Particle size distribution of aggregate effects on the reinforcing roles of carbon nanotubes in enhancing concrete ITZ

By virtue of their superior mechanical properties and huge surface area, carbon nanotubes (CNTs) have become a potential representative in the field of the nanoengineered concrete, which provides an excellent opportunity to reinforce concrete interfacial transition zone (ITZ) characteristics. Adjusting the most reasonable aggregate gradation of concrete to maximize the enhancement effects of CNTs to ITZ is the key to popularizing the application of nano reinforcement in practical engineering. Hence, in this work, we investigated the reinforcing roles and mechanisms of CNTs on the concrete ITZ, and the corresponding influence on the mechanical performance and impermeability properties under different aggregate particle size distributions. The results reveal that CNTs can promote nucleation effects to generate hydration products growth and act as the refined templates to produce finer microstructure in concrete ITZ. Compared with plain concrete, the reinforcing ratios of CNTs on the ITZ characteristics, mechanical performance and impermeability present a quadratic function correlation with the Talbot index. The optimal effects of CNTs on the reinforcement of concrete ITZ characteristics appear at 0.8 Talbot index, reducing about 30% ITZ width and 22.8% abrasion crack width in ITZ. The corresponding mechanical properties and impermeability improve 20.7–35.6% and 38.1–43.6%, respectively. Low Talbot gradation index would result in the uneven dispersion of CNTs among the capillary pores. In contrast, high Talbot gradation index may enlarge the ITZ range, increase the amount and width of abrasion cracks in ITZ, and further weaken the reinforcing effects of CNTs.