Search

Compared with natural aggregate, the content of hardening cement in recycled aggregate is larger, which leads that the water absorption of recycled aggregate is larger and its performance such as robustness is poorer. And the engineering field pays much attention to the problem of the recycled fine aggregate which can be used in the durability requirements of recycled concrete or not. Using the method of fast freezing and thawing the influence of quality and replacement ratio of recycled coarse aggregate on the frost resistance of recycled concrete was researched basing on ordinary concrete frost resistance performance. The results showed that, in terms of the frost resistance capacity, the order is in: ordinary concrete>high-quality recycled coarse aggregate concrete>normal quality recycled coarse aggregate concrete. After 250 freeze-thaw cycles, the mass loss rate of general quality recycled coarse aggregate concrete is 5%, relative dynamic elastic modulus is 60% when replace rate was 100%.

This paper studied the properties improvement of recycled coarse aggregate by the physical strengthening technology (particle-shaping method). Through the analysis for obtained properties which consist of density, crush index, bulk density and water absorption. etc of recycled coarse aggregates in different strengthening technologies, the categories of recycled coarse aggregate could be assessed and determined. The results showed that ordinary recycled coarse aggregates that was handled twice by using particle shaping equipment can achieve the standard of class Iaggregates and its water absorption ratio at 24h was 1.2%, the apparent density reached 2575kg/m3, crush index value was 9%, the void ratio was 45%, all property parameters were close to those of natural coarse aggregate.

To improve the utilization of tailings, the basic properties of tailings and theirs influence on self-leveling mortar performance are experimental studied in this paper. The results show that the tailings can completely replace the natural sand to produce self-leveling mortar since the advantages of better fluidity, less water consumption, smaller time loss and high strength. The strength decreases with the addition of mineral admixtures, but it can still satisfy the requirements of standard JC/T 985-2005 "Cementitious self-leveling floor mortar ". Moreover, this method reduces pollution and production costs effectively.

Very fast transient overvoltage (VFTO) can be generated during the operation of disconnect switch (DS). Especially in ultra high voltage (UHV) gas insulated substation (GIS), VFTO is a threat to the safety of the power system equipment. It is very important to measure VFTO waveforms accurately. VFTO waveforms are comprised of high frequency voltage superimposed on the power frequency voltage in source side of DS and high frequency voltage superimposed on step-wise voltage in load side. How to trigger oscilloscope to acquire data is a big problem in measuring process. According to the features of VFTO waveforms, new triggering device consisting of a high pass filter is designed. The output of measurement sensor is used as the input of the high pass filter, and the output of the high pass filter is used to trigger oscilloscope. When the DS is not operated, there are no signals output from the high pass filter and the oscilloscope is waiting for trigger. After the operation of DS, the high frequency signals will pass the filter to trigger oscilloscope to acquire data. The device can guarantee the oscilloscope to complete a data acquisition properly.

Traditional Hough transform (HT) methods based on parameters decomposition do not give good result for concentric circle detection, for the reasons of its large amount of calculations, high demand of storage space and low efficiency in real-time application. To compensate the weaknesses, this paper employs a kind of improved Hough transform method which aims at reducing the parameters space. In this paper, the detection method is further improved through adding an edge detection procedure based on global threshold. The experimental results show that this algorithm meets the on-line detection of high accuracy requirement, with superior real-time performance and stronger anti-interference ability.