High pressure and high strain rate behavior of cementitious materials: Experiments and elastic/viscoplastic modeling

The goal of this dissertation was to experimentally investigate the high rate and high pressure mechanical response of a mortar and concrete mix and use or develop a constitutive model able to describe the observed behavior. Triaxial compression tests at a strain rate of 10−6/ s, and for confining pressures ranging from 0 to 0.5 GPa were conducted. Dynamic tests in the range 60/s to about 160/s under both unconfined and confined conditions were conducted using the University of Florida's 7.62 cin diameter split Hopkinson pressure bar (SHPB). The data obtained in such tests allowed the quantification of the combined effects of confining pressure and strain rate on the deformation and strength of the materials. For mortar, dilatancy has been observed at high levels of the principal stress difference for both dynamic and quasi-static conditions. The unconfined dynamic compressive strengths are approximately double those of the quasi-static compressive strengths. Most of the confined SHPB mortar specimens showed very little damage post-test other than some chipping around the top edges, most likely due to localized tensile effects.; For the concrete selected for this research. WES5000, quasi-static hydrostatic tests conducted up to a pressure of 0.5 GPa allowed for the accurate determination of the dependence of the bulk modulus on pressure and the correct estimation of the material's compaction properties when subjected to pressures in the range encountered in dynamic events. For confined quasi-static conditions, the material exhibited hardening behavior up to failure. Both compressibility and dilatancy regimes of the volumetric behavior were observed, the dilatancy threshold being highly dependent on the level of confinement. The unconfined dynamic strength is as high as 1.5 times the quasi-static strength, the material generally exhibiting far more cracking under similar loading conditions than was observed in mortar. The confined dynamic tests showed similar stress-strain response as the quasistatic tests conducted at the same level of confinement. A decrease in strain rate sensitivity with increasing confining pressure was observed.; A new elastic/viscoplastic model that captures compressibility and dilatancy, as well as strain rate effects has been developed for concrete. (Abstract shortened by UMI.)...