In this study, the effect of pressure application (0–50 MPa) to fresh concrete right after casting and during the first 24 hours of hardening has been examined. Supplementary cementitious materials in a form of silica fume, nanosilica and ground quartz sand were used. The aim of pressure application was to reduce porosity, thus improving concrete mechanical properties. Considerable reduction in porosity and a subsequent increase in compressive strength reaching the level of Ultra-High Performance Concrete (UHPC) were achieved. Mechanical and physical properties were tested and gas sorption porosimetry, mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), as well as scanning electron microscopy (SEM) were used for material characterization.