Synergistic effects of CNTs/SiO2 composite fillers on mechanical properties of cement composites

This paper investigated the hybridization use of carbon nanotubes (CNTs) with nano-SiO2 in cement composites. The (CNTs)/SiO2 composite fillers were designed and prepared by electrostatic self-assembly technology to reinforce cement composites. The mechanical properties, microstructure and hydration characteristics of cement composites incorporating CNTs/SiO2 fillers were systematically researched. The morphology and optical microscopy results show that the CNTs inside CNTs/SiO2 fillers tended to unwind due to the mechanical separation and steric hindrance of nano-SiO2 particles with certain size, and its agglomeration degree in the suspension greatly alleviated over time. With the appropriate incorporation of CNTs/SiO2 fillers (containing 0.10 wt% CNTs and 0.50 wt% nano-SiO2), the flexural strength, compressive strength and flexural toughness of the cement mortar matrix were sharply increased by 33.5%, 36.5% and 56.0% after curing for 28 days compared to the plain sample, respectively. Microscopic observations show that appropriate nano-additives can densify and refine the hydrated microstructure, and the crack-bridging, debonding and pull-out behaviors of CNTs were all observed. Hydration analysis quantitatively reveals that CNTs/SiO2 fillers significantly accelerated the cement hydration process by virtue of the nano-nucleating action. The reinforcing mechanisms of CNTs/SiO2 fillers can be attributed to the proposed synergistic effects of CNTs/SiO2 fillers, which mainly include the better dispersion stability of CNTs, the nucleating effect of nano-additives and the pozzolanic reaction by nano-SiO2, thus positively leading to increased mechanical properties.

Automated summary

This paper investigates the use of carbon nanotubes (CNTs) and nano-SiO2 in cement composites. The results show that the mechanical properties of the cement composites are significantly improved with the appropriate incorporation of CNTs/SiO2 fillers. Microscopic observations reveal that CNTs enhance the performance of cement composites through crack-bridging, debonding, and pull-out behaviors. Hydration analysis indicates that CNTs/SiO2 fillers accelerate the cement hydration process through the nano-nucleating action. The reinforcing mechanisms of CNTs/SiO2 fillers can be attributed to the synergistic effects of CNTs dispersion stability, the nucleating effect of nano-additives, and the pozzolanic reaction by nano-SiO2.