We consider a nonlinear interaction of elastic waves in inertial mixtures of solid deformable bodies. Using the equations of the second approximation, we study some peculiarities of generation of the second harmonic and properties of three-wave resonance interaction of quasi-harmonic longitudinal waves. It is shown that when considering low frequencies, we may assume that the acoustic properties of a mixture are similar to the acoustic properties of a concrete while with the growth of frequencies the magnitude of the second harmonic does not exceed the initial amplitude value and thus the acoustic properties of the mixture are similar to the acoustic properties of metals and alloys. For the case of three-wave resonance interaction, we determine the range of frequencies such that space-type beatings may take place.