As conventional wood or steel formwork
system is impermeable (IMF), the migration within the mix ceases
as the concrete/formwork system interface is reached. Visually,
this may be observed on all concrete surfaces through the presence
of blowholes following formwork removal.
This is a problem because the first line of defence
of all structural elements against carbonation, chlorides, frost
and abrasion, is the coverzone. It is therefore imperative this
region is durable.
Engineered Formwork System.
This formwork is built out of prefabricated modules with a metal
frame (usually steel or aluminum) and covered on the application
(concrete) side with material having the wanted surface structure
(steel, aluminum, timber, etc.). The two major advantages of formwork
system, compared to traditional timber formwork, are speed of construction
and lower life-cycle costs (barring major force, the frame is almost
indestructible, while the covering if made of wood; may have to
be replaced after a few - or a few dozen - uses, but if the covering
is made with steel or aluminum the form can achieve up to two thousand
uses depending on care and the applications).
The formwork system is built on site out of timber and plywood or
moisture-resistant particleboard. It is easy to produce but time-consuming
for larger structures, and the plywood facing has a relatively short
lifespan. It is still used extensively where the labor costs are
lower than the costs for procuring re-usable formwork system. It
is also the most flexible type of formwork system, so even where
other systems are in use, complicated sections may use it.