Process control in microwave heating of concrete - Microwave-Assisted Concrete Technology: Production, Demolition and Recycling - page 174

e number and location of temperature monitoring points required to monitor
heating uniformity is detemined by considering the size of the concrete
component in relation to microwave frequency.

Fibre optic temperature sensors are installed on the temperature monitoring
points determined in the last step.

Microwave heating starts/continues.

e dierence between the temperatures of dierent sets (two points) of
monitoring points is calculated at dierent times and checked against the
allowable limits set by the operator (∆ T ∆Tallowable) ).

For every two points
(∆ T ≤ ∆ T ∆Tallowable) )

For any two points
(∆ T > ∆ T ∆Tallowable) )

Heating stops and adjustments including
adjustment of the location of samples in
the cavity, microwave frequency and
microwave power are made to reduce
the temperature gradient.

Figure 5.2 A feedback control mechanism for microwave-assisted selective demolition
of concrete.

interface with the natural aggregates in the RCA. The temperature required
to fracture or detach the adhering mortar in this method is in the range of
150°C-200°C, depending on the strength of mortar. Temperature monitor-
ing during the microwave separation process is crucial to avoid underheat-
ing or overheating of the RCA, thus ensuring the optimal quality of RCA
produced. Although underheating can affect the efficiency of the mortar
removal process, overheating may have considerable negative effects on the
properties of the natural aggregates present in the RCA. Additional unnec-
essary costs and undesirable environmental impact may be introduced if
the microwave separation process is inefficient. Adjusting the microwave
power and heating duration based on temperature feedback can be used as
a possible feedback control mechanism to avoid RCA overheating or under-
heating during the microwave separation process.
Similar to the microwave-assisted methods described so far, temperature
monitoring is the most common process control methodology adopted in