Time to remove formwork to cater for early thermal movement, Civil Engineering

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Q. Time to remove formwork to cater for early thermal movement?

Let's take a circular column as an illustration to explain effect of internal restraint to thick sections. 

When temperature is increasing, temperature in the core is higher than outer zone. The inner core would have a higher expansion and exert pressure to the outside. Induced compressive stress will yield the formation of radial cracks near the surface of concrete.

When temperature drops, concrete at outside drops to surrounding temperature whereas the concrete at central region continues to cool down. Contraction associated with inner concrete persuades tensile strains and forms cracks tangential to circular radius. 

It is advantageous for thick sections (say >500mm) to have late removal of formwork to decrease early thermal cracking. This is to enable more time for the centre of concrete section to cool down progressively to decrease the risk of thermal cracking. It is effective in controlling thetemperature differential across the cross section of concrete structures and decreasing the potential of internal cracking because of early thermal movement.


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