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 necessary power 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 doubt newly constructed 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 rolled varies 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. It was 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 of use:—

“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 the bed 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 made until 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 as follows:—

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 grit from 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.

MESSRS. AVELING AND PORTER’S 15-TON STEAM ROAD ROLLER.