Grouts and Concretes for the Waste Isolation Pilot Project (WIPP)
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GROUTS AND CONCRETES FOR THE WASTE ISOLATION PILOT PROJECT (WIPP) LILLIAN D. WAKELEY U.S. Army Engineer Waterways Vicksburg, MS 39180-6199, USA
Experiment
Station,
3909 Halls Ferry Road,
ABSTRACT The Structures Laboratory of the U.S. Army Engineer Waterways Experiment Station has conducted research on cement-based composites for the Waste Isolation Pilot Project (WIPP) since 1977, in cooperation with Sandia National Laboratories. Field testing requirements guided initial development of grouts. Concurrent and later laboratory studies explored the chemical stability and probable durability of these mixtures. Beginning in 1985, a series of small-scale seal performance tests at the WIPP prompted development of an expansive salt-saturated concrete. Important lessons learned from this ongoing work include: (1) carefully tailored mixtures can tolerate phase changes involving Ca, Al, and S049 without loss of structural integrity; (2) handling and placement properties are probably more crucial to the mixtures than is exact phase composition; and (3) for the environment of a geologic repository, demonstrated chemical durability will be the best indicator of long-term performance.
INTRODUCTION Research on and development of cement-based materials for plugging and sealing at the Waste Isolation Pilot Project (WIPP) site has been underway at the Structures Laboratory of the Waterways Experiment Station (WES) since 1975, in cooperation with Sandia National Laboratories (SNL). Early in the Materials Development Program, placement of specially formulated grouts and concretes was judged to be one of the principal techniques for sealing boreholes and access shafts from the surface to the repository horizon. Although policy about the role of cementitious materials in the repository sealing system has changed over the years, development, testing, and field placement of candidate mixtures have continued at WES to the present. Such materials currently are viewed as a critical component, possibly for the first hundred years after repository closure. Since 1958, the WES Concrete Technology Division (CTD) has developed and fielded pumpable, durable, cement-based grouts for many projects downhole and underground. This work has included grouting casings of several diameters, the largest of which was two and one half metres, in a borehole of just over three metres in diameter. WES experience developing grouts for the Nevada Test Site, and for correcting problems in and under hydraulic structures, has proven useful when applied to plugging and sealing experiments and demonstrations at the WIPP. As the requirements of research and development at the WIPP changed through the 1980's, we also developed and placed concretes formulated for specific underground tests at the WIPP [1].
WES AT THE WIPP In the mid 1970's, grout development for the WIPP involved both WES and SNL people, and other experienced grouters from oil-well service companies such as Dowell and Halliburton. That early work emphasized field placement criteria rather than materi
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