The influence of rheological parameters of cement paste on the dispersion of carbon nanofibers and self-sensing performance

This paper aims to study the influence of rheological parameters of cement paste on the dispersion of carbon nanofibers (CNFs) and the subsequent electrical resistivity. Three groups of cement paste with water-cement ratio (w/c) of 0.4, 0.35, and 0.3 and three groups with w/c of 0.4 incorporating 10% silica fume (SF), 20% granulated blast-furnace slag (SL) and 0.4% carboxymethylcellulose sodium (CMC) were prepared. The CNFs were incorporated at 2.25% of binder volume. Different dosages of superplasticizer were added for each group, to obtain variable rheological performances of fresh paste. The average value and variability coefficient (C_v) of electrical resistivity for 16 specimens were determined for each mixture. Scanning electron microscopy (SEM) observation and piezoresistivity were tested on selected samples. Results showed that slump flow increased and the viscosity decreased with more addition of superplasticizer and higher w/c. For each group of cement paste, the slump flow of around 200 mm is most favorable for enhancing the dispersion of CNFs. The addition of CMC and SF improved the dispersion of CNFs, but SL had a disadvantageous influence. The lower C_v value and better dispersion of CNFs due to the rheological performance of cement paste led to the improved piezoresistivity.