The Hazard and Detection of Chloride Ion in Concrete

The chloride ion in concrete mainly comes from chloride salt (one of the cement raw materials), sand, water and admixtures. If the chloride ion content exceeds the standard, the steel bars in the concrete will be easily corroded, which will reduce the chemical resistance, wear resistance and strength of the concrete, affect the durability of the concrete, and lead to a decrease in the quality of the concrete.

When it is suspected that concrete components contain chloride ions, the chloride ion content in concrete and its penetration depth should be detected according to the following requirements:

1. If the chloride ion in the concrete is an admixture type, it is only necessary to detect the chloride ion content in the concrete. If it is an extravasation type, it is necessary to detect the chloride ion concentration distribution from the surface to the inside of the concrete, so as to judge the penetration depth.

2. In the detection of chloride ion content in concrete and its penetration depth, the detection units are divided according to the working conditions and concrete quality. The number of samples in each detection unit should be no less than 3. When the uniformity is poor, the detection samples should be increased.

3. The content of chloride ions in concrete can be detected by drilling core, the diameter of the core sample is 100mm and the length is 50~100mm. After crushing the concrete core sample, remove the large particle aggregate, grind it until it passes through a 0.08mm sieve, suck out the metal iron filings in the sample with a magnet, dry it in an oven at 105~110 °C for 2 hours, take it out and put it in a drying dish Cool to room temperature, and then use the silver nitrate titration method or the potassium thiocyanate solution titration method to detect the chloride ion content per unit mass of concrete according to Appendix C, and then convert the chloride ion to the percentage of the cement weight according to the mixing ratio.

4 The concentration distribution or penetration depth of chloride ions in concrete can be detected by core drilling method or layered powder extraction method:

1) Core drilling and slicing method: Drill a core sample with a length of 100~150mm at the sampling and testing position, and then cut the core sample into slices with a thickness of 5~10mm, and measure the chloride ion content of each slice according to Article 3.

2) Layered powder extraction method: Use the powder extraction machine to grind the powder in layers from the surface to the inside, and grind the powder every 1mm, 2mm, 5mm or 10mm, and then measure the chloride ion content of the powder.

3) Take the average value of the measured chloride ion content of several samples in the same layer as the representative value of the chloride ion content at the midpoint of the layer, and draw the chloride ion concentration distribution curve along the depth.

By detecting and judging whether the chloride ion in concrete exceeds the standard, take precautions in advance to avoid damage to the reinforced concrete structure.