# Mechanical, Electrical and Fractural Characteristics of Carbon Nanomaterial-Added Cement Composites
## 3 Results  
### Mechanical Properties  
The flexural strength and compressive strength of the CNM/cement composites at various ratios and dosages at 28 days of curing are shown in Figures 4 and 5, respectively. Figure 3: Experimental setup for measuring compressive strength. CNT/cement samples showed an increase in flexural strength with an increase in CNT content ratio of up to 0.6%. On further increasing the CNT content ratio up to 1.0%, the flexural strength value sharply decreased. The flexural strength of cement composite increased to 5.41%, 16.69%, and 45.68% for 0.1%, 0.3%, and 0.6% CNT content, respectively, compared with the cement-only sample. Compressive strength results showed that the inclusion of 0.3% CNT of cement weight exhibited the highest increase in CNT/cement composite samples. The compressive strength of the composites was 119.45 MPa at 0.3 wt.% CNT, which denoted a higher compressive strength than that of all other CNM/cement sample ratios, corresponding to a 112.80% increase compared with that of the cement-only sample. CNT addition resulted in significant improvements in both mechanical properties compared to those of the cement-only samples. This overall improvement in mechanical properties can be attributed to the reinforcing behavior of CNT, i.e., crack bridging, gap filling, modification of the microstructure, and nucleation effects of CNT on the cement matrix [72; 73]. Criteria such as the water/cement ratio, dispersion of CNT, and low porosity [70; 73; 74; 75; 76] are also crucial in improving the mechanical properties of composites. However, in the current study, CNT/cement composites with 1.0% CNT content exhibited  
Figure 4: Flexural strength of CNT/cement composite samples, GNP/cement composite samples, graphene/cement composite samples, and CNF/cement composite samples with increasing CNM content ratios at 28 days of curing. Figure 5: Compressive strength of CNT/cement composite samples, GNP/cement composite samples, graphene/cement composite samples, and CNF/cement composite samples with increasing CNM content ratios at 28 days of curing. decreased flexural strength, and compressive strength, which could be due to improper dispersion of the high CNT content. It has been reported that due to van der Waals forces, CNTs tend to agglomerate, and the likelihood of agglomeration increases with higher CNT dosages in cement composites [77]. Microstructural observations conducted by [PERSON] et al. [78] revealed significant CNT agglomeration at a 0.5% dosage compared to 0.15% and 0.25%. Similarly, [PERSON] and [PERSON] (2016) [11], as well as [PERSON] and [PERSON] (2015) [17], reported a reduction in the mechanical properties of cement composites at higher CNT contents, attributing the deterioration to CNT agglomeration at elevated concentrations. For all mechanical properties, a CNT content ratio between 0.3% and 0.6% showed more positive results compared with those obtained at other ratios. Other studies have also reported the same pattern. [PERSON], [PERSON], and [PERSON], 2016 [11], and [PERSON] and [PERSON], 2015 [17], concluded that the optimum concentration of CNT for an increase in compressive strength is between 0.1% and 0.3%. Similarly, a study conducted by [PERSON] et al., 2019 [13], illustrated that compared to 0.2% and 0.6% CNT content of cement weight, 0.4% CNT content increased the compressive strength of cement mortar. From these results, a conclusion can be drawn that the optimum concentration of CNT for increasing the mechanical strength of cement composites should be in the range of 0.1-0.6%. GNP/cement samples exhibited the maximum increase in flexural strength of 7.56 MPa at a 1.0% GNP content ratio. Adding GNP content at a ratio of 1.0% improved the flexural strength of cement composites by 27.17% compared to that of the cement-only sample.