Steam Curing Parameter Optimization for Precast UHPC Components: Temperature, Humidity, and Time Control Standards

Steam curing is a key process for activating the strength potential of UHPC. Scientific parameter settings can bring about a qualitative leap in the mechanical performance and durability of ultra-high performance concrete. Drawing on 28 years of UHPC production experience, Qinglong Group has participated in developing industry curing standards and, combining climatic conditions across multiple regions of China with engineering practice, has developed a set of steam curing solutions suited to different scenarios.

1. Heating Stage: Smooth Transition and Crack Prevention Are Core????️

The core principle of the heating stage is slow and steady, avoiding sudden temperature rises that cause thermal stress inside components. It is recommended to keep the heating rate at 15-20°C/h, with a final temperature not exceeding 70°C. When producing UHPC curtain wall panels for the Shenzhen Yirui Biotechnology Building, Qinglong adopted a gradient heating mode, gradually raising the temperature from ambient to 65°C, effectively preventing micro-cracks in thin-walled components. These parameter settings match the hydration characteristics of UHPC while maintaining production efficiency, making them especially suitable for regular components such as flat panels and L-shaped panels. For hollowed-out or irregularly shaped components, the heating rate should be slowed to 10-15°C/h to ensure uniform temperature across all parts of the component.

2. Constant Temperature Stage: Precise Matching of Humidity and Time

The constant temperature stage is a critical period for UHPC strength development, requiring simultaneous control of the two core parameters: temperature and humidity. The temperature should be maintained at 60-70°C and the relative humidity kept at no less than 90%. The duration should be adjusted according to component thickness and performance requirements: 12-24 hours for regular components, extendable to 24-48 hours for thick, large components or those with high strength requirements. When producing UHPC sculptures for the Shanghai Astronomy Museum, Qinglong adopted a 24-hour curing scheme at a constant 70°C for components thicker than 3 meters, combined with an internal temperature measurement system for real-time monitoring, ensuring the compressive strength of components met design requirements. In addition, steam must be evenly distributed during the constant temperature stage to avoid localized drying that causes surface dusting.

3. Cooling Stage: Slow Cooling for Structural Stability

The key control point in the cooling stage is preventing shrinkage cracks caused by excessive temperature differences. The cooling rate should not exceed 15°C/h, and curing may only end when the temperature difference between the component surface and the ambient environment is less than 20°C. In the Hainan International Convention and Exhibition Center project, considering the higher ambient temperatures of the tropical region, Qinglong adopted a combination of natural cooling and forced ventilation to ensure smooth cooling and prevent damage to components from sudden temperature changes after leaving the curing kiln. For components in important projects, 7 days of natural curing after cooling is also required to further enhance durability.

Steam curing parameters must be comprehensively optimized based on the UHPC mix proportion, component shape, and production environment—there is no one-size-fits-all approach. As a national-level "Specialized, Refined, Distinctive, and Innovative" enterprise with a provincial-level R&D center, Qinglong Group can determine the optimal curing scheme through testing, while using BIM technology in production to simulate the curing process and precisely control temperature and humidity changes. From the Nanning Liyuan Hotel to the Singapore Defence Service Center project, Qinglong's scientific curing techniques safeguard the quality of UHPC components.