## 5 Factor Affecting the Properties of GPC  
### Molarity of Activators  
It is the most crucial step in preparing the geopolymer concrete because its type concentration, and amount significantly affect both fresh and hardened properties of GPC. Different types of activators along with varying molarities were studied in literature [49; 55; 57; 125; 126; 134]. In addition, type and concentration of numerous activators were also suggested for the different type of aluminosilicates-based GPC. [PERSON] et al. [2] investigated the factors that affect the mechanical properties of GGBFS-based GPC. They found that with the increase of NaOH molarity, the compressive strength of alkali-activated slag increases due to a rise in alkalinity that results in the formation of a high amount of hydration products. [PERSON] et al. [116] evaluated the 7-day strength and setting time of GPC comprising of various binders. The authors found ascending trend in the compressive strength and decline in workability of fly ash-based geopolymer when molarity increased from 10M to 16M. The increase showed strong correlation as shown in the Figure 23. According to the authors [116], this increase is due to the improvement of dissolution rate of aluminosilicates that improve poly-condensation process and geopolymeric structure (Figure 23). Conversely, [PERSON] et al. [38] evaluated the effect of different alkaline activator solutions having activator content of 35% (A35), 40% (A40), and 45% (A45) of total binder weight on the fresh and hardened characteristics of GPC. It was noticed that increasing activator content from 35-45% reduces the strength of both GPC and mortar (Figure 24), which might be due to precipitation of aluminosilicate gel at higher alkali content. In addition, the reduction increases with the age of the mortar upto more than 60% after 60 days in the case of A45. In addition, algorithmic increase was found with respect to age (Figure 24).  
Figure 23: Relationship between molarity and compressive strength, modified from [116]; Elsevier 2018.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Durability Parameters** & **Relationship with Durability** & **Impact on Durability** & **Remarks** \\ \hline \multirow{4}{*}{Wetting-drying cycles} & \multirow{2}{*}{Inverse relation} & & The wetting-drying and heating-cooling cycles \\  & & & will influence the compressive strength and \\  & & & internal microstructure of GPC. Higher weight \\  & & & loss in these cycles will result in poor durability \\  & & & condition of GPC. \\ \hline \multirow{4}{*}{Acid attack} & \multirow{2}{*}{Inverse relation} & & Any type of acid attack depends on the \\  & & & exposure conditions of GPC samples. The acid \\ \cline{1-1}  & & & attack in GPC is dependent on both the \\ \cline{1-1}  & & & physical condition of GPC sample and chemical \\ \cline{1-1}  & & & composition of geopolymeric mixture. \\ \hline \end{tabular}
\end{table}
Table 8: _Cont._[PERSON] et al. [162] concluded that the alkaline liquids containing soluble silicates showed the vigorous rate of reaction when compared to the hydroxides. [PERSON] et al. [163] investigated the strength effect of FA-based concrete with the use of different alkaline activators such as NaOH + Na\({}_{2}\)SiO\({}_{3}\), NaOH + K\({}_{2}\)SiO\({}_{3}\), and KOH + Na\({}_{2}\)SiO\({}_{3}\) of different molarity at 90 \({}^{\circ}\)C. The alkaline activator consisting of a combination of KOH and Na\({}_{2}\)SiO\({}_{3}\) showed higher compressive strength when compared to the other two mixtures, as displayed in Figure 25. Hence, it is concluded that the type and concentration of molarity effects the compressive strength of GPC. In addition, with increase in molarity, the compressive strength of GPC increases.  
Figure 24: Effect of activator content on compressive strength, adopted from [38]; Elsevier, 2014.  
Figure 25: Comparison of compressive strength of different activator combinations for 10M at 90 \({}^{\circ}\)C, modified from [163], [PERSON], 2016.