Influence of multi-walled carbon nanotubes on the multi-scale performance of internally cured concrete containing pre-wetted lightweight aggregate

Abstract

Multi-walled carbon nanotubes (MWCNTs) is an effective reinforcing nanomaterial in concrete given its outstanding filling, nucleation and bridging effects. This study evaluates the enhancement of MWCNTs on internally cured concrete (ICC) containing pre-wetted lightweight aggregate (LWA) through mechanical tests, SEM-EDS and XRD evaluations. The variations in the dosages of MWCNTs and LWA and the connection between water-to-binder (w/b) ratios and MWCNT dosages were considered. Results show that adding MWCNTs benefits the mechanical performance of LWA-ICC but at a dosage of less than 0.25 wt%. A richer C–S–H phase can be identified in both the interfacial transition zone and the general matrix with the addition of MWCNTs. The internal curing of LWA presents a positive synergistic effect with MWCNTs and can offset the adverse influence of LWA’s low-strength given a dosage of less than 40 vol%. An increased w/b ratio leads to a porous microstructure with a richer phase in calcium hydroxide, resulting in decreased mechanical performance. However, the negative effect of a high w/b ratio, i.e., 0.55, on concrete performance can be improved given a higher MWCNT dosage of 0.25 wt%.