In situ-grown carbon nanotubes enhanced cement-based materials with multifunctionality

Abstract

Smart cementitious materials integrated with carbon nanotubes (CNTs) have potential applications as sensors in structural health monitoring (SHM). The sensitivity to strain (gauge factor) and strength of such materials are limited by the difficulty in dispersing CNTs. Here we synthesized CNTs in situ on the surface of fly ash (FA) to significantly improve the CNT dispersibility and enable the cement mortar to exhibit an outstanding strain-sensing capability. The mortar with CNT-coated FA (CNT@FA) at 2.0 wt% CNT concentration had a gauge factor of 6544, about one order of magnitude higher than that of mortar with commercial CNTs under the same condition. Its electrical resistivity can reversely vary as high as 69% upon cyclic compressive loading. The great self-sensing ability of cement mortars reinforced with in situ-grown CNTs was explained by two mechanisms: 1) the high possibility of the breakup/formation of CNT conductive paths provided by the unique morphology of CNT@FA; 2) high ratio of tunneling resistance with respect to the total resistance caused by the good dispersion of CNTs, which is demonstrated by optical microscopy measurements. The compressive and flexural strength values of the mortars with CNT@FA are also higher than those of the plain mortar at an age of 28 days. The CNT@FA mortars with enhanced electrical and mechanical properties have potential applications in assessing the conditions of civil engineering structures.