Civil Engineering Reference
In-Depth Information
45
40
35
30
25
20
15
10
5
0
300 (0.470)
350 (0.466)
400 (0.462)
450 (0.455)
Microwave Power in Watts (water/cement ratio after heating)
4.5-hour microwave cured
7-day microwave cured
7-day normal cured
Figure 2.29
Effects of microwave power on compressive strength of concrete at 400 W.
(From Leung, C.K.Y. and Pheeraphan, T., Very high early strength of micro-
wave cured concrete.
Cement and Concrete Research
, 1995,
25
(1):136-146.
With permission.)
in the long-term strength can be achieved. Figure 2.23 shows that, for the
mortar samples tested, a microwave power of 400 W may provide the best
compromise considering both early and later age strengths.
The effect of microwave power on the strength development of
microwave-cured concrete is slightly different compared to the microwave-
cured mortar (Figure 2.29). At lower powers, the 7-day strength of concrete
shows relatively lesser sensitivity to microwave curing, and the microwave-
cured specimens show relatively similar 7-day strengths as the standard-
cured concrete specimens. Comparing Figures 2.23 and 2.29 shows that
microwave-cured concrete specimens show less decrease in the 7-day com-
pressive strength at 400 W and 450 W than the corresponding microwave-
cured mortar specimens.
The majority of the experiments on microwave curing of cement paste, mor-
tar, and concrete reported in the available literature have been performed by
applying a fixed microwave power throughout the curing process. However,
it has been debated that the use of constant power may lead to unnecessary
overheating during the curing process. This is because of the variation in the
dielectric properties of concrete/mortar as the concrete/mortar dries. Leung
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