Effect Of Steel Fibers And Polypropylene Fibers On Properties Of Expansive Self-consolidating Concrete

Self-consolidating concrete has been widely used due to its excellent working performance.However, due to the high content of cementitious materials, it issusceptible to shrinkage cracking. This reduces the durability of structural elements and shortens the lifespan of buildings.Therefore, it is important to reduce the shrinkage cracking of self-consolidating concrete.Currently, there are two ways to reduce the shrinkage cracking of self-consolidating concrete:one is to use expansive agent and the other is to use fibers reinforcement. However, literatures regarding combined use of expansive agent and fibersin concrete are quite limited. In this study,experimental and analytical work on self-stressing-consolidating concrete with combination of expansive agent and fibersare conducted.A series of tests are conducted to investigate the effect of fibers (steel fibers and polypropylene fibers) on workability of fresh concrete, mechanical properties as well as shrinkage performanceof hardened concrete. Slump flow, J-ring, V funnel and L-box tests are carried out to evaluate the filling ability andpassing ability of the fresh concrete. Mechanical properties including cubiccompressive strength, axial compressive strength, splitting tensile strength and flexural strength of hardened concrete are also studied. The ultrasonic pulse velocity test is used to detect compactness of concrete. Shrinkage performanceof hardened concrete is testd by vertical comparator.Test results indicate that the dosage of expansive agent can not only increase the early strength of concrete, but also improve the strength at 28 days within a certain range. Fibers reduce the compressive strength at 7 days of the expansive self-consolidating concrete, while it does not influence the 28 days strength noticeably.Axial compressive strength of self-consolidating concrete decreases with increase of expansive agent.But steel fiber can significantly improve the axial compressive strength of expansive self-consolidating concrete, and it increases with the increase of fiber content.Steel fibers can improve the linear load-deflection relationship of bending beams, and thebeam specimen with 0.50% steel fibers dosage shows deflection hardening behavior. And free expansion rate of ESCC reduces with the increase of steel fibers content. Meanwhile, the self-stress will increase.Pulse velocity testresults in different group and at different layers indicates the good compactness and uniformity of hardened concrete.It also shows that additon of polypropylene(PP) fibers reduces working performance of self-consolidating concrete and does not contribute to the increase of mechanical properties very much. But PP fiber could improve the absorption of energy, and improve the deformation capacity of the specimens. Last but not least, test results show thatpolypropylene fibersdose not limit the shrinkage of self-consolidating concrete much.