This study focuses on the characterization of low-velocity (lower than 100 km/h) rockfall impact loads transferring to a thick steel-reinforced concrete (SRC) slab through a protective sand layer. A full-scale experimental tests campaign was performed, each test consisting in releasing a concrete block which, after a vertical free-fall, impacts a sand protective layer placed over a SRC slab, in order to represent an isolated rockfall impact to which an actual SRC structure could be exposed. During the impact, the vertical pressure distribution was observed using several pressure cells installed at the sand-slab interface. A total of 35 tests were carried out, systematically combining sand layer thickness (D), block's equivalent diameter (B), and free-fall drop height (H), related to impact velocity. The masses of the released blocks were in the range of 117 to 7399 kg, corresponding to diameters in the range of 0.42 to 1.79 m. Five free-fall drop heights, up to 33 m, were considered, to reach impact velocities up to 90 km/h, covering the range of most velocities observed in actual rockfall studies. Three thicknesses of the sand layer protecting the thick SRC slab were considered: 1, 1.5 or 2 m. Data reduction from this full-scale impact tests program makes it possible to characterize, for a given thickness of protective sand layer, the time-space pressure pulse distribution applied to the protected structure during the impact for a large range of rock boulder masses and speeds actually observed in the field.