Study of clay-cement slurries with mechanical and electromagnetic waves

This paper describes the results of a test program in which the setting and hardening of cement, bentonite-cement slurries, and attapulgite-cement slurries are monitored in the laboratory with mechanical-shear and electromagnetic waves. Specimens are prepared by prehydrating the clay before adding cement. The presence of clays in soil-cement slurries delays hydration and its manifestation. The complex permittivity emerges as a sensitive indicator of ongoing reactions. Permittivity reflects changes in the mobility of water, liberation and entrapment of ions, changes in specific surface, and variations in double-layer phenomena. The increase in shear-wave velocity reflects the rise in effective stress due to consolidation, the decrease in double-layer repulsion, and the higher rigidity of the mixture as a result of cementation. Early stages of hydration denoted by changes in permittivity do not contribute to the formation of a rigid, cemented network. Overall, it is shown that the simultaneous measurement of permittivity and shear-wave velocity provides complementary microlevel information on the fundamental dependency between chemical reactions, physical changes, and rigidity in cementitious materials. The application of these results to field situations will lead to the development of nonintrusive, nondestructive monitoring techniques.