Liquid-solid flows, in both heterogeneous and saltation regimes, are critical in the transport of suspended solid particles in pipelines prone to particles settling and accumulating on the bottom of the pipe, eventually blocking the flow and risking flow assurance. Numerical simulation of a statistically developed and steady twophase liquid-solid flow in a horizontal pipe is performed by solving Reynolds-Averaged Navier-Stokes (RANS) equations within an Eulerian-Eulerian framework to predict the complex interaction among particles and between particles and their transporting fluid and surrounding walls. Particles are treated as a secondary fluid phase with viscosity determined using the Granular Kinetic Theory (GKT), including its three potential contributions, i.e., frictional, collisional and kinetic interactions. A case study for a horizontal pipe flow with mono-disperse and bi-disperse liquid-particle mixtures, at different flow velocities and particle-bulk concentration, is presented. Particles concentration for statistically steady heterogeneous and saltation regimes without a fixed bed are presented. Governing equations for each phase are solved numerically using ANSYS-Fluent platform which is based on the finite volume method to integrate the equations about each control volume and turning the problem into a system of algebraic equations. A second-order spatial discretization is implemented across the model. Bulk concentrations of solid particles in water were considered in percentage of 10% and 20%. Solid particles of 0.125mm and 0.440mm in diameter were used in the study, while bulk velocities of 1m/s, 2m/s and 3m/s were prescribed.