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In this study, the pozzolanic activity of low-grade natural sepiolite was enhanced by calcination for further utilizing as a supplementary cementitious material. Sampled sepiolite was calcinated at 400, 600, 700, 800, 900, and 1000 °C, and the calcinated sepiolite were characterized and respectively blending with pastes for examining their rheological and hydration behaviors. It was found the pozzolanic activity of sepiolite was maybe mainly determined by the active Si phase content, and 800-SP showed the highest pozzolanic activity. The rheological behaviors of fresh paste blended with sepiolite calcinated at different temperatures shows obviously different. In early curing stage, the addition of sepiolite obviously accelerated the cement hydration. But in later curing stage, comparing with U-SP, the calcinated sepiolite showed hindering effect on cement hydration, and this effect was obviously regular with the increasing calcinated temperature. Additionally, by comparing with all pastes blended with sepiolite, which blended with 800-SP showed the highest compressive strength values.

This study investigated the effect of mechanical activated waste magnetite tailing (MWMT) as a pozzolanic material substitute for cement on the properties of cement-based products. The rheological behaviour (yield stress and plastic viscosity) of fresh mortar containing MWMT was investigated and approximated using the Bingham plastic model, and the mechanical properties (flexural and compressive strength) of mortar containing MWMT were studied. Results of the Frattini and strength activity index tests showed that MWMT was a low-activity pozzolanic material, consistent with the Ca(OH)2 content and mineral composition analysis. MWMT has a beneficial effect on the rheological behaviour of fresh mortar because the low specific surface area of MWMT overcomes the adverse effect of its rough and angular particles. The mechanical properties of mortar weaken as the MWMT content increases. However, the pozzolanic activity of MWMT enhances the rate at which the strength values increase as the MWMT content increases from 28 to 90 d.

This study aims to clarify the role of bio-deposition in improving the properties of recycled concrete aggregate (RCA) to enhance its reusability. Two bio-deposition treatments were investigated (immersion and spraying). The physical properties, pore structure, and micro-morphology of the RCA were investigated both before and after treatment, and the compressive and flexural strength of mortars prepared with treated and untreated RCA were also analysed. In addition, the micro-mechanical properties of the hydration products of bio-calcium carbonate were determined. The results showed that the water absorption, porosity, and crushing values of treated RCAs were lower than those of untreated RCAs. The compressive and flexural strength of mortars made with untreated RCAs were lower than those of mortars with treated RCAs. The results show that bio-calcium carbonate and its hydration products have a positive effect on the interfacial transition zone of the mortars, thereby reducing crack widths and improving the micro-mechanical properties.

In a wide variety of high-power pulsed devices, vacuum surface flashover plays an important role in the system performance. The capability of grooved dielectric to hold off high-voltage pulse is investigated experimentally by using a long pulse electron beam accelerator, which is capable of generating a quasi-square wave with pulse duration of 180 ns and output voltage of 100-400 kV. It is found that both concavely and convexly grooved dielectrics increase promisingly the flashover time lags. With groove width of 2 mm, depth of 2 mm, period of 4 mm, electrode gap spacing of 100 mm, and diode voltage of 265 kV, the flashover time lag for polycarbonate is found to increase from 93.0 ns to 182.6 ns. While for polytetrafluoroethylene, its flashover time lag is increased from 45.0 ns to 81.2 ns, and for high-density polyethylene, its flashover time lag is increased from 72.4 ns to 100.5 ns. Electrical and optical diagnoses on temporal evolution of flashover channel confirm that surface flashover in vacuum is characterized by three-phase development, namely the secondary electron emission avalanche (SEEA), impact ionization in desorbed gas, and the final plasma driven breakdown. Based on this analyzing, it is found that the increase of flashover time lags is mainly due to the suppressing of SEEA process by using grooved structures.

As the development of the pulsed power technology, high voltage pulse transformer (HVPT) is usually used instead of Marx generator as a charging device for the pulse forming line (PFL) of intense electron-beam accelerator (IEBA), and which make the IEBA compact. However, during the operation of the IEBA, the HVPT may be destroyed for the failure of electrical insulation and the over-voltage. So in this paper, the output voltage characteristics of IEBA, characteristics of the voltage at the output terminal of HVPT at four kinds of load conditions are analyzed, including load matching, load short, load open, and surface flashover in the vacuum chamber. It is found that load short, load open, and surface flashover in vacuum chamber will affect the voltage at the output terminal of HVPT, and an oscillation wave could be formed, which affect the electrical insulation of HVPT and decrease the lifetime of HVPT. Meanwhile, the waveform of the load voltage is also modified, especially at the conditions of load open and surface flashover in vacuum chamber. When the load is open, the amplitude of the output main pulse of IEBA is twice the charging voltage of BPFL. However, the amplitude of the output pulse of IEBA is modified by the voltage at the output terminal of HVPT, and the resistance of main switch channel has a great effect on the amplitude of the load voltage. When surface flashover occurs in the vacuum chamber, the pulse duration of the output voltage will be decreased. So, during the operation of IEBA, load short, load open and surface flashover in vacuum chamber should be avoided.

An experimental investigation of surface flashover characteristics in vacuum pressure of 1.3×10-2 Pa (10-4 Torr) was introduced by using a quasi-square pulse generated by an intense electron beam accelerator (IEBA) with duration of 180 ns and voltage of 180-300 kV, and the gap spacing length was varied from 100 to 210 mm. Polymethyl methacrylate (PMMA), High density Polyethylene plastics (HDPE) and Polyamide (PA) were chosen as the investigating insulator dielectrics in this paper. The effects of insulator material, applied voltage and gap spacing length on the surface flashover characteristics are presented. Meanwhile, the delay time, flashover current and impedance of the flashover channel are also discussed.

The Blumlein pulse forming line (BPFL) consisting of an inner coaxial pulse forming line (PFL) and an outer coaxial PFL is widely used in the field of pulsed power, especially for intense electron-beam accelerators (IEBA). The output voltage waveform determines the quality and characteristics of the output beam current of the IEBA. Comparing with the conventional BPFL, an IEBA based on a strip spiral type BPFL can increase the duration of the output voltage in the same geometrical volume. However, for the spiral type BPFL, the voltage waveform on a matched load may be distorted, which influences the electron-beam quality. In this paper, the output waveform of an IEBA based on strip spiral BPFL is analyzed. It is found that there is fluctuation on the flattop of the main pulse, and the flatness is increased with the increment of the output voltage. According to the time integrated pictures of the cathode holder during the operation of the IEBA, the electron emission of the cathode holder is one of the reasons to cause the variance of the flatness. Furthermore, the distribution of the current density of spiral middle cylinder of the BPFL is calculated by using electromagnetic simulation software, and it is obtained that the current density is not uniform, and which leads to the nonuniformity of the impedance of BPFL. Meanwhile, when the nonuniformity of the BPFL is taken into account, the operation of the whole accelerator is simulated using a circuit-simulation code called PSpice. It is obtained that the nonuniformity of the BPFL influences the flatness of the output voltage waveform. In order to get an ideal square pulse voltage waveform and to improve the electron beam quality of such an accelerator, the uniformity of the spiral middle cylinder should be improved and the electron emission of the cathode holder should be avoided. The theoretical analysis and simulated output voltage waveform shows reasonable agreement with that of the experimental results.

An intense electron-beam accelerator, which consists of a primary storage capacitor system, a magnetic core Tesla transformer, Blumlein pulse forming line of water dielectric, and a field-emission diode, are constructed and described. The experimental results show that the output voltage of transformer is more than 740 kV, the rise time is about 5 µs, the diode voltage is about 596 kV, electron beam current is about 60 kA, the duration is about 100 ns, and the power is 36 GW when charging voltage is 40 kV. It was suitable to drive magnetically insulated transmission line oscillator. And it can be also used in materials surface modification. This accelerator is very compact and works stably and reliably.

Experiments on the surface flashover under 180-ns quasi-square waves with voltage of several hundred kilovolts are reported. In the experiments, employing a 280-kV 180-ns full-width at half-maximum (FWHM) voltage on the load, no flashover occurred. When the voltage was up to 350 kV, even 420 kV, surface flashover along the insulator occurred, and it started at the top part of the applied voltage pulse, so the FWHM of the output voltage of pulse generator was reduced to 150 ns, even 120 ns. Also, the experiment results show that surface flashover channel could be recovered quickly if a heteropolarity voltage was applied on the flashover channel. Finally, the characteristics of the surface flashover are present, including the flashover time, flashover current, and resistance.

A radial-current aqueous resistive solution load was applied to characterize a laser triggered transformer-type accelerator. The current direction in the dummy load is radial and is different from the traditional load in the axial. Therefore, this type of dummy load has smaller inductance and fast response characteristic. The load was designed to accommodate both the resistance requirement of accelerator and to allow optical access for the laser. Theoretical and numerical calculations of the load's inductance and capacitance are given. The equivalent circuit of the dummy load is calculated in theory and analyzed with a PSPICE code. The simulation results agree well with the theoretical analysis. At last, experiments of the dummy load applied to the high power spiral pulse forming line were performed; a quasisquare pulse voltage is obtained at the dummy load.