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Cost Coal-Tar

pavements, square, yard, cents, laid, average and maintenance

COST COAL-TAR Construction. The first cost of coal-tar pave ments has been only a trifle under the prevailing prices for sheet asphalt pavements. In Washington D. C., from 1873 to 1878, 745,305 square yards of coal-tar pavements of various kinds were laid at prices ranging from $1.74 to $3.70 per square yard. These pavements proved very unreliable, either through inherent defects in the materials used or owing to faulty methods of construction; and consequently for some years thereafter no coal-tar pavements were laid. A return to coal-tar pavements in 1887-89 was forced upon the city by the act of Congress which specified that no con tract should be made for asphalt pavements for a greater price than $2.00 per square yard. The lowest bid received for such pavements was $2.25 per square yard, and consequently a con siderable quantity of tar pavements was laid, the prices of it being from $1.98 to $2.00 per square yard. These pavements were laid under the specifications in § 700-05.

Maintenance. Up to June 30, 1887, the average cost of maintaining all the coal-tar distillate pavements laid from 1871 to 1878 was 7.2 cents per square yard per annum; but the work of one contractor was so poor that it was necessary to re-surface the pavements laid by him when they were only two years old, and excluding the work of this contractor the cost of maintenance was 5.5 cents per square yard per annum.* " For the first five years, the annual average was 3.7 cents per square yard; for the second five years, 6 cents; and for the last five years, 6.6 cents. That a durable coal-tar pavement can be laid is proved by the fact that the average cost of maintenance of 158,595 square yards of Vul canite pavement (for specifications of the same see § 700-05) was only 2.9 cents per square yard per annum for fourteen years, for the first five years the average being 0.3 cents per square yard, for the second five years 4.2 cents per square yard, and for the last four years 4 cents per square yard." t Up to June 30, 1901, the average cost of maintenance of the tar pavements laid in Washington in 1887-89 had been 3.5 cents per square yard per annum. This result was obtained as follows: The Report of the Operations of the Engineering Department of the District of Columbia for the year ending June 30, 1901, pages 8 to 51, gives the location, the kind, and the details of the cost of all the pavements in Washington, including the average annual cost per square yard for the pavement laid under each contract.:

During 1887-89, 132,063 square yards of pavement were laid under thirty-six contracts, and the average of the annual cost under the several contracts is 3.5 cents per square yard, as stated above. This method of deducing the average takes no account of the areas of the different pieces, and consequently is not mathematically cor rect; but the error is immaterial. The areas range mostly from 2,000 to 4,000 square yards, one, however, being 18,000. The avcrage age of the pavements was 12.6 years. Of the thirty-six pieces of tar pavement as above, fourteen had been re-surfaced before July 1, 1901, the average age at the time- of re-surfacing being 11.7 years.

The above data on the cost of maintenance of coal-tar distillate pavements suggest a comparison with the correspond ing data for asphalt pavements. According to Table 47. page 442, there were laid in Washington during the years 1886, 1887, 1S89, and 1890, 114,408 square yards of asphalt pavement, for Viich the cost of maintenance was 1.13 cents per square yard per annum. The corresponding cost of tar pavements laid from 1886 to 1889 was 3.5 cents, and therefore we may conclude that the cost of maintenance of tar pavements is practically three times as much as that of asphalt pavements. Any attempt thus to com pare the cost of maintenance of tar and asphalt pavements is open to the criticism that the mathematical process of deducing the average is not strictly correct, and also that the amount of traffic may not be the same in the two cases, and further that part of the repairs in each case was due to openings made in the streets inde pendent of the condition of the pavements; but nevertheless the general conclusion is at least approximately true. The use of tar pavements has practically been abandoned, chiefly on account of the excessive cost of maintenance.