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Types of Wood-Block Pavement the

blocks, pavements, sand, filled, wood, usually and laid

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TYPES OF WOOD-BLOCK PAVEMENT.

THE

use of wood blocks for the surfaces of pave ments began a little before 184o, and since that time many types of construction have been tried with vary ing degrees of success. The first pavements in London, in 1839, consisted of hexagonal blocks of fir, six to eight inches in diameter and about six inches deep, placed on a base of gravel. In 1841 a pavement of round beech blocks was laid upon a foundation of planks and sand. The wood soon decayed and the pavement was removed.

In Philadelphia, square hemlock blocks were laid in 1839 and hexagonal hemlock blocks probably a little earlier. Both were quickly destroyed by the decay of the blocks. In New York and Boston similar pave ments were constructed at about the same time and with much the same result.

In 1855 a pavement of tamarac blocks wa,s laid in Quebec. This pavement was placed upon a base formed of a flooring of one and one-half inch boards laid longitudinally and crossed at right angles by a second flooring of inch boards. A layer of sand one half inch thick was placed over the boards. The tamarac blocks were ten to fifteen inches in diameter and twelve inches long, small pieces of wood being forced into the spaces between the blocks. The joints were filled with a mixture of sand, cement, and tar. This heavy construction is reported as having given very good wear, with no decay.

Cedar Block Pavements. In the earlier wood pave ments of the United States, cedar blocks were com monly employed. These blocks were used in the form of whole sections of the tree on account of the liability of the wood to split off between the layers when cut to a rectangular shape, as well as to reduce waste to a minimum. They usually varied from 4 to 9 inches in diameter and 4 to 8 inches in depth. In some cases the blocks were cut to a true cylindrical form, the sap wood as well as the bark being cut away by passing the block through sets of knives, gauged to turn out true cylinders of given size. The use of sapless blocks increases the life of the pavement by augmenting the resistance of the material both to the wear of traffic and to the disintegrating influences of the atmosphere.

These pavements were usually placed upon a founda tion of boards laid upon sand. The planks were com monly tarred and laid lengthwise of the street, being nailed to scantling or other boards placed across the street and bedded in the sand. This construction has

the disadvantage of lacking firmness as well as of being perishable, although in some instances good results have been obtained by its use.

The construction of a pavement of this type is shown in Fig. 25. Blocks of varying sizes are employed, being set in contact with each other in such a way as to leave the spaces between the blocks as small as possible. Usually the joints are filled with sand and gravel, sometimes with a coating of tar; or in some cases the joint is partially filled with tar and then com pletely filled with sand or small gravel. When the ordinary coal-tar paving cement filling is used, the joints are first filled nearly full of sand or gravel, which is pounded down with a bar, after which the hot cement is poured in until the joint is well filled.

These pavements, on account of the plentiful supply of timber were constructed for very low first cost and undoubtedly served a very useful purpose in many instances, permitting the improvement of many streets to an extent which at that time would have otherwise been impossible. They lifted the streets out of the mud, although the pavements did not usually last long and were afterward replaced by more durable materials. Pavements of this type wear rapidly under traffic, soon becoming uneven, and their use has, for the most part, been discontinued on account of their lack of economy.

Nicholson Pavement. Rectangular wooden blocks set like the cedar blocks, upon a plank foundation were at one time quite extensively used and known as Nicholson pavements. In these pavements the blocks are set with their longest dimension transverse to the length of the street. They are usually arranged in courses across the street, being placed close together in the courses, and arranged to break joints in adjpining courses. Between courses a joint is usually made t to inch in width for the purpose of affording a foothold to horses. In the older pavements of this character a much wider joint was employed, some as much as an inch in width, with the idea that they were necessary to secure proper foothold. The joints were filled in the same manner as in the round block pavement. These pavements like the cedar blocks have given place for the most part to more economical kinds of construction.

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