Carbon Nanofibers Grown in CaO for Self-Sensing in Mortar

Abstract

Intelligent cementitious materials integrated with carbon nanofibers (CNFs) have the potential to be used as sensors in structural health monitoring (SHM). The difficulty in dispersing CNFs in cement-based matrices, however, limits the sensitivity to deformation (gauge factor) and strength. Here, we synthesise CNF by chemical vapour deposition on the surface of calcium oxide (CaO) and, for the first time, investigate this amphiphilic carbon nanomaterial for self-sensing in mortar. SEM, TEM, TGA, Raman and VSM were used to characterise the produced CNF@CaO. In addition, the electrical resistivity of the mortar, containing different concentrations of CNF with and without CaO, was measured using the four-point probe method. Furthermore, the piezoresistive response of the composite was quantified by means of compressive loading. The synthesised CNF was 5–10 μm long with an average diameter of ~160 nm, containing magnetic nanoparticles inside. Thermal decomposition of the CNF@CaO compound indicated that 26% of the material was composed of CNF; after CaO removal, 84% of the material was composed of CNF. The electrical resistivity of the material drops sharply at concentrations of 2% by weight of CNF and this drop is even more pronounced for samples with 1.2% by weight of washed CaO. This indicates a better dispersion of the material when the CaO is removed. The sensitivity to deformation of the sample with 1.2% by weight of CNF@CaO was quantified as a gauge factor (GF) of 1552, while all other samples showed a GF below 100. Its FCR amplitude can vary inversely up to 8% by means of cyclic compressive loading. The method proposed in this study provides versatility for the fabrication of carbon nanofibers on a tailored substrate to promote self-sensing in cementitious materials.

Strain Monitoring of Concrete Using Carbon Black-Based Smart Coatings

“…Alternatively, carbon-based materials have been gaining popularity in self-sensing applications due to their high durability [37], good electrical performance [38], and corrosion resistance [39]. Extensive research has been conducted on carbon nanotubes (CNTs) [40,41], carbon nanofibres (CNFs) [42][43][44], natural graphite (NG) [45,46], and graphite nanoplates (GNPs) [47]. Out of the available carbon-based fillers, carbon black (CB) was used in this study as it presents great environmental and financial viability [48,49] due to its production process and the small concentrations required in cementitious binders for electrical enhancement.…”

PVDF-based coatings with CNT additions for strain monitoring of mortar substrates subjected to bending

“…Self-sensing concrete, although widely studied [6][7][8], is limited to the physical limitations of carbon-based composites and, therefore, cannot be used in existing structures. Polymer-based thin layers, on the other hand, can be easily applied on top of new and existing structures.…”