# Electrical Characteristics of Ultra-High-Performance Concrete Containing Carbon-Based Materials
## 4 Conclusions  
UHPC mixed with different types of carbon materials (CNT dispersions, milled fibers, chopped fibers, and expanded graphite) was investigated in this study. The mechanical properties and conductivities of the concrete specimens were analyzed according to the mixing contents of the carbon materials added.  
In all specimens (except the CNT specimen), the compressive strength decreased as the mixing content of the carbon material increased. MF and CF prevented the formation of a dense UHPC microstructure, while expanded graphite absorbed large quantities of water, limiting the availability of moisture for concrete hydration and forming numerous pores. Therefore, carbon materials exhibited a negative effect on the enhancement of compressive strength in UHPC.  
The tensile strengths of the CNT and MF specimens were similar, while the specimen containing graphite exhibited the lowest tensile strength. The specimen containing CF exhibited high tensile strength owing to the bridging effects of steel fibers; this confirmed that millimeter-sized carbon fibers significantly influence the tensile strength of UHPC.  
The modified concrete exhibited higher conductivity than general concrete due to the formation of a conductive network by the steel fibers in UHPC. The specimen containing CF exhibited particularly high conductivity, which increased on increasing its mixing content (with an optimal value of 1.5%). Although the conductivity of the CNT and MF specimens increased as their mixing content increased, their conductivity was not very high; the graphite specimen exhibited poor performance in increasing its mixing content. Therefore, millimeter-sized carbon fibers significantly influenced the conductivity of UHPC.  
In summary, this study confirmed that the conductivity of UHPC can be enhanced by the mixing of millimeter-sized carbon fibers with steel fibers. Furthermore, chopped fibers exhibited a positive effect on the tensile strength of concrete. This study could guide future research on the conductivity enhancement and multi-functionalization of UHPC. Moreover, further research optimizing the length/shape of carbon fibers used and mixing contents could facilitate vast improvements in concrete technology.  
Figure 10: Alternating current measurements at the age of 28 days.  
**Author Contributions:** Conceptualization, K.L. and K.K. ([PERSON]); methodology, N.L. and G.R.; investigation, K.L.; data curation, K.L., N.L., G.R. and K.K. ([PERSON]); writing--original draft preparation, K.L.; writing--review and editing, K.L. and K.K. ([PERSON]); supervision, K.K. ([PERSON]); funding acquisition, K.K. ([PERSON]). All authors have read and agreed to the published version of the manuscript.  
**Funding:** Research for this paper was carried out under the KICT Research Program (project no. 20220140-001, Development of based technology for the integration and connection of the Korean Peninsula infrastructure) funded by the Ministry of Science and ICT.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.