1. Steam curing construction technology is adopted for precast beams in winter to accelerate the growth of concrete strength and elastic modulus. Boiler technical parameters and supporting facilities are selected according to the scale of health maintenance.

2. The steam curing process of concrete generally includes four stages: static stop, heating, constant temperature and cooling. The static stop stage refers to the stage from the completion of concrete pouring to the temperature rise at room temperature, which generally takes 2 ~ 6 h, which can enhance the ability of concrete to resist structural damage in the temperature rise stage; The heating stage refers to the stage when concrete rises from room temperature to constant temperature. In order to avoid cracks on the concrete surface caused by rapid temperature rise and volume expansion, the heating rate should be controlled within15℃/h; Constant temperature stage is the fastest growth stage of concrete strength, and the time to keep constant temperature is generally 48 ~ 72 h, which is related to the variety of cement in concrete, and the curing temperature of ordinary portland cement should not exceed 60℃. In the cooling stage, the concrete has hardened. If it is cooled too fast, surface cracks will appear in concrete. Therefore, the general cooling rate should be controlled at ≯10℃/h.