The Paving of Roadways.*
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It would be difficult to discover when and where the first roadway was constructed, for in prehistoric times man was always a social or a fighting animal, and therefore for both reasons men desired to reach one another as readily as possible. 'lite beating of a way through forest land was no doubt the first suggestion fur roadways, and when it came about that heavier loads than man could conveniently be made to carry had to be transferred from one place to another, it naturally suggested itself to the minds of men that the most sensible thing was to make a permanent highway. Roads existed before cities, and even in our own country we have the remains of the ancient roads that intersected the country. We have the Regina Viarum, the Appian Road, and, before these, India, Egypt, Greece, Italy, with their old civilisations, had their fine main roads from the city to city and across vast stretches of country. some of these roadways, such as that constructed by the Carthaginians, were composed of a solid intessellation of granite blocks. The Grecian roads were of less massive construction than the Roman, consisting for the most part of oblong blocks. The Romans were, huwever, essentially the road makers of the ancient world the roadways chiefly consisting of gravel and beaten stone, the surface being slightly arched. As throwing some light also on the origin of roads it may be mentioned that the Via Salaria, the earliest Roman road, was constructed for the convenience of bringing salt to the city of Romulus from the salt works. This salt-work road ultimately led to the construction of the Appian, Flaminian, and sEntilian roads. The office of Curator Viarum, a road surveyor, was bestowed upon the most illustrious members of the Senate, and it may be some satisfaction to those present to know that Pliny the Younger once held the office of Commissioner of Sewers on the sEmilian Road—while after his victory at Mantinea Ersaminondas was appointed chairman of the Board of Scavengers at Thebes. Not only were these Men great road makers, but to carry their roads the most direct mete, mountains had frequently to be pierced and bold arches thrown across rivers.
I need not linger any longer on these days of antiquity, but will come down to more recent times, when the unsatisfactory state of the roads and their neglect induced Parliament to introduce an Act authorising a small toll to pay the expenses of upkeep. This was in Charles the Second's reign. To illustrate the conditions of roads at an earlier period, the death of Queen Elizabeth was not known in some of the remote villages of Devonshire until the courtiers of James had ceased to wear mourning for her; the Hebrews of York heard of the massacre of their people in London, at Richard the First's Coronation, six weeks after the event. The distribution of news was then dependent on the state of the roads, and their condition may he pretty well gauged by the incidents referred to. After the decline of the fine Roman roads, generations appear to have passed before great attention was paid to their upkeep. In fact, from the time of the Romans to the year 1688, matters of greater moment occupied the people's attention—foreign invasions and internal disagreements being the chief. In 1285, however, the first Act of Parliament relating to roads was passed. In the reign of henry VIII, the first important attempt at improvement was made by an Act allotting to parishes the care of the roads passing through them and appointing road surveyors. The funds were to be obtained from a pound rate, levied on the land holders, and assistance in labour was enforced:1E From this period we may pass along to the beginning of the macadam era. Macadam laid it down as a principle that "a road ought to be considered as an artificial flooring, forming a strong, smooth, solid surface, at once capable of carrying great weights, and over which carriages may pass without meeting any impediments." The limit of roadways at this time was soft., footpaths being daft. wide. For turnpike roads, however, approaching a populous town the prescribed width was dolt. It will not be inappropriate to this review of the subject to reproduce the exact method suggested by Macadam. Thie was to spread broken stones 2in. in diameter, equally, so as to form a layer about loin. thick over the road surface, after it had been levelled and properly drained. 'Phis system was principally applied to roads already made, and no new materials were to be brought to the road, unless in the absence of a quantity of clean stone equal to a thickness of loin. The old stone material was removed, carried to the roadside and broken to such a size that no piece exceeded doz. in weight. The road was laid as flat as passible, leaving'a fall of 3in. from the middle to the sides. In order to regulate the size and weight of the stones, the former not exceeding tin, longitudinally, and the latter as stated, iron sieves with circular holes were employed. The figure given as
the cost of preparing and newly-forming a rough road to a depth of 41n., is about a penny to twopence per square yard. No grouting or binding material was to be used. When this system was first introduced, most of the granite pavement of the principal thoroughfares of London was taken up and broken, and the road macadamised; but the alternate dust and mud which this kind of paving generated, soon suggested a change. It may be remarked that this method of dealing with roads had nothing novel about it, except that Macadam was the first to adapt it to Eng'ish roadways. The idea of breaking stones had long beee in use in Sweden, Switzerland, and other countries, and such roads were very extensively laid in different foreign countries long before Macadam introduced them into this country.
The next development in road-making was effected by Telford, who did his first work in this direction on the Highland roads of Scotland, and no less than 920 miles were laid out under his direction. His method was to lay "on dry-bottomed ground, gravel of a proper quality, out of which all stones above the size of a hen's egg shall have been previously taken, to a depth ofisrin in the middle, and gin. at the sides ; and the stones which are taken out of the gravel, and do not exceed 410. in size, may be laid for that thickness below the gravel, and ih that case loin. only of cleansed gravel will be required." Special directions were also drawn up by him in the event of the groyne being soft or swampy, while great consideration was given to the matter of drainage. In 18'6 Telford undertook the work ot improving the road from Glasgow to Carlisle. The method adopted in this case differed from that first referred to. Here the metalling was to consist of two beds or layers, viz. :—a bottom course of stones, each yin, in depth, to be carefully set by hand, with broadest end downwards, all cross-banded or jointed, and no stone to be more than sin. wide on top—these stones to be either good whinstone, limestone, or hard freestone; the vacuities between to be carefully filled with smaller stones packed by hand, so as to bring to an even and firm surface; the tor; course or bed to be yin. in depth, to consist of properly broken stones, none to exceed fox, in weight, and each to pass through a circular ring 24in. in diameter in their largest dimension— these to be of hard whinstone, the quality of both bottom and top metal to be determined by the inspector. Over the upper bed, or course of metal, to be a binding of gravel of lin. in thickness upon an average ; the cross section of the finished roadway to have a curvature of 6in. in the middle raft., and from that on each side a declivity at the rate of half an inch in a foot, to within r8in, of the fences; the remaining space of ain. to have a curvature of sin., making in all about gin. on each side below the finished roadway. To keep this road iii repair after it was made required at least 8o cubic yards of broken stone per mile, and at the most 120 per annum, the cost of which varied from ‘20 to L46 per mile.e
Since this period there was little change in the manner and method of paving until we come to the time when new forms of paving material began to he introduced, and modern requirements demanded qualities and conditions not previously insisted on. Each of these different descriptions of paving materials will be dealt with in their proper place.
Tar Macad am.
The use of tar macadam is by no means a new form of paving, for Nottingham, to quote one place alone, had one important roadway, London Road, Broadway, laid with it, so far back as 1840, and it was referred to in detail, in the paper read by Mr. Arthur Brown, A.M.Inst.C.E., Borough Engineer of Nottingham, in the year 1884, before the Association of Municipal Sanitary Engineers and Surveyors.
The method of doing the work, he said, has been greatly improved, and it is now (that is 1.8841 uniformly done on the following principle :—A bed of tarred round gravel or ironetcne slag. riin. or sin, thick, is laid for a bottom coat, and the upset coat from rim to 'kin. thick of fine ironstone slag, limestone or granite screenings. These materials are well dried on a floor of heated iron plates, and mixed with a composition of pitch. tar, and creosote oil; each layer is well rolled, and the top coat is sprinkled with spar. It is of the utmost importance that the slag, etc., should be perfectly dry, and that the pitch, tar, and oil should be of the best quality. At this time also there were about 185,000 square yards of asphalt macadam carriageways in the borough of Nottingham, of which about '130s000 yards had been laid between 188° and i885. Since that time a very large area of roadways has been laid on this system.
To put the matter briefly, the advantages of tar macadam over ordinary macadam are:—economy in upkeep ; the ensuring of a solid surface ; the prevention of dust, consequently mud; and
increased facility of traffic. It will be recognised how amenable to the production of these disagreeable elements ordinary macadam is, when it is stated that in one mile of roadway of in yards width, no less than 6cio tons of sand, or similar material is used as the cementing agent to bind the stone together. Now, in view of the change that is gradually, but surely, coming over toe traffic in the country, this is a very important matter, and it is here that tar macadam, said to possess non-dust making qualities, shows its advantage and applicability. The method of preparing and laying tar macadam will bring out these characteristics. The granite or limestone is, after being broken to the proper sizes, treated with a composition of tar, etc., which penetrates below the surface; this acts as a preservative and as a deterrent of dust, seeing that the material is not affected by climatic influences, while it should form a very sanitary pay:ng. The roadway itself is formed of three layers of material. The foundation consists of stones of about sin, laid to a depth of 41in. to 5in. ; this is thoroughly 7-olled, and another layer put on with stones gauged to pass a three-quarter ring, and this, after being rolled, is followed by a grouting of 'Jim material. The whole surface is then rolled until thoroughly consolidated, so that a solid mass of tarred macadam is the result. It appears to me that such a paving must offer many advantages over ordinary macadam, especially in the directions already referred to, namely, its less liability to dust, its economy of upkeep, its great sanitarirress, and longer life.
Stone and Composite Paving.
The method of laying roads on Macadam's erinciples, or what is known as macadamising, has already been referred to, This was once the only method of paving roads and streets, even in London, and although his ideas have been modified, the fundamental principle is retained, and what are termed macadamised roads are the most extensive among paved highways. During the last few year-a, however, different methods have been introduced for treating the material by immersing in tar or pitch. while the system of laying has also undergone considerable change. It is, however, still known as macadam, although the material employed is now frequently limestone or slag instead of granite. On the point of a suitable stone for road paving, Mr. Thos. Aitken gives, in his well-known book, the qualities which should be possessed by it :—Iiardness, or that disposition of a solid which renders it difficult CO displace its parts among themselves ; toughness, the quality by which it will endure light but rapid blows without breaking ; weather resistance, nonliability to he a.ffected by the weather; and binding properties. A new method of armouring macadam roads, which is in use on the Continent, and is being introduced into this country by Messrs. Brunton and Trier, of r, Great George Street, is also worth great consideration. This was fully described in the municipal journal, " The Street," in October, and from this I reproduce particulars. The honour of first trying the road covering in question belongs to Baurath Gravenhorst, of Stade, in the provinse of Hanover, who many years ago showed that the destruction of road metal spread in the usual manner is chiefly caused by the stones, which vary so greatly in shape, size, and strength, crushing each other under the pressure of the traffic. To avoid this, he selected stones of approximately equal size and cubical shape, and placed thera singly side by side on the carefully levelled and rolled surface of the old road. The result was a mosaic-like covering, which proved to be of extraordinary durabiiity. The next step was to increase the size of the stenes, and make them specially for the purpose, the two sizes now in general use being 34-in. by din,, and ain. to 41in. in depth. It is important that the depth of the stones should not vary much, but otherwise no great regularity is required, even stones with triangular heads being used. After removing as little as possible from the surface of the road, it is levelled and rolled, and the stones placed in position, sand being used sparingly and only for the purpose of bringing up the shallow stones to the level of those of full depth. Sand is then spread over the surface and allowed to remain for some days, so as to work into the joints. Many of these roads in Wiesbaden have been down six years, and show practically no signs of wear ; whilst in other parts of Germany there are roads with a 12 years' record. Basalt, being the cheapest local stone, is used on the roads shown, although it is by no means the best stone for the purpose, owing to the liability of a considerable percentage of the setts to disintegrate, and of the others to wear smooth and flake all round the edge. Owing to the small heads of the setts and the numerous irregular joints, the new paving affords excellent feethold, and is used on steep inclines with success. Granite and similar stone is far preferable to basalt for small sett paving. The roughness of the heads of the small setts wears off under the traffic, leaving an even surface, over which the wheels pass as easily as over asphalt, but affording an incomparably better foothold, without becoming slippery in damp weather. The most important application of the new pavement is undoubtedly the armouring of old macadam roads ; but it is also being used on new roads with concrete foundation, and for replacing large setts—as affording a better foothold, requiring much less tractive power, and being far less noisy than the latter. The small setts placed in sand have been found as stable and durable as when set in cement, mid it is billy in towns and for hygienic reasons that they are laid in a dry mixture of three parts sand to one of cement, and afterwards watered ; or the joints may be filled with pitch. The advantages of the new road armouring are said to be :HI) Durability ; (a) Absence of dust and ease of cleansing; (3) Excellent foothold ; (4) Reduced resistance to traction, compared with large granite setts ; (s) Noiselessness, approximating to the noise of traffic on asphalt ; f6) Low first cost, which varies according to locality—the entire cost of paving the Wiesbaden roads on this system being ss. per superficial metre. Mr. Ifeward Humphreys, the well-known consulting engineer and road expert, who visited Germany recently in the interests of road improvement, speaks very highly of this method of paving.
The essentials of a perfect paving may be summed up as follows 7—It must have a perfectly solid foundation; it roust be non-absorbent ; it must have a smooth and even surface, offering the least resistance to traction; non-slippery, noiseless, durable ; net subject to expansion or contraction ; easily cleaned and repaired ; and lastly, we may say, it should have a pleasing appearance. This is, of course, an ideal which has never yet been attained, and I do not suppose ever will be. Paving may be said to be " what it is—where it is" ; by which I mean that the value of any for in of paving is according to its suitability to the locality in which it is used, and to the traffic which has to pass over it. It would be entirely out of place, for instance, to lay dawn a road of softwood paving in the vicinity of docks where a very heavy and continuous traffic has to pass over it, and to condemn it as a bad form of paving because it wore out so rapidly. In the selection of a paving material every condition
to which it has to be subjected must be thoroughly considered. There are few, if any, materials which are adaptable to every purpose, and there is no standardisation of paving materials by which one can make a selection for a special set of conditions ; choice must be decided by experience. I shall hope to be able to do something in this paper towards simplifying the problem which every surveyor is confronted with, and as an appendix to the list of essentials of a paving already given, a table is given below which shows the comparative qualifications of different paving materials now on the market. This table appeared in an official publication issued from the Office of the Agent-I;eneral for Western Australia some three years ago:— There are different descriptions of asphalt. Mineral ruck asphalt is a natural product, a pure limestone impregnated with mineral bitumen. Asphalt was first introduced into London for roadways in the year 1869, having been adopted in Paris 35 years previously. The three chief descriptions of asphalt are :— Val de Travers, obtained from Switzerland; Seyssel from France ; Lirnmer from Hanover ; and there is also another. of which we have heard, known as Trinidad Lake Asphalt (which is Trinidad Lava). Those chiefly used in London arc Val de Travers, Linoner and French. These asphalts are chiefly used in the compressed form. The rock asphalt is broken Into cubes of about three inches, and then pulverised in a disintegrator, and reduced to fine powder, which must be capable of passing through a sieve having a mesh of about _zo as inch, then placed in specially-designed roasters with revolving cylinders, and heated to a temperature of about 28o degrees Fahrenheit. Asphalt is undoubtedly a fine pavement for level thoroughfares, and, although it is more slippery than any form of paving, it has, when properly prepared and laid, a smooth, even surface, is impervious to moisture, and easy of traction. Moreover, it is very durable, and is rapidly laid and repaired. It also forms a very sanitary pavement. In all paving operations the foundation is the true roadway, and the surface is the veneer or cusnion, whether it be of asphalt, hardwood, softwood, or other material. To make a good asphalt carriage-way a proper foundation is as necessary as it is for any other material used for street paving. In many American cities this has been "scamped," with disastrous results ; for while a really first-class asphalt pavement is, in the words of the nursery rhyme, "very, very good ; when it is bad it is horrid." No paving is sanitary unless it is kept clean, and asphalt is no exception to the rule. It has the advantage, however, from its smoothness, of being cleansable rapidly and easily, and it dries quickly; these advantages are also characteristic of the best hardwood paving. On asphalt, wheels run smoothly and quietly, but the sharp, metallic click of horses' feet is a very disturbing noise. In the busier streets this is not
so noticeable as in quiet thoroughfares where there are private houses and hotels. As a paving, asphalt is particularly susceptible to climatic conditions.
As to the cost of asphalt paving, we quote Mr. Aitken "The approximate cost of asphalt rock pavements in the City of London at the present time, exclusive of foundations, is," he says, "as follows (per square yard)" : Val de Travers asphaltiio.thick, 9s. 9d.; sin. thick, 1.2s. 6d.
Limrner asphalt ... 95. 6d. ; „ iss.
French 9s. 6d. ; „ 125. tO 12S. 6d."
Like those already detailed, the cost for annual maintenance varies according to the locality and amount of traffic passing along the thoroughfare; but is generally repaired free of cost for the first two or three years. In regard to cost, Mr. Ostoby, Borough Engineer of Camberwell, has given figures in his report gf actual experience, and I therefore quote these. Mastic asphalt is heated and laid in a plastic condition, being levelled down by spreaders. Compressed asphalt is reduced to the form of powder, heated, and laid down in the powder form while hot. It is then beaten down, and the bitumen and limestone consolidate into a homogeneous mass. As regards first cost, the Mastic asphalt is the cheaper of the two, but its life is not
so long as when compressed ; it has not, however, been used largely for roadways, as it is liable to get soft in hot weather and ruts easily form in it. The London County Council will grant loans on it for a term of seven years only, and I can find no information as to its being likely to last any longer. The Compressed asphalt costs more in the first instance, and has been largely used in the City and Holborn, where it has been down with heavy traffic from 17 to 20 years. The London County Council will only grant loans, I understand, for a term of ten years; this period Mr. Oxtoby has considered in his calculation, which is as under :— Mastic Asphalt, iiin. thick, on and including 6in. Portland cement concrete, costs about ins. 6c1. per yard super.
First Cost.—z,000 yds. super., 1:in. Mastic 4 s. d.
Asphalt, on 6in. Portland cement concrete at los. 6d. L675 added for con tingencies) ... 600 o o Cost every seven years. —I,000 yds. super. Taking up old asphalt and repaving with new Mastic Asphalt itin. thick
on existing foundations, refloated at 7s. 350 Contingencies so o o
£400 0 0 Repayment of principal and interest for si years will be :— First seven years Principal, Loon; total interest seven years at 31 per cent., .4.9o. Second seven years: Principal, Laao ; total interest seven years at 3: per cent., £60. Third seven years: Principal, £460. Total cost for 21 years for z,000 yds. super., Zi.,6lis. Average cost per yard super. per annum for 21 years, is 6.4d.
Compressed Asphalt, sin, thick, on similar foundations, costs about iss. per yard super.
First Cost.-1,000 yds. super., 2i0. Compressed Asphalt on and including 6in.
Portland cement concrete at 15s. 75a o Contingencies ... so o o Total first cost. ... 4800 o o
Every to years.-1.,00o yards super. Taking up old asphalt and repaving with new sin, compressed, on old foundations re
floated at its. 6d. -•-; -3.1.:575 o o Contingencies ... 25 o 0
L600 o o Repayment of principal for 23 years :—First io years: Principal, LSoo ; total interest for it) years at 31 per cent., £i65; Second to years: Principal, Locio; total interest for to years at 3: per cent., £123 155. ; making a total cost for so years, per is3oe yards super., £1,688 155. Average cost per yard super per annum for 20 years, is. 8,26d.
(To be continued.)