360R-06 Design of Slabs-on-Ground
R-52 ACI COMMITTEE REPORT
tải về 2.35 Mb. Chế độ xem pdf
|
| 360R-52
ACI COMMITTEE REPORT curling. Because the quality of cement may vary from brand to brand and within brand, comparative cement mortar shrinkage tests (ASTM C 157) conducted before the start of a project are desirable. 13.4.3 Influence of slump—Table 13.1 shows that a 6 to 7 in. (150 to 180 mm) slump concrete will have only 10% more shrinkage than a 3 to 4 in. (76 to 100 mm) slump concrete. This increase in shrinkage potential would be anticipated if the slump increase was due to additional water or admixtures that increase the shrinkage. If shrinkage is to be kept to a minimum, then slump control is only a small factor in the equation. Slump by itself is not an adequate indicator of expected shrinkage. Many factors should be specified and controlled to have a satisfactory slab with regard to shrinkage in the hardened state. 13.4.4 Influence of water-reducing admixtures—Water reductions of approximately 7% may be achieved with ASTM C 494 Type A water-reducing admixtures, but their effect on shrinkage and curling is minimal. Tremper and Spellman (1963) and others, however, have found that chloride- based admixtures of this type definitely increase shrinkage of the concrete. Some water-reducing admixtures increase concrete shrinkage, even at reduced mixing water contents, as shown by numerous investigators (Ytterberg 1987). A reduction in mixing water content, permitted by the use of water reducers, will not always decrease shrinkage proportionally. In many cases, shrinkage is not changed significantly by the introduction of a water-reducing or high-range water- reducing admixture (Types A and F, ASTM C 494) or by a nominal decrease in slump from 5 to 3 in (130 to 76 mm). Designers should note that ASTM C 494 allows concrete manufactured with admixtures to have up to 35% greater shrinkage than the same concrete without the admixture. tải về 2.35 Mb. Chia sẻ với bạn bè của bạn:
|