Rehydration of katoite as a layered double hydroxide: an in situ study

Antonia Alana Lima Pacheco; Thiago Ricardo Santos Nobre; Marcel Hark Maciel; Celso Valentim Santilli; Antonio Carlos Vieira Coelho; Sérgio Cirelli Angulo

doi:10.21809/rilemtechlett.2021.130

Authors

Alana Pacheco Department of Construction Engineering, Escola Politécnica, University of São Paulo https://orcid.org/0000-0002-6470-5849
Thiago Ricardo Santos Nobre Department of Construction Engineering, Escola Politécnica, University of São Paulo https://orcid.org/0000-0001-9439-6648
Marcel Hark Maciel Department of Construction Engineering, Escola Politécnica, University of São Paulo https://orcid.org/0000-0003-3345-2209
Celso Valentim Santilli Institute of Chemistry, São Paulo State University https://orcid.org/0000-0002-8356-8093
Antonio Carlos Vieira Coelho Department of Metallurgical and Materials Engineering, Escola Politécnica, University of São Paulo https://orcid.org/0000-0001-7362-6643
Sérgio Cirelli Angulo Department of Construction Engineering, Escola Politécnica, University of São Paulo https://orcid.org/0000-0001-9700-1621

DOI:

https://doi.org/10.21809/rilemtechlett.2021.130

Keywords:

Alternative cement, Calcium aluminates, Katoite, Layered double hydroxide, Rehydration

Abstract

Calcium aluminate layered double hydroxides (Ca-Al LDHs) constitute a considerable part of cementitious waste fines. Although cementitious waste fines have proven to be recyclable by thermal treatment at moderate temperatures (400–700 °C), understanding how each phase rehydrates and contributes to the binding properties of rehydrated cementitious materials is still necessary. In this study, the de(re)hydration of katoite is investigated through in situ techniques, and its applicability as an alternative cement or supplementary cementitious material (SCM) is discussed. The research employed X-ray diffraction, isothermal calorimetry, in situ wide-angle X-ray scattering (WAXS), and rotational/oscillatory rheometry. Katoite synthesized by a mechanochemical process was dehydrated at 400 °C, producing mainly mayenite. During rehydration, calorimetry presents high heat production in the first minutes. WAXS shows prompt recovery of katoite and increasing formation of monocarboaluminate (Ca-Al LDH) after 30 s of rehydration. The findings confirm the direct association between rapid heat release and phase reformation. Rehydrated pastes present a high yield stress and an increasing storage modulus, indicating rapid binding properties. The consolidation is also correlated with cumulative heat and monocarboaluminate formation. The results indicate the potential of calcined katoite for use as rapid set alternative cement or SCM.