Polypropylene (PP) fibres (fibrillated PP) obtained by inducing splits in PP films were treated under radio frequency (RF) (30 kHz) SiCl4-plasma conditions in a stainless steel, parallel plate, capacitively coupled reactor. Analytical investigations carried out on the pale yellow-coloured fibre demonstrated the presence of OH groups and Si atoms on the PP surfaces, resulting in improved wettability and decreased contact angle values. Surface morphologies estimated using atomic-force microscopy indicated the presence of a very rough surface structure for the plasma-treated substrates in comparison with the unmodified samples. Comparative test data from PP fibre-reinforced concrete and SiCl4-cold plasma-treated PP fibre reinforced concrete showed improved mechanical characteristics (flexural strength, flexural toughness, and toughness indices) for all of the plasma-treated fibre-based composites.