Research on Tensile Softening Constitutive Relation of Macro Polypropylene Fiber Reinforced Concrete
In order to reveal strengthening and toughening mechanisms of the macro polypropylene fiber reinforced concrete,the tensile softening constitutive relation of the macro polypropylene fiber reinforced concrete was investigated.Three fiber lengths,i.e.20 mm,30 mm and 40 mm,and three mass contents,i.e.0.13％,0.17％and 0.21％,were selected.Mechanical and fracture properties of the macro polypro-pylene fiber reinforced concrete,i.e.tensile strength,initial cracking load,and the maximum load,were studied by the splitting tensile test and the three-point bending fracture test,and the tensile softening con-stitutive relation was derived by the improved J-integral method.The results showed that the cohesive stress decreased rapidly with the increase of the crack opening displacement.Compared with the ordinary con-crete,the stress free opening displacement of the macro polypropylene fiber reinforced concrete significantly increased and the fracture process zone length significantly increased,indicating that the brittleness degree significantly reduced.According to the simplified method recommended by Wittmann,a bilinear softening curve for the macro polypropylene fiber reinforced concrete was proposed,in which the cohesive stress at the turning point σs=0.135f,the crack opening displacement at the turning point ws=0.054Gf/ft,and the stress free opening displacement w0=14.417Gf/ft.With the increase of fiber length and mass content,the stress free opening displacement w0 significantly increased,indicating that the brittleness degree signifi-cantly decreased.
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