BANGLADESH POWER DEVELOPMENT BOARD TENDER ... - BPDB

a gauge so that a predetermined quantity of water can be injected direct into themixer drum. If concrete is to be mixed by hand, it shall be approved by the Board.The Contractor shall take all precautions to protect the concrete from the effectsof injurious materials.17.6.10 PLACINGThe concrete shall be placed in the positions and sequences indicated on theapproved drawings immediately after mixing under the supervision of the Boardor his representative.Prior to placing the concrete all deleterious substance such as organic matter,standing water, flowing water, wood fragments shall be removed from the surface against which the concrete is to be placed. When concrete is to be placedagainst a construction joint or adjacent to a set surface the whole surface shall bethoroughly roughened. It shall be cleared of all loose and foreign matter andwashed with water immediately before fresh concrete is placed.The concrete shall be fully compacted throughout the layer and it shall bethoroughly worked against the formwork and round the reinforcement withoutdisplacing them Unless otherwise directed by the Board, approved power drivenvibrators of the immersion type shall be used. Vibrators shall penetrate to the fulldepth of the concrete layer and shall re-vibrate that layer to ensure that thesuccessive layers are well knitted together. The placing of concrete shall not bepermitted under the following conditions unless specifically approved by theBoard.a. If it rainsb. If it is poorly illuminated during night workC. If ordered to stop by the Board or his representative.17.6.11 TRANSPORTATIONReady mixed concrete shall be transported speedily to the point of placing by ameans that shall be approved by the Board and which shall give little chance forsegregation of materials. Generally, the transportation of ready mixed concreteshall be limited to within one hour. Concrete delivered in excess of the time limitshall be rejected. When concrete is observed to have segregated or startedsolidifying at the transportation of placing, it shall be rejected and replaced.17.6.12 CURINGConcrete shall be protected during the first stage of hardening from the harmfuleffects of sunshine, drying winds, hot weather and rain or running water. Theconcrete shall generally be wet-cured for at least 7 days. The curing method forconcrete shall be submitted to the Board for approval.Ghorasal 200 MW to 300 MW Gas Turbine Peaking Power Plant Project (Vol-2 of 3)171