## 5 Discussion
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Author** & **Aim** & **Results** \\ \hline [PERSON] et al. [48] & The effect of SC/SS dosage on the strength of FA/ slag GPP & The increment of slag content and activator dosage caused the increase of compressive strength. The increase of W/b ratio reduced compressive strength. The developed pastes with 30 wt \% activator dosage along with 0.21 w/ b ratio and FA/ slag ratio of 2:1 produced mortar with 72 MPa compressive strength. \\ \hline [PERSON] et al. [49] & The effect of SS/SH on mechanical and durability of GPC containing RCA. & The increase of SS/SH can improve GPC strength. The usage of RCA decreased GPC strength by up to 28%. The enhancement of SS/SH ratio can help to reduce the chloride ions permeability leading to the reduction of GPC absorption. SS/SH ratio of three showed higher density and less porosity compared to the lower ratios. \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._effective curing temperature for polymerization and further enhanced the formation of N-A-S-H because of the exothermic nature of the hydration reaction. The additional calcium also accelerated hardening and dissolution by preparing extra nucleation sites. On the other hand, the enhancement of OPC beyond 20% led to an increase in calcium content and consequently, a reduction of silica and alumina values, which was due to high calcium amount and low silica and alumina in OPC. On the contrary, in the chemical combination of fly ash, less calcium and high amount of silica and alumina are available. Thus, this led to the lack of sufficient alumina and silica in order to produce N-A-S-H polymerization in this concrete mix design. Also, higher calcium increased the water demand for hydration, which was released from water-filled pores resulting in extra void spaces. Therefore, it can be concluded that the optimal amount of OPC that would be effective for the high compressive strength of this type of concrete is 20% based on the findings achieved in this research. Based on the study by [PERSON] et al. [38], it is known that the compressive strength is directly associated with porosity and water absorption. This means that an increase in compressive strength resulted in the reduction of porosity and water absorption up to 20% OPC, whereas there was a slight increase for the rate of water absorption and porosity while increasing the value of OPC by 30% in this attempt. Other obtained observations from the specimens at ages of 90 and 365 days are in accordance with the previous test (28 days). The main significant reason for this phenomenon is the fact that the addition of OPC co-existed with GPC products (N-A-S-H, C-A-S-H) due to the additional hydration products. This resulted in incremental concrete strength and the reduction of water absorption in a concurrent manner. As discussed above, there is a substantial increase in the compressive strength of concrete with the high amount of fly ash after seven days more than that of OPC due to pozzolanic reactions. The difference of approximately 10% can be seen in the mean values of compressive strength of fly ash. Type V cement plays the main role in terms of the sulfate attack as it contains limited values of C\({}_{3}\)A (tricalcium aluminate) and C\({}_{4}\)AF participating in the process of chemical sulfate attack, however most companies are struggling to find a more comprehensive solution which resists against sulfate attack better than this type of cement. Some literature in recent years have proved that the use of fly ash, particularly low-calcium or class F, effectively enables an increase in concrete resistance against sulfate attacks [56; 57; 58; 59; 60; 61; 62; 63]. However, the improvement of concrete resistance to sulfate attack by the use of class C fly ash containing a high value of calcium is suspected as the materials with rich lime have the ability to produce their own calcium hydration independently. Therefore, the concrete containing fly ash with a high value of calcium is to be exposed against sulfate attack.