Microwave-assisted selective demolition of concrete - Microwave-Assisted Concrete Technology: Production, Demolition and Recycling - page 90

Figure 3.2 Concrete deteriorated because of chloride contamination. (Courtesy of
James Bushman, Bushman & Associates, Inc., 6395 Kennard Road, PO Box
425, Medina, OH 44256 USA.)
corrosion. The formation of rust caused by the corrosion is an expansive
reaction and can result in cracking and spalling of the concrete cover of the
corroding steel (Figure 3.2). Second, the salt may deteriorate the concrete
surface through crystallisation. Crystallisation of salts may damage the
concrete through the development of crystal growth pressures. As a result
of evaporation, the salts are concentrated and deposited in the concrete
pores and may continue to the point at which they cause cracking.
To rehabilitate structures exposed to chloride attack, some amount of
concrete removal and replacement is usually necessary. Considering the
amount of the surface area involved, removal of surface concrete using con-
ventional concrete removal techniques is time consuming, energy intensive
and laborious, and usually results in damage to the underlying concrete
and may even compromise the stability of the structure as a whole. An
efficient method to remove the surface concrete without causing damage to
the underlying concrete is highly appealing if available.
3.3 STATE- OF- THE- ART SELECTIVE CONCRETE
DEMOLITION TECHNIQUES
To better understand the need for developing more efficient selective demo-
lition tools for concrete, it is important to gain some level of understand-
ing about the advantages and disadvantages of available state-of-the-art
selective demolition technologies. A number of viable technologies for the
selective demolition of concrete are reviewed in this section. It is impor-
tant to note that only a few of the following techniques have actually been