The objective of this study is to evaluate the modified performance of concrete with mixing of iron ore tailings in order to solve the shortage of natural sand and make full use of industrial waste. Firstly, the raw materials of mixing were analyzed, and the test ratio was determined. Secondly, the workability and mechanical property of concrete specimens with different amounts of iron ore tailings as replacement were tested. Results show that 35% replacement of natural aggregate by iron ore tailings is optimal. Finally, tests of impermeability, frost resistance, and carbonation resistance were further performed for the concrete specimens with optimal amount of iron ore tailings. The compression performance of the specimens after a durability test was determined. The change in the mechanical properties of the specimens was obtained after seepage, freezing-thawing, and carbonation. Findings showed that the performance of the concrete with 35% replacement of iron ore tailings is basically equivalent to that of natural sand concrete. Hence, it can be utilized in engineering applications.

The ageing disintegration, the damage, and failure mechanism of water-saturated soft rock are of significance to hazard prevention for deep mining. In this paper, indoor experiments, including disintegration behaviour tests in water, uniaxial compression failure tests of rock samples with different water contents, and variations in the microstructure of mudstone under saturated water contents, were conducted. The investigation results show that the saturated water content of mudstone is 16.96% and that the rock mass bursts completely after being immersed in water for 72 h. With increasing water content, the uniaxial strength and elastic modulus at the prepeak stage present significant attenuation. However, Poisson’s ratio varies little, which indicates that the swelling of cemented mudstone is not obvious when meeting water. In addition, the failure pattern of mudstone changes from overall splitting failure to block fragmentation failure. Due to ion-exchange adsorption and the wedging action of water molecules, the edge of contact between particles changes from staggered to smooth, which leads to the expansion of pores, the loosening of mudstone structures, and a decrease in mechanical strength. Therefore, the diffusion, migration, and particle expansion of illite and other clay minerals in mudstone are the main factors leading to the structural damage and strength reduction of weakly cemented rock under water-rock interactions.

No abstract

This paper systematically examines the feasibility of using ultrasonic vibration excitation for rock breakage and fragmentation; it focuses on the failure mechanisms of rock mass under the impact of ultrasonic waves, and the development of ultrasonic technology. Laboratory testing using a self-designed system was conducted in this paper to further validate the efficiency and reliability of rock breakage using ultrasonics. The results show that: (i) under the effects of both the high speed impact of ultrasonic vibration excitation and induced rock vibration excitation, a fracture is initiated and propagates rapidly within and outside of the rock. Under ultrasonic vibration excitation for 140 s, the compressive strength decreased by 45.6%; (ii) under the excitation of ultrasonics, the rock specimens failed completely in a short time from inside to outside, and there are distinct fissures in the internal nucleation of the rock. It is suggested that ultrasonic excitation provides a novel and promising option for rock fragmentation and breakage, which optimises the efficiency of underground hard rock engineering.