The Mechanics Performance Test Of Multi-scale Polypropylene Fiber Concrete And The Study Of Tension And Compression Damage Constitutive Model

Multi-scale polypropylene fiber concrete (MPFC) refers to the new type ofcomposite building materials that the same quality with different geometry of two ormore than two kinds of polypropylene fiber mix in concrete. Polypropylene fine fibercan prevent the early plastic cracking of concrete, but in the hardened process ofconcrete, toughness and crack resistance is improved very small. Steel fiber can reducethe crack number, shorten the crack length and improving toughness for hardening ofthe concrete, but steel fiber is easy to rust and the price is higher. Polypropylene crudefiber is a new kind of enhanced toughening materials, has a good performance atcorrosion resistant and the price is lower, so steel fiber can be substituted by thepolypropylene crude fiber in the engineering of the relatively bad environment. In viewof the above background, researches carried out in this paper would use a combinationmethods including testing research, theoretical analysis and numerical simulation, themain research contents and conclusions can be drawn as follows:①The crack resistance tests of MPFC show that the polypropylene fine fiber isbetter than crude fiber in the plastic state concrete for crack resistance effect, however,the polypropylene crude fiber is better than fine fiber in the hardening stage; Thecracking resistance of multi-scale polypropylene fiber has both positive and negativeeffects in the plastic state concrete and it is the almost same for anti-cracking effect tocrude fiber in the hardening phase.②The uniaxial tension tests of MPFC show that the peak tensile loads of MPFCwere increased; The decline period of the stress-strain curve of uniaxial tensile load forMPFC appears strain hardening characteristics for low stress, and the tensile toughnessof MPFC is better than that of only mixing polypropylene fiber concrete.③The compressive tests of MPFC show that the compressive peak load of MPFCis increased; The MPFC compressive stress-strain curve of the decline is flat than theplain concrete. The stress decrease slowly with increasing strain after peak for MPFC,stress-strain curve area is larger, the compressive resilience performance is improved.④Four-point bending tests of MPFC show that the bending strength of MPFCincrease slightly; The decline period of the load-deflection curve of bending load forMPFC appears strain hardening characteristics in low load and low load curve area islarger, the flexural toughness of MPFC is greater than that of the polypropylene finefiber concrete and is better than that of the polypropylene crude fiber concrete. The relationships between tensile and flexural properties are established by the comparisonof basic mechanical indexes under tensile and bending load. MPFC flexural-tensilestrength ratio is between2.15to2.80, flexural toughness index is greater than thetensile toughness index, but the same change in the overall trend of the data.Thecomparison results show that the four-point bending test method is a simple andpractical method to estimate the special mechanical performance of MPFC substitutingfor the uniaxial tensile test method.⑤According to the results of tensile and compressive test, established the MPFCdamage constitutive model of tensile, compression characteristic, getting the curveshape parameter of polypropylene fiber concrete damage factor. It provides a theoreticalbasis for widely application in engineering with MPFC.⑥On the basis of the finite difference theory，finite difference expression oftension and compression damage constitutive models for multiple-scales polypropylenefiber concrete were derived; Combined with the good redevelopment platform ofFLAC3Dsoftware and using VC++program to achieve the secondary development ofdamage model for multi-scale polypropylene fiber concrete, the dynamic linkcalculation procedure of the models were obtained. And through the simulation andtest numerical example to verify the correctness and rationality of the secondarydevelopment program model.⑦The secondary development calculation program for the damage model ofmulti-scale polypropylene fiber concrete was applied to numerical analysis ofmulti-scale polypropylene fiber tunnel lining. The results show that the multi-scalepolypropylene fibers improved the deformation resistance and the rigidity of theconcrete.