Effect of Carbon and Steel Fibers on the Strength Properties and Electrical Conductivity of Fiber-Reinforced Cement Mortar

Cement-based composites are generally non-conductors with high electrical resistivity, but they can be used as conductors by incorporating conductive materials. Recently, research has been actively conducted to develop high-conductive fiber-reinforced cement mortar (FRCM) due to increased interest in multifunctional cement mortar required by the market today. Thus, the present paper investigated the effect of the developed conductive FRCM containing carbon and steel fibers on the fresh and mechanical properties as well as electrical conductivity. The performance of conductivity FRCM was studied based on flow, unit weight, air content, three-point flexural, compression, and electrical resistance tests. In addition, their performance was also compared and reviewed with plain mortar (PM). Furthermore, the surface shape and element components of the developed conductive FRCM fracture surface were analyzed using a scanning electron microscopy (SEM) and an energy dispersive X-ray spectrometer (EDS). The results showed that the addition of steel fibers slightly decreased the relative flow value, whereas the incorporation of carbon fibers is very disadvantageous in terms of fluidity due to the fiber ball phenomenon. The unit weight of mixture containing carbon fibers was somewhat decreased, whereas the changes in the amount of air contents were relatively insignificant regardless of the fiber volume fractions. The flexural strength of conductive carbon fiber-reinforced cement mortar (CFRCM) and steel fiber-reinforced cement mortar (SFRCM) was significantly improved compared to that of PM. The compressive strength of CFRCM decreased significantly as the volume fraction of carbon fibers increased. Overall, even if the steel fibers were added up to 1.25%, the effect of improving the electrical conductivity of SFRCM was insignificant. In the case of the CFRCM used in this study, it was found that the percolation threshold existed between 0.3% and 0.4% fibers, and it was thus thought that the optimum dosage of carbon fiber should be secured by at least more than 0.4% in terms of electrical conductivity. Therefore, the most important factor for the electrical conductivity effect was found to be carbon fiber, whereas the effect of steel fiber was insignificant.