What Risks Can Excessive Chloride Ion Content in GRC Materials Cause? How to Control It?

Controlling chloride ion content in GRC materials is a lifeline for structural safety and durability. Qinglong Group regards chloride ions as the "invisible killer" of GRC—excessive content can trigger a triple risk of steel reinforcement corrosion, fiber degradation, and matrix damage. According to GB/T 50476 (Standard for Durability Design of Concrete Structures), Qinglong's internal control standards are stricter than the national standard, requiring the water-soluble chloride ion content in GRC to be no more than 0.06% of the cementitious material mass. In the marine environment project of the Hainan International Convention and Exhibition Center, we ensured that 120,000 square meters of GRC roofing remained free of corrosion damage for ten years through strict chloride control, demonstrating the importance of scientific control.

The Mechanism and Hazards of Chloride-Induced Steel Corrosion

When GRC contains corrosion-resistant steel reinforcement or steel embedded parts, chloride ions destroy the passivation film and trigger electrochemical corrosion. Qinglong research shows that once chloride ion content exceeds the critical value (typically 0.05%–0.08%), the corrosion risk increases sharply. Corrosion products expand 3 to 7 times in volume, generating enormous internal stress that causes cracking and spalling of the GRC cover layer. In coastal areas, this risk is especially prominent, so chloride ion content must be strictly controlled.

The Corrosive Effect of Chloride Ions on Glass Fibers

Chloride ions react with cement hydration products to form Friedel's salt while releasing hydroxide ions, locally raising the pH value and intensifying alkali attack on glass fibers. Qinglong laboratory accelerated tests show that GRC specimens with excessive chloride ion content retained less than 70% of fiber strength after one year. This not only affects long-term mechanical performance but may also cause sudden component failure due to fiber embrittlement.

A Comprehensive and Systematic Chloride Control System

Qinglong has established a full-process chloride control system from raw materials to finished products: strict control of chloride ion content in raw materials such as sand, aggregates, and water; a strict ban on sea sand; selection of low-chloride admixtures; and regular cleaning of production equipment to prevent chloride accumulation. In the Wuhan Han Show Theatre project, we even applied deionization treatment to the mixing water to ensure chloride ion content was absolutely safe.

Testing and Monitoring of Chloride Ion Content

Qinglong laboratories are equipped with professional rapid chloride ion analyzers to conduct sampling tests on every batch of raw materials and finished products. We have also built a database of chloride ion content in raw materials, with focused monitoring of high-risk materials. For major projects, we additionally embed chloride ion detection sensors in components to achieve long-term monitoring. This all-round control system ensures the long-term safety of GRC components.