## 4 Results and Discussion
### Effect of GONF on the Strength of Hardened Cement Paste and Concrete  
The effect of different percentages of GONF and different mix design methods (Dry- and Wet-mix design methods) on the strength of hardened cement paste was investigated. Figure 7 shows the compressive and flexural strengths of cement paste with different percentages of GONF. The specimen IDs with PD indicate that the specimens were made with Dry-mix design. The results show that the compressive and flexural strengths of PD specimens are higher than the control OPC paste at 7 and 28 days. It clearly shows that the addition of GONF in cement paste mix can lead to an improvement in strength. It is interesting to note that the strength of PD specimens increased with the increasing increment of GONF up to 0.05 wt. % The compressive strength of the PD specimens at 7 and 28 days with 0.05% GONF increased by 14.9% and 19.6%, respectively. The flexural strength of PD specimens at 7 and 28 days increased even more when 0.05% GONF is incorporated (33.9% and 28.0% increments for PD0.05). This phenomenon might be explained with the following rationale. First, GONF as a two-dimensional nanomaterial can interlock with other hydration products thus it prevents nano- and micro-cracks with its own properties (high tensile strength and modulus). Second, the dissolved ions from cement grains may react with oxygen groups at the edge of GONF to produce more cement hydration products such as calcium silicate hydrate (C-S-H) and calcium hydroxide (Ca(OH)\({}_{2}\)) when compared to the control OPC paste. Third, GONF as a nano-scale material can fill the nano- and micro-pores of the cement matrix. This phenomenon is called either nano- or micro-filler effect. \begin{table}
\begin{tabular}{c c c c} \hline
**Specimen ID** & **Mini Slump Test (cm\({}^{2}\))** & **Initial Setting (hour)** & **Final Setting (hour)** \\ \hline P & 155.48 (100\%) & 5.75 (100\%) & 9.5 (100\%) \\ PD0.01 & 155.32 (99.9\%) & 5.55 (96.5\%) & 9.25 (97.4\%) \\ PD0.05 & 121.28 (78\%) & 5.3 (92.2\%) & 9.1 (95.8\%) \\ PD0.1 & 116.61 (75\%) & 5.5 (95.7\%) & 9.45 (99.5\%) \\ PD0.5 & 107.28 (69\%) & 5.85 (101.7\%) & 10 (105.3\%) \\ PD1 & 93.29 (60\%) & 6.05 (105.2\%) & 10.1 (106.3\%) \\ PW0.01 & 155.42 (99.9\%) & 5.75 (100\%) & 9.65 (101.6\%) \\ PW0.05 & 129.05 (83\%) & 5.5 (95.7\%) & 9.5 (100\%) \\ PW0.1 & 122.83 (79\%) & 5.8 (100.9\%) & 9.75 (102.6\%) \\ PW0.5 & 111.95 (72\%) & 5.9 (102.6\%) & 10.1 (106.3\%) \\ PW1 & 105.73 (68\%) & 6.15 (107\%) & 10.55 (111.1\%) \\ \hline \end{tabular}
\end{table} 
Table 5: The results of mini slump tests, initial and final setting times. The optimum content of GONFs for cement paste (0.05%) might be due to more cement hydration products and two-dimensional interlocking between hydration products even though there was the reduction of workability (Table 5). In other words, the optimum content of GONFs for cement paste (0.05%) was the outcome of offsetting between positive and negative effects of GONFs in cement paste. To compare the effect of different mix design methods (Dry- and Wet-mix designs), PW specimens which were made with Wet-mix design were tested. The results show the same pattern of strength improvement as compared with PD specimens. All PW specimens have higher compressive and flexural strengths when compared to the control OPC paste (see Figure 8). It also shows that the strength of GONF-combined paste increases with the increasing increment of GONF up to 0.05%. The compressive strength of PW specimen at 7 and 28 days with 0.05% GONF increase by 26.9% and 25.5%, respectively. The flexural strength of PW specimens at 7 and 28 days also increased with 0.05% GONF (34.8% and 37.3% increments for PW0.05). As it can be seen, the strengths of PW specimens are higher than the strengths of PD specimens with 0.01 and 0.05% GONFs. Compressive and flexural strengths at 28 days of PW0.05 are approximately 9% and 10% higher than PD0.05. This phenomenon could be explained with the following rationale.