COMPRESSED ASPHALTE ROADWAYS - Zhumadian CYS Powder Coating Co., Ltd.

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.

———–+———-+———-+———–+———–+———–
| | | | Total Cost| Average
| | | First Cost| of Repairs| Cost
| | | per | per Square| per Square
|Date when | | Square |Yard during| Yard per
Situation.|laid New. | Life. | Yard. | Life. | Annum.
———–+———-+———-+———–+———–+———–
| |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.

—————–+———-+————-+————+————+
| | | | |
| | | | |
| | | | |
| | |Years to be | |
| | | maintained | First Cost |
| Date when| Name of | by | per |
Situation. | Laid. | Contractor. |Contractor. |Square Yard.|
—————–+———-+————-+————+————+
| | | | £ _s._ _d._|
King William |Feb. 1873 |Improved Wood| 16 | 0 18 0 |
Street | | Paving Co. | | |
| | | | |
| | | | |
Ludgate Hill |Nov. 1873 | Ditto | 16 | 0 18 0 |
| | | | |
| | | | |
| | | | |
Portions of Great| | | | |
Tower Street and |Sept. 1873| Ditto | 16 | 0 16 0 |
| | | | |
Seething Lane | | | | |
| | | | |
Bartholomew Lane |Jan. 1872 | Carey |No agreement| 0 12 6 |
| | | | |
Ditto |Dec. 1871 |Improved Wood| 3 | 0 16 0 |
| | Paving Co. | | |
| | | | |
Duke Street |May, 1873 | Mowlem and | [84]5 | 0 15 0 |
| | Co. | | |
| | | | |
| | | | |
Houndsditch | Not yet | Ditto | [84]7 | 0 17 0 |
| laid | | | |
| | | | |
| | | | |
Ditto | Ditto | Carey | [84]7 | 0 13 6 |
| | | | |
| | | | |
—————–+———-+————-+————+————+

—————–+————————+————+————
| | 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.

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.

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.

—-+————-+———–+———–+———-+———+—-
|Original Cost| Interest |Maintenance|Scavenging| |
| per Square |on original|per Square |per Square| |
| Yard. | Cost. | Yard. | Yard. | Total. |
+————-+———–+———–+———-+———+
| _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.

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.

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