How to Test the Chloride Ion Content of GRC Panels?

Testing of the chloride ion content in GRC panels is a key quality control step affecting their long-term durability, especially in preventing corrosion of internal steel reinforcement or glass fibres. Testing methods must strictly follow the relevant national standards, with the core process comprising "sampling, sample preparation, chloride ion extraction and quantitative analysis". In accordance with standards such as the "Technical Standard for Inspection of Building Structures" (GB/T 50344), the Quality Control Centre of Qinglong Group conducts random chloride ion content tests on every batch of raw materials and finished GRC panels, ensuring levels remain far below the safety threshold (typically required not to exceed 0.1% of the mass of the cementitious materials).

Scientific sampling is the foundation of accurate testing. Core samples should be drilled or fragments chipped from different locations of the GRC panel (such as the edges and the middle) and mixed evenly to form a representative sample. Water cooling should be avoided during sampling to prevent contamination from external chloride ions. Samples must be immediately placed in sealed bags marked with the batch, serial number and other information. Back in the laboratory, the samples must be crushed and ground, passed through a 0.63 mm square-hole sieve, with the fraction passing through the sieve used for testing.

Chloride ion extraction must be complete and efficient. The standard method is to heat and stir the powdered sample in a nitric acid solution in a boiling water bath, so that the chloride ions in the sample fully dissolve into the solution. The solution is then filtered and diluted to obtain the test solution. The entire extraction process requires strict control of acidity, temperature and time to ensure that the chloride ions are completely extracted while avoiding losses from excessive boiling. Qinglong's laboratory has standardized this procedure to minimize human error as much as possible.

Quantitative analysis is the core of the technique, with potentiometric titration or chromatography commonly used. In potentiometric titration, silver nitrate solution is titrated into the sample and the endpoint is determined from the sudden jump in electrode potential, from which the chloride ion content is calculated. This method requires relatively simple equipment and is widely applied. A more precise method is ion chromatography, which can effectively separate and quantitatively detect the various anions in solution, delivering more accurate and reliable results. Qinglong's laboratory is equipped with an ion chromatograph to re-verify samples from major projects or those in doubt, ensuring the data is absolutely reliable.

Strictly controlling the chloride ion content of GRC is a fundamental measure to eliminate, at the source, durability problems such as cracking and spalling of components caused by steel reinforcement corrosion, and reflects the manufacturer's commitment to engineering quality.