A Closer Look at Prevailing Civil Engineering Practice - European ...

A Closer Look at Prevailing Civil Engineering Practice, What, Why and How
Vincent T. H. CHU
Release agent:
Form oils:
Materials that contain ingredients which are
chemically combined with cement.
Diesel oils or other oil types.
Form releaser
and demoulding agent: General terms to describe materials which perform
separation of forms from concrete.
6. How can release agent help to separate formwork from concrete
There are generally two main types of form releaser: barrier type or
chemically active type.
For barrier type (e.g. form oil), it creates a barrier between the form and the
fresh concrete. However, the quick evaporation of diesel oils affects clean
air.
For chemically active type (e.g. release agent), an active ingredient (e.g.
fatty acid) chemically combines with calcium (lime) in the fresh cement
paste. This calcium/fatty acid product (grease or metallic soap) is stable
and causes the formwork to release from the hardened concrete. It is this
slippery, greasy, non-water soluble soap which allows the easy releasing
of formwork from hardened concrete.
7. What are the potential problems of excessive application of form
oils
The problems of excessive application of form oils are:
(i) It stains the surface of hardened concrete.
(ii) Excess oils have nowhere to escape and find its way inside the
cement paste and form holes subsequently. The oils bead up
because of its incompatibility with water in chemical nature.
(iii) Higher cost is associated with increased usage of form oils.
(iv) In a relatively short time essentially most diesel oil evaporates so
that it creates environmental problem.
8. Curing time in summer is less than that in winter. Why
While concrete sets, it gains hardness and strength as the process of
hydration slowly spreads the entire body of material. Curing should be
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