How to Set Steam Curing Parameters for Precast UHPC Components?

The steam curing regime of precast UHPC components is a key process step in achieving ultra-high performance. It is by no means simple "heating," but rather a systematic engineering effort involving precise control of the "heating rate, constant temperature and duration, and cooling rate." Through extensive testing in its CNAS-accredited laboratory and the accumulation of project data, Qinglong Group has developed a scientific, replicable standardized steam curing parameter system designed to maximize the material potential of UHPC while preventing cracking caused by thermal stress.

The core of the steam curing regime is a stepped temperature control curve. Taking Qinglong's standard process as an example: after the component is cast, a resting stage is carried out first (at room temperature, 2-4 hours), allowing the UHPC to gain preliminary setting strength sufficient to resist the stresses generated by subsequent heating. Then comes the heating stage, in which the heating rate is strictly controlled within 15-20°C per hour, slowly and uniformly raising the kiln temperature to the target constant temperature (typically 70°C ± 5°C or 90°C ± 5°C). If the temperature rises too quickly at this stage, the vaporization and expansion rate of internal moisture will exceed the venting capacity of the paste's pores, easily causing surface blistering or cracking of the component.

The constant temperature stage is the core period for strength development. The temperature setting depends on the design goals of the cementitious system: medium-temperature curing at around 70°C focuses on balancing performance development with energy consumption, with a constant temperature duration generally of 12-24 hours; high-temperature curing at around 90°C can more fully activate the pozzolanic activity of silica fume and promote a highly densified matrix, allowing the constant temperature duration to be shortened to 8-12 hours. Qinglong adjusts the constant temperature duration based on the component's thickness and mix proportion to ensure that the core also achieves full hydration. The final cooling stage is equally critical: the cooling rate must be controlled within 20-25°C per hour, and components may only leave the kiln once the temperature difference between the kiln interior and the outside is less than 30°C, in order to avoid shrinkage cracks caused by sudden cooling. This rigorous process is what guarantees the stable and outstanding performance of Qinglong UHPC.