Cement pastes with UV-irradiated polypropylene: Fracture energy and the benefit of adding metakaolin

Adding fine plastic-based aggregates to cement pastes can allow for recycling waste while increasing the tensile strength and fracture toughness of the paste. However, the hydrophobicity of plastic causes poor cohesion with the cement paste, affecting the mechanical properties of the composite. Pre-irradiation with UV-C light reduces the hydrophobicity of the plastic, thus increasing the tensile strength of the paste while preserving compressive strength. This paper presents new experimental results, mainly showing that: (i) UV-C irradiated micro-sized polypropylene powder increases the tensile strength and fracture energy of CEM-I cement pastes; (ii) blending cement with metakaolin amplifies the positive effect of polypropylene addition in both untreated and UV-treated forms. These findings indicate that cement-metakaolin pastes containing UV-irradiated polypropylene may be an asset when crack resistance is key, such as in nuclear waste storage and oil/gas well cementing.