WOOD-BLOCK PAVEMENT
92. Sub-grade.—The sub-grade for wood-block pavement shall be prepared as specified in Section 26, and shall be finished to a surface ... inches below the pavement datum.
93. Foundation.—The foundation for wood-block pavement shall be Portland cement concrete ... inches thick, prepared as specified in Sections 28, 29, 30, 31, 32, 33, 34, 35, 36 and 37. The upper surface of the concrete foundation, when completed, shall be at a distance below the pavement datum equal to the depth of the blocks to be laid, plus one-half (½) inch, and must not vary more than one-fourth (¼) inch above or below that depth.
MATERIALS
94. Wood-blocks.—The wood-blocks may be made of Long-leaved yellow pine (Pinus palustrus), Lob-lolly pine (Pinus tæda), Short-leaved pine (Pinus echinata), Cuba pine (Pinus heterophylla), Black gum (Nyssa sylvatica), Red gum (Liquidambar styraciflua), Norway pine (Pinus resinosa), or Tamarack (Larix laricina), or of other species of wood of equal strength and toughness and of a texture permitting as satisfactory preservative treatment as those herein named. But, as far as practicable, only one species of wood shall be used on any one contract.[[51]]
Only wood from live, sound trees shall be used. The lumber from which the blocks are cut shall be properly manufactured, free from bark, and with full square corners. It shall be free from decay, dottiness, brashness, shakes, large season cracks, loose or unsound knots over three-fourths (¾) inch in diameter, and all other imperfections which may, in the opinion of the Engineer, be detrimental. “Fat” pine containing so much resin that it will not take up the specified quantity of creosote oil in treatment may be rejected. Second-growth timber, and Southern pine showing, outside of a radius of three (3) inches from the heart, nine (9) or less annual growth rings to the inch, will not be accepted.
The paving blocks made from the lumber hereinbefore specified shall be well manufactured and truly rectangular and square edged. Their depth (parallel to the fiber) shall be ... inches,[[52]] their length shall not be less than six inches nor more than three times their depth, and their width shall be from two and one-half (2½) to three and one-half (3½) inches, but at least one-fourth inch less than their depth.
All the blocks for any one contract shall be of the same standard depth and width, and the individual blocks shall not vary more than one-eighth inch from the designated depth and width.
95. Creosote Oil.[[53]]—The oil used for the preservative treatment of the paving blocks shall be coal-tar creosote oil, commonly known as dead oil of coal-tar, without admixture or adulteration with other oils or tars. Oils produced or resulting from the distillation of water-gas tar, blast-furnace tar, producer-tar, lignite-tar, petroleum-oil tar, or wood-tar, or, containing an admixture of any of these will not be accepted. The creosote oil shall not contain more than five per cent. (5%) of tarry matter nor more than two per cent. (2%) of water. Its specific gravity at a temperature of 100° F. shall be not below 1.03 nor above 1.08. Not less than ninety-nine per cent. (99%) shall be soluble in hot benzol. It shall not contain more than eight per cent. (8%) of tar acids. When two hundred (200) grams are subjected to distillation at gradually increasing temperatures, not more than five per cent. (5%) of distillate shall distil over up to a temperature of four hundred degrees F. (400° F.), nor more than thirty-five per cent. (35%) shall distil over up to a temperature of four hundred and fifty-five degrees F. (455° F.), and not more than eighty per cent. (80%) shall distil over up to a temperature of six hundred degrees F. (600° F.). After complete distillation there shall not remain more than two per cent. of coke. The residue remaining, upon sulphonating a portion of the total distillate, shall not exceed one per cent. (1%). The above tests shall be made in accordance with the methods prescribed in the “Report of the Committee on Preservative Treatment of Poles and Cross-arms” of the National Electric Light Association, 1911.
96. Preservative Treatment.—The paving blocks shall, after they are cut to the proper dimensions, be subjected to preservative treatment with the creosote oil specified in Section 95.
The contractor may employ any of the standard methods in common use for impregnating the blocks, provided that uniform results are attained, complying with the following requirements:
The wood shall not be heated during any part of the process to a temperature exceeding two hundred and sixty degrees Fahrenheit (260° F.).
All parts of every block shall be reached and penetrated by the oil. The quantity of oil found in the blocks after treatment shall average not less than ... pounds per cubic foot of wood.
The oil in the treating tanks during the process of impregnation shall not become diluted with water to the extent of more than five per cent. (5%) and if the percentage of water in the oil during the process of treatment shall exceed two per cent. (2%) the quantity of the oil to be injected in the wood as stipulated hereinbefore shall be increased in a like ratio; for example, if the oil in the treating tanks shall be found to contain four per cent. (4%) of water the quantity required to be found in the blocks after treatment shall be four per cent. (4%) greater than herein specified.
The quantity of oil injected shall be determined primarily by tank measurements, but shall be verified by actual determination of the quantity of oil in the treated blocks by the following method: representative treated sample blocks shall be selected and an auger hole one inch in diameter bored entirely through the block parallel to the fiber, the borings all collected, thoroughly mixed, and the quantity and ratio of oil to wood in the borings determined by extracting the oil completely with carbon di-sulphide. The center of the auger hole shall be located midway between the sides of the block and at a distance from the end of the block equal to one-third (⅓) of the length of the block. At the time of treatment the blocks shall not be green or saturated with water, but they shall, preferably, not be thoroughly seasoned. After treatment, and until used, the blocks shall, during dry weather, be frequently well drenched with water to prevent excessive drying out and cracking.
97. Laying the Wood-Blocks.—The concrete foundation shall be cleaned and swept to remove all dirt and débris and shall be thoroughly dampened immediately in advance of the setting of the blocks. Upon the concrete foundation shall be spread a layer of mortar about one-half inch thick, made of one part Portland cement and two parts sand with sufficient water to make a moderately stiff paste.[[54]] The mortar shall be thoroughly mixed and shall be spread in place over the concrete foundation immediately in advance of setting the blocks to such a thickness that when the blocks are set and properly tamped their tops shall conform accurately to the pavement datum.
Upon this mortar bed the blocks shall be set with their fiber vertical, in straight, parallel courses at right angles to the axis of the street, except at street intersections where they shall be set at an angle of forty-five degrees with the axis of the street. The blocks shall be set as close together as practicable. Blocks in adjoining courses shall break joint at least three inches. Blocks of such lengths shall be selected as to make as little splitting as practicable in filling out ends of courses. Where splitting is necessary, no fractional block shall be used whose length is not at least equal to its width.
After the blocks are thus set the whole surface of the pavement shall be rammed with a rammer weighing not less than twenty pounds, a plank ten (10) inches wide, two (2) inches thick and four feet long being interposed between the rammer and the pavement and moved about as the ramming progresses until the blocks are forced into a firm seat in the mortar bed and their tops brought accurately to the pavement datum. The ramming shall be completed before the mortar under them has begun to set, but no ramming shall be done, during the progress of the work, nearer than three feet to the edge of the block setting, except where the block setting may be suspended, as at the end of the day’s work, when all the blocks then set shall be rammed.
The top surface of the pavement when completed shall conform so truly to the pavement datum that correctly formed templates twelve (12) feet long applied to the surface shall show at no place a departure of more than three-sixteenths (³⁄₁₆) inch therefrom.
98. Filling the Joints.—After the block setting is completed, perfectly dry, fine sand shall be spread over the pavement surface and swept about until every joint into which the sand will penetrate shall be completely filled. The remaining sand shall be left upon the pavement for such time as the Engineer may direct, when it shall be removed by the Contractor.[[55]]
99. Inspection.—The lumber for paving blocks will be inspected before it is cut into blocks. The blocks will also be inspected upon delivery to the street and as they are laid. Blocks that have, in treatment or subsequent handling, developed open season cracks or wind shakes or other imperfections that may prevent their durability or usefulness in the pavement shall be rejected and removed from the street.
100. Chamfered Blocks.—Where wood-block pavement is laid on streets or parts of streets having a gradient of more than 3%, the blocks shall not be less than four (4) inches long, and the upper side-corners of the blocks shall be chamfered to a depth of three-eighths (⅜) inch, the chamfered surface to make an angle of 40 degrees with the vertical sides of the blocks; or such other construction shall be used as will, in the opinion of the Engineer, provide an equally good foot-hold for horses.
101. Expansion Joints.—Before the blocks are set there shall be placed along and against each curb a board of trapezoidal section having a width one inch greater than the depth of the blocks, the upper edge of which shall have a thickness of three-eighths (⅜) inch for each ten feet or fraction thereof of the width of the street between curbs, and a bottom width one-fourth (¼) inch less than the top. The paving blocks at the beginning and end of each course shall be set against this board. After the ramming of the blocks has been completed, these boards shall be carefully withdrawn and the space between the curbs and the paving blocks shall be completely filled with the bituminous paving cement described in Section 90.
102. The street shall not be opened to travel until such time as the mortar under the blocks shall have become well set, nor until the Engineer shall so direct.