The cast-in-place concrete lining construction process represents about 25% of the total railroad tunnel construction period. Moreover, the construction period for lining concrete depends on the speed of the curing process of the lining concrete. Therefore, in cold weather when the air temperature in mountain railroad tunnel is consistently 10 degrees or below, equipment for heat insulation of cast-in-place concrete lining, such as a portable fossil fuel heater, must also be prepared to maintain an appropriate curing temperature in the tunnel. It generally takes about 24 to 36 hours to reach the compressive strength (3 to 5MPa) required to remove the lining form.
Recently, microwave heat curing technology has been developed as a way of substantially reducing the concrete curing time, to achieve a reduction in the total construction period. The microwave heating system developed in this technology is comprised of a microwave generator, cavity, insulator, and exothermic body (microwave irradiated pyrogen). In this system, microwaves generated from the magnetron are irregularly reflected inside the cavity, and rapidly heat up the exothermic body so that the heat is transferred to the lining form and the concrete in turn, resulting in the accelerated hydration of concrete.
Based on the field test data from the construction of the railroad tunnel cast-in-place concrete lining, it is found that this technology is able in 6 to 12 hours to complete the curing of concrete lining sufficiently to remove the form. It is hoped that this approach will substantially reduce the construction period and cost of tunnel lining, even during cold-weather.