## 2 Experimental Details  
### Materials  
#### 2.1.1 Precursor  
The raw materials used to produce the one-part metakaolin-based geopolymer binder (hereafter called OMGPB) included GGCS and MK. The MK used was supplied by Kaolin Group, Western Cape, South Africa. The GGCS was produced by Arcelor Mittal Steel Plant located in Vanderbijlpark and supplied by Pretoria Portland Cement (PPC) Ltd., Pretoria, both in Gauteng, South Africa. The MK is flash calcined with a high pozzolanic reactivity. The XRF analysis shows that MK is predominantly composed of SiO\({}_{2}\) (71.7%) and Al\({}_{2}\)O\({}_{3}\) (20.7%), while GGCS is rich in CaO, SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and MgO, as depicted in Table 1. These findings align with previous studies [13; 14; 16], confirming the consistent chemical composition of MK and GGCS. Further, the percentage sum of SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and Fe\({}_{2}\)O\({}_{3}\) for MK is over 70% recommended by ASTM C618 [35] for pozzolanic materials, hence classifying MK as Class N pozzolan. Further, the basicity modulus (Mb) of GGCS was assessed using Equation (1), which is the ratio of the basic oxides to the acidic oxides present in the slag. The basicity coefficient (\(K_{b}\)) was also evaluated to obtain the suitability of GGCS for concrete application (Equation (2)). The \(M_{b}\) and \(K_{b}\) are 1.06 and 1.93, respectively;hence, the GGCS is a basic slag (since the \(K_{b}>1.1\)). These results align with the findings of [PERSON] and [PERSON] (2018), supporting the pozzolanic reactivity of GGCS as a beneficial precursor in geopolymerisation processes. In addition, the chemical composition of the recycled aggregate was also determined for a better understanding of their influence on the resultant matrix (Table 1). \[\text{M}_{\text{b}}=\frac{\text{CO}+\text{MgO}}{\text{SiO}_{2}+\text{Al}_{2} \text{O}_{3}} \tag{1}\]  
\[\text{K}_{\text{b}}=\frac{\text{CaO}+\text{MgO}+\text{Al}_{2}\text{O}_{3}}{ \text{SiO}_{2}+\text{TiO}_{2}} \tag{2}\]  
The specific particle size distribution (PSD) analysis was performed on the precursors using a Mastersizer 2000 instrument and presented in Figure 1. The PSD of MK and GGCS range from 0.02 to 2000 \(\upmu\)m with uniformity coefficients of 1.46 and 0.799, respectively, depicting a more uniform distribution of GGCS particles compared to MK (Table 2). The specific gravity of MK and GGCS are 2410 kg/m\({}^{3}\) and 2900 kg/m\({}^{3}\), respectively. The specific surface area of MK is 0.838 m\({}^{2}\)/g compared to the GGCS with 0.921 m\({}^{2}\)/g, as shown in Table 2, which signifies the higher reactivity of GGCS. The scanning electron microscope (SEM) analysis was performed on the precursors using a Zeiss MERLIN (Jena, Germany) instrument available at Central Analytical Facility (CAF), Stellenbosch University to assess their surface morphology, as presented in Figure 2. The Zeiss MERLIN is an instrument manufactured by Carl Zeiss Microscopy GmbH in Jena, Germany. MK particles are observed to consist of some spherical and non-spherical particles. In contrast, GGCS predominantly consists of mixed-size angular particles, which aids its interlocking and mechanical bonding potential in the OMGPC matrix. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Compound** & **Al2O3** & **CaO** & **Fe2O3** & **MgO** & **Na2O** & **SiO2** & **TiO2** & **K2O** & **Others** \\ \hline GGCS & 14.49 & 38.24 & 1.38 & 11.90 & 0.18 & 32.93 & 0.51 & 0.55 & 0.04 \\ MK & 20.67 & 0.04 & 1.73 & 0.83 & 0.36 & 71.74 & 0.86 & 3.12 & 0.04 \\ RESIN8 & 3.14 & 10 & 0.43 & 0.35 & 0.05 & 7.07 & 1.42 & 0.04 & 0.08 \\ FWG & 1.76 & 10.61 & 0.62 & 0.63 & 12.41 & 71.92 & 0.08 & 0.49 & 0.13 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of Precursors and recycled aggregates. Figure 1: Particle size distribution of precursors.