GAIL (India) Limited

27Before commencement of work, the Contractor shall submit for the approval of the Engineer, thedetails of the methods he proposes to adopt for concreting.The placement of concrete shall preferablybe by tremie chute or any other approved method.In structures of heavy/complicated reinforcement or in complicated form works, the Contractor shallprovide sufficient number of windows in the form works as directed by the Engineer to check theplacement and compaction of concrete in different stages. Such windows shall be closed as soon as theconcreting reaches the bottom level of the same.3.28.2 Concreting Under WaterThe mix and method of concrete to be placed under water shall be approved by the Engineer.Under water, concrete shall contain at least ten (10) per cent more cement over that required for normalplacement.An account of extra cement so used shall be maintained by the Contractor and the Engineer jointly andthe extra cement used shall be separately paid for. Plumbing of water shall not be permitted for twentyfour (24) hours after completion of placement. No flow of water, natural or artificial, shall bepermitted during placement and upto twenty four (24) hours after completion of placement.3.28.3 Cold Weather ConcretingWhen conditions are such that the ambient temperature may be expected to be 4.5oC or below duringthe placing and curing period, the work shall conform to IS: 7861 (Part-II).3.28.4 Hot Weather ConcretingConcrete shall not normally be placed when the atmospheric temperature exceeds 40°C in the open. If,in spite of programming concrete work in the cooler hours of early morning, evening or night,placement is necessary in too hot a weather, then the Contractor shall take at least the followingadditional precautions:1. Stock-pile aggregates in shade2. Do not use fresh, factory hot cement3. Use cold water4. Cool form work by sprinkling water without collecting water inside5. Reduce to minimum the time interval between mixing and placing6. Place, vibrate and finish as quickly as possible7. Initiate curing as soon as concrete hardens.Positive temperature control by methods like pre-cooling, post cooling or cooling of concrete bycirculating cold water through small embedded pipe lines inside concrete, if required, shall be specifiedand shall be undertaken.3.28.5 Concreting in Large Pours (Mass Concrete)The aim of controlling the concreting in large pours is to reduce cracking caused by shrinkage due toheat of hydration. The Contractor shall submit detailed proposal to the Engineer for approval about themethod of pouring and the measures to reduce heat of hydration, which he proposes to adopt.The maximum height of lifts will depend on the type of cement used. The use of cement having lowheat of hydration, could allow greater lifts.The Contractor shall provide all the necessary arrangements like pre-cooling of aggregates, cooling offresh concreting by passing cold water through pipes placed inside the concrete or such other measuresat least 38 hours before the placement of concrete and also provide the facility for recording oftemperature at least 24 hours prior to placement of concrete.The minimum interval between concreting of successive lifts, separated by horizontal constructionjoint, shall be six days or as directed by the Engineer.