Thermal Cracking

[jike]

We have a special concrete mix design that we are using so that we can apply a coating to a concrete containment vessel earlier than 28 days. How do I determine if thermal cracking will be an issue?

 

[LittleWheels]

There are various methods to calculate cracking, CIRIA C660 for one

http://www.ciria.org/acatalog/C660.html

provided you know sufficient information about the mix and its properties. A test specimen (preferably instrumented) can be very useful.

 

[concretemasonry]

The 28 days does really mean much since it is typically a time period for laboratory curing under controlled conditions to produce or meet a standard. A special mix is only that and other factors can reduce it to much less than expected performance.

In addition to the special mix design, the ACTUAL curing conditions can have as much or more effect on the shrinkage/curing of the concrete vessel.

Maintain a proper moisture content in the concrete (especially important with a 2-sided shell) and limit the temperatures to reduce rapid curing and higher shrinkage. Uniformity of the moisture within the concrete is particularly important with thicker sections where the center can cure at a different rate than the exterior, which can disrupt the long term bond of a coating.

Many special efforts to limit shrinkage require a full, long term curing.

 

[oneintheeye]

the site methods can have big effects. Even choice of shutter. You will need to consider the rate of rise and fall of your special mix. May not be as normal OPC. For instance GGBS replacement has a lower heat gain that OPC but it goes on for longer.