# Graphene Nanoplatelets Impact on Concrete in Improving Freeze-Thaw Resistance
## 3 Results and Discussion
### Compressive Strength Evolution  
To study the effect of GNP on the compressive strength evolution of the concrete, the compressive strength of the samples of 28 day and different F-T cycles was measured. Figure 7a illustrates 28 day compressive strength with different GNP additives concrete; it can be found that the concrete compressive strength can be improved by adding GNP up to 0.3%, the enhancement of compressive strength in GC0.02, GC0.05, GC0.1, GC0.2, and GC0.3 relative to that of GC0 was 18.61%, 22.40%, 19.78%, 8.84%, and 1.42%, respectively. When the water cement ratio and coarse aggregate of concrete are the same, the porosity of concrete will greatly affect the compressive strength of samples. There may be two reasons for the increase of strength of the graphene concrete: One is that GNP can accelerate the hydration process of cement [14], which leads to the refinement of pore structure; the other is that graphene nanoplatelets fill the holes in concrete, as evidenced by the SEM results. However, adding 0.4% of GNP had an adverse impact on enhancing the compressive strength of the specimen. The reason for the reduction of 28 days compressive strength in the concrete containing 0.1-0.4% GNP, in comparison with the samples containing 0.05% and 0.02% GNP could be the lack of uniform distribution and nanoplatelets agglomeration and the formation of weak regions in the concrete. The micro structural morphology corroborates the evolution of the strength. However, [PERSON] et al. [12] added the GNP in to the concrete, and the GNP content from 0.5% up to 2.5% at 0.5% increment, they reported that GNP has no beneficial or adverse impact on the compressive strength of the concrete, we inferred that they come to this conclusion is that they took a larger increment of graphene content and did not find the appropriate dosage.  
Figure 7: **(a)**. Twenty-eight-day compressive strength of different GNP additives. **(b)**\(D_{f}\) versus F-T actions. The compressive strength of concrete with different GNP additives.  
To research the changing trend of compressive strength of the sample in tests, compressive strength loss ratio \(D_{f}\) was defined as follows:  
\[D_{f}=\left(1-\frac{f_{n}}{f_{0}}\right)\times 100\% \tag{3}\]  
where \(f_{n}\) is the compressive strength of the sample after exposure to the nth cycles, \(f_{0}\) is the compressive strength of the sample before the experiment. Figure 7b shows the compressive strength loss ratio after F-T actions. The results show that GNP has a remarkable impact on the compressive strength of specimens during the whole test, the compressive strength loss ratio \(D_{\mathrm{f}}\) of graphene concrete samples are lower than that of control concrete. After 200 cycles, \(D_{\mathrm{f}}\) was 75.39% in the control sample; this means it destroyed according to the China national standard [23], while \(D_{\mathrm{f}}\) was 22.60%, 19.59%, 24.85%, 27.25%, 30.02%, and 39.02% in the samples containing 0.02%, 0.05%, 0.1%, 0.2%, 0.3%, and 0.4% GNP. After 200 F-T cycles, the compressive strength of GC0.02 and GC0.05 were 29.1 MPa and 31.2 MPa, respectively. Therefore, adding GNP can significantly improve the durability of concrete under F-T cycles, a probable reason is that there were few or no cracks or fine holes between the crystals in graphene concrete, which greatly reduced the water penetration into the concrete, thus reducing the frozen-heave force; hence, the freeze-thaw resistance of the material was improved. In addition, adding more than 0.05% GNP in this test presented a decreasing trend in improving the compressive strength of graphene specimen in F-T cycles. This means that the mass fraction of GNP is 0.05%wt of the cement; the effect is best in this experiment.