  The dynamics of ideally polarizable spherical particles in concentrated
suspensions under the effects of nonlinear electrokinetic phenomena is analysed
using large-scale numerical simulations. Particles are assumed to carry no net
charge and considered to undergo the combination of dielectrophoresis and
induced-charge electrophoresis termed dipolophoresis. Chaotic motion and
resulting hydrodynamic diffusion are known to be driven by the induced-charge
electrophoresis, which dominates the dielectrophoresis. Up to a volume fraction
$\phi \approx 35\%$, the particle dynamics seems to be hindered by the increase
in the magnitude of excluded volume interactions with concentration. However, a
non-trivial suspension behaviour is observed in concentrated regimes, where the
hydrodynamic diffusivity starts to increase with a volume fraction at $\phi
\approx 35\%$ before reaching a local maximum and then drastically decreases as
approaching random close packing. Similar non-trivial behaviours are observed
in the particle velocity and number-density fluctuations around volume
fractions that the non-trivial behaviour of the hydrodynamic diffusion is
observed. We explain these non-trivial behaviours as a consequence of particle
contacts, which are related to the dominant mechanism of particle pairings. The
particle contacts are classified into attractive and repulsive classes by the
nature of contacts, and in particular, the strong repulsive contact becomes
predominant at $\phi > 20\%$. Moreover, this transition is visible in the pair
distribution functions, which also reveal the change in the suspension
microstructure in concentrated regimes. It appears that strong and massive
repulsive contacts along the direction perpendicular to an electric field
promote the non-trivial suspension behaviours observed in concentrated regimes.
