How long does hydration continue?
The hydration process is faster in initial period and continues indefinitely at a decreasing rate.
Even after a long time there remains an appreciable amount of unhydrated cement. For instance, after 28 days of initial contact with water, grains of cement have been found to hydrated to a depth of just 4µm-8µm after a year.
Powers calculated that complete hydration under normal conditions is possible only for cement particles smaller than 50µm. However, full hydration has been obtained by grinding cement in water continuously for five days.