Influence of electrodes and testing conditions on resistance and piezoresistivity of carbon nanofibers cement paste

This paper investigated the influence of embedded electrode and pasted electrode on the resistivity behavior of carbon nanofibers (CNFs) cement paste by using the alternating current (AC) method. The dosage of CNFs ranged from 0.75% to 3.125 % by volume of cement and the samples were measured after four treatment conditions including oven dried for 3 days, being sealed for 30 days, immersed in tap water or 3.5% NaCl solution for 30 days respectively. The piezoresistive performances of carbon nanofibers cement pastes (CNFP) with two types of electrodes under oven dry state were also studied. Results indicated that the average value and variability coefficient (C_v) of electrical resistivity were reduced by the increase of AC frequency only if the CNFs content was less than 2.5 vol.%. The immersion of water and NaCl solution reduced the resistivity of CNFP when the CNFs dosage is below 2.5 vol.%. The CNFP with pasted electrodes presented higher resistivity than the specimen with embedded electrodes when the CNFs content was lower than 3.125 vol.%. However, as the CNF content exceeded 2.5vol.%, the resistivity of CNFP with two types of electrodes were almost the same. The CNFP with two electrode types presented different piezoresistive performances at various amount of CNFs. A computational model for the piezoresistivity of CNFs cement paste was obtained from this research. The results of this research also demonstrated the improving effects of CNFs on the ductility and axial compressive strength of CNFP.