The lattice Boltzmann method (LBM) is used to simulate turbulent channel flows in the presence of spherical particles. In these simulations, the particles' surface is fully resolved by relying on the immersed boundary method (IBM). First, a single-phase turbulent flow at a frictional Reynolds number of Re-tau = 180 is simulated and used for validation by comparison with published data. The results show very good agreement with reference benchmarks. Starting from these results, a particle-laden flow is considered by direct numerical simulation (LBM-DNS), resolving all relevant scales. Both single-phase and particle-laden flows are modeled at the same frictional Reynolds number by applying the same driving force and initial flow conditions. Particle-to-fluid density ratios of rho(r) = 1.0 and 1.2 are considered and the particle radius a is adjusted to either 0.06 or 0.1 times the half-channel height H. The solid phase volume fraction is changed between 0.015 and 0.06. Results of the multiphase cases reveal that the presence of finite-size particles decrease the mean streamwise velocity. In the case of rho(r) = 1 and a/H = 0.1, the mean velocity reduces by 3.0 and 7.9% for volume fractions of 1.5 and 6%, respectively. Attenuation of turbulence by addition of particles is observed as well. The higher the volume fraction, the larger the degree of attenuation. Moreover, particles decrease the maximum streamwise velocity fluctuations by weakening the large-scale streamwise vortices. The root-mean-square of the streamwise velocity component increases in the region very close to the wall and in the core regions. The spanwise and normal velocity fluctuations are increased close to the wall but show minor changes far from the wall. Small particles (a/H = 0.06) cause more reduction of mean streamwise velocity at the same volume fraction in comparison with larger ones. At phi = 1.5%, the maximum rms of streamwise velocity fluctuations with small particles is lower than that with large particles. Finally, heavy particles lead to different velocity profiles in the upper and lower parts of the domain. In all cases, an equilibrium position close to the wall is observed, at which local particle concentration shows a maximum. (C) 2017 Elsevier Ltd. All rights reserved.