| Along with the development of construction industrialization in China,the building mode is transform fromed cast-in-situ to precast structure system.The production process and performance of traditional vibrating compacting concrete(VCC)can not meet the requirement of the construction of industrial structure adjustment in some key components and parts.Thus,high performance concrete with selfcompacting performance and good tensile properties is demanded urgently.As a kind of high performance concrete,self-compacting steel fiber reinforced concrete(self-compacting SFRC)owns the advantages of no-vibrating job during casting process of self-compacting concrete(SCC),and excellent mechanical properties under tension of traditional steel fiber reinforced concrete(SFRC).The reasonable system of mix proportion design method and preparation technology bottleneck restricts the development of its industrial application.Based on this,a complete and reasonable mix design method of self-compacting SFRC combined with the statistics anlysis and tests is presented.Then,the workability,mechanical properties and shape effect of pouring quality for self-compacting SFRC were studied.The results of this paper would provide theory support for the performance evaluation and industrial production of self-compacting SFRC.The detailed research work and the main achievements are listed as follows(1)Pull-out test was adopted to study the bond properties of steel fiber and self-compacting matrix.The influence of matrix strength,fiber type,embedment length,embedment angle as single factor,spacing and mixed angles of fiber as compounded factors and curing age as environmental factor on the bond properties were systematically studied.Test results showed that,the enhancement mechanism and degree of fiber in matrix were affected by the type,embedment angle and spacing of fiber.Hooked-end steel fiber has excellent cracking resistance in the serviceability limit state;while crimped steel fiber has excellent bonded energy dissipation in the bearing capacity limit state.The bond properties of fiber in matrix is closely related to the flexural strength of the matrix at the same curing age,and the nature of influence of curing age on the fiber bond properties is the growth of matrix strength with curing age.Taking into account of the bond properties,fiber tensile strength and matrix strength,hooked steel fibers of HF-2,HF-4,HF-5 and crimped steel fiber of CF-2 match the matrix of self-compacting SFRC with w/b=0.31.The mortar matrix of machine-made sand is superior to the matrix of standard sand in terms of flexural strength and fiber-matrix bond properties.Based on the test results,formulas of the ultimate bond strength,residual bond strength,peak displacement of fibers are proposed.Formulas of the ultimate bond strength and peak displacement of inclined hooked-end steel fiber and inclined crimped steel fiber are proposed.(2)The method of statistical analysis was adopted to systematically study the characteristic composition,the relationship of water-binder ratio and compressive strength,and the relationship of compressive strength and tensile strength,for self-compacting SFRC.Series packing tests of steel fibers and aggregates solid skeleton were carried out to build the relationship of the fiber factor and the void fraction of solid skeleton,and determine the relationship of fiber factor and the optimal of sand ratios.A direct mix design method was proposed for self-compacting SFRC.16 groups self-compacting SFRC mixes with different types and volume fractions of steel fibers were made,using the direct mix design method and the increasing water consumption design method,respectively.Their working performance and basic mechanical properties were tested to verify the rationality of the design method.Test results showed that,the direct mix design method for self-compacting SFRC has favorable applicability,and its tolerance to steel fibers is significantly better than the method of increasing water consumption,comprehensive considering the workability,density and mechanical properties.In addition,the applicability of workability test methods and indicators of SCC in self-compacting SFRC were demonstrated,and several modified advises were proposed.The variable-spacing J-ring with spacing as 2 times of the fiber length is suitable for testing the passing ability of self-compacting SFRC.The dynamic segregation test recommended in the specification of SCC combined with modified limited value is equivalent to the static segregation test,and it is suitable for evaluating the segregation resistance of the self-compacting SFRC.(3)Standard specimens of self-compacting SFRC with different water-binder ratios,types and volume fractions of steel fibers were produced using the direct mix design method,and their mechanical performance under tensile,bending,compressive load were systematically studied.The test results showed that,the addition of steel fiber in self-compacting SFRC reduces the compressive strength at the curing age less than 90 days,and is favorable to the compressive strength at the curing age more than 90 days.The enhancement of steel fibers on the tensile properties of self-compacting SFRC is both influenced by the fiber factor and the matrix strength.The enhancement degrees are different for the same steel fiber in concrete with different water-binder ratios and curing ages.The axial and splitting tensile strengths,the flexural strengths after micro-cracking,and the corresponding toughness of self-compacting SFRC are positively correlated with the fiber factor.Based on tests and statistical analysis,forecast models of long-term compressive strength and flexural load-deflection curves of self-compacting SFRC were proposed.Both of them have good fitness with test results.(4)One-dimensional and two-dimensional bending members of self-compacting SFRC were designed and produced.The fiber distribution in three-dimensions,compressive strength,and flexural performance of the components in different position were quantitatively studied to determine the shape effects of casting quality for the self-compacting SFRC.Test results showed that,self-compacting SFRC in the beam and slab realized self-consolidating,and its mechanical properties in different position of components met the design requirements.Steel fibers in beams were mostly parallel to the template and the flow direction.Steel fibers in slabs were tend to perpendicular to the flow direction with the increasing flow distance,the tangentially distributed steel fibers increased with the flow distance,while the radial distributed steel fibers decreases with the increasing flow distance.The addition of fiber improved the homogeneity of compressive mechanical properties of beam and slab,and the degree of improvement increases with the volume fraction of steel fiber.Based on the test results,forecast models of fiber factors of the tangentially and the radial distributed steel fibers with flow distance in the self-compacting SFRC slab are proposed.The models of flexural strength and the first residual flexural strength with the effective fiber factor of standard specimens are also suitable for the flexural properties of different positions for beams and slabs.The flexural properties of self-compacting SFRC along the flow direction of beam and perpendicular to the flow direction in the slab were similar with those of standard specimens in the serviceability limit state;and were superior to those of standard specimens in the bearing capacity limit state.Considering the characteristics of fiber distribution,the pouring port is suitable to be put in the location of self-compacting SFRC beams with small moment,and the position of the pouring port and the flow direction of self-compacting SFRC slab need to consider the directionality of the bending performance. |
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