360R-06 Design of Slabs-on-Ground
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| 5.4—Joint protection
Joints should be protected to ensure their long-term perfor- mance. Regardless of the materials chosen for protection, the joint must have adequate load transfer, and the surfaces of adjacent slabs should remain in the same plane. For wheeled traffic, there are two ways to protect a joint: fill the joint with a material to restore surface continuity, or armor the edges with steel angles or plates. Certain types of semirigid epoxy or polyurea are the only materials known to the committee that can fill joints and provide sufficient shoulder support to the edges of the concrete and prevent joint breakdown. Such joint materials should be 100% solids and have a minimum Shore A hardness of 80 when measured in accordance with ASTM D 2240. Refer to Section 5.5 for more details on joint filling and sealing. For large slab placements where sawcut contraction joints are not used, and the joint width at the construction joints may open significantly, such as post-tensioned slabs, or slabs cast with shrinkage-compensating concrete, it is recom- mended that the joints be protected with back-to-back steel angles ( Fig. 5.15 ) or bars, as shown in Fig. 5.14 . It is critical that the top surfaces of the angles or bars used to armor be true. Milling may be required to produce a flat surface if conventional rolled shapes or bar stock is used for this purpose. Steel-armored joints less than 3/8 in. (9 mm) in width can be sealed with an elastomeric sealant as described in ACI 504R. Armored joints where width is 3/8 in. (9 mm) or greater should be filled full depth with semirigid epoxy or polyurea joint filler, or with a joint filler with an integral sand extender to provide a smooth transition for wheel traffic. Construction and sawcut contraction joints that are unstable will not retain any type of joint filler. Joints are unstable if there is horizontal movement due to continued shrinkage or temperature changes, or vertical movement due to inadequate load transfer. Regardless of the integrity of initial construction, the continued movement of a filled, curled, undoweled joint under traffic may prematurely fatigue the filler/ concrete interface to failure. Joint edge protection provided by supportive filler is increased when load-transfer provisions are incorporated in the joint design. tải về 2.35 Mb. Chia sẻ với bạn bè của bạn:
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