Gas suction during concrete pumping induces a transition from steady-state to unsteady flow, significantly compromising boom stability. This study investigates unsteady flow characteristics in different pipelines of a pump truck. First, a geometric fluid domain model of C40 concrete pipelines was established, and grid independence was verified. A three-phase flow mathematical model was subsequently developed, comprising gas-liquid control equations, solid particle motion equations, and a laminar flow model. The gas and liquid phases were simulated using Fluent, while solid particle interactions were modeled with Rocky DEM. Flow characteristics in straight pipes, elbows, and combined pipelines were analyzed via coupled CFD-DEM simulations. Finally, a comparative analysis evaluated the effects of pipeline structures and pumping parameters on concrete flow. Results indicate that increasing gas volume fraction reduces pressure in straight pipes and elbows while decreasing excitation forces in straight pipes. Excitation forces in elbows remain unaffected. Increasing the straight pipe attitude angle elevates pressure but reduces excitation forces. Larger elbow curvature radii increase pressure with negligible impact on excitation forces.