Is the hydration reaction in the powdered cement paste sample continue? For example, the cement paste sample was cured at 28 days and then powdered. The hydration reaction is continued in this sample after 28 days?
Yes, hydration and also carbonation will continue. Hydration is not terminated after 28 d. There is still water and humidity within the sample, which is available for further hydration. Additionally, grinding exposes fresh unhydrated clinker surfaces.
It is highly recommended to stop hydration by solvent exchange to prevent further hydration and also carbonation as far as possible, see:
Article RILEM TC-238 SCM recommendation on hydration stoppage by sol...
Article Report of TC 238-SCM: hydration stoppage methods for phase a...
Thanks, I mean, cement paste of specimen by grinding, and after the powder, it continues hydration?
Yes, hydration may continue and also carbonation. Hydration stoppage should be done, and then the samples should be measured e.g. by XRD or TGA as soon as possible in order to avoid especially carbonation. You may store the samples in a desiccator over silica gel, but not for too long.
Dear Frank Winnefeld
Thank you so much
The amount of CaCO3 can be caused by the Carbonation process at powder cement paste that shows XRD analysis.
Yes! As noted by Frank, hydration could go on for several months especially depending on the amount of SCMs in the cement. To stop hydration at a desired age, methods such as solvent exchange may be employed.
Hydration of cement needs water. If hardened cement is ground to powder again and left in dry atmosphere, water will evaporate and leave the incompletely hydrated cement powder behind. In this regard, unless you supplement moisture to the ground cement powder continuously by some means such as by mist spray, hydration will not be able to continue.
Dear Sai Kit Yeung
Thanks for answer
The hydration of cement is continuing in the free air, although it is low.
We have to do a special method to stop hydration.
Do you have a valid reference for what you are saying?
Cement has a tendency to absorb moisture from the atmosphere. When it absorbs moisture, it further hydrates after it's initial hydration.
This is correct, anhydrous cement phases will absorb moisture from the environment and continue hydration. Depending on the clinker phase, hydration starts above a certain threshold of relative humidity. Please consult the following papers for more information:
Dubina, E., L. Black, R. Sieber and J. Plank (2010). "Interaction of water vapour with anhydrous cement minerals." Advances in Applied Ceramics 109(5): 260-268.
Dubina, E., L. Wadsö and J. Plank (2011). "A sorption balance study of water vapour sorption on anhydrous cement minerals and cement constituents." Cement and Concrete Research 41(11): 1196-1204.
The key message however is: Stop the hydration by gentle solvent exchange before grinding and measure your powdered sample as fast as possible as it may alter.
Yeas the hydration will continue in case of the powder not exposed to direct sun rays and wind
Many thanks to all for the interesting comment and great discussions
Please report the valid reference such as articles if you have
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