Investigating the behavior of clay in cement systems

Subsurface repositories for the disposal of anthropogenic waste and the long term storage of energy products involves a system of multiple barriers which could include natural rock, metallic waste containers, engineered bentonite, and cement to maintain containment integrity. At the bentonite- cement interface or within the clay-cement matrix complex coupling and collective Thermal-Hydraulic-Mechanical-Chemical interactions (THMC) can result when changes in saturation occur.

A key question is: Do changes in saturation lead to geochemical-geomechanical alterations that influence the integrity of local matrix and the surrounding environment?

Clay-cement interactions were investigated with:

i) Cation exchange experiments where clays (sodium and calcium rich bentonite/montmorillonite, montmorillonite K10, and calcined kaolinite) were suspended in cement porewater for 7 days to analyze the elemental exchange between materials

ii) Structural analysis of bentonite that was embedded in a cement matrix (submerged in 50°C water and mixed with cement pastes) to investigate changes in clay characteristics

iii) Acoustic Emission monitoring and X-Ray Microscopy of geo-architected synthetic rocks with localized or distributed clays bodies within a cement matrix to extract geophysical signatures and monitor damage evolution in clay-rich systems

Results demonstrate the dynamics of clay-bearing systems because damage can be generated and propagated in cement-clay environments. Moreover, montmorillonite materials interacting with cement experience cation exchanges and structural changes that lead to geomechanical-geochemical coupling.

Acknowledgment: Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions, LLC., a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-NA-0003525. The views expressed in the article do not necessarily represent the views of the U.S. DOE or the United States Government. A portion of the experimental data is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Geosciences Research Program under Award Number (DE-FG02-09ER16022).