聚丙烯粗纤维混凝土拉伸软化本构关系研究

Research on Tensile Softening Constitutive Relation of Macro Polypropylene Fiber Reinforced Concrete

为了揭示聚丙烯粗纤维的增强增韧机理,开展了聚丙烯粗纤维混凝土拉伸软化本构关系的研究,选取了三种纤维长度,即20、30、40 mm,和三种纤维质量掺量,即0.13%、0.17%、0.21%,通过劈裂拉伸试验与三点弯曲断裂试验研究聚丙烯粗纤维混凝土的力学及断裂性能,包括抗拉强度、起裂荷载和峰值荷载。采用改进J积分法推导聚丙烯粗纤维混凝土的拉伸软化本构关系。结果表明:随着裂缝张开位移的增加,黏聚应力快速降低;与普通混凝土相比,聚丙烯粗纤维混凝土应力自由张开位移显著增大,混凝土断裂过程区长度显著增加,材料脆性程度显著降低。根据Wittmann推荐的简化方法,提出了聚丙烯粗纤维混凝土双线型软化曲线,曲线中的转折点处的黏聚应力σ_(s)=0.135f_(t),转折点处的裂缝张开位移w_(s)=0.054G_(f)/f_(t),应力自由张开位移w_(0)=14.417G_(f)/f_(t)。随着纤维长度与质量掺量的增加,应力自由张开位移w_(0)显著提高,表明材料脆性程度显著降低。

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 constitutive 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 concrete,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 pointσ_(s)=0.135f_(t),the crack opening displacement at the turning point w_(s)=0.054G_(f)/f_(t),and the stress free opening displacement w_(0)=14.417G_(f)/f_(t).With the increase of fiber length and mass content,the stress free opening displacement w_(0) significantly increased,indicating that the brittleness degree significantly decreased.