Self-heating characteristics of electrically conductive cement composites with carbon black and carbon fiber

Abstract

This study aimed to investigate the self-heating characteristics of electrically conductive cement composites (ECCCs) and propose an effective and affordable mix design for ECCC blocks that are applicable to the accelerated curing of concrete with carbon black and carbon fibers employed as conductive agents. Twelve mix proportions were prepared by varying the carbon black and carbon fiber contents. A voltage application protocol was designed and used to examine the self-heating capacities of the mixtures. The results show that the presence of carbon fibers was critical so that the electrical resistivities of ECCCs with 0.2 vol% carbon fibers were less than 0.16% of that without conductive agents. For a given content of carbon fiber, an increase in the carbon black content up to 0.8 vol% led to a drastic decrease in electrical resistivity, and achieved the highest average surface temperature of ECCC equal to approximately 77 °C. However, the use of 1.2 vol% carbon black caused an increase in the electrical resistivity. Further, the trends were in accordance with the change in the dispersion degree of carbon black, as analyzed via fluorescence microscopy. Finally, two selected ECCC blocks (with 0.4 vol% carbon fiber and 0 vol% or 0.8 vol% carbon black) were tested for the accelerated curing of ordinary cement paste, charged at 25 V DC for 24 h. The cement paste cured using the blocks with 0.8 vol% carbon black attained more hydrated phases, and at least an 11% reduction in porosity at 24 h of curing.