Hydrogen NMR spin-lattice relaxation times were measured as a function of time to determine the kinetics of hydration for the Dave Johnston and Laramie River coal fly ashes and for the Lurgi spent oil shale. The kinetic data were compared to the hydration of Portland cement. It was found that the hydration kinetic data for the spent shale were similar to Portland cement with the exception that the dormant period was about 10 times longer. The dormant periods for the coal fly ashes differed from each other and from Portland cement. The Laramie River coal fly ash had almost no dormant period. The extent of hydration for the materials after 119 h can be ranked accordingly: Portland cement > Lurgi spent shale similar or equal to Laramie River coal fly ash > Dave Johnston coal fly ash. Data from this study show that an NMR spin-lattice relaxation time measurement may be a good predictor of the compressive strength of hydrated Portland cement and fly ash. (C) 2001 Elsevier Science Ltd. All rights reserved.