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 thus paved, 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 will cover, 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. Walker
on 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 was spread 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.

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 of 6 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 dry weather 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]