Chloride Binding of Cementitious Materials Exposed to Sodium Chloride Using X-Ray Fluorescence

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Title: Chloride Binding of Cementitious Materials Exposed to Sodium Chloride Using X-Ray Fluorescence

Author(s): Marisol Tsui-Chang, Chunyu Qiao, Luca Montanari, Prannoy Suraneni, and W. Jason Weiss

Publication: Materials Journal

Volume: 116

Issue: 5

Appears on pages(s): 173-179

Keywords: chloride binding; sodium chloride; titration; X-ray fluorescence

Date: 9/1/2019

Abstract:
Chloride binding is typically studied by exposing a certain quantity of powdered hydrated cement paste to chloride salt solutions, and by comparing the differences in final and initial chloride concentrations after equilibrium is achieved. Chloride concentrations are generally determined by titrating the solutions using manual or automatic titration. Chloride-binding isotherms are obtained by repeating this process for a range of chloride concentrations. While titration produces accurate results, the process can be labor-and time-intensive. In this work, chloride-binding isotherms are obtained by testing chloride solutions using a calibrated X-ray fluorescence (XRF) device and were evaluated by comparison with titration. Testing was performed on a cement paste with a water-cement ratio of 0.42, exposed to sodium chloride salt solutions ranging from 0 to 5 mol/L at 23°C. Chloride concentrations determined by titration and XRF were similar (differences averaged approximately 3% for the various solutions tested); however, chloride-binding isotherms obtained using the two methods showed significant differences (differences averaged approximately 49% for different chloride binding contents) due to assumptions regarding solution density. When the solution density was accurately measured using a pycnometer, chloride-binding isotherms obtained using titration and XRF were very similar, with differences averaging less than 6%. The importance of accurate density measurements for such calculations is demonstrated mathematically. While these results are preliminary and need to be verified for other salt solutions and cementitious paste compositions, they suggest that the use of XRF may provide a promising alternative to determine chloride-binding isotherms in cementitious materials.