stances, however, the portions of the road to be repaired should be picked or scarified, otherwise the macadam will be, to a great extent, pulverized by being placed between two hard substances, namely, the surface of the road and the roller wheels. In rolling patches of metalling it is necessary to sprinkle water over the surface to aid consolidation, the detritus in the old macadam being generally sufficient to form a binding for the new coating. This is swept over the surface; then, by repeated passages of the roller with occasional watering, all the interstices of the stones are filled up and the surface is made perfectly hard and smooth.

This method of improving the surface of roads is undoubtedly a very decided advance on the barbarous system of consolidating the macadaın by the wheel traffic formerly resorted to, and which, unfortunately, is still in operation in many districts at the present time. It must be admitted as a general principle, however, that when rolling patches of metalling, the whole width of the roller wheels cannot be brought into use simultaneously or continuously. For very small repairs, or on roads which have been rolled and are slightly out of repair at places, the process of mechanical scarifying, applying a small quantity of fresh materials, and rolling, improves a road surface considerably, and it may thus be made nearly equal in durability and appearance to a road which has been coated and consolidated.

372. Rolling Patchwork. The following is an instance, and the remarks are applicable to a greater or less extent in rolling all metal patches.

When a patch of metalling, 3, 4, or 5 feet in width, has to be consolidated, the effect of rolling is such that a part of the breadth of the engine wheels overlaps the metal patch, consequently that part is doing no actual work so far as consolidating the new coating of metal is concerned. It has been already stated that the rolling width of a 15-ton roller is 7 feet, while in one of 12 tons weight it is 6 feet; hence, to obtain the advantage of the full effective width of a roller the breadth of the metal patch would require to be increased accordingly. This, in effect, means adapting the extent of repairs to the rolling width of the engine, irrespective of the actual necessities of the road. Assuming, then, that this has been satisfactorily arranged, the length of the metal coating has to be considered, and it may happen that by this system of working the new material is spread with but little space between the patches, which will admit of the maximum amount of surface area of metalling being rolled. It is obvious, nevertheless, that as the roller commences work clear of the metal patch, or on the old portion of the road (a process which is repeated each turn the engine makes), and also overlaps the width, a considerable amount of the benefit of rolling is wasted on the portion of a road which is probably in excellent order. In other words, the cost of rolling patches of metalling is considerably greater than when continuous coatings are spread to the full width.

The author has found from experience that 30 cubic yards of metalling

spread in isolated patches can be consolidated during the autumn and winter months with a 15-ton roller.

373. Cost of Rolling Patches of Metalling.-The cost of rolling thin coatings of metalling applied on the patching system, including sweeping, horse, and water tank, but exclusive of spreading the macadam, is 8d. per cubic yard. It is necessary to add, however, that in some cases many of the patches were partially consolidated by the wheel traffic previous to the work being undertaken by the roller.

The County Surveyor of Nottingham has carried out the patching system of repairing road and steam rolling on an extensive scale for some years past with good results.

He uses 12-ton rollers, and the average cost of consolidating the metalling, including small repairs to the plant, is 9d. per ton. This is an average for working all the year round, the operations being carried on during the summer months on the roads which are nearest the best supply of water.

This system is mostly followed where limited quantities of metalling are applied annually, and especially when the cost of the broken stones reaches a high figure, the object being to obtain a smooth surface, but so treated a road would, of course, not have a reserve of strength capable of withstanding fluctuations of traffic.

The quantity of material spread in patches which can be consolidated by the roller each day under ordinary circumstances is on an average 30 tons; in many instances, however, 20 tons may be considered good work, especially where the exigencies of the passing traffic necessitate frequent stoppages during the operations.

374. Rolling Continuous Coatings of Metalling.-For the reasons given, and because of the time lost by the roller travelling to distant parts of a district repeatedly year after year, the author prefers to consolidate coatings of metal in long stretches spread to the necessary width, as the experience gained in carrying out the two systems clearly shows that in that here referred to there is greater economy in working expenses as well as increased efficiency. The roads are also more uniform in strength, while a more regular wearing and durable surface is obtained by a system of continuous coatings with consolidation by steam rolling.

The additional quantity of metalling necessary to keep a roller constantly at work in some districts might, at first sight, be considered a serious obstacle to the introduction of road-rollers on economical grounds alone. No doubt this would be the case if, in addition to the annual quantity usually allocated for patching purposes, a great amount of metalling were supplied to coat long stretches, or otherwise to ensure the roller being continually employed.

375. By adopting a graduated system, however, so that certain roads, * A Paper read before the Incorporated Association of Municipal and County Engineers, vol. xxii., on 'Steam Rolling,' by E. Purnell Hooley.

to be rolled in the course of a period of three or four years, may be arranged for in advance and added to as the work proceeds year by year, the previous annual quantities of material applied to these roads can, by judicious management, be reduced considerably in view of a thorough repair being undertaken within a limited period of time.

In working out this system of concentrating the metalling, due consideration must be given to the requirements of particular roads and certain sections of a road, where circumstances indicate that attention and the application of macadam are necessary to prevent the crust of the road becoming destroyed. It is advisable, not only when rollers are being introduced for the first time, but as rolling operations are extended, to prepare a list of those roads which it may be considered necessary to undertake in the first instance, and those to be dealt with later in rotation.

376. The roads, extending probably many miles, which it is intended to roll during the season following the previous year's supply of metalling, should be repaired by only employing the quantity of material that is just sufficient to maintain a fairly good surface without allowing the road coating to become tracked.

By this means, and when the following year's supply is prepared, a quantity of macadam nearly equal to two years' ordinary allocation is thus reserved until the rolling operations are commenced. This arrangement

may be extended so that a three or four years' supply may be applied and rolled on any particular road.

As a means to an end, this is the only method which can be followed, unless larger quantities of material can be procured at a cheaper rate. Methods have been described in the chapters ou Quarrying and Stonebreaking, by which material can be procured at a small cost.

Undoubtedly a country road can, by careful attention, be kept in good repair with a small quantity of material for a limited period of time, and by allocating a quantity of macadam, to be applied only when the road shows signs of giving way, a large amount of metalling may be reserved and concentrated on roads where found necessary in connection with rolling operations. Adverse weather in the form of alternating frost and thaw, will no doubt injuriously affect certain portions of the road surface, but apart from a trifling expenditure in labour to remedy this, the weak spots can be specially treated previous to or at the same time as the general repairs are effected.

It has already been shown that under the old system of repairing roads. by patching and consolidating the coatings by wheel traffic, a layer of macadam one stone thick serves to bear the ordinary traffic without failure of the road surface for a considerable number of years. Any reduction,. therefore, of the annual quantity of metalling applied, as a temporary measure, will not materially affect the strength of the road for a time.

Experience shows that by judiciously arranging the annual allocation of material for repairs, the actual quantity previously used can be reduced by 75 per cent., when rolling operations are to be undertaken the following season, and 50 per cent. in the case of roads which are to be rolled the second year. On these roads which are to have attention during the third season, a quantity of metalling amounting to a 25 per cent. reduction on the former quantity applied will be sufficient for ordinary repairs. It is obvious that by this method of reducing the quantity of road metal, in advance and in regular rotation, a sufficient supply of material will be provided to keep the roller employed in consolidating either large patches of metalling, or wide continuous coatings. It may be well to state here that a reduction in the quantity of metalling used, when spread in continuous stretches and rolled, will give a saving of about 25 per cent. of the total amount formerly applied in patching which was consolidated by vehicular traffic.

377. If the macadam used for repairs is hand-broken, it can be stored in depôts or brought direct from the source of production to the road under repair, care being exercised to avoid unnecessary haulage, which, besides entailing extra cost, does not add in any way to the efficiency of the work.

It happens at times in some counties that a supply of suitable material cannot be obtained in the immediate neighbourhood of the roads to be repaired. This may necessitate the metalling being brought from a considerable distance, even from points beyond the limits of the county where the operations are to be carried out. In such circumstances the cost of maintaining the roads is considerably increased, owing to the high rate paid for haulage by rail or otherwise, which often amounts to three or four times the initial cost of the macadam at the source of production.

378. Example of the Methods adopted in Arranging for Rolling Operations. Where quarries exist, the rock of which is suitable for producing road metal, and are so conveniently situated in relation to the road where the repairs are to be made that the material can be conveyed by carts or by engines and traction wagons, the following method of arranging the work is usually adopted.

The fixing of the portable stone-breaking machine and all the other accessories being arranged as described in Chapter VI., the points on the road at which the supply of metalling should commence and terminate from the different quarries may best be illustrated by giving an example taken from actual practice.

A road, A B, fig. 120, extending to 5 miles, was repaired by a continuous coating of metal, the width ranging from 14 to 18 feet, while the depth of the macadam varied from one stone thick to 4 inches. The section A d, of the main road A B, had been previously maintained with material of a hard and tough nature, over which a heavy traffic passed. The surface

of the road was considerably worn, which necessitated a coat of metalling 4 inches thick being applied.

The section de was repaired with the same material as the previous section, but the traffic passing over it was of a moderate description; the repairs being effected by scarifying the old surface, bringing it into proper contour, aud applying a coat of metalling one stone thick. The section e B, the wheel traffic over which is considerable, was maintained with a material of a highly siliceous nature, while the surface had become badly cupped, necessitating the coating being scarified and the old material screened to remove the high percentage of small or exhausted material.

This small stuff was laid aside and used afterwards for binding the new metal coating, the thickness to which the macadam was laid being 3 inches between ef, and 4 inches between ƒ B.

The quarries from which the metalling was taken are marked a, b, c in fig. 120.

In deciding from which of the two quarries a and b the material should be taken for repairing the portion of the section from A towards d, the

18 miles0.61----1.27-

18'wide

18 wide 4" thick

Melalling-18 wide-14' wide --·

4"thick one stone H----3" thick

FIG. 120.-Plan showing how to economize haulage from quarries to main road.

rock being of equal quality, the relative distances and the probable expense of working had to be taken into consideration.

The conditions as regards the access to, and the service roads leading from both quarries were very much alike, consequently the cost of haulage per ton-mile did not enter into the question.

The point to be decided was the distance from the points a and b to the .commencement of the section at A. On referring to the measurements on sketch plan, it will be seen that, so far as the mileage is concerned, the quarry a would, for a distance of 3ths of a mile from A towards d, be the preferable one so far from which to procure the material for repairs. The quantity of macadam required for this section A d of the road, to the width