Microwave-assisted selective demolition of concrete - Microwave-Assisted Concrete Technology: Production, Demolition and Recycling - page 95

surface of the material [2]. The abrasive material is normally aluminium
oxide or silicon carbides. Abrasive particles should have sharp edges with
diameters of about 10-50 μm. This process is most effective on flat sur-
faces and can be used on “hard-to-reach” areas such as ceilings. The main
disadvantage of this process is the comparatively large amount of second-
ary waste produced [3]. In addition, the abrasive jetting removal method
has been reported to be effective only when a thin layer of the surface is to
be removed.
One variation of the abrasive jetting technique, known as high-pressure
liquid nitrogen blasting, uses liquid nitrogen as the jet material [2]. In
this method, the concomitant effect of the embrittlement caused by liquid
nitrogen and the abrasive action of the grit is expected to result in slight
improvements in removal efficiency.
Wet ice blasting, in which a compressed air jet is used to propel a mixture
of water and ice crystals onto the surface to be removed, is another varia-
tion of abrasive jetting. [3].
3.3.6 Other methods
The most commonly used methods for the selective removal of concrete
were reviewed in the previous sections. However, in addition to these
methods, various other removal technologies are available that could have
potential for the selective removal of concrete. These methods include
sponge blasting, CO 2 blasting (dry ice blasting), electrohydraulic scabbing,
shot blasting, soda blasting, and laser ablation. The surface removal rates
of these methods range from 1 to 20 m 2 /h, depending on the method and
the type of the equipment used. Although these methods have been used in
a variety of other applications, they have seldom been used in practice to
remove concrete. The application of such methods for the selective removal
of concrete requires further investigation.
3.4 MICROWAVE- ASSISTED DEMOLITION
OF CONCRETE
Microwave heating recently has been considered as an efficient alterna-
tive to conventional methods in the selective demolition of concrete. As
described in Chapter 1, the microwave penetration depth in the materi-
als and the microwave absorption by materials vary with microwave
frequency and the dielectric properties of the materials. As a result, micro-
waves can be used to heat the materials selectively through choice of an
appropriate microwave frequency range for a particular penetration depth
in a given material. Appropriate design of the microwave applicator will
enable the user to focus the microwave energy onto the desired area. This