Abstract
Carbon nanofibers (CNFs) were directly synthesized on Portland cement particles by chemical vapor deposition. The so-produced cements contained between 2.51–2.71 wt% of CNFs; depending on the production batch. Several mortar mixes containing between 0 and 10 wt% of the modified cement were produced and the electrical properties at various ages and the load sensing capabilities determined. The percolation threshold related to the electrical conductivity was detected and corresponded to the amount of the present CNFs, 0.271, 0.189, 0.135 and 0.108 wt%. The observed threshold depended on the degree of hydration of the Portland cement. The studied mortars showed a strong piezoresistive response to the applied compressive load reaching a 17% change of the electrical resistivity at an applied load of 3.5 MPa and 90% at 26 MPa. This initial study showed that the studied material is potentially suitable for future development of novel fully integrated monitoring systems for concrete structures.
Highlights
Carbon-based materials, especially carbon nanotubes (CNTs) and carbon nanofibers (CNFs), incorporated into Portland cement based matrixes have been studied over the last couple of years
More curly CNTs incorporated into polymer matrixes resulted in a higher percolation threshold and a lower maximum electrical conductivity [23,24]
Carbon nanofibers were directly synthesized on Portland cement particles using chemical vapor deposition in the presence of a mixture of ethylene and hydrogen
Summary
Carbon-based materials, especially carbon nanotubes (CNTs) and carbon nanofibers (CNFs), incorporated into Portland cement based matrixes have been studied over the last couple of years. To function properly these composites require the presence of a sufficient amount of the conductive material, evenly dispersed throughout the isolative matrix to create a continuous electrical path. Within the traditional percolation theory, Equation (2) is based on the assumption that the electrical conductivity is only depended on the conductivity of the filler, in this case of the CNF. Studies on polymer-based matrixes showed that increasing the aspect ratio between length and diameter (L/D) of the CNTs produced higher ultimate conductivity values [23]. More curly CNTs incorporated into polymer matrixes resulted in a higher percolation threshold and a lower maximum electrical conductivity [23,24]. After the hydration process the solidified matrixes showed twice the compressive strength and 40 times higher electrical conductivity than the reference samples. Aoft1e2r t°hCe/mcleinanuingdeprroacnesins,etrht eatsmamospplehsere, werdeecgoaoslseeddduonwdnertova2c0u0u◦mC aatnadrcaoteoloefd12do◦Cw/nmtion 2u0n°dCerinananinaertgaotnmaotsmpohsepreh,edre.gassed under vacuum and cooled down to 20 ◦C in an argon atmosphere
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