Search

Copyright of Journal of Northeastern University (Natural Science) is the property of Dongbei Daxue Xuebao and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To study the damage mechanism and ultrasonic properties of thermal-damaged engineered cementitious composites（ECC）, ultrasonic monitoring and compression tests were performed on ECC specimens exposed to high temperatures（20, 105, 250, 400, 600 and 800 ℃）. Results indicate that the changes in waveform amplitude, main frequency amplitude, energy, and compressive strength of thermal-damaged ECC are the same; the energy ratio in the 40～50 kHz band is the largest, which is about 15% of the total energy in the 0～300 kHz band. The wave velocities of ECC specimens heated from 20 to 250 ℃ show no significant changes, and decrease when heated above 400 ℃. The reason can be relate to free water vaporizes, hydration products decompose, and aggregate physical properties change at high temperature, which leads to the increasing of pore vapor pressure and damaging to the aggregate interfaces, thus the internal cracks in the ECC are generated and expanded. Scanning electron microscopy test results indicate that PVA fiber softens, melts, and vaporizes with increasing temperature. Voids and pores are generated in the ECC matrix and connect with cracks forming into networks, which are beneficial to the releasing of the pore vapor pressure and reducing the thermal damage of ECC. Results also show that the ultrasonic characteristics can effectively reflect the thermal damage evolution process in the ECC. [ABSTRACT FROM AUTHOR]

Diesel pool fire experiments on different diesel water ratios were conducted under various ventilation conditions. The flame temperature， the radiation heat flux and the mass loss rate were measured， and the fire splash phenomenon was observed in order to analyze the combustion characteristics and the diesel pool fire spread rules. Results show that the diesel pool fire with 1∶1 diesel water ratio is always in the boilover status and the splash continuously occurs in the fire developed stage under natural ventilation conditions; both the temperature and the radiant heat flux reach the maximum value in the continuous splash. With the decreasing of the diesel water ratio， the flame temperature and the radiant heat flux are reduced and the frequency and the intensity of splashing are reduced either. If the air velocity is increased to 1.0m/s， the combustion is intensified significantly by the ventilation speed and the duration time of the developed stage of fire is increased. When the air velocity is further increased to 1.5m/s， the pool fire is hard to reach the developed stage or only last for a short time， which illustrates the negative impact of ventilation velocity increasing. [ABSTRACT FROM AUTHOR]