1925 (#1403-1607) - Laserfiche WebLink

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~t~c~ent capacity to weigh the entire batch to be mixed, l'he required amount of asphalt cement for each batch shall be measured by actual weighing with the scales attached to the asphalt cement bucket. The mixture shall be made in an approved twin pug mixer, having at least forty-eight (48) paddles which shall rotate not less than seventy (70) nor more than ninety (90) revo- lutions per minute. The hot coarse aggregate and sand, and the cold stone dust shalI be placed in the mixer and thoroughly mixed for not less than fifteen (15) seconds; after which the hot asphalt cement shatl be added and the whole mixed for at least .one (1) minute or longer if necessary to produce a homogeneous mixture, in which all particles of the mineraI aggregate are uniformly coated. Time shall be allowed for charging the mixer, but in no case shall the time be less than ten (10) seconds. An accurate time piece shall be provided at the mixer. Mixer paddles shall be replaced when worn to such length that they cannot reach all of the material in the bottom of the mixer. 81~C~.'ION 5. TRANSPORTATION OF MIXTURE. The asphaltic concrete base mixture shall be transported from the paving plant to the work in tight vehicles, previously cleaned of all foreign materials, and each load shall be covered with canvas, or other suitable material, of sufficient size to protect it from weather conditions. No loads shall be sent out so late in the day as to interfere with spreading and compacting the mixture during the daylight. Each load on reaching its destination shall have a temperature of not less than two hundred fifty (250) degrees Fahrenheit. 81~CTION §. LAYING. Prior to the arrival of the asphaltlc concrete base mixture on the work, the prepared subgrade or underlying course shall be cleaned of all loose and foreign materials. The mixture shall be laid only when the prepared subgrade or underlying course is dry or at least free from standing water and only when weather conditions are suitable. Upon arrival on the work it shall be dumped either inside or outside of the area on which it is to be spread. It shall be immediately distributed into place by means of hot forks or hot shovels and spread with hot rakes to correct depth in a uniform layer. .All material must be turned or handled while spreading, from the place in which it was dumped. When shovels are used, the materials shall be dumped upon metal platforms. No more asphaltic concrete base shall be placed in advance of laying the surface course than can be covered by two day's run of the paving plant on surface mixture. SRCTION 7. ROLLING. Immediately after the base has been spread, it shall be thoroughly rolled with a power roller weighing not less than eight (8) tons and having a weight per linear inch of tire width of not less than two hundred ten (210) pounds. Following the first rolling and while the asphaltic concrete is still hot, it shall be re-rolled with a power roller weighing not less than twelve (12) tons and having a weight per linear inch of tire width of not less than four hundred (400) pounds. Rolling shall start longitudinally at the sides and procede toward the center of the pavement, overlapping on successive trips by at least one-half the tire width of the roller, until all roller marks are eliminated. The motion of the rollers shall at all times be slow, to avoid displacement of the hot mixture and any displacement shall at once be corrected by the use of rakes and the addition of fresh mixture when required. Rolling shall proceed at an average rate not exceeding two hundred (200) square yards per hour per roller, and shall continue until no further compression is possible. To prevent adhesion of the asphaltic concrete base mixture to the roller, the wheels shall be kept properly moistened, but excess of either water or oil will not be permitted.