Study On Uniaxial Tensile Mechanical Properties Of Aligned Steel Fiber Reinforced Cementitious Composites

Adding steel fiber into concrete can give play to its strengthening and toughening effect and overcome the shortcomings of low tensile strength,high brittleness and easy-cracking significantly.The distribution direction of steel fiber in the matrix has a great impact on the effect of strengthening and toughening,accordingly,it influences tensile mechanical properties of steel fiber reinforced cementitious composites.Steel fibers are arranged according to a certain rule in aligned steel fiber reinforced cementitious composites(ASFRC),the most effective state of strengthening and toughening is that the fiber orientation is same to the orientation of the principal tensile stress,and the tensile properties of the material are improved obviously.At present,study on the tensile properties of ASFRC is rarely reported.For this purpose,the tensile properties of ASFRC were studied quantitatively by carrying out uniaxial tensile test in this paper.The main research work and achievements are as follows:(1)Design and prepare ASFRC and SFRC specimens with different fiber content,fiber type and matrix strength.The ASFRC specimens were prepared by exerting an external uniform magnetic field to achieve controlling the orientation of steel fibers in freshly mixed cement mortar and the steel fibers were in the same orientation as the tensile stress.(2)The uniaxial tensile stress-strain curves of ASFRC and SFRC under different factors were obtained by carrying out uniaxial tension test with the modified bonding steel plates method in this paper.Uniaxial tensile mechanical properties of ASFRC and SFRC were compared,and the effect of fiber content,fiber type and matrix strength on the uniaxial tensile properties was analyzed quantitatively.Results show that,the uniaxial tensile strength and toughness of ASFRC are greater than those of SFRC,and the increase of uniaxial tensile toughness of ASFRC is more obvious.With increase of the fiber content and the matrix strength,the uniaxial tensile properties of ASFRC and SFRC improve gradually,and those of the ASFRC improve more significantly than that of the SFRC.The uniaxial tensile properties of heterotypic(hooked and wave shape)steel fiber reinforced cement mortar are higher than those of cylindrical steel fiber,and fiber alignment increases the superiority of heterotypic steel fiber more obviously.(3)The strain field of specimens was measured and calculated by the digital image correlation method,and the damage and fracture evolution law of specimens under uniaxial tensile load was studied.Results show that,the tensile damage and fracture of steel fiber reinforced cement mortar specimens has single cracking and multiple cracking,when water cement ratio reaches 0.32 and fiber content reaches 2%,ASFRC specimens appear multiple cracking obviously.(4)Based on the uniaxial tensile model of fiber reinforced cementitious composites,the bridging stress of aligned steel fiber in cementitious composites was analyzed,and then the tension-softening curves of aligned steel fiber reinforced cementitious composites was studied.The rationality and applicability of the model was verified by the comparison between the test curve and the model prediction curve.