## 5 Results and Discussions  
### Basic Property Test  
Figure 7 shows the specimens before and after the compressive and flexural strength tests. Figure 8 shows the compressive strengths of the specimens with different amounts of activated carbon with admixture ratios of 5%, 10%, and 15%. The compressive strength test was conducted on days 1, 3, 7, 14, 21, and 28 after the specimen was produced, following the KS F 4042 test method. Owing to its fast-hardening nature, a relatively high initial strength was measured for all the specimens. The 28-day strength of general mortar was 63.9 MPa, while conductive mortar showed reduced strengths of 51 MPa (5%), 48.8 MPa (10%), and 34.7 MPa (15%) depending on the amount of conductive material. The strength varied depending on the curing time and the amount of conductive material. The strength of activated carbon was lower than that of sand #6, and it was determined that the strength decreased with increasing amounts of activated carbon. However, it is judged that even with more than 15% activated carbon, the compressive strength of the mortar will be sufficiently manifested because all the measured mortars satisfied the test criterion of 20 MPa for testing polymer cement mortar for concrete structure repair outlined in KS F 4042 [34]. Figure 9 shows the flexural strengths of the specimens with different amounts of activated carbon. Flexural strength was measured in the same manner as compressive strength. The flexural strength was approximately 1/5-1/7 of the compressive strength. As shown in Figure 9, the 28-day strength of general mortar was 13.1 MPa, and conductive mortar showed reduced strengths of 12.4 MPa (5%), 11.6 MPa (10%), and 10.5 MPa (15%) depending on the amount of activated carbon. Nevertheless, all the measured mortars satisfied the test criterion of 6 MPa for testing polymer cement mortar for concrete structure repair outlined in KS F 4042 [34]. Compared to the compressive strength, there was no significant difference in the flexural strength between the general mortar and conductive mortars. Because the flexural strength is governed by the attachment of aggregates and mortar, the addition of activated carbon has a minimal impact on the flexural strength. However, a reduction in flexural strength was evident depending on the amount of activated carbon. Similar to the compressive strength, the lower strength of activated carbon compared to grade sand #6 is considered to be the cause of the strength reduction. Nevertheless, even with more than 15% activated carbon, the flexural strength of the mortar was sufficiently manifested. Figure 7: Prepared specimen (**a**), specimen after compressive strength test (**b**), and specimen after flexural strength test (**c**). Next, as presented in Table 2, with the new testing specimens, the bonding strength, permeability quantity, water absorption coefficient, moisture permeation resistance, and length variation ratio were measured according to KS F 4042 using only the 5% activated carbon specimen. The 5% activated carbon was finally selected for application to the bridge structure to evaluate the initial feasibility. Note that the results in Table 2 are different from those in Figures 8 and 9 because the measurement in Table 2 was much later than 28 days for the newly made specimens. The flexural strength was 6.5 MPa, and the compressive strength was 42.1 MPa. Although the strength decreased due to the inclusion of activated carbon, the basic properties were satisfactory. The most important indicator of repair mortar is the bond strength, and the results under standard conditions and after thermal cycling both exceeded 1 MPa, demonstrating excellent bond strength. The permeability, water absorption coefficient, and moisture penetration resistance were below the allowed limits, while the resistivity was reduced.