How Should Reinforcement Cover Thickness in GRC Be Controlled? Reinforcement Protection Technical Specifications and Practice

The thickness of the rebar cover in GRC directly affects the risk of reinforcement corrosion and the service life of components. Properly controlling cover thickness is a key technical requirement for ensuring structural safety. Scientific control methods must combine component type, service environment, and construction techniques—this is also one of the core control points in Qinglong's GRC production and installation.

1. Core Control Standards for Rebar Cover Thickness

According to the industry standard Technical Standard for Building Application of Glass Fiber Reinforced Cement (GRC) (JGJ/T423-2018), the rebar cover thickness in GRC must be determined based on component type and environmental class. For ordinary indoor components, cover thickness must be ≥15mm; for components in general outdoor environments, ≥20mm; for components in harsh environments such as coastal areas with high salt spray or industrial pollution, ≥25mm. Qinglong has established stricter corporate standards for different projects, generally increasing the cover thickness of outdoor components to 22-28mm to ensure durability. For thin-walled GRC components such as decorative moldings, the total component thickness must be controlled while maintaining the required cover thickness. Qinglong achieves a balance between the two by optimizing rebar layout and cross-section design; for example, even in a 100mm-thick decorative molding, the rebar cover can still reach 20mm.

2. Key Factors Affecting Cover Thickness Control

Mold precision is the fundamental guarantee. Deviation of rebar positioning devices inside the mold directly leads to uneven cover thickness; Qinglong uses high-precision steel molds and dedicated positioning bars to ensure rebar position deviation is ≤±2mm. During production, excessive vibration can easily cause rebars to sink, making the bottom cover too thin and the top too thick; Qinglong adopts a high-frequency, low-amplitude vibration process to control vibration time and intensity. Excessively high rebar density increases the difficulty of controlling cover thickness, so rebar spacing and diameter must be optimized. In the production of large GRC components, Qinglong uses BIM technology to simulate rebar layouts and avoid congested areas in advance. In addition, overly large aggregate particle size in raw materials can easily lead to locally insufficient cover; quartz sand with a particle size ≤1.2mm must be selected, and Qinglong strictly controls aggregate gradation to ensure cover uniformity.

3. Control Processes and Inspection Methods for Rebar Cover Thickness

During the production stage, a three-step control method of "position–fix–recheck" is adopted. Dedicated spacers, made of a material consistent with the GRC matrix to avoid electrochemical corrosion, are installed when fabricating the rebar cage, with spacer spacing ≤500mm. After the rebar cage is placed into the mold, dedicated clamps are used to secure it and prevent displacement. Before pouring, cover thickness is rechecked with rulers and an ultrasonic testing instrument; any non-conforming areas must be readjusted. Qinglong has introduced automated rebar positioning equipment to improve positioning accuracy and efficiency. For finished product inspection, a rebar locator is used to sample-test each batch of components, ensuring a cover thickness pass rate of ≥95%. After installation, destructive testing is performed on key areas to verify the actual thickness. For example, in the GRC curtain wall project of Shenzhen Longhua Xiangshan Science and Technology Park, Qinglong's rigorous testing ensured that all rebar cover thicknesses met the standards.

4. Qinglong's Optimized Protection Solutions for Rebar Cover

For projects in harsh environments, Qinglong adopts a dual protection approach of "thicker cover + anti-corrosion treatment": on coastal projects, rebar cover thickness is increased to 25-30mm, and rebars are further treated with epoxy coating to reduce corrosion risk. For irregular, complex components, flexible positioning technology is used to ensure uniform cover thickness at curved sections; for example, for the double-curved GRC exterior wall panels of the Guangxi New Media Center, customized positioning fixtures enabled precise control of rebar cover on complex curved surfaces. A cover thickness traceability system has been established, with rebar layout drawings, positioning inspection data, and finished product inspection reports recorded for each batch of components to ensure quality traceability. Thanks to this well-developed control system, Qinglong GRC components in outdoor projects such as the Changying Global 100 Fantasy Park in Hainan have shown no obvious rebar corrosion after many years of use, ensuring structural safety and stability.