Hybrid smart cementitious materials incorporating ladder scale carbon fiber reinforcement: An experimental investigation

This research presents the results of a study of carbon nano- and/or micro-modified cement pastes composites and hybrid cement pastes reinforced with single-walled carbon nanotubes (SWCNTs), and micro-scale carbon fibers (CFs) in terms of strength, flexural toughness, electrical conductivity and sensing ability. The crucial parameter investigated in this research is the various concentrations of a) the nano-reinforcement 0.05, 0.1, 0.2, 0.3, and 0.5 wt. % of cement; the amount of 0.1 wt. % exhibiting the best mechanical and electrical performance, b) the micro-scale reinforcement 0.05, 0.1, and 1.0 wt. % of cement and c) the synergistic effect between the types of fibers used. The determination of the cement pastes’ flexural and compressive strength was investigated through 3-point bending and compressive tests. Toughness was determined by conducting linear elastic fracture mechanics (L.E.F.M.) experiments on notched specimens to analyze the post-peak behavior and characterize the hybrid cement paste’s ductility. SWCNT-modified cement pastes exhibit a 20.3 % and 6 % increase in flexure and compression; however, the highest increase in flexure was observed in the case of hybrid reinforcement by 56 %. Additionally, the hybrid mix exhibited the finest post-peak behavior reflected by the increase in energy absorption ability by 142 % higher than the nano-scale reinforcement and 2082 % higher than the reference mix. Strain sensing ability was determined by measuring the electrical resistance while applying compressive loading simultaneously. Results expose that the hybrid reinforcement, at multiple scales, beneficially alters the structure of the cement paste in a smart material providing that with the ability to track changes in its resistivity by 24.2 % (Δρ/ρ0) while at the same time demonstrating outstanding flexural strength and toughness. Subsequently, this research provides new perspectives on the design of hybrid reinforced cementitious materials exhibiting enhanced mechanical properties and self-sensing ability for multiple structural applications.