CFD-DEM study on the effect of coarse aggregate characteristics on pipe blockage in concrete pumping

Abstract

Concrete pumping technology is widely applied in the construction industry, especially in high-rise buildings and large-span bridges. However, during the actual pumping, concrete may bleed or get segregated, leading to the blockage of a pipe. In order to improve the pumping efficiency and reduce the blockage risk, the flow of fresh concrete with a single-size coarse aggregate(CA) in pipe was simulated, and the effects of size and shape, and volume fraction of CA on the pipe blockage were studied using a Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) coupling method. The flow velocity, pressure distribution and flow state during the concrete pumping process were also analyzed for in-depth understanding of the flow behavior of concrete in the pumping pipe. It was proposed to use the peak pressure on the pumping pipe to characterize the risk of pipe blockage. The cause of pipe blockage formation was analyzed by tracking the movement law, mass and velocity distribution of CA. The obtained results show that local accumulation of CA at the peak pressure position can increase its concentration and decrease the average velocity, causing the peak pressure to rise and increasing the risk of pipe blockage. The risk of pipe blockage increases gradually with increasing size of CA. The most prone blockage takes place at the bend and shifts downward with increasing size of CA. The shape of CA has a lesser impact on the location of the blockage. However, as the shape changes from spherical to ellipsoidal to flaky, the peak pressure gradually increases, thus raising the risk of blockage. With increasing volume fraction of CA, the peak pressure also increases. In order to reduce the risk of pipe blockage, it is recommended that the size of CA should be less than 20 mm, the volume fraction should be no more than 30 %, and the shape should be spherical or ellipsoidal as far as possible.