Civil Engineering Reference
In-Depth Information
any additional increase in temperature is not only less effective but may
also have detrimental effects on the concrete properties. A variety of meth-
ods for accelerated curing of concrete at elevated temperatures have been
investigated and used over the past few decades. These methods include
convection heating by circulation of a hot liquid (water or oil) through the
formwork, electric resistance heating, low- and high-pressure steam cur-
ing, and microwave curing. One of the drawbacks associated with most of
these elevated temperature curing methods is the increase in the rate of the
humidity loss from concrete at elevated temperatures, which can in turn
lead to severe shrinkage and cracking problems. Therefore, any method for
the curing of concrete at elevated temperatures should also ensure adequate
humidity to prevent excessive moisture loss.
Four main parameters should be considered generally when design-
ing an elevated-temperature concrete-curing process: rate of temperature
rise, maximum temperature, rate of heating, and uniformity of heating.
Controlling the rate and uniformity of heating are highly important to
minimise the development of differential thermal stresses in the concrete.
Curing at elevated temperatures using the majority of conventional heat-
ing methods may result in the development of differential thermal stresses
as a result of the rapid increase in the temperature as well as the non-
uniform heating of the concrete elements. Such differential thermal stresses
negatively affect the properties of the cured concrete through introducing
new microcracks or increasing the growth rate of the pre-existing cracks.
It is generally recommended to restrict the maximum curing temperature
of concrete to 60°C to 70°C. The maximum temperature limits in con-
crete curing at elevated temperatures are mainly caused by the well-known
decrease in the long-term strength of concrete with an increase in its early
strength development rate. In the following, various traditional elevated-
temperature curing methods are reviewed. The microwave-curing method
is discussed in detail later in this chapter.
2.4.1.1 Accelerated curing using convection and conduction
Curing at elevated temperatures is traditionally performed using some
form of conduction/convection heating-based methods. One of the meth-
ods commonly used is to increase the temperature of the forms by pumping
hot water or hot oil through them or by heating them electrically [3]. The
temperature of the concrete placed in the forms being heated gradually
increases through conductive heat transfer. Proper insulation of formwork
is highly important to improve the energy efficiency of this method. In
addition, similar to any other method based on curing at elevated tempera-
tures, ensuring sufficient humidity to compensate for the humidity loss dur-
ing high-temperature curing is important to maximise the benefits derived.
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