4.3 Influence of free water and strain-rate on the confined behavior of microconcrete

Quasi-static and dynamic QOC tests were performed on dry and water-saturated microconcretes in [16]. The dynamic tests exhibited an important dissimilarity between dry and saturated specimens concerning both deviatoric and hydrostatic behaviors. First, dried microconcretes exhibited a continuous compaction whereas saturated specimens showed a non-linear (hardening) hydrostatic behavior (Figure 11(b)). Moreover, a strong and continuous increase of the strength with pressure was noted with dry samples whereas water-saturated specimens exhibited an almost-perfect saturation of the strength (Figure 11(a)). The quasi-static results allowed highlighting the reason of this dissimilarity (Figure 11(c, d)). On the one hand, dried specimens behave similarly in dynamic tests and no strain rate effect is observed. On the other hand, the behavior of saturated specimens gradually tends to that of dried specimens when the loading rate is decreased, and an expulsion of water during slow quasi-static tests was observed. Finally, it was concluded that, waterpressure inside saturated microconcrete plays a major role on their fast-quasi-static or dynamic confined behavior by reducing drastically their shear strength.
