Electrically conductive cement-based composites have been widely used to build functional and smart constructions. In these composites, carbon nanofibers (CNFs) can be used as electrically conductive fillers to reduce the electrical resistivity of the cement matrix. Unlike other CNF modified composites, such as CNF/polymers or CNF/ceramics, which have porosity lower than 5%, the CNF/cement composites, however, have porosity higher than 20%. As a result, the electrical conduction phenomenon of this composites is more complicated than the others. Previous studies have investigated the electrical conduction phenomenon of CNF/cement composites by using CNF dosage as the main factor; however, the free water content and temperature coefficient were not systematically discussed. In this study, the percolation of the electrical conduction was analyzed by using external applied DC voltage, CNF dosage, and free water contents as parameters. Specifically, the percolation critical exponents were used to calculate the percolation backbone density. It was found that there is a critical DC voltage, which turns the electrical-resistivity temperature coefficient of the CNF/cement composites from positive to negative. Furthermore, the results demonstrate that the percolation of the CNF/cement composites is also governed by the polarization phenomenon of the CNFs. This study not only elucidates the synergistic effects of CNF dosage, free water contents, and temperature coefficient on the electrical resistivity of CNF/cement composite but also helps to understand the mechanisms of the dynamic electrical resistivity variation with applied DC voltage. The results will be beneficial to design and manufacture high effective functional and smart CNF/cement structures.

导电水泥基复合材料已被广泛用于构建功能性和智能化结构。在这些复合材料中，碳纳米纤维（CNF）可用作导电填料，以降低水泥基体的电阻率。与孔隙率低于5％的其他CNF改性复合材料（例如CNF /聚合物或CNF /陶瓷）不同，CNF /水泥复合材料的孔隙率高于20％。结果，该复合材料的导电现象比其他复合物更为复杂。以往的研究以CNF用量为主要因素研究了CNF /水泥复合材料的导电现象。但是，没有系统地讨论自由水含量和温度系数。在这个研究中，通过使用外部施加的直流电压，CNF剂量和游离水含量作为参数来分析电导的渗透。具体而言，使用渗流临界指数来计算渗流主链密度。发现存在临界DC电压，其将CNF /水泥复合材料的电阻温度系数从正变为负。此外，结果表明，CNF /水泥复合材料的渗透也受CNF极化现象的支配。这项研究不仅阐明了CNF用量，游离水含量和温度系数对CNF /水泥复合材料电阻率的协同作用，而且有助于理解施加直流电压时动态电阻率变化的机理。