Monitoring small-strain stiffness and permeability of geomaterials for environmental use

Cement-bentonite (CB) mixtures, compacted soil-lime (SL), and compacted soil-lime-fly-ash (SLFA) mixtures are frequently used materials in environmental engineering. The properties of these materials change over time due to chemical reactions between the binder, soil, and/or water. The acceptance criteria for these materials are usually defined by specific property values, such as permeability, stiffness, and shear strength, measured at certain curing times. The small-strain shear modulus, G0, can be non-destructively measured using the Bender Element method. The present paper illustrates the trend of G0 in CB, SL, and SLFA mixtures over curing time until 60-90 days. In addition, the hydraulic conductivity, k, was also measured. Three different CB mixtures, one SL mixture, and one SLFA mixture were examined. It was observed that the G0 for the CB mixtures increased as the curing time progressed, while the k decreased noticeably. The ratio of cement to water in CBs seemed to play a key role in determining the G0, while other factors, like the use of additives, also significantly affected the k. For SL and SLFA mixtures, the G0 was found to rise with curing time, showing a pattern reflecting the advancement of pozzolanic reactions between the soil and binders, and the permeability correspondingly decreased within one order of magnitude.