TY - JOUR AU - Lima Pacheco, Antonia Alana AU - Santos Nobre, Thiago Ricardo AU - Hark Maciel, Marcel AU - Santilli, Celso Valentim AU - Vieira Coelho, Antonio Carlos AU - Cirelli Angulo, Sérgio PY - 2021/03/16 Y2 - 2024/03/28 TI - Rehydration of katoite as a layered double hydroxide: an in situ study JF - RILEM Technical Letters JA - RILEM Tech Lett VL - 6 IS - 0 SE - DO - 10.21809/rilemtechlett.2021.130 UR - https://letters.rilem.net/index.php/rilem/article/view/130 SP - 8-16 AB - <p>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 <em>in situ</em> techniques, and its applicability as an alternative cement or supplementary cementitious material (SCM) is discussed. The research employed X-ray diffraction, isothermal calorimetry, <em>in situ</em> 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.</p> ER -