Influence of free water on the quasi-static and dynamic strength of concrete in confined compression tests

The behaviour of concrete under high pressure and dynamic loadings is experimentally investigated in the present paper. The specimen is confined in a cylindrical elastic steel ring that insures a quasi-uniaxial strain state of loading. It is subjected to static and dynamic (with strain rates in the range from 1e−6/s to 200/s) axial compressive loadings. Transverse gauges glued on the lateral surface of the ring allow for the measurement of the confining pressure so that the volumetric and the deviatoric response of the specimen can be computed. At high or intermediate strain rates, water saturated and dried specimens show strongly different results: i.e. a continuous increase of strength with pressure in dried specimens and a quasi nil strength enhancement in water-saturated specimens. This difference is not observed with quasi-static loadings. As explained through a basic poromechanics analysis, this dissimilarity is mainly attributed to an increase of pore pressure inside the saturated concrete during fast (quasi-static or dynamic) experiments.