Workability of Gap-Graded Versus Continuously-Graded Concrete and the Correlation Between Slump and Vebe Time

摘要

The most important physical property of plastic concrete with respect to placement is workability, the ease with which a stiff mix with low slump can be compacted into a uniform mass. Heretofore, however, very little is known about the workability of gap-graded concrete. It is, in fact, even more workable than continuously-graded concrete of the same maximum size of coarse aggregate. The general prejudice that gap-graded concrete is harsher than its continuously-graded counterpart must, therefore, be dispelled with experimental evidences before gap-grading can be introduced into general practice. In the work presented herein involving 330 mixes, the workability in the plastic state of both gap-graded and continuously-graded concretes of various mix proportions, has been measured concurrently by the slump of a standard cone and by a Vebe consistometer. The results are compared for gap-graded versus continuously-graded concretes on the basis of equal maximum size of coarse aggregate, water-cement ratio, and aggregate-cement ratio. The comparison has shown the relative ease of placing gap-graded concrete to attain uniform compaction. (Author)