Interface Modulation Of Ultra-High Performance Concrete And Its Application On Machine Tool Foundation

Ultra-high performance concrete(UHPC)belongs to a new type of cementitious materials,which is characterized by excellent compressive strength and superior durability.Considering its outstanding mechanical performance,UHPC exhibits great potential in the fields of long-span bridges,thin-walled structures and protective engineering.However,the single crack failure mode is still observed in UHPC under static tension load,which indicates the fracture toughness of UHPC is limited.The reason is that the interfacial bond state between steel fibers and matrix is not ideal.The interfacial sliding of UHPC often occurs under dynamic load,and its damping capacity should be improved.In these situations,the brittle failure of UHPC may happen and poses a threat to structure safety.It can be seen that the interfacial performance between steel fiber and matrix is critical to the UHPC properties.The interface modulation belongs to an important tool for improving the tensile performance,toughness and damping properties of UHPC.Currently,the research on the chemical bonding at the interface is not in-depth in UHPC.In terms of physical bonding,the overall interface status is influenced by steel fiber distribution,it is worth exploring the design of UHPC mechanical performance from the perspective of steel fiber distribution.Based on the above analysis,this paper focuses on the modulation approaches of interfacial performance.The effect of chemically modified steel fibers on the static and dynamic mechanical properties of UHPC was studied.The UHPC with outstanding toughness was developed through hybridizing polymer fibers.The strength prediction model of UHPC was established based on the spatial distribution characteristics of steel fibers.The influence of interfacial modulation approaches on the damping characteristics of UHPC was analyzed.The feasibility of the application of UHPC with interfacial modulation in the field of vibration control for machine tool was explored.The findings can provide the methodological and theoretical foundations to promote the engineering application of UHPC.The main work is as follows:An approach for enhancing the interfacial performance of UHPC based on chemically coated steel fibers is proposed.The mechanical strength,static and impact toughness of UHPC containing chemically modified steel fibers were investigated.The results show that the chemically modified steel fibers can effectively improve the compressive strength,flexural strength,static and impact toughness of UHPC.The use of chemically modified steel fibers can also delay first cracking and increase peak load displacement of UHPC.The UHPC with chemically modified steel fibers exhibits resistance to the dynamic loads and shows a desirable failure mode.The macro and micro mechanical properties of the interface in UHPC were determined.Chemical modification can accelerate the hydration reaction of cement clinker,promote the volume fraction of the C-S-H phase,and reduce the width of ITZ,leading to the improvement in the interfacial shear strength and pullout energy.Chemical films act as a“bonded bridge”that adheres the UHPC matrix to steel fiber surface firmly.As a result,the interfacial performance and toughness of UHPC enhance significantly.Considering the characteristics of metal and nonmetal fibers,the fibers hybridization is utilized to improve the interfacial performance of UHPC.The mechanical strength,fracture toughness and failure mode of UHPC with different content of polyvinyl alcohol(PVA)fibers were studied.The results show that the combination of steel fibers and PVA fibers can enhance flexural strength,tensile strength,fracture toughness and tensile ductility.The failure mode of UHPC with low fiber content shifts from single crack mode to multiple crack mode.The incorporation of PVA fibers can facilitate the load transfer at the interface due to the large interfacial area.Microscale observations show that the steel fibers and PVA fibers can work synergistically to impede the propagation and expansion of cracks,thus the improvement in the failure mode of UHPC is observed under tension load.The effect of steel fiber aspect ratio and matrix rheological parameters on the mechanical properties,tensile failure mode and crack propagation characteristics of UHPC was investigated.The mechanical strength,tensile performance and fracture toughness of UHPC first increase and then decrease with the rise of steel fiber aspect ratio.The nanocellulose fiber(NCF)was utilized to modify the rheological properties of UHPC.The addition of NCF improves the mechanical strength,tensile performance and fracture toughness of UHPC.The crack propagation characteristics of UHPC were determined by digital image correlation(DIC)technology.Under the conditions of appropriate aspect ratio and NCF concentration,the first cracking of UHPC is delayed,and the strain rate along the crack decreases.As a result,the UHPC exhibits a multiple cracks failure mode under tension load.A strength prediction model of UHPC is established based on the steel fibers distribution.The orientation and local distribution coefficients were calculated based on the X-ray computed tomography(CT)scanning results.The intensification factor of steel fibers was introduced to correct the existing fiber-matrix model.The relational models among steel fiber aspect ratio/rheological parameter,steel fiber orientation factor and mechanical strength of UHPC were established.The validity of the prediction model is verified by the collected data from existing literature.Based on this model,the design and regulation of mechanical strength for UHPC can be achieved from the perspective of steel fiber distribution.The influence of different interfacial modulation approaches on the damping characteristics of UHPC under static and dynamic excitations was evaluated.The chemically coated steel fibers increase the interface friction and chemical bonding,and the incorporation of PVA fibers changes the interfacial area and interfacial bond state.The different aspect ratios of steel fiber and the addition of NCF improve the overall interface status.As a result,the damping ratio,loss factor and energy dissipation ratio of UHPC enhance significantly.The feasibility of the application of UHPC with interfacial modulation in the field of vibration control for machine tool was analyzed.The vibration control of UHPC machine tool bed was estimated by numerical simulation.The multi-criteria analysis demonstrates that UHPC with chemical modification of steel fibers exhibits the best overall performance from the perspectives of damping performance,mechanical strength,processability and economic benefit.Numerical simulation results reveal that the vibration reduction effect of UHPC with interfacial modulation meets the requirements of ultra-precision machining.