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

Chloride ions are a key harmful component affecting the durability of GRC materials. Excessive content can trigger a series of quality risks and, in severe cases, lead to component failure, threatening building safety. Establishing a full-process chloride ion control system is a core step in ensuring the long-term stable use of GRC products.

I. Core Risk Manifestations of Excessive Chloride Ion Content

The most direct risk of excessive chloride ions is corrosion of the reinforcement materials. Even alkali-resistant glass fibers will suffer surface erosion after long-term exposure to high concentrations of chloride ions, resulting in reduced fiber tensile strength and consequently lower overall load-bearing capacity of GRC components. Qinglong laboratory data shows that when chloride ion content exceeds 0.1%, the fiber strength decay rate can reach more than 20%. For GRC components with steel bar frameworks, chloride ions accelerate steel corrosion, causing volume expansion that leads to surface cracking and spalling of components, and in severe cases structural damage. In addition, chloride ions reduce the freeze-thaw resistance and impermeability of GRC, making components prone to frost-heave damage in severe cold environments. Projects in coastal areas face further aggravated risks due to salt spray — for example, a coastal GRC curtain wall with uncontrolled chloride content showed large-area cracking after only 5 years of use.

II. Main Sources of Chloride Ions and Control Points

Chloride ions mainly originate from raw materials and the production process. Aggregates are one of the main sources — sea sand and quartz sand containing chlorine impurities directly introduce large amounts of chloride ions; using chlorine-containing admixtures can also lead to excessive content; using seawater or chlorine-containing wastewater as production water poses the same risk. Control must run through the entire process. Raw material intake is the first control point: Qinglong tests every batch of aggregates and admixtures for chloride ion content, and substandard materials are strictly prohibited from entering the warehouse. During production, chlorine-free admixtures and clean drinking water are used, and mixing equipment must be cleaned regularly to avoid contamination from residual chloride ions. During transportation and storage, components must be kept away from chlorine-containing chemicals, and coastal projects must take proper moisture-proof and salt-spray-proof measures.

III. Control Standards and Testing Methods for Chloride Ion Content

According to the industry standard Glass Fibre Reinforced Cement (GRC) Decorative Products (JC/T940-2022), the chloride ion content in GRC materials should be ≤0.1% (calculated by the mass of cementitious materials), and important projects require control below 0.06%. Testing must adopt professional methods, most commonly the silver nitrate titration method, which precisely determines chloride ion content through chemical titration. Qinglong's provincial-level R&D center is equipped with dedicated testing equipment, and every batch of products must undergo chloride ion testing to ensure compliance. For large projects, it is recommended to specify chloride ion content indicators and acceptance criteria in the contract. Qinglong can provide third-party testing reports to ensure the data is authentic and traceable.

IV. Qinglong's Full-Process Chloride Ion Control Solution

Qinglong has established a three-level chloride ion control system of “source control – process monitoring – finished product testing.” At the source, low-chlorine raw materials are selected: aggregates use natural quartz sand treated with water washing to remove impurities, with chloride ion content ≤0.02%; chlorine-free high-performance admixtures are chosen, such as polycarboxylate superplasticizers. The production process uses automated metering to avoid human contamination, and mixing water is purified to ensure chloride ion content meets standards. In the finished product stage, in addition to routine testing, chloride ion migration tests are additionally conducted for projects in special environments such as coastal and severe cold regions to ensure the safe use of components. Relying on 28 years of industry experience, Qinglong has successfully applied its chloride ion control technology to domestic and international projects including Hainan Poly Peninsula No.1 and the Singapore National Defence Service Centre, effectively improving product durability.