# Influence of Mix Proportions on Rheological Properties, Air Content of Wet Shotcrete--A Case Study
## 1 Introduction  
We shotcrete is a kind of self-compacting concrete technology, in which fresh wet shotcrete is pumped into the pipeline, and then sprayed onto the receiving surface under the function of compressed air [1, 2, 3, 4, 5, 6, 7]. Wet shotcrete is widely used in the construction industry, such as slope maintenance and underground space engineering. Especially in the complex coal mine roadway, compared with dry mix shotcrete, wet shotcrete has the advantages of low dust concentration and less rebound, which reduces the mining hazards such as pneumoconiosis. In the application of wet shotcrete, the pumping process is the initial important process to ensure successful conveying without blockage. Pumpability refers to the pumping capacity of fresh wet shotcrete, i.e., fresh concrete should have proper fluidity and stability when transported through pipes under pressure. At present, a lot of research has been devoted to the study of measurement techniques that evaluate the pumpability of fresh concrete. Especially in the field of self-compacting concrete, rheological and tribological properties of fresh concrete have been recognized as two key factors that affect the pumping performance of fresh concrete [7, 8]. Fresh concrete ingredients affect the rheological properties. Literature [8] reviewed the effects of internal components of fresh concrete and external admixtures on rheological properties, including cement, fly ash, slag, silica fume, limestone powder, coarse and fine aggregates, and admixtures (water-reducing agent, viscosity agent, and air-entraining agent). [PERSON] et al. [9, 10] studied the effect of cement fineness and chemical composition on the rheological properties of concrete, and pointed out that the larger the surface area of the cement, the higher the content of tricalcium aluminate and alkali, the worse the workingperformance of fresh concrete. [PERSON] et al. [11] found that the increase of cement paste content reduced the plastic viscosity and yield stress of fresh concrete; especially for mixtures with large differences in aggregate shapes and poor particle gradation, and increasing the cement paste content has a positive effect on concrete pumping. [PERSON] et al. [12] studied the effect of different coarse aggregate sizes on the rheological properties of fresh concrete, as the aggregate size increases, the plastic viscosity increased. [PERSON] et al. [13] studied the rheological and mechanical property of fresh cemented materials incorporating silica fume, and assessed the applicability of using silica fume as a partial cement replacement. [PERSON] et al. [14] obtained through experiments: the rheological parameters (plastic viscosity and shear stress) of fresh concrete mixed with fly ash are lower than those of concrete without fly ash. In addition, with the increase of fly ash content increases, the plastic viscosity and shear stress gradually increase. The addition of silica fume increases the plastic viscosity and yield stress of the fresh concrete, and enhances the flocculation inside the concrete [15,16]. [PERSON] et al. [17,18] used the IBB rheometer to measure the influence of mineral admixtures on the performance of wet shotcrete, and concluded that the pumpability and shotcretability of fresh concrete can be improved by adding silica fume and fly ash at the same time. In the early stage, slump and pressure bleeding tests were combined to predict the pumpability of fresh concrete [19,20]. However, the good slump cannot guarantee good pumping performance in field application. [PERSON] [21] studied the pumping pressure according to the rheological and tribological characteristics of fresh wet shotcrete moving in small diameter hose. Based on the full-scale pumping test, [PERSON] et al. [22] analyzed the influence of fresh concrete rheology, tribology, pipe radius, and flow rate on pumping pressure.