Study On Bonding Performance Of The Interface Between Steel Fiber And Magnesium Phosphate Cement Matrix

Magnesium phosphate cement?MPC?is a new type of high performance material that combines the characteristics of ceramics,cements and refractory materials.It has properties of fast hardening,early strength,solidification hardening at low temperatures,high bonding and low shrinkage;However,magnesium phosphate cement-based materials are still brittle materials and their tensile strength is weak.The addition of short steel fibers can toughen and strengthen the cement matrix,and the toughening effect of steel fibers depends to a large extent on the fiber-matrix bond properties.In this paper,the fiber pull-out test was used to study the effect of cement matrix ratio,age,cement type,and the type and spacing of steel fiber on the bond performance.The microscopic characteristics of the interfacial transition zone were analyzed by means of nanoindentation and scanning electron microscopy,and the mechanism of various factors affecting the bonding performance was revealed.The main findings are as follows:?1?The interface bonding properties between steel fiber and cement matrix are closely related to the strength of the matrix.The appropriate cement matrix ratio and silica fume content can not only increase the matrix strength from 26.8 MPa to 40.3MPa,but also increase the interface density and reduce the thickness of the interface weak area.The microstructure of the interface area is improved and the interface adhesion properties are optimized.?2?In the early stage of hydration of MPC,steel fiber can better exert its reinforcing and toughening effect on the magnesium phosphate cement-based material of steel fiber.The 6h interfacial adhesion performance index reached almost half of 7d,and the minimum value of 1d interface hardness reached 90%of 7d.The interfacial bonding properties of specimens at early curing stage maintained well.?3?Compared with three cements with similar compressive strength,when steel fibers are pulled out from the MPC substrate,more cement particles adhere to the surface,and the hardness and elastic modulus of the MPC interface area are the largest.The bonding properties are optimal,and the enhancement and toughening effects on the MPC matrix are the most significant.?4?The interface bonding properties of different types of steel fibers and substrates are quite different.Micro steel fiber diameter is smaller and copper plating is applied on the surface.The strength and Young's modulus of the brass are smaller than that of steel.When the magnesium phosphate cement matrix is pulled out,the surface of the fiber is damaged to a large extent,and more gelatinized particles are adhered.The energy consumed during the pull-out process is more,and the toughening effect on the substrate is optimal.However,if the fiber spacing is too small,the adhesion between the individual fibers and the matrix may be impaired and the reinforcing effect of the steel fiber cement-based material may be reduced.The fiber end hooks greatly enhance the reinforcing and toughening effect of the fiber on the magnesium phosphate cement matrix.The degree of optimization of the interface bonding properties is closely related to the compressive strength of the matrix and the surface properties of the fibers,but the correlation with the cement category is small.The deformation along the length of the fiber increases the mechanical anchoring force,the interface bond strength and the material utilization rate are the highest.?5?The water stability of the interface bonding performance is weak,especially in the initial stage of water immersion.The effect of M/P on the stability of the bond water was significant.The KH₂PO₄ was the most abundant in the M/P sample and the bond water stability was the weakest.When the M/P is 4,the influence of the interface is the smallest,and the retention rate of the matrix strength and the retention rate of the interface bond strength are the highest.