Steam Curing Parameter Optimization for Precast UHPC Components: A Guide to Strength Enhancement and Performance Assurance

Steam curing is a critical step in the production of precast UHPC components, and scientifically set parameters directly determine the components' strength development, microstructural density, and long-term durability. Drawing on 28 years of UHPC/GRC/GRG/GRP production experience and practices from thousands of projects, Qinglong Group has developed steam curing solutions suited to different scenarios, and its core technologies have been incorporated into the formulation of the industry standard General Technical Conditions for Non-Load-Bearing Ultra-High Performance Concrete (UHPC) Components.

I. Scientific Logic for Setting Core Steam Curing Parameters

The high strength of UHPC derives from a low water-binder ratio (0.16-0.22) and full hydration of active powders. Steam curing must follow the principle of "gentle heating, sufficient constant-temperature holding, and slow cooling" to prevent internal cracking caused by thermal stress. Verified through orthogonal experiments by Qinglong Group, the baseline curing parameters for conventional precast UHPC components are: heating rate ≤15°C/h, constant temperature 50-60°C, holding time 12-18h, cooling rate ≤10°C/h, and ambient relative humidity ≥90%. This parameter combination enables the 7-day compressive strength of components to reach over 85% of the design value and the 28-day strength to meet the industry standard of ≥150MPa. For example, in the Yangshengtang Pharmaceutical Hangzhou Industrial Park project, the UHPC exterior wall panels produced by Qinglong with these baseline parameters achieved a 100% strength compliance rate.

II. Differentiated Adjustment of Curing Parameters for Different Component Types

For thin-walled UHPC components (thickness ≤15mm), the heating rate must be reduced to ≤10°C/h and the constant temperature controlled at 45-55°C to prevent rapid surface water loss caused by high temperatures. In the colored hollow carved panel project for the Liyuan Hotel in Nanning, Qinglong reduced the surface cracking rate of components to below 0.3% through this adjustment. For large, thick components (thickness ≥50mm), the holding time must be extended to 24-36h with a segmented holding mode (first holding at 40°C for 6h, then raising to 60°C for 20h) to ensure full internal hydration. The 12㎡ extra-large UHPC wood-grain translucent panels at Century Plaza on Nanjing East Road for Shanghai New World achieved a core-to-surface strength difference of ≤5MPa precisely through this solution.

III. Key Control Points and Technological Innovations in Steam Curing

During the heating stage, the rate must be strictly controlled. Qinglong employs an intelligent temperature control system for real-time monitoring, achieving temperature uniformity of ≤±3°C through zoned air supply via steam pipes to prevent localized overheating. Humidity control is especially important during the constant-temperature stage, as a relative humidity below 90% causes surface sanding on UHPC. Qinglong innovatively adopted a "steam + atomization" dual moisture-retention technology, stabilizing the curing environment humidity above 95% and significantly improving the surface finish of components. Components may only leave the curing chamber when the temperature difference between the component core and the ambient environment is ≤20°C. In the Yirui Biotech Building project in Shenzhen, Qinglong effectively reduced the impact of thermal stress on components through a gradient cooling scheme (a 5°C reduction every 2h).

IV. Adaptation of Curing Parameters for Special Scenarios

When producing in low-temperature environments (ambient temperature ≤5°C), pre-curing (holding at 20°C for 4h) must be performed before starting steam curing, with the heating rate further reduced to ≤8°C/h. For example, during winter construction of the Ouargla hotel project in Algeria, Qinglong ensured that component strength development was unaffected by low temperatures through this adjustment. For UHPC components with decorative surface layers, the constant temperature must be lowered to 45-50°C to prevent pigment discoloration caused by high temperatures. In the Shanghai Astronomy Museum public art sculpture project, Qinglong achieved 98% color consistency of components through this optimization.

Optimizing steam curing parameters requires comprehensive consideration of component type, thickness, environmental conditions, and performance requirements. As a nationally recognized Specialized, Refined, Distinctive, and Innovative enterprise, Qinglong Group has a provincial-level R&D center and 58 related patents, enabling it to provide customers with customized curing solutions. Leveraging its full-chain service capabilities, Qinglong maintains control throughout the entire process—from raw material proportioning and mold design to curing operations—ensuring that every precast UHPC component delivers outstanding strength and durability, providing reliable material assurance for construction projects.