Abstract

Sulfate attack on cement matrix is still a "confused world" especially when magnesium sulfate (MgSO4) is the sulfate source. Accurate assessment of sulfate attack is essential for evaluating the structural integrity and durability of concrete in relevant environments. This study presents a portable fiber-optic Raman probe approach with 125 μm spatial resolution, designed for depth-resolved sulfate ingress monitoring in tricalcium silicate (C₃S, Alite) pastes. The probe is also used to evaluate the effectiveness of surface carbonation in mitigating sulfate attack. The results demonstrate a strong correlation between sulfate penetration depth and Raman spectral intensity ratios of sulfate-related vibrational modes to the hydroxyl bending mode at 356 cm⁻¹. In non-carbonated C3S paste specimens, sulfate ingress reached a depth of 1.0–1.2 mm after seven months of exposure to 5 % MgSO4 solution, confirmed by Raman mapping and SEM-EDS sulfur distribution analysis. In contrast, carbonation-treated specimens exhibited significantly reduced sulfate penetration: after 4 h of carbonation treatment, sulfate ingress was limited to 0.4 mm, while 8 h of carbonation resulted in nearly complete suppression of sulfate ingress. Raman spectroscopy further revealed that carbonation treatment forms a protective CaCO3 layer, evidenced by an enhanced 1083 cm⁻¹ carbonate peak, which prevents sulfate attack by impeding ion diffusion. SEM-EDS analysis corroborated the Raman findings, showing a dense 30 μm carbonation layer after 8 h of CO2 exposure. Elemental sulfur mapping confirmed that carbonation effectively mitigates sulfate ingress, aligning with Raman intensity ratio trends. Overall, these results validate the effectiveness of the fiber-optic Raman probe for sulfate attack depth assessment and demonstrate that carbonation treatment significantly enhances the sulfate resistance of C3S paste.

Department(s)

Electrical and Computer Engineering

Second Department

Civil, Architectural and Environmental Engineering

Publication Status

Full Text Access

Keywords and Phrases

Carbonation treatment; Durability; Fiber-optic Raman probe; Magnesium sulfate attack; Tricalcium silicate (C3S)

International Standard Serial Number (ISSN)

0950-0618

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2025 Elsevier, All rights reserved.

Publication Date

26 Sep 2025

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