MESSRS. AVELING AND PORTER’S 15-TON STEAM ROAD ROLLER.
MESSRS. AVELING AND PORTER’S 15-TON STEAM ROAD ROLLER.
MESSRS. GREEN AND SON’S 15-TON STEAM ROAD ROLLER AND TRACTION ENGINE COMBINED.
MESSRS. GREEN AND SON’S 15-TON STEAM ROAD ROLLER AND TRACTION ENGINE COMBINED.
In Paris the Gellerat steam roller is used, and another is also known, which is manufactured by Messrs. Morland and Sons.
A 15-ton steam roller costs about 650l.in the first place, the cost of working it &c., has been given in theearly pagesof this chapter.
The advantages of steam road rolling may be summed up asfollows:—
(1.) The saving of wear and tear to vehicles and horses. Roads should be madeforthe traffic, and notbyit.[51]
(2.) Economy; as it is said that a saving of from 30 to 50 per cent. is effected by reason of the roads being better made thus obviating the necessity for such frequent sweeping and scraping.
(3.) The roads can be made or repaired at any season of the year.
(4.) The avoidance of cruelty to horses, cattle, and sheep, as in the case of newly metalled unrolled roads.
(5.) A saving of road metal. (a) Because it need not be broken so small. (b) Because there are no loose stones to be kicked about and lost. (c) Because there is no abrasion of the stones, only one surface of the stone being exposed. (d) Because no ruts can be formed in which water can lie to rot the stone. (e) Because a thinner coating of metal can be employed.
(6.) The roller can be advantageously used for other purposes.
(7.) Rolled streets have a better appearance, they are easier of traffic as having more evenness of surface and superior hardness, and it is contended that if steam rollers were more general there would not be such an outcry for other descriptions of pavement for roadways.
(8.) The steam roller soon finds out the good from thebad metal for roads, it is also contended that it also does this with respect to the gas and water mains, the latter, however may be looked upon as a rather doubtful advantage.
(9.) The avoidance of the necessity of the continued employment of men raking the metal into the ruts.
In Mr. Paget’s valuable little pamphlet upon the subject of steam rolling[52]may be found the followingremarks:—
“One of the main advantages attending the rolling of roads by steam-power, consists in the diminished proportion of mud or soluble matter which is then incorporated in the structure of the road surface. If the surface of an ordinary road that has not been rolled is broken up and the material washed, it is found that as much as half of it is soluble matter, mud, dirt, and very fine sand; the stones, having only been thrown loosely upon the road, have lain so long before becoming consolidated by the traffic, and have undergone in the meantime such extensive abrasion that the proportion of mud, dirt, and pulverised material in the metalling is increased to that extent, and the stones are really only stuck together by the mud. This accounts for the fact that although an unrolled macadamised road may indeed, after long use, have a surface that is pretty good and hard in dry weather, and may offer then a very slight resistance to traction, yet it will quickly become soft and muddy when there is any rain. By the employment, however, of a steam roller upon the newly-laid metalling of a macadamised road the stones are rolled in and well bedded at once, and the surface is thus consolidated into a sort of stone felt, capable of resisting most effectually the action of ordinary traffic, and containing the smallest quantity of soluble matter to form mud in wet weather.”
Having given the advantages of steam road rolling, I will now proceed to give the disadvantages.
(1.) The first cost; this to a small borough or town is often the great stumbling block. It is a pity that two or three of them could not join, and procure one between them at joint cost, thus avoiding the individually heavy burden.
(2.) The risk of damage to gas and water mains and services; or even of cellars under the streets in some of the older towns.
(3.) The interference to traffic whilst the roller is at work; the result is generally unsatisfactory if, to avoid this, the machine is worked during the night.
(4.) The noise and smoke.
(5.) The risk of frightening horses.
(6.) If too heavy a roller is used, the foundation of the roadway may be injured or the metal may be crushed instead of bedded.
(7.) The necessity of using so much binding material and water.
Before closing this chapter it will be necessary to say a few words upon rollers drawn by horses.
These are always unsatisfactory: they are expensive to use, as a large team of horses and a number of attendants are necessary; they are difficult to turn, and the horses’ feet displace almost as many stones as the roller compresses into their beds.
They cannot be of greater weight than 10 tons, even when on the hydrostatic principle, and they are clumsy and difficult of manipulation.
If a roller is to be used at all, let it be a steam road roller of the most modern description, and of the best manufacture.
[42]Vide‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. lviii. p. 95. (The first steam roller was made in the year 1864.)[43]The first steam roller used in England was, I believe, in the year 1872; in Paris about 1864.[44]This should be collected and “weathered” so as to get rid of mud and any organic matter in it.[45]In Paris 3 to 3·75 ton miles of roller are applied to every cubic yard of metal; in America 5 ton miles are thought necessary.[46]Vide‘Roads, Streets, and Pavements,’ by Q. A. Gillmore, p. 89.[47]VideAveling and Porter’s pamphlet on ‘Steam Road Rolling,’ p. 32.[48]VideAveling and Porter’s pamphlet on ‘Steam Road Rolling,’ p. 33.[49]Vide‘The Use of Steam Rollers,’ by A. W. Parry, Reading.[50]Some road surveyors contend that for gravelled roads 6-ton rollers are heavy enough, for macadam roads 12-ton rollers.[51]Traffic in making a roadway is apt to grind off the sharp edges and spoil the metal before it is set.[52]‘Report on the Economy of Road Maintenance and Horse Draught through Steam Rolling, with special reference to the Metropolis,’ by Frederick A. Paget, C.E., etc. etc., London 1870, to which I refer my readers for many scientific and useful facts upon this subject.
[42]Vide‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. lviii. p. 95. (The first steam roller was made in the year 1864.)
[43]The first steam roller used in England was, I believe, in the year 1872; in Paris about 1864.
[44]This should be collected and “weathered” so as to get rid of mud and any organic matter in it.
[45]In Paris 3 to 3·75 ton miles of roller are applied to every cubic yard of metal; in America 5 ton miles are thought necessary.
[46]Vide‘Roads, Streets, and Pavements,’ by Q. A. Gillmore, p. 89.
[47]VideAveling and Porter’s pamphlet on ‘Steam Road Rolling,’ p. 32.
[48]VideAveling and Porter’s pamphlet on ‘Steam Road Rolling,’ p. 33.
[49]Vide‘The Use of Steam Rollers,’ by A. W. Parry, Reading.
[50]Some road surveyors contend that for gravelled roads 6-ton rollers are heavy enough, for macadam roads 12-ton rollers.
[51]Traffic in making a roadway is apt to grind off the sharp edges and spoil the metal before it is set.
[52]‘Report on the Economy of Road Maintenance and Horse Draught through Steam Rolling, with special reference to the Metropolis,’ by Frederick A. Paget, C.E., etc. etc., London 1870, to which I refer my readers for many scientific and useful facts upon this subject.
It has been asserted that where a roadway has a traffic exceeding 1000 vehicles per diem, that to maintain it as a macadamised roadway is not economical.[53]However that may be, it is unquestionable that for very heavy traffic blocks of hammer-dressed stone, laid upon a concrete or hard gravel bed, have been in use for a great number of years, and indeed the Romans, who were great road makers, introduced the system (the Archaic, as it is sometimes called) into this country more than 2000 years ago; the size of the paving stones was, however, much larger than modern science finds necessary.
There is no doubt that a roadway paved with granite or whinstone setts, upon a hard concrete foundation, presents a most enduring pavement, costing but a few pence per annum in repairs[54]and cleansing, and in other respects it answers nearly all the requirements of traffic except in two very important particulars—it becomes very greasy and slippery under certain conditions of the weather after having been laid any time, and it is an intolerable nuisance in any great thoroughfare, from the incessant din and clatter arising from the wheels of vehicles and the iron shoes of the horses striking upon it; so great is the noise in some thoroughfares thuspaved, that tradesmen are compelled to keep their doors and windows tightly closed in order that they may be able to conduct their business, and it is known to injuriously affect the nerves and health of persons who are obliged to live in the vicinity of such streets. It is a bad pavement too for horses to travel upon, the jar upon the legs of the unfortunate animals soon telling upon them.
Great improvements, however, have in recent years been introduced to correct these faults. The setts are now made very narrow, about 3 inches in width, or 4 setts to 14 inches including the joints: this gives a better foothold for the horse, the hoof having but a little way to slip before being arrested by a joint; it also lessens the noise, and helps besides to prevent the edges of the stones becoming worn or the pavement wearing unevenly.
Running the joints with an asphaltic composition instead of ordinary grouting has also materially conduced to deaden the noise.
Taking the question of cost into account—and cost of this description of paving, be it remembered, is considerably affected by weight, when carriage of the stone has to be considered—the following sizes of stones may be taken as satisfactory.[55]
The following table,[56]showing the number of square yards that 1 ton in weight of different sizes of granite setts willcover, may be of use, but this must vary with the specific gravity of the stone employed.
The question of the best class of stones to employ as a paving material must to a great measure depend upon local circumstances, but it is important to select such stones as are very hard and durable, but which will not wear smooth and slippery nor round by reason of the chipping off of their edges.
Nearly all granites are suitable for this work, but Carnarvonshire syenite[57]is said to be the best material that can be used, although, being denser than granite, it is heavier and consequently more expensive.
At one time large quantities of paving stones were used in London and Liverpool which were brought from Bombay and China, as ballast for ships trading between those ports.
Mount Sorrel from Leicestershire and the Welsh stones are said to wear slippery[58]as well as porphyry, whereas the presence of felspar in the granite always keeps it rough under traffic.
Of the granites, that from Dalbeattie in Scotland is said to be the best.
The table on the next page, prepared by Mr. Walker in 1831, showing the wear of different stones, may be of interest.
Table showing the Result of Experiments made by Mr. Walkeron the wear of Stones in 1830-31, a period of 17 Months.
The Aberdeen granite as at present laid in the City of London, 3 inches wide by 9 inches in depth, has a life of about 15 years.[59]In the City of Durham whinstone setts of the same width last 17 or 18 years, in Manchester similar granite setts last 15 to 20 years. On this subject Mr. Deacon, the then Borough Engineer of Liverpool, has collected some most valuable information, and I refer my readers to a paper read by him before the Institution of Civil Engineers in 1879,[60]for a great deal of useful information on this and other subjects connected with roadways.
Various methods have been adopted for constructing granite paved streets, some of which I will proceed to describe.
One of the first really good granite pavements introduced into London was that known as the “Euston Pavement,” and it was constructed in the following manner: The foundation was shaped to the intended surface of the finished roadway; upon this a layer of coarse gravel was spread 4 inches in thickness, this was well rammed,[61]and upon it wasspread 4 inches of gravel mixed with a small quantity of chalk to bind it; this again being well rammed, upon it was placed a similar layer only composed of finer gravel, and upon this foundation the stones were placed, being bedded upon about an inch of fine sand. The stones used were Mount Sorrel granite, which were hammer-dressed and squared, 3 inches in width by 4 inches in depth; they were set close together at right angles with the lines of the kerb, they were then thoroughly rammed by the pavior. The whole surface was afterwards covered with screened gravel which was allowed to find its way into the joints and thus steady the entire pavement.
The following section will explain this.
Road section
In many cases the foundation is simply formed by shaping the soil to the required contour, and covering this with 3 or 4 inches of gravel or cinders, which is afterwards either rammed or consolidated by the traffic; upon this the setts are placed as closely as possible, the joints are then filled with fine gravel well worked in with a “cramming iron,” the whole surface being then covered with a grouting of lime and sand, which is brushed into the joints with a stumpy broom.[62]
In Leeds, Manchester, Salford, and many other important cities, I believe the foundations are formed in the manner just described, but of greater depth, the grouting also is a bituminous mixture, which I will presently describe, instead of the ordinary lime grouting.
The paved streets of Manchester are proverbial for their excellence, which is attributable to the manner in which the foundations of the streets are consolidated by the traffic before any setts are placed on them; in many cases the old macadamised surface of a street being utilised as a foundation, this process being almost identical with that recommended by Sir Henry Parnell fifty years ago.[63]
Where the traffic is heavy, however, a firmer foundation even than this is necessary, and up to the present time no better foundation has been introduced than that of good Portland cement concrete. This should be at least 9 inches in thickness, and be composed of one part of Portland cement, two parts of clean sharp river sand, and four parts of clean river ballast, or broken stones, or other suitable material. The surface of the concrete, after having been placed in position, should be smoothed over with the shovel, so as to present the proper convexity and have an even surface for the granite setts to be bedded upon.
Another description of foundation now very extensively used where the traffic is heavy, is that known as “Bituminous Concrete,” which is made as follows:
The ground being excavated to the proper depth and contour, broken stone as for macadam is spread for a depth of6 or 9 inches; this is then levelled and thoroughly rolled with a light roller, a boiling mixture of pitch and tar, or creosote oil is then poured over the whole surface until every interstice is filled, when a thin layer of small broken stone is spread upon it, and then well rolled until it consolidates.
It may be well to observe here that in all works involving concrete foundations and paving in streets, the traffic should be entirely stopped if at all possible. Streets paved half at a time are never quite satisfactory, and the concrete should have at least a week to set before the pavement is placed upon it.
Upon a foundation of either Portland cement or bituminous concrete, the granite setts themselves should be grouted with a bituminous mixture instead of cement or lime grouting. This renders the pavement more impervious to moisture, makes it less noisy, and adds considerably to its strength; the mode of applying it is nearly similar to that of ordinary grouting. The setts are placed on about an inch of sand and well rammed, the boiling mixture is then poured over the whole surface, which is then covered with a thin coating of small, sharp gravel.
The following table of the proportions necessary for the bituminous mixture may here be of use.
Proportions for Bituminous Mixture.[64]
The objections to this method of paving are only temporary: the nuisance arising from the fumes of the boiling mixture whilst it is being applied, and the necessity for dryweather to make the operation successful. Healey’s Patent Pitch Boilers[65]are said to moderate, if not entirely to do away with the former, and the latter can be arranged by only doing the work at favourable seasons, or if the worst come to the worst, to cover the work with tarpaulins raised on trestles.
Before closing this chapter I should like to draw attention to the question of provision for wheel tracks, or tramways paved with stone, asphalte, or other hard material, and a track for horses giving a firmer foot-hold, similar to those so highly spoken of in Milan and other Italian cities. An excellent description is given of them by Mr. P. le Neve Foster, Jun., in an appendix to a report on the Application of Science and Art to Street Paving and Street Cleansing of the Metropolis (1872).
The roadway where stone tramways are employed cannot be of convex section; on the contrary, it should be concave, with the channel, gutter, or water table in the centre. This is in itself an obvious advantage, and I trust that the question of these tramways may at some future date receive more attention from English engineers; the great objection to them in this country being that the smooth tram-track would be very slippery and apt to throw horses down when passing on and off, but they have many advantages which should not be passed over without consideration.[66]
[53]Birmingham in 1854 had not, I believe, a single mile of paved streets; the principal ones are now nearly all paved with granite setts, and over 20,000 square yards were so paved in 1880.[54]It is said that the cost per annum per square yard of granite paved roadways is but 3d., whereas the same cost for macadamised roadways under the same circumstances is 1s.6d.[55]In Paris after considerable research into the question, the engineers of the Ponts et Chausseés, decided that the size of the paving stones, which used formerly to be 9 inches square should be 4 inches wide by 6¹⁄₄ inches long by 6¹⁄₄ inches deep, the stone that is used being a grit sandstone, from the forest of Fontainebleu.[56]Vide‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. lviii. p. 66.[57]Syenite is a hard, greenish-grey metamorphic rock, composed principally of silica, alumina, and lime, in conjunction with magnesia, iron, etc. Its specific gravity is 2·96.[58]Mr. Boyle, District Surveyor of Manchester, says: “I would caution you against the use of the old blue Penmaenmawr stone as being an extremely slippery stone, and one which makes a dangerous pavement.”Vide‘Proceedings of the Association of Municipal and Sanitary Engineers,’ vol. iii. p. 58.[59]The old granite paving of London used only to last eight years.Vide‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. ix. p. 222.[60]Vide‘Street Carriageway Pavements,’ by George Frederick Deacon, M. Inst. C.E., ‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. lviii. p. 1et seq.[61]The pavior’s rammer is about 55 lb. in weight, with an iron ring at its foot; this is swung with some dexterity between the legs, and is allowed to fall with great force upon the earth or stones it is in use upon.[62]The usual specifications for the Guidet paving blocks (in New York) require that they shall be of granite, equal in hardness to the Quincy granite, of durable and uniform quality, each measuring not less than 3¹⁄₂ nor more than 4¹⁄₂ inches in width on the upper surface or face, and not less than 10 nor more than 15 inches in length, and not less than 8 nor more than 9 inches in depth. Blocks of 3¹⁄₂ inches in width on the face to be not less than 3 inches in width at the base; all other blocks to measure on the base not more than 1 inch less in width or in length than on the face. The blocks are set upright in close contact on their edges in courses, with the longest dimensions and the continuous joints running across the street, breaking joints lengthwise of the street.The ends of the blocks are dressed off so as to give close joints in the direction of the draught, while the broad vertical sides of the blocks are left rugged or uneven, or with the split rock-face so that the continuous joints running across the street are somewhat open.Vide‘Roads, Streets, and Pavements’ by Q. A. Gillmore, p. 157.[63]Vide‘A Treatise on Roads,’ by Sir Henry Parnell, p. 130.[64]As these ingredients often vary very much in their constitution, the surveyor must use his judgment to a great extent as to these proportions.[65]These boilers are now much used for such purposes, they hold from 60 to 500 gallons and are light and portable; the temper of the bituminous mixture also remains uniform whilst being drawn off, and there is very little evaporation or waste arising from them.[66]Since writing the above, the Liverpool and Manchester tram-road was designed I believe on this principle.
[53]Birmingham in 1854 had not, I believe, a single mile of paved streets; the principal ones are now nearly all paved with granite setts, and over 20,000 square yards were so paved in 1880.
[54]It is said that the cost per annum per square yard of granite paved roadways is but 3d., whereas the same cost for macadamised roadways under the same circumstances is 1s.6d.
[55]In Paris after considerable research into the question, the engineers of the Ponts et Chausseés, decided that the size of the paving stones, which used formerly to be 9 inches square should be 4 inches wide by 6¹⁄₄ inches long by 6¹⁄₄ inches deep, the stone that is used being a grit sandstone, from the forest of Fontainebleu.
[56]Vide‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. lviii. p. 66.
[57]Syenite is a hard, greenish-grey metamorphic rock, composed principally of silica, alumina, and lime, in conjunction with magnesia, iron, etc. Its specific gravity is 2·96.
[58]Mr. Boyle, District Surveyor of Manchester, says: “I would caution you against the use of the old blue Penmaenmawr stone as being an extremely slippery stone, and one which makes a dangerous pavement.”Vide‘Proceedings of the Association of Municipal and Sanitary Engineers,’ vol. iii. p. 58.
[59]The old granite paving of London used only to last eight years.Vide‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. ix. p. 222.
[60]Vide‘Street Carriageway Pavements,’ by George Frederick Deacon, M. Inst. C.E., ‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. lviii. p. 1et seq.
[61]The pavior’s rammer is about 55 lb. in weight, with an iron ring at its foot; this is swung with some dexterity between the legs, and is allowed to fall with great force upon the earth or stones it is in use upon.
[62]The usual specifications for the Guidet paving blocks (in New York) require that they shall be of granite, equal in hardness to the Quincy granite, of durable and uniform quality, each measuring not less than 3¹⁄₂ nor more than 4¹⁄₂ inches in width on the upper surface or face, and not less than 10 nor more than 15 inches in length, and not less than 8 nor more than 9 inches in depth. Blocks of 3¹⁄₂ inches in width on the face to be not less than 3 inches in width at the base; all other blocks to measure on the base not more than 1 inch less in width or in length than on the face. The blocks are set upright in close contact on their edges in courses, with the longest dimensions and the continuous joints running across the street, breaking joints lengthwise of the street.
The ends of the blocks are dressed off so as to give close joints in the direction of the draught, while the broad vertical sides of the blocks are left rugged or uneven, or with the split rock-face so that the continuous joints running across the street are somewhat open.Vide‘Roads, Streets, and Pavements’ by Q. A. Gillmore, p. 157.
[63]Vide‘A Treatise on Roads,’ by Sir Henry Parnell, p. 130.
[64]As these ingredients often vary very much in their constitution, the surveyor must use his judgment to a great extent as to these proportions.
[65]These boilers are now much used for such purposes, they hold from 60 to 500 gallons and are light and portable; the temper of the bituminous mixture also remains uniform whilst being drawn off, and there is very little evaporation or waste arising from them.
[66]Since writing the above, the Liverpool and Manchester tram-road was designed I believe on this principle.
In the year 1843 Mr. Charles Cochrane, the President of the ‘Association for the promotion of Improved Street Paving, etc.,’ in a paper which he read before the Institution of Civil Engineers, on the State of the Streets of the Metropolis, said that there existed at that date 100,000 yards of wood pavement.[67]He further states that it is said to be slippery, but that he approves of it as the best material hitherto used, “both as regards its general economy and durability as well as its facility of traction, and more especially its extreme cleanliness.”
Two years previous to this date, Mr. Edward Lomas condemned wood pavement as slippery, and recommended granite pavement for horses with wood tram-tracks for the wheels of vehicles.[68]
Since these dates the question of wood paving has made giant strides, many companies and private firms having started business as wood paviors, with many various methods, which they strongly advocate as being superior to the others; amongst them I will enumerate and describe the following:
—The ground being consolidated, a layer of sand is made the basis of the pavement, and assumes the shape the surface of the street is intended to take. Red-wood boards 1-inch in thickness are then laid across the roadway, from kerb to kerb, placed together so as to break joint; boards of the same material andthickness are then laid longitudinally, and breaking joint in the same manner.[69]On this foundation red-wood blocks are placed in rows, taking the same direction as the under flooring.
Between each row of blocks, a strip of wood ³⁄₄ × ³⁄₄ inch is nailed to the block and flooring, the blocks in all cases breaking joint; the spaces thus formed between the rows of blocks are then run with a thick composition which fills all vacant spaces there may be between the strip and the block, covering the strip about ¹⁄₈ of an inch. Gravel, dried and sifted through ³⁄₄-inch mesh, is then put in, solidly rammed, and composition poured in; the pavement is then covered to a depth of ¹⁄₂ an inch with dried gravel and composition for the purpose of indurating the surface, and filling the spaces flush with the top of the block, a slight covering of sand is then spread, when the traffic may immediately pass over.
—After the ground is properly prepared, 6 or 9 inches of concrete is laid, on this is laid a bed of asphalte not less than ¹⁄₂-inch in thickness; then wood blocks 3 by 8 by 5 inches or 3 by 9 by 5 inches, of good, sound, yellow Baltic timber are laid with joints ¹⁄₂-inch in width, these joints are filled from 2 inches up with heated asphalte, the remaining 3 inches being filled with a grouting of hydraulic lime, and clean, sharp, fine river grit or sand, the whole being covered with a top dressing of fine, sharp sand, which wears in with the traffic.
—Upon a bed of concrete, cross grained planks were to be placed side by side and be forced together by pressure so as to form a compact homogeneous surface of wood.[70]
—The special feature of this system is thatPitch Pineblocks are used laiddirectupon the concrete foundation, the blocks being grooved on each side so that the grouting (composed of Portland cement) shall run in and form a key.
—This system consists of a concrete foundation, upon which strips of wood 2 inches wide by ¹⁄₂ an inch in thickness are laid. Upon these, wood blocks 3 inches in breadth are placed, and then hot asphalte is poured into the joints, which conglomerates the whole.
—The main feature of this patent consists in placing common felt on the concrete bed, and between the joints of the wood blocks; thus, it is contended, giving elasticity and allowing for the expansion and contraction of the blocks. The blocks are also bevelled on the top and grooved in a particular manner.
—In this case the blocks are cut 4 inches wide by 9 inches long, and 5 or 6 inches deep, according to the traffic; these blocks are shaped with alternate convex and concave ends, and are laid on a bed of sand about 2 inches thick, the joints between the blocks, which have been left about ³⁄₈ inch wide, being filled with a grouting of lime and sand.
method of laying wood paving is to form a foundation of concrete, varying in thickness according to the nature of the subsoil and the traffic; then to pave with blocks of yellow deal, 3 inches wide and 6 or 7 inches deep; the joints, which vary from ³⁄₈ to ¹⁄₂ inch, are filled in with sand and lias lime, and the surface is afterwards indurated by strewing it with shingle.
—This company lays claim to the speciality of using hard woods as well as pine, and that the pine blocks they employ are preserved or mineralised so as to be more durable than the wood in its natural state.[71]
—This is principally in use in the United States, and consists of rectangular blocks of pine laid upon a close flooring of pine boards, 1 inch thick, laid lengthwise with the line of street, their ends resting on similar boards laid transversely from kerb to kerb, the boards being thoroughly tarred and laid upon a bed of sand. The joints of the wood blocks are run with an asphaltic mixture, and the whole surface is finally covered with hot coal tar and sprinkled with fine sand and gravel.
—This is also American, the blocks resting directly upon sand or gravel about 6 inches in thickness.[72]“The blocks are set in courses transversely across the street, so as to break joint lengthwise of the street, the courses being separated from each other 1 inch by a continuous course of wooden wedges placed close together edge to edge, and extending from kerb to kerb. These wedges are set in the first instance with their tops flush with the top surface of the blocks. After the whole pavement shall have been well rammed, so as to give each block a firm bed, the wedges are driven down about 3 inches, and the open joints thus formed above them between the courses are filled in with a concrete composed of hot coal tar and fine roofing sand and gravel. The surface of the pavement may then be coated with coal tar prepared by boiling with pitch, and finished off with a thin layer of sand.”
—Mr. P. Marshall, the City Surveyor of Norwich, states[73]that the wood pavement in that city is “simply laid on the road formation levelled up with shingle. The blocks are grouted in with blue lias lime and well rammed down. This makes a splendid road, and is superior to any portion of the road that has been laid withconcrete. This wood paving, 5 inches deep, laid as described, costs 7s.per yard super. We have had some down here now for 2 years, and have had no settlement whatever. It is a very important matter, for it makes wood paving possible for country towns.”
—This pavement consists of composite blocks 12 inches by 15 inches, cast in iron moulds with two rows of wood placed at an equal distance from either side and each other, the vacant spaces being filled with granite broken as for macadam; over all is poured a boiling composition of pitch, chalk, and sand. The blocks are thus treated at the works, and are, when cool, taken to the street, laid on a concrete foundation, and grouted with cement grouting.
—This is composed of blocks sawn at an angle of 60°, the grain of the wood running in the same direction. Each end of the block rests on the other, transversely to line of street. Between the rows of blocks a plank, the same depth as the blocks, but with the grain of the wood horizontal, is placed. The blocks, which on one side of the plank lean in an opposite direction to those on the other, are secured or dowelled together by wooden pins running through the plank and piercing the blocks about an inch.
In Chicago, U.S.A., cedar blocks 6 inches square, set on a composition of tar and gravel, are used, and are said to make a very durable pavement.
The following sanitary objections to wood as a material for pavements are made in the Report on the Application of Science and Art to Street Paving and Street Cleansing of the Metropolis (1872) page 17.
“The General Board of Health set aside wood as an ineligible material for this amongst other reasons, that street surfaces ought to be impermeable; and for roads of light traffic and cheap construction, they looked to modifications ofmacadam, with bituminous binders of mineral tar. Since then wood has been reproduced for the purpose, and strongly pressed in improved forms for trial. It certainly offers the advantage of a great gain in noiselessness over granite, more especially from the horses’ feet, though with some disadvantage from a dead rumble and vibration; and further it has the advantage of being more available than smooth pavements for inclines. But hygienists object to its use on grounds which, in the absence of sanitary science, are overlooked, but which it is important to particularise as showing the dangerous state of ignorance and incompetency of the authorities by whom they are not entertained or are disregarded.”
The sum total of these charges against wood as a pavement consists in the following: “Wood is porous, it is composed of bundles of fibres, it absorbs and retains wet, foul wet especially.” Whyfoulwet should be absorbed more than ordinary wet does not transpire.
There is no doubt that wood in its natural state does absorb a large quantity of water,[74]but this can be avoided in wood paving by preserving the wood of which it is composed by one of the following processes.
The fibres of the wood are also compressed, and no open joints between the blocks are permitted, by paving the blockstransversely, with butt joints closely packed together, and by filling the cross joints with an asphaltic or other impervious grouting.
Wood paving should, however, be laid in streets with moderate traffic, and plenty of sun and air. In confined spaces such as courts, it soon rots and becomes a source of much unhealthiness.[75]
Many reports have been from time to time made on the advantages and disadvantages of wood paving, and much has been said and written upon the subject, so that I will only touch upon some of the principal questions at issue.
The first of importance is that of durability, and although the life of a hard wood constantly exposed to attrition is amazing, as may be seen on the stairs of the Metropolitan Railway Stations, and in many cog wheels of old machinery, still some diversity of opinion exists as to what may be fairly put down as the wear per annum of the surface of a street paved with wood blocks.
It must be remembered that to arrive at any fixed ratio of wear, a standard of traffic should be fixed; but this unfortunately has not hitherto been done, so that the results of observations are bound to differ considerably. It must also not be lost sight of that the reason of excessive wear in a wood pavement generally arises from wide joints being the means of causing the edges of the blocks to abrade and become worn.
Mr. D. T. Hope, in a paper he laid before the Scottish Society of Arts, upon some most careful investigations he had made on this subject, gives the wear as ¹⁄₈ of an inch in 18 months on blocks laid with vertical fibre, which he proved was the best manner of laying them to ensure the longest life.
Mr. Deacon estimated the wear at from 1³⁄₈ inch to 2⁵⁄₁₆ inches per annum.[76]
Mr. Copland estimated the wear at ³⁄₁₆ of an inch per annum.[77]
Mr. Howorth estimates the life of wood paving at 25 years per inch of wood, if an absolutely uniform quality of wood fibre could be assumed.[78]
Mr. Haywood says,[79]“Wood pavements with repairs have in this City (London) had a life varying from 6 to 19 years, and that with repairs, an average life of about 10 years may be obtained.”
The life of wood is no doubt extended by being preserved by one of the processes I have enumerated, but as its life may be taken as an average of 8 to 10 years, and as the blocks are bound to wear unevenly, they should be made as shallow as is consistent with stability; as it is an undisputed fact that the foundation of a roadway is the important carrier of the traffic, the surface material, of whatever it may be constructed, only acting as a skin to preserve it. If the blocks are too thick, unnecessary capital is locked up.
Wood pavement was laid in Sunderland[80]in 1859 with strips of creosoted red pine, creosoted beech wood, and unpreserved oak, the bulk of the paving being unpreserved red deal, and this was replaced in 1867.
In 1877, on renewing the pavement, it was found that the creosoted wood suffered less from wear and tear than the unpreserved, so the whole was done with creosoted red pine,the original strip of creosoted red pine was left untouched, the strip of oak was turned, and the beech was merely raised; and there is no doubt that the best wood pavement is that which can be constructed in the simplest manner, as for instance deal blocks 4 or 5 inches deep, laid with a close joint upon a Portland cement concrete bed, the blocks being well grouted in with Portland cement grouting, their surface being afterwards sprinkled or strewn with sand or sharp gravel.
The woods employed for paving are beech and oak, both of which are said to be too slippery, elm, which is not durable, pitch pine and Baltic fir. Memel and Dantzic timber is better than Riga, the best wood for the purpose being said to be Wyborg or St. Petersburgh red deals.
All sappy wood must be at once rejected as unsuitable. This is a great objection to creosoting or other preserving processes, as it hides defects in the wood.
The advantages of wood paving may be summed up asfollows:—
(1.) It is the quietest of all known pavements, wheels make scarcely any noise upon it and there is no clatter of horses’ hoofs.
(2.) It is much safer than either asphalte or granite pavements for horses travelling upon it and if a horse falls he can rise more easily.
(3.) The traction necessary upon it, though slightly greater than upon asphalte, is compensated for by the better foothold given to horses.
(4.) It is clean. If well constructed there should be no mud made upon it; all that appears upon its surface should arise either from its being imported upon it, or from the gravel with which it is sometimes necessary to dress the surface.
(5.) It presents a uniform and slight elasticity, which is of great benefit to vehicles passing over it.
(6.) It may be laid on a gradient of 1 in 20 with safety to the traffic.
The principal objections to wood as a pavingare:—
(1.) It is said to absorb moisture and to smell offensively, but this has often been refuted.[81]
(2.) It is said to be difficult to cleanse without the aid of water, as dirt adheres to the wood, and lingers in the joints.
(3.) It is not easy to open it or repair it, for the purposes of gas and water pipes, etc., and rather a large surface has to be removed for this purpose, and it has to be left a little time after repairs before traffic is again allowed on it.
(4.) The wood swells if wet, and cases are on record of the side kerbs of streets being raised, and lamp posts thrown down, by the pressure of the wood thus swelling.[82]
With regard to the cost of wood paving. This must vary in different localities, according to the value of labour, of materials, and in the manner in which the work is done.
The practice of most of the companies engaged in this class of work is to make a fixed charge per square yard for the pavement, including the concrete but excluding the excavation, and they also guarantee to keep the pavement inrepair free of charge for one or two years, and then for so many years after, at so much per yard per annum.
About 14s.per square yard is generally the first charge for constructing, and 1s.per square yard is the annual charge for maintenance.
Upon the subject of cost the following tables[83]may be useful.
Table showing the Actual Duration and Costof certain Wood Pavements in the City of London.
Table showing First Cost, and Tendered Cost per Annumfor Maintaining Certain Wood Carriageway Pavements in the City of London.