Effect of Fibers and Expansive Agent on Shrinkage of Self-Consolidating Concrete under Two Curing Schemes

摘要

Adding the proper amount of expansive agent (EA) to concrete is an effective way to control shrinkage cracking. Fiber can be treated as a secondary reinforcement for controlling shrinkage and improving the crack resistance and mechanical properties of the concrete. To date, studies on shrinkage for concrete with fiber and expansive agent integration are very limited, especially for hybrid steel and polypropylene (PP) fibers. In this study, shrinkage tests for 21 mixtures of self-consolidating concrete (SCC) with different expansive agent dosages, fiber types [steel fibers (SF), PP fibers, and hybrid steel and PP fibers], fiber contents, as well as the incorporation of expansive agents and fibers were carried out. The shrinkage of the tested SCC at 10 h through 5 days after placement was analyzed to study the effects of different factors on early-stage free shrinkage. To study the effect of curing conditions on shrinkage, both sealed cure (S-Cure) and top-surface exposure cure (TE-Cure) were investigated for comparison. The test results showed that curing conditions had a significant impact on the shrinkage and expansion of the studied SCC mixtures. The shrinkage of SCC under TE-Cure was 5-10 times the shrinkage under S-Cure. The free expansion of expansive SCC (ESCC) under TE-cure was smaller than the free expansion under S-Cure. As the amount of expansive agent increased, the effect of curing conditions on the expansion of concrete change increased. Under both curing conditions, at equivalent fiber factors, the shrinkage-restraining effect of PP fibers on SCC was higher than that of steel fibers. Meanwhile, for ESCC, steel fiber presented a higher restraining effect on expansion than PP fibers.