Effect of Active Mineral Additives on the Dispersion of Multiwalled Carbon Nanotube and the Electrical Properties of Piezoresistive Cementitious Composites

Piezoresistive cementitious composites (PCC) have demonstrated significant potential for structural health monitoring in civil infrastructure, but the dispersion of conductive phases in cementitious composites is critical for PCC's mechanical and electrical properties. To develop an effective dispersion method, this study investigated the effect of two different active mineral admixtures (AMA), including silica fume (SF) and metakaolin (MK), on the dispersion of multiwalled carbon nanotube (MWCNT) within the cementitious matrix and the electrical properties of PCC, considering the particle sizes, dosages, and shape characteristics of AMA. The experimental results indicate that either SF or MK could increase the gauge factor (GF) of PCC by improving the dispersion of MWCNT, but MK showed better enhancement than SF. AMA with a volume weighted mean diameter D[4,3] of 5-8 μm could effectively disperse bulky MWCNT agglomerates into smaller clusters and enhance the GF. It is demonstrated that a high GF in PCC did not necessarily require low apparent porosity and electrical resistivity. Good dispersion of MWCNT was critical for GF of PCC. The MWCNT dispersion and GF of the PCC blended with SF gradually decreased when the SF dosage increased from 5% to 15%; however, further increasing the SF dosage to 20% led to a slight increase in the MWCNT dispersion and GF. Given the increasing MK dosage, the dispersion of MWCNT and the GF gradually decreased.