Flash Set
Summary
Flash Set - A flash set is the irreversible rapid initiation of hydration in fresh concrete shortly after mixing.
Technical Information
Identifiable from its increased heat of hydration, a flash set is can cause rapid rigidity in a concrete as the initial hydration phases occur faster than planned. This cannot be reversed and, unlike false setting, further mixing will not restore the plasticity of the concrete. Water can be added to improve the plasticity of the concrete, however, this has negative implications for the long-term performance of the concrete, and so is not advised.
Some possible reasons for a flash set are:
- Not enough gypsum in the cement mix.
- High cement and/or air temperature.
- The effect of certain cement admixtures.
In the occurrence of a flash set it is advised to finish the concrete promptly, without re-tempering or re-mixing.
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