How to Control the Rebar Cover Thickness in GRC?

In GRC, the steel reinforcement cover thickness must be strictly controlled at ≥25mm (as required by standards). This is achieved through four key steps: design optimization, mold positioning, construction control, and quality inspection. With high-precision molds and standardized processes, Qinglong keeps cover thickness deviation within ≤±2mm, ensuring the reinforcement does not corrode and component strength does not degrade, making it suitable for reinforced GRC load-bearing components.

1. Design Optimization: Defining Cover Thickness and Construction Details

The design phase lays the foundation for cover control. Determine thickness by scenario: ≥25mm for general environments, ≥30mm for coastal corrosive environments, and ≥35mm for high-temperature environments; Qinglong uses a 30mm cover thickness for reinforced GRC in coastal projects. Optimize reinforcement layout: avoid overly concentrated bars with a minimum spacing of ≥30mm to ensure the concrete fully encapsulates them; Qinglong optimizes bar arrangement through BIM modeling with no dense clustering. Set up protective construction details: exposed bar ends are treated with anti-corrosion coatings; Qinglong applies epoxy zinc-rich primer to the bar ends of reinforced components to enhance corrosion resistance. Account for construction tolerances: a ±2mm construction deviation is reserved at the design stage to avoid insufficient actual thickness; Qinglong's design documents clearly specify the allowable cover deviation range.

2. Molds and Positioning: Precisely Controlling Cover Thickness

Mold precision and positioning measures are the core of control. Mold precision control: steel mold dimensional deviation ≤±1mm ensures uniform wall thickness after component forming; Qinglong's CNC-machined molds achieve ±0.5mm precision. Positioning fixtures: high-strength plastic or concrete spacers at spacing ≤500mm fix the reinforcement in place; Qinglong's spacers have strength ≥ that of the GRC matrix to prevent crushing under pressure. Reinforcement cage fixation: cages are secured with tying bands or welding to prevent displacement during pouring; Qinglong's reinforcement cages are firmly tied with no loosening. Reserved inspection access: observation ports on the molds make it easy to check cover thickness; Qinglong assigns dedicated personnel to verify through the observation ports during production, ensuring accurate positioning.

3. Construction Control and Quality Inspection: Ensuring Final Compliance

Construction process control and subsequent inspection verify cover thickness. Pouring process control: layered pouring (each layer ≤300mm thick) is used to prevent poker vibrators from striking the reinforcement; Qinglong uses immersion vibrators at a frequency ≥12,000 cycles/min with no bar displacement. Curing quality control: insufficient curing causes GRC shrinkage cracking and compromises cover integrity; Qinglong uses constant temperature and humidity curing to prevent cracks in the cover. Inspection method: ultrasonic thickness gauges are used, with ≥3 test points per component; Qinglong achieves 100% inspection coverage. Rectification measures: where cover thickness is found insufficient (<22mm), high-pressure grouting reinforcement is applied; to date, Qinglong has never had a batch of products requiring rectification.