Microwave-assisted accelerated curing of precast concrete - Microwave-Assisted Concrete Technology: Production, Demolition and Recycling - page 52

Figure 2.9 Ponding of a concrete floor. (Courtesy of Alec Johnson, Nong Khai Design
Co., Ltd., 1070/1 Prajak Road, Tambon Nai Muang, Amphoe Muang, Changwat
Nong Khai, 43000 Thailand.)
not be more than 5°C lower than that of the concrete to avoid development
and growth of thermal cracks. Ponding is mostly used in the curing of large
horizontal surfaces such as concrete floors and pavements. In this method,
a dam or dike is erected around the edges of the horizontal concrete element
to maintain the ponding water, which is added later (Figure 2.9). Ponding is
an effective curing method for preventing moisture loss from concrete and
maintaining a uniform temperature within the concrete. Ponding is a fast,
effective, and inexpensive curing method when water is plentiful and when
there is a ready supply of dam materials such as clay. Prior to applying the
ponding method, it should be ensured that ponding does not disrupt subse-
quent construction operations. Because of the considerable labour and level
of supervision requirements, ponding is usually used only for small jobs.
Spraying is an alternative water curing method that is also commonly
used when water is easily accessible. Spraying is especially effective when
the ambient temperature is well above the freezing temperature and when
ambient humidity is low. This method is applicable for both horizontal and
vertical surfaces. In water spraying, a fine spray such as that used by most
sprinklers is used to continuously spray water onto the surface and thereby
increase the relative humidity of the air over the concrete surface to slow
evaporation from the surface. Similar to other wet curing methods, it is
crucial that the sprinklers are able to maintain a continuously wet concrete