BANGLADESH POWER DEVELOPMENT BOARD TENDER ... - BPDB

(b) Transverse Joints: The transverse joints consist of the expansion jointsand contraction joints. The expansion joint shall in principle be formed at every40m and the contraction joint shall be formed at an interval of every 8m betweenthe expansion joints. In the expansion joints, 19 mm (3/4") preformed expansionmoulding strip shall be placed and bituminous Dealer shall be poured afterremoving the strip and before opening the road to traffic.(c) Dowels :In all longitudinal joints, 75cm long tie dowel bars of 3/4" ddiameters shall be used for concrete pavements. In all contraction joints, 75cmlong slip dowel bars of 3/4" diameter shall be embedded in the concrete. All dowelbars shall be placed at an interval of 75 cm. The remaining half of the dowel barsfor the transverse joints shall be painted, greased, and wrapped with wax paperbefore concreting the next slab. The slip dowel bars in the expansion joints shallprovide a cap having adequate size and type at the end of the bars.(iii)MixingHand mixing of concrete will not be permitted. Machine mixers, if used, shall havea standard mixer of an approved type with a capacity of at least 0.76cu.m. (1cubic yard). Truck mixers, if used, shall be of the revolving drum type, watertight,and so constructed that the concrete can be mixed to ensure uniform distributionof material throughout the mass. The procedures of concrete mixingshall be in accordance with the Specification for Concrete Work Section.(iv)PlacingConcrete shall be placed only on aggregate sub-base that has been prepared aspreviously prescribed and approved by the Board. The concrete shall be depositedin such a manner as to require as little handling as possible, and shall immediatelybe distributed or spread by shovelling or by other approved methods, to suchdepth, and grade, that when compacted, the finished grade of the pavement willbe attained correctly. Vibrators of approved type and capacity for the purposeintended shall be used to sufficiently compact the concrete.(v)FinishingAfter the concrete has been deposited, distributed and vibrated, the concrete shallbe struck off and screeded by mechanical means approved by the Board. Thefinishing machine shall be of the screeding and trowelling type designed andoperated both to strike off and to compact. Hand finishing may be employed inlimited areas where finishing machines can not be operated. Finishing of concreteshall be done, as directed to the satisfaction of the Board. All finished surfacesshall be tested with a 3-meter straight edge and it shall not vary more than 1cmin 3m from the designed surface. Any variation of the surface from the desiredcrown or cross-section shall be properly corrected.(vi)Removal of Formwork and RepairAll forms for concrete shall remain in place undisturbed for not less than twentyfour(24) hours after the concrete is placed, after which the forms may beremoved. In the removal of formwork, care should be taken so as not to breakthe edges of the pavement. In case portions of the concrete are spalled, theyGhorasal 200 MW to 300 MW Gas Turbine Peaking Power Plant Project (Vol-2 of 3)178