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(18") to thirty inches {30"~ apart rather than for {onger <br />periods at wider intervals. In general, to prevent <br />segregation of ingredients, vibration shall continue only long <br />enough to accomplish thorough consolidation and complete <br />embedment of the reinforcement and fixtures. <br />10.5.4 LIMITATIONS <br />Vibrators shall not be used as a means of moving concrete <br />to a desired placement area. This action shall be accom- <br />plished by correct initial placement. The Contractor shall <br />provide a sufficient number of vibrators and operators so <br />that consolidation is started immediately after the first <br />concrete has been deposited in the forms. <br />10.6 DEPOSITING IN COLD WEATHER <br />The Contractor shall provide adequate equipment for heating materials and <br />protecting the concrete during freezing or near freezing weather. Unless <br />the temperature is at least 40~ F (4.4~ Cl, concrete materials shall be <br />heated so that the temperature of the concrete at time of placement is not <br />less than 55~ F (13~ Cj. Said equipment shall be available at all times and <br />shall be used for the period specified in this specification. All work during <br />cold weather shall be executed in accordance with ACI 306R. <br />10.7 DEPOSITING IN HOT WEATHER <br />When concrete must be placed during hot weather, 90o F (32~ Cj or <br />above, the Contractor shall follow the procedures outlined in ACI 305R. <br />10.8 METHODS FOR BONDING JOINTS, TOPPING, OR PATCHING HARDENED <br />CONCRETE <br />10.8.1 Concrete on which other concrete is to be placed shall be <br />either plastic or thoroughly hardened, but not in a semi- <br />hardened state that may be disrupted and weakened by the <br />added load and the jarring of placement. <br />10.8.2 To provide bond between successive lifts of concrete, the <br />exposed surface shall be cleaned and roughened without <br />loosening the embedded aggregate. Brooms or air-water <br />jets shall be used after the start of initial setting of the <br />concrete. Sandblasting or air tooling shall be employed <br />after the concrete has hardened. In all cases, the surface <br />film and laitance, or diluted paste, shall be removed and a <br />reasonably high percentage of aggregate exposed. <br />Immediately before the new concrete is placed the old <br />surface shall be clean, damp, and free from standing pools <br />of water. <br />SPEC B -CONCRETE <br />PAGE 16 <br />