On the relevance of volume increase for the length changes of mortar bars in sulfate solutions

Journal Article · Mon Apr 01 04:00:00 EDT 2013 · Cement and Concrete Research

DOI:https://doi.org/10.1016/J.CEMCONRES.2013.01.002· OSTI ID:22323129

Kunther, Wolfgang ^[1]; Lothenbach, Barbara ^[1]; Scrivener, Karen L. ^[2]

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1. Empa, Laboratory for Concrete and Construction Chemistry, Überlandstrasse 129, CH-8600 Dübendorf (Switzerland)
2. EPFL, Laboratory of Construction Materials, CH-1015 Lausanne (Switzerland)

The ingress of sulfate ions into cementitious materials leads to the formation of ettringite, gypsum and other phases. The increase in solid volume through the formation of these phases is often assumed to be the only reason for expansion. In this paper we systematically compare the volume increase predicted by thermodynamic modeling to macroscopic expansion for mortars made with CEM I in different sulfate solutions and for mortars made with a range of blended cements in sodium sulfate solution. It is shown that the length changes cannot be explained by simple volume increase alone. A more plausible explanation of expansion lies in the theory of crystallization pressure, in which crystals forming from a supersaturated solution may exert pressure on their surroundings. It is observed that expansion occurs in systems where thermodynamic modeling predicts the co-existence of ettringite with gypsum. In such a case, if monosulfate and gypsum are both present locally, the solution can be highly supersaturated with respect to ettringite, whose formation in confined conditions (such as within C–S–H) can then exert expansive forces.

• OSTI ID: 22323129
• Journal Information: Cement and Concrete Research, Journal Name: Cement and Concrete Research Vol. 46; ISSN 0008-8846; ISSN CCNRAI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CEMENTS
CRYSTALLIZATION
CRYSTALS
GYPSUM
IONS
MORTARS
SODIUM SULFATES
SOLIDS
SOLUTIONS