Research And Toughening Mechanism Of Interface Bonding Property Between Basalt Fiber And Cement Matrix

Strain Hardening Cementitious Composites(SHCC)is tough materials of excellent crack control capabilities.At present,the reinforcing fibers commonly used in SHCC are mainly polyvinyl alcohol and other organic synthetic fibers.The composite materials made of them have poor UV aging resistance and high temperature resistance,and the cost is high,which is difficult to apply in large quantities in practical engineering applications.Basalt fiber is a green inorganic fiber with good mechanical properties,high temperature resistance and UV aging resistance,but it is currently difficult to achieve high toughness properties in reinforcing cementitious composites.In this paper,the basalt fiber is modified reasonably based on the characteristics of basalt fiber,and the mechanical properties of the modified basalt fiber and the interfacial bonding properties of the fiber and the cement matrix are studied.The strain hardening mechanism under axial tensile load and the whole process of multiple cracking were analyzed,and the mechanism of high toughness was explained based on the single fiber pull-out test.The main research contents are as follows:(1)Modified three different specifications of basalt fiber with epoxy resin,and tested its tensile mechanical properties and density.(2)The orthogonal test of four factors and three levels was used to study the influence of the matrix water-binder ratio,fly ash content,sand rate and sand fineness modulus on the interface bonding properties between the modified fiber and the cement matrix.The experiment found that the water-binder ratio has a significant effect on the interface bonding strength,and the amount of fly ash has a significant effect on the single fiber pull-out energy.(3)The effect of modified fiber type,fiber content,length and water-binder ratio in modified fiber reinforced cement-based composites tensile strength was studied by dog bone tensile test.The experiment showed that the addition of twisted 133 tex modified fiber can better achieve the strain hardening and multiple cracking performance of cement-based composites under axial tensile load,and the energy criterion and strength of the ECC design are combined through a single-slit tensile test to explain the mechanism of strain hardening.(4)The multiple cracking process can be analyzed by the digital image correlation method.The analysis results show that the crack width of the modified basalt fiberreinforced cementitious composites under axial tensile stress is less than 50 μm.(5)The single-fiber oblique pull-out test is conducted,and the results showed that the fiber inclination angle is at 15°～30°,and the pull-out force is significantly improved;When the inclination angle is moderate(45°～60°),the extraction force is slightly increased;when the fiber inclination angle is greater than 60°,the main failure model is the breaking and destruction of fibers,and the extraction force is seriously reduced.