[3] The structure of pure liquid tricalcium aluminate contains mostly AlO4 tetrahedra in an infinite network, with a slightly higher concentration of bridging oxygens than expected from the composition and around 10% unconnected AlO4 monomers and Al2O7 dimers.

Its presence in clinker is solely due to the need to obtain liquid at the peak kiln processing temperature (1400–1450 °C), facilitating the formation of the desired silicate phases.

Sulfate ions in solution lead to the formation of an insoluble layer of ettringite (3CaO • Al2O3 • 3CaSO4 · 32 H2O over the surface of the aluminate crystals, passivating them.

Tricalcium aluminate is associated with three important effects that can reduce the durability of concrete: Because they are even more basic, the alkali-loaded polymorphs are correspondingly more reactive.

The feed and fuel in the kiln system are preferably controlled chemically to keep the sulfate and alkalis in balance.

However, this stoichiometry is only maintained if there is substantial surplus oxygen in the kiln atmosphere: if "reducing conditions" set in, then sulfur is lost as SO2, and reactive aluminates start to form.