What Risks Are Caused by Excessive Chloride Ion Content in GRC Materials? How to Control It?

Chloride ion content is a key indicator in GRC material quality control, and exceeding the limit will cause serious durability problems. Based on 28 years of quality control experience, Qinglong Group believes that controlling chloride ion content in GRC not only relates to the material's own lifespan but also directly affects building structural safety. The following is a systematic analysis of the hazards of excessive chloride ion content and the corresponding control measures.

Excessive chloride ion content in GRC materials poses a risk of steel reinforcement corrosion. Although GRC is mainly reinforced with glass fibres, some special components may be fitted with steel reinforcement cages. When chloride ions penetrate to the steel surface and reach a critical concentration, they destroy the passivation film and trigger electrochemical corrosion. Qinglong Group's quality control system explicitly stipulates that the water-soluble chloride ion content in GRC must not exceed 0.1% of the mass of cementitious materials—a requirement stricter than the national standard—which ensures the long-term safety of components.

Chloride ions also aggravate freeze-thaw damage in GRC. During freeze-thaw cycles, chloride ion solutions have a lower freezing point, which intensifies expansion pressure and causes microcracks to propagate. In northern China projects in which Qinglong Group participated, such as a municipal engineering project in Northeast China, we ensured the durability of GRC components in severe cold climates through strict control of chloride ion content. Test data show that components with chloride ion content controlled below 0.06% retained a relative dynamic elastic modulus of over 90% after 300 freeze-thaw cycles.

Controlling chloride ion content must start at the source of raw materials. Qinglong Group has established a strict supplier audit system to ensure that raw materials such as sand, water and admixtures meet chloride ion content requirements. In particular, regarding the use of sea sand, the company explicitly prohibits the use of untreated desalinated sea sand, eliminating the introduction of chlorides at the source. In the Shenzhen Pingshan High-tech Zone Comprehensive Service Center project, this strict raw material control system provided a guarantee for the quality of the 30,000-square-metre GRC curtain wall.

Quality control in the production process is equally important. Qinglong Group's production bases are equipped with rapid chloride ion testing equipment, and sampling tests are conducted on every batch of incoming raw materials and outgoing products. Meanwhile, by optimising the mix proportion and incorporating mineral admixtures, the pore structure can be refined and the chloride ion diffusion coefficient in GRC reduced. Test results show that, through scientific mix design, the chloride ion diffusion coefficient can be controlled below 2×10⁻¹²m²/s, significantly improving the durability of GRC.