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Question on curing and drying

What is the difference between drying and curing of concrete?

Answer

Concrete has an inherent quantity of water within the mix from the time of batching, about 200 litres per cubic metre. The majority of this water is not required to hydrate the cement but is needed to improve the consistence or workability of the concrete to ease handling. The water that is not chemically combined or held by capillary action within the concretes pore structure is free to evaporate i.e. dry.

Curing is the process of preventing the loss of moisture from the young concrete whilst maintaining a satisfactory temperature regime. The purpose of minimising moisture loss is to achieve a high level of hydration of the cement in the surface layer of the concrete and thus improve durability.

The rate of drying of concrete depends on the ambient conditions in which the element exists. BS 8204-2 suggests that under good drying conditions concrete bases of 150mm thickness drying from one face will take more than one year to dry. The application of impermeable or timber flooring materials must take this long drying period into account.

To assist curing, the top surface of the freshly-cast concrete should be covered as soon as possible, for example with a layer of polythene, to prevent drying out. Alternatively, the surface could be covered with wet hessian or sprayed with a proprietary curing compound.

 
Acknowledgement: The Concrete Society
 
Other references:BS 8204 ´Screeds bases and insitu floorings´
 

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