The early shrinkage characteristics of hand-placed concrete

Abstract

Summary The shrinkage characteristics of fresh concrete from 10 to 15 minutes up to 2 or more days after mixing have been examined for a variety of mixes suitable for compaction by hand. The apparatus used for these tests, which is still in the prototype stage of design, is described briefly. Under drying conditions, apparent expansion of the concrete, thought to be caused primarily by settlement of the specimen in the apparatus, occurs immediately after placing up to a time between 1½ and 4½ hours after mixing; by this time the concrete has stiffened sufficiently not to flow. Shrinkage, varying between 1 × 10−4 and 13 × 10−4 takes place during the next 6 to 8 hours; there is then little further movement for a day or more. Concrete kept under water shows a greater apparent expansion, and no early shrinkage. For mixes of approximately constant workability, the amount of early shrinkage under drying conditions appears to increase as the richness of the mix increases (with corresponding changes in the water/cement ratio), and it also increases as the amount of bleeding within the concrete decreases.