Civil Engineering Reference
In-Depth Information
90
80
70
60
50
40
30
20
10
0
Case M5
Case M2
Case M3
Case M1
Case M4
0
10
20 30
Time during Microwave Heating (Minutes)
40
50
60
70
80
90
Figure 2. 31
Temperature histories for various mortar specimens during microwave
curing. (From Leung, C.K.Y., and Pheeraphan, T., Determination of optimal
process for microwave curing of concrete.
Cement and Concrete Research
,
1997,
27
(3):463-472. With permission.)
are compared in Figure 2.31. As shown in Figure 2.30, the outcome of the
microwave-curing process could vary significantly depending on the curing
regime used. The M1 and M4 regimes seemed to provide the best combi-
nations of early and later age strengths. When two or more regimes result
in relatively similar outcomes in terms of compressive strength develop-
ment, other criteria, such as energy consumption, can be used to select the
optimal-curing process. For the cases discussed, the energy consumption of
regime M1 and M4 can be estimated as 0.309 kWh and 0.302 kWh, respec-
tively, using the area of power-versus-time curves for the two regimes [15].
Similar to mortar, microwave curing of concrete is also sensitive to
the microwave power regime used. Figure 2.32 shows the variation in the
compressive strength of concrete specimens (w/c = 0.4) subjected to four
different microwave power regimes. In the first regime (C1), concrete speci-
mens were cured at a constant microwave power of 412 W for 45 minutes.
The second batch of concrete (C2) was microwave cured for 45 minutes by
limiting the temperature reached to below 80°C using the temperature-
feedback system (maximum power of 750 W). The third batch of concrete
(C3) was cured for 45 minutes by limiting the maximum temperature to
85°C (maximum power of 1200 W). The fourth batch of concrete (C4) was
microwave cured for 45 minutes at a controlled temperature determined
using the power-versus-time curve for C2. In this regime, a reversed history
with power at time
t
for C4 equal to power at time (45 minutes -
t
) for case
C2 was applied. With this method, C4 concrete specimens receive the same
amount of energy as C2 but less energy during the earlier stage of micro-
wave curing and more at the later stage. As shown in Figure 2.32, both
Search WWH ::
Custom Search