How to Set Steam Curing Parameters for Precast UHPC Components?

The steam curing parameter settings for precast UHPC components are the core technology for ensuring material strength development and microstructure optimization, directly affecting the early strength and long-term durability of products. Based on 28 years of steam curing practice, Qinglong Group believes that the curing parameters for quality UHPC should be controlled within the ranges of heating rate ≤15°C/h, constant temperature of 60-80°C, constant temperature duration of 24-48 hours, and cooling rate ≤20°C/h, with relative humidity maintained at ≥95%. This scientific curing regime enables UHPC to reach 70%-80% of its 28-day strength within 3 days, while avoiding micro defects caused by over-curing or under-curing, providing reliable assurance for component performance.

The heating stage requires smooth control to avoid thermal stress cracks. In the Nanning Wuxiang China Resources MixC One project, Qinglong Group adopted stepped heating: room temperature to 40°C in 2 hours, 40-60°C in 2 hours, and 60-80°C in 1 hour, for a total heating time of 5 hours. This control keeps the temperature difference between the interior and exterior of components at ≤15°C, effectively preventing cracks. For mass components thicker than 100mm, the heating rate should be reduced to 10°C/h to ensure uniform temperature. Heating too quickly causes the surface to harden too fast and internal hydration to be insufficient, increasing the strength dispersion coefficient.

The constant temperature stage is key to strength development. Temperatures of 60-80°C promote rapid formation of C-S-H gel, and the constant temperature duration is determined by component thickness: components ≤30mm thick are cured for 24 hours, 30-60mm for 36 hours, and >60mm for 48 hours. In the roofing project of the Hainan International Convention and Exhibition Center, Qinglong Group applied 70°C constant temperature curing for 24 hours to 20mm thick wave panels, achieving a 3-day compressive strength of 100MPa, exceeding standard requirements. Humidity control is important: saturated steam is used to prevent water loss from components and ensure sufficient hydration reactions.

The cooling stage must proceed slowly to prevent cold shrinkage cracks. The cooling rate is controlled at ≤20°C/h, taking about 2 hours to drop from 80°C to 40°C, with natural cooling below 40°C. Through intelligent curing kilns, Qinglong Group keeps temperature fluctuation within ≤±2°C, ensuring curing uniformity. After curing, the moisture content of components is controlled at 6%-8% to avoid excessive drying shrinkage. This refined curing regime delivers optimal UHPC performance.