How to Set Steam Curing Parameters for Precast UHPC Components?

The steam curing parameter settings of precast UHPC components are a key process step determining the final performance of the material, requiring precise coordination across four dimensions: "temperature control, humidity management, time setting, and heating/cooling rate". Through 28 years of process accumulation, Qinglong Group has established a scientific steam curing regime: typically adopting the standard process of "ambient temperature rest (2-4h) → slow heating (10-15℃/h) → constant temperature curing (60-90℃, 24-72h) → controlled cooling (≤15℃/h)". In the production of roof UHPC panels for the Hainan International Convention and Exhibition Center, we precisely controlled constant temperature curing at 90℃ for 48 hours, achieving a 1-day compressive strength of 150MPa for the components while effectively controlling microcracks caused by thermal stress. Optimizing steam curing parameters is one of the core technologies for enhancing UHPC performance.

Scientific Setting Principles for Temperature Parameters

The constant temperature curing temperature is usually set within the range of 60-90℃, depending on the characteristics of the cementitious system. Qinglong's practice shows that the optimal constant temperature for Portland cement-based UHPC is 80±5℃, while for sulphoaluminate cement-based UHPC it can be raised to 90℃. If the temperature is too low, the hydration reaction will be insufficient and strength development slow; if too high, the C-S-H gel structure may coarsen, affecting long-term performance. In the Yangshengtang Pharmaceutical Hangzhou Industrial Park project, we achieved the optimal balance between strength and durability through constant temperature curing at 80℃.

The Necessity of Humidity Control

Steam curing must maintain a relative humidity above 95% to prevent moisture evaporation from the components. Qinglong's curing kilns are equipped with automatic spray systems to ensure the kiln interior remains in a saturated steam environment at all times. Appropriate humidity not only promotes the hydration reaction but also effectively reduces autogenous shrinkage. Test data from our Shenzhen Yirui Biotechnology Building project showed that high-humidity curing can reduce the 28-day autogenous shrinkage of UHPC by more than 20%.

Precise Control of Time Parameters

Curing time is closely related to temperature, and Qinglong applies the "temperature-time equivalence" principle for optimization. Under standard conditions, 72 hours of curing is required at 60℃, 48 hours at 80℃, and this can be shortened to 24 hours at 90℃. However, excessively short curing times may result in insufficient internal hydration, affecting long-term stability. We monitor the hydration process in real time through electrical resistivity monitoring, enabling dynamic time adjustment.

Fine Management of Heating and Cooling Rates

Heating and cooling rates directly affect the magnitude of thermal stress. Qinglong strictly controls the heating rate at ≤15℃/h and the cooling rate at ≤10℃/h. Excessively rapid temperature changes can cause excessive temperature differences between the interior and exterior of components, resulting in cracks. When curing super-large-volume components, we also set multiple temperature plateaus during the constant temperature stage to achieve gradient curing and ensure the uniformity of material performance.