RoadwayLarge illustration(66kB)
Large illustration(66kB)
The total width of street is 36 feet, of which the roadway takes 24, leaving a footpath 6 feet in width on each side.
The surface of the finished roadway is a segment of a circle, the crown being level with the heels of the footpaths on each side; the formation surface is parallel with it, and of course the depth of this and the thickness of foundations and metal must depend upon local circumstances. It will be seen that the haunches are drained with 3-inch common drain-pipes. This may be omitted if the ground is thoroughly dry, but it is often a great help to a road.
Thepaths,kerbing, andchannellingwill be described in their respective chapters.
It must be borne in mind that on a perfectly level road a more convex section is necessary than on a gradient.
It is wrong to make the sides of a roadway weaker than the centre, especially in streets with shops on each side, or on hills where drags are likely to be used. On hills, too, be it remembered, the channels should take the surface water; any ruts from wheel tracks acting as watercourses are disastrous. Hauling timber on a macadamised roadway is also very damaging.
The great objections to macadamised roadways are asfollows:—
(1.) They manufacture too much mud and dust.[23]
(2.) They are too absorbent.
(3.) They are very noisy and damaging to vehicles and horses when fresh metalled.
(4.) They constantly require mending, but never seem quite sound.
(5.) They are frequently encumbered by men and carts engaged in either repairs, cleansing, or watering.
(6.) They are very expensive to maintain and cleanse.
(7.) They are bad for a horse to fall upon, as such falls generally damage the knees.
The following notes upon the maintenance of macadamised roadways may here be ofservice:—
(1.) Roads should be inspected in wet weather, as hollows and other imperfections are then easily detected; a hollow place extends very rapidly if neglected.
(2.) All ruts should be filled in at once. If there are three parallel, the centre rut should be first filled in; the traffic is thus slightly diverted, as a horse will avoid new metal.
(3.) Ruts should not be allowed to form; the surface of the road ought never to lose its regular section.
(4.) A road should be thoroughly repaired directly it shows the least sign of being fairly worn all over.
(5.) The right season of the year for repairs is the autumn, although where a steam roller can be used almost any time will do. If the surface of the road is very hard it should be “lifted”[24]previous to repairs.
(6.) All loose stones should be picked off at once or put together in hollow places upon the roadway, as, if allowed to remain, they are not only dangerous to horses, but are liable to be crushed, or to be forced through the skin of the roadway, thus causing it damage.
(7.) Water lodging upon a road does great mischief, but it should not be let off by digging a trench with a pickaxe to the side of roadway, as is sometimes done.
(8.) A roadway when very dry sometimes suffers through disintegration of the surface.
(9.) Scraping the mud off a roadway may damage it by loosening stones; sweeping the surface when wet is best.
(10.) A heavy shower does a road good by washing it; acontinuous drizzle, especially after frost, is very ruinous to a roadway.
(11.) A good cleansing is sometimes worth a coat of metal.[25]
In some towns in England bituminous or asphalte macadamised roadways are made. This consists in mixing ordinary coal tar with the road metal ordinarily employed for macadamised roads, only it must be borne in mind that the metal employed must be limestone or some other soft material, otherwise it will not wear down evenly with the tar, and thus a lumpy surface will be produced in course of time.
The method of mixing is by heating the stone, which has of course been previously broken to the required size, and then thoroughly mixing and incorporating it with the tar. This is then carried to the roadway, is spread in the ordinary manner and well rolled to the proper contour, a surface being afterwards given to it by a coating of about 2 inches thick, composed of a similar mixture, the stones of which are of much smaller size.
Another method is to place about 6 inches of the broken metal described above upon the necessary foundation. Upon this a boiling mixture composed of about 50 gallons of creosote oil and 1 ton of pitch is poured until every interstice is filled with the mixture. Whilst this is still warm, a thin layer of small broken stone is spread upon the surface and well rolled; more small stones or chippings are added, and the whole is rolled until the surface of the roadway has attained its proper contour and presents a perfectly smooth and clean appearance, little inferior to that of real asphalte.
Dry weather is essential whilst this class of roadway is in course of construction, and they require careful watching, as, upon the skin becoming broken, the whole roadway soon breaks up. They have, however, many advantages over ordinary macadamised roadways when finished, not the least of them being their imperviousness to moisture, and the ease with which they are cleansed.
[12]The first road “engineer” in this country was John Metcalf of Knaresborough, who was born in 1717, and who, although totally blind, was the first person to introduce a methodical system of road repairs.Vide‘Roads and Road Makers,’ by Henry Alexander Glass.[13]Vide‘A Treatise on Roads,’ by Sir H. Parnell (1833).[14]The total width of roadway being thirty feet.[15]It is necessary to give a new roadway more convexity than it will have when finished, for however carefully it is raked or attended to when being rolled, the top is sure to flatten and spread towards the haunches.[16]Instead of parallel lines it is sometimes well to place these stones diagonally from centre to kerb or “herring-bone” fashion, thus greatly facilitating the under drainage.[17]In metalling a road it is better to put on the coats gradually, than to give the whole thickness of metal at once.[18]The method adopted in Chicago, U.S.A., for forming their roadways is as follows:—The road bed is prepared of the proper contour and well-rolled with a 15-ton steam roller until it is even, firm, and compact; on this bed rubble stone is carefully placed by hand with its broadest surface downwards, then 12 inches of metal are added 6 inches at a time, thoroughly rolled to bond it well, it is then topped with 4 inches of crushed trap rock or some other equally hard stone, which will not disintegrate through the action of the weather, nor pulverise under the pressure and wear of vehicles upon it; this is again, thoroughly well rolled so as to compact and bind it together.[19]“If roads be kept dry they will be maintained in a good state with proportionally less expense. It has been well observed that the statuary cannot saw his marble, nor the lapidary cut his jewels without the assistance of the powder of the specific materials on which he is acting; this, when combined with water, produces sufficient attrition to accomplish his purpose. A similar effect is produced on roads, since the reduced particles of the materials, when wet, assist the wheels in rapidly grinding down the surface.” Parnell’s ‘Treatise on Roads,’ 1883. More modern writers have likened macadamised roadways to “stone mills on which the stones are ground into dust when dry, or mud when wet.”[20]Vide‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. lx.[21]Vide‘Annales industrielles de Paris,’ Oct. 21st and Nov. 4th, 1877.[22]Vide‘Annales industrielles de Paris.’[23]A report of the Paddington Vestry on “wood and other pavements,” (1878) states macadam as a mud producing material is twelve times worse than wood, and six times worse than granite cubes.[24]This is also sometimes called “stocking” or “chequering,” and consists of making furrows across a roadway with a sharp pickaxe, about a couple of inches in depth, thus removing any irregularities, and also allowing the new metal to bed properly.[25]In Birmingham, good cleansing is said to have reduced the amount of metal necessary for the maintenance of the roadways from 20,000 tons per annum to 13,000 tons.
[12]The first road “engineer” in this country was John Metcalf of Knaresborough, who was born in 1717, and who, although totally blind, was the first person to introduce a methodical system of road repairs.Vide‘Roads and Road Makers,’ by Henry Alexander Glass.
[13]Vide‘A Treatise on Roads,’ by Sir H. Parnell (1833).
[14]The total width of roadway being thirty feet.
[15]It is necessary to give a new roadway more convexity than it will have when finished, for however carefully it is raked or attended to when being rolled, the top is sure to flatten and spread towards the haunches.
[16]Instead of parallel lines it is sometimes well to place these stones diagonally from centre to kerb or “herring-bone” fashion, thus greatly facilitating the under drainage.
[17]In metalling a road it is better to put on the coats gradually, than to give the whole thickness of metal at once.
[18]The method adopted in Chicago, U.S.A., for forming their roadways is as follows:—The road bed is prepared of the proper contour and well-rolled with a 15-ton steam roller until it is even, firm, and compact; on this bed rubble stone is carefully placed by hand with its broadest surface downwards, then 12 inches of metal are added 6 inches at a time, thoroughly rolled to bond it well, it is then topped with 4 inches of crushed trap rock or some other equally hard stone, which will not disintegrate through the action of the weather, nor pulverise under the pressure and wear of vehicles upon it; this is again, thoroughly well rolled so as to compact and bind it together.
[19]“If roads be kept dry they will be maintained in a good state with proportionally less expense. It has been well observed that the statuary cannot saw his marble, nor the lapidary cut his jewels without the assistance of the powder of the specific materials on which he is acting; this, when combined with water, produces sufficient attrition to accomplish his purpose. A similar effect is produced on roads, since the reduced particles of the materials, when wet, assist the wheels in rapidly grinding down the surface.” Parnell’s ‘Treatise on Roads,’ 1883. More modern writers have likened macadamised roadways to “stone mills on which the stones are ground into dust when dry, or mud when wet.”
[20]Vide‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. lx.
[21]Vide‘Annales industrielles de Paris,’ Oct. 21st and Nov. 4th, 1877.
[22]Vide‘Annales industrielles de Paris.’
[23]A report of the Paddington Vestry on “wood and other pavements,” (1878) states macadam as a mud producing material is twelve times worse than wood, and six times worse than granite cubes.
[24]This is also sometimes called “stocking” or “chequering,” and consists of making furrows across a roadway with a sharp pickaxe, about a couple of inches in depth, thus removing any irregularities, and also allowing the new metal to bed properly.
[25]In Birmingham, good cleansing is said to have reduced the amount of metal necessary for the maintenance of the roadways from 20,000 tons per annum to 13,000 tons.
The only true test of the fitness of any stone for use as a road metal is by an experimental trial upon a certain length of roadway; but in making the first selection for such trials it is well to make the followinginvestigations:—
(1.) Ascertain from local persons, such as masons, quarrymen, and others, their opinion of the qualities of the stones in the neighbourhood.
(2.) Make a trial of the stone for toughness. This can be done by setting a good stone-breaker to work upon a heap of the stone as quarried and carefully watching how much he can break in an hour.[26]
(3.) Ascertain what power the stone has to resist abrasion. This is done in France by putting the broken metal into a revolving cylinder and then carefully noting by weight what the cubes lose by contact with each other. Another plan may be adopted by pressing the stone against a grindstone with a uniform pressure, and noting the loss caused by such contact.
(4.) The power to resist compression may be easily ascertained by placing small cubes in an hydraulic press and noting under what pressures each cube will crush.
(5.) The effect of weather is not easily ascertained artificially, although it is suggested that a good test may be made by soaking the stone in a saturated solution of sulphate of soda; and then on exposure to the air, if soft, it is said the stone will disintegrate as if under the action of thaw succeeding frost.[27]
The specific gravity of a stone is no criterion whatever as to its fitness. Clay-slate has a higher specific gravity than a tough flint, and yet the former is almost useless as a road metal; the latter, on the contrary, often making excellent roadways.
The qualities necessary for a really good road metal are hardness, toughness, not easily decomposed or affected by the weather, and at the same time the stone when broken ought to have some power of cohesion without the necessity of much binding material. The question of cost I put aside at once, as it is well known that the best road metal is always the cheapest where there is much or heavy traffic.
Local circumstances must to a great extent determine what stone to use upon a roadway, but the following list may be ofuse:—
—This is a granite in which hornblende takes the place of mica, and is an excellent road material; the darker the colour the more durable it is found to be.
—This should have more felspar than quartz, and have as little mica as possible; the closer the grain the better. Coarse-grained granites soon decompose.
—Some of these are excellent for road metal. Basalts of dark colour and close grain should be selected. Greenstones with similar characteristics are good; as is also Whinstone.
—Is inferior to granite; it has mica in layers and is not a good road metal.
—These are useless, as they crumble on exposure or degenerate into mud.
—The Metamorphic, Silurian, and Carboniferous limestones may be used if crystalline in appearance, but the Lias and Oolitic are of little use.[28]
—Some of these, if cherty or containing a large percentage of iron, may be used; but as a rule they are quite unfitted for use as a road metal.
—These, if tough, make excellent roadways; but unfortunately they are sometimes too brittle for heavy traffic. Surface-picked flints are better than those from a quarry.[29]
—These are found on sea shores and river beds. They are composed of very various rocks, and are much water-worn and rounded; when broken they sometimes answer very well if mixed with gravel to bind them.
—This, if of a flinty character, and not too much mixed with earthy matter, makes good roads for light traffic, if carefully watched or well rolled during formation. Pit gravel should always be screened through wire screens of 1¹⁄₂ to 1³⁄₄ gauge, and the small can be used for footpaths.
In some places it is difficult to obtain any natural stone for the purposes of road metal; in these cases slag from blast furnaces or ordinary clinkers from furnaces are sometimes used. Oyster shells are used on the roadways near the Gulf coasts[30]and charcoal in Michigan, United States.[31]I have myself made a most excellent roadway with coral on the coast of Jamaica, and no doubt many strange materials have been, and still are, used for this purpose.
“I never mix” is an adage that should be followed by surveyors as regards road metal. Do not mix a soft material with one that is harder for either construction or maintenance of a roadway; the effect is what is known as a “bumpy” road, arising from the fact of the soft stone wearing faster than the hard. The hardest metal should be kept for the top or surface layer of the roadway.
As an instance of the extreme difficulty besetting the question of the best material for road metal, I will here give atable showing the comparative coefficients of quality assigned to them by the engineers of the French Department of the Ponts et Chaussées.[32]
Coefficients of Quality of Road Materials.
It will be seen by the above table how different are the results obtained from materials of the same character.
Breaking stone for the purpose of using it as a road metal was, until comparatively recent years, always effected by hand; now, as in other cases, machinery has stept in and somewhat supplanted manual labour. Hand-broken road metal, however, still finds favour with road surveyors; it is better broken, and in some districts, the occupation finds employment for persons who otherwise would be thrown on the rates for support.
In breaking stone by hand the breaker sits and strikes thestone with a small cast-steel chisel-faced hammer, weighing about one pound, at the end of a long, straight-grained but flexible ash stick.[33]The breaker also has another hammer, weighing about five pounds, with which he reduces the size of the large stones before breaking them into the proper size for road metal. This latter size is often a matter of choice, some engineers preferring it to be broken so small as will pass through a ring of only 1¹⁄₂ inch in diameter; others are content with 3 inches, especially where the roads are steam rolled. An old method of gauging used to be “such a size as the stone breaker could put in his mouth,” but this was unsatisfactory to all persons concerned, and “to pass all ways through a ring of 2¹⁄₂ inches internal diameter” is now the size most generally adopted.
Mr. Codrington says[34]“a good stone breaker will break 2 cubic yards of hard limestone to the ordinary gauge in a day, and some men will break more. Hard silicious stones and igneous rocks can only be broken at the rate of 1¹⁄₂ or of 1 cube yard per day; of some of the toughest, such as Guernsey granite, a man can only break on an average half a cube yard per day. River gravel, field stones, or flints, which are already of a small size, can be broken at the rate of 3 or 4 cube yards per day.”
This may be taken as fairly representing a day’s work, the price for breaking however must vary considerably in different localities on account of the variety of the stones to be broken and the value of labour; in some districts the road metal does not cost more than 1s.per cube yard, in others 2s.6d.and 2s.8d.is not considered too high, and it was to meet and reduce this great expense that steam stone-breaking machines have been introduced. These machines are known as “Ellison’s,” “Newall and Archer’s,” “Hope’s,” and “Blake’s,” the latter being that which is best known and most generally used in this country.
“ARCHER’S” STONE BREAKER.“BLAKE’S” STONE BREAKER.“NEWALL AND ARCHER’S” STONE BREAKER.
“ARCHER’S” STONE BREAKER.
“BLAKE’S” STONE BREAKER.
“NEWALL AND ARCHER’S” STONE BREAKER.
The foregoing illustrations will give a general idea of the manner in which the stone is broken or crushed between strong iron jaws; in all cases a revolving perforated screen is necessary (not shown in the drawings) to separate the stone broken to proper gauge from that which is too large, and also from the spalls or chippings.
The Blake’s or “Blake Marsden’s” machines are of various sizes and weights; the following particulars with respect to them, as advertised, may be of use.[35]
Mr. Till, the Borough Engineer of Birmingham, speaking of the work done by one of Blake’s machines in 1874, says:[37]“The stone-breaking machine at Holliday Street will break on an average 40 tons of ragstone per day, at a cost, exclusive of wear and tear of machine, of 10¹⁄₂d.per ton, but it produces16 per cent. of dust or fine stone; of the remainder one-fifth has to be rebroken by hand, the whole is very irregular in size and very flaky in comparison with hand-broken stone. The machine is much more efficient in breaking granites or pebbles. It has, however, been found very useful during the last two years, in consequence of the difficulty of obtaining labour.”
Mr. Jacob, the Borough Engineer of Barrow in Furness, read an excellent paper on the subject of stone-breaking machinery to the members of the Association of Municipal and Sanitary Engineers, at their meeting in Manchester in 1875,[38]giving a full description of one of Blake’s machines, to which I will refer my readers.
Mr. Codrington[39]gives the result of breaking whinstone in a 16-inch by 9-inch Hope machine, from which it appears that the total cost, including wages, coal, oil, cottonwaste, etc., wear and tear of machinery, and, I presume, interest on first cost of machine, was about 1s.per cube yard. This effected a saving of 10d.per cube yard as compared with the same stone broken by hand, and the machine broke 40 tons of stone per diem.
To make a stone-breaking machine pay, it is necessary:
(1.) To give it nearly constant work.
(2.) That the stone to be broken shall be too tough to break economically by hand.
(3.) That the machine shall be at the quarry, so as to save the expense of much handling.
(4.) To exercise care in feeding, to give it a sufficient supply without allowing an undue quantity of stone to pass in at one time.
(5.) As about 20 per cent. of grit or dust is produced, thismust be used for foot-paths, or as a binding material for roads, or in asphalte or tar paving.
In addition to the grit which is produced, a great many long and thin pieces of stone pass through the machine, which have to be again broken by it before they could be used as road metal; and having once taken this form, they will frequently pass several times through the machine before they get properly broken.
The wear and tear of a stone-breaking machine is very considerable, as can be easily imagined; it has been known to reach as high as 62·5 per cent.[40]of the first cost of the machine in one year. The objections to stone-breaking by machinery are principally:
(1.) In some districts labour can be successfully employed in this manner.
(2.) Hand-broken stone is sharper in fracture, as it is done by a blow and not by gradual pressure, whereas machine-broken stone is often flaky or with rounded edges, and frequently each stone may be cracked and shaken by the pressure.
(3.) Want of uniformity in the size of the stones.
The smaller the stone is broken the heavier a cubic yard of it will weigh, as the percentage of vacant space between each stone will be less. It has been found by experiment, however, that 55 per cent. of ordinary road metal is solid, so that the weight of a cubic yard of it can easily be ascertained in the following manner.[41]
Multiply the weight of a cubic foot of any stone by 27 to bring it to a cubic yard, and then multiply this by 0·55: the result will be the weight of a cubic yard of the same stone when broken for metalling.
A cubic yard of Guernsey granite broken to pass through a 2¹⁄₂ inch ring has been weighed, and gives an average of 1 ton 3 cwt. 2 qrs.
A cubic yard of ordinary broken road metal will, when properly spread, cover an area of about 30 square yards of surface of a roadway.
The following specimen specification for the supply of stone either unbroken or broken may be of use.
(1.) The road metal must at all times be clean and free from clay or other dirt, and fully equal to the sample; if required to be broken, each cube must have a square face and sharp edges, and pass all ways through a 2¹⁄₂ inch ring.
(2.) The metal must be delivered in (name of town) free of all charge to the corporation, either at a railway station or at one of the depôts of the corporation, at the option of the contractor, such option to be declared in the tender.
(3.) The metal must be supplied on the order of the borough engineer in such quantities as he may specify, and must be delivered within the time specified in the order. The contractor shall not be required to supply and deliver more than tons in any one week; but the corporation will be at all times ready to take the metal in larger quantities.
(4.) The bill of lading or railway invoice shall be taken asprimâ facieevidence of the weight of metal supplied; but the corporation retain the right to test the accuracy of such bill of lading or railway invoice, by passing the metal over a weighbridge as it is received.
(5.) Metal delivered at a depôt by carts shall be measured when broken and paid for at the rate of cwt. per cubic yard.
(6.) The corporation retain the right to reject all metal which shall not be equal to the sample, or at their option to pay a reduced price according to its value.
(7.) Quarterly payments will be made by the corporation on the certificate of the borough engineer, and within one month from the date of such certificate.
(8.) The borough engineer shall be the sole judge as to the fitness of the metal supplied, and his certificate, in writing, shall be conclusive evidence upon the point as between the corporation and the contractor.
(9.) If the contractor shall make default in the supply and delivery of road metal in accordance with the terms of this specification, and within the time specified for the purpose in the order of the borough engineer, the corporation shall be at liberty to obtain such road metal as they may deem fit and necessary from another source, and any excess in price or other loss they may consequently incur, shall be recoverable by them from the contractor as liquidated and ascertained damages.
(10.) Tenders must be sent in only on the prescribed form, and the person tendering must insert in his tender the name of two persons who will join him in a joint and several bond to the corporation in the sum ofl.for the due performance of the contract.
(11.) Each person tendering must send to the office of the borough engineer a sample of the road metal he offers, accompanied by a full description, and the name and position of the quarry from which it is produced; such sample to be not less that one cwt. in weight, and to be retained by the corporation in the event of the tender being accepted.
(12.) The corporation do not bind themselves to accept the lowest or any tender; and they further retain the right to reject a contractor in the event of his failing to find sureties to their satisfaction in compliance with the 10th condition.
(13.) The word “corporation” shall mean the mayor,aldermen and burgesses, of in their capacity as the urban sanitary authority for . The word “contractor” shall mean the person whose tender is accepted, and who has signed these conditions; and the words “borough engineer” shall mean the engineer to the said corporation for the time being.
Since writing this chapter my attention has been directed to a stone-breaking machine which is said to substitute a “knapping” for that of the usual crushing motion which is so generally the great defect in these machines: I allude to that known as “Baxter’s patent knapping-motion stone breaker,” by which a rapid jerk or blow is given instead of the slow crushing movement, thus (it is contended) causing less waste from dust and chippings, and also less strain of the machinery and less power to drive it.
[26]Toughness is not all that is required. Leather would be very difficult to break with a hammer, but it would not make a good road metal.[27]I have tried this experiment, but without success, except on such soft stones as were evidently unfitted for use as a road metal.[28]Many hundreds of miles of roadways in this country are made with limestones; they often make an excellent surface, as they possess a considerable power of binding together, but weather and very heavy traffic affect them considerably: as they all have a strong affinity for water, their very power of thus cementing themselves together causes a quantity of dust in dry, and mud in wet weather.[29]A flinty or quartzose stone seems to harden with exposure. This is notably the case in pebbles; old pebble paving taken up and broken makes a most hard and durable road metal.[30]‘Roads, Streets and Pavements,’ by Q. A. Gillmore, p. 10.[31]Ibid.[32]Vide‘The Maintenance of Macadamised Roadways,’ by Thomas Codrington, p. 33, a most excellent work upon this subject.[33]Mr. W. Bold considered a hammer weighing 1¹⁄₄ lb. of an elliptical form, pointed at the ends, the area of each end being about ¹⁄₁₀₀th of a square inch, to be the most suitable to break hard stones.Vide‘Minutes of Proceedings, Institution of Civil Engineers,’ vol. i. (1840) p. 50.[34]‘The Maintenance of Macadamised Roads,’ by Thomas Codrington, p. 38.[35, 36]No doubt the price of the machine varies with the price of iron, etc.[37]Vide‘Report of the Borough Surveyor of Birmingham to the Paving and Street Improvement Sub-Committee,’ p. 11.[38]Vide‘Proceedings of the Association of Municipal and Sanitary Engineers,’ vol. ii. p. 76.[39]Vide‘The Maintenance of Macadamised Roadways,’ by Thomas Codrington, p. 41.[40]Vide‘Proceedings of the Association of Municipal and Sanitary Engineers,’ vol. ii. p. 82.[41]Vide‘The Maintenance of Macadamised Roadways,’ by Thomas Codrington, p. 45.
[26]Toughness is not all that is required. Leather would be very difficult to break with a hammer, but it would not make a good road metal.
[27]I have tried this experiment, but without success, except on such soft stones as were evidently unfitted for use as a road metal.
[28]Many hundreds of miles of roadways in this country are made with limestones; they often make an excellent surface, as they possess a considerable power of binding together, but weather and very heavy traffic affect them considerably: as they all have a strong affinity for water, their very power of thus cementing themselves together causes a quantity of dust in dry, and mud in wet weather.
[29]A flinty or quartzose stone seems to harden with exposure. This is notably the case in pebbles; old pebble paving taken up and broken makes a most hard and durable road metal.
[30]‘Roads, Streets and Pavements,’ by Q. A. Gillmore, p. 10.
[31]Ibid.
[32]Vide‘The Maintenance of Macadamised Roadways,’ by Thomas Codrington, p. 33, a most excellent work upon this subject.
[33]Mr. W. Bold considered a hammer weighing 1¹⁄₄ lb. of an elliptical form, pointed at the ends, the area of each end being about ¹⁄₁₀₀th of a square inch, to be the most suitable to break hard stones.Vide‘Minutes of Proceedings, Institution of Civil Engineers,’ vol. i. (1840) p. 50.
[34]‘The Maintenance of Macadamised Roads,’ by Thomas Codrington, p. 38.
[35, 36]No doubt the price of the machine varies with the price of iron, etc.
[37]Vide‘Report of the Borough Surveyor of Birmingham to the Paving and Street Improvement Sub-Committee,’ p. 11.
[38]Vide‘Proceedings of the Association of Municipal and Sanitary Engineers,’ vol. ii. p. 76.
[39]Vide‘The Maintenance of Macadamised Roadways,’ by Thomas Codrington, p. 41.
[40]Vide‘Proceedings of the Association of Municipal and Sanitary Engineers,’ vol. ii. p. 82.
[41]Vide‘The Maintenance of Macadamised Roadways,’ by Thomas Codrington, p. 45.
The march of civilisation has decided that road rolling is a necessity for macadamised roads, instead of allowing the stones of which they are composed to be worn in by the traffic, as was formerly the custom. In Calcutta bullock rollers were used so long ago as the year 1855, and it was the cruelty of this operation that suggested to Mr. W. Clark the necessity for a steam roller,[42]the outcome of which was the well-known roller as manufactured and supplied by Messrs. Aveling and Porter of Rochester, and now so generally used throughout this country, as well as in American and other foreign towns.[43]
Steam rolling saves money as well as suffering, and the legislature have recognised the importance of a sanitary authority becoming possessed of a steam roller by permitting money to be borrowed for the purchase of a roller as for a permanent work. (Sect. 234 Glenn’s Public Health Act 1875, footnote to Sub. Sect. (1).)
Mr. Albert W. Parry, the Borough Surveyor of Reading, has prepared some tables on the subject of steam road rollers, from information he received on this subject, in answer to some questions he addressed to the surveyors of a number of towns a few years ago. It appears from this tabulated statement that thirty-three 15-ton steam rollers were in use, six 10-ton rollers, one 21-ton roller, one 8-ton roller, one 9¹⁄₂ ton roller,one 14¹⁄₂-ton roller, one 17-ton roller, and one 25-ton roller; this latter not being much used, as it was found to be too heavy.
The average gross cost per annum of necessary repairs to the rollers, other than those which could be effected by the men in charge of it, amounted to 35l.12s.The number of men employed to attend to the roller and cost of labour per day varied considerably, from one case (South Shields) where “one engine-man at 26s.per week, and an old scavenger with the flag” were found to be sufficient; to another (Gloucester) where the cost per day is stated as follows: “one man works the engine at 5s.per day, one boy with signal flag, 1s.8d., two men spreading gravel or sand at 3s., two men watering and sweeping to keep water from running off in channels.”
Some of the older rollers require a steersman as well as a driver, and the Locomotives Amendment Act requires two men with flags, but this is seldom really necessary. The sweepers, spreaders and sprinklers should be taken as irrespective of the actual cost of the roller, which may therefore be assumed to be the wages of the engine-man, say 5s.per diem, and a boy or old man with a flag at 2s., thus making a total for labour of 7s.per diem.
The fuel that is consumed by a 15-ton roller seems to be from 3 to 5 cwt. of coke per diem, common gas coke being generally used, though steam coal would no doubt answer equally well, some of the smokeless Welsh descriptions being of course necessary.
With regard to the question “When not used for rolling roads, to what other use (if any) do you put the engine power?” there are not many towns that use the machine for any other purpose than rolling, but the following uses may be enumerated to which the machines have been applied:—Driving a stone-breaker, a mortar-mill, a saw-bench, a chaff-cutting machine, a bean-crusher, etc. It has also been used in connection with pumping, and to produce the necessarypower for the electric light, and it is frequently employed as a traction engine.
The driving rollers usually have provision by which spikes may be fitted into holes in their faces, in order that they may be used for lifting or chequering roads. These, however, apparently do not answer; the working of a machine in this manner is said to shake and strain it considerably, and the holes in the rollers, which are plugged with wood when not in use, are objectionable, as these plugs wear out and the road metal gets into the holes, and the surface of the road is picked up as the rolling proceeds; besides this, the spikes seem to have no effect unless the surface of the roadway being operated upon is soft.
With reference to the use of binding material, the most commonly used and that which receives most favour is road grit or scrapings,[44]sharp sand is also employed, as well as gravel if clean, and also stone chippings and screenings; these should be of the same material of which the road is made, if possible, and no doubtnewlyconstructed roads require more care in the binding material than simple repairs. The steepest gradient upon which a roller will act appears to be 1 in 9 in Blackburn, with a 15-ton roller, but this must require a very heavy pressure of steam, and 1 in 14 seems to be a gradient that gives no trouble to roll either up or down; in going down hill, of course it is a mere question of sufficient break power.
The number of superficial yards rolled per day must vary extremely with circumstances: the class of material, the amount of binding and water used, the gradient and pressure of steam maintained, and the amount of rolling considered necessary,[45]being amongst the various influences. From the above returns I find that the number of square yards rolledvaries from 500 to 3000 per diem, the average for 42 towns being 1105 square yards per diem.
The cost per square yard rolled, including all charges, may be assumed to be between ¹⁄₂d.and 1d., and the cost of binding material about 3d.per square yard. With reference to the necessity of binding material, the following, facts are interesting.
Mr. Wm. H. Grant, Superintending Engineer of the New York Central Park, in his report upon the park roads, says:[46]“At the commencement of the macadam roads, the experiment was tried of rolling and compacting the stone by a strict adherence to Macadam’s theory, that of carefully excluding all dirt and foreign material from the stones, and trusting to the action of the roller and the travel of teams to accomplish the work of consolidation. The bottom layer of stone was sufficiently compacted in this way to form and retain, under the action of the rollers (after the compression had reached about its practical limit) an even and regular surface; but the top layer, with the use of the heavy roller loaded to its greatest capacity, it was found impracticable to solidify and reduce to such a surface as would prevent the stones from loosening and being displaced by the action of waggon-wheels and horses’ feet. No amount of rolling was sufficient to produce a thorough binding effect upon the stones or to cause such a mechanical union and adjustment of their sides and angles together, as to enable them mutually to assist each other in resisting displacement. The rolling was persisted in with the roller adjusted to different weights up to the maximum load (12 tons) until it was apparent that the opposite effect from that intended was being produced. The stones became rounded by the excessive attrition they were subjected to, their more angular parts wearing away, and the weaker and smaller ones being crushed.”
“The experiment was not pushed beyond this point. Itwas conclusively shown, that broken stones of the ordinary sizes, and of the very best quality for wear and durability, with the greatest care and attention to all the necessary conditions of rolling and compression, would not consolidate in the effectual manner required for the surface of a road while entirely isolated from and independent of other substances. The utmost efforts to compress and solidify them while in this condition after a certain limit had been reached, were unavailing.”
From the foregoing it is very evident that some description of binding material is essential in making a road under a roller. Where traffic is allowed to consolidate a road it is different, as then the stones are knocked about and are sufficiently abraded against each other to form a binding material for themselves. Too much binding material or too much water should not be used in forming a road with a steam roller. It is unfortunately frequently the case that a road is made quickly only to go to pieces with the traffic in a few weeks. The surface of a well-constructed macadamised roadway should after being rolled look almost like an encaustic pavement. If there is too much binding material in the joints of the stones, the first heavy rain washes it out and the surface of the roadway quickly goes to pieces.
The following description of the manner in which it is recommended that the roller should be applied is taken from an excellent little pamphlet on Steam Road Rolling, by Messrs. Aveling and Porter, the well-known makers of steam-rollers, and although local circumstances must guide the surveyor in all his works, the particulars may be ofuse:—
“In the best practice the roadway is excavated, graded, and properly formed to a depth of 14 inches from the level of the gutters, with a cross section conforming to the cross section of the road when finished; it is then thoroughly and repeatedly rolled with the steam roller, all depressions being carefully filled and rolled before the stone is put on. On thebed thus formed and consolidated a layer of stones 8 inches thick is set by hand, and rammed or settled to place by sledge hammers, all irregularities of surface being broken off and the interstices wedged with pieces of stone. The intermediate layer of broken stone, of a size not exceeding 3 inches in diameter, is then evenly spread to a depth of 4 inches and thoroughly rolled, and this is followed by rolling in half-an-inch of sand. The surface layer of stone, broken to a size not larger than 2 inches diameter, and to a form as nearly cubical as possible, is then put on to a depth of 3 inches, thoroughly rolled, and followed as before by sand, also rolled. Finally, a binding composed of clean, sharp sand is then applied, well watered and most thoroughly rolled with the steam roller, until the surface becomes firm, compact and smooth, the superfluous binding material being swept off and removed.”
And the following account of the method adopted in the United States at Hartford may also be of interest.[47]
“The surface of the road is excavated to a suitable depth—say, 18 inches; preparing the form for the pavement with the precautions as for a common pavement; 4 inches of gravel and proper drainage where required, provided blocks of stone of any irregular shape are selected for the pavement, of about 7 inches in thickness. The blocks are set by hand with great care, as closely in contact at their base as practicable. The surface between the blocks is filled with chippings of stone carefully laid in. A layer of broken stone, 4 inches thick, is laid over this pavement. The road-covering thus prepared should be rolled with the steam roller until the upper layer has become perfectly compact and consolidated. The second layer, about 3 inches in depth, is then laid on; a coating of clean coarse gravel, 1¹⁄₂ inch thick, termed ‘binding,’ is spread over the surface, and the whole well rolled as before, and you have the requisites of a good road—viz., clean, hard, and even at all seasons. No road should be considered madeuntil it is completely rolled. A road made in the manner above described, and kept perfectly clean, hard, and even, with materials of a good tough quality, would show extremely little wear on the surface; indeed, it has been found in France to be less than ¹⁄₂ an inch in a year, on a road of great traffic.”
In the neighbourhood of New York the steam roller is used asfollows:—
Two and a half inches of trap rock is laid and lightly rolled until the stones have become a little compacted, then coarse screenings are added, and it is again rolled; after this a layer of about 2 inches of stones are added and rolled with coarse screenings as before. Fine screenings or stone dust is then applied, and the roadway is then rolled until every interstice is filled up; it is then well watered and again rolled.
With reference to the employment of the steam roller in repairs of roads, the following description is given of the method adopted by the Surveyor to the Tottenham Local Board, near London.[48]
“When a road becomes so full of holes or so worn as to require coating throughout its entire length and width, it should be hacked completely over and raked into a segmental form in its transverse section to remove irregularities, and so that the road may have a fall from the crown to the channel of not less than one inch to a yard. It should then be coated with stone broken as nearly cubical as possible and to an uniform gauge. When spread it should be slightly coated with gravel screenings, or the grit sweepings from the roads, which are equally suitable for the purpose when in proper condition. The road should then be watered and rolled, beginning with the road at the channels, and ending at the crown of the road, until a smooth surface is obtained, more stones being added to fill up any inequalities that may exist, until the whole is consolidated. By constantly sweeping the gritfrom the sides to the crown of the road as the roller passes over, every stone is thoroughly grouted into its bed.”
Mr. R. Read, the Surveyor of Gloucester, says:[49]“The road should be thoroughly well lifted and the metalling spread in three-inch layers evenly, and rolled once or twice before the gravel or other binding material is spread; then spread gravel or sand evenly and well watered with fine distributor until the stone is entirely covered, and the sand does not adhere to the roller. Dam up the road channels to prevent water and sand running off into sewers and let men scoop up the water, and throw it back on the road, as it collects in the gutters.”
In all cases the sides should be rolled first to such a degree of firmness that when the roller passes over the centre or crown of road, its weight, which tends to spread the metal or make it work off towards the sides, may be resisted by their consolidation.
With reference to the effect of the weight of steam road rollers upon roadways, it may be well here to compare that of a 15-ton roller with other burdens that a road has to bear, taking each case at per inch of width of tire.
An ordinary loaded two-wheeled cart presses with a weight of about 9 cwt. per inch width of tire, a loaded wagon about 7¹⁄₂ cwt., a 9-ton traction engine about 3³⁄₄ cwt., and a 15-ton steam road roller about 3¹⁄₂ cwt. So that as far as the surface of the roadway is concerned, a roller affects it the least of any of the above loads.
It has, however, been found that where rollers of more weight than 15 tons are used,[50]not only are they unwieldy, but, from their great weight, the solidity of the foundation of the roadway may be interfered with, and also there is great danger of damaging gas or water mains and services, besides any cellars that may be constructed under the roadway.
The steam rollers which are principally used in this country, are those manufactured by Messrs. Aveling and Porter, and those by Messrs. Green and Sons, drawings of both of which are here represented.