PROTON NMR RELAXATION STUDY OF CALCIUM ALUMINATE HYDRATION REACTIONS

Proton NMR relaxation study of calcium aluminate hydrates was performed. The proton spin-lattice relaxation time (T1,ef) was measured as a function of curing time at room temperature and at 65-degrees-C, respectively. At both temperatures a continuous decrease of T1,ef with time was observed in the initial curing period corresponding to the hydration of CA. After 10 hours of curing at room temperature, at which time T1,ef reaches its minimum value, T1,ef increases gradually with prolonged curing time. The increase in T1,ef is explained in terms of partial dehydration of the CAH10 phase to form C2AH8. Similar behavior was observed at 65-degrees-C as well. In the latter case, however, T1,ef reaches its minimum value after 20 min. Two increases of T1,ef then follow, which can be explained as a result of two consecutive releases of water, according to the reaction schemes 3CAH10 --> 3/2C2AH8 + 3/2AH3 + 27/2H and 3/2C2AH8 --> C3AH6 + 1/2AH3 + 9/2H.