General relativity: literature request on mixture theory

Hi everyone,

Thankful to anyone who can share literature references (that you deem
important) about the theory of mixtures, e.g. fluid mixtures, in general
relativity.

Examples:
- Kodama, Sasaki, https://doi.org/10.1143/PTPS.78.1
- Giovannini, https://doi.org/10.1016/j.physletb.2005.07.013

What I'm specifically interested about is the relationship between the
energy-momentum tensor of a mixture and those of the constituents. The
works above simply take the sum of the constituent energy-momentum
tensors, which is not really what's done in the Newtonian theory of
mixtures, and they don't focus on the relativistic theory of mixtures in
itself.

Probably a bit niche, but I thank you for any material you may have.
Luca