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Among the water leakage issues in hydraulic tunnels, the issue of water leakage through expansion joints accounts for nearly 90%, making it the primary defect of hydraulic tunnels and posing serious safety hazards to hydraulic structures. To address the issue of water leakage through hydraulic expansion joints, this study investigated a polyurethane polymer grouting sealing material. Traditional sealing and leaking stoppage materials used for hydraulic expansion joints had drawbacks, such as high viscosity, excessive rigidity resulting in the failure to adapt to the deformation of expansion joints, and poor adhesion to concrete. The mechanical properties and impermeability of grouting materials prepared by blending polyurethane with epoxy resin were analyzed through orthogonal and single-factor tests. The excellent sealing and leaking stoppage effects of polyurethane polymer were demonstrated and the optimal mix ratio of the polymer grouting material was determined. Results show that, (1) the gel formed by the reaction of polyurethane and epoxy resin has good mechanical properties. (2) The compressive strength of the grouting material continuously increases with the increase in the dosage of the curing agent and reaches the maximum of 0.98 MPa. The tensile strength of the grouting material initially increases then decreases, and the maximum value is 0.7 MPa. The elongation at break is negatively correlated with the dosage of the curing agent, and the minimum value is 54%. (3) Magnesium oxide can improve the mechanical properties and setting time of the grouting material. The setting time of the grouting material initially increases then decreases with the increase in the dosage of magnesium oxide. Moreover, the compressive strength increases with the increase in the dosage of magnesium oxide, and the swelling rate upon contact with water decreases with the increase in the dosage of magnesium oxide. The comprehensive property is optimal when the dosage of magnesium oxide is 1%. (4) With the increase in the dosage of magnesium oxide, the water pressure at which the grouting material permeates the specimen increases then decreases, and the maximum water permeation pressure is 0.5 MPa. This study provides a good reference and basis for assessing the impermeability of polyurethane polymer grouting materials. [ABSTRACT FROM AUTHOR]

The breakdown process of high-voltage pulse discharge under water involves rapid changes in the plasma channel, which are influenced by various factors, such as time, electric field, and thermal field. Accurately measuring the plasma channel is challenging due to technological limitations. This study proposed the theory of equivalence and equivalent numerical simulation for underwater pulsed discharge to understand the breakdown process and the role of the plasma channel in high-voltage pulse discharge under water. It established the equivalence theory and numerical simulation of the discharge breakdown process by considering the delay characteristics of discharge breakdown and the plasma channel model. The plasma channel was described intuitively and quantitatively, providing a concise and effective analysis of the complex breakdown process. Results indicate that (1) the breakdown channel undergoes an initial plasma channel stage accompanied by heating effects, which then transforms into an arc channel, leading to breakdown and detonation. (2) The equivalent resistance of the plasma channel is approximately 10 Ω, and the equivalent radius of the initial channel is around 0.1 μm. Breakdown is difficult to achieve when the electrode spacing is 0.5 cm and the charging voltage Um is below 5.5 kV, with an estimated minimum charging voltage of approximately 6 kV required for breakdown. (3) Equivalence theory enables effective quantification of the equivalent radius and equivalent resistance in the breakdown process, providing a representative measure of breakdown process stability. It proves to be an effective method for monitoring the operation of discharge equipment in practical engineering. The study provides a reliable reference for assessing the breakdown process of underwater high-voltage pulse discharge and monitoring the performance of pulse discharge equipment. [ABSTRACT FROM AUTHOR]

Plastering mortar plays a protective role for building surface. Its mechanical properties are influenced by different factors. To improve the mechanical properties and solve the problems of mortar cracking and falling, this study proposed a method of studying the change in mechanical properties in accordance with the mesh number of quartz sand. The optimal mesh number of quartz sand was selected by measuring the water-cement ratio and consistency of fresh mortar, the compressive and flexural strength, and the water absorption rate of specimen. On the basis of the mesh number, an orthogonal test was designed using silica fume, calcium sulphoaluminate expansion agent, and polycarboxylate superplasticizer. The performance changes caused by the mesh number of quartz sand and the dosage of additives were analyzed, and plastering mortar with good mechanical properties was determined. Results demonstrate that the key to modification is to strengthen hydration reaction and compactness because cement mortar is porous and brittle. The mechanical properties of plastering mortar decrease with the increase in quartz sand mesh, and the effect is the best when 60-80 mesh quartz sand is used. When the additives are used for modification, the best effect can be obtained when mixing 3% silica fume, 5% calcium sulphoaluminate expansion agent, and 0.5% polycarboxylate superplasticizer. In this case, the compressive strength of the plastering mortar increases by about 22.8% and the water absorption decreases by about 2.4% compared with that before modification. The conclusions obtained in this study can provide an important reference for the modified application of plastering mortar. [ABSTRACT FROM AUTHOR]

Underwater high-voltage (HV) pulse discharge mainly involves the process of HV discharge, breaking down water and releasing huge amounts of electrical energy, which is then rapidly converted into plasma. The plasma expands and creates shock waves and bubble pulsation effects. These effects are the main ways in which electrical energy transfers into mechanical energy. A breakdown process analysis model and an experimental method are proposed with a view to revealing the energy conversion characteristics during underwater pulse discharge and to understand the basic physical process. A plasma channel model was established in combination with the existing fundamentals of electricity and theoretical analysis. In addition, the discharge process was analyzed, along with shock wave and bubble pulsation action characteristics, on the basis of an under-water pulse discharge experiment. Meanwhile, theoretical analysis revealed the basic physical process involved in the electrical energy conversion effect. The results demonstrate the following: (1) The "vaporization-ionization" breakdown model divides the breakdown process into three stages (i.e., heating effect, breakdown detonation and mechanical energy effect stages); (2) the heating effect stage is a phase prior to breakdown, which possesses significant heating characteristics and generates initial plasma; (3) a large electric current (104A) during the breakdown process heats the plasma channel to a high-temperature, where it becomes dense; this condition is followed by an instant decrease in channel resistance; the breakdown current peak depends on the residual voltage at the moment of breakdown; (4) during the breakdown detonation stage, discharge breakdown occurs, along with electric arc detonation. After the heating gasification process, when the electrical field intensity is sufficient, the high-temperature HV plasma rapidly expands outward, resulting in a rapid conversion from electrical energy to mechanical energy. Thus, shock waves are formed, followed by bubble pulsation. The proposed method provides a good prospect for the application of underwater HV pulse discharge technology in the field of engineering. [ABSTRACT FROM AUTHOR]

Strong shockwaves can be formed by pulse discharge in water, and are applicable in fields such as control blasting, oil production, and national defence construction. Wave front-time is an important parameter in shockwave theory and effect. In order to reveal the relationship between the wave front-time and electrical energy and hydrostatic pressure, this study proposed a wave front-time analysis model. The relations between these conditions and shockwave front-time were derived and combined with theoretical information. The shockwave front-time was obtained at several sites under different conditions of hydrostatic pressure, breakdown energy, and propagation distance. Results indicate that shockwave front-time decreases with increasing breakdown energy, when electrical energies are in the range of 1500- 3500 J. Wave front-time increases with increasing hydrostatic pressure, when hydrostatic pressures are in the 0-4 MPa range. Wave front-time increases with increasing propagation distance within 4 m. The breakdown energy and hydrostatic pressure have significant effects on the increase of the front-time as the propagation distance increases. The findings provide references for experiments on pulse discharge in water and evaluation of shockwave performance. [ABSTRACT FROM AUTHOR]