Study of hydrated phases present in calcined paper sludge (metakaolinite)/saturated CaO dissolution system cured at 40 °C and 28 days of reaction

The present research is a part of an experimental study about obtaining recycled metakaolinite from a Spanish paper sludge waste as complementary cementing material. The mineral phases formation from paper sludge calcined at different temperatures (700, 750 and 800 °C) and two times of stay in the furnace (2 and 5 h) mixed with saturated lime dissolution are obtained mineral phases: C-S-H gel, stratlingite, tobermorite, hydrotalcite. The C-S-H gels generated in the first stages lose crystallinity and filled the existing holes between stratlingite and hydrotalcite. The different mineral evolves according to their stability fields toward crystalline aggregates more compact where the gels fill hollow.