## 4 Mechanical Properties of Geopolymer Concrete
### Influencing Factors on GPC Compressive Strength
[27], the effect of temperature on the characteristic of GPC was well documented. In this experimental program, pull-out tests were employed on GPC specimens under ambient condition and after exposure to 100, 300, 500 and 700 \({}^{\circ}\)C. The alkaline-silicate activator with the desired SiO2/K2O molar ratio of 1 was provided one day before the experimental test. The results showed that GPC has similar or better bond properties compared to OPC at ambient temperature (300 \({}^{\circ}\)C) and beyond 300 \({}^{\circ}\)C, which shows that GPC is able to be a practical alternative to OPC, especially in the case of high temperature where the resistance against fire is one of the significant design considerations. Most early studies, as well as current research, focus on the fact that the process of OPC production is attributed to pessimistic aspects on environments due to CO2 emission as a primary greenhouse gas; hence, [PERSON] et al. [28] conducted the study to show that the development of rubberized geopolymer concrete (RGPC) along with the improvement of GPC strength and durability are two main exigencies to be considered in this study. The following constituents were considered for the GPC mix proportioning in this study, based on Taguchi method:  
* Ratio of Alkaline activator to fly ash by mass: 0.4
* Ratio of SS to SH: 2.5
* Molarity of SH solution: 14 M
* Additive dosage: 2%  
This research indicated the assessment of strength studies, such as compressive strength, split tensile strength, flexural strength, and elasticity modules in addition to durability parameters like abrasion resistance of fly ash-based GPC, and subsequently compared the experimental observation with rubberized OPC concrete (ROPC), in which the compression of experimental outcomes proved that the RGPC has notable superiority in comparison with ROPC. This has also been explored in another investigation by [PERSON] et al. [29], where the increase of parameters such as water to solid (W/S) ratio had a considerable factor in the reduction of compressive strength in geopolymer mortars (GPMs) in contrast with Portland cement mortars (PCMs). The W/S ratio was considered from 0.275 to 0.6 by keeping the constant value of paste or free water content (Figure 2). All constituent material in this investigation was placed in a dry location at typical temperature (20 \(\pm\) 2 \({}^{\circ}\)C), except for mixing water which was maintained at 17 \(\pm\) 1 \({}^{\circ}\)C. The comparison of GPMs and PCMs showed that the lower content of free water is needed for GPMs and rapid strength increments, as well as shorter setting time in this concrete mix proportion. Further details in relation to abovementioned research are summarized in Table 1.  
Figure 2: The effectiveness of w/s ratio and w/c ratio on the flow of geopolymer mortars (GPM) and Portland cement mortars (PCM) mixes: (a) the constant past value; (b) the constant free water content [29]. \begin{table}
\begin{tabular}{c c c} \hline
**Author** & **Aim** & **Results** \\ \hline \multirow{6}{*}{[PERSON] et al. [23]} & & GPC and OPC concretes of four different grades and workability levels at standard curing (ambient) conditions (23 \({}^{\circ}\)C) were experimentally studied. The compressive strength of GPC at early ages (1-3 days) was significantly lower than that of OPC. From 28 to 90 days, the growth of the strength enhancement in GPC was considerably higher than that of OPC.