Abstract
In this work, multi-scale cementitious composites containing short carbon fibers (CFs) and carbon nanofibers (CNFs)/multi-walled carbon nanotubes (MWCNTs) were studied for their tensile stress sensing properties. CF-based composites were prepared by mixing 0.25, 0.5 and 0.75 wt.% CFs (of cement) with water using magnetic stirring and Pluronic F-127 surfactant and adding the mixture to the cement paste. In multi-scale composites, CNFs/MWCNTs (0.1 and 0.15 wt.% of cement) were dispersed in water using Pluronic F-127 and ultrasonication and CFs were then added before mixing with the cement paste. All composites showed a reversible change in the electrical resistivity with tensile loading; the electrical resistivity increased and decreased with the increase and decrease in the tensile load/stress, respectively. Although CF-based composites showed the highest stress sensitivity among all specimens at 0.25% CF content, the fractional change in resistivity (FCR) did not show a linear correlation with the tensile load/stress. On the contrary, multi-scale composites containing CNFs (0.15% CNFs with 0.75% CFs) and MWCNTs (0.1% MWCNTs with 0.5% CFs) showed good stress sensitivity, along with a linear correlation between FCR and tensile load/stress. Stress sensitivities of 6.36 and 11.82%/MPa were obtained for the best CNF and MWCNT-based multi-scale composite sensors, respectively.
Highlights
Cementitious composites are extensively used in civil infrastructures and are susceptible to deterioration of their properties over time
Significant entanglements or agglomeration can be observed in the case of carbon nanofibers (CNFs)
The incorporation of CNF and multi-walled carbon nanotubes (MWCNTs) (0.1 and 0.15% of cement weight) in carbon fibers (CFs)-based composites led to a significant decrease in the electrical resistivity of cementitious composites
Summary
Cementitious composites are extensively used in civil infrastructures and are susceptible to deterioration of their properties over time. The monitoring of real-time conditions and performance of structures, which is known as structural health monitoring (SHM), is performed mainly in the critical zones of the structures using various sensors [1,2]. The collected data are used to evaluate the health conditions of structures in order to take timely maintenance actions. SHM is frequently performed using various sensors such as optical fiber sensors, electrical resistance strain gauges, piezoelectric (PZT) ceramics, etc., each one of which has their own limitations [1,2]. Investigations on the piezoresistive cementitious composites (i.e., composites which show change in their electrical resistivity with mechanical stress/strain) for SHM applications have accelerated considerably [1,2,3].
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