## 4 Mechanical Properties of Geopolymer Concrete
### Concurrent Efficiency of Fly Ash and OPC on Mechanical Properties
\begin{table}
\begin{tabular}{c c c} \hline
**Author** & **Aim** & **Results** \\ \hline [PERSON] et al. [33] & The effect of different SPs on Alkali & In contrast, N had better performance in the case of low W/P ratio in AAMs containing Na\({}_{2}\)SiO\({}_{3}\). Reducing water content in AAMs with Na\({}_{2}\)SiO\({}_{3}\) had negligible effect on compressive strength. \\ \hline [PERSON] et al. [34] & The effect of combinative material & GGBS dosage lower than 25\% had a slight effect on the workability and strength of GRAC. The optimal mechanical performance and workability in terms of GRAC was obtained by using 50\% FA and 50\% GRAC with W/B ratio = 0.5. \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._Regarding the porosity of PCC, this concrete property is typically in the range of 15-25%, which is a larger amount than the concrete with higher density. In fact, the high porosity can lead to structural and environmental defects, especially in the case of concrete strength [40]. Therefore, [PERSON] et al. [40] firstly presented the comprehensive experimental investigation in terms of the effect of material proportion, such as cement-aggregate ratio by mass (C/A) on porosity and determination of optimum value for PCC compressive strength. The second stage was the choice of FA as supplementary cementitious material in order to replace PP at the optimum C/A ratio determined in the previous step. Experimental results showed that C/A and FA percentage as PP replacement have considerable influence on the concrete properties (Figure 3). As for the mix design of geopolymer paste (GPP), the effects of ground granulated blast furnace slag (GGBFS) content along with sodium silicate solution to sodium hydroxide solution (SS/SH) mass ratio and additional water to binder (Aw/Bi) mass ratio on the compressive strength, setting time and workability of GPPs were experimentally investigated in a study by [PERSON] et al. [41], to conduct GPC tests based on the optimum mix design of GPP previously obtained in the first stage of this study. It was shown that GPC properties were relatively better than those of OPC concrete (Figures 4 and 5). Having reviewed the improvement of compressive strength and workability of GPCs, other concrete properties affected by this additive material were considered as well. Recently, the development of durable cementitious material is the most important issue, which is related to sulphate attacks and acid attacks, as well as chloride penetration. Therefore, concrete durability improvement is essential in order to reduce concrete permeability by utilizing laboratory methods, in which a superplasticizer is one of the methods which has the potential to improve workability resulting in porosity reduction [42]. Hence, the concurrent effect of pozzolanic and superplasticizer on strength, workability and concrete durability as three significant aspects in the construction field was experimentally studied in the program conducted by [PERSON] et al. [42]. It was found that sorptivity value of the concrete mixes blended with SPs was lower than that of control mixes without SP. Durability improvement was seen for concrete specimens containing SP compared to those without SP. More details regarding these prior experimental studies mentioned above are presented in Table 3.  
Figure 3: The relationship between: (**a**) compressive strength after 28 days and cement–aggregate ratio by mass (C/A) ratio; (**b**) concrete porosity and C/A ratio [40]. Figure 4: Effect of ground granulated blast furnace slag (GGBFS) content on the compressive strength of geopolymer pastes [41]. Figure 5: Effect of alkaline solution to binder (Al/Bi) ratio and sodium silicate solution to sodium hydroxide solution (SS/SH) ratio on compressive strength of geopolymer paste compared to conventional concrete (OPC) [41].