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

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.

MgAl-Layered Double Hydroxide Nanoparticles as Smart Nanofillers To Control the Rheological Properties and the Residual Porosity of Cement-Based Materials

“…This was consistent with the rapid development of binding properties during monocarboaluminate (CaAl-LDH) formation from the rehydration of calcined katoite Ca 3 Al 2 (OH) 12. Furthermore, the recovered LDH could also induce the heterogeneous nucleation of the system (cement/water) to form hydrated products, especially the aluminate layered double hydroxides …”

“…This was consistent with the rapid development of binding properties during monocarboaluminate (CaAl-LDH) formation from the rehydration of calcined katoite Ca 3 Al 2 (OH) 12. 61 Furthermore, the recovered LDH could also induce the heterogeneous nucleation of the system (cement/water) to form hydrated products, especially the aluminate layered double hydroxides. 5 The rheological behavior observed during LDH regeneration in simulated concrete pore solution (Figure S7) demonstrated that in the initial minutes of the test, the storage component was greater than G′ of the reference cement paste, with the value increasing further as the lamellae reconstruction continued, because of crystallite aggregative growth in the c direction.…”

Cimento Portland Reciclado (R-PC): redução da demanda de água, análise ambiental e uso como ligante otimizado.

“…When anhydrous calcined fines are exposed to water again, they rapidly regain chemically bound water (XINWEI;ZHAOXIANG;XUEYING, 2010;ANGULO et al, 2015a;LIMA PACHECO et al, 2021). The R-PC generates a large amount of heat in the first few minutes of rehydration as ordinary Portland cement (OPC) (ANGULO et al, 2015a), recovering combined water in C-S-H (ANGULO et al, 2022), in part of the CaO (quicklime) formed (MENÉNDEZ;ANDRADE;VEGA, 2012).…”