ABSTRACT
Abstract Cement-based wasteforms are one of the most widely applied site remediation and waste disposal options, yet definitive understanding and quantification of processes controlling long-term performance is lacking. In the U.S., wastes are required by law to be placed in the unsaturated zone but wasteform performance is evaluated using laboratory tests (TCLP, ANSI/ ANS-16.1) that specify fully water saturated conditions. These tests ignore the potentially important role of reaction with soil gases in influencing wasteform performance. The presented research represents a combined experimental and modeling program approach to evaluate the role of the carbon dioxide reactive component of soil gas on the long-term performance of cementitious wasteforms. A series of wasteforms were exposed to an accelerated environment for carbonation and then subjected to leaching tests. Results are analyzed by comparison of experimental data with theoretical models of the leaching process. The results indicate that carbonation increases the apparent diffusion coefficient for unreactive species while resulting in stronger chemical binding of metals through solid solution in calcite. The net effect can be either positive or negative and depends upon the species being considered. Keywords: Cementitious wasteform, concrete carbonation, long-term performance
Solidification and stabilization with cementitious materials is perhaps the most widely accepted and economically attractive waste management option for disposal of lowlevel radioactive wastes. Advantages of cementitious wasteforms include (a) availability of materials locally on a worldwide basis, (b) low cost, (c) ability to tailor the mixture for different wastes, and (d) high physical strength of the resulting wasteform. The solidified wasteform can be developed in place (grouting of wastes), or can be poured
into steel drums or concrete canisters for later disposal, or formed directly into large monoliths. Although cementitious material is used primarily for its structural and physical properties, the effect of cementitious materials on the geochemical environment in the immediate vicinity of the concrete is pronounced.
