Determination of Lubrication Layer Thickness and Its Effect on Concrete Pumping Pressure

The flow of six kinds of fresh concrete under different flow rates and lubrication layer thickness (T_LL) values in the horizontal pipe was numerically simulated. The influence of the T_LL on the pressure per unit length (P_L) was analyzed. It was determined that the formation of the lubrication layer (LL) significantly reduces the P_L in concrete pumping. As the T_LL increased, the P_L decreased. However, the degree of reduction in the P_L gradually decreased as the T_LL increased. Relating the simulated P_L with the experimental P_L, the size of the T_LL was obtained, which was between 1 and 3 mm. The minimum and maximum were 1.23 and 2.58 mm, respectively, and the average value was 1.97 mm. The strength (S24, S50), the size of the aggregate (A10, A20, A25), and the flow rate of pumping all affected the T_LL. The type of fresh concrete and the flow rate of pumping significantly affected the P_L, which impacted the T_LL. However, the T_LL also impacted the P_L. Finally, this made the T_LL change within a certain range. When P_L > 14,000 Pa/m, 2 mm < T_LL< 3 mm; on the other hand, 1 mm < T_LL< 2 mm. Therefore, we can use CFD to simulate the flow of all types of concrete in the actual pumping pipeline with a T_LL of 2 mm to obtain their pumping pressure and guide the actual construction.