a matter of considerable importance which should not be lost sight of. Cement grouting makes a wood pavement much more noisy than one formed with a pitch composition which is of a slightly elastic nature. The arrises of the blocks, especially in wide-jointed pavements, becoming worn or rounded, the cement filling is exposed, which soon becomes disintegrated by the action of the horses' feet.

As bearing on the matter of dry rot in wood paving, the following interesting practical observations on the subject may be given * :

"It is worthy of mention that while the above contracts were being carried out (construction of two new thoroughfares, viz., Martin Place and Queen Street, Sydney, 1894) it was necessary to remove some of the old blocks from the adjoining streets in order to make proper junctions with the new works, and, in doing so, it was observed that the effect of a cement joint on the timber was most injurious, while a bituminous joint acted as a preservative. Two cases met with, are deserving of special attention.

"(a) At one end of Queen Street it was necessary to remove a considerable area of pavement which had been laid six years, in which a cement joint had been adopted, the width of joint being maintained by iron studs projecting inch from the face of the block; here it was found that dry rot had set in wherever the wood had been in contact with the cement. Different kinds of timber had been used, but every block was more or less affected. On this being observed, other portions of the pavement which had been similarly constructed were examined, but all were found to be in the same state; a microscopical examination of the timber thus affected showed no signs of fungoid growth. It is therefore assumed that the dry rot was a decomposition of the timber brought about by chemical action— such as combination of the oxygen in the cement with the carbon in the wood, forming carbonic acid gas.

"(b) At the other end of Queen Street, where blocks were removed which had been laid eight years, in which the joints had been caulked with a mixture of tar, pitch and basalt screenings, the timber was found to be in a perfect state of preservation; and although the road had sustained a daily traffic of approximately 25,000 tons for eight years, it was in almost as good a state as when first laid. The blocks, which were originally 6 inches deep, made a perfect junction with the new 6 inch blocks, the greatest wear observable in the old blocks after eight years' service being inch."

474. When pitch grout is adopted as the material for forming the joints, the blocks can be laid practically close or with a space not exceeding inch in width, which, besides making an impervious and more durable pavement, prevents the spreading of the fibre of the wood, and admits of a smooth

* "On Australian Hard Wood for Pavements," by W. A. Smith, M.I.C. E., Minutes of Proc. of C. E., vol. cxvi. p. 264.

surface being retained; while the facility for cleansing the pavement is greatly increased.

As

475. The bituminous composition being of a slightly elastic nature, absorbs and equalizes the expansion of the blocks; it also acts as a preservative to the wood. One disadvantage, of which mention has been already made, is that the joints must be made only when the wood is thoroughly dry, wet weather being detrimental to its use. Under these circumstances it is usual to cover over the pavement with tarpaulins. the bituminous grout hardens almost immediately after the joints are filled, traffic may be allowed to pass over the pavement on the completion of the work. Special travelling boilers are generally employed for preparing the pitch and creosote oil composition; the mixture, when of a proper consistency and in a boiling state, is drawn off in suitable buckets, or into wheeled carriers, transported to the pavement under construction, and poured into the joints. The usual method (already described) is to dip the blocks into the boiling mixture, then lay them in position close together. Pitch grouting, with a 1 inch joint, costs about 7d. per square yard of paving.

476. Expansion Joints.-When wood pavements were first introduced. into the principal towns in this country, it was the custom to allow a wide expansion joint at the kerbs or channels at each side of the carriageway. This arrangement was necessary, partly owing to the use of untreated wood, partly to the wide joint between the blocks, and partly to those joints being grouted with cement. By creosoting the deal blocks and by extending the use of hard woods as a paving material, the necessity for a wide expansion joint has been to a great extent obviated. The earlier wood pavements generally had an expansion joint at the channels of 1 inch for every 8 or 10 feet in width of thoroughfare; this, however, has been gradually reduced, and at the present time an allowance of 1 to 2 inches on each side of a 60 foot roadway is considered sufficient for hard wood pavements when the blocks are jointed with pitch grout. The expansion joints are filled up in a variety of ways, sand, loam, and clay being the material which was used to a considerable extent in the earlier pavements; but these joints are now in most instances filled with a hot mixture of pitch and creosote oil, similar to that used in forming the joints of the pavement. Fig. 125 shows a crosssection of a wood pavement.

477. The merits and demerits of close and wide joints, from a maintenance and sanitary point of view, and as affording a good foothold for horses, has in recent years been carefully investigated, and practical deductions have been drawn from the observations made.

The generally accepted opinion-that wide joints afford greater safety for horses travelling over the pavement on a level or comparatively level roadway is not borne out by actual experience in the use of these differently constructed pavements. Where wide joints have been adopted the effect of

the hoof and wheel traffic has been to spread and disintegrate the fibre of the wood blocks, rounding the edges and forming a corduroy surface. This evil increases with the width of the joint, and as a consequence the pavement is reduced to a state of disrepair long before the blocks are worn out, and the life of the pavement is materially reduced.

Unnecessarily wide joints retain a large quantity of dirt, produce a noisy pavement, and increase the expense of cleansing the surface. Imperfect scavenging of a wood pavement produces a greasy film on the surface in dry weather and slimy slop after rain, consequently the pavement becomes slippery. This serious defect can only be effectively obviated by washing the carriageway with water and the occasional application of sand to render it

11⁄2"Expansion joint
Wood blocks
4" to 5" deep
53"plank, 12ft. long

P.C.Concrete 6'deep

fit for either pedestrian or vehicular traffic. When these objectionable conditions exist, combined with the disagreeable odours emitted under such circumstances, they add greatly to the discomfort of those using the thoroughfare. The essentials for a satisfactory wood pavement may be summarized thus: it should be properly constructed, carefully maintained and renewed at frequent intervals, and efficiently scavenged.

478. The relative lifetime of soft and hard woods as paving materials cannot as yet be given with that certainty which in the light of longer experience will be made possible. On many of the thoroughfares in London subject to heavy and continuous traffic where soft wood has been in use for a number of years, the actual life or duration of the pavement, before renewal becomes necessary, is considered to be from seven to eight years. The first pavement of Australian hard wood has only been in use since 1889, and is at the present time in good condition, so that the life of this class of paving material may be estimated as at least twelve years.

In Sydney, New South Wales, the lifetime of the hard woods, such as black butt and tallow wood, on carriageways subject to very heavy traffic is considered to be twenty-one years. "In one of the busiest thoroughfares of that city where wood blocks were laid thirteen years ago (1881) and which are at the present time (1893) in a perfect state of preservation, the blocks have only been worn down inch; judging from their present condition, there

Y

appears to be no reason why they should not do good service for another ten years."*

It is also stated that Queen Street (Sydney), paved with wood and sustaining a daily traffic of approximately 25,000 tons, showed 1 inch as the gross result of eight years' wear (when some of the blocks were removed). This thoroughfare is 100 feet wide and situated on gradients of 1 in 22 and 1 in 24. The yard tonnage is therefore approximately 256,000 tons per

annum.

Later carriageway pavements in Sydney † "laid upon a good foundation of concrete with New South Wales hard woods, with slape or butt joints, with convexity of 1 in 60 or 1 in 80, as the longitudinal gradient may suggest, properly cleansed and maintained, is the best and most suitable form of pavement for heavy and continual traffic; and that the best timbers for such work are tallow wood, black butt, blue gum, red gum and mahogany. These timbers, having been so laid in Sydney streets, have, upon examination, shown wear at the rate of from to inch per annum, and have not required repairs of any kind whatsoever. The cost of the first wide jointed pavement, including all labour, materials, etc., was about 27s. per yard super., while recently, pavements with the close joints in Sydney cost 15s. 6d. per yard." This difference in cost is accounted for by the greater quantity of pitch in the wide joint, the consequent larger amount of labour required, and the higher wages paid for laying the blocks when first introduced.

1 80

80

"Twenty-one hours' observation show that 350 vehicles per hour pass at King and George Streets, Sydney, with a width of carriageway of 36 feet. On a width of 74 feet in George Street South, they pass at the rate of 500 vehicles per hour, and you can estimate each vehicle as representing one ton on an average."

It will be apparent, from the relative wear of deal and hard wood pavements in the towns of this country, as indicated by the statistics now available, that the Australian hard woods last longer when the blocks are laid close together with impervious joints. It is, of course, generally admitted that the life of Australian hard woods is considerably longer than that of deal, but much depends on the method adopted in laying the pavement, the amount and weight of traffic passing along the thoroughfare, the gradient and other circumstances of a local nature.

479. The amount of wear of hard wood paving blocks in different thoroughfares in the city of London, with the approximate extent and class

*

"Australian Hard Woods for Pavements," by Mr. W. A. Smith, M.I.C.E., Proc. Inst. Civ. Engineers, vol. cxvi. p. 266 (1894).

"Hard Wood Pavements in Sydney, New South Wales," by R. W. Richards, A.M.I.C.E., Proc. Assoc. Municipal and County Engineers, vol. xxiii.

of the traffic passing over them, and also the comparative wear where a soft wood paving had previously existed, will now be given.

Observations made on the wood pavement in Westminster Bridge Road showed that the amount of wear of the Jarrah blocks was, during a period of seven years, equal to from 1 inch to 1 inch, or about inch to inch annually.*

The traffic going towards Westminster over this thoroughfare is given as 334 tons per foot in width of road in twelve hours, from 6 a.m. to 6 p.m. (see Nos. 1, 7, and 8, in Table XLIX.).

The following detailed statistics on the wear of hard wood paving and the weight of traffic passing over several carriageways in the Vestry of St. Pancras, London, give most valuable information on the subject. †

"Between February 23 and March 11, 1893, a portion of the western end of Euston Road was repaved, and, with the special object of proving the durability of the different timbers employed, the length in question was paved in four blocks. From the line of the south side of Southampton Street, a length of 63 feet was paved with Jarrah, the next length of 63 feet was paved with yellow deal, the next length of 62 feet was paved with Karri, and a closing length of 49 feet with yellow deal."

"The wear upon these different lengths has been recently measured (1896) and may be taken as at three years from the date of laying. It proves to be inch on the Jarrah, inch on the Karri, and 13 inch on the deal blocks. These measurements were taken in the centre line of traffic, where the wear might be regarded as greatest, and at about the centre of each length of wood. It was found that the reduction in depth was the same on both sides of the road. These figures are equivalent to inch per annum on the Jarrah and Karri, and 11 inch on the deal, and the relative rates of wear are as 1 to 6."

"The results (record of the traffic during seven days, July 1895) showed that during the seven days, 110,977 tons of traffic, i.e. vehicles and their loads, not including horses, passed along this portion of the road; this may be taken as equal to 5,770,800 tons per annum, or 575,544 tons per yard in width per annum. The omnibus traffic during the week amounted to 8575 tons, or 7.72 per cent. of the total traffic.

also obtained upon This portion of the

"Observations both as to wear and traffic were another length of Euston Road, at St. Pancras Church. road was paved with Jarrah blocks between April 30 and May 24, 1894. The road has therefore been under traffic for say 12 years, and the wear has

* "Hard Wood Paving," by J. P. Norrington, A. M.I.C.E., Engineer and Surveyor, Lambeth Vestry, London, Proc. Assoc. of Municipal and County Engineers, vol. xxii.

"Wear of Hard Wood Paving and the Weight of Traffic thereon," by W. Nisbet Blair, A.M.I.C.E., Vestry Surveyor, St. Pancras, Proc. Assoc. of Municipal and County Engineers, vol. xxii., 1895-96.