A pressure transmitter was installed at a specific position in a concrete conveying line to disclose the pressure drop when compressed air was conveyed during concrete spraying. A statistical analysis of the pressure at different positions was undertaken. Experimental results demonstrated that in the accelerate zone of horizontal conveying of concrete in the line, the pressure drop mainly occurred during the acceleration, collision, and friction processes. The momentum equation was introduced during the experiment, which interpreted the pressure drop caused by the accelerated conveying of concrete. The theoretical equation was corrected based on the results of theoretical experiments by introducing the value of α, and the experimental results were then optimized, thus obtaining an approximate model of pressure drop during the conveying of concrete. In addition, experimental results were compared with a model equation that showed the reliability of the proposed model. Research conclusions are of great significance to regulate the pressure drop in the conveying line of concretes, to design working parameters of concrete spraying devices, and to predict the ultimate distance for the conveying of concrete.

In order to adapt to dry and wet environment in mine roadways and improve the performance of sealing materials under different environmental conditions, this study selected the materials based on their ability to spray and found that the materials with a viscosity of 1500–6000 MPa·s can achieve a balance between performance of spray and wall‐hanging performance. Next, by selecting high‐elastic polyacrylate emulsion and ordinary Portland cement as the film‐forming agent and gel, respectively, mix proportion factors of the nonreactive thin spray‐on liner (TSL) were analyzed by using the Taguchi method. Moreover, fluidity, setting time, sealing properties, compressive strength, bending strength, and bonding strength of those materials were measured. It was disclosed that addition of an appropriate amount of polyacrylate emulsion can enhance the effects of fibers. By observing the morphologies of the materials’ bonding surfaces and comparing the factors influencing bonding strength between both dry and wet walls, it was uncovered that the adhesive property of cement‐based sealing materials was mainly affected by the water‐cement ratio. Eventually, bonding strength and sealing properties were selected as primary optimization indexes, while setting time, bending strength, and compressive strength were selected as secondary optimization indexes. The appropriate proportions of two types of TSLs for dry and wet walls were (W/C = 50%; P/C = 6%; F/C = 1%; T/C = 0.2%) and (W/C = 45%; P/C = 6%; F/C = 1%; T/C = 0.4%), respectively. A prepared TSL can be used for filling rock fractures in mine roadways. In addition, TSL exhibited a great performance for dry and wet walls under different environmental conditions. The present study may provide an insightful guidance and reference for the investigation of TSL sealing materials applied in the mine roadways.

In recent years, with the rapid development of the coal-mining industry, the output of gangue has increased at a faster pace, while its utilization remains relatively low. The accumulation of a large amount of gangue has brought about a large environmental problem. In order to improve the utilization rate of waste gangue, and to solve the secondary environmental problems caused by gangue pollution, this paper conducted research on an economic and environmentally friendly gangue-based self-compacting concrete. This study designed aggregate industrial-analysis experiments to analyze the moisture content of the gangue and limestone, finding that the moisture content of gangue is 39% higher than that of limestone. By orthogonal experimental methods, the study investigated the fluidity, compressive strength, splitting strength and abrasion resistance of self-compacting gangue concrete. It was concluded that the optimal replacement rate of gangue for coarse aggregate is around 30%, the optimal replacement rate of fly ash for cement is around 30%, the optimal addition of polycarboxylate superplasticizer is 0.5% of the mass of cementitious materials, and the optimal rate of shear steel fibers is around 1% of the concrete capacity. In addition, this paper investigated the interfacial transition zone (ITZ) of the aggregate–cement slurry and found that the ITZ of gangue aggregate and cement mortar is more likely to generate AFT crystals, which will contribute more to the improvement of the strength of concrete in the early stage. In addition, a field-effect analysis was carried out in this study, and it found that gangue-based self-compacting concrete, as an environmentally friendly material, can basically meet the design requirements of C30 paving concrete.