Study on Mechanical and Rheological Properties of Solid Waste-Based ECC

As one of the main raw materials of engineered cementitious composite (ECC), fly ash exerts the “ball effect” and “pozzolanic effect” in concrete, which improves the working performance of concrete and enhances the strength of the concrete matrix. Polyvinyl alcohol (PVA) fiber has been widely used in the preparation of ECC, while ground fly ash can be used to enhance the performance of ECC as a kind of high-activity admixture. In this paper, the compressive strength, flexural strength and flexural toughness of ECC prepared from different types of fly ash (raw fly ash, sorted fly ash and ground fly ash) are compared, and the rheological properties of the ECC are analyzed by studying the two parameters of yield stress and plastic viscosity. The results show that the smaller the particle size of fly ash is, the more sufficient it reacts with Ca(OH)2 produced by cement hydration, and the more it can improve the compressive strength and flexural strength of the matrix. In addition, the smaller the particle size of fly ash, the higher the yield stress and plastic viscosity of ECC; therefore, the distribution of PVA fiber in ECC is more uniform, thereby improving the flexural toughness and ductility of ECC

Mathematical Modeling and Finite Element Analysis of Residual Stress (RS) Field after Multipass Ultrasonic Surface Rolling

In order to achieve the change rule of the induced residual stress (RS) field after multipass ultrasonic surface rolling (USR), a mathematical model of the induced residual stress (RS) field after multipass ultrasonic surface rolling is first established. Then, the coupling mechanisms of the RS field after dual-pass USR and multipass USR are analyzed, respectively. Subsequently, a finite element (FE) model is established, and the influence of the interval between two adjacent rolling paths LS is investigated. Finally, both the mathematical model and the FE model are experimentally verified. The results show that both the mathematical model and the FE model can predict the RS field after multipass USR. Two adjacent RS fields will couple with each other in their overlapping regions. For a relatively small interval LS, the RS field after multipass USR can be fully coupled, so as to form a uniform compressive RS layer. In this study, when LS = 0.05 mm, the values of the surface compressive RS, the maximum compressive RS, the depth of the maximum compressive RS, and the depth of the compressive RS layer reach 426.71 MPa, 676.54 MPa, 0.05 mm, and 0.54 mm, respectively

Influence of Basalt Fiber on Mechanical Properties and Microstructure of Rubber Concrete

The utilization of waste rubber in concrete will reduce pollution and improve the efficiency of resource utilization. The effects of rubber particles and basalt fibers on the compressive strength and splitting tensile strength of concrete were investigated. In addition, the influence of basalt fibers on the mechanical properties and micropore structure of rubber concrete (RC) were analyzed using scanning electron microscopy (SEM) and X-ray computed tomography (CT). The distribution of rubber particles in concrete was also studied. The results indicate that the effects of basalts fibers on the mechanical properties of rubber concrete were significant. The rubber particles were evenly distributed in the concrete. Compared with normal concrete (NC), rubber concrete with 10% rubber particles had lower compressive strength and splitting tensile strength. Compared with rubber concrete, basalt fiber rubber concrete (BFRC) with 2% basalt fibers had no obvious effect on the compressive strength, while significantly improving the splitting tensile strength, refining the pores of rubber concrete, and reducing the porosity of the matrix. The effects of basalt fiber on the properties and pore distribution of RC should be considered in future applications

Numerical Simulation Study on Lining Damage of Shield Tunnel under Train Load

Under the long-term dynamic load influence of trains, shield tunnel structures are damaged. With the increase in operating number, cumulative damage gradually increases. When cumulative damage increases to a certain value, the tunnel lining produces cracks and loses tensile strength, which leads to tunnel deformation, damage, etc. In serious cases, the tunnel ceases operation, causing traffic accidents and casualties. Based on the finite element software ABAQUS, this paper analyses the change rule of tunnel lining damage under long-term dynamic train load and explores the influence of tunnel buried depth on the change rule of tunnel lining damage. The excitation force function is used to generate a series of dynamic and static loads superimposed by sine functions to simulate the dynamic loads of trains. Load is applied above the tunnel by writing DLOAD subprogram. The results show that the damage of tunnel lining mainly occurs at the arch foot and the structural damage in other places can be neglected. Under the same loading condition, the greater the tunnel lining damage is. Under the same loading conditions, the tunnel lining damage increases with the increase in buried depth. According to the test results, the mathematical expressions of cumulative damage value versus loading times at the location prone to fatigue damage. It provides theoretical reference for safety evaluation and protection of tunnel structure under long-term train load

Study on the Effect of Pile Foundation Reinforcement of Embankment on Slope of Soft Soil

In order to study the working mechanisms of pile foundations applied to embankment engineering on weak slope foundations, a finite element model of embankment on weak slope foundation reinforced by a pile foundation is established. The influence of the position and the length of the pile foundation on the stability of the embankment is studied, and the mechanical response of the pile foundations are also studied. The results show that the different positions of the pile foundation have great influence on the safety factor and deformation of the embankment. The safety factor varies greatly from one reinforcement location to another. The maximum vertical deformation of the embankment reinforced by the 3 m pile is 27 times that of the 7 m. With different pile lengths, the horizontal displacement of the pile foundation can be significantly reduced by approximately 83.3% at most. The research results may provide more scientific help for the design of embankments on soft soil slopes reinforced by pile foundations

Research on an Off-Chip Microvalve for Pneumatic Control in Microfluidic Chips

A compact, rapid, and portable off-chip pneumatic control valve is significant for the miniaturization and integration of external pneumatic systems for microfluidic chips. In this work, an off-chip microvalve with a high-speed electromagnetic switch actuator and a polydimethylsiloxane (PDMS) material valve body has been designed to be easily encapsulated, simulated using MATLAB/Simulink software, and tested in a micromixer. Multi-physical coupling mathematical models are developed based on the elastic deformation force of the valve membrane, the driving force of the valve core, and the fluid force in the microchannel. Two single microvalves are used to form a three-way microvalve, which can control the air pressure in a pneumatic microchannel on the microfluidic chip. The relationship between the flow–duty cycle, the flow–pressure difference of the single electromagnetic microvalve, and the load pressure of the three-way microvalve is simulated and analyzed. Sample mixing performance controlled by the proposed off-chip three-way microvalve was tested to evaluate the pneumatic control capability, and the results show that the undertaking can fully satisfy the needs of a pneumatic microfluidic chip for most applications