Introduction - Microwave-Assisted Concrete Technology: Production, Demolition and Recycling - page 5

concrete during its life cycle. In this topic, the applications of microwave
heating in concrete technology are categorised into three areas as follows:
1. Microwave-assisted accelerated curing of concrete
2. Microwave-assisted selective demolition and drilling of concrete
3. Microwave-assisted recycling of concrete
These applications are briefly explained in the sections that follow.
1.2.1 Microwave- assisted accelerated
curing of concrete
Precast concrete is widely used in modern construction to increase the speed
of construction and to enhance the quality of the concrete products. Precast
concrete components are normally fabricated in the prefabrication plant
and then shipped to the construction site for installation [4]. An impor-
tant aspect affecting the production rate of a prefabrication plant and thus
the speed of construction is the time required for concrete to gain enough
strength to allow for demoulding and transportation of components to the
construction site. At present, the use of special cement compositions or
conventional curing at elevated temperatures (with or without steam) is
commonly used to accelerate the strength development of the precast con-
crete components. The use of such techniques, however, has its drawbacks
and limitations. For instance, conventional curing at elevated temperatures
typically takes more than 24 hours for concrete to reach sufficient strength.
Such a long heating duration leads to significant energy use, carbon foot-
print, and costs. Moreover, the use of chemical accelerators and rapid-
hardening cements may cause long-term durability problems that are as yet
not well understood [5].
Microwave curing is believed to have great potential to revolutionize the
curing of precast concrete [5]. Microwave heating at lower ISM frequen-
cies (such as 915 and 2450 MHz) can be used to heat the concrete uni-
formly and significantly reduce time required for curing. Previous studies
have shown that, unlike steam-cured concrete, microwave-cured concrete
can gain considerable strength in just a few hours without compromising
its long-term properties [5-7]. Such reduced curing times can significantly
decrease energy consumption and thus the carbon emissions associated
with conventional curing processes aside from the other advantages arising
from less energy consumed for storage of the precast components before
being transported for installation. Chapter 2 of this topic reviews the
recent achievements in using microwave curing for accelerating the strength
development rate of freshly cast concrete. A detailed description of the phe-
nomena involved in the microwave curing of concrete as well as the factors
affecting curing efficiency is presented.