Civil Engineering Reference
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single-mode transmission in the waveguide is usually transformed into mul-
timodal propagation in the horn. This is the case; within a typical open-
ended waveguide, the penetration of the field is usually controlled by the
dimensions of the waveguide. The smaller the waveguide cross section, the
smaller the depth of penetration into the load will be. Horn applicators can
be used as an easy means to increase the coverage area of the microwave
applicators in applications such as microwave-assisted selective demolition
of concrete and microwave-assisted removal of tile and surface finishes
from concrete floors and walls as discussed in the previous chapters.
6.4.3 Continuous- flow applicators
A number of applications of microwave heating in concrete technology,
including accelerated microwave curing of prefabricated concrete compo-
nents and microwave-assisted separation of mortar from RCA, can take
advantage of continuous-low processing, which leads to lower labour
costs and higher outputs compared to batch processing. The principles of
microwave heating and applicator design discussed previously apply also
to continuous flow applicators and processes. However, there are special
considerations that should be taken into consideration in the design and
planning of continuous microwave heating processing. In continuous-low
applicators, the microwave power is supplied to a cavity with microwave-
sealed openings in the form of open-ended ports. The load or material is
conveyed via conveyor belts through the cavity via the input port before
exiting via the output port. Providing a microwave attenuation mechanism
at each port of such continuous-throughput cavities is essential to ensure
the safety of operators in the presence of the high-power microwave field.
Figure 6.30 shows a typical continuous-throughput microwave heating sys-
tem in which the load is conveyed through the microwave cavity at a con-
stant velocity via a conveyor belt system.
When processing materials using a continuous-throughput microwave
heating system, it is crucial to estimate the power required to process the
load volume being fed into the microwave system by considering the veloc-
ity of the conveyor belt. The properties and size of the components treated
by such continuous microwave systems could vary considerably depending
on the particular application, including accelerated microwave curing of
precast concrete. The selection of an inappropriate power level or lack of a
dynamic mechanism for feedback control of the microwave power based on
the variations in the volume and properties of the load during processing
could result in nonuniformity in the quality of the microwave-treated loads.
The total microwave power needed in a continuous-throughput microwave
heating system can be estimated using the following equation:
PRCThR
pr
=
+
(6.19)
p
fg ol
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