360R-06 Design of Slabs-on-Ground
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- DESIGN OF SLABS-ON-GROUND 360R-23
| 5.1.2 Construction joints—Construction joints are placed
in a slab to define the extent of the individual placements, generally in conformity with a predetermined joint layout. If concreting is ever interrupted long enough for the placed concrete to harden, a construction joint should be used. In areas not subjected to traffic, a butt joint may be adequate. In areas subjected to wheeled traffic, heavy loads, or both, joints with dowels are recommended ( Fig. 5.5 ). A keyed joint is not recommended for load transfer because the male and female key components lose contact when the joint opens due to drying shrinkage. This can eventually cause a breakdown of the concrete joint edges and failure of the top side portion of the key. Construction joints or bulkheads can be wood, metal, or precast concrete; they should be placed at the proper elevation with the necessary support required to keep the bulkheads straight, true, and firm during the entire placing and finishing procedure. If dowels are required, provisions should be made along the bulkhead to ensure proper alignment during construction and finishing operations. Dowel alignment devices should be rigidly attached to the bulkhead with nails DESIGN OF SLABS-ON-GROUND 360R-23 or screws. These devices allow the dowel to be inserted through the bulkhead while maintaining the proper alignment of the dowel parallel to the surface and each other and perpendicular to the joint face. The dowels should be inserted into the dowel alignment device just prior to concreting operations to minimize disturbance during construction; refer to Fig. 5.5. All construction joints should be internally vibrated at frequent intervals to properly consolidate and densify the concrete at the joint and around the dowels. Vibratory screeds, laser-guided screeds, and hand-rodding techniques do not provide sufficient internal vibration. This is particularly imperative when large, top-size coarse aggregate concrete is used adjacent of armored joints, round and square dowels, or diamond-shaped load plates. tải về 2.35 Mb. Chia sẻ với bạn bè của bạn:
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