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t <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />well scrubbed -in by means of stiff bristle brushes whenever possible. New <br />concrete shall be deposited before the neat cement dries. <br />F. Deposit concrete to maintain, until the completion of the unit, a horizontal <br />plastic surface. Vertical lifts shall not exceed 24- inches and preferably <br />18- inches. <br />G. Chutes for conveying concrete shall be of U- shaped designed and sized to <br />insure a continuous flow of concrete. Flat (coal) chutes shall not be <br />employed. Chutes shall be metal or metal -lined and each section shall <br />have approximately the same slope. The slope shall not be less than 25 <br />nor more than 45 degrees from the horizontal and shall be such as to <br />prevent the segregation of the ingredients. The discharge end of the chute <br />shall be provided with a baffle plate or spout to prevent segregation. If the <br />discharge end of the chute is more than 5 feet above the surface of the <br />concrete in the forms, a spout shall be used, and the lower end maintained <br />as near the surface of deposit as practicable. When the operation is <br />intermittent, the chute shall discharge into a hopper. Chutes shall be <br />thoroughly cleaned before and after each run, and the debris and any water <br />shall be discharged outside the forms. Concrete shall not be allowed to <br />flow horizontally over distances exceeding 5 feet. <br />H. In thin sections of considerable height, concrete shall be placed using <br />suitable hoppers, spouts with restricted outlets, or otherwise, as required or <br />approved. <br />Concrete during and immediately after depositing shall be thoroughly <br />compacted by means of suitable tools. Internal type mechanical vibrators <br />shall be employed to produce required quality of finish. Vibration shall be <br />done by experienced operators under close supervision and shall be carried <br />on long enough to produce homogeneity and optimum consolidation without <br />permitting segregation of the solid constituents of "pumping" or migration of <br />air. All vibrators shall be supplemented by proper wooden spade puddling <br />adjacent to forms to removed included bubbles and honeycomb. This is <br />essential for the top lifts of walls. All vibrators shall travel at least 10,000 <br />rpm and be of adequate capacity. At least one vibrator shall be used for <br />every 10 cubic yards of concrete placed per hours. In addition, one spare <br />vibrator in operating condition shall be on the site. <br />J. Concrete slabs on the ground shall be well- tamped into place and <br />foundation material shall be well- tamped, and rolled until thoroughly <br />compacted prior to placing concrete. <br />K. Concrete shall be deposited continuously in layers of such thickness that no <br />concrete will be deposited on concrete which has hardened sufficiently to <br />cause the formation of seams and planes of weakness within the section. If <br />a section cannot be placed continuously, construction joints may be located <br />at points as provided for in the Drawings or approved by the Engineer. <br />03300 -10 03- 4138.0 <br />