## 2 Experimental Details
### Methods  
#### 2.2.1 OMGPC Mix Design  
The mix design was obtained by the packing density method of the aggregates with reference to [PERSON] et al. [40]. The optimum bulk density was obtained by varying the percentage of CA to Malmesbury sand (henceforth called MS) in different proportions at 90:10, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45, and 50:50. The obtained optimum bulk density was used to calculate the packing density for each aggregate proportion. The maximum packing density at a CA:MS of 60:40 was then used for the mix design to obtain the binder, MS, and CA contents in the mix. A Taguchi experimental design approach was adopted to obtain the proportion of the binding materials. Single-Factor and Orthogonal Experimental Design Using Taguchi Approach  
The Taguchi Method is a systematic approach that utilises the Design of Experiment principles to reduce data variability and examine numerous variable parameters with \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Fibre**} & **Length** & **Diameter** & \begin{tabular}{c} **Young’s** \\ **Modulus** \\ **(GPa)** \\ \end{tabular} & \begin{tabular}{c} **Elongation** \\ **(\%)** \\ \end{tabular} & \
\begin{tabular}{c} **Specific** \\ **Gravity** \\ **(g/cm\({}^{3}\))** \\ \end{tabular} &
\begin{tabular}{c} **Tensile** \\ **Strength** \\ **(MPa)** \\ \end{tabular} \\ \hline PVA & 8 & 40 & 41 & 6 & 1.3 & 1600 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Properties of PVA fibre. Figure 4: PSD of OMGPC aggregates. a minimal number of trials. By considering multiple control factors, the method aims to obtain more precise and quantitative results from minimal experiments [41]. Hence, single-factor and orthogonal experiments were designed in accordance with [PERSON] [42] and [PERSON] et al. [43]. The single factor mainly includes the percentage proportion of GGCS and MK (A) and the proportion of SS, SH, and CH (B). Experimental formula A: the mixed percentage proportions of GGCS and MK were 70:30, 60:40, and 50:50. However, it was reported by [PERSON] et al. [44] and [PERSON] and [PERSON] [45] that more than 60% GGBS will result in higher shrinkage which will reduce the durability of the material. Hence, fibre was incorporated to reduce the shrinkage of the matrix. Experimental formula B: the mixed percentage proportions of SS, SH, and CH to the binder were 30:40:30, 40:40:20, and 50:30:20. The orthogonal experimental design method was used to determine the effect of each of the designed parameters on the 7-day (7-d) compressive strength (\(f_{\text{c}}\)) of OMGPC for optimum design, as depicted in Table 5. There are two parameters (A and B) of the orthogonal experiment, with three levels for each parameter. It is assumed that there is no interaction between the two parameters. The experimental design of the orthogonal arrays consisted of 9 OMGPC mixes designed according to the orthogonal design table L\({}_{3}\)(3\({}^{2}\)), as shown in Table 6. The setting time of the geopolymer concrete mixture was investigated with 1%, 2%, and 3% contents of the retarder to obtain the efficient content for the mixture and the activator/binder ratio. The efficient retarder/binder ratio was 0.025 (2.5% by wt. of the binder), the water/solid was 0.55 (55%), and the SP to binder ratio was 0.012. 1.5% of PVA by volume of the binder was added to all the trial mixes. Table 6 shows that K\({}_{1}\) is more efficient in experimental A, while K\({}_{2}\) and K\({}_{3}\) are more efficient in experimental B. Hence, K\({}_{1}\) and K\({}_{3}\) were selected for experimental A and B,