Interactions between Concrete and Brine at the Waste Isolation Pilot Plant (WIPP) Site, New Mexico
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INTERACTIONS BETWEEN CONCRETE AND BRINE AT THE WASTE ISOLATION PILOT PLANT (WIPP) SITE, NEW MEXICO STEVEN J. LAMBERT*, E. JAMES NOWAK*, LILLIAN D. WAKELEY**, POOLE** *Sandia National Laboratories, P. 0. Box 5800, Albuquerque, **Structures Laboratory, Department of the Army, Waterways tion, Corps of Engineers, 3900 Halls Ferry Road, Vicksburg,
AND TOY S. NM87185 Experiment StaMS 39100-6199
ABSTRACT A concrete liner emplaced in 1984 in a shaft at the Waste Isolation Pilot Plant has served as a natural laboratory for observing interactions among concrete, evaporite rocks, and brine. During a routine inspection of the liner in the spring of 1990, discoloration, deposition of secondary salts, wet areas with exposed aggregate grains, softening of paste, surficial spalling, and cracking were observed locally on the concrete surface of the liner. Some construction joints showed apparent leakage of brine from behind the liner, which was nominally 50 cm thick. Seepage brines were nearly saturated relative to CaCl 2 and contained lesser amounts of MgCl 2 and KCI, and minor NaCl. The liner surface was locally altered to a 1-2 cm friable hygroscopic layer containing little cement paste; concrete cores (7 or 10 cm diameter) through the liner at depths of 248, 254, 255, and 271 m showed similar degrees of alteration at the liner/rock interface. The most profound alteration of concrete was developed in a -7 cm zone subparallel to and straddling the construction joint cored at a depth of -254.5 m. This zone was extensively microfractured, transected aggregate grains, and contained brucite, gypsum, magnesium hydroxychloride hydrate, and locally calcium chloroaluminate instead of the usual phases of hydrated portland cement. Several mechanisms of chemical degradation have been proposed, the most likely being attack by magnesium ions. INTRODUCTION
Background The Waste Isolation Pilot Plant (WIPP) was authorized by Public Law 96-164 "as a defense activity of the DOE [Department of Energy] for the express purpose of providing a research and development facility to demonstrate the safe disposal of radioactive wastes from the defense activities and programs of the United States." The WIPP facility has been excavated at a depth of 660 meters in bedded rock salt of the Salado Formation (Ochoan Epoch, Permian Period) in the Delaware Basin of southeastern New Mexico. The waste-handling shaft was designed to function throughout the operational period of the WIPP (approximately 30 years). The concrete liner of the Waste shaft was placed between November, 1983, and April, 1984. The liner was constructed from the surface downward to a depth of approximately 250 meters (nominally 50 cm thick). Then a key (nominally 1 meter thick) to support the liner was constructed upward from a depth of approximately 275 meters to approximately 250 meters in 2.5 to 3 meter lifts; more than two weeks elapsed between placing the concrete at the bottom of the liner and placing the concrete at the top of the key. In addition, the concrete at the top of the key wa
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