Uniaxial confined compression tests of cementitious materials

This paper aims at presenting the development of an experimental setup to perform confined compression tests of mortar and cement paste specimens at high pressures. The paper presents the effect of water/cement ratio (w/c) as well as the ratio of fine aggregate (sand) and its maximum grain size on the measured pressure – volumetric strain dependence (equation of state). Decrease of w/c ratio in a cement paste mix results in increase of the secant bulk modulus of the loading branch. The study includes unloading and reloading at different load levels. The bulk modulus of the reloading branch of a given composition depends almost linearly on the pressure magnitude. The secant bulk modulus (loading branch) of mortar specimens increases monotonically with the volumetric sand fraction. The experimental study shows a good repeatability of the different cement paste specimens and of specimens with fine sand; a relatively large scatter of the results is obtained for specimens with coarse sand. The developed damage was identified and recorded at the end of each test. In cement paste specimens cracks were identified only in the case of w/c = 0.50, while in the other specimens, no cracking was observed. In the mortar specimens with coarse sand, perpendicular cracks to the specimen axis were observed, while in the specimens, that contain fine sand, no damage has been indicated.