Microwave-assisted accelerated curing of precast concrete - Microwave-Assisted Concrete Technology: Production, Demolition and Recycling - page 51

4°C

21°C

40

38°C

30

20

17 28 90

Time (days)

Figure 2.8 Compressive strength of concrete cured initially at different temperatures
followed by curing continuously at 21°C. (Reprinted, with permission, from
Proceedings-American Society for Testing and Materials , 1951, copyright ASTM
International, 100 Barr Harbor Drive, West Conshohocken, PA 19428.)

in the early strength but an increase in the long-term strength of concrete.
Temperatures below 10°C are generally undesirable for the development of
early strength of concrete. The development of early strength is consider-
ably retarded at temperatures below 4°C. The decrease in the early strength
development rate continues with a further decrease in temperature, down
to −10°C, at which little or no strength development will occur.

2.3.3 Standard curing methods
The curing process after placement of concrete in the formworks is tradi-
tionally performed using one of the following two methods:

1. Water curing , in which measures are taken to supply additional water
to compensate for the loss of moisture and to maintain sufficient mix-
ing water in the concrete during the early hardening days.
2. Sealed curing , in which measures are taken to reduce the loss of mois-
ture from the surface of concrete.

2.3.3.1 Water curing
In water curing, water is supplied directly to the concrete using various
methods, including ponding, spraying, or covering the concrete surface
with saturated coverings. The temperature of water used for curing should