Microwave-assisted accelerated curing of precast concrete - Microwave-Assisted Concrete Technology: Production, Demolition and Recycling - page 39

Microwave- assisted accelerated
curing of precast concrete
2.1 BACKGROUND
Precast concrete is defined as concrete that has been mixed, cast, and cured
at a location that is not its final destination. As opposed to in situ concrete,
which is cast and cured on site, precast concrete is produced by casting in
reusable forms and curing in a controlled environment off site (Figure 2.1).
Traveling distances between the precast site and the installation site may be
a few metres when on-site prefabrication is used to distances of tens or even
hundreds of kilometres between precast yard and construction site.
Because of the many economic and environmental advantages, concrete
precasting is widely used in modern construction. Prefabrication of concrete
components off site generally leads to improved quality because of better
control over the production process. In addition, precasting has many other
advantages in terms of enhanced construction safety as the production pro-
cesses take place in a controlled environment with overhead cranes and
generally at ground level. Precasting can capitalise savings derived from the
high reuse rate of formwork in terms of number of components cast and
rate of demoulding. Other benefits include faster completion and better
quality of finishes.
Precast concrete has many applications, as both structural and archi-
tectural components. Almost every structural component can be precast
off site to some degree. Precast architectural panels are commonly used
as building facades, including as exterior walls and sound and even blast
proofing. It may be noted that the majority of storm water drainage, water
and sewage pipes and conduits, and tunnels make use of precast concrete
units. In practice, much attention has been placed on improving the effi-
ciency of the precast production process. One major factor with an impact
on efficiency is the turnaround time associated with casting and demould-
ing operations. Achieving an adequate strength level as quickly as possible,
sufficient for demoulding and handling operations, is key. A higher early
strength development rate can lead to considerable economic and environ-
mental benefits. The strength development rate of concrete is influenced
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