Hydration of Calcium Aluminate Cements: A Solid‐State 27 Al NMR Study

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Abstract
This paper presents the results of a study of the hydration of calcium monoaluminate (CA) and Lafarge Secar 71 (CA + CA2) using 27Al MAS and 1H‐27 Al CPMAS NMR spectroscopy. CPMAS, high H0 magnetic field strengths (11.7 T), and high MAS spinning speeds (13–14 kHz) provide significant new information about the Al structural environments present during hydration and about the mechanisms of hydration. Important results include the following: (1) Hydrated Al(4) and Al(6) environments are present during the incubation period. This observation is consistent with previously published hydration models. (2) The overall conversion of Al(4) in unhydrated phases to Al(6) in hydrated phases and the crystalline phases detected by XRD are similar to the results of previous studies. (3) There are previously undetected hydrated reaction intermediates present during the main reaction stage. At temperatures above 25°C this phase contains Al(4), and at 4°C it contains Al(4) and possibly Al(5). The incubation period observed for this reaction may be related to the nucleation of this phase.