Study On The Mechanical Properties And Empirical Models For PVA Fiber Reinforced Cement Based Composites

Polyvinyl alcohol fiber reinforced cementitious composites（PVA Reinforced Engineered Cementitious Composites,referred to as PVA-ECC）,compared with normal concrete,PVA-ECC has higher ultimate tensile strain capacity.It is a kind of fiber-reinforced cement based composites with high toughness and excellent energy absorption performance It can be used to solve the safety and durability problems caused by low tensile and shear strength and brittleness of traditional building cement-based materials concrete.At present,there is no unified index for the calibration of PVA-ECC material properties.In order to solve this problem,the existing PVA-ECC uniaxial compression test data were investigated,sorted out and analyzed,and the recommended size of PVA-ECC uniaxial compression test standard block（side length of 70.7mm cube block）was given.On this basis,the axial compression test of different sizes of cube blocks including standard block under the same mix proportion was carried out,and according to the test results.Through the analysis of the data,the mechanical indexes of PVA-ECC compression test with various non-standard test blocks were obtained:elastic modulus E,peak stress f_cu,peak strainε_cu,inflection point stress in the descending section of the curve,and the corresponding strain values(f_0.85,ε_0.85,f_0.2,ε_0.2)were converted from the standard cube test block.Based on this,the existing PVA-ECC uniaxial compression test data are further standardized and analyzed,and a uniaxial compressive stress-strain empirical model of PVA-ECC is proposed,which is suitable for the cube with side length of 70.7mm and compressive strength of f_cu in the range of 30～60MPa.The existing PVA-ECC tensile modal empirical models are all proposed based on specific test data,which is lack of universality.Based on the standardized analysis of the compressive strength f_cu of PVA-ECC in the range of 30～60MPa proposed in the previous study,the existing uniaxial tensile mechanical indexes(initial crack stress f_tc,initial crack strainε_tc)within the compressive strength f_cu range,Peak stress f_tp,peak strainε_tp).The existing test data has no mechanical indexes(ultimate tensile stress f_tu,ultimate tensile strainε_tu)of the tensile stress-strain drop section.In this paper,the transformation relationship between the peak tensile stress f_tp and the peak compressive stress f_cu and the mechanical index of the tensile stress-strain decline section are obtained by uniaxial tensile test.The characteristics of the curve are analyzed.The stress-strain curve is simplified into linear elastic stage,strain hardening stage and strain softening stage,and the uniaxial tensile mechanical index(initial crack stress f_tc,initial crack strainε_tc)is analyzed The empirical model is suitable for PVA-ECC with compressive strength of 30～60MPa and ultimate tensile strain of more than 1.0%.In order to verify the applicability of the PVA-ECC uniaxial compression/tension empirical model proposed in this paper,uniaxial compression/tension test and finite element simulation were carried out.Firstly,by analyzing the existing test data,the mix proportion range of PVA-ECC with compressive strength of 30～60MPa and ultimate tensile strain of more than 1.0%（PVA fiber content of 1.0%～2.0%,W/B of 0.32～0.40;S/B of 0.25～0.4）is obtained.In this range,six groups of mix proportions were randomly selected to carry out PVA-ECC uniaxial compression and uniaxial tensile tests,and the compressive/tensile stress-strain curves were obtained.Compared with the empirical model,the applicability of the empirical model proposed in this paper was verified.Secondly,based on the empirical model proposed in this chapter,the four point bending Fe（finite element）model of R/ECC beam is established by using concrete damaged plastic model（CDPM）in ABAQUS software,and the finite element simulation of four point bending test of R/ECC beam is carried out.The reliability of the empirical model and FE modeling is evaluated by comparing the finite element simulation results with the experimental results,and a reliable material empirical model is proposed for the finite element simulation.