Hybrid fibre-reinforced cementitious composites with short polyethylene and continue carbon fibres: Influence of roving impregnation on tensile and cracking behaviour

Hybrid externally-bonded reinforcements are considered a viable technique for strengthening existing concrete structures. They combine high-performance impregnated textiles with matrices containing dispersed microfibres to foster the ductility and toughness of the composite system. In this paper, the mechanical performance of textile-reinforced strain-hardening cement-based composites (TR-SHCC) is investigated in detail. A novel high-performance inorganic binder based on limestone calcined clay cement (LC³) is reinforced with both polyethylene (PE) dispersed microfibres and carbon fibre (CF) textiles as continuous biaxial reinforcement. The CF yarns are impregnated by an automated process to improve the monolithic response under uniaxial tensile loading and to ensure high production consistency. Fully inorganic suspensions, i.e., geopolymer and cement-based, are being investigated, as they can provide superior thermal stability compared to traditional polymeric impregnating agents. Interphase adhesion is investigated by single-yarn pull-out tests, microscopy and µCT at various micro scales. On the one hand, the improved adhesion promoted by cement impregnation resulted in the finest and most diffuse crack pattern. Conversely, the strength of the overall composite is mainly governed by the tensile failure of the yarns, irrespective of the bond, and dispersed fibres consistently improve the post-cracking stage and the strength of the hybrid composites.