Application of X-ray principles to quantify sulfur oxidation states in concrete

Abstract

This study introduces a novel mathematical approach rooted in X-ray spectroscopy principles to evaluate the oxidation state of sulfur, which is then applied in concrete and cementitious materials. Unlike previous studies that relied on an empirical quadratic relationship based on the ratios of characteristic X-ray lines (SKα, SKβ, and SKβ') for sulfur oxidation state determination, unique linear relationships between the intensities of the three X-ray lines for each oxidation state and total sulfur were utilized. Rational equations are then derived by combining these linear relationships for each species. Two independent rational calibration curves are constructed using the SKβ/SKα and SKβ'/SKβ ratios for samples containing sulfide-sulfate mixtures, irrespective of total sulfur concentration within the range of 0.3% to 2.0% by weight of concrete. These equations demonstrated interchangeability across three simulated matrices (Portland cement, concrete, and silica) and two sulfide species (pyrrhotite and pyrite). Absolute quantification of sulfide and sulfate species in concrete is achieved by independently measuring total sulfur. Compared to previous quadratic and linear equations, this approach is shown to minimize the difference between the experimental and calculated ratios of the calibration samples. Agreement was also observed between the sulfate ratio calculated through the rational approach and gravimetric analysis for concrete samples.

Keywords:

• Sulfate
• sulfide
• sulfur speciation
• pyrrhotite
• wavelength dispersive x-ray fluorescence

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

This work was performed under the following financial assistance awards 60NANB20D135, 70NANB21H113 and 60NANB23D187 from U.S. Department of Commerce, National Institute of Standards and Technology. The authors acknowledge the undergraduate students and researchers of the Geoenvironmental and the Advanced Cementitious Materials & Composites laboratories of the Department of Civil and Environmental Engineering at UConn for their support, especially to Kira Cuneo, Ethan Beattie, Harley Jeanty and Ryan Soucy.