Combined effect of recycled tire rubber and carbon nanotubes on the mechanical properties and microstructure of concrete

The application of recycled tire rubber (TCR) in concrete replacing conventional aggregates offers high recycling potential. However, the poor bonding between the hydrophobic rubber particles and the cement matrix weakens the material's mechanical properties. This study investigated the combined effect of carbon nanotubes (CNTs) and TCR on the mechanical properties of concrete, as well as microstructure characteristics. The different CNTs, surfactants, and ultrasonic dispersion time were subjected to a screening procedure in cement paste. Concrete production and mechanical performance tests are carried out after obtaining the above parameters. The results show that the improvement of the compressive strength of concrete by CNTs is negatively correlated with the content of TCR. The reinforcement behavior of CNTs has no subordinate properties among compressive strength, flexural strength, and splitting tensile strength. The morphological characteristics of CNTs-reinforced crumb rubber concrete (CNTCRC) revealed that CNTs refined the micropores as fillers. Furthermore, the poor interfacial bonding between TCR and cement matrix together with microcracks was modified due to the bridging effect of CNTs. In addition, the working mechanisms of TCR and CNTs in the cement hydration reaction were conceptually explored to help understand the reinforcing mechanism of CNTs on the macro level.