# One-Dimensional Modeling of the Pressure Loss in Concrete Pumping and Experimental Verification
## 1 Introduction  
With the rapid progress of urbanization, the demand for concrete pumping technology is increasing, while the modern concrete pumping technology has significant advantages [1]: wide application range, high pumping flexibility, and reduction in the pouring time. The modern concrete pumping technology has gradually replaced the traditional and become an important technical means in construction. Therefore, the study of pressure loss during pumping has become more and more important and has been a major concern in this field [2]. The concrete can be transported to the designated pouring location mainly by rely on pumping pressure provided by a pump truck [3, 4]. But the process of pumping in the pipe is complicated, and excessive fluctuation of pumping pressure is extremely unfavorable, which will cause a series of problems such as pipeline rupture, and even cause pumping failure. Therefore, the pumping pressure provided by the pump truck is important in the concrete pumping process [5]. The pressure loss of concrete during pumping is an important reference standard for the regulation of pumping pressure. There are many factors affecting the pressure loss, including pipe geometry, pumping flow, lubricating layer, and aggregate particle size [6]. Related scholars have launched a series of research into the rheological characteristics of concrete aggregate particles in the pumping process [7], such as rheological behavior analysis [8], pumping model construction [9], and pressure loss impact analysis [10]. In the pumping process, the concrete in the pumping pipe moves forward in the pump pipe under the action of pressure. The aggregates and mortar generate a nonuniform shearfield under the combined effect of the pumping pressure and friction on the pipe wall. The aggregate particles move from high shear force area to low shear force area, and the mortar is squeezed to the pipe wall through the aggregate gaps, causing the concrete in the pumping pipe to be divided into a lubrication layer and a plunger layer [10; 11]. Some scholars used ultrasonic detection to measure the thickness of the lubrication layer at different flow rates, discovering that the flow behavior of the lubrication layer is similar to that of mortar [12]. Therefore, the rheological properties of the lubricating layer can be characterized by measuring the rheological parameters of mortar. Some scholars also used different experimental tools to study the flow characteristics of the lubrication layer, and found that the roughness of the pipe wall also significantly affected the flow of concrete in the pipe [13]. According to the flow characteristics of the lubricating layer, the content of aggregate particles in the lubricating layer is much less than that in the plunger layer. Therefore, the lubricating layer thickness can be obtained by observing the flow difference between the lubricating layer and the plunger layer [14]. With the deepening of the understanding of the lubrication layer, scholars proposed a variety of methods to measure the thickness of the lubricating layer, such as ultrasonic wave (UVP) and particle image velocimetry (PIV) [15]. Their study results found that the thickness of the lubricating layer was between 1 and 5 mm. According to the rheological characteristics in the concrete pumping process, [PERSON] et al. [16] measured the thickness of the lubrication layer using an ultrasonic detection method under different concrete grades and aggregate sizes. The results indicate that the pipeline flow of pumping concrete was significantly affected by the coarse aggregate particles, but the thickness of the lubrication layer does not change much. [PERSON] et al. [17] used the ASTM C109 flowmeter experimental method to study the effects of the concrete sand-cement ratio, water-cement ratio, and aggregate sizes on the flowability of mortar, and established a prediction model for mortar flowability. [PERSON] et al.