Armoured Macadam Roads.
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The necessity for a more efficient means of forming road sarfaces has become more urgent during the past few years, owing to the increased scope of .motor-propelled traffic, and various methods have been tentatively adopted to mitigate the evils that are due to the faulty construction of many of our existing main roads, which do not carry motor traffic efficiently. The result is an absence of economy both for the car or wagon owner and the highway ;authority. The greatest enemy to motorism to-day is the dust which is raised by high-speed motorcars when travelling over unpaved. road surfaces where setts, wood blocks, or similar materials are not laid, but, from the road maintenance point of view, there are also the great troubles which are attributable to the cutting-up of ordinaty macadam roads by slower-moving heavy motor traffic. Very few mails with metalled surfaces are, as a matter of fact, constructed with a view to carrying the traffic of the present day ; that is why macadamised roads as a whole are either dusty, greasy, or not strong enough to bear heavIt' motor traffic. In many cases they fail in every respect. Various. schemes have been adopted by our road engineers and surveyors to overcome these difficulties, but practically all the measures have been palliatives only : dust-laying experiments have been not more than partially satisfactory at best, and their applications have been successful only where the traffic is light. A road surface which, in the writer's opinion, will overcome the difficulties, has been adopted in various parts of Germany. It is known there as " Kleinpilaster," and consists of small granite paving blocks about 3 inches to 31 inches square by 3 inches to 4 inches in depth. The cost of providing these small blocks, if they were made and dressed by hand, would be prohibitive, but within the last few years a machine has been invented which enables them to be split so cheaply that the cost of roads armoured with them compares very favourably with that of ordinary first-class macadam roads. This saving in first cost, considered in conjunction with the fact that upkeep and renewals are practically nil for a number of years, accounts for an annual cost which is less than for a first-class macadam road. The writer has inspected many roads in Germany which are paved with these small granite blocks. In the Stade district, 22 miles north-west of Hamburg, the armouring has been [aid for over 124 miles, and it is giving the greatest satisfaction : a portion of this was laid zo years ago by the originator of the " Kleinpfiaster " type of road surface or armouring, Herr Gravenhorst. The traffic on these roads is fairly heavy, owing to the number of breweries, sugar factories, and other works in the neighbourhood, whilst a portion of the Alster Krug Chaussee, in I lam burg, which was a macadam road carrying -very heavy traffic, was armoured with the small blocks, some five years ago, under the supervision of the Hamburg city engineer, and is in perfect condition to-day. The Hamburg officials are Mt confident of its superior merits that instructions have been given for the remainder of this road to be similarly treated. Under the old conditions, when this road was macadamised, it had to be relaid three times in every two years, but now the road surface where armoured, notwithstanding five years of heavy traffic, has a perfect contour and every appearance of lasting for many years to come, In the Wandsbeck and Altona district, roads have been 'laid for several years, and they show practically no signs of wear. Again, in the Rheinland Province, many miles of road have been similarly treated where they are subjected to very heavy colliery traffic, and these are giving such good results that the State has now voted an additional .35o,000 for armouring the roads in this district alone. In the same way authorities in Berlin and Westphalia are proceeding to extend the svstem considerably. The illustrations show armoured roads in the important town of Wiesbaden. The Rheinstrasse carries the traffic of the railway stations and the post office, which are situated on either side. The spaces between the tramrails are armoured in a similar manner, Iwo rows of large setts being placed between the outside of the rails and the armoured road surface.
The small blocks are made in various sizes as follows, the dimensions being in inches and fractions of an inch : 2 to 31 x 2:1 to 31 top surface x 24 to 3.1 deep 4 X 3 o 4 7, 33 X 3,o o 4 7' 3:11 X 21 1 13 4 o 41 IP It is found in actual practice that, though the small granite blocks may not appear to have a perfectly uniform surface when laid, within a few weeks after traffic has passed over them the roughness wears off and the surface becomes perfectly even. The camber can be much reduced as compared with unarmoured macadam roads, the result
being a much more even distribution of the traffic. The smaller sizes are used on country roads where the traffic is not exceptionally heavy, and the larger sizes for roads entering towns where traffic is more frequent. When any old macadam road is to he laid with these small blocks, as little of the macadam as is consistent with the thickness of the armour is removed, the contour corrected, and the surface rolled hard. The small granite blocks a:e carted to the road, and then wheeled by barrows into longitudinal rows or heaps, the own who load the barrows selecting the deepest setts and tipping them into the two centre heaps, whilst the shallower setts are wheeled to the outer rows. A better contour is formed on the roadway by this selection, and the surface is kept perfectly regular. The paviors then lay the blocks diagonally, or in concentric circles, care being taken to place setts of full depth directly on to the hard road surface, sand being used only to level the short setts. When several yards are laid, sand is brushed between the joints, and the whole carefully rammed. Besides the absence of dust, very important features of these armoured roads are their practical noiselessness under iron-tyred vehicular traffic, the great mdoction of tractive effort they ensure, and the good foothold they pmvide. The joints are so numerous and irregular, and the surface so even, that wheels pass over them as _easily as over asphalt, whilst affording an incomparably better grip for horses' hoofs or motors' wheels. Should a country road be required to carry exceptionally heavy traffic, or one in a town to be made impervious for sanitary reasons, pitch and gravel grouting is used between the joints. It has been found quite unnecessary, and indeed harmful, to use cement between the stones, as the resiliency of the road is destroyed thereby. It is, of course, an absolute necessity that the granite used for the armouring should be of the very best quality, and perfectly homogeneous in character ; it would otherwise be impossible to secure a perfectly uniform and regular surface. The writer has supplied the small blocks to the Liverpool Corporation, in whose city they have now been laid for about six months, and the results go to prove that the satisfactory experience in Germany and the claims put forward in this article are being fully substantiated. It is also interesting to note that the county surveyor of Lancashire is putting down the small blocks or road armouring in various parts of the county where very heavy motor-wagon traffic has to be dealt with.
The orogress of small-sett armoured roads has, as mentioned above, received a great scmulus by the introduction of the patent sett-making rnachiae. it is essentially a drop
hammer, with a strong, sharp-edged chisel firmly held on the anvil. The monkey carrying the hammer head is raised by friction rollers, and is controlled by the foot of the operator, through a system of levers, in such a way that heavy or rapid light blows can be given with perfect ease and certainty. A good operator will make about 2,500 small setts with one of these machines in a 9-hour day, and of far better quality than it is possible to make by hand.
A. HENRY' NVHEEURK.