How to Steam Cure GRC Components in Low Temperature Environments? — Qinglong Group Winter Construction Technical Guide

Steam curing of GRC components in low-temperature environments is a key technology for ensuring engineering quality, while improper curing may lead to quality problems such as insufficient strength and cracking. Based on its experience with multiple winter projects in northern regions, Qinglong Group has developed a low-temperature steam curing process comprising four stages—preheating, temperature raising, constant temperature, and cooling—ensuring that GRC components can still harden and develop strength normally in environments below 5°C.

The preheating stage must be slow and uniform. After the components, together with their molds, are placed into the curing kiln, the temperature is raised slowly to 20°C at a rate not exceeding 10°C per hour. In a project in Shenyang, Qinglong Group adopted zoned temperature control technology to ensure that the temperature difference between the interior and exterior of large components does not exceed 15°C, avoiding cracks caused by thermal stress. The preheating time is determined by component thickness, with 1 hour of preheating required for every 10mm of thickness to ensure even heat transfer. The key at this stage is to be "slow"—rapid temperature raising must be avoided.

Controlling the rate is crucial during the temperature-raising stage. The temperature is raised to the set temperature (usually 60±5°C) at a rate of 15-20°C per hour. Qinglong Group's intelligent curing kilns are equipped with multi-point temperature sensors to monitor the internal temperature of components in real time. For components thicker than 50mm, stepped temperature raising is applied: first raising the temperature to 40°C and holding for 2 hours, then raising it to 60°C, allowing the heat of hydration to be released in an orderly manner. In the Harbin project, this control kept the temperature difference between the center and surface of components within 20°C, effectively preventing cracking.

The constant-temperature stage ensures sufficient hydration. The constant-temperature duration is determined by component thickness: 20mm thick panels are held for 8 hours, extended by 2 hours for every additional 10mm. In the Changchun project, Qinglong Group determined the optimal constant-temperature duration through testing, enabling the 3-day strength of GRC to reach more than 70% of its 28-day strength. During the constant-temperature period, humidity is kept above 95% to prevent premature moisture evaporation from affecting strength development.

The cooling stage must be controlled slowly. The temperature is lowered at a rate not exceeding 15°C per hour until the temperature difference from the ambient environment is less than 20°C. Cooling too quickly causes the surface to shrink too rapidly, resulting in cracks. Qinglong Group combines natural cooling with forced ventilation to ensure uniform cooling. After curing is complete, the components must continue to cure for 3 days in a 20°C environment to complete the strength stabilization process.