Tensile Properties Of New Hybrid Fiber Reinforced Cementitious Composites (NHyFRCC)

Fiber plays an important role in overcoming brittleness and improving tensile properties of cement-based materials.The cementitious composite has multi-level structure characteristic,a new hybrid fiber system composed of micron scale calcium carbonate whisker?CW?and millimeter scale polyvinyl alcohol?PVA?fiber,steel fiber?SF?can strengthen and toughen cement-based materials and improve their tensile properties at multi-level and multi-scale levels.In this paper,the tensile properties of NHyFRCC,including tensile strength,tensile toughness and tensile stress-strain curve,were systematically studied by direct tensile test and indirect tensile test?bending test and splitting test?.The effects of PVA fiber length and fly ash on the tensile properties of NHyFRCC,direct tensile test method,direct tensile constitutive model and the relationship between fiber dispersion and direct tensile properties were focused.The main results and conclusions of this paper are summarized as follows:?1?Effect of calcium carbonate whisker on tensile properties of steel-PVA hybrid fiber reinforced cementitious composites.The direct tensile strength,bending tensile strength and splitting tensile strength of steel-PVA fiber reinforced cement-based composites are improved by the addition of calcium carbonate whisker.Among them,N3?1.5 vol.%SF+0.4 vol.%12mm PVA+1 vol.%CW?has the best tensile strengths,reaching 6.86 MPa,19.69 MPa and16.93 MPa,respectively.Similarly,whisker improves its toughness through micro-cracking resistance and optimization of interface properties between SF-PVA hybrid fibers and cement-based materials,and its equivalent bending strength,bending toughness,post-bending crack strength(PCS₆₀)and direct tensile toughness are all improved.?2?Influence of PVA fiber length on tensile properties of HyFRCC.With the same fiber ratio,the tensile properties of 12 mm PVA fiber system are better than that of 6 mm PVA fiber system,including tensile strength and tensile toughness.The splitting strength,bending strength and direct tensile strength can be increased by 21.9%,19.8%and 18.7%,respectively.?3?Effect of fly ash on tensile properties of NHyFRCC.Replacing cement with appropriate fly ash by weight can optimize the matrix,improve the bonding between fiber and matrix,and improve the tensile properties of NHyFRCC.When the content of fly ash is 5%,the flexural tensile strength and flexural toughness of N3 increase by 32.7%and 21.0%,respectively,reaching 22.14 MPa and 21.63 N·m,compared with the comparison samples.When the content of fly ash is 15%,its direct tensile strength and tensile toughness reach the maximum values of 7.59 MPa and 64.41 kJ/m³,which are 10.6%and 11.3%higher than the control.?4?The direct tensile constitutive model of NHyFRCC is constructed based on the test results.A three-stage NHyFRCC tensile stress-strain model composed of linear and rational fraction is established by regression analysis.The experimental data are highly correlated with the model,which can provide reference for the application of NHyFRCC material in structural design and simulation?5?The relationship between fiber dispersion and tensile properties.Direct tensile performance parameters?ultimate tensile strength,tensile toughness?of NHyFRCC have a good multivariate quadratic function relationship with fiber characteristic parameters,fiber number,fiber dispersion coefficient and fiber orientation factor.Hence,direct tensile properties of NHyFRCC can be predicted by fiber characteristic parameters and fiber dispersion parameters,which is of great significance to guide material design and performance optimization...