Concrete, as the cornerstone of modern architecture, its durability is directly related to the safety and lifespan of engineering structures. However, among the many "invisible killers" of concrete, chloride ions are undoubtedly the most dangerous one. It is like a latent corrosive agent, once it exceeds the standard, it will silently erode the steel bars inside the concrete, causing corrosion and volume expansion of the steel bars, ultimately leading to concrete cracking, peeling, and even structural damage. This not only brings huge economic losses, but also may endanger life safety. Therefore, strict control of chloride ion content in concrete mixing and curing water is a key link to ensure the long-term stability and durability of concrete structures. This is not only a technical requirement, but also a solemn commitment to engineering quality and public safety.

The impact of chloride ions on the durability of concrete is mainly reflected in the corrosion of steel bars. Concrete itself has a certain alkaline environment, which can form a passive film on the surface of steel bars, thereby protecting them from corrosion. However, when the concentration of chloride ions in concrete reaches a certain threshold, these chloride ions will damage the passive film on the surface of the steel reinforcement, causing it to lose its protective effect. Once the passivation film is damaged, oxygen and moisture will come into direct contact with the steel bars, triggering electrochemical reactions and leading to steel corrosion. After the corrosion of steel bars, their volume will expand by 2-6 times. This expansion force will generate huge tensile stress on the surrounding concrete, ultimately leading to concrete cracking, protective layer peeling, and accelerating the further corrosion of steel bars, forming a vicious cycle. Especially in harsh environments such as humidity and salt spray, the erosion effect of chloride ions will be more significant, and the damage to concrete structures will be more rapid and severe.

These limits are based on extensive scientific research and engineering practice experience, aimed at controlling the amount of chloride ions entering concrete from the source, thereby effectively delaying or avoiding the occurrence of steel corrosion. Strictly adhering to these standards is a fundamental prerequisite for ensuring the safety and durability of concrete structures. In addition, for concrete in special environments, such as marine concrete or structures that have been exposed to high chloride environments for a long time, the requirements for chloride ion control will be more stringent. It may be necessary to use concrete with lower cement water cement ratio, higher density, or special materials that resist chloride ion penetration.

1Silver nitrate titration method (Mohr's method)

This is a classic chemical analysis method that titrates chloride ions in water samples with silver nitrate standard solution, using potassium chromate as an indicator. When the color of the solution changes from yellow to brick red, the titration endpoint is reached. This method is relatively simple to operate, cost-effective, and suitable for routine laboratory testing.

2Ion selective electrode method (ISE method)

This is a fast and sensitive electrochemical analysis method. Measure the potential of chloride ions in water samples using a chloride ion selective electrode, and then quantify it based on the relationship between potential and chloride ion concentration. This method has the advantages of fast response speed, wide measurement range, and strong anti-interference ability, especially suitable for on-site rapid detection and online monitoring, such as the ERUN-SZ-CL620 developed and produced by Yingrun GroupWater quality chloride ion online analyzerIt is based on this principle. It has high sensitivity, rapid signal response, accurate measurement, stable performance, and simple maintenance. It can be used for rapid determination of water-soluble chloride ion content in inorganic materials such as concrete, sand and gravel, and cement.

3Ion chromatography

This is a high-precision and high-efficiency analysis method. Separate chloride ions from other ions in water samples using an ion chromatograph, and then perform detection and quantification. This method has the advantages of high sensitivity, good selectivity, and the ability to analyze multiple ions simultaneously. It is commonly used in arbitration analysis or situations with high requirements for detection results.

4Spectrophotometry

Using chloride ions to react with specific reagents to generate colored substances, the content of chloride ions is determined by measuring the absorbance of the colored substances. This method is relatively simple to operate, but may be subject to interference from other ions.

The selection of appropriate detection methods should comprehensively consider factors such as detection accuracy requirements, detection speed, cost, and on-site conditions. For daily quality control, the ion selective electrode method has been widely used due to its fast and convenient characteristics; For scientific research or arbitration, high-precision methods such as ion chromatography are more suitable.

2Raw material control

In addition to mixing water, other raw materials for concrete, such as sand, stone, cement, admixtures, etc., may also introduce chloride ions. Therefore, all raw materials should undergo chloride ion content testing, especially sea sand, which usually has a high chloride ion content and must undergo desalination treatment and pass testing before use. Strictly controlling the quality of raw materials is an important defense line for controlling the total chloride ion content of concrete.

3Selection of additives

Some additives may contain chloride ions, such as early strength agents, antifreeze agents, etc. When selecting additives, priority should be given to those that do not contain chlorine or have low chlorine content, and the product manual should be consulted to understand their chloride ion content. If necessary, chloride ion testing should be conducted on additives.

4Maintenance water management

The quality of maintenance water is equally important after pouring concrete. If the chloride ion content in the maintenance water is too high, chloride ions will penetrate into the interior of the concrete and cause corrosion to the steel bars. Therefore, maintenance water should also comply with relevant standards and avoid using seawater or water with high salt content for maintenance.

5Process monitoring and recording

In the process of concrete production and construction, a comprehensive monitoring system for chloride ion content should be established, and regular sampling and testing of mixing water, raw materials, and finished concrete should be carried out, with detailed records kept. Once the chloride ion content exceeds the standard, corrective measures should be taken immediately, the cause should be traced and dealt with.