Chloride effect on sulfate attack in hydrated Portland-limestone cement assessed by 29Si NMR spectroscopy and thermal analysis

0575568 - ÚTAM 2025 RIV NL eng C - Conference Paper (international conference)
Sotiriadis, Konstantinos - Mazur, A. - Tolstoy, P. M. - Frankeová, Dita
Chloride effect on sulfate attack in hydrated Portland-limestone cement assessed by 29Si NMR spectroscopy and thermal analysis.
Materials Today: Proceedings. Amsterdam: Elsevier, 2023. E-ISSN 2214-7853.
[International congress on materials and structural stability /4./. Rabat (MA), 08.03.2023-10.03.2023]
R&D Projects: GA ČR(CZ) GC21-35772J
Institutional support: RVO:68378297
Keywords : limestone cements * sulfates * chlorides * thaumasite * NMR spectroscopy * thermal analysis
OECD category: Materials engineering
https://doi.org/10.1016/j.matpr.2023.06.185

Structural alterations in the C-S-H phase of hydrated Portland-limestone cements, caused by magnesium sulfate attack, were quantitatively assessed using 29Si MAS NMR spectroscopy, considering the presence of sodium chloride in the corrosive medium and the limestone content in cement. Quantitative information about crystalline deterioration products (ettringite, thaumasite, gypsum, brucite) was retrieved from thermogravimetric analysis. Scanning electron microscopy combined with elemental analysis indicated their accumulation areas. Formation of cross-linked silicate chains and reduction of bridging/pairing SiO4 tetrahedra in C-S-H was noted. The presence of chlorides decreased cross-linking of SiO4 tetrahedra and reduced gypsum formation and Ca depletion from the matrix. Precipitation of brucite at the edge of the specimens possibly inhibited the promotion of the attack process. Chlorides penetrated deeper into the matrix compared to sulfates. Increasing limestone content in cement led to a higher mean chain length of cross-linked chains and AlO4/SiO4 ratio in the sulfate-bearing environment. The extent of C-S-H degradation in the cement pastes with the highest limestone content was independent of the exposure conditions. Cement with approx. 12% limestone content can be considered of equal performance to ordinary Portland cement in severe sulfate–chloride solutions.
Permanent Link: https://hdl.handle.net/11104/0345328