evaporating out of the paste. At 24 hours after mixing, the samples were
de-molded; they were then cured by microwave energy.
2.3 Microwave curing
The microwave system used was a monochromatic microwave at a
frequency of 2.45 GHz, as shown in Fig. 1 [11]. Microwave energy was
generated by a magnetron and transmitted directly along the propagation
direction (+z) of a rectangular wave guide toward a water load situated at
the end of the waveguide to ensure that a minimal amount of microwave
energy would be reflected back to the sample. A warming water load was
circulated through the cooling tower in order to reduce the temperature in
the water load system.
A cement paste sample was arranged perpendicular to the
propagation direction. A Type K thermo-couple with a 0.1 mm diameter
was inserted at the center of the sample for the purpose of monitoring the
temperature rise.
3. Analytical investigation
Inorder to analyze heat generation by microwave energy inside the
hardened cement paste, electromagnetic distribution inside a rectangular
wave guide and thermal models were taken onto account. A
electromagnetic plane wave in TE
10
mode was taken into account for
calculating the electric-magnetic fields. Since a microwave of the TE
10
mode propagates uniformly iny-direction, the electromagnetic field can
be considered on the x–z plane of a two-dimensional model (Fig. 2).
Thus, such correspondent electromagnetic and temperature fields can be
contemplated in a two-dimensional model. Fig. 2 illustrates the physical
model for the microwave heating of the cement paste using a rectangular
wave guide. The proposed model makes the following assumptions [12]:
(a) Cement paste materials (cement plus water) are themselves
composed of non-magnetic materials.
(b) The electrical properties of the rectangular wave guide’s walls
are perfect conductors that can reflect waves completely.
(c) The absorption of microwave energy by air in the rectangular
wave guide is negligible.
(d) The effect of the polyethylene sample container on the
electromagnetic and temperature fields can be neglected.
In order to analyze the behavior of electric and magnetic fields in the
wave guide, fundamental equations governing the fields, that is,
Maxwell’s equations, are used. As the above-stated assumptions, the
electromagnetic field can be written in terms of the component notations
of electric and magnetic field intensities as in Eq. (1) [12]:
(a)
① Rectangular Wave Guide
② Directional Coupler
③ Isolator
④ Reflexionless Termination
⑤ Power Monitor
⑥ Magnetron
⑦ Sample
⑤
②
④
④
⑦
②
⑤
①
⑥ ③
②
⑤
④
④
Incident Wave
Reflection Wave
Transmission Wave
(b)
(c)
Fig. 1. (a) Experimental setup, (b) Schematic showing direction of
microwave components (Incident wave, reflected wave, and
transmission wave) and (c) Size of specimen.
x
z
y
Magnetron
Thermometer&
Fiber sensor
Processing
Computer
Power
monitor
Specimen
54.6 mm
Cement
paste
50mm
110.0 mm Cement
paste
housing
677
evaporating out of the paste. At 24 hours after mixing, the samples were
de-molded; they were then cured by microwave energy.
2.3 Microwave curing
The microwave system used was a monochromatic microwave at a
frequency of 2.45 GHz, as shown in Fig. 1 [11]. Microwave energy was
generated by a magnetron and transmitted directly along the propagation
direction (+z) of a rectangular wave guide toward a water load situated at
the end of the waveguide to ensure that a minimal amount of microwave
energy would be reflected back to the sample. A warming water load was
circulated through the cooling tower in order to reduce the temperature in
the water load system.
A cement paste sample was arranged perpendicular to the
propagation direction. A Type K thermo-couple with a 0.1 mm diameter
was inserted at the center of the sample for the purpose of monitoring the
temperature rise.
3. Analytical investigation
Inorder to analyze heat generation by microwave energy inside the
hardened cement paste, electromagnetic distribution inside a rectangular
wave guide and thermal models were taken onto account. A
electromagnetic plane wave in TE
10
mode was taken into account for
calculating the electric-magnetic fields. Since a microwave of the TE
10
mode propagates uniformly iny-direction, the electromagnetic field can
be considered on the x–z plane of a two-dimensional model (Fig. 2).
Thus, such correspondent electromagnetic and temperature fields can be
contemplated in a two-dimensional model. Fig. 2 illustrates the physical
model for the microwave heating of the cement paste using a rectangular
wave guide. The proposed model makes the following assumptions [12]:
(a) Cement paste materials (cement plus water) are themselves
composed of non-magnetic materials.
(b) The electrical properties of the rectangular wave guide’s walls
are perfect conductors that can reflect waves completely.
(c) The absorption of microwave energy by air in the rectangular
wave guide is negligible.
(d) The effect of the polyethylene sample container on the
electromagnetic and temperature fields can be neglected.
In order to analyze the behavior of electric and magnetic fields in the
wave guide, fundamental equations governing the fields, that is,
Maxwell’s equations, are used. As the above-stated assumptions, the
electromagnetic field can be written in terms of the component notations
of electric and magnetic field intensities as in Eq. (1) [12]:
(a)
① Rectangular Wave Guide
② Directional Coupler
③ Isolator
④ Reflexionless Termination
⑤ Power Monitor
⑥ Magnetron
⑦ Sample
⑤
②
④
④
⑦
②
⑤
①
⑥ ③
②
⑤
④
④
Incident Wave
Reflection Wave
Transmission Wave
(b)
(c)
Fig. 1. (a) Experimental setup, (b) Schematic showing direction of
microwave components (Incident wave, reflected wave, and
transmission wave) and (c) Size of specimen.
x
z
y
Magnetron
Thermometer&
Fiber sensor
Processing
Computer
Power
monitor
Specimen
54.6 mm
Cement
paste
50mm
110.0 mm Cement
paste
housing
677
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