# Mechanical, Electrical and Fractural Characteristics of Carbon Nanomaterial-Added Cement Composites
## 3 Results
### Fractural Characteristics  
As shown in Figure 6a,b, the CNM/cement composites significantly improved the fracture energy and toughness compared to those of the cement-only sample.  
For CNF/cement composites, maximum fracture energy and toughness, at a 1.0% content ratio, were 9.22 N/m and 0.81 MPa/m\({}^{1/2}\), respectively. Compared to cement-only samples, the CNF-added samples with a 1.0% dosage showed an increase in fracture energy and fracture toughness of 59.40% and 41.76%, respectively. The fracture energy of CNF/cement composites increased by 30.54%, 50.91%, and 28.55% when the CNF contents were 0.1%, 0.3%, and 0.6%, respectively, compared to that of the cement-only sample. Meanwhile, the fracture toughness of the CNF/cement composites increased by 22.29%, 28.79%, and 20.06% when the CNF contents were 0.1%, 0.3%, and 0.6%, respectively, compared to that of the cement-only sample. The overall improvement in the fractural characteristics of the CNF-added cement composite is likely due to the CNF nanostructure, which consists of a conical-shaped graphite plane that improves the mechanical properties by creating an interfacial bond between the cement and CNF [18; 79; 80]. The pore-filling ability of CNF also improves the fracture energy by restricting nanocrack propagation in cement composites when well-dispersed [39; 81].  
Regarding the CNT/cement composite case, the maximum fracture energy and toughness were 7.99 N/m and 0.84 MPa/m\({}^{1/2}\), respectively, achieved at a 0.6% content ratio.  
Figure 6: CNM-added composite samples: (**a**) fracture energy; (**b**) fracture toughness at 28 days of curing.  
Compared to the cement-only sample, adding 0.6% CNT to a cement composite increased fracture energy and toughness by 38.06% and 46.06%; further increasing the CNT content decreased the fractural characteristics. Improper dispersion of 1.0% CNT content on cement matrix may lead to agglomeration, which could cause a decrease in flexural characteristics. The overall improvement compared to the cement-only samples could be attributed to crack bridging and interconnectivity between the CNT and the hydration product, leading to a load transfer [24; 25].  
Regarding GNP/cement composites, the maximum fracture energy and toughness occurred at a 1.0% content ratio and were 8.48 N/m and 0.71 MPa/m\({}^{1/2}\), respectively. Due to the 1.0% GNP addition, the fracture energy increased by 46.57% and the fracture toughness by 24.44%, compared to the cement-only composite results. The fracture energy of GNP/cement composites increased by 4.42%, 27.19%, and 30.96%, when the GNP content was 0.1%, 0.3%, and 0.6%, respectively, compared to the cement-only samples. The improvement in the fractural characteristics of the GNP-added cement composites can be attributed to GNP's ability to improve the density of cement composites, which leads to crack bridging [82].  
Compared with other CNM-added composites, cement composites created with a graphene content ratio of 1.0% demonstrated the most significant improvement. For graphene/cement composites, the maximum fracture energy and toughness occurred at a 1.0% content ratio and were 12.57 N/m and 0.86 MPa/m\({}^{1/2}\), respectively. Adding 1.0% graphene increased the fracture energy by 117.26% and fracture toughness by 50.09% compared to cement-only sample results. The fracture energy of the graphene/cement composite increased by 41.69%, 29.09%, and 31.49% when the graphene contents were 0.1%, 0.3%, and 0.6%, respectively, compared to that of the cement-only sample. Similarly, graphene/cement composite fracture toughness increased by 32.73%, 23.83%, and 24.4% when the graphene content was 0.1%, 0.3%, and 0.6%, respectively, compared to that of the cement-only sample. Graphene forms bonds in the cement matrix to improve the load-transfer capacity and fracture characteristics [24]. Correlation graphs between load and displacement of CNM-added cement composite are shown in Figure 7.