n d that a r o u g h , r e g u l a r f r a c t u r e s e e m s to give the best results. The h a r d e r the stone the better, a l t h o u g h b l a s t f u r n a c e slag has g i v e n good results when properly chosen. A s to size, this is d e p e n d e n t s o m e w h a t upon the thickuess of c o a t i n g that it is d e s i r e d to lay, and the l a r g e s t size in the m i x t u r e s h o u l d apparently be a b o u t r~ inch less than the finished thickness o f the layer. In general, we d e s i r e to lay a d e n s e m i x t u r e , and this involves either g r a d i n g the stones b e f o r e 1nixing, or by s p r e a d i n g layers of the different s i z e s and then m a k i n g a h o m o g e n e o u s m i x t u r e by rolling the stones together on the surface. T h e r e are two g e n e r a l m e t h o d s in use for m a k i n g d e n s e stone a g g r e g a t e s for c e m e n t concrete w o r k w h e r e a m i n i m u m perc e n t a g e of v o i d s is of even more importance than in o u r w o r k . The one consists in u s i n g the m a x i m n m quantity of the l a r g e s t size stone, and then filling the v o i d s by the use of a l a r g e quantity o f very fine mortar, any particle of w h i c h will e n t e r the v o i d s in the l a r g e stone. The o t h e r m e t h o d b r o u g h t out b y Mr. W. D. F u l l e r , ~rop0rtions the stone by tlie parabolic f o r n m l a w h e r e d=

P2D 10000

d = a n y g i v e n diam. P = p e r c e n t a g e of m i x t u r e smaller t h a n this diam. D=largest diam. of s t o n e used.

Two c u r v e s are g i v e n for 2-inch and I ~ - i n c h stone, the sizes u s u a l l y used for tar M a c a d a m . Mr. F u l l e r combines his stone m i x t u r e s a f t e r mechanical analyses, so that they most n e a r l y approach this curve. F o r instance, with I ~ - i n c h stone as the l a r g e s t size, he requires t h a t - 02 82 7° 57 4~ 25

per per per per per per

cent. cent. cent. cent. cent. cent.

shall shall shall shall shall shall

pass t h r o u g h pass t h r o u g h pass t h r o u g h pass t h r o u g h pass t h r o u g h pass t h r o u g h

~ inch sieve. ~ inch sieve. ~ inch sieve. ~- inch s i e v e . { inch sieve. x~a inch sieve.

This m i g h t be approximated tl~en by "

3o p e r cent. x½ i n c h e s to } inch. 28 per cent. {- inch t o ¼inch. 42 per cent. ] inch to d u s t .

H o w e v e r , in this w o r k we g e n e r a l l y r e q u i r e a g r e a t e r proportion of the l a r g e stone. C o n s i d e r i n g the quantity of v o i d s in

DEVELOPMENT

OF

MODERN" ROAD S U R F A C E S .

29I

~ e different size s t o n e that w e might use, it w i l l be found that will vary with different classes of rock, depending on its ~ v a g e and fracture, hardness, kind and adjustment of crusher. The following figures * may be of service: HARD TRAp, ROTARY CRUSHBR. Per cent. of voids loose, per cent. of voids, compremed. ~ t inches to x i n c h . 54-5 " 43.7 linch t o It i n c h . 54.5 42.8 ~ t ~ du~t. 45.0 3o.6 b

of stone,

I w ¢d, t o ~ . s i n c h e ~t o | i n c h . | inch t o | i n c h .

SOFT TRAP, JAW CRUSHBR. Per cent. ofvoids, looJe. Percent.of voids, compreemd~/. SZ.O 40.6

5z.o

35.9

GRAVBL.

,t

8i,m o f ~ o n e .

inch.

Per c~m¢. of voids, loose

36.5 34.o

Per cent. of vdds,compre~ed

28.= 27.0

AssUmi."ng n o w a percentage of v o i d s in the compressed s t o n e 43 per cent. and in sand of 27 per cent., the following would give a d e n s e m i x t u r e : Pounds. xooo

z89 •2

Mat,~dal.

z~ i n c h e s stone. inch one. Sand. B i t u m i n o u s cement.

Volumetric pe~entap. 60. o 5.7 z I. 3 3. o

W h i l e this m i x t u r e w o u l d h a v e , theoretically, a low perof v o i d s , yet a s the s u r f a c e of the particles w h i c h must be c o v e r e d by the b i t u m i n o u s b i n d e r r i s e s very r a p i d l y as the size o~ the particles decreases, considerably more b i t u m i n o u s b i n d e r is r e q u i r e d . It is f o u n d that a b o u t I o per c e n t . by v o l u m e of the stone m i x t u r e s h o u l d be cement. This w o u l d give then Pounds. xooo 4oo xoo 74

Material. z½i n c h e s stone. ~ inch d u s t . Sand. B i t u m i n o u s cement,

Volumetric perce~tare. 6o. o 24. o 6: o zo. o

If it is d e s i r e d t o use only two s i z e s of stone, the following m i x t u r e m i g h t be used : Pounds. xooo 370 6o

Material. z½ i n c h e s stone. | inch d u s t . Compound.

* Quoted i n T a y l o r and T h o m p s o n , s VOL. CXLVIII, N o . xoo6--~2

"Concrete,

Volumetric percentage. 66.5 24.5 9. o P l a i n and Reinforce&"

292

W . H . FULWEILER.

A s i m i l a r m i x t u r e was used in some G o v e r n m e n t e x p e r i m e n t s at N e w t o n , M a s s . , very successfully. In some sections t a ~ sand was rolled i n t o the s u r f a c e , w h i c h g a v e a very s m o o t h finish i The q u e s t i o n of the selection of" a p r o p e r b i n d e r for this w o r k and the specifications for different qualities, has b e e n , t h e s u b j e c t of considerable scientific and practical i n q u i r y and e x p e r i m e r ~ d u r i n g the past t h r e e y e a r s . A t the present time t h e r e are t w o committees from scientific' societies, viz. : The A m e r i c a n Society o f C i v i l Engineers~ o f w h i c h committee Mr. W . W . C r o s b y , C h i e f E n g i n e e r of the M a r y l a n d Geological S u r v e y , is chairman, and P r o f . M. : H . B l a n c h a r d , A s s i s t a n t E n g i n e e r of the S t a t e B o a r d of P u b l i c R o a d s of R h o d e I s l a n d , is secretary, and The A m e r i c a n S o c i e t y for T e s t i n g Materials, w h o s e Committee on S t a n d a r d T e s t s f o r R o a d M a t e r i a l is h e a d e d by Mr. L o g a n W . P a g e , D i r e c t o r o f the Office of P u b l i c R o a d s , as chairman, and Mr. P r e v o s t H u b b a r d , A s s i s t a n t C h e m i s t of the Office of P u b l i c R o a d s , is secret a r y . In view of the fact that both of t h e s e committees w i l l p r e s e n t reports d u r i n g the c o m i n g s u m m e r , - o n l y a g e n e r a l s u r v e y of this ~uestion will be given. The m a t e r i a l s in g e n e r a l use a t the p r e s e n t time consist wholly, o r as m i x t u r e s , o f coal tar, w a t e r g a s tar, coke oven 'tar, asphaltic base o i l s , both c r u d e and r e s i d u e b l o w n o i l s , sulphate pitch and a n u m b e r of n a t u r a l b i t u m e n s , such as Gilsinite, etc. It is not difficult t o see that with such a collection o f materials b i d d i n g for p u b l i c favor, that a p r o p e r choice w o u l d be a d i ~ c u l t one. In g e n e r a l , the asphaltic oils and r e s i d u e s have g i v e n very: much b e t t e r results in w a r m , dry climates, such a s C a l i f o r n i a and the S o u t h , than in o u r d a m p e r and c o l d e r n o r t h e r n climate. H ~ r e the v a r i o u s tar preparations have been more successful. C r u d e coal tar was used in the earlier experiments, but it was~ soon f o u n d t o y i e l d b e t t e r results w h e n partially refined, especially when the ammoniacal l i q u o r and some of the l i g h t oils were removed. W a t e r g a s tar was f i r s t used in I 9 o 4 - 5 at O m a h a , N e b . , a n d at T u n b r i d g e W e l l s in Eng,l a n d , as a dust-Iaying treatment; k n o w n now as " t a r painting." I t p r o v e d very successful, as it had the f o U o w i n g a d v a n t a g e s over the coal tar f o r m e r l y employed, ( I ) It was cheaper. (2) B e i n g more f l u i d , it c o u l d be applied c o l d . ( 3 ) It penetrated the s u r f a c e more readily.

DEVELOPMENT OF MODERN ROAD SURFACES.

293

(4) It resisted wet weather better, and seemed to churn less in winter. (5) It contains very much less free carbon than coal !mr, which probably accounts for advantage 4. The success attending its use as a dust layer led to trials of its use as a surface treatment w i t h screenings, but the crude w a t e r gas tar did not contain sufficient binder, and they were not successful. During the past two years, however, a refined grade of tar has been prepared which u ~ t e s all the advantages of penetrat~0n and resistance to moisture and churning with the toughness and strength of the other preparations. The exceedi n g l y low percentage of free carbon in the w a t e r gas tar preparation is undoubtedly the cause of its superior behavior. The question of the percentage of free carbon is already recognized as important, and nearly all specifications restrict it. A t the coming meet of the American Society for Testing Materials, Mr. Prevost Hubbard will read a paper on its influence on bituminous materials for road work. In general, it acts as diluent while giving the material a false vicosity. So that in one pound of material there would be from i8 to 25 per cent. more active binder (material insoluble in CS~) in a water gas tar pitch than a coal tar preparation. Furthermore, the free carbon seems to exercise a hydroscopic property, tending to absorb moisture, which has a deteriorating effect on the coating and is undoubtedly responsible for the churning that sometimes occurs in winter. The question of specifications has been gone into very thoroughly by Mr. Prevost Hubbard, of the Office of Public Roads, in Bulletin No. 34, entitled " Dust Preventatives," some brief abstracts for different materials being given at the end of the paper. In general, I believe that we require a compound that, while developing the greatest binding property, will not become too fluid at high temperatures, that it will run under a summer sun, and yet will be elastic enough not to become brittle and crack at the winter temperatures: To this must be added a further proviso, that it shall not contain such a percentage of volatile oils that their loss under the exposure to the elements during its use in the road will impair either its strength or elasticity. T}~is could be secured by specifications which would require at certain temperatures dependent upon the climate of the locality, certain

294

W . H . FULWEILER.

b i n d i n g strengths and viscosities, together with a m a x i m u m a l l o w a b l e loss in the vaporization test, w h i c h consists in h e a t i n g a s t a n d a r d w e i g h t o f the m a t e r i a l a t some fixed temperature~ for a definite time w h i l e e x p o s i n g a' fixed s u r f a c e . The q u e s t i o n of the perfecting o f a m a c h i n e that will give a c c u r a t e f i g u r e s for the b r e a k i n g s t r e n g t h is, of course, the imp o r t a n t one, and is now occupying the attention of the m e m b e r s of the two Committees mentioned above. I t m a y be necessary t o briquette the m a t e r i a l with a s t a n d a r d s a n d , but in any event, the b r e a k i n g load will u n d o u b t e d l y have t o be applied as a s u d d e n shock, and the b r e a k i n g strength r e c o r d e d on some form of s p r i n g balance. CONCRETE SURFACING.

T h e r e are s e v e r a l m e t h o d s o f road construction that have lately b e e n b r o u g h t i n t o notice in an e n d e a v o r to find a s u r f a c e that s h o u l d be d u s t l e s s and w i t h s t a n d h e a v y m o t o r traffic, and a l t h o u g h t h e y , a r e not in any w a y related t o the subject, we feel that they s h o u l d a t l e a s t be briefly mentioned. They a r e the use of c e m e n t s u r f a c i n g and s m a l l g r a n i t e or composition setts, Concrete road s u r f a c i n g was p r o b a b l y i n t r o d u c e d by J. Mitchell a t Inverness, E n g . , a b o u t I 8 6 5 , w h e n he patented a c e m e n t concrete for this p u r p o s e c o m p o s e d of: Broken stone, 4 parts. Sharp sand, I ¼ to II~ parts. Portland cement, I part.

The s u r f a c e was t o be laid in two layers 7 t o 8 in~.hes deep in all. In g e n e r a l , the c h i e f objection to concrete s u r f a c e s for road p u r p o s e s is the fact that they c r a c k b a d l y from temperature c h a n g e s , and a f f o r d but l i t t l e foothold for h o r s e s . In the form of p a v i n g w h i c h was introduced in Bellefontaine, O., in I 8 9 6 , and is now exploited as the H a s s a m pavement, covered by U. S. P a t e n t No. 819,652, they e n d e a v o r t o p r e v e n t c r a c k i n g with a m e t a l reinforcement. T h e r e has lately been introduced an acid wash for concrete s u r f a c e s that attacks the s u r f a c e coating of c e m e n t and e x p o s e s the a g g r e g a t e , thus g i v i n g a better footing, so that t h e s e two objections m a y in time be overcome. C e m e n t s u r f a c i n g has been t r i e d at T o u l o u s e and Grenoble, F r a n c e , but w i t h o u t notable success. A g r e a t deal of it was put in at P a n a m a , w h e r e it i s said t o be q u i t e successful, b u t its h i g h cost,

DEVELOPMENT OF MODERN ROAD SURFACES.

295

$2.oo per square yard, precludes its use for anything but city ~reets. At Newton, Mass., they tried a surface grouting of concrete on a Macadam surface, but it scaled badly and eventually had to be abandoned. At the Brookfields Track, a motordrome in England, the concrete surface that was first used failed so badly under the action of heavy racing cars at a speed of fram 8o to ioo miles per hour, that it had to be nearly all replaced. The surface seemed to lose a thin st~rface skin; and then the concrete failed, like.Macadam, ruts forming to a ~depth of several inches: • On the Motor Parkway, in Long Island, where the Vanderbilt Cup Races are held, the Hassam paving was used, but so far it seems to have withstood the effects of both winter weather and the high speed. However, much of this parkway is on tangents and fairly flat, while at the Brookfields Track it is nearly all on a curve and steeply banked. Again, the speed at Brookfields was considerably higher and the machines were heavier. SETS.

There are three forms of block, or set, paving that have 'considerable promise. Nonskidamacrete is a compound block formed under pressure with a cement concrete base and a tar Macadam top. They are laid on a concrete or Macadam sub-base, and are held in place with a tar grouting. They have not been in use long enough to gain an insight into their durability, but they are said to be cheap, noiseless and all that their name implies. Dorrite is anotherblockpaving made by compressing a tarred gravel with 2o per cent. of tar into 4-inch blocks, with a pressure of 2 ~ tons per square inch. This is a German invention, is laid as the Nonskidamacrete, and is also an experiment. Kleinpflaster is a random block made by a patented machine from granite. It was first introduced at Stade, near Hanover, Germany, in 1885. The blocks are laid on a ~ - i n c h bed of sand over either a concrete or Macadam foundation. The blocks are usually 2 ~ - or 3x~-inch cubes, and are laid as closely as possible, then weU tamped and any joints brushed with sand. They:afford a good foothold, and seem to last 2o years under h e a v y traffic. They cost in Germany $I.5O per square yard in place. A later modification of this is the Durax, the distinctive

296

W . H . FULWEILgR.

f e a t u r e b e i n g that the blocks are laid in s e g m e n t s of a circle with c h o r d s of 5 t o 6 feet, at r i g h t a n g l e s , t o the c e n t r e line o f the street. This is said t o make the p g v i n g q u i t e noiseless. The olocks are now g r o u t e d with an elastic tar preparation, and cost a b o u t $ I . 5 o a s q u a r e yard in E n g l a n d . C a p t a i n B i n g h a m , of the R o y a l C o m m i s s i o n on M o t o r T r a i tic, in E n g l a n d , d e c l a r e d that this was the best and most economical m e t h o d of obtaining a s t r o n g , noiseless, non-skiddirtg and d u s t l e s s road s u r f a c i n g for all k i n d s of tl:affic. This m e t h o d does not seem t o have been used as yet in this country. GENERAL REVIEW.

In considering the s u b j e c t o f road treatment generally, and the application o f tars o r oils in particular, t h e r e a r e f o u r g e n e r a l factors that m u s t be t a k e n i n t o consideration: I. 2. 3. 4.

The TJae The The

climatic conditions. road surface, i.¢., material and condition. traffic which the road has to bear. money available.

The m e t h o d s , as m e n t i o n e d before, w h i c h were orig!nated in a hot, dry climate, c a n n o t be expected to yield the same excellent results in c o l d , d a m p o n e s . A g a i n , some considerations such as foot-hold and spalling from f r o s t need n e v e r be considered in u n i f o r m l y w a r m parts of the country. The asphaltic oils have g e n e r a l l y f a i l e d in this latitude, but have been s u c c e s s f u l elsew h e r e , w h i l e w a t e r and coal g a s tar p i t c h has g i v e n satisfactory results. I n considering the q u e s t i o n of the influence of the p r e s e n t road s u r f a c e in general, a s p h a l t oils have g i v e n b e t t e r results on g r a v e l , and tars on M a c a d a m . It w o u l d obviously not pay to tear up a good M a c a d a m s u r f a c e and lay tar M a c a d a m , but it s h o u l d be tar painted or t a r r e d with screening u n t i l r e a d y for r e s u r f a c i n g , and then r e b u i l t as a tar M a c a d a m r o a d . The same w o u l d a p p l y t o g r a v e l . If, h o w e v e r , the road was b a d l y ravelled but not too d e e p l y w o r n , it m i g h t be r e s u r f a c e d by the penetration m e t h o d with good results. W i t h sand or clay r o a d s some modification, w h i c h w o u l d result in a t h o r o u g h a d m i x t u r e o f the b i n d e r with the soil, f o l l o w e d by t h o r o u g h compacting, s e e m s to be the most advisable. W h i l e a s p h a l t oils have hitherto been used a l m o s t exclusively, yet I

DEVELOPMENT OF M O D E R N ROAD SURFACES.

297

believe in this latitude a proper tar c o m p o u n d w o u l d give m u c h successful results. W e feel that a more i n t e l ~ i ~ u i r y into the possible traffic that a~tr~w~e a m y be expected to bear w o u l d frequently prevent failure from the use of unsuitable materials and methods. Frequently the traffic of a road is considered and reported as very rsght pleasure traffic, w h e n a carefu! ~Ijrvey will reveal quite the opposite. A traffic c e n s u s m a d e on J u n e 20, I 9 o 8 , on a s t r e e t in M o n t clair, N. J . , gave 6.5 tons per foot w i d t h per h o u r , w h i l e a busy s t r e e t in N e w a r k , N. J., gave only 4.o t o n s . The Montclair street was p a v e d w i t h M a c a d a m , and was not d e s i g n e d for h e a v y traffic, w h i l e the N e w a r k s t r e e t was p a v e d with B e l g i a n blocks set on concrete, p r o b a b l y the s t r o n g e s t p a v i n g possible. T h e g r e a t n u m b e r of m o t o r cars that are y e a r l y increasing m u s t be considered w h e n e v e r any new construction is contemp l a t e d , as the e n t i r e t r a v e l is u s u a l l y diverted t o each new road even at a sacrifice of several m i l e s in distance. A g a i n , it w o u l d d o u b t l e s s pay t o c o n s i d e r the possibility of p a v i n g certain points, w h e r e t r a v e l is concentrated or u n u s u a l l y s e v e r e conditions are t o be expected such as the-approaches and c r o s s i n g s of main r o a d s , s h a r p c u r v e s and the approaches t o s h a r p g r a d e s , with a more p e r m a n e n t form of p a v i n g and use a c h e a p e r form on the tangents and l e s s e r traveled portions. H o w e v e r , the determining f a c t o r is usually, how much will it cost, and not how long will it last ? In the m a j o r i t y of o u r r u r a l communities t h e r e is a l a r g e m i l e a g e of road that is a l w a y s j u s t a b o u t to b e c o m e impassable--something m u s t be done to keep them open t o travel, so that a little is s p e n t here and t h e r e and no p e r m a n e n t g o o d is s e c u r e d . I n some few instances in the o l d e r settled sections w h e r e the road s y s t e m has been more completely developed, the m a i n p r o b l e m is one of maintenance, and it is here that we find a more intelligent view prevailing of the w i s d o m o f d o i n g each piece of w o r k thoroughly. Of course, the A m e r i c a n practice of "working o u t " the road tax is resrJonsible for the lack o f m o n e y with w h i c h t o make p e r m a n e n t improvem e n t s in the r o a d s , but the feeling is g a i n i n g g r o u n d that in, many c a s e s it will w e l l r e p a y a b o r o u g h t o issue b o n d s for this purpose, p u t t i n g in some p e r m a n e n t form of construction that will give the benefit of good r o a d s , w h i l e the m o n e y that was more

298

W . H . FULWSIL~-a.

f o r m e r l y s p e n t in maintenance will more than pay the s i n k i n g fund c h a r g e s . Two very good p a p e r s on the most ~ i c a l m e t h o d of p r o c e d u r e from a financial standpoint have been w r i t t e n ~ b y F r e n c h engineers, who, o f c o u r s e , are concerned principally with the cost of m a i n t a i n i n g t h e i r p r e s e n t r o a d s , as I believe the F r e n c h N a t i o n a l R o a d s y s t e m is now complete. P. C a u f o u r i e r , in L e G e n i e C i v i l , vol. lii, No. 16, p. 268, goes i n t o the q u e s t i o n o f the p r o b a b l e life of the road u n d e r v a r i o u s treatments and different intensities of travel, and he g i v e s some equations w h i c h , when the p r o p e r constants are a s s u m e d , will show the economical m e t h o d t o be used. H i s g e n e r a l conclusions w e r e that tar painting was only economical with very hard m a t e r i a l u n d e r h e a v y travel, or with very poor m a t e r i a l u n d e r l i g h t travel. T h a t t a r r i n g with a c o a t of hard screening was good with h e a v y travel o n poor s u r f a c i n g . That tar M a c a d a m was good in h e a v y travel even with poor metal. T h a t frequently w h e n t h e r e is but little difference i n the a n n u a l c h a r g e , it will p r o v e more economical t o use the b e t t e r ( m o r e permanent) m e t h o d . A n o t h e r article p u b l i s h e d in the ,4~tncdes des P o r e s et Chauss~s, part 5, 19° 8 , plots c u r v e s s h o w i n g the a n n u a l c o s t s at 4 per cent. interest for v a r i o u s classes of p a v i n g , thus s h o w i n g the different life that each s h o u l d attain t o be e q u a l l y economical. H o w e v e r , t h e s e t a b l e s a p p l y only t o F r e n c h conditions, but they show that t h e r e is a g r o w i n g d e s i r e t o c o n s i d e r the m a t t e r o f road finances in a more scientific m a n n e r . Mr. H. P. M a y b u r y , a prominent E n g l i s h road engineer, in r e v i e w i n g the a r g u m e n t s for and a g a i n s t tar M a c a d a m , f e e l s that in his district, w h e r e they have some snow in w i n t e r and i t is q u i t e hilly, and w h e r e the p r e s e n t s u r f a c i n g is granite, that on a c c o u n t of the slipperiness of tar M a c a d a m in w i n t e r , the d a n g e r of u s i n g it in hills, its first cost, together with some little traffic dust in s u m m e r , that it is not the best, even u n d e r the h e a v y m o t o r traffic. H e s u g g e s t s b u i l d i n g a very d e e p , s t r o n g s u r f a c e with a f l a t c a m b e r o f not over I t o 30, u s i n g l a r g e hard s t o n e ( 2 ~ - and 2-inch g r a n i t e ) for the s u r f a c e , with j u s t e n o u g h s m a l l s t o n e to fill the interstices, and g r o u t e d with tar, keeping the dust down with m a c h i n e tar painting, as the best solution of the p r o b l e m s h o r t of some form of Kleinpflaster or D u r a x p a v i n g . The F i r s t International Road C o n g r e s s a g r e e d that a firm,

D E V E L O P M E N T OF MODERN ROAD SURFACES.

299

well d r a i n e d foundation was the f i r s t essential; that tar properly a p p l i e d as a s u r f a c e application w o u l d lay the dust and protect the r o a d : f r o m f i g h t m o t o r traffic, but that for h e a v y m o t o r traffic the s u r f a c e material t o a d e p t h of 2 inches s h o u l d be m i x e d with the b i n d e r . W e m a y say for a tar treatment properly applied that it m a k e s a road : ,.,

Dustless; " More hygienic; Less troublesome and expensive to keep clean; Less mud ; N o w a t e r cuts; More p!easing to travel over from its resiliency; Less expensive in the long run to maintain.

: The Office of P u b l i c R o a d s m a d e a c e n s u s of the r o a d s of the U ~ i t e d S t a t e s in 19o4, with the f o l l o w i n g r e s u l t s : T o t a l m i l e a g e of p u b l i c r o a d s , 2,161,57o; of this 7.14 per cent. were improved roads. xo8,233 miles o f g r a v e l . 38,622 miles o f stone. 6,81o miles of shell, oil, etc. 153,665

D u r i n g the five y e a r s just past t h e r e has been a g r e a t a w a k e n ing in the interest in good r o a d s , and from the 19o8 R e p o r t of the Office o f P u b l i c R o a d s w e now have I24~4(~8 miles of gravel road. 4345o triles o f stone road. 8,512 miles of shell, oil, etc. I76,43o miles o f improved road.

L e a v i n g o u t the 8,512 m i l e s of s h e l l and oil r o a d , we have I77,ooo m i l e s of recognized improved r o a d . In E n g l a n d and W a l e s t h e r e are 23,826 miles o f main road. 95,211 miles of side road. 119,o37 miles.

On these r o a d s E n g l a n d is s p e n d i n g , practically in maintenance alone, $ 3 4 7 a mile on main road and $1o7 a mile per year on the side r o a d s . In F r a n c e the length of r o a d s and a n n u a l expenditure per mile are as f o l l o w s :

30o

NOTES AND COMMENTS.

National roads, State roads,

- za,oo9 miles a6,x88 miles iaS.Sm miles x55,og 3 miles

Total, Average per mile--$Io2.o0.

321,812 miles.

Important town roads, Village roads,

We

a r e s p e n d i n g less than $ 4 o .

~a3o x8o 33o 55

per per per per

mile. mile. mile. mile.

But our r o a d s a r e in the

b u i l d i n g , and the next f o r t y y e a r s will see a n e n o r m o u s increase in the m i l e a g e of good r o a d s . W e a l r e a d y have S t a t e aid laws in 23 S t a t e s , and d u r i n g I 9 0 8 , I 6 S t a t e s s p e n t $I8,ooo,ooo and b u i l t 1,8oo m i l e s of new r o a d . W h e n we c o n s i d e r that in districts w h e r e the r o a d s are i m p r o v e d , the attendance of school c h i l d r e n is 77 per cent., w h i l e in t h o s e districts w h e r e poor r o a d s p r e v a i l it is only 53 per cent., and that from the best f i g u r e s obtaihab]e the A m e r i c a n f a r m e r is s p e n d i n g from 13 to 25 cents per ton mile m o r e than he s h o u l d on e v e r y load he h a u l s t o the railroad station, we c a n n o t but feel that the c o u n t r y as a w h o l e will a w a k e n t o the s o u n d n e s s of good r o a d s as an investment, and that we w i l l , as a nation, soon e x c e l the w o r l d in the m a t t e r of i m p r o v e d r o a d s . They c a n n o t be built~in one year nor ten. but if tl~e m o v e m e n t is even properly s t a r t e d nothing can keep it back. W i t h the increasing use of m o t o r cars some f o r m of s u r f a c e treatment is absolutely essential t o p r e s e r v e the integrity o f a M a c a d a m s u r f a c e . I t has been universally admitted that tar properly treated and applied fulfills this p u r p o s e a d m i r a b l y .

R E D U C E D D I A M E T E R C A R D COMPASS. INFORMATION has been received by the Bureau o f Manufactures that a patent reduced diameter card compass has just been exhibited in Liverpool and caused great interest to people concerned in British shipping, its value b e i n g described as follows: I t appears in many respects a desirable improvement on the compass now generally used, especially by securing the card magnification o f the markings without eye-strain, and by permitting the use o f cards o f small diameter as compared with that of the ordinary comnass. I t also affords g r e a t e r steadiness and freedom from that i n e r t h which is associated with cards o f full diameter in use at the present time. F o r many years the desirability has been recognized for adopting some suitable means o f enlarging the markings o r calibration o f compass cards to enable helmsmen to readily d e t e c t any deviation from the. course. Hitherto it h a s been a common practice tor seamen to use o r d i n a r y lens magnifiers, o r have large compass cards provided; Compasses with x2-inch and I 5 d n c h cards have been used, but there are disadvantages connected with them on account o f their unsteadiness in a seaway owm~ to t h e period of vibration and inertia, hence they have not

N O T E S AND COMMENTS.

3m

been altogether successful. Lens magnifiers are only used to a limited extent, as they cause the same strain to the helmsman's ~ e s as a result from the use o f stron~ spectacles, a n d the lenses have to be fitted on the compass 81ass, which is said to be undesirable. The reduced diameter card compass invention h a s been bt~mEht out with the object ,~)f d o i n g away w i t h t h e disadvantages referred to.~ T h e r e h a s been introd~.,ed to this compass a n arrangement whereby the m a r k i n g s or calibrations of the card can be increased to a l m o s t any size without any o f the drawbacks encountered in the ordinary compass. C L O S E R AND

MORE

ACCURATE~'STI~VN6

oBTAINED.

I n this invention a magnifying mirror, which is adapted t o magnify the mark'T'ngs on the card to any desired extent, is placed inside the compass bowl on the f o r w a r d part so that the top of the compass may be remove¢ without affecting the m i r r o r . T o the compass card is added S d o w n - t u r n rim on which the degrees are marked, the figures b e i n g reversed so that they show normally in the magnifying mirror. Instead o f the steersman viewing the compass card direct, he steers by the magnified image shown in the mirror, and the least movement o f the vessel is at once detected. Closer and more accurate steering, it is alleged, is attained by the new card compass, as the slightest de~iatlon from the course is immediately observed. As the helmsman is viewing the magnified reflection and not the object directly t h r o u g h the magnifier, there is no straining of the eyes, in fact the strain is said to be considerably less than when steering with the usual to-inch card now so extensively used. The inventors say that exhaustive praetical tests have been made at sea under all w e a t h e r conditions with results which have undoubtedly insured the success of this new magnifying system of steering. Navigational experts to whom this patent has been shown expressed their approval o f the practical advantages o f it, and recognized the convenience it afforded to seamen.

L I T H O G R A P H I C S T O N E INDUSTRY. S M A L L G E R M A N TOWN FURNISHES

THE WORLD'S SUPPLY.

The quarrying and preparing for market of lithographic stones is a unique industry carried on near Solenhofen, about 45 miles south o f Nuremberg, on the main railway line to Munich. The town is an unimportant one of about !,3oo inhabitants, the stone quarries b e i n g in the hills back of the town at a level o f some 1,5oo feet a b o v e the sea. So far as is now known, the area in which these stones a r e f o u n d is not more than 4 o r 5 miles long by 2 o r 3 miles wide. I n this limited area quarrying has been carried on for more than a century, and from it practicallythe world's supply of lithographic stones has been obtained. The stone, as is ~;eli known, is a s~cies of compact limestone o f peculiar texture and of a yellowish-gray o r blmsh-gray color, hard bluish stones b e i n g the more valuable. I t is f o u n d in layers varying in thickness from a half inch, ~or even less, up to 6 or 7 inches. The layers extend from near the surface o f the g r o u n d to a depth of 75 o r Ico feet, o r e v e n more, and are apt to be much b r o k e n by fractures o r seams and layers of worthless rock and earth. S M A L L PERCENTAGE OF MARKETABLE S T O N E .

I n the best quarries not more than one-twelfth of the material removed is marketable stone, a n d much of this is of little value because of the small sizes in which it can be found c l e a r of cracks or flaws. The quarrying is carried on by several different firms and by a corporation. About 1,2oo w o r k men are employed in the various quarries and i n the work o f cutting and dressing the stone for m a r k e t . The stones are lifted carefully from~t h e i r

302

NOTES

AND

COMMENTS.

position in the quarries in various marketable sizes and a r e then h a u l e d to buildings near by. H e r e the surfaces--for some m a r k e t s one and for others both--are g r o u n d down, chiefly with coarse sand rubbed on by heavy machines, w a t e r b e i n g constantly applied during the process. One concern h a s recently introduced a heavy machine fitted with a carborundum planer, which rapidly smooths t h e ' s u r f a c e o f the stones as they are passed back and forth under the planer, somewhat as heavy p l a n k in a planing mill. The stones a r e f u r t h e r smoothed by machinery and by hand, the edges b e i n g neatly trimmed and corners rounded. I f the stones are 6 inches o r 7 inches thick when taken from the quarries, as is sometimes the case, they are sawed t h r o u g h once by heavy saws fitted on the edges with diamonds and operated by steam power. The finished stones vary m size from 6 by 8 inches to 44 by 64 inches, and vary in price, when ready for shipment, from 15 o r 20 cents up to $65 o r $70, dependlng upon the size and quality. I n recent years the thinner stones which would b r e a k under the pressure to which they a r e subjected in printing, are, i n s o m e cases, securely cemented to other stone slabs, thus g i v i n g the requisite strength. I t is a notable fact that the i n d u s t r y has never been a source o f great profit to those engaged in it. The explanation is that the amount of dead wOrk in the quarries is large, and the proportion of perfect stone of marketable size is so small as to leave little margin of profit at the prices at which the stones are sold. I t frequently happens that a f t e r a stone h a s been g r o u n d smooth, or perhaps Men sawed t h r o u g h at Considerable expense, a chalky vein, small pebbles, o r other defects appear in the surface, greatly lessening its value. These defects become apparent when a damp sponge is passed over the surface o f thd stone. FUTURE SUPPLY.

Those ~nterested in the lithographic:stone industry say that the d e m a n d for this product has not rapidly increased in recent years. At the present rate o f quarrying they believe the supply at Solenhofen should last for from lOO to 2oo years, o r even longer. The stones are at present exported to all civilized countries of the globe. G e r m a n y is the largest buyer; France, Italy, E f t # a n d , and the United S t a t e s a r e the next in importance in the o r d e r named. The declared values o f the exports o f lithographic stones to the United S t a t e s for the eight years beginning with J a n u a r y I, I9oo, were as follows: YEAR.

IgOO x9o1 I9O2 19o3

VALUE.

. . . . . . . . . . . . . . . . . . . . . . $Io5,949 ...................... 131,632 ...................... 135,01o ...................... 138,ooo

YEAR, 19o4 . . . . . . . . . . . . . . . . . . . . . .

VALUE, $149,316

19o5 . . . . . . . . . . . . . . . . . . . . . . 124,719 19o6 . . . . . . . . . . . . . . . . . . . . . . . ~57,t~8 r9o7 . . . . . . . . . . . . . . . . . . . . . . z61,9o5 --Consular Report.