Calcium, magnesium, iron and aluminum in hydraulic cement samples

Significance of the topic

Accurate determination of major oxide components in hydraulic cement is critical for ensuring material performance, durability and compliance with industry standards. Calcium, magnesium, iron and aluminum oxides influence setting time, mechanical strength and chemical resistance. Reliable analytical techniques are therefore essential for quality control in cement production and research.

Objectives and Study Overview

This study presents a sequential photometric titration method to quantify Ca, Mg, Fe and Al in digested Portland cement samples. Following acid digestion under controlled conditions, each element is selectively titrated using EDTA or bismuth nitrate titrants monitored by an Optrode photometric sensor. The protocol aims to streamline analysis, reduce reagent consumption and avoid high‐temperature steps.

Methodology and Instrumentation

Sample digestion involves reacting 4 g of cement with ammonium chloride, concentrated HCl and HNO₃, followed by heating at 200 °C for one hour and filtration to remove silicates. Photometric titrations at 610 nm are performed under specific pH conditions with tailored indicators:

• Calcium: pH 12, murexide indicator, EDTA titrant (0.1 M)
• Magnesium: pH 10, methylthymol blue indicator, EDTA titrant (0.1 M)
• Iron: pH 1.5–2, sulfosalicylic acid indicator, EDTA titrant (0.025 M)
• Aluminum: back‐titration at pH 3.5, xylenol orange indicator, Bi(NO₃)₃ titrant (0.05 M)

The instrumentation comprises a Metrohm titrator with MET mode, 2 mL and 5 mL burettes, an Optrode photometric electrode and a pH electrode.

Main Results and Discussion

Distinct titration curves were obtained for each element, enabling precise determination of equivalence points. Use of two EDTA concentrations improved endpoint resolution for Fe vs Ca/Mg. Bismuth nitrate proved an effective back‐titrant for Al, avoiding the need for boiling and offering stable complex formation at pH 3.5. Repeatability of titrant consumption demonstrated method robustness.

Benefits and Practical Applications

The proposed photometric titration approach offers multiple advantages:

• Eliminates high‐temperature steps for aluminum analysis
• Utilizes cost‐effective EDTA instead of specialized chelators
• Reduces reagent volumes and associated waste
• Compatible with automation and routine QA/QC workflows in cement laboratories

Future Trends and Potential Applications

Further development may focus on automation through flow injection analysis, integration of miniaturized photometric sensors for on‐site monitoring, and coupling with spectroscopic techniques for multi‐element profiling. Adaptation to other construction materials, such as slag or fly ash, could extend method utility. Digital integration of titration data with laboratory information management systems aligns with Industry 4.0 objectives.

Conclusion

The described photometric titration protocols provide a rapid, accurate and reproducible route to determine key oxides in hydraulic cement. By leveraging EDTA and bismuth nitrate titrants under controlled photometric detection, the method meets standard requirements while enhancing laboratory efficiency.

References

• ISO 29581-1: Cement — Test methods — Part 1: Analysis by wet chemistry
• EN 196-2: Methods of testing cement — Part 2: Chemical analysis of cement