Mr. Wm. H. Grant, Superintending Enginee_The Municipal and Sanitary Engineer's Handbook

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.

[Illustration: MESSRS. AVELING AND PORTER’S 15-TON STEAM ROAD ROLLER.]

[Illustration: MESSRS. GREEN AND SON’S 15-TON STEAM ROAD ROLLER AND

TRACTION ENGINE COMBINED.]

In Paris the Gellerat steam roller is used, and another is also known,

which is manufactured by Messrs. Morland and Sons.

A 15-ton steam roller costs about 650_l._ in the first place, the cost

of working it &c., has been given in the early pages of this chapter.

The advantages of steam road rolling may be summed up as follows:--

(1.) The saving of wear and tear to vehicles and horses. Roads should be

made _for_ the traffic, and not _by_ it.[51]

(2.) Economy; as it is said that a saving of from 30 to 50 per cent. is

effected by reason of the roads being better made thus obviating the

necessity for such frequent sweeping and scraping.

(3.) The roads can be made or repaired at any season of the year.

(4.) The avoidance of cruelty to horses, cattle, and sheep, as in the

case of newly metalled unrolled roads.

(5.) A saving of road metal. (_a_) Because it need not be broken so

small. (_b_) Because there are no loose stones to be kicked about and

lost. (_c_) Because there is no abrasion of the stones, only one surface

of the stone being exposed. (_d_) Because no ruts can be formed in which

water can lie to rot the stone. (_e_) Because a thinner coating of metal

can be employed.

(6.) The roller can be advantageously used for other purposes.

(7.) Rolled streets have a better appearance, they are easier of traffic

as having more evenness of surface and superior hardness, and it is

contended that if steam rollers were more general there would not be

such an outcry for other descriptions of pavement for roadways.

(8.) The steam roller soon finds out the good from the bad metal for

roads, it is also contended that it also does this with respect to the

gas and water mains, the latter, however may be looked upon as a rather

doubtful advantage.

(9.) The avoidance of the necessity of the continued employment of men

raking the metal into the ruts.

In Mr. Paget’s valuable little pamphlet upon the subject of steam

rolling[52] may be found the following remarks:--

“One of the main advantages attending the rolling of roads by

steam-power, consists in the diminished proportion of mud or soluble

matter which is then incorporated in the structure of the road surface.

If the surface of an ordinary road that has not been rolled is broken up

and the material washed, it is found that as much as half of it is

soluble matter, mud, dirt, and very fine sand; the stones, having only

been thrown loosely upon the road, have lain so long before becoming

consolidated by the traffic, and have undergone in the meantime such

extensive abrasion that the proportion of mud, dirt, and pulverised

material in the metalling is increased to that extent, and the stones

are really only stuck together by the mud. This accounts for the fact

that although an unrolled macadamised road may indeed, after long use,

have a surface that is pretty good and hard in dry weather, and may

offer then a very slight resistance to traction, yet it will quickly

become soft and muddy when there is any rain. By the employment,

however, of a steam roller upon the newly-laid metalling of a

macadamised road the stones are rolled in and well bedded at once, and

the surface is thus consolidated into a sort of stone felt, capable of

resisting most effectually the action of ordinary traffic, and

containing the smallest quantity of soluble matter to form mud in wet

weather.”

Having given the advantages of steam road rolling, I will now proceed to

give the disadvantages.

(1.) The first cost; this to a small borough or town is often the great

stumbling block. It is a pity that two or three of them could not join,

and procure one between them at joint cost, thus avoiding the

individually heavy burden.

(2.) The risk of damage to gas and water mains and services; or even of

cellars under the streets in some of the older towns.

(3.) The interference to traffic whilst the roller is at work; the

result is generally unsatisfactory if, to avoid this, the machine is

worked during the night.

(4.) The noise and smoke.

(5.) The risk of frightening horses.

(6.) If too heavy a roller is used, the foundation of the roadway may be

injured or the metal may be crushed instead of bedded.

(7.) The necessity of using so much binding material and water.

Before closing this chapter it will be necessary to say a few words upon

rollers drawn by horses.

These are always unsatisfactory: they are expensive to use, as a large

team of horses and a number of attendants are necessary; they are

difficult to turn, and the horses’ feet displace almost as many stones

as the roller compresses into their beds.

They cannot be of greater weight than 10 tons, even when on the

hydrostatic principle, and they are clumsy and difficult of

manipulation.

If a roller is to be used at all, let it be a steam road roller of the

most modern description, and of the best manufacture.

[42] _Vide_ ‘Minutes of Proceedings of the Institution of Civil

Engineers,’ vol. lviii. p. 95. (The first steam roller was made in the

year 1864.)

[43] The first steam roller used in England was, I believe, in the

year 1872; in Paris about 1864.

[44] This should be collected and “weathered” so as to get rid of mud

and any organic matter in it.

[45] In Paris 3 to 3·75 ton miles of roller are applied to every cubic

yard of metal; in America 5 ton miles are thought necessary.

[46] _Vide_ ‘Roads, Streets, and Pavements,’ by Q. A. Gillmore, p. 89.

[47] _Vide_ Aveling and Porter’s pamphlet on ‘Steam Road Rolling,’ p.

32.

[48] _Vide_ Aveling and Porter’s pamphlet on ‘Steam Road Rolling,’ p.

33.

[49] _Vide_ ‘The Use of Steam Rollers,’ by A. W. Parry, Reading.

[50] Some road surveyors contend that for gravelled roads 6-ton

rollers are heavy enough, for macadam roads 12-ton rollers.

[51] Traffic in making a roadway is apt to grind off the sharp edges

and spoil the metal before it is set.

[52] ‘Report on the Economy of Road Maintenance and Horse Draught

through Steam Rolling, with special reference to the Metropolis,’ by

Frederick A. Paget, C.E., etc. etc., London 1870, to which I refer my

readers for many scientific and useful facts upon this subject.

CHAPTER VIII.

PITCHED PAVEMENTS.

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]

Depth 6 to 8 inches

Width 2¹⁄₂ „ 3 „

Length 5 „ 9 „

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.

Depth. Width. Square yards.

5 inches × 3 inches covers 4¹⁄₃

6 „ × 3 „ „ 3²⁄₅

4 „ × 4 „ „ 5¹⁄₃

7 „ × 3 „ „ 3

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.

----------------+-------+---------------+-------+-----------+--------

----------------+-------+---------------+-------+-----------+--------

Guernsey | 4·734 | 7 1 12·75| 4·50 | 0·951 | 1·000

Herm | 5·250 | 7 3 24·25| 5·50 | 1·048 | 1·102

Budle | 6·336 | 9 0 15·75| 7·75 | 1·223 | 1·286

Peterhead (blue)| 3·484 | 4 1 7·50| 6·25 | 1·795 | 1·887

Heytor | 4·313 | 6 0 15·25| 8·25 | 1·915 | 2·014

Aberdeen (red) | 5·375 | 7 2 11·50| 11·50 | 2·139 | 2·249

Dartmoor | 4·500 | 6 2 25·0 | 12·50 | 2·778 | 2·921

Aberdeen (blue) | 4·823 | 6 2 16·0 | 14·75 | 3·058 | 3·216

----------------+-------+---------------+-------+-----------+--------

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.

[Illustration]

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]

Creosote

Pitch. Tar. Pitch. oil.

For grouting in pavements 1 to 1 or 3 to 1

For foundations or lower layer 3 to 1 or 3¹⁄₂ to ¹⁄₂

of asphalte macadam

For upper layer of asphalte 2¹⁄₂ to 1¹⁄₂ or 3¹⁄₄ to ³⁄₄

macadam and for foot paths

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]

[53] Birmingham in 1854 had not, I believe, a single mile of paved

streets; the principal ones are now nearly all paved with granite

setts, and over 20,000 square yards were so paved in 1880.

[54] It is said that the cost per annum per square yard of granite

paved roadways is but 3_d._, whereas the same cost for macadamised

roadways under the same circumstances is 1_s._ 6_d._

[55] In Paris after considerable research into the question, the

engineers of the Ponts et Chausseés, decided that the size of the

paving stones, which used formerly to be 9 inches square should be 4

inches wide by 6¹⁄₄ inches long by 6¹⁄₄ inches deep, the stone that is

used being a grit sandstone, from the forest of Fontainebleu.

[56] _Vide_ ‘Minutes of Proceedings of the Institution of Civil

Engineers,’ vol. lviii. p. 66.

[57] Syenite is a hard, greenish-grey metamorphic rock, composed

principally of silica, alumina, and lime, in conjunction with

magnesia, iron, etc. Its specific gravity is 2·96.

[58] Mr. Boyle, District Surveyor of Manchester, says: “I would

caution you against the use of the old blue Penmaenmawr stone as being

an extremely slippery stone, and one which makes a dangerous

pavement.” _Vide_ ‘Proceedings of the Association of Municipal and

Sanitary Engineers,’ vol. iii. p. 58.

[59] The old granite paving of London used only to last eight years.

_Vide_ ‘Minutes of Proceedings of the Institution of Civil Engineers,’

vol. ix. p. 222.

[60] _Vide_ ‘Street Carriageway Pavements,’ by George Frederick

Deacon, M. Inst. C.E., ‘Minutes of Proceedings of the Institution of

Civil Engineers,’ vol. lviii. p. 1 _et seq._

[61] The pavior’s rammer is about 55 lb. in weight, with an iron ring

at its foot; this is swung with some dexterity between the legs, and

is allowed to fall with great force upon the earth or stones it is in

use upon.

[62] The usual specifications for the Guidet paving blocks (in New

York) require that they shall be of granite, equal in hardness to the

Quincy granite, of durable and uniform quality, each measuring not

less than 3¹⁄₂ nor more than 4¹⁄₂ inches in width on the upper surface

or face, and not less than 10 nor more than 15 inches in length, and

not less than 8 nor more than 9 inches in depth. Blocks of 3¹⁄₂ inches

in width on the face to be not less than 3 inches in width at the

base; all other blocks to measure on the base not more than 1 inch

less in width or in length than on the face. The blocks are set

upright in close contact on their edges in courses, with the longest

dimensions and the continuous joints running across the street,

breaking joints lengthwise of the street.

The ends of the blocks are dressed off so as to give close joints in

the direction of the draught, while the broad vertical sides of the

blocks are left rugged or uneven, or with the split rock-face so that

the continuous joints running across the street are somewhat open.

_Vide_ ‘Roads, Streets, and Pavements’ by Q. A. Gillmore, p. 157.

[63] _Vide_ ‘A Treatise on Roads,’ by Sir Henry Parnell, p. 130.

[64] As these ingredients often vary very much in their constitution,

the surveyor must use his judgment to a great extent as to these

proportions.

[65] These boilers are now much used for such purposes, they hold from

60 to 500 gallons and are light and portable; the temper of the

bituminous mixture also remains uniform whilst being drawn off, and

there is very little evaporation or waste arising from them.

[66] Since writing the above, the Liverpool and Manchester tram-road

was designed I believe on this principle.

CHAPTER IX.

WOOD PAVING.

In the year 1843 Mr. Charles Cochrane, the President of the ‘Association

for the promotion of Improved Street Paving, etc.,’ in a paper which he

read before the Institution of Civil Engineers, on the State of the

Streets of the Metropolis, said that there existed at that date 100,000

yards of wood pavement.[67] He further states that it is said to be

slippery, but that he approves of it as the best material hitherto used,

“both as regards its general economy and durability as well as its

facility of traction, and more especially its extreme cleanliness.”

Two years previous to this date, Mr. Edward Lomas condemned wood

pavement as slippery, and recommended granite pavement for horses with

wood tram-tracks for the wheels of vehicles.[68]

Since these dates the question of wood paving has made giant strides,

many companies and private firms having started business as wood

paviors, with many various methods, which they strongly advocate as

being superior to the others; amongst them I will enumerate and describe

the following:

_The Improved Wood Pavement Company._--The ground being consolidated, a

layer of sand is made the basis of the pavement, and assumes the shape

the surface of the street is intended to take. Red-wood boards 1-inch in

thickness are then laid across the roadway, from kerb to kerb, placed

together so as to break joint; boards of the same material and

thickness are then laid longitudinally, and breaking joint in the same

manner.[69] On this foundation red-wood blocks are placed in rows,

taking the same direction as the under flooring.

Between each row of blocks, a strip of wood ³⁄₄ × ³⁄₄ inch is nailed to

the block and flooring, the blocks in all cases breaking joint; the

spaces thus formed between the rows of blocks are then run with a thick

composition which fills all vacant spaces there may be between the strip

and the block, covering the strip about ¹⁄₈ of an inch. Gravel, dried

and sifted through ³⁄₄-inch mesh, is then put in, solidly rammed, and

composition poured in; the pavement is then covered to a depth of ¹⁄₂ an

inch with dried gravel and composition for the purpose of indurating the

surface, and filling the spaces flush with the top of the block, a

slight covering of sand is then spread, when the traffic may immediately

pass over.

_The Asphaltic Wood Pavement Company._--After the ground is properly

prepared, 6 or 9 inches of concrete is laid, on this is laid a bed of

asphalte not less than ¹⁄₂-inch in thickness; then wood blocks 3 by 8 by

5 inches or 3 by 9 by 5 inches, of good, sound, yellow Baltic timber are

laid with joints ¹⁄₂-inch in width, these joints are filled from 2

inches up with heated asphalte, the remaining 3 inches being filled with

a grouting of hydraulic lime, and clean, sharp, fine river grit or sand,

the whole being covered with a top dressing of fine, sharp sand, which

wears in with the traffic.

_Croskey’s Wood Pavement._--Upon a bed of concrete, cross grained planks

were to be placed side by side and be forced together by pressure so as

to form a compact homogeneous surface of wood.[70]

_Lloyd’s Patent Keyed Wood Pavement._--The special feature of this

system is that _Pitch Pine_ blocks are used laid _direct_ upon the

concrete foundation, the blocks being grooved on each side so that the

grouting (composed of Portland cement) shall run in and form a key.

_Harrison’s Wood Pavement._--This system consists of a concrete

foundation, upon which strips of wood 2 inches wide by ¹⁄₂ an inch in

thickness are laid. Upon these, wood blocks 3 inches in breadth are

placed, and then hot asphalte is poured into the joints, which

conglomerates the whole.

_Henson’s Wood Pavement._--The main feature of this patent consists in

placing common felt on the concrete bed, and between the joints of the

wood blocks; thus, it is contended, giving elasticity and allowing for

the expansion and contraction of the blocks. The blocks are also

bevelled on the top and grooved in a particular manner.

_Carey’s Wood Pavement._--In this case the blocks are cut 4 inches wide

by 9 inches long, and 5 or 6 inches deep, according to the traffic;

these blocks are shaped with alternate convex and concave ends, and are

laid on a bed of sand about 2 inches thick, the joints between the

blocks, which have been left about ³⁄₈ inch wide, being filled with a

grouting of lime and sand.

_Messrs. Mowlem and Company’s_ method of laying wood paving is to form a

foundation of concrete, varying in thickness according to the nature of

the subsoil and the traffic; then to pave with blocks of yellow deal, 3

inches wide and 6 or 7 inches deep; the joints, which vary from ³⁄₈ to

¹⁄₂ inch, are filled in with sand and lias lime, and the surface is

afterwards indurated by strewing it with shingle.

_Patent Ligno-Mineral Paving Company._--This company lays claim to the

speciality of using hard woods as well as pine, and that the pine blocks

they employ are preserved or mineralised so as to be more durable than

the wood in its natural state.[71]

_Nicholson’s Wood Pavement._--This is principally in use in the United

States, and consists of rectangular blocks of pine laid upon a close

flooring of pine boards, 1 inch thick, laid lengthwise with the line of

street, their ends resting on similar boards laid transversely from kerb

to kerb, the boards being thoroughly tarred and laid upon a bed of sand.

The joints of the wood blocks are run with an asphaltic mixture, and the

whole surface is finally covered with hot coal tar and sprinkled with

fine sand and gravel.

_Stowe’s Wood Pavement._--This is also American, the blocks resting

directly upon sand or gravel about 6 inches in thickness.[72] “The

blocks are set in courses transversely across the street, so as to break

joint lengthwise of the street, the courses being separated from each

other 1 inch by a continuous course of wooden wedges placed close

together edge to edge, and extending from kerb to kerb. These wedges are

set in the first instance with their tops flush with the top surface of

the blocks. After the whole pavement shall have been well rammed, so as

to give each block a firm bed, the wedges are driven down about 3

inches, and the open joints thus formed above them between the courses

are filled in with a concrete composed of hot coal tar and fine roofing

sand and gravel. The surface of the pavement may then be coated with

coal tar prepared by boiling with pitch, and finished off with a thin

layer of sand.”

_Wood Paving in Norwich._--Mr. P. Marshall, the City Surveyor of

Norwich, states[73] that the wood pavement in that city is “simply laid

on the road formation levelled up with shingle. The blocks are grouted

in with blue lias lime and well rammed down. This makes a splendid road,

and is superior to any portion of the road that has been laid with

concrete. This wood paving, 5 inches deep, laid as described, costs

7_s._ per yard super. We have had some down here now for 2 years, and

have had no settlement whatever. It is a very important matter, for it

makes wood paving possible for country towns.”

_Shiel’s Composite Block Paving._--This pavement consists of composite

blocks 12 inches by 15 inches, cast in iron moulds with two rows of wood

placed at an equal distance from either side and each other, the vacant

spaces being filled with granite broken as for macadam; over all is

poured a boiling composition of pitch, chalk, and sand. The blocks are

thus treated at the works, and are, when cool, taken to the street, laid

on a concrete foundation, and grouted with cement grouting.

_Prosser’s Wood Pavement._--This is composed of blocks sawn at an angle

of 60°, the grain of the wood running in the same direction. Each end of

the block rests on the other, transversely to line of street. Between

the rows of blocks a plank, the same depth as the blocks, but with the

grain of the wood horizontal, is placed. The blocks, which on one side

of the plank lean in an opposite direction to those on the other, are

secured or dowelled together by wooden pins running through the plank

and piercing the blocks about an inch.

In Chicago, U.S.A., cedar blocks 6 inches square, set on a composition

of tar and gravel, are used, and are said to make a very durable

pavement.

The following sanitary objections to wood as a material for pavements

are made in the Report on the Application of Science and Art to Street

Paving and Street Cleansing of the Metropolis (1872) page 17.

“The General Board of Health set aside wood as an ineligible material

for this amongst other reasons, that street surfaces ought to be

impermeable; and for roads of light traffic and cheap construction, they

looked to modifications of macadam, with bituminous binders of mineral

tar. Since then wood has been reproduced for the purpose, and strongly

pressed in improved forms for trial. It certainly offers the advantage

of a great gain in noiselessness over granite, more especially from the

horses’ feet, though with some disadvantage from a dead rumble and

vibration; and further it has the advantage of being more available than

smooth pavements for inclines. But hygienists object to its use on

grounds which, in the absence of sanitary science, are overlooked, but

which it is important to particularise as showing the dangerous state of

ignorance and incompetency of the authorities by whom they are not

entertained or are disregarded.”

The sum total of these charges against wood as a pavement consists in

the following: “Wood is porous, it is composed of bundles of fibres, it

absorbs and retains wet, foul wet especially.” Why _foul_ wet should be

absorbed more than ordinary wet does not transpire.

There is no doubt that wood in its natural state does absorb a large

quantity of water,[74] but this can be avoided in wood paving by

preserving the wood of which it is composed by one of the following

processes.

(1) Burnetising Chloride of zinc is used in this process.

(2) Kyanising Corrosive sublimate is used.

(3) Renwickising Boiling in coal tar.

(4) Boucherising Sulphate of copper is used.

(5) Bethelising Creosote heated to 200° F. is used.

(6) Seelyising Creosote is also used, the wood being first boiled.

(7) Hayfordising Creosote is also used, wood being unseasoned.

The fibres of the wood are also compressed, and no open joints between

the blocks are permitted, by paving the blocks transversely, with butt

joints closely packed together, and by filling the cross joints with an

asphaltic or other impervious grouting.

Wood paving should, however, be laid in streets with moderate traffic,

and plenty of sun and air. In confined spaces such as courts, it soon

rots and becomes a source of much unhealthiness.[75]

Many reports have been from time to time made on the advantages and

disadvantages of wood paving, and much has been said and written upon

the subject, so that I will only touch upon some of the principal

questions at issue.

The first of importance is that of durability, and although the life of

a hard wood constantly exposed to attrition is amazing, as may be seen

on the stairs of the Metropolitan Railway Stations, and in many cog

wheels of old machinery, still some diversity of opinion exists as to

what may be fairly put down as the wear per annum of the surface of a

street paved with wood blocks.

It must be remembered that to arrive at any fixed ratio of wear, a

standard of traffic should be fixed; but this unfortunately has not

hitherto been done, so that the results of observations are bound to

differ considerably. It must also not be lost sight of that the reason

of excessive wear in a wood pavement generally arises from wide joints

being the means of causing the edges of the blocks to abrade and become

worn.

Mr. D. T. Hope, in a paper he laid before the Scottish Society of Arts,

upon some most careful investigations he had made on this subject, gives

the wear as ¹⁄₈ of an inch in 18 months on blocks laid with vertical

fibre, which he proved was the best manner of laying them to ensure the

longest life.

Mr. Deacon estimated the wear at from 1³⁄₈ inch to 2⁵⁄₁₆ inches per

annum.[76]

Mr. Copland estimated the wear at ³⁄₁₆ of an inch per annum.[77]

Mr. Howorth estimates the life of wood paving at 25 years per inch of

wood, if an absolutely uniform quality of wood fibre could be

assumed.[78]

Mr. Haywood says,[79] “Wood pavements with repairs have in this City

(London) had a life varying from 6 to 19 years, and that with repairs,

an average life of about 10 years may be obtained.”

The life of wood is no doubt extended by being preserved by one of the

processes I have enumerated, but as its life may be taken as an average

of 8 to 10 years, and as the blocks are bound to wear unevenly, they

should be made as shallow as is consistent with stability; as it is an

undisputed fact that the foundation of a roadway is the important

carrier of the traffic, the surface material, of whatever it may be

constructed, only acting as a skin to preserve it. If the blocks are too

thick, unnecessary capital is locked up.

Wood pavement was laid in Sunderland[80] in 1859 with strips of

creosoted red pine, creosoted beech wood, and unpreserved oak, the bulk

of the paving being unpreserved red deal, and this was replaced in 1867.

In 1877, on renewing the pavement, it was found that the creosoted wood

suffered less from wear and tear than the unpreserved, so the whole was

done with creosoted red pine, the original strip of creosoted red pine

was left untouched, the strip of oak was turned, and the beech was

merely raised; and there is no doubt that the best wood pavement is that

which can be constructed in the simplest manner, as for instance deal

blocks 4 or 5 inches deep, laid with a close joint upon a Portland

cement concrete bed, the blocks being well grouted in with Portland

cement grouting, their surface being afterwards sprinkled or strewn with

sand or sharp gravel.

The woods employed for paving are beech and oak, both of which are said

to be too slippery, elm, which is not durable, pitch pine and Baltic

fir. Memel and Dantzic timber is better than Riga, the best wood for the

purpose being said to be Wyborg or St. Petersburgh red deals.

All sappy wood must be at once rejected as unsuitable. This is a great

objection to creosoting or other preserving processes, as it hides

defects in the wood.

The advantages of wood paving may be summed up as follows:--

(1.) It is the quietest of all known pavements, wheels make scarcely any

noise upon it and there is no clatter of horses’ hoofs.

(2.) It is much safer than either asphalte or granite pavements for

horses travelling upon it and if a horse falls he can rise more easily.

(3.) The traction necessary upon it, though slightly greater than upon

asphalte, is compensated for by the better foothold given to horses.

(4.) It is clean. If well constructed there should be no mud made upon

it; all that appears upon its surface should arise either from its being

imported upon it, or from the gravel with which it is sometimes

necessary to dress the surface.

(5.) It presents a uniform and slight elasticity, which is of great

benefit to vehicles passing over it.

(6.) It may be laid on a gradient of 1 in 20 with safety to the traffic.

The principal objections to wood as a paving are:--

(1.) It is said to absorb moisture and to smell offensively, but this

has often been refuted.[81] (2.) It is said to be difficult to cleanse

without the aid of water, as dirt adheres to the wood, and lingers in

the joints.

(3.) It is not easy to open it or repair it, for the purposes of gas and

water pipes, etc., and rather a large surface has to be removed for this

purpose, and it has to be left a little time after repairs before

traffic is again allowed on it.

(4.) The wood swells if wet, and cases are on record of the side kerbs

of streets being raised, and lamp posts thrown down, by the pressure of

the wood thus swelling.[82]

With regard to the cost of wood paving. This must vary in different

localities, according to the value of labour, of materials, and in the

manner in which the work is done.

The practice of most of the companies engaged in this class of work is

to make a fixed charge per square yard for the pavement, including the

concrete but excluding the excavation, and they also guarantee to keep

the pavement in repair free of charge for one or two years, and then

for so many years after, at so much per yard per annum.

About 14_s._ per square yard is generally the first charge for

constructing, and 1_s._ per square yard is the annual charge for

maintenance.

Upon the subject of cost the following tables[83] may be useful.

TABLE SHOWING THE ACTUAL DURATION AND COST OF CERTAIN WOOD PAVEMENTS IN

THE CITY OF LONDON.

-----------+----------+----------+-----------+-----------+-----------

-----------+----------+----------+-----------+-----------+-----------

| |Yrs. Mths.|£ _s._ _d._|£ _s._ _d._|£ _s._ _d._

Cornhill |May, 1855 | 10 2 |0 12 2 |0 17 4¹⁄₂|0 2 11

|July, 1865| 6 8 |0 11 6 |0 8 9³⁄₄|0 3 0¹⁄₂

| | | | |

Gracechurch|Nov. 1853 | 11 7 |0 12 8 |0 17 1¹⁄₂|0 2 6³⁄₄

Street |June, 1865| 6 0 |0 11 6 |0 6 11 |0 3 0³⁄₄

| | | | |

Lombard |May, 1851 | 9 4 |0 9 6 |0 6 0 |0 1 7³⁄₄

Street |Sept. 1860| 10 7 |0 9 2 |1 0 2 |0 2 9

| | | | |

Lothbury |May, 1854 | 12 3 |0 12 6 |1 8 4³⁄₄|0 3 4

|Aug. 1866 | 6 1 |0 12 6 |0 3 5³⁄₄|0 2 7¹⁄₂

| | | | |

Mincing |July, 1841| 19 1 |0 14 4 |0 13 4 |0 1 5¹⁄₄

Lane |Aug. 1860 | 13 0 |0 9 2 |1 2 6³⁄₄|0 2 5¹⁄₄

| | | | |

Bartholomew|May, 1854 | 12 3 |0 12 6 |0 17 5³⁄₄|0 2 5¹⁄₄

Lane |Aug. 1866 | 5 5 |0 12 6 |0 3 11¹⁄₄|0 3 0¹⁄₄

-----------+----------+----------+-----------+-----------+-----------

Foundations are included, but no excavation.

TABLE SHOWING FIRST COST, AND TENDERED COST PER ANNUM FOR MAINTAINING

CERTAIN WOOD CARRIAGEWAY PAVEMENTS IN THE CITY OF LONDON.

-----------------+----------+-------------+------------+------------+

| | | | |

| Date when| Name of | by | per |

-----------------+----------+-------------+------------+------------+

| | | | £ _s._ _d._|

King William |Feb. 1873 |Improved Wood| 16 | 0 18 0 |

| | | | |

Ludgate Hill |Nov. 1873 | Ditto | 16 | 0 18 0 |

| | | | |

| | | | |

| | | | |

| | | | |

Ditto |Dec. 1871 |Improved Wood| 3 | 0 16 0 |

| | | | |

Duke Street |May, 1873 | Mowlem and | [84]5 | 0 15 0 |

| | Co. | | |

| | | | |

| | | | |

| | | | |

-----------------+----------+-------------+------------+------------+

-----------------+------------------------+------------+------------

| | Total Cost |

| |of Pavements|

| | during |

| Agreed Cost of | Contract |Average Cost

| maintenance per | Term, | per Square

| Square Yard for the | per Square | Yard per

Situation. | Contract Term. | Yard. | Annum.

-----------------+------------------------+------------+------------

| | £ _s._ _d._| £ _s._ _d._

King William | 1 year free | 2 0 6 | 0 2 6¹⁄₄

Street |15 years at 1_s._ 6_d._ | |

| = 1_l._ 2_s._ 6_d._ | |

| | |

Ludgate Hill | 1 year free | 2 0 6 | 0 2 6¹⁄₄

|15 years at 1_s._ 6_d._ | |

| = 1_l._ 2_s._ 6_d._ | |

| | |

Portions of Great| 1 year free | 1 14 9 | 0 2 2

Tower Street and |15 years at 1_s._ 3_d._ | |

| = 18_s._ 9_d._ | |

Seething Lane | | |

| | |

Bartholomew Lane | ---- | ---- | ----

| | |

Ditto | 3 years free | 0 16 0 | ----

| | |

Duke Street | 2 years free |{

| 3 years at 1_s._ |{

| = 3_s._ |{

| |{These pavements

Houndsditch | 2 years free |{will no doubt last

| 5 years at 9_d._ |{some years longer

| = 3_s._ 9_d._ |{than the contract

| |{term of maintenance.

Ditto | 2 years free |{

| 5 years at 1_s._ |{

| = 5_s._ |{

-----------------+------------------------+-------------------------

In the wood pavements the cost of the foundation is included, but no

excavation.

The pavements at the end of each financial year are to be in a good

sound condition.

The following table[85] is also given as showing the comparative cost

of wood paving with macadam and bituminous concrete paving in

Liverpool.

----------+--------+----------------------------+-----------+---------

| | Deductions from | | Sinking

| | First Cost to determine |Interest on| Fund

|Original| Cost of Renewal. | Original |invested

|Cost per+-------------+--------------+ Cost at |at 3

Des- | Square | Cost of |Allowances for| 4¹⁄₂ per |per

----------+--------+-------------+--------------+-----------+---------

| _s. d._| _s. d._ | _s. d._ | _d._ | _d._

No. 6. | | | | |

Concrete | 3 9 | Nil | Nil | 2·0 | Nil

| | | | |

No. 7. | | | | |

Wood |15 1·5| 2 0 | Nil | 7·5 | 4·3

| | | | |

No. 8. | | | | |

Macadam | 6 9 | Nil | Nil | 3·4 | Nil

----------+--------+-------------+--------------+-----------+---------

----------+-----------+----------+----------+---------

| | | |

| | | | Total

Des- |Maintenance|Scavenging|Gravelling| Annual

cription |per Square |per Square|per Square|Cost per

of | Yard per | Yard per | Yard per | Square

Pavement.| Annum. | Annum. | Annum. | Yard.

----------+-----------+----------+----------+---------

| _s._ _d._ | _d._ | _d._ |_s._ _d._

No. 6. | | | |

Bituminous| | | |

Concrete | 0 9 | 2·4 | .. | 1 1·4

Pavement | | | |

| | | |

No. 7. | | | |

Wood | 0 1·0 | 2·7 | 5·0 | 1 8·5

Pavement | | | |

| | | |

No. 8. | | | |

Macadam | 1 0 | 8·0 | Nil | 1 11·4

Pavement | | | |

----------+-----------+----------+----------+---------

In concluding this chapter upon wood paving, I will give a specimen

specification for work of this description.

_Excavation._--Excavate the ground to a depth of -- inches below the

level of the proposed finished surface of the roadway.[86] The formation

surface thus excavated must be well watered and rolled or punned if

found necessary, and any soft or made earth removed to such a depth as

may be found to be sufficient.[87]

_Foundation._--Upon the excavated formation surface a bed -- inches

thick of concrete is to be laid, composed of one part of good approved

Portland cement to two of fine, sharp river sand, and three of clean

river ballast or broken stone. The concrete to be finished off with an

even and smooth top surface conforming with the contour line of proposed

finished roadway.

_Wood Blocks._--Upon the concrete thus laid, and after it has

sufficiently set, wood blocks are to be laid.[88] These blocks must be

of the best description of Baltic red timber[89] (or such other timber

as shall be specified), sound and thoroughly well seasoned, free from

all sap, shakes, large and loose knots or other defects, and any that

may be rejected by the surveyor as unfitted for the work shall be at

once removed from the works or broken up. The blocks must not be less

than 6 inches or more than 12 inches in length by 3 inches in width and

6 inches in depth, they are to be carefully laid with the fibre of the

wood placed vertically, their ends must butt with close joints to each

other, and each course must be kept ³⁄₈ of an inch apart by means of

wooden laths, which are afterwards removed.

_Joints._--The joints are then to be carefully run with a grouting

composed of one part of best approved Portland cement to two parts of

fine, sharp, clean river sand. (In some cases a hot bituminous mixture

or asphalte is run between the joints as a grouting.)

_Top Dressing._--The whole surface of the pavement is then to be spread

with a coating, at least ¹⁄₂-inch in thickness, of fine sharp gravel or

chippings.

The following heads of general conditions under such a contract may also

be useful.

Alteration of gullies, sewer man-holes etc., will be done at the expense

of the sanitary authority.

Contractor must make good at once any damage caused to gas or water

mains or services--time penalty for delay.

Maintenance of work after completion for a specified time.

Power must be reserved to surveyor to suspend work during bad weather or

from other causes.

Heavy time penalties for non-completion of contract by a certain date.

Payments to be made to contractor on surveyor’s certificate, up to 80

per cent. of whole contract, remaining 20 per cent. to be paid at end of

(say) 2 years after completion.

With the above specimen specification I conclude the chapter on Wood

Paving.

[67] The first wood pavement laid in London was in front of the Old

Bailey, in 1839.

[68] _Vide_ ‘Minutes of Proceedings of the Institution of Civil

Engineers,’ vol. i. p. 131.

[69] This specification is the company’s own, as advertised when they

first began business; for many reasons the boards have since been

discontinued, and other alterations introduced into the system.

[70] I am unable to ascertain if this plan has ever been tried

anywhere.

[71] It is also affirmed by the Borough Surveyor of Sunderland that

this process dispenses with watering. _Vide_ ‘Proceedings of the

Association of Municipal and Sanitary Engineers and Surveyors,’ vol.

iii. p. 72.

[72] _Vide_ ‘A Practical Treatise on Roads, Streets, and Pavements,’

by Q. A. Gillmore, p. 166, which see also for a good account of wood

pavements in the United States.

[73] _Vide_ ‘Wood Pavements,’ by Henry Allnutt, 1880, p. 22.

[74] The power of absorbing water by wood varies from 9·37 to 174·86

per cent. in dry wood. In its ordinary state the power varies from

4·36 to 150·64 per cent. The quantity of water contained in wood in

its natural state varies from 4·61 to 13·56 per cent. _Vide_ ‘Minutes

of Proceedings of the Institution of Civil Engineers,’ vol. lvi. p.

300.

[75] _Vide_ ‘Roads and Roadways,’ by George Waller Wilcocks, 1879, p.

34.

[76] _Vide_ ‘Minutes of Proceedings of the Institution of Civil

Engineers,’ vol. lviii. p. 82.

[77] _Ibid_, vol. lx. p. 293.

[78] _Ibid_, vol. lviii. p. 45.

[79] ‘Report upon Asphalte and Wood Pavements,’ by William Haywood,

(1874) p. 44.

[80] See ‘Paper on Wood Pavements,’ by R. S. Rounthwaite, Boro’

Surveyor, Sunderland, ‘Proceedings of the Association of Municipal and

Sanitary Engineers and Surveyors,’ vol. vii. p. 48.

[81] The surveyor of the parish of St. George’s Hanover Square,

London, says, “My experience of wood, and I have laid down 25,000

yards, is that it is perfectly free from smells, even on a cab rank.”

Report of a Committee of the Paddington Vestry on Wood and other

Pavements (1878) p. 30.

[82] Mr. Allnutt says on this: “As to the swelling of the wood, it has

been remarked that even brick walls have been forced out. We do not

see what provision can be made for this; but leaving the channel by

the kerb stone for the last work may relieve the lateral pressure, and

perhaps it would be as well for the blocks not to be so dry when being

laid down.” _Vide_ ‘Wood Pavement as carried out on Kensington High

Road, Chelsea, etc.’ by Henry Allnutt (1880) p. 15.

[83] _Vide_ ‘Report on Asphalte and Wood Pavements,’ by William

Haywood, 1874, pp. 38 and 41.

[84] The Ligno-Mineral Paving Company and the Improved Wood Paving

Company offered to maintain their pavements, if laid, for terms of ten

years and fourteen years respectively; their tenders were not

accepted.

[85] _Vide_ ‘Paper on Street Carriageway Pavements,’ by G. F. Deacon,

‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol.

lviii. p. 23.

[86] If the road material thus excavated is macadam, it may be

screened and used as concrete in the foundation, if approved by the

surveyor. The granite pitching of crossings, channel gutters, etc.,

must remain the property of the sanitary authority, as well as the

surplus macadam.

[87] It is important to give sufficient notice to gas and water

companies in order that they may attend to their mains and services

before the foundations are put in.

[88] Sometimes about half an inch of fine sand is spread upon the

surface of the concrete upon which the wood blocks are bedded.

[89] If the blocks are to be creosoted, the number of pounds of

creosote that should be absorbed in a cubic foot of the wood should be

specified; this is generally about 10 lb. of creosote to 1 cubic foot

of wood.

CHAPTER X.

COMPRESSED ASPHALTE ROADWAYS.

The word asphalte in its generally accepted sense implies a natural rock

consisting of pure carbonate of lime, intimately combined and

impregnated with mineral bitumen in very variable proportions; that used

for roads or footpaths should not contain less than 7 or more than 12

per cent. of bitumen.

The rock when broken takes an irregular fracture without definite

cleavage; it is principally derived from Val de Travers, Seyssel,

Sicily, Chieti, Auvergne, Lobsann, and Limmer. Its grain should be

regular and homogeneous, the finer the grain the better.[90]

When exposed to the atmosphere asphalte gradually assumes a grey tint,

by reason of the bitumen evaporating from the surface leaving a thin

film of limestone behind. The stone is usually taken from open quarries,

but at Val de Travers shafts are sunk and the general treatment is

similar to a coal mine.

Bitumen, it must be borne in mind, is itself a mineral product found in

Trinidad and some other places; it is composed of carbon, hydrogen, and

oxygen.

The weight of a cubic yard of natural asphalte is about 3874 lbs., its

specific gravity is 2·114, but this of course varies with its percentage

of bitumen.

The following is a test for asphalte given by Mr. Deland in a paper he

read before the Institution of Civil Engineers in the year 1880.[91]

“A specimen of the rock freed from all extraneous matter, having been

pulverised as finely as possible, should be dissolved in sulphurate of

carbon, turpentine, ether or benzine, placed in a glass vessel and

stirred with a glass rod. A dark solution will result, from which will

be precipitated the pulverised limestone. The solution of bitumen should

then be poured off. The dissolvent speedily evaporates, leaving the

constituent parts of the asphalte, each of which should be weighed so as

to determine the exact proportion. The bitumen should be heated in a

lead bath and tested with a porcelain or Baumé thermometer to 428° Fahr.

There will be little loss by evaporation if the bitumen is good, but if

bituminous oil is present the loss will be considerable--gritted mastic

should be heated to 450° Fahr. The limestone should next be examined. If

the powder is white and soft to the touch it is a good component part of

asphalte, but if rough and dirty on being tested with reagents it will

be found to contain iron pyrites, silicates, clay, etc. Some asphaltes

also are of a spongy or hygrometrical nature. Thus, as an analysis which

merely gives so much bitumen and so much limestone may mislead, it is

necessary to know the quality of the limestone and of the bitumen.

“For a good compressed roadway an asphalte composed of pure limestone

and 9 to 10 per cent. of bitumen, non-evaporative at 428° Fahr., is the

most suitable. Asphaltes containing much more than 10 per cent. of

bitumen get soft in summer and wavy, those containing much less have not

sufficient bind for heavy traffic, although asphalte containing 7 per

cent. of bitumen properly heated does well for court yards, as it sets

hard when cold.”

For roadways “compressed” asphalte should be used and not “mastic,”

which is only fitted for footpaths, court-yards, etc. Compressed

asphalte roadways are constructed as follows:

The asphalte rock is first crushed in a “Blake’s” or other suitable

crusher, then pulverised in what is known as a “Carr’s disintegrator,”

until it is reduced to a powder; this powder is then heated up to

between 212° and 250° Fahr. in revolving cylinders and is laid about

2¹⁄₂ inches in thickness upon a concrete foundation previously prepared

for its reception, the powder is carefully raked to the required contour

and then either rolled or punned with iron punners previously heated to

prevent the adhesion of the powder to them.

A roadway thus prepared presents many advantages over macadam, granite

setts or wood, the following passage amply describing one of them:[92]

“An indispensable feature of a weight-carrying pavement must be the

absolute exclusion of water at the surface as nearly as it can be

insured, and in this one respect it cannot be questioned that a surface

like asphalte has no equal, the absorption being so gradual as to be

inappreciable during any possible continuance of moisture.”

In addition to this indisputable fact the advantage of durability is

claimed for asphalte, but this must vary considerably with the quality

of the material and of the work. Mr. Hayward estimates the life of an

asphaltic Val de Travers compressed roadway at 17 years, and it is

claimed for it that it will wear until it becomes quite thin, very heavy

traffic breaking it up when it is worn to about ³⁄₄ of an inch thick.

Another advantage claimed for asphalte is cleanliness, and this is

evidently indisputable, as, being impervious, none but imported mud or

dust can be formed upon it.

In addition to the foregoing the following advantages are also claimed:

Pedestrians can walk on asphaltic roadways as well as on the footways.

It is comparatively noiseless under traffic, though in this case wood

is better, as the clatter of the iron-shod horses’ feet upon asphalte is

very apparent.

It is expeditiously laid, and when repairs are necessary they can easily

be effected; no pavement shows less signs of openings being made in it

for gas and water-pipe repairs than asphalte.

The rapid laying causes less inconvenience to traffic in the streets.

Ease of traction; but here steps in the one great objection to asphalte

as a roadway paving, viz. danger to horses by slipping and falling, of

which I shall say more hereafter.

Cellars and vaults under the streets are kept dry, by reason of its

impermeability to moisture.

Easily cleansed, especially by mechanical sweeping, and snow is easily

removed.

It is very pleasing to the eye, being so uniformly regular and of good

colour.

There is no vibration or concussion in travelling over it, and apart

from the question of safety it is delightful to drive over it.

It is a cool pavement at night; it does not absorb heat during the day,

and consequently none radiates from it after the sun has gone down.[93]

The great objection to asphalte as a material for roadways arises from

the fact that it is extremely slippery when damp,[94] irrespective of

temperature, and this in the climate of England is frequently the case.

The result of this slipperiness is, that not only do horses frequently

fall upon it, but it is also difficult to stop a horse when drawing a

load, thus causing more risk to foot-passengers of being run over, and

straining the horse considerably in its efforts. Again, in thoroughfares

crowded with vehicular traffic, constant stoppages occur, and in

starting again it is painful to witness the struggles of the horses to

keep their footing and overcome the inertia of their load. When a horse

falls he has very great difficulty in rising, but on the other hand,

although he may be strained, a horse never breaks his knees upon this

class of pavement. How far this might be altered if _all_ the streets of

a town were paved with asphalte, is a fair matter for argument, as it is

asserted that horses are very nervous on going from one pavement to

another, and accidents frequently happen in consequence.

The strewing of sand upon asphalte renders it less slippery, but in

addition to the interference of the traffic whilst this is being done,

there are the further objections, of the possible injury of the sand

cutting into the asphalte, the expense of labour and materials, and the

mud caused thereby which has afterwards to be removed. Another plan is

to frequently wash the asphalte with water, but this is expensive and

only of temporary benefit.

Another objection to asphaltic roadways is that they cannot with safety

be constructed of greater gradient than 1 in 60, and it must also be

borne in mind that fine weather is necessary both for the construction

and repairs of a roadway of this description.

Very little smell, and that not of an unpleasant character, arises from

the work when compressed asphalte is being used, the mastic is however

temporarily unpleasant to those who dislike the odour.

With reference to the question of the cost of compressed asphalte for

roadways: it is of course a matter depending upon local circumstances as

to the first cost, but it must be remembered that the compressed

asphalte hitherto laid has been nearly all that of the Val de Travers

Company, who charge a fixed price per square yard for laying according

to thickness required, the distance of the locality from London, and

other local circumstances. With reference to maintenance, this is a

question dependent mainly upon traffic, but here again the company will

undertake to keep in repair at so much per square yard per annum for a

certain number of years.

It would, however, perhaps be a better plan not to enter into such an

agreement, but to arrange for repairs under a schedule of prices, but

this must greatly depend upon the character of the work in the first

place, and other local considerations.

Mr. Ellice Clarke gives the following as the cost of Val de Travers

compressed asphalte.[95]

The cost is reduced to 100,000 tons per annum per yard of width.

----+-------------+-----------+-----------+----------+---------+----

+-------------+-----------+-----------+----------+---------+

| _s._ _d._ | _d._ | _d._ | _d._ |_s._ _d._|

| 18 0 | 9·7 | 3·6 | 0·4 | 1 1·7|

----+-------------+-----------+-----------+----------+---------+----

Nothing is charged for renewal, as the annual sum for maintenance

provides the asphalte in perpetuity.[96]

The following table[97] may here be of use:

TABLE SHOWING THE AGREED COST PER ANNUM OF CERTAIN ASPHALTE CARRIAGEWAY

PAVEMENTS IN THE CITY OF LONDON.

-----------+------------+--------+----------+-----------------------+

-----------+------------+--------+----------+-----------------------+

| | |£ _s. d._| |

|(Compressed)| | | = £1 2_s._ 6_d._ |

| | | | |

| | | | = 15_s._ 0_d._ |

| | | | |

| | | | = 11_s._ 3_d._ |

| | | | |

| | | | = 11_s._ 3_d._ |

| | | | |

| | | | = 11_s._ 3_d._ |

| | | | |

| | | | = 11_s._ 3_d._ |

| | | | |

| | | | = 11_s._ 3_d._ |

| | | | |

| | | | = 11_s._ 3_d._ |

-----------+------------+--------+----------+-----------------------+

-----------+---------------+------------

| Total Cost of |

| Pavements |Average Cost

|during Contract| per Square

| Term per | Yard per

Situation.| Square Yard. | Annum.

-----------+---------------+------------

| £ _s._ _d._ | £ _s._ _d._

Cheapside | 2 0 6 | 0 2 4¹⁄₂

and Poultry| |

| |

Gracechurch| 1 12 0 | 0 10 1¹⁄₂

Street | |

| |

Finsbury | 1 7 3 | 0 1 7¹⁄₄

Pavement | |

| |

Moorgate | 1 7 3 | 0 1 7¹⁄₄

Street | |

| |

Ditto | 1 7 3 | 0 1 7¹⁄₄

| |

Lombard | 1 7 3 | 0 1 7¹⁄₄

Street | |

| |

Cornhill | 1 6 3 | 0 1 6¹⁄₂

| |

Mincing | 1 3 3 | 0 1 4¹⁄₂

Lane | |

| |

-----------+---------------+------------

The cost of foundations is included in this table, but their thickness

is not mentioned; the excavation was done for the contractors.

With the one serious objection of slipperiness, compressed asphalte

seems a most suitable material for the surface of a roadway, but that

objection is of considerable weight when we reflect that the great

object of roadways is that of “traffic,” and it is for that purpose they

are constructed; still, in cities where a heavy _business_ traffic is

going on, this class of roadway has so many advantages that where cheap

horses are driven it might be used; where, however, valuable horses are

used for pleasure driving, as in the west end of London and the

corresponding better parts of cities, some other description of roadway

should be maintained.

Mastic asphalte will be described in the chapter on footpaths.

_Specimen Specification for a Compressed Asphalte Roadway._

_Excavation and Concrete._--The excavation and concrete[98] foundation

may be specified to be executed in a manner similar to that contained in

the specimen specification for wood paving,[99] except of course that

the excavation will be shallower in this case.

_Asphalte._--The asphalte to be used shall be the pure unadulterated

natural rock known as the Val de Travers, and be unmixed with any

foreign or other matter whatever. The rock after being properly broken,

shall be ground in a Carr’s disintegrator to a powder of such fineness,

that not more than per cent. shall be left on a sieve containing

meshes to the square inch and decrepitation by heat will not be

accepted. This powder shall be heated to 240° F. or such other

temperature as shall be found desirable, so as to eliminate all

moisture, and carefully transported to the street in covered iron carts,

in order that not more than 20° F. of heat shall be lost in transit. The

powder must be spread upon the concrete inches in thickness[100] and

carefully raked so as to have regularity of depth and surface.

_Ramming._--The powder must then be rammed with iron punners of not less

weight than 10 lb. heated so as to prevent the adhesion of the asphalte.

The ramming must be done lightly at first, so as to ensure equality of

thickness, and afterwards augmented to heavy blows. Where the rammers

are not available a T tool must be employed.

To meet some of the objections to compressed asphalte as a material for

roadways the “Imperishable Stone Paving Blocks” have been introduced in

America; they consist of asphalte formed into rectangular blocks under

pressure of about one ton to the square inch, these are laid close

together without any grouting, and a pavement of this description is

said to combine all the advantages of wood and asphalte, though

sufficient time has not yet elapsed to prove this.

In Salford, Manchester, etc., I believe “Woodward’s Patent Molten

Ironstone Blocks” are used with some success where there is not any very

exceptionally heavy traffic.

One of the principal reasons of durability in asphalte pavement is its

elasticity, and it should be remembered that compressed asphalte does

not begin to “wear” until all compression has ceased; this is the case

with no other system of pavement--stone and wood both begin “wearing”

from the day the traffic commences. Under ordinarily heavy traffic it

may be estimated that it will take two years to complete the compression

of asphalte, and the weight of a square foot of this pavement will at

the expiration of that time be nearly the same as on the day it was

laid, though the thickness is reduced during the first two years as

much as it will be in the following eight.

Much is said about the advisability of _good_ and _dry_ concrete, but it

may be as well to explain the reasons that necessitate so much care in

the foundation. First, it should be always borne in mind that asphalte

pavement is nothing more than a tough “carpet,” and has no power of

itself of offering resistance to heavy traffic; consequently, if the

substratum or concrete is not thoroughly solid and resisting, the weight

of traffic will crush it, and the asphalte will at once give way in all

directions. The concrete should be made strong enough to resist the

traffic, and the asphalte is a simple covering to protect the concrete

from direct contact with the wear and friction caused by the traffic. So

much for the strength, but the dryness is of even still greater

importance; for the best asphalte, laid by skilled workmen, on

thoroughly first-rate but damp concrete, will rapidly go to pieces--a

phenomenon takes place, which, although quite natural, is little

realised by most engineers. When the hot asphalte is laid, the water is

immediately sucked up and turned into steam, which tries to escape

through the heated powder, and the result is that although the surface

of the asphalte is smooth, the mass is really disintegrated from

underneath by its bitter enemy “water,” and as soon as the surface

begins to wear, the fissures formed by the passing of the steam appear

on the surface and the whole pavement falls to pieces: thus accounting

for some of the failures this description of roadway has met with under

unskilled treatment.

This completes the subject of roadways; I will turn to that of footpaths

in the next chapter.

[90] In this respect the Seyssel is the best, being of a very fine

grain.

[91] _Vide_ ‘Minutes of Proceedings of Institution of Civil

Engineers,’ vol. lx.

[92] _Vide_ Mr. Howarth’s paper on ‘Wood as a Paving Material under

Heavy Traffic,’ ‘Minutes of Proceedings of the Institution of Civil

Engineers, vol. lviii. p. 35.

[93] In Paris and other cities liable to civil war or internal

commotions, it is contended as an advantage of asphalte that it cannot

be used for the construction of barricades, breastworks, or rifle

pits.

[94] _Vide_ Mr. Haywood’s Report upon Asphalte and Wood Pavements,

also Report on the Application of Science and Art to Street Paving and

Cleansing of the Metropolis,’ and numerous other pamphlets and reports

by eminent authorities upon the subject.

[95] _Vide_ ‘Asphalte and its Application to Street Paving,’ by E. B.

Ellice Clarke, ‘Proceedings of the Association of Municipal and

Sanitary Engineers,’ vol. vi. p. 52.

[96] The asphaltic roadways of Paris, of which there were 290,000

square yards in the year 1878, cost from 10_s._ to 12_s._ per square

yard to lay, and about 8·83 pence per square yard per annum to

maintain, including the charge for renewing ¹⁄₁₅th part of the surface

every year, which is the method adopted there. _Vide_ ‘Annales

Industrielles,’ 1878.

[97] _Vide_ Mr. Haywood’s report on asphalte and wood pavements, 1874.

[98] “Lime concrete ruins compressed work.” _Vide_ ‘Asphalte and its

Application to Street Paving,’ by B. Ellice Clarke. ‘Proceedings of

the Association of Municipal and Sanitary Engineers and Surveyors,’

vol. vi. p. 46.

[99] See p. 94 _ante_.

[100] It must be ²⁄₅ths more in thickness than that specified as

finished.

CHAPTER XI.

FOOTPATHS.

As in the case of roadways, so with footpaths: the foundation is of

primary importance, whatever material may be used for the surface. Where

this material may be classed under the head of “Paving,” concrete[101]

makes the best foundation. For gravel, tar paving, or other similar

surface, a hard core bottom well drained is sufficient. The materials of

which a footpath can be formed are almost innumerable, but the following

may be given as embodying most of them:

(1.) Natural asphalte, compressed and mastic.

(2.) Yorkshire flagging--Caithness flagging.

(3.) Blue lias, and Devonian limestone flagging.

(4.) Concrete.

(5.) Bricks.

(6.) Granite slabs.

(7.) Artificial asphaltes, including tar pavement.

(8.) Gravel.

First on the list stands natural asphalte, compressed and mastic.

The compressed has been thoroughly described in the preceding chapter;

it is sometimes used for footpaths where there is a very heavy traffic,

and answers admirably.

I will, however, now deal solely with mastic asphalte, which means the

rock ground to powder, mixed with a certain proportion of bitumen to act

as a flux, and then subjected to heat; this is sometimes used in

conjunction with fine sharp clean river sand, but more often with finely

crushed stone about the size of peppercorns, and is styled “gritted

asphalte.”

As long ago as the year 1838, Mr. F. W. Simms speaks of asphalte mastic

from Pyrimont, near Seyssel, and says “it may be considered a species of

mineral leather”[102]--a very good description of its surprisingly

tough, hard, durable and pliant properties.

The usual method of the preparation of the mastic is as follows:--

According to the amount of bitumen contained in the natural stone, from

5 to 8 per cent. of refined Trinidad bitumen[103] is placed in a large

caldron which is usually provided with agitators driven by steam power;

when this is thoroughly melted, the powdered asphalte is added little by

little, the heat being raised to between 390° and 480° F., the mixture

kept well stirred and “cooked” for about five hours. It is then turned

out into iron moulds, most companies having a special pattern with a

trade mark for this purpose.

The caldrons generally used contain from 1¹⁄₂ to 2 tons of mastic.

Some companies in large towns are provided with caldrons on wheels,

commonly called “Locomobiles,” in which case the grit is mixed with the

mastic in the fixed caldrons, and the whole mass run out into the

locomobiles (which are also provided with agitators worked by an endless

chain attached to the axle of the wheels), and transported direct to

where the work has to be done. This system, though undoubtedly the best,

is not practicable except in large towns; the more usual method of

laying mastic footpaths is to send the asphalte cakes to the works,

where they are remelted in small round street caldrons, containing from

8 to 12 cakes each, weighing from 40 to 50 lbs., the grit being

sometimes added in the fixed caldrons, sometimes in the street caldrons,

this amount of grit varying from 20 to 60 per cent. according to the

nature of the work.

The grit makes the asphalte more difficult to spread, but it lessens the

cost and makes a very durable path. The affinity between the asphalte

and grit is so great that, in breaking a sample, the actual pieces of

grit will be found broken in half.

The asphalte should be spread from ¹⁄₂ to ⁷⁄₈ of an inch in thickness

(if compressed 1 inch is the minimum), and should be brought hot on to

the works in covered caldrons on wheels, the test of its being ready and

fit to lay being made by plunging a wooden spatula into it, which should

come out without any of the asphalte adhering to it, and also by jets of

light smoke darting out of the mixture.

The mastic should be taken from the caldron with a warmed ladle, and put

into buckets previously heated, then thrown out on the concrete (which

should be perfectly dry) near the spreader, who spreads it skilfully

with a wooden stave, spreader, or spatula. The surface should then be

floated and dusted over with fine sand, portland cement, or stone dust.

Dishonest contractors sometimes substitute inferior materials for

natural asphalte, such imitations being made of ground chalk, fire-clay,

and pitch or gas tar, or ground limestone mixed with bitumen.

A sample of the footpath after it is laid should be cut out (this is

easily effected by heating the surface with a piece of hot mastic), in

order to see that the proper thickness is given, and by applying a light

to the sample, the smell will readily tell if real asphalte or any

inferior material has been used. Stockholm tar or common pitch should

not be allowed to be substituted for Trinidad bitumen, or it will spoil

the mastic.

Asphalte mastic footpaths are excellent in every way, the only

objections to them being the necessity for the grit, and the temporary

unpleasant smoke and smell whilst being laid. It is also necessary to

put stone sills round the cellar openings and coal shutes, etc., for it

to butt against, but it makes an invaluable pavement, especially for

courts, alleys, back yards, etc., for sanitary and other reasons.

The proportions of asphalte, bitumen and grit are given as follows by

Mr. Delano in his translation of a paper by M. Ernest Chabrier, on the

applications of asphalte.[104]

“One ton of sanded mastic requires 13 cwt. of pure block mastic, 2 qrs.

12 lb. of bitumen, 7 cwt. of grit or sand washed and dried,” and it

takes 2 cwt. of coal to heat it. He further says that one workman can

easily prepare 3 tons of material in 12 hours.

The following table gives the number of square yards that a ton of

prepared Sicilian rock asphalte will spread.

----+--------------+---------------------+----------+----

| | With about | |

|Without grit. |25 per cent. of grit.|Thickness.|

+--------------+---------------------+----------+

|square yards. | square yards. | inches. |

| 63 | 80 | ³⁄₈ |

| 51 | 65 | ¹⁄₂ |

| 32 | 40 | ³⁄₄ |

| 26 | 33 | 1 |

| 16 | 20 | 1¹⁄₂ |

| 12¹⁄₂ | 16 | 2 |

----+--------------+---------------------+----------+----

A skilled workman properly assisted can lay 140 to 180 square yards in a

day.[105]

With regard to the price of asphalte mastic footpaths, this is quite a

local question, and is not worth while discussing. The life of a

footpath thus treated may be reckoned at about 15 years under ordinary

traffic; the concrete will remain untouched and what is left of the

asphalte may be remelted, so that a renewal is not so costly as the

first expense.

_Yorkshire Flagging._--This pavement is too well known to need any

description from me; it is an excellent pavement in many ways, and is

most pleasant to walk upon, there being a cling or foothold not

experienced in any other material.

The objections to this description of pavement are:--

(1.) Its first cost, which is undoubtedly high as compared to its

durability.

(2.) The fact of uneven wearing: one stone will be found soft next to a

hard one; the former wears, leaving a pit which forms a pool for water

in due course, and has to be removed.

(3.) Unless very carefully bedded, a stone will see-saw; this is very

unpleasant in wet weather, water accumulates beneath, and as the

pedestrian treads on one end of the stone a squirt of dirty water up to

his knees, and a stumble, remind him that the stone is loose.

(4.) Liability to crack when any heavy goods are thrown upon it.

The following specimen specification for Yorkshire flagging pavement may

be of use.

_Specimen Specification for Yorkshire Flagging Foot Pavements._

The old flagging (where and when directed) to be taken up, refaced,

squared, and relaid.

The new flagging is to be chisel-dressed to a fair face, true, out of

winding, and not less than 3 inches thick,[106] to be properly squared

and not pitched off only, or undercut, but to hold good to the square;

to have not more than fourteen pieces to the hundred superficial feet;

the joints must be set flush, and bedded and pointed with the best blue

lias mortar.

The bed for the flagging both old and new, if any is required, to be

made with proper earth, gravel, or dry rubbish, and all surplus earth

and rubbish to be carted from the streets as it arises from the works.

The flagging to be properly cut and rebated to receive all area

gratings, coal shoots, rain water troughs, &c.

Any damage done to gas or water service pipes in digging for the

flagging, or in any way connected with the work, to be made good by the

contractor, as also all and every other damage to windows, wood, or

glass work; and the contractor will be held responsible for, and will

make compensation for any injury that the public may sustain through the

negligence of his workmen, or otherwise.

The whole of the flags to be of the very best quality, from Halifax, the

quarries in the neighbourhood of Bradford or in Yorkshire, and subject

to the approval of the surveyor.

The contractor to provide all lights and proper guards at night, and

when old paving is to be taken up the work is to be done under the

direction of the surveyor, and if considered necessary, the stones are

to be removed from the streets to be re-faced and squared. No stone to

be stacked in the streets.

The flagging to be measured after the work is completed.

The contractor to provide all stone, materials, tools, implements, horse

and cart hire, and pay all railway dues, freightages, etc., and also to

provide all labour of every kind for properly completing the work to the

full and entire satisfaction of the surveyor. Payment will be made as

the work proceeds, on the certificate of the surveyor.

Should the contractor fail to perform the work to the satisfaction of

the surveyor, he then shall have power to execute the work and charge

the same to the contractor, and deduct the cost from any amount that may

be due to him; and in the event of the cost being more than the amount

due, or if there shall then be no sum due to the contractor, such cost

shall be paid by the contractor to the mayor, aldermen, and citizens,

and the same shall be recoverable from him as liquidated and ascertained

damages.

_Caithness Flagging_ is now used very largely instead of Yorkshire; it

comes from Thurso in Scotland, and it is contended for it that it

possesses many excellent qualities, amongst others may be enumerated the

following:

(1). It is impervious to wet.

(2.) It is not slippery nor does it wear so.

(3.) It does not scale or flake.

(4.) It dries rapidly after rain.

(5.) Its appearance is cheerful.

(6.) Great durability, as it does not abrade.

(7.) Frost has no effect upon it.

(8.) Can be re-used when half worn.

(9.) Cleanliness; for, not being porous, no dirt or dust can adhere to

it.

(10.) Vehicular traffic may be turned over it without injury to the

path.

(11.) Economy; as natural forces can be used, thus saving labour, and it

can be laid from 1¹⁄₂ to 2 inches thick only.

(12.) Having sawn edges, the joints are expeditiously and well made.

(13.) Its whole surface wears evenly.

The following table was compiled by the well-known firm of Kirkaldy, by

direction of Mr. Tarbotton the Borough Engineer of Nottingham, in order

to ascertain the resistance to a gradually increased bending stress upon

Yorkshire flagging as compared with Caithness.

YORKSHIRE.

--------+-------+---------------------------+--------

| | Dimensions. |

| +-------+--------+----------+Ultimate

--------+-------+-------+--------+----------+--------

K | lbs. |inches.| inches.| inches. | lb.

1918 | 184 | 36 | 24·07 | 2·46 | 4·744

1919 | 163 | 36 | 24·03 | 2·22 | 3·398

1920 | 107 | 36 | 23·90 | 1·50 | 1·459

+-------+-------+--------+----------+--------

Mean | 151 | 36 | 24·00 | 2·06 | 3·200

--------+-------+-------+--------+----------+--------

CAITHNESS.

--------+-------+---------------------------+--------

| | Dimensions. |

| +-------+--------+----------+Ultimate

--------+-------+-------+--------+----------+--------

K | lb. |inches.| inches.| inches. | lb.

1921 | 215 | 36 | 24·06 | 2·59 | 17·274

1922 | 178 | 36 | 24·05 | 2·15 | 12·711

1923 | 114 | 36 | 23·90 | 1·38 | 6·211

+-------+-------+--------+----------+--------

Mean | 169 | 36 | 24·00 | 2·04 | 12·065

--------+-------+-------+--------+----------+--------

By which it appears that the balance in favour of Caithness flagging is

8·865 lbs.

The objection to this style of flagging is, that however varied the

sizes of the stones selected may be, as they have sawn edges and are

very hard to cut with a chisel, a difficulty sometimes arises in

finishing rounded corners of footpaths, and against uneven frontages of

shops or buildings abutting on the footpath; this is especially the case

in old towns.

_Blue Lias Flagging._--A blue lias flagging does not make a first-rate

pavement, as although it is very cheap, durable, clean, and has many

other good qualities, it sometimes wears slippery and is then dangerous

to pedestrians; but the Devonian limestone, which is much used in the

west of England, has not apparently this defect.

_Concrete Footpaths._--These have been tried in this country, but

generally without success; the concrete or cement cracks, and in

addition to this the paths wear slippery and greasy, and as some time is

necessary in order to allow the concrete to thoroughly set before the

traffic can be allowed on them, they have not found much favour.

In the United States, however, concrete footpaths seem to be made

successfully; the following detail particulars of such a foot-pavement

will, I think, be of great interest and use.[107]

“Concrete footpaths should be laid upon a form of well-compacted sand,

or fine gravel, or a mixture of sand, gravel and loam. The natural soil,

if sufficiently porous to provide thorough sub-drainage, will

answer.[108]

“It is not usual to attempt to guard entirely against the lifting

effects of frost, but to provide for it by laying the concrete in

squares or rectangles, each containing from 12 to 16 superficial feet,

which will yield to upheaval individually, like flagging stones, without

breaking and without producing extensive disturbance in the general

surface.

“When a case arises, however, where it is deemed necessary to prevent

any movement whatever, it can be done by underlying the pavement with a

bed of broken stone, or a mixture of broken stone and gravel, or with

ordinary pit gravel containing just enough of detritus and loam to bind

it together. In high latitudes this bed should be 1 foot and upwards in

thickness, and should be so thoroughly subdrained that it will always be

free from standing water. It is formed in the usual manner of making

broken stone or gravel roads already described, and finished off on top

with a layer of sand or fine gravel, about 1 inch in depth, for the

concrete to rest upon.

“The concrete should not be less than 3¹⁄₂, and need rarely exceed 4 to

4¹⁄₂ inches in thickness, the upper surface to the depth of ¹⁄₂ an inch

should be composed of hydraulic cement and sand only. Portland cement is

best for this top layer. For the rest, any natural American cement of

standard quality will answer. The following proportions are recommended

for this bottom layer.

Rosendale or other American cement 1 measure

Clean sharp sand 2¹⁄₂ „

Stone and gravel 5 „

“It is mixed from time to time as required for use, and is compacted

with an iron-shod rammer in a single layer to a thickness less by ¹⁄₂ an

inch than that of the required pavement. As soon as this is done and

before the cement has had time to set, the surface is roughened by

scratching, and the top layer, composed of,

1 volume of Portland cement, and

2 to 2¹⁄₂ volumes of clean fine sand,

is spread over it to a uniform thickness of about 1¹⁄₂ inch, and then

compacted by rather light blows, with an iron-shod rammer. By this means

its thickness is diminished to ¹⁄₂ an inch. It is then smoothed off and

polished with a mason’s trowel and covered up with hay, grass, sand, or

other suitable material to protect it from the rays of the sun, and

prevent its drying too rapidly.

“It should be kept damp and thus protected for at least 10 days, and

longer if circumstances will permit; and even after it is opened to

travel, a layer of damp sand should be kept upon it for two or three

weeks, to prevent wear while tender.

“At the end of one month from the date of laying, the Portland cement

mixture forming the top surface will have attained nearly one-half its

ultimate strength and hardness, and may then be subjected to use by

foot-passengers without injury.

“The rammers for compacting the concrete should weigh from 15 to 20 lb.,

those used on the surface layer from 10 to 12 lb. They are made by

attaching rectangular blocks of hard wood shod with iron to wood handles

about 3 feet long, and are plied in an upright position. Certain

precautions are necessary in mixing and ramming the materials in order

to secure the best results. Especial care should be taken to avoid the

use of too much water in the manipulation. The mass of concrete, when

ready for use, should appear quite incoherent, and not wet and plastic,

containing water however in such quantities that a thorough ramming with

repeated though not hard blows will produce a thin film of moisture upon

the surface under the rammer, without causing in the mass a gelatinous

or quicksand motion.”

Under the head of Concrete may be included many artificial stone

pavements, such as “Bucknell’s Granite Breccia” “Ransome’s Artificial

Stone,” “Eureka Concrete,” “Granolithic,” and the “Silicated Victoria

Stone,” this last being worth a description. The stone is really a

concrete, formed by mixing very superior Portland cement with crushed

Thames gravel, furnace or iron slag, Kentish rag-stone, granite

chippings, or other suitable material carefully washed. This fine

concrete, after being mixed in the moulds forming the slabs, is

thoroughly incorporated by being rocked or jiggled in a trembling

machine; this motion, as can be easily understood, making the whole mass

even and homogeneous when it sets. The cost of the slabs is about 9_d._

per square foot, 3 inches in thickness, and they make an excellent

footpath.

_Brick Footpaths._--These are sometimes constructed of ordinary bricks

laid on their sides, but soon wear, and are unsuitable for the

purpose.[109] Staffordshire blue paving bricks make an excellent

footpath. These are bricks made of stoneware highly vitrified; they

should be about 12 inches in length by 6 inches wide, by about 2⁷⁄₈

inches in thickness, their surface being chequered with a diamond

pattern so as to prevent their being slippery. They are exceedingly

hard and durable if well burnt, and to ascertain this a brick should be

broken across and the colour, etc., noted.

They should be laid in cement mortar upon a bed of concrete or sand. The

objections to this class of pavement are as follows:

(1.) The colour is objectionable; being very dark, the footpaths give a

street the appearance of mourning.

(2.) The difficulty of breaking up the path for gas or water services,

or for other purposes.

(3.) The hardness of the bricks makes them awkward to cut to rounded

corners, or for water trunks, coal-holes, etc.

(4.) A loaded hand-barrow driven over them will sometimes break off the

chequered pattern.

(5.) They are slippery in a frost after snow.

But notwithstanding these disadvantages, they make a most wonderfully

durable and useful pavement for back streets.

_Granite Slab Pavement._--This is sometimes adopted, large granite

slabs, 6 inches in thickness being laid; they are very useful when there

are cellars underneath, or where heavy vehicular traffic is intended to

cross the foot pavement. Granite is of course excessively durable, but

it wears very slippery with traffic and must then be tooled or axed; in

process of time this wears it out, and its first cost is heavy.

This description of pavement can be laid with advantage in front of

markets or similar buildings.

_Artificial Asphalte Pavements._--The cost of obtaining natural rock

asphalte from the mines, and the knowledge that it is composed of two

very simple ingredients, limestone and bitumen, has led to a great

number of artificial asphaltes being introduced, especially for foot

pavements. “British Rock Asphalte” is a name by which many of the

compositions are known; “Beauchamp’s Mendip Mountain Machine-made

Granite Asphalte” is a high-sounding title; “Prentice’s Mineral Foreign

Rock Asphalte” is another.

All these, and many more of the same description, are really what may be

better and more correctly described as “tar concrete” or “tar paving,”

and consist of different modifications of the homely coal-tar and

limestone.

So long ago as the year 1840, “Lord Stanhope’s Composition” was well

known; it was made as follows:

Three gallons of Stockholm tar, 2 bushels of well-dried chalk, 1 bushel

of fine, sharp, clean sifted sand, the whole being boiled in an iron

caldron.

Tar paving is now made in many and various ways by different surveyors

of towns, some making it with hot compositions, some with cold. A

description will be found in the chapter on Macadamised Roadways, page

46, of one method of making it, a modification of this being all that is

necessary for foot pavements.

The best paths of this description that I have seen are to be found at

Torquay, and by the kind permission of Mr. John Little, County Surveyor

of Devon, and late Surveyor of Torquay, I give his useful specification

in detail, as follows:

_Tar Concrete for Footpaths._

PROPORTIONS OF MATERIALS.

12 barrow loads of engine ashes.

4 „ „ screened slaked blue lias lime.

4 „ „ small spar or sharp grit.

34 gallons of best gas tar.

20 bucketsful, say 70 to 80 gallons of water.

_Method of Mixing._--On a clean flagged or wooden floor spread three

barrow-loads of ashes, then about one barrow-load of lime, and so on

until the whole of the dry materials (or one mixing) has been spread;

then throw over them about three bucketfuls of tar, and before mixing it

with them add (say) six bucketfuls of water; then mix as for concrete,

and when the liquids are pretty well absorbed add a similar quantity,

mix again, and so on until all the liquids have been absorbed; the mass

will then be something of the consistency of ordinary mortar. Next pass

the whole three times _at least_ through a pug mill: if this be not done

the concrete will be a failure. An ordinary hand pug-mill will not be

sufficient; the knives are not strong enough, nor will it incorporate

the materials thoroughly, but an upright pug-mill, worked by steam power

where practicable, or by at least one horse, should be used.

It will be found that as the mass emerges from the pug-mill a large

proportion of the water will run from it; means should therefore be

provided for allowing the water to escape freely from the floor.

_Method of Laying._--Prepare the path for a layer of concrete 3 inches

in thickness, on a hard dry bottom, inclining from the inside to the

kerb, at the rate of ¹⁄₂ an inch to a foot for pathways not more than 6

or 7 feet wide, but for wider pathways an inclination of ³⁄₈ of an inch

to a foot will be sufficient.

A template the full width of the path having been provided, lay concrete

with a shovel on the inner side of the path for a length of (say) 15

feet and a width of 1 foot, at such a height that when it has been well

rammed and patted with shovels it shall be the exact height intended for

the path; this is to form a resting-place for one end of the template,

the kerb forming that for the other end; then fill the intervening space

with concrete up to the template, treading and ramming it solidly for

about twenty minutes, and as it gets into shape, patting it with shovels

and smoothing with a trowel; then, with an iron (not stone) roller

weighing about 5 cwts., roll for two hours, trimming and filling up

hollows where necessary; then go on with another length, and

occasionally roll the first for half-an-hour, and so on. Experience

alone will decide the quantity of rolling necessary after the first day

or two, as weather and other causes tend to a more rapid solidification

of the concrete at some times than at others.

On the third day, sprinkle a small quantity of sea or other very fine

sand on the concrete, and allow it to remain for two or three days after

the path has been in use--it should then be removed.

_General Remarks._--The ashes should not be those from a saw-mill or

other place where wood ashes would be mixed with them. All ashes, spar

or grit, and lime, should be passed through a screen of ³⁄₈-inch mesh.

The lime should be the best blue lias, slaked under cover; it should be

allowed to lie for at least four days, but not more than six days,

before it is used. The spar or grit should be sharp and angular.

Great care should be taken to keep the concrete free from mud or dust;

it should be tipped from the carts or barrows, either directly into

place, or, if this cannot be done, a few slabs or boards should be laid

down, on which it may be tipped.

The path should not be used until the concrete is sufficiently solid to

bear a man’s weight without taking the impression of his boots.

It has been found by experience that the laying of this concrete should

not be commenced before May, and that it should not be continued beyond

the end of September (or middle of October, if the weather is very

fine). Frost is fatal to it before it has become hard, and continuous

cold wet weather retards considerably the hardening.

There can be no doubt that a pavement of this description for traffic

that is not too heavy answers every requirement; for streets of greater

traffic, genuine mastic asphalte should be used.

Before closing my remarks on artificial asphalte pavements, the

following description of an American method may be interesting:

On a dry foundation is placed a coat of rough clinkers from anthracite

coal or iron clinkers from a foundry, mixed with sand and tar in the

proportions of 15 cubic feet of fine sifted ashes, 14¹⁄₂ cubic feet of

pit sand, and 1¹⁄₂ cubic feet or 9 gallons of tar. This is laid about 3

to 4 inches thick and well rolled. Over this is placed a coating from 1

inch to 1¹⁄₂ inch thick, composed of 15 cubic feet of coarse sifted

ashes, 15 cubic feet of clinkers, and 1¹⁄₄ cubic feet or 8 gallons of

tar. It must be then well rolled and sanded, care having been taken that

the materials are thoroughly mixed.

_Gravel Footpaths._--For the suburbs of a town and in the country,

nothing looks so pretty as a gravel footpath.

The same rules that apply to a macadamised roadway apply to a gravel

footpath. They must be well “bottomed,” and well drained and well

rolled. Limestone or other stone chippings may with advantage be used

with a pit gravel for constructing paths of this description, and a

barrelled surface looks better and is more enduring than a hanging path.

The following cross sections of footpaths will explain themselves better

than any long description:

[Illustration]

Gravel footpaths are sometimes tarred over when thoroughly consolidated.

This must be done only when the weather is quite settled and fine: the

least rain will spoil the whole operation; it consists in simply tarring

over the surface of the footpath in the same manner that a gate or wall

or any other substance would be tarred. The surface of the path must

previously have been swept perfectly clean, and immediately as the

tarring is completed, fine stone dust must be sprinkled on its surface;

the traffic should be diverted from it for a few hours, and it is then

ready.

Care must be taken that the tar is not too thin in consistency, and that

the coat is not put on too thick. Treating a path in this manner saves

gravel, which is washed or kicked off it if left with an ordinary

surface; but a cold night, a slight shower, or inferior tar will make

the whole process abortive, and the path will be in a fearful mess in

the winter.

[101] Concrete is especially necessary as a foundation for asphalte,

as it has little or no power of resistance to vertical pressure in

itself, and indentations in its surface would be very unsightly as

well as hold water. The concrete should be perfectly dry and

thoroughly set before the asphalte is laid on it.

Mr. Wm. H. Grant, Superintending Engineer of the New York Central Park,