A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
reason, formwork is subjected to a higher pressure exerted by fresh
concrete in winter than in summer.
Fig. Diagram of design concrete pressure diagram on formwork.
5. Is late removal of formwork beneficial to cater for early thermal
movement? (F3)
Let us take a circular column as an example to illustrate effect of internal
restraint to thick sections.
When the temperature is rising, temperature in the core is higher than that
at outer zone. The inner core will have a higher expansion and exert
pressure to the outside. The induced compressive stress will result in the
formation of radial cracks near the surface of concrete.
When the temperature drops, the concrete at the outside drops to
surrounding temperature while the concrete at the central region continues
to cool down. The contraction associated with inner concrete induces
tensile strains and forms cracks tangential to the circular radius.
It is beneficial for thick sections (say >500mm) to have late removal of
formwork to reduce early thermal cracking. This is to allow more time for
the centre of concrete section to cool down gradually to reduce the risk of
thermal cracking. This is effective in controlling the temperature differential
across the cross section of the concrete structures and reducing the
potential of internal cracking due to early thermal movement.
6. Comparing the rate of “Formwork exceeding 300mm wide,
horizontal or at any inclination up to and including 5 o to the
horizontal” with the rate of “Formwork exceeding 300mm wide, at any
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