360R-06 Design of Slabs-on-Ground
DESIGN OF SLABS-ON-GROUND 360R-33
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| DESIGN OF SLABS-ON-GROUND 360R-33
the concrete in excess of its early tensile strength, thereby cracking the slab. As drying shrinkage continues, cracks open wider. This may present maintenance problems, and if the crack width exceeds 0.035 in. (0.9 mm), aggregate interlock (load transfer) becomes ineffective. Refer to Section 5.2 for additional information on aggregate interlock. Cracking due to shrinkage restraint may be limited by closer joint spacing, additional distributed reinforcement, or post-tensioning. 8.1.2 Shrinkage-compensating concrete compared with conventional concrete—Shrinkage-compensating concrete is used to limit cracking and curling . Shrinkage-compensating concrete is made with cement conforming to ASTM C 845 rather than ASTM C 150 or C 595. Therefore, the volume change characteristics are different. Shrinkage-compen- sating concrete undergoes an initial volume increase during the first few days of curing, and then undergoes drying shrinkage. The drying-shrinkage characteristics of shrinkage- compensating concrete are similar to those of portland- cement concrete. The drying shrinkage of shrinkage- compensating concrete is affected by the same factors as portland-cement concrete. These include water content of the concrete mixture, type of aggregate used, aggregate gradation, and cement content. The water content influences both the expansion during curing and subsequent shortening due to drying shrinkage. Figure 8.1 illustrates the typical length-change characteristics of shrinkage-compensating and portland-cement concrete prism specimens tested in accordance with ASTM C 878 (ACI 223). In shrinkage-compensating concrete, the expansion is restrained internally by the bonded reinforcement, which is placed in tension. As a result of this expansive strain, compression is developed in the concrete, which in turn is relieved by drying shrinkage and some creep. With shrinkage-compensating concrete, it is intended that the restrained expansion be greater than the resultant long-term shrinkage, as shown in Fig. 8.2, so the concrete will remain in compression. The minimum recommended amount of concrete expansion for slabs-on-ground, measured in accordance with ASTM C 878, is 0.03%. tải về 2.35 Mb. Chia sẻ với bạn bè của bạn:
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