Pipe flow of pumping wet shotcrete based on lubrication layer

Abstract

Wet shotcrete can reduce dust and improve supporting strength, however, safe and efficient pipage is a key technical part of wet shotcrete process. The paper studied the pipe flow law of wet shotcrete based on lubrication layer by build the experimental pumping circuit of wet shotcrete that can carry out a number of full-scale pumping tests. The experimental results show there was a linear relationship between pressure loss and flow rate. Combined with the Buckingham rheological equation, the computing equations of the yield shear stress and plastic viscosity were deduced through linear regression. A simple analytical method allowing for a rough estimation of the pumping pressure was proposed and used when considering the lubrication layer of wet shotcrete in pipes. In addition, two kinds of particulate distributive models were established along the time axial to analyze the formation of lubrication layer which is related with particles migration. By computational fluid dynamics simulation, the lubrication layer thickness of different mix proportions was estimated. A new method for measuring the thickness of lubrication layer was proposed to verify it by binarization processing. Finally, according to the comparative analysis of experiments, simulation and computed value, it can be seen that the lubrication layer plays a key role in the process of wet shotcrete flow and with the increase of lubrication layer thickness pipe pressure declines gradually.

Pet Fiber Reinforced Wet-Mix Shotcrete with Walnut Shell as Replaced Aggregate

“…It can be seen in Figure 9a that slump declined slightly with increasing walnut shell replacement while the pressure drop also decreased from 0% to 75% (except point W3), which was expected because aggregates mixed with walnut shells are likely to cluster closely due to the thin walnut shells instead of some approximately spherical particles. Because thin shell with convex and concave portions is easily generating the framework of aggregates, also called aggregate interlock characteristic due to angular and rough edges of crushed shell [65], to resist the flow, then reduce the slump in Figure 10 (SW), and appropriate framework of aggregates can avoid separation at the same time improving flow of concrete with low pressure drop per meter in Figure 10 (FW) under the primeval condition of lubrication layer near inner pipe has been formed [66]. As shown in Figure 10, h 2 > h 1 means adding crushed walnut shell or fibers decreased the slump.…”

Research on Pressure Drop in the Accelerate Zone of Horizontal Conveying of Concrete Spraying

“…Concrete spraying technology is extensively applied in underground projects (e.g., railway and tunnel) and tunnel construction in coal mines in China [1][2][3]. Because of its associated conveniences, wind-driven concrete spraying technology has been widely applied.…”

“…ese authors believed that understanding the velocity of particles in the steady-state region was vital for reliably designing the entire conveying process [6]. Brown showed that the flow of particles and fluid were the primary causes of pressure drop during pneumatic transmission and constructed a linear equation to express pressure drop during the velocity stabilization zone [7], and it can be described as ΔP ss � ΔP c + ΔP f , (1) where ΔP ss is the constant pressure drop, ΔP c is the pressure drop caused by concrete, and ΔP f is the pressure drop caused by compressed air.…”

Numerical and Experimental Research on Convergence Angle of Wet Sprayer Nozzle

“…Currently, when it comes to shotcrete, a large amount of researches pay their attention on the pumpability and shootability of fresh concrete [11][12][13] or the mechanism of sprayed concrete [14,15]. Lianjun Chen et al [16] summarized the technologies for reducing cement dust during shotcrete from new process, new apparatus to new materials, as well as the pathological damage of cement dust.…”