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B. Layers of concrete shall not taper nor be wedge shaped but shall be built <br />with squared ends and level tops. Deposit concrete continuously or in <br />layers of such thickness that no concrete will be deposited on concrete <br />which has hardened sufficiently to cause the formation of seams or planes <br />of weakness within the section. Place concrete at such a rate that concrete <br />being integrated with fresh concrete is plastic. Use vibrators to blend the <br />plastic concrete layers. <br />C. Remove temporary spreaders in forms when concrete has reached an <br />elevation rendering their service unnecessary. <br />D. Align slab top surfaces to screed contours by strikeoff or if the nature of the <br />finished surface so requires, by vibrating screeds or roller pipe screeds. <br />E. Do not place concrete in supported elements until concrete previously <br />placed in columns or walls is no longer plastic and initial shrinkage has <br />occurred. <br />' F. Keep covers available at site to protect freshly placed concrete from rain. <br />No exterior concrete shall be placed during rain. Fresh concrete exposed to <br />rain shall be inspected by the Engineer. Engineer shall decide if the <br />damaged concrete be repaired or removed and replaced with no additional <br />expense to the client. <br />3.15 CONSOLIDATION: <br />t <br />07/06 03300 -16 05 -5564 <br />1 <br />A. Consolidate concrete until voids are filled and free mortar appears on the <br />surface. Consolidate concrete by means of internal vibrators. <br />B. Vibrators: Minimum frequency of 8,000 vibrations per minute, massive <br />head, with sufficient amplitude to effectively consolidate concrete. <br />' <br />C. Employ a sufficient number of vibrators to consolidate the concrete within <br />15 minutes after depositing in forms. Maintain at least one spare vibrator <br />available at the site of each structure during concrete placement. Do not <br />hold vibrators against the forms or against the reinforcing steel. <br />D. The location, manner, and duration of the application of vibrators shall be <br />such as to secure maximum consolidation of the concrete without causing <br />segregation of mortar and coarse aggregate and without causing water or <br />cement past to flush to the surface. The thickness of the layers shall be not <br />greater than can be satisfactorily consolidated by vibrators. Vibrators shall <br />vertically penetrate into the previous layer at regular intervals. <br />t <br />07/06 03300 -16 05 -5564 <br />1 <br />