## 2 Geopolymer Mortar (GPM)
### Geopolymer Mortar Mechanical Properties
#### 2.2.2. Geopolymer Mortar Flexural Strength  
In cement mortars, compressive and flexural strength are tightly linked. However, due to the incredible fragility of the geopolymer and its firm adherence to the aggregate particles, geopolymer mortars have high flexural strength but poor compressive strength [49]. With the addition of sand concentration to 77%, the flexural strength of GPM improves and reaches its maximal value, which slowly decreases because there is an insufficient binder to hold the grains together [20]. Thus, these findings indicate the formation of coarse pores and increased porosity. The alkali activator solution type and curing temperature impact GPM's flexural strength considerably [50]. According to the results of [PERSON] et al. [50], the GPM with a curing temperature of 28 \({}^{\circ}\)C has higher flexural strength than mortars with curing temperatures of 60 \({}^{\circ}\)C and 90 \({}^{\circ}\)C. Additionally, the activator solution of sodium aluminosilicate hydrate has lower flexural strength than the sodium hydroxide solution [51]. [PERSON] et al. [52] studied the influence of curing conditions on the strength of Class-C FA geopolymer at W/F0.35, where he concluded \"For Class-C FA GPM with a water/ash ratio of 0.35 (CF35-C), the findings showed that before the age of 7 d, the non-standard curing shows much higher flexural strength than the standard curing. After steam curing for 24 h and 6 h, flexural strength increased sharply at the age of 1 d; then, strength developed slowly\". [PERSON] et al. [53] studied the flexural strength of GPM with various sodium concentrations and cured it for 24, 48, and 72 h at temperatures ranging from 45 \({}^{\circ}\)C to 116 \({}^{\circ}\)C. [PERSON] et al. [53] showed the GPM containing 13% sodium after 24 h of heat curing at 116 \({}^{\circ}\)C had the maximum flexural strength, while the GPM incorporating 4.0% sodium after 24 h of heat curing at 106\({}^{\circ}\)C had the lowest flexural strength. [PERSON] et al. [54] investigated the effect of Ground granulated blast-furnace slag (GGBFS) content on the ultimate flexural strength of GPM specimens cured at ambient temperature and variations in flexural strength with increasing GGBFS volume at curing ages of 7, 14, and 28 days; the results showed that at all ages, increasing the GGBFS content increased the ultimate flexural strength of GPM significantly. At 7 days, the flexural strength was improved by increasing the GGBFS content from 10 to 20, 30, and 40%, respectively. Flexural strength increased with longer curing durations, with flexural strength values for 10S, 20S, 30S, and 40S combinations rising at 14 and 28 days, respectively, compared to flexural strength values at 7 d. This is seen in Figure 11. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Ref.** & **Additives** & **Remarks** \\ \hline [PERSON] et al. [45] & PC mortar, slag, and zeolite & The compressive strength of GPM increased by up to 48\% in the first seven days compared to the cement mortar after 28 days. \\ \hline [PERSON] [44] & NaOH dosages & A high NaOH dosage increases mortar compressive strengths. \\ \hline [PERSON] et al. [47] & palm oil fuel and ash metakaolin & The high volume of palm oil fuel and ash metakaolin replacement has been found to reduce compressive strength at an early curing age. \\ \hline [PERSON] et al. [46] & blending silica-rich MK and palm oil fuel ash & The Weibull distribution is suitable for analysing the blended GPM. \\ \hline [PERSON] et al. [47] & sisal fibre (SF), coconut fibre (CF), and glass fibre (GF) & The compressive strengths of GPM reinforced with SF, CF and GF both dropped a lot more than those reinforced with SF. \\ \hline [PERSON] [48] & construction and demolition waste (CDW) & The mixed fraction had the highest strength values due to the maximum packing density. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Effect of different additives on geopolymer concrete compressive strength. According to [PERSON] et al.