Mechanical and hydraulic characterization of plastic concrete for seepage cut-off walls

Abstract

This paper describes a series of laboratory tests performed to characterize the mechanical and hydraulic properties of plastic concrete (PL-C). PL-C is used in the construction of seepage cut-off walls in dams and it comprises cement, aggregate, and water mixed with sodium bentonite. The addition of sodium bentonite causes a reduction in strength and improved ductility after failure compared with normal concrete. The mechanical properties of PL-C are studied using a series of unconfined compression tests and confined compression tests performed while simultaneously permeating water through PL-C specimens. Stress relaxation and controlled rate of loading tests are also performed to investigate the rate-sensitivity and time-dependency of plastic concrete. The test results show that the hydraulic conductivity of PL-C increases between two and three orders of magnitude during triaxial compression due to yielding, crack formation, and dilation of the cracks. Such changes in the behaviour of PL-C should be minimized during design by controlling the working strains and using erosion-resistant mixes. In addition to these findings, PL-C exhibits significant time-dependent behaviour similar to that observed for clays, and the variation of compressive strength versus confining stress is comparable to normal strength concrete.