Influence of the Ca/Si ratio of the C–S–H phase on the interaction with sulfate ions and its impact on the ettringite crystallization pressure

Journal Article · Sun Mar 15 04:00:00 EDT 2015 · Cement and Concrete Research

DOI:https://doi.org/10.1016/J.CEMCONRES.2014.12.002· OSTI ID:22475494

Kunther, Wolfgang ^[1]; Lothenbach, Barbara ^[2]; Skibsted, Jørgen ^[1]

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1. Instrument Centre for Solid-State NMR Spectroscopy, Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), Aarhus University, DK-8000 Aarhus C (Denmark)
2. Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Concrete/Construction Chemistry, Überlandstrasse 129, 8600 Dübendorf (Switzerland)

The effect of the Ca/Si ratio of the calcium–silicate–hydrate (C–S–H) phase on the interaction with sulfate ions is investigated for C–S–H phases (Ca/Si = 0.83, 1.25, 1.50) and mortar samples of blended Portland cements. It is shown that leaching of calcium from C–S–H and portlandite affects the composition of the pore solution and contributes to the developing crystallization pressure of ettringite. Sulfate profiles show that sulfate binding before cracking is similar for different Ca/Si ratios whereas the highest expansion rates are observed for the mortars with the highest Ca/Si ratios. After leaching in sulfate solutions, the C–S–H samples have been characterized by {sup 29}Si MAS NMR, thermogravimetric analysis, and elemental solution analysis. Generally, the exposure to sulfate solutions results in decalcification of the C–S–H, which increases with decreasing Ca/Si ratio. The data are in good agreement with thermodynamic modeling, indicating that equilibrium is almost achieved in the leached systems. Finally, the expansion of mortar samples exposed to sulfate solutions was much less at lower Ca/Si ratios of the cement blends. This reduced expansion can be related to the decrease of the supersaturation of the pore solution with respect to ettringite at lower Ca/Si ratios of the C–S–H and in the absence of portlandite.

• OSTI ID: 22475494
• Journal Information: Cement and Concrete Research, Journal Name: Cement and Concrete Research Vol. 69; ISSN 0008-8846; ISSN CCNRAI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CALCIUM SULFATES
CRYSTALLIZATION
HYDRATES
LEACHING
MOLECULAR IONS
MORTARS
MULTI-ELEMENT ANALYSIS
NMR SPECTRA
PORTLAND CEMENT
SILICATES
SILICON
SILICON 29
SUPERSATURATION
THERMAL GRAVIMETRIC ANALYSIS