« EelmineJätka »
coating of a well-maintained road the proportion of stones of various | already described) is essential, and it is generally desirable to loosen sizes varies, but generally from one-third to one-half is found to the old surface to ensure the incorporation of the new coating with consist of detritus under three-eighths of an inch in diameter, and it. Scraping and attention are required between one coating and there is a very constant proportion of about one-fifth of mud and another and also slight repairs to the surface, as, however well the detritus under one-thirtieth of an inch in diameter. This appears materials may be laid and rolled, the wear of the ordinary traffic to be the amount necessary to fill the voids between the fragments will search out places which have escaped the full pressure of the of stone when compacted together. In an ill-kept road, from which roller and produce inequalities. the mud is not removed, the proportion of detritus is much higher, Besides a regular application of new materials to replace wear, and mud may constitute nearly one-half of the coating. In pro there must be in road maintenance on proper principles a systematic portion as the detritus and mud are kept down to the minimum by removal of the detritus by scraping or sweeping, which must be constant removal from the surface, so will the road be able to resist regarded as keeping the whole coating in proper condition, and not the action of wet and frost and the wear of the traffic.
as mere surface cleansing. The wear should also be reduced as far The wear of materials, resulting in their gradual reduction to as possible by providing sufficient thickness to carry the traffic, by detritus, is due to the joint action of the traffic and the weather, keeping an even surface on which water can never stand and soak, which cause surface wear, wear arising from cross breaking, and and by good drainage both of surface and subsoil. An adequate from rubbing of the stones together. When there is no movement amount of skilled manual labour is necessary for economy of mainin the body of the road, and the wear is confined to the crushing tenance, and this and the constant attention which is required to and grinding at the surface, it is the least possible ; but, when a keep a road in good order are best secured by putting a man in road is weak from insuflicient thickness or solidity on a yielding permanent charge of a defined length. In the autumn and winter, foundation, bending and cross breaking of the coating take place when more labour is wanted, extra men should work under the under passing loads in addition to the surface wear, and the effects directions of the permanent road labourer, whose knowledge of his are aggravated by the softening action of water finding its way into length of road will enable him to employ them to the best advantage. the road through cracks formed in the surface and by the disinte Concrete macadam, formed by grouting with lime or cement Concrete grating action of frost. The wear and waste are thus far larger than mortar a coat of broken stone laid over a bed of stone previously and tar on roads of suflicient strength, properly maintained. The destruc- well rolled, has been tried as an improvement on an ordinary mactive eflect of wheels is greater as the diameter is less, and to a much macadamized surface, but not hitherto with much success. When adam. greater degree as the tire is narrower. On hard and strong roads cleanliness is of importance, and great durability is not required, tar 110 greater width of wheel than 11 inches is useful, as a wider tire macadam or bituminous concrete may be usefully employed. It does not bear evenly, but on yielding roails a greater width is of is sometimes made by first spreading a coating of broken stone and some advantage, though it does not prevent damage from bending consolidating it by a roller, and then pouring over it a mixture of and cross breaking of the whole coating under excessive loads. coal-tar, pitch, and creasote oil, upon which a layer of smaller A good deal of attention has been given by French engineers to stone is spread and rolled in, and the surface finished with stone the measurement of traffic, wear, and the consumption of road chippings rolled in. More usually the broken stone and bituminous materials. Without a knowledge of the amount of traflic accurate mixture are well incorporated together before they are spread, the comparisons of wear are impossible, and an account of the traflic on stone sometimes being previously heated. The lower layer, about the roads of France is taken periodically in "collars” or horses 4 inches thick, may be of stone broken to 24 inches gauge, and the drawing loads, and in the weight drawn. Traflic as measured by next layer, about 2 inches thick, may be of smaller stone. Each weight drawn has of late been observed in some of the streets of layer must be well rolled, and when perfectly solid a thin coating London and Liverpool, and has been reduced for comparison to the of fine stone or granite chippings is spread over the surface and weight per foot or yard of width of the carriage-way. Wear may rolled in. Hard limestone is found to be more suitable than silibe measured by loss of thickness in the coating; but the loss of cious or igneous rocks for this material. A road surface well made stone in proportion to detritus must also be ascertained before all in this manner will last several years under light traffic without the effects of wear can be determined. The accurate measurement any repairs, and it can easily be patched when necessary. of wear as practised by the French engineers is a complicated process, Stone Pavements.—Early pitched roadlways consisted of pebbles STONE and it must sullice here to state that measured by thickness the or rounded boulders, bedded in the natural surface or in sand or PAVEwear is seldom found to exceed half an inch, or on the most fre- gravel. The next step in advance was to employ roughly-squared MENTS. quented roads of France one inch, of consolidated surface per year, blocks; but the wide and irregular joints admitted the water to and that about 100 cubic yards of good materials per mile per year the subsoil, and the mud worked up and the stones sank irreguare considered as the average consumption under 100 collars of traffic larly under the traffic. Telford, who was called upon to report on per day. Observations in the United Kingdom on roads well and the street pavements of the parish of Hanover Square in 1824, saw systematically maintained have confirmed these results.
the necessity of cutting off all connexion between the subsoil and The new materials may be added to the road either in thin coats the paving stones. He recommended a bed of about 6 inches of Foundaand small patches year by year or in a thick coat consolidated by clean river ballast, rendered compact by being travelled upon for tion. rolling. The first method, by which the wear is replaced annually some time before the paving was laid, but he subsequently conand the traffic is depended on to work the materials into the road, sidered that nothing short of 12 inches of broken stone, put on can be followed with excellent results, and at no great inconveni in layers 4 inches thick and completely consolidated by carriages ence to the public under proper management when the traflic is not passing over them, would answer the purpose. He recommended excessive. Considerable care in the use of materials is required paving stones of considerable depth and of from 4 to 6 or 75 that none may be unnecessarily applied. The annual employment inches in breadth for the greatest thoroughfares, and he pointed of one-fifth or one-sixth the quantity which it would take to cover out the importance of working the stones flat on the face and square the whole surface one stone in thickness is often suflicient to replace on all sides, so as to joint close and preserve the bed or base as wear, and it will then take five or six years to coat every part of the nearly as possible of the same size as the face, and of carefully road if it is covered regularly. It is therefore important to apply placing together in the same course stones of equal breadth. Many the new materials only where they are needed, and not to use them pavements thus laid with stones of considerable breadth still rewhere the road is already sufficiently thick. The irregularity of main, but experience proved that it was a mistake to suppose that wear and of thickness enables a good roadman to judge where new broad stones having a larger base would support better the weight materials must be applied, and he will apply them in small quanti- and shocks of heavy traffic ; on the contrary, a wide stone has a ties wherever weak places appear. To facilitate this the materials tendency to rock on its bed, and also to wear round on the top and should be placed in heaps by the roadside in the summer, and they become slippery. To obtain an evener surface and a better footshould be carefully spread in the autumn and attended to after- hold for the horses the stones were reduced in width, and in 1840 wards to ensure consolidation without waste. By good manage a granite pavement was laid by Walker on Blackfriars Bridge, ment a large quantity of materials may be incorporated in a road which may be considered the first of modern set pavements. The before the midille of the winter without harassing the traslic, and stones were 3 inches broad and 9 deep; they were laid on a bed the strength may not only be maintained but increased. of concrete 1 foot thick and were jointed with mortar. The reduchard strong road consolidation may be ailed by loosening the sur tion of breadth to about 3 inches was generally followed, but it is face with a pick; generally only the margin of a patch need be only of late years that a concrete foundation has been employed to picked up. But if the road is soft or weak it is better not to disturb any great extent, the frequent breaking up to which streets are the surface at all. Binding may sometimes be used to aid con subject having prevented it. In London a foundation of broken solidation, but it is seldom necessary if the materials are properly stone has been continued in the chief thoroughfares, the sets being laid and attended to, as the coating alrealy contains detritus enough. evenly bedded in gravel upon it and rammed with a heavy wooden In the second method a coating of materials is laid on at once rammer. Hard core—a mixture of broken stone, clinker, brick suflicient to endure the wear of several years with such slight rubbish, and old building materials—has also been largely used to repairs as may be necessary to keep a good surface, and, when the form a foundation. In the northern towns of England cinders wear has gone as far as it can be safely allowed to go, the process is have been employed, and where the traffic is exceptionally heavy repeated. Unless the wear is very considerable there is no economy a pitched foundation of stones on edge has been laid when the in this method, though the convenience to the public, especially in sets were not paved upon an old macadamized surface. The contowns, is undeniable. Consolidation by rolling (after the manner crete for a foundation to a paved street should be made with the
best Portland cement, thoroughly mixed in proper proportions the joints have for many years past been made by first filling with the sand and gravel or other materials used, water being them with clean gravel, well shaken in by ramming, and then added as sparingly as possible. A thickness of 6 inches of well-pouring in a composition of coal-tar, pitch, and creasote oil. The made cement concrete is sufficient for the heaviest traffic, and it Manchester pavements are good examples of this system of trusting can be cut out in slabs for pipe-laying or repairs and can be relaid to impervious jointing to prevent unequal settlement. The foundaand cemented in its place. To obtain the best result a new tion, where there is not already an old road surface, is a bed of foundation should not be paved upon for a week. A foundation cinders about 1 foot thick, over which are laid 3 inches of gravel, of bituminous concrete is sometimes used where only a thin bed which are thoroughly consolidated by allowing the traffic to pass can be laid, in consequence of there being an old foundation which over them. The sets are evenly bedded and well rammed after the it is undesirable to disturb. It is made by pouring a composition joints have been filled with clean gravel, ramming and gravelof coal-tar, pitch, and creasote oil while hot over broken stone ling being repeated till the joints are full of gravel. The inixture levelled and rolled to the proper form, and then spreading a thin of coal-tar, pitch, and creasote oil, well boiled, is then poured over layer of smaller broken stone over the surface and rolling it in. the surface and allowed to percolate and fill up all interstices in It has the advantage that it can be paved upon a few hours after the joints, and the pavement is finished by covering it with small it has been laid.
gravel. Joints so formed are impervious to wet and have a certain Materials. The best materials for pavement sets are the hard igneous and amount of elasticity; the foundation is kept dry; and the pavement
metamorphic rocks, though millstone grit and other hard sedi- keeps its form well for many years. The objection is made that in
for a foundation of credit rontofr. Join ting Joints simply filled in with gravel are of course pervious to water, A concrete foundation for a wood porementarywarn to have been Founda
and a grout of lime or cement does not make a permanently water first employral in a puvint laiil in 1572 in (1. lund Street boy tion.
ends inclining in opposite directions in alternate courses. The those that are unsound, knotty, or badly shaped should be careupper edges of the blocks were chamfered, and there was a cham- fully rejected, as defective blocks soon cause holes in the surface fered groove near the bottom. In a few years this form of block and must be replaced, or the adjoining blocks will suffer undue was abandoned for rectangular blocks, and mineralized fir was sub wear and the surface become irregular. The breadth of the blocks stituted for beech. The blocks were bedded in Portland cement never now exceeds 4 inches, and it is generally 3, the length being and laid with joints one-fourth of an inch wide, partly filled with determined by the breadth of the deal or batten from which they asphalt and then grouted with mortar. The adoption of a bed are cut. The depth is usually 5 or 6 iuches; 5 inches are conof concrete as the weight-bearing foundation of the road marks a sidered by many to be enough to give sufficient depth for as long new departure, and in all the more recent systems of wood pave as the pavement will retain a sufficiently good surface without ment a substantial foundation of concrete is an essential feature. renewing the wood, and blocks of that depth have been laid in In Norwich, however, a large quantity of wood pavement has been many London streets. It is doubtful if any advantage is derived laid on the old street foundation, the blocks being bedded in gravel from creasoting or from dipping the blocks in creasote oil or coal and sand and rammed, and the joints grouted with lime and sand. tar. Dipping affords a cover for the use of defective or inferior The experience of from four to seven years has proved the pavements wood, and thorough creasoting, though it preserves the wood from to be successful, but the foundation is exceptionally dry and hard decay, has little or no influence on the wear, which in almost all and the traffic not very heavy. With a concrete foundation there cases determines the life of the blocks. is no reason for complicated shapes and contrivances for locking With a curved cross section like that already described a rise Cross the blocks together; and wood pavements in their modern form from the mean level of the channels to the crown of the road equal section consist of rectangular blocks (obtained by cutting off the end of a to one-sixtieth or one-seventieth of the width of the carriage-way deal plank), bedded on the concrete with the fibres of the wood is enough. The necessary profile must be accurately given to the vertical, thus constituting a slightly elastic wearing surface on a concrete foundation when wet. Wooden moulds or templates are rigid foundation, by which the weight of the trallic is borne. There fixed across the street 10 or 12 feet apart, over which a straight. is, however, considerable variation in the method of bedding and batten is worked to give the concrete the required form and a jointing the blocks. The Asphaltic Wood Pavement Company laid smooth surface. The inoulds are removed when the concrete is half an inch of asphalt upon the concrete, and formed the lower partially set and the spaces are made good with cement mortar. part of the joint of asphalt and the upper part of a grout of Port In a level street provision should be made in the foundation for a Foundalaud cement and gravel, the advantage claimed being a slightly fall in the side channels towards the gullies of not less than 1 in tion. elastic bed for the blocks and water-tight joints. The blocks have | 150, and the necessary modifications of cross section at the interbeen laid in unset cement over the concrete and rammed to an even section of streets must also be provided for. Every care should be surface; but the ramming is liable to split the blocks, and the taken to ensure a good homogeneous concrete for the foundation, indentations formed in the cement surface of the foundation have as upon that the strength of the road depends. With a well-made to be removed when the time comes for renewing the blocks. It | Portland cement concrete a thickness of 6 inches is sufficient. It is now more usual to bed the blocks directly on the concrete, a should be allowed to set thoroughly before the blocks are laid, smooth surface being formed either with the concrete itself or by and traffic should not be allowed to pass over it for a week. The a floating of cement, and to fill the joints with a grout of cement finished pavement should be covered with a thin layer of sharp and gravel. A cement joint aclheres to the blocks, resists wet, yrit, which is forced into the wood by the traffic and forms a hard
and does not wear down too much below the surface of the wood, face. Several applications of grit are desirable at first, and from Henson and so form a receptacle for mul. In Henson's system, which time to time afterwards, both as a protection to the wood and to pave has been largely usel, the blocks are belded and jointed with prevent slipperiness. Systematic cleansing is required to prevent ment. ordinary roofing felt, a strip of which, cut to a width equal to the slipperiness and foul smells, and to preserve the pavement. Cleans
depth of the blocks, is placed between every two courses. The joint ing may be aided by washing, and when it is thoroughly carried is maule as close as possible by driving up the blocks as every eight out but little watering is required to keep down the dust. A wood or ten courses are laid with heavy mallets, -a plank being laid along pavement is the quietest for the residents, pleasant to travel over, the face of the work. A perfectly close and slightly elastic joint is and favourable to the wear of vehicles. Traction on it is easy and thus formed. A continuous layer of felt is likewise laid over the foothold good, so that it may be laid on gradients as steep as 1 in 20. concrete foundation to give a slightly elastic bed to the blocks. A The wear of wood pavements in London is stated by Mr Stayton V-shaped groove along the centre of every fourth block was at to be from ·065 inch per year in Sloane Street, with a traffic of 279 first considerell necessary for foothold, but its use has been dis tons per yard of width per day, to 456 inch per year in Fleet Street, continuell except on gradients steeper than 1 in 30. The surface with a trallic of 1360 tons per yard of width per day. Reduced to of the pavement is dressell over with a hot bituminous compound, a standard of traffic of 750 tons per yard per day, the comparative and covered with fine clean grit. This method of laying a wood annual wear becomes .175 in the former and .251 in the latter street. pavement, although soinewhat more expensive, is probably the In Parliament Street, Westminster, blocks removed after four years best that has hitherto been deviseed for smoothness and durability. in places where patching was required had lost 14 to 13 inches in The blocks are laid in courses across the streets, any change in thickness, equal to one-third of an inch per year under traffic stated the direction of the latter being accommodated by shorter courses to be 1106 tons per yard of width per day. From information ending with wedge-shaped blocks. At street junctions the courses afforded by Mr Haywood it appears that in the City of London are laid diagonally, or meeting at right angles. Two or three under traffic of from 300 to 660 vehicles per yard of width per courses are laid parallel with the kerb to form a water channel. day of 12 hours the wear is from 2 to 3 inch per year, and that in The blocks may be laidl closo end to end across the street if some King William Street, London Bridge, under a traffic of about 1200 allowance be maile for expansion by wet, without which the kerb vehicles per yard of width in 12 hours the wear was found to be stones and footways will be displaced, or the courses will be bent 24 inches in 34 years in the middle of the road, or ·81 inch per year. in reversed curves. To afford relief the joints of the courses parallel | This is the heaviest traffic to which wood pavement has been subto the kerb) may be left open, or the course next the kerb may bejected. The wear is generally considered to be as much due to the left out until expansion has ceased, the space being temporarily horses' feet as to the wheels, and the action of the former is more filled in with sand. In the direction of the traflic joints more or destructive on steep gradients. Towards the end of the life of the less wide are generally thought necessary for foothold. A wide blocks the wear is more rapid than at first. Few wood pavements joint allows the fibres of the wood to spread and give way at the retain a sufficiently good surface after about six years' wear without upper corner of the blocks for want of lateral support, and it also extensive repairs, and it is probably not advantageous to lay blocks forms a receptacle for mud and wet. Experience has shown that of a greater depth than will provide for a duration of seven years; the space of three-fourths of an inch or one inch, once thought 5 inches are almost always sufficient for this. necessary for footholl, may safely be reduced to one-fourth or Wood pavements of plain blocks on a cement concrete bed are Cost. three-eighths of an inch. For spacing the courses to form the now (1885) laid at from 10s. 6d. to 12s. 6d. per square yard, a conjoints strips of wood of the proper thickness may be laid in and siderable reduction on the prices paid for patented systems a few removed before the joints are filled, or they may be nailed to the years ago. Of the above prices 2s. 30. to 3s. 9d. is the cost of the lower part of the blocks. Two fillets have been nailed on, or three foundation, which does not require renewal like the blocks. Ascast-iron studs fixed in the sides of each block to keep them steady suming the average life of the latter to be seven years, Mr Stayton in place until the joints are filled and thoroughly set. The latter estimates the annual cost of wood paving in Chelsea with a traffic
inethod secures more uniformity in the width of the joints. of 500 to 750 tons per yard of width per day to be ls. 9d. per square Materials. There is some difference of opinion as to the best material for a yard, which includes the cost of original construction, repairs and
wood pavement. Pitch pine and the harder red and yellow deals renewals, and interest, spread over fifteen years. Cleansing and
39.0 .33 02 202
rock, and from 10 to 12 in that from Val de Travers. Asphalts con
Per square yard per year.
..ls. 1ļu. taining less than the former proportion have not sufficient coher
Wood pavement ence for street pavements, and those containing more than the
..ls. 11 d. latter proportion soften from heat in the summer. Asphalt is employed either as a mastic or compressed. The mastic is pre- Asphalt paving may he placed between wood and bituminous conviously prepared in cakes and is melted for use in caldrons with a crete in the above order. These comparisons show the high cost small quantity of bitumen, and for a street pavement is thoroughly
of a macadamized surface in a street where the traffic is great. mixed with sand or grit. It is spread in one thickness on a concrete
However well it may be maintained, a macadainized street must foundation, covered with sand, and beaten to an even surface. This
be dirtier and dustier than any pavement, though it is superior material has not proved so successful for street surfaces as com
to them all in safety and to set pavements in the matter of noise. pressed asphalt. To produce this the rock asphalt, previously
Bituminous concrete or asphalt macadain is cheaper, cleaner, and reduced to a fine powder by mechanical means, is heated in revolv- quieter than ordinary macadam and is sufficiently durable when ing ovens to from 220° to 250°, spread while still hot, and compressed
the traffic is not heavy. For heavy traffic no pavement is so econointo a solid mass by hot disk -shaped rammers, and afterwards
mical as granite sets; but for the sake of quiet and cleanliness a smoothed with irons heated to a dull redness. The original rock is wood or asphalt pavement is often preferable. Asphalt can be thus as it were reconstructed by taking advantage of the power of kept cleaner than any other pavement and is the pleasantest to coherence of the molecules under pressure whenhot. In heating travel over ; wood, on the other hand, is quieter for the residents, the powder the moisture combined in the limestone must be driven
less slippery, and can be laid on steeper gradients. off without reducing the proportion of the bitumen more than is
The comparative ease of draught on various surfaces is largely Draught. unavoidable. The powder cools very slowly and inay be conveyed Joubted if dynamometer experiments, however carefully made, aro
influenced by the amount of foothold afforded, and it may be long distances from the ovens; it may even be kept till the next day before use. When laid it should still retain a temperature of altogether conclusive. The tractive force is influenced by the from 150° to 200°. It is spread evenly with a rako by skilled gradient, the diameter of the wheels
, the friction of the wheel axles, workinen for the whole width of the street to a thickness about
and the speed, as well as by the resistance of the road surface, and
these must be all taken into account to obtain accurate results. two-fifths greater than the finished coating is intended to be. Rainming is commenced with light blows to ensure equality of Some recent experiments madle, under the direction of Sir J. W. compression throughout and is continued with increased force until
Bazalgette, with Easton and Anderson's horse dynamometer on the whole is solidified. The ramming follows up the spreading,
London street surfaces gave the following mean results : so that a joint is required only when the work is interrupted at
Tractive force on the level.
Macadamizcil surface the end of a day, or from some other cause.
..-10.7 to 119 lb per ton.
Asphalt has been laid an asphalt pavement may be used for traffic. When fmishell, its thickness may be from 11 to 21 inches, according to the traffic ; a greater thickness than the latter cannot be evenly The gross load was 4 tons, drawn at a speed of from 2 to 6 miles compressed with certainty. The asphalt loses thickness by com an hour. It is remarkable that the tractive force on asphalt is so pression under the traffic for a long time and to the extent, it is high; but the other results are consistent with former experiments said, of one-fifth or one-fourth, but the wear appears to be very small. by Morin, Macneill and others. A pavement in Paris which had lost more than one-fourth of its The comparative safety of granite, wood, and asphalt pavements Safety. thickness was found to have lost only 5 per cent. of its weight in the City of London was the subject of careful observations, which after sixteen years' wear. The pavement in Cheapside, after four were fully reported on by Jr W. Haywood in 1873. The pavements teen years under exceptionally heavy traffic, has been reluced, where selected were granite sets 3 inches wide, ligno-mineral pavement of not repaired, from its original thickness of 2! to about 13 inches. beech blocks 35 inches wide, improved wood pavement of fir blocks Tho wear-resisting power of the asphalt is due to its clasticity; 3 inches wide, and Val de Travers compressed asphalt pavement. tracks are made by the wheels at first, but when thoroughly On known lengths of these the traffic, the accidents to horses, the compressed by the trallic the surface retains little or no trace of weather, and other circumstances were observed for fifty days, and the heaviest londs. Repairs are easily and quickly madlo by cut when the distance traversed was taken into account it was found ting out defective places and ramming in fresh heated powler, that as a mean result a horse might be expected to travel 132 miles which can be done in the early morning without stopping the on granite without falling, 191 on asphalt, and 146 on the imtraffic. An unyielding foundation is indispensable ; it should be proved wood pavement. The condition of the weather hail considerof the best Portland cement concrete, 6 inches in thickness, which alle effect: on the granite when dry a horse might be expected to must be well set and perfectly dry throughout before the asphalt travel 78 miles without falling, when damp 10s, and when wet is laid, or the steam generated on the application of the hot powder 537 ; on wood when damp 193 miles, when wet 132, and when dry will prevent coherence and lead to cracks and holes in the asphalt
, 6-16 ; on asphalt when damp 125 miles, when wet 192, and when which quickly enlarge under the traflic. For the same reason the dry 2:23. It thus appeared that would pavement was less slippery asphalt should be laid in dry weather. The concrete foundation than cither granite or asphalt in a marked degree, it being only must be carefully formed to the proper profile, with an inclination more slippery than granite when both parements were wet. About towards the sides of not more than 1'in 50, which is sufficient 85 per cent of the falls on the wood pavement were falls on the with so smooth a surface. About 1 in 50 is the steepest gradient knees, which are less likely to injure the horses and are less inconat which an asphalt pavement can be safely laiil. When either venient to the traffic than other falls. On the granite the falls wero dry or wet it afforis good foothold for horses, but when beginning falls on the knees or complete falls in about equal proportions, with to get wet, or drying, it is often extremely slippery. This is said about 7 per cent of falls on the haunches. On the asphalt 13 per to be due to dirt on the surface, and not to the nature of the cent. were complete falls and 24 per cent. falls on the launches. material. Sanil is strewell over the surface to remely the slip Il’ateriny.-On macadamized roails in Great Britain watering is Waterprines; it tends, however, to wear out the asphalt, and great only good for the road itself when the materials are of a very sili- ing. cleanliness is the best preventive. An asphalt pavement can be cious nature and in dry weather. With other materials the effect kept cleaner than any other, is impervious to moisture, and dries is to soften the road and increase wear. In and near town waterquickly. It is noiseless, except from the clatter of horses' feet on ing is required for the comfort of the inhabitants, but it should it ; it is the pleasantest pavement to travel up, but it has the not be more than enough to ly the dust without woltening the drawback of imperfect foothold and slipperiness at times. The roail, and the amount required for this may be really reduced by cost of a compressed asphalt pavement 2 to 2} inches thick on a keeping the surface free from ind, and lisa-loping off the clust Portland crennent concreti foundation 6 inches thick is from 1:35 when slightly wetted. Parements are watered to call them as to lois, il syarı yarıl, and the maintenance is usually undertaken well as to lay the dust, but it must be remembered that both for a period of seventeen years by the company laying the privm wool and asphalt are more slippwly when wrt, and thout therefore mont, the first two years free and at 31. to 1s. Oil. per square varil, watering should be obviated as far as ponajbolo ly though Jeansaccording to the traili, in succeeding years.
ing: Hydrostatic vans, loy improvements in the di-tributing pipes Com lumpurrimi Street Surfiuers. — The comparative cost of various and regulating valves, water a wide trark uniformly with an amount paratire street surfaces in Liverpol, including interest on first cost, sinking of water which can be seeruliatood at pleasure. When hydrant exist cost. fund, maintenance, inil scavenging, when reduced to a uniform in connexion with a wito's supply at high pro--lll", true watering
standard eratlie of 100,000 tons per annum for each vard in wilth can be effected by a movable home and jet, a mnother la more of the carriage-way, is given by Jr Deacon as follows:
effective in cleansing the 411:28, but n-ing a murli largi qanity Per square yanl per yrar.
of water. Another method whirh has 11 tril, lint not much de pavement of hari tanites
usel, is to lay perforated pipes at the brk of the kesh on mah Bfter granites
side of the road, from which jets to thosen pin tlir urfa.. Bituminous concrete
The first coat is considerable, and the openings for the juts are
23. 11 il
liable to choke and set out of order. D. 17*t* nt salts have leven
sed street watering, lis whii h the faci kepur moi-t, lut at Taking the standard of traffic at 10.000 tons per annum for each the expense of the moisture in the air. Sea water has the same yani in width, the cost for the last three parements is :
I wtfect in a less degree.
Cleans Cleansing.–The principal streets of a town are generally cleansed ROANNE, a town of France, at the head of an arroning. daily, either by hand-sweeping and hand-scraping or by machines. dissement in the department of the Loire, lies on the left Whitworth's machine consists of a series of revolving brooms on
bank of the Loire in 46° 2' 26" N. lat. at a height of an endless chain, whereby the mud or dust is swept up an incline
It is now the point of junction into the cart. A less costly and cumbersome machine consists of | 912 feet above the sea. a revolving brush mounted obliquely, which sweeps a track 6 feet for the railway from Paris (262 miles north-north-west) to wide and leaves the dust or mud on one side to be gathered up by Lyons (50 miles south-east), via Tarare, with the line from hand. A horse scraping- machine which delivers the mud at the Paris to St Étienne (50 miles south-south-east), and a side is also used, the blacles of the scrapers being mounted obliquely branch connecting Roanne with Paray le Monial, and as and covering a width of 6 feet. For general use, more especially in the country, scraping machines worked by a man from side to the terminus of the Roanne-Digoin Canal (1832-38) the side of the road, and scraping a width of about 4 feet, are more town is the real starting-point of the Loire navigation. convenient. All street surfaces suffer from the constant breaking up and dis; mention the ruins of a castle with a tower dating from
Besides the modern town-house (1868-73), it is enough to turbance to which they are subjected for the purpose of laying and repairing gas and water pipes. Subways, either under the middle the 11th century, and a fine bridge of seven arches conof the roail or near the kerbs, in which the pipes may þe laid and necting Roanne with the industrial suburb of Le Côteau be always accessible, have often been advocated, and in a few instances have been constructed; but they have not hitherto found manufacture, employing 1200 hands.
on the right bank of the river. Cotton is the staple
Hosiery, hats, general farour. Foot Footways.-Gravel is the most suitable ma ial for country or
woollen yarn, weaving looms, chemicals, and paper are ways. suburban footways ; it should be bottomed with a coarser material, also produced; and, as the town stands in the centre of
well drained, and should be laid with a roller. An inclination the Loire and Rhone coal-field (output 4224 tons in 1884)
and in the neighbourhood of the St Étienne coal-field, it Where greater
In 1881 cleanliness is desirable and the traffic is not too great a coal-tar has a considerable trade in coal and coke. concrete similar to that already described, but of smaller materials, Roanne had a population of 24,992. makes a good and economical footway: The coating should be 23 Roanne (Rodomna, Ptolemy; Roidomna, Tab. Peut.) was an or 3 inches thick, composed of two or three layers cach well rolled, ancient city of the Segusiani and a station on the great Roman the lower layer of materials of about 1} inches gauge, and the upper road from Lyons to the ocean. The absence of coins later than of a half or a quarter of an inch gauge, with Derbyshire spar, or fine the time of Constantius II. among the numerous local relics of granite chippings over all. Concrete footways require to be care the Roman period seems to show that the town was sacked by the fully made anul must be allowed to set thoroughly before they are barbarians in the 4th century. In 1447 the lordship of Roanne used. Concrete has a tendency to crack from contraction, especially became the property of the celebrated banker Jacques Cour. A when in a thin layer, and it is better to lay a footway in sections, favourite scheme of his was to make the town a great industrial with joints at intervals of about 2 yarıls. Concrete slabs, especially centre by regulating the course of the Renaison, an affluent from when silicated and constituting artificial stone, make an excellent the Monts de la Madeleine which joins the river a little higher up; footway. The material is composed of crushed granite, gravel, or his death prevented its execution, but the subject has since been other suitable material, mixed with Portland cement and cast in frequently revived. moulls, and when set saturated with silicate of sola. This paving ROBBERY. See THEFT. has proved more durable than York stone flagging, but it is more
ROBBIA, DELLA, the name of a family of great disslippery, especially when made with granite. York stone makes a gooil and pleasant foot pavement, but is somewhat expensive con
tinction in the annals of Florentine art. Its members sidering its durability ; it is apt to wear unevenly and to scale off are enumerated in chronological order below.1 when the stone is not of the best quality. It should not be laid I. LUCA DELLA ROBBIA (1399 or 14002-1482) was the of a less thickness than 2 inches; 2 or 3 inches are more usual.
son of a Florentine named Simone di Marco della Robbia. The flags should be square jointed, not under-cut at the edges, and should be well bedded and jointed with mortar. Caithiness flag is According to Vasari, whose account of Luca's early life is much more durable than York stone and wears more evenly; it is little to be trusted, he was apprenticed to the silversmith impervious to wet and dries quickly by evaporation: The edges Leonardo di Ser Giovanni, who from 1355 to 1371 was are sawn, and the hardness of the stone renders it difficult to cut working on the grand silver altar frontal for the cathedral and bricks made of seoria froin iron furnaces are both very durable, at PISTOIA (2.v.); this, however, appears doubtful from the though somewhat brittle. Asphalt either laid as mastic or com great age which it would give to Leonardo, and it is more pressed is extensively used for footways; the former is considered probable that Luca was a pupil of Ghiberti
. During the inferior in durability to York stone and the latter superior to it. early part of his life Luca executed many important and on 4 inches of cement concrete, and 1 inch of asphalt is desirable exceedingly beautiful pieces of sculpture in marble and where there is great traflic.
bronze. În technical skill he was quite the equal of Kerbing. Footways in a street must be retained by a kerbing of granite, Ghiberti, and, while possessing all Donatello's vigour,
York stone, l'urbeck, or other stone sufliciently strong to stand the dramatic power, and originality, he very frequently ex-
celled him in grace of attitude and soft beauty of expresA granite kerb is usually about 12 by 6 inches, either placed on sion. No sculptured work of the great 15th century ever edge or laid on the flat. When set on edge a kerb is generally surpassed the singing gallery which Luca made for the bedded on gravel with a mall; when laid on the flat a concrete bed cathedral at Florence between 1431 and 1440, with its ten
is desirable. Side In a macadamized street pitched or paved water channels are magnificent panels of singing angels and dancing boys, channels. required, to prevent the wash of the surface water from under- far exceeding in beauty those which Donatello in 1433
mining the kerh. The pitching consists of cubical blocks of hard sculptured for the opposite gallery in the same choir. This stone about 4 inches deep, bedded on sand
or mortar, or preferably magnificent work now lies scattered in various parts of the on a bed of concrete. A paved channel consists of flat stones about 1 foot widle inclining slightly towards the kerb. Moulded bricks
1 Genealogical tree of Della Robbia sculptors :-
Simone di Marco.
(1488-1560), (1475-1550 ?), (1470 ?), (1469-1529?), (1468 7), For fuller information on the subject see Sir Henry Parnell, A Treatise on worked mostly
Dominican worked mainly
? Not 1388, as Vasari says. See a document printed by Gaye, Carthe commissioners of sewers of the City of London.
(T. C.) teggio Inedito, i. pp. 182-186.
Florence an e.