Individual and combined effects of chloride, sulfate, and magnesium ions on hydrated Portland-cement paste

Technical Report · Tue Mar 01 04:00:00 EST 1994

DOI:https://doi.org/10.2172/10147904· OSTI ID:10147904

Poole, T. S.; Wakeley, L. D.; Young, C. L. ^[1]

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1. Army Engineer Waterways Experiment Station, Vicksburg, MS (United States). Structures Lab.

Ground water with a high concentration of magnesium ion is known to cause deterioration to portland cement concretes. A proposed mechanism for this deterioration process published previously involves an approximate 1:1 replacement of Ca ions by Mg ions in the crystalline phases of hydrated cement. The current study was undertaken to determine which ions, among magnesium, chloride, and sulfate, cause deterioration; whether their deleterious action is individual or interdependent; and to relate this mechanism of deterioration to the outlook for a 100-yr service life of concretes used in mass placements at the Waste Isolation Pilot Plant. Loss of Ca ion by cement pastes was found to be strongly related to the concentration of Mg ion in simulated ground-water solutions in which the paste samples were aged. This was true of both salt- containing and conventional cement pastes. No other ion in the solutions exerted a strong effect on Ca loss. Ca ion left first from calcium hydroxide in the pastes, depleting all calcium hydroxide by 60 days. Some calcium silicate hydrate remained even after 90 days in the solutions with the highest concentration of Mg ion, while the paste samples deteriorated noticeably. The results indicated a mechanism that involves dissolution of Ca phases and transport of Ca ions to the surface of the sample, followed by formation of Mg-bearing phases at this reaction surface rather than directly by substitution within the microstructure of hydrated cement. Given that calcium hydroxide and calcium silicate hydrate are the principal strength-giving phases of hydrated cement, this mechanism indicates the likelihood of significant loss of integrity of a concrete exposed to Mg-bearing ground water at the WIPP. The rate of deterioration ultimately will depend on Mg-ion concentration, the microstructure materials of the concrete exposed to that groundwater, and the availability of brine.

• Research Organization: Sandia National Labs., Albuquerque, NM (United States); Army Engineer Waterways Experiment Station, Vicksburg, MS (United States). Structures Lab.
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 10147904
• Report Number(s): SAND--93-7040; ON: DE94011247
• Country of Publication: United States
• Language: English

Related Subjects

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12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
36 MATERIALS SCIENCE
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
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CALCIUM
CHEMICAL AND PHYSICOCHEMICAL PROPERTIES
CHEMICAL REACTION KINETICS
CHLORIDES
CONCRETES
CORROSION, EROSION, AND DEGRADATION
DISSOLUTION
GROUND WATER
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MAGNESIUM IONS
MICROSTRUCTURE
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RADIOACTIVE WASTE STORAGE
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SULFATES
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WIPP