The Study On The Workability And Shear Behavior Of Fiber Reinforced Self-Compacting Concrete

The poor workability of traditional concrete and the high dense space or inaccuracy arrangement of shear reinforcement in structural members not only reduce the casting quality of concrete, but also decrease the effective bond between matrix and reinforcement and the thickness of concrete cover, which directly reduce the safety and durability of structures. High-Performance Concrete has been studied in many countries in European and North America; Fiber Reinforced Self-Compacting Concrete (FRSCC) is one of the key research directions. Some studies have shown that FRSCC has high workability and high toughness, which are important prerequisites for the structure application of FRSCC, in order to reduce the amount of stirrup, increase the its space and maintain good durability of structures. At present the studies on the workability, rheological properties, mixture design, flexural toughness, and shear toughness of FRSCC are inadequate, and the investigation on the shear behavior of Steel Fiber Reinforced Self-Compacting Concrete (SFRSCC) structures is limited at home and abroad.The progresses in the research on workability of Self-Compacting Concrete (SCC), toughness of Fiber Reinforced Concrete (FRC), shear behavior of RC beams, and shear strength of steel fiber reinforced beams are summarized in this paper. On this basis and funded by the National Natural Science Foundation-The study on the workability and mechanic behavior of hybrid fiber reinforced Self-Compacting Concrete (No.50578026), the following aspects are carried out:(1) The workability of fresh fiber reinforced concrete mixture is studied using the widely used methods in the world. FRSCC reinforced by high alkali-resistant glass fiber, modified polypropylene fiber, hybrid fiber, and steel fiber are obtained, which satisfies the requirements of workability and strength. The mixture calculation and adjustment programs during the experiment are analyzed and compared with some existing SCC and FRSCC mixture design methods. A practical mixture design process for FRSCC is proposed.(2) Based on the Bingham model and Tresca criteria, a differential equation on slump flow velocity and slump flow diameter is established. The relationship between yield stress and slump flow diameter and a function between slump flow time and average viscosity are derived. The average viscosity can reflect the plastic viscosity. The slump flow model are used to calculate the slump flow velocity of polypropylene fiber reinforced mortar mixture and the yield stress and average viscosity of steel fiber reinforced Self-Compacting Concrete. The results show the proposed model can be applied to estimate the rheological parameters of SCC and FRSCC.(3) The early age restrained shrinkage property and the hardened strength and toughness of FRSCC are studied. The influences of high alkali-resistant glass fiber, modified polypropylene fiber, hybrid fiber and steel fiber on the energy absorption and the residual strength of SCC beams are analyzed using DBV 1998 and Rilem TC 162-TDF, respectively. Predictive equations are suggested for evaluation of the compressive strength and flexural strength of SFRSCC. A test and analysis procedure to evaluate the shear strength and toughness is suggested. The results show that hybrid fiber can significantly resist the early age shrinkage and cracking of SCC, the suggested method can comprehensively evaluate the shear toughness of SFRSCC, steel fiber can obviously improve the flexural toughness and shear toughness of SCC.(4) The influences of steel fiber on the crack pattern, load capacity, deflection, bending reinforcement strain and stirrup strain, as well as concrete strain in shear span of reinforced SCC beams are studied. The main parameters varied are the dosage of steel fiber, the ratio of stirrup, the ratio of bending reinforcement and the shear span ratio. The results show that steel fiber can improve the pattern of cracks; the failure mode of beams may change from shear to moment when the dosage of steel fiber is increased beyond a certain value; steel fiber can enhance the shear capacity or flexural capacity of reinforced SCC beams, and reduce the deflection of beams, and the strain of bending reinforcement, stirrup and concrete, the effect is much distinct for the fiber dosage of 60kg/m3; when steel fiber acts compositely with stirrup, the amount of stirrup may be reduced, the space of stirrup may be increased, the beams can still achieve the ductile flexural failure at the same time.(5) The contributions of steel fiber to shear mechanisms of reinforced SCC beams are analyzed. The results show steel fiber can improve the beam action and the arch action; steel fiber can introduce the truss action into the beam without stirrups. The beam action, arch action and truss action of reinforced SCC beams mixed with steel fiber are expressed with compression strength, effective fiber reinforced factor, ratio of bending reinforcement, equivalent ratio of steel fiber, shear span ratio, relative shear span ratio, and so on. Shear strength predictive equations are suggested. The results of 81 tests of reinforcement-steel fiber reinforced concrete beams and 66 tests of reinforcement-steel fiber reinforced SCC beams are used to determine the coefficients in models. The comparisons between calculated values and the experimental values are shown to validate the proposed theoretical treatment.