Concrete structure construction with a high strength grade in cold regions is a significant problem that has elicited considerable research attention. In this work, we firstly prepared steel-fiber-reinforced high-strength concrete (HSC) at −20 °C for winter concrete construction in a cold region. Specifically, the combination of graphene nanoplatelet (GNP) incorporation and electric thermal (ET) curing could effectively improve the performance when preparing high-strength concrete (GNP-HSC) at −20 °C. The optimal amount of steel fiber added in this work was determined numerically and experimentally to be 2.5 vol%. The temperature development regularity of the ET-cured sample was also recorded during the whole curing process. Mechanical property results indicated that the combination of GNP incorporation and ET curing could effectively stimulate the strength formation of HSC samples to 91.2 MPa at early age, which is remarkable for concrete construction at −20 °C. Moreover, microstructural analyses (including XRD, TG and SEM analyses) were further conducted to verify the advantages of GNP incorporation and ET curing on the hydration products, hydration degree and microstructure of HSC samples. This work provides new insights into the application of GNP as a nanoscale material to improve the performance of HSC structures at extremely low temperatures.

A gas and coal dust explosion is potential hazard in majority coal mines. A coal mine mobile refuge chamber is a new class of device for miners those who are unable to escape after an accident which can provide basic survival conditions. In this paper, in order to study the propagation law of an underground methane/air mixture explosive wave, and check the failure mode of a coal mine mobile refuge chamber, a full-sized underground tunnel model and a refuge chamber model have been established in ANSYS/LS-DYNA (LSTC, R7.0.0, Livermore, CA, USA, 2014). The simulation results show that the reflected wave pressure on the front surface of the refuge chamber was about twice as high than the incident wave. The pressure on various locations of the chamber was also analyzed. When the peak pressure of the explosive shockwave reached 0.64 MPa, the maximum displacement and stress occur at the center of the front door and the joint of stiffeners and the front plate, respectively. Most parts of the coal mine mobile refuge chamber were in a plastic failure state and the refuge chamber could be defined as damaged. The front door, the front plate, the connecting flange, and the stiffeners on each side were the primary key components. In the end, suggestions were proposed for the refuge chamber.

A new syntactic foam material was prepared by screening three different average particle sizes of cenospheres (150, 200, and 300 µm) from industrial waste fly ash. Axial impact testing on syntactic foam filler and foam-filled tubes was conducted using a drop hammer test machine. The effects of parameters, such as the size of cenospheres and the impact velocity, on the mechanism of deformation, mechanical characteristics, and capacity for energy absorption of the specimen were investigated. On this basis, the differences in compressive properties exhibited by the syntactic foam-filled tubes under the two loading conditions were investigated. The results indicate that with the decrease in the average diameter of cenospheres, the initial peak crushing load and mean crushing load of foam-filled tubes increase, while the compression efficiency decreases. The specific energy absorption (SEA) of the syntactic foam-filled tube can reach 25 J/g. With the increase of impact velocity, the SEA of the specimen increases slightly. It was demonstrated that the syntactic foam-filled tube exhibits a higher effective energy absorption ratio under impact loading compared to quasi-static loading.