New Automatic Titrator TitroLine® 5000 from SI Analytics: For Chemical Additives in Ready-Mixed Concrete Production

Concrete is a construction material obtained by homogeneous mixing of cement, aggregates (sand, gravel, crushed stone), chemical admixtures, mineral admixtures and water. Producers of ready-mixed concrete must specify the maximum chloride content permitted in the admixtures used in concrete production. High chloride content causes corrosion of reinforcement in concrete. According to EN-934-2 standard, this ratio is a maximum of 1000 ppm, or 0.1%. Chloride in concrete production can come from the admixture, as well as from the aggregates and water used.

The standard used in Turkey for the determination of water-soluble chloride content in chemical admixtures is TS EN 480-10. This standard covers the method for detecting water-soluble halogens other than fluorides in admixtures. The total water-soluble halogen content is expressed as chloride content. According to this method, chloride ions are determined in admixture materials through precipitation using silver nitrate solution. Cl - + Ag+ → AgCl

This test is classically conducted using a pH meter, working electrode, reference electrode and burette.

The admixture sample is weighed at 10 ± 1 gram if liquid, or 5 ± 1 gram if powder, diluted with 100 ml water, 5 ml dilute nitric acid is added and titrated with silver nitrate solution. The consumption is recorded. A blank titration is also performed under the same conditions and the consumption is recorded.

If the admixture used contains mutually interfering components or reducing agents:

The admixture sample is weighed at 10 ± 1 gram if liquid, or 5 ± 1 gram if powder, diluted with 100 ml water, 5 ml sodium hydroxide and 10 ml hydrogen peroxide are added. To prevent loss of chloride ions, the pH value must be maintained above 8.5. If necessary, more sodium hydroxide solution should be added. The solution is boiled for 30 minutes with a heated magnetic stirrer and then allowed to cool. Then 10 ml dilute nitric acid is added, the pH value is checked to ensure it is below 5, and if not, more dilute nitric acid is added. Then it is titrated with silver nitrate solution. The consumption is recorded. A blank titration is also performed under the same conditions and the consumption is recorded.

If thiocyanates are present in the admixture used:

The admixture sample is placed in a 500 ml beaker. If the sample is liquid, it is weighed at 10 ± 1 gram, or 5 ± 1 gram if powder, 10 ml hydrogen peroxide is added. A strong exothermic reaction occurs. After the reaction is complete, 10 ml hydrogen peroxide is added again. This procedure is repeated three times. The solution is slowly heated to boiling point, boiled for 2 hours, then cooled to room temperature. The solution is transferred to a beaker containing 250 ml distilled water and then 10 ml dilute nitric acid is added, the pH value is checked to ensure it is below 5, and if not, more dilute nitric acid is added. Then it is titrated with silver nitrate solution. The consumption is recorded. A blank titration is also performed under the same conditions and the consumption is recorded.

V : Silver nitrate solution used in titration, ml

Vo : Silver nitrate solution used in blank titration, ml

n : Normality of silver nitrate solution, mol/l

m : Sample weight, g

This manual titration procedure using a pH meter, burette, working electrode and reference electrode is subject to user error. However, with the TitroLine® 5000 automatic titrator, the same analysis is performed in a much shorter time, with greater precision, and highly reproducible analysis results are obtained.

The motorized piston system on the TitroLine® 5000 automatic titrator allows silver nitrate solution to be introduced into the system. Instead of two electrodes used in the manual system (working electrode and reference electrode), a single combined silver electrode is used for analysis. The magnetic stirrer supplied with the titrator ensures homogeneous mixing of the prepared solution. After blank titration, the silver nitrate consumption found is recorded in the device's memory. Additionally, the normality of the silver nitrate solution used in the analysis and the sample weight values are entered into the device. During analysis, if desired, the titration curve can be monitored in real-time on the device's display. At the end of titration, the chloride content is displayed as a percentage on the device's screen; no separate calculation is required. With a portable memory device connected to the device's USB port, measurement results can be saved as PDF and transferred to a computer.

The TitroLine® 5000 automatic titrator, aside from chloride content determination, is a precise and practical device that can be used for various applications in water, wastewater, environmental analysis and food analysis.