Microwave-assisted accelerated curing of precast concrete - Microwave-Assisted Concrete Technology: Production, Demolition and Recycling - page 79

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M1 M2 M3 M4 M5

Microwave Power Variation Scheme

7-day microwave cured

4.5-hour microwave cured

7-day normal cured

Figure 2.30 Compressive strength of microwave-cured mortar specimens subjected
to various microwave power variation regimes. (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
permisson.)

and Pheeraphan recommended that a temperature-feedback control system
be used to avoid unnecessary overheating by limiting the overall tempera-
ture reached in the specimens to below 80°C [15]. Figure 2.30 compares
the compressive strength development of the mortar specimens that were
microwave cured at five different microwave power variation regimes [15].
The first batch of mortar specimens (M1) were subjected to constant power
at 412 W for 45 minutes. The second batch of mortar specimens (M2) were
microwave cured for 90 minutes by limiting the temperature reached to
below 60°C using a temperature-feedback system that regulates the power
(maximum power of 600 W). The third batch (M3) was microwave heated
up to 50°C in the first 20 minutes and up to 8°C in the next 25 minutes.
The fourth batch (M4) was microwave cured for 45 minutes by limiting the
temperature reached to 80°C (maximum power of 1200 W). The fifth batch
(M5) of mortar specimens was cured at a constant power of 800 W for the
first 20 minutes, followed by heating below the temperature limit of 80°C
using the temperature-feedback system for another 25 minutes. The result-
ing average mortar temperatures reached throughout these curing processes