By subsequent tamping or rolling if necessary the

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Unformatted text preview: ndations Unless otherwise specified, the under-drainage shall be blanketed as specified under 4.9.6.2. 4.10 Placing system for Concrete 4.10.1 No concrete shall be placed until the place of deposit has been thoroughly Inspected and approved, all reinforcement, inserts and embedded metal properly secured in position and checked, and forms thoroughly wetted ( except in freezing weather) or oiled. Placing shall be continued without avoidable interruption while the section is completed or satisfactory construction joint made. 4,10.2 Within Forms -Concrete shall be systematically deposited in shallow layers and at such rate as to maintain, until the completion of the 17 IS : 457 - 1957 unit, a plastic surface approximately horizontal throughout. Each layer shall be thoroughly compacted before placing the succeeding layer. In general, the thickness of layers shall not exceed the following limits: a) Vibrated mass concrete b) Hand compacted mass concrete c) Reinforced concrete 45 cm (or 18 in) 30 cm ( or 12 in ) 25 cm (or 10 in) The batches shall be deposited vertically in such a manner as to avoid segregation, air pockets, or damage to other recently placed concrete. The concrete shall not be caused to flow or be worked along the forms for any distance, but shall be compacted as close to the point of deposit as practicable. Wherever necessary, both the forms and reinforcement shall be protected against splashing, and all accumulations of partially set, dried, or caked mortar which may impair the bond or show in the finished faces shall be removed and wasted before commencing concreting operations. 4.10.3 No concrete shall be deposited at any time except in th presence of an authorized inspector, nor shall any concrete be placed outside regular working hours unless due notification thereof is given in sufficient time to make proper provision for inspection. Wherever concrete is being deposited at night or under artificial light, both the places of dcposit and the mixing and conveying equipment shall be adequately illuminated so that all operations are properly observed and inspected. 4.10.4 Temperature of Concrete - When deposited in the forms, concrete shall have a temperature of not more than the maximum values as determined by concrete cooling studies, and appropriate measures shall be taken to attain this requirement. Such measures may include%ne or all of the following operations: a) b) c) d) Cooling of aggregates by spraying with water and air blasting, Cooling of water used in mixing by refrigeration, USC of cooling towers, and Arranging the placing of concrete during the cooler hours of the day. In addition to the above, it may be necessary to control the tcmperaturc rise of the concrctc after it has been placed by the one or more methods determined by temperature control studies. All lifts l~lnccd on rock foundation shall not exceed 75 cm ( or 21 ft 1. 4.10.5 Cleaning Joints 4.10.5.1 The joints shall be thoroughly cleaned so as to ex se sound concrete s...
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