The march of civilisation has decided that road rolling is a necessity
for macadamised roads, instead of allowing the stones of which they are
composed to be worn in by the traffic, as was formerly the custom. In
Calcutta bullock rollers were used so long ago as the year 1855, and it
was the cruelty of this operation that suggested to Mr. W. Clark the
necessity for a steam roller,[42] the outcome of which was the
well-known roller as manufactured and supplied by Messrs. Aveling and
Porter of Rochester, and now so generally used throughout this country,
as well as in American and other foreign towns.[43]
Steam rolling saves money as well as suffering, and the legislature have
recognised the importance of a sanitary authority becoming possessed of
a steam roller by permitting money to be borrowed for the purchase of a
roller as for a permanent work. (Sect. 234 Glenn’s Public Health Act
1875, footnote to Sub. Sect. (1).)
Mr. Albert W. Parry, the Borough Surveyor of Reading, has prepared some
tables on the subject of steam road rollers, from information he
received on this subject, in answer to some questions he addressed to
the surveyors of a number of towns a few years ago. It appears from this
tabulated statement that thirty-three 15-ton steam rollers were in use,
six 10-ton rollers, one 21-ton roller, one 8-ton roller, one 9¹⁄₂ ton
roller, one 14¹⁄₂-ton roller, one 17-ton roller, and one 25-ton roller;
this latter not being much used, as it was found to be too heavy.
The average gross cost per annum of necessary repairs to the rollers,
other than those which could be effected by the men in charge of it,
amounted to 35_l._ 12_s._ The number of men employed to attend to the
roller and cost of labour per day varied considerably, from one case
(South Shields) where “one engine-man at 26_s._ per week, and an old
scavenger with the flag” were found to be sufficient; to another
(Gloucester) where the cost per day is stated as follows: “one man works
the engine at 5_s._ per day, one boy with signal flag, 1_s._ 8_d._, two
men spreading gravel or sand at 3_s._, two men watering and sweeping to
keep water from running off in channels.”
Some of the older rollers require a steersman as well as a driver, and
the Locomotives Amendment Act requires two men with flags, but this is
seldom really necessary. The sweepers, spreaders and sprinklers should
be taken as irrespective of the actual cost of the roller, which may
therefore be assumed to be the wages of the engine-man, say 5_s._ per
diem, and a boy or old man with a flag at 2_s._, thus making a total for
labour of 7_s._ per diem.
The fuel that is consumed by a 15-ton roller seems to be from 3 to 5
cwt. of coke per diem, common gas coke being generally used, though
steam coal would no doubt answer equally well, some of the smokeless
Welsh descriptions being of course necessary.
With regard to the question “When not used for rolling roads, to what
other use (if any) do you put the engine power?” there are not many
towns that use the machine for any other purpose than rolling, but the
following uses may be enumerated to which the machines have been
applied:–Driving a stone-breaker, a mortar-mill, a saw-bench, a
chaff-cutting machine, a bean-crusher, etc. It has also been used in
connection with pumping, and to produce the necessary power for the
electric light, and it is frequently employed as a traction engine.
The driving rollers usually have provision by which spikes may be fitted
into holes in their faces, in order that they may be used for lifting or
chequering roads. These, however, apparently do not answer; the working
of a machine in this manner is said to shake and strain it considerably,
and the holes in the rollers, which are plugged with wood when not in
use, are objectionable, as these plugs wear out and the road metal gets
into the holes, and the surface of the road is picked up as the rolling
proceeds; besides this, the spikes seem to have no effect unless the
surface of the roadway being operated upon is soft.
With reference to the use of binding material, the most commonly used
and that which receives most favour is road grit or scrapings,[44] sharp
sand is also employed, as well as gravel if clean, and also stone
chippings and screenings; these should be of the same material of which
the road is made, if possible, and no doubt _newly_ constructed roads
require more care in the binding material than simple repairs. The
steepest gradient upon which a roller will act appears to be 1 in 9 in
Blackburn, with a 15-ton roller, but this must require a very heavy
pressure of steam, and 1 in 14 seems to be a gradient that gives no
trouble to roll either up or down; in going down hill, of course it is a
mere question of sufficient break power.
The number of superficial yards rolled per day must vary extremely with
circumstances: the class of material, the amount of binding and water
used, the gradient and pressure of steam maintained, and the amount of
rolling considered necessary,[45] being amongst the various influences.
From the above returns I find that the number of square yards rolled
varies from 500 to 3000 per diem, the average for 42 towns being 1105
square yards per diem.
The cost per square yard rolled, including all charges, may be assumed
to be between ¹⁄₂_d._ and 1_d._, and the cost of binding material about
3_d._ per square yard. With reference to the necessity of binding
material, the following, facts are interesting.
Mr. Wm. H. Grant, Superintending Engineer of the New York Central Park,
in his report upon the park roads, says:[46] “At the commencement of the
macadam roads, the experiment was tried of rolling and compacting the
stone by a strict adherence to Macadam’s theory, that of carefully
excluding all dirt and foreign material from the stones, and trusting to
the action of the roller and the travel of teams to accomplish the work
of consolidation. The bottom layer of stone was sufficiently compacted
in this way to form and retain, under the action of the rollers (after
the compression had reached about its practical limit) an even and
regular surface; but the top layer, with the use of the heavy roller
loaded to its greatest capacity, it was found impracticable to solidify
and reduce to such a surface as would prevent the stones from loosening
and being displaced by the action of waggon-wheels and horses’ feet. No
amount of rolling was sufficient to produce a thorough binding effect
upon the stones or to cause such a mechanical union and adjustment of
their sides and angles together, as to enable them mutually to assist
each other in resisting displacement. The rolling was persisted in with
the roller adjusted to different weights up to the maximum load (12
tons) until it was apparent that the opposite effect from that intended
was being produced. The stones became rounded by the excessive attrition
they were subjected to, their more angular parts wearing away, and the
weaker and smaller ones being crushed.”
“The experiment was not pushed beyond this point. It was conclusively
shown, that broken stones of the ordinary sizes, and of the very best
quality for wear and durability, with the greatest care and attention to
all the necessary conditions of rolling and compression, would not
consolidate in the effectual manner required for the surface of a road
while entirely isolated from and independent of other substances. The
utmost efforts to compress and solidify them while in this condition
after a certain limit had been reached, were unavailing.”
From the foregoing it is very evident that some description of binding
material is essential in making a road under a roller. Where traffic is
allowed to consolidate a road it is different, as then the stones are
knocked about and are sufficiently abraded against each other to form a
binding material for themselves. Too much binding material or too much
water should not be used in forming a road with a steam roller. It is
unfortunately frequently the case that a road is made quickly only to go
to pieces with the traffic in a few weeks. The surface of a
well-constructed macadamised roadway should after being rolled look
almost like an encaustic pavement. If there is too much binding material
in the joints of the stones, the first heavy rain washes it out and the
surface of the roadway quickly goes to pieces.
The following description of the manner in which it is recommended that
the roller should be applied is taken from an excellent little pamphlet
on Steam Road Rolling, by Messrs. Aveling and Porter, the well-known
makers of steam-rollers, and although local circumstances must guide the
surveyor in all his works, the particulars may be of use:–
“In the best practice the roadway is excavated, graded, and properly
formed to a depth of 14 inches from the level of the gutters, with a
cross section conforming to the cross section of the road when finished;
it is then thoroughly and repeatedly rolled with the steam roller, all
depressions being carefully filled and rolled before the stone is put
on. On the bed thus formed and consolidated a layer of stones 8 inches
thick is set by hand, and rammed or settled to place by sledge hammers,
all irregularities of surface being broken off and the interstices
wedged with pieces of stone. The intermediate layer of broken stone, of
a size not exceeding 3 inches in diameter, is then evenly spread to a
depth of 4 inches and thoroughly rolled, and this is followed by rolling
in half-an-inch of sand. The surface layer of stone, broken to a size
not larger than 2 inches diameter, and to a form as nearly cubical as
possible, is then put on to a depth of 3 inches, thoroughly rolled, and
followed as before by sand, also rolled. Finally, a binding composed of
clean, sharp sand is then applied, well watered and most thoroughly
rolled with the steam roller, until the surface becomes firm, compact
and smooth, the superfluous binding material being swept off and
removed.”
And the following account of the method adopted in the United States at
Hartford may also be of interest.[47]
“The surface of the road is excavated to a suitable depth–say, 18
inches; preparing the form for the pavement with the precautions as for
a common pavement; 4 inches of gravel and proper drainage where
required, provided blocks of stone of any irregular shape are selected
for the pavement, of about 7 inches in thickness. The blocks are set by
hand with great care, as closely in contact at their base as
practicable. The surface between the blocks is filled with chippings of
stone carefully laid in. A layer of broken stone, 4 inches thick, is
laid over this pavement. The road-covering thus prepared should be
rolled with the steam roller until the upper layer has become perfectly
compact and consolidated. The second layer, about 3 inches in depth, is
then laid on; a coating of clean coarse gravel, 1¹⁄₂ inch thick, termed
‘binding,’ is spread over the surface, and the whole well rolled as
before, and you have the requisites of a good road–viz., clean, hard,
and even at all seasons. No road should be considered made until it is
completely rolled. A road made in the manner above described, and kept
perfectly clean, hard, and even, with materials of a good tough quality,
would show extremely little wear on the surface; indeed, it has been
found in France to be less than ¹⁄₂ an inch in a year, on a road of
great traffic.”
In the neighbourhood of New York the steam roller is used as follows:–
Two and a half inches of trap rock is laid and lightly rolled until the
stones have become a little compacted, then coarse screenings are added,
and it is again rolled; after this a layer of about 2 inches of stones
are added and rolled with coarse screenings as before. Fine screenings
or stone dust is then applied, and the roadway is then rolled until
every interstice is filled up; it is then well watered and again rolled.
With reference to the employment of the steam roller in repairs of
roads, the following description is given of the method adopted by the
Surveyor to the Tottenham Local Board, near London.[48]
“When a road becomes so full of holes or so worn as to require coating
throughout its entire length and width, it should be hacked completely
over and raked into a segmental form in its transverse section to remove
irregularities, and so that the road may have a fall from the crown to
the channel of not less than one inch to a yard. It should then be
coated with stone broken as nearly cubical as possible and to an uniform
gauge. When spread it should be slightly coated with gravel screenings,
or the grit sweepings from the roads, which are equally suitable for the
purpose when in proper condition. The road should then be watered and
rolled, beginning with the road at the channels, and ending at the crown
of the road, until a smooth surface is obtained, more stones being added
to fill up any inequalities that may exist, until the whole is
consolidated. By constantly sweeping the grit from the sides to the
crown of the road as the roller passes over, every stone is thoroughly
grouted into its bed.”
Mr. R. Read, the Surveyor of Gloucester, says:[49] “The road should be
thoroughly well lifted and the metalling spread in three-inch layers
evenly, and rolled once or twice before the gravel or other binding
material is spread; then spread gravel or sand evenly and well watered
with fine distributor until the stone is entirely covered, and the sand
does not adhere to the roller. Dam up the road channels to prevent water
and sand running off into sewers and let men scoop up the water, and
throw it back on the road, as it collects in the gutters.”
In all cases the sides should be rolled first to such a degree of
firmness that when the roller passes over the centre or crown of road,
its weight, which tends to spread the metal or make it work off towards
the sides, may be resisted by their consolidation.
With reference to the effect of the weight of steam road rollers upon
roadways, it may be well here to compare that of a 15-ton roller with
other burdens that a road has to bear, taking each case at per inch of
width of tire.
An ordinary loaded two-wheeled cart presses with a weight of about 9
cwt. per inch width of tire, a loaded wagon about 7¹⁄₂ cwt., a 9-ton
traction engine about 3³⁄₄ cwt., and a 15-ton steam road roller about
3¹⁄₂ cwt. So that as far as the surface of the roadway is concerned, a
roller affects it the least of any of the above loads.
It has, however, been found that where rollers of more weight than 15
tons are used,[50] not only are they unwieldy, but, from their great
weight, the solidity of the foundation of the roadway may be interfered
with, and also there is great danger of damaging gas or water mains and
services, besides any cellars that may be constructed under the roadway.
The steam rollers which are principally used in this country, are those
manufactured by Messrs. Aveling and Porter, and those by Messrs. Green
and Sons, drawings of both of which are here represented.
[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.
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.
—————-+——-+—————+——-+———–+——–
| Super-| |Loss of| |
| ficial| | weight| Loss per |
|area in| Original | by |superficial|Relative
Name of stone. | feet. | weight. | wear.| foot. | losses.
—————-+——-+—————+——-+———–+——–
| |cwt. qrs. lbs.| | |
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.
