# Performance of Pozzolan-Based Reactive Magnesia Cement Mixes against Sulphate Attack
## 2 Materials and Methods  
### Sample Preparation  
The RMC (i.e., calcined magnesite 92/200) was obtained from Richard Baker Harrison, while the siliceous fly ash and slag were obtained from Engro Corporation. These raw materials were analysed using a Cilas model particle size analyser and a Rigaku model X-ray fluorescence (XRF) instrument in order to determine their average particle size and chemical composition. The average size of their particles is within the range of 14-17 \(\mu\)m, which was interpreted from the test results shown in Figure 1. A semi-automatic pelletiser was used to compact a powder sample in a circular metal disc, which was then analysed using XRF to obtain the data presented in Table 1. In this study, fly ash of anthracite origin was used. RMC is mainly composed of MgO, while slag, which is rich in CaO and SiO\({}_{2}\), tends to form Ca-based products in RMC mixes. The samples were heated to 1000 \({}^{\circ}\)C in order to determine the loss of ignition (LOI), which was higher in the case of the RMC and slag than in the case of fly ash. Figure 2 shows the XRD results of these raw materials. The powder samples were ground to a size of less than 45 \(\mu\)m using a standard sieve and then scanned using a Bruker D8 model XRD with a source of Cu K\(\alpha\). The operating current was 40 mA, and the voltage was 40 kV. Mullite and quartz minerals were found in the fly ash, periclase in the RMC, and traces of calcite and quartz in the slag. Granite aggregate of a maximum size of 9.5 mm was used under saturated dry surface conditions during the preparation of the samples. The properties of the aggregate were evaluated according to EN 12620 [32] guidelines. The average specific gravity and water absorption of the aggregates were determined to be 2.6 and 0.4% by weight, respectively. The addition of crushed sand affects the carbonation mechanism of Mg-based products and therefore was not considered when designing the concrete samples. The RMC-based concrete mixes were made with an aggregate-to-binder ratio of 1.5, with their details being listed in Table 2. The raw materials were mixed in a Hobart mixer with a capacity of 60 L for four minutes. The fresh mix was sticky but did not flow. It was put into an acrylic mould (size: 50 mm \(\times\) 50 mm \(\times\) 50 mm) in two equal layers, which were consolidated using a vibrating table. The top surface was smooth-finished using a flat blade. The cube sample was demoulded after 72 h and stored in a concrete carbonation chamber for up to 4 weeks. During this period, the temperature inside the chamber was maintained at 25 \({}^{\circ}\)C, the concentration of CO\({}_{2}\) was 10%, and the relative humidity (RH) was 70%. The demoulding period of the concrete samples was decided based on several experimental trials because they contain pozzolanic materials, which lower the rate of strength development at initial ages. Figure 3 illustrates the sample mixing process and carbonation treatment. \begin{table}
\begin{tabular}{c c c c} \hline
**Oxide Compounds** & **RMC (\%)** & **Fly Ash (\%)** & **Slag (\%)** \\ \hline Calcium oxide, CaO & 1.6 & 1.2 & 37.8 \\ Silicon dioxide, SiO\({}_{2}\) & 2 & 58.6 & 32.3 \\ Aluminium oxide, Al\({}_{2}\)O\({}_{3}\) & - & 30.4 & 16.6 \\ Iron oxide, Fe\({}_{2}\)O\({}_{3}\) & 0.6 & 4.7 & 0.8 \\ Magnesium oxide, MgO & 91.5 & - & 9.3 \\ Potassium oxide, K\({}_{2}\)O & - & 1.5 & - \\ Titanium dioxide, TiO\({}_{2}\) & & 2 & - \\ Refractory oxide, R\({}_{2}\)O\({}_{3}\) & 1 & - & - \\ Loss on ignition, LOI & 3.3 & 1.6 & 3.2 \\ \hline \end{tabular}
\end{table} 
Table 1: XRF results of the raw materials. Figure 1: Particle size distribution of the raw materials. Figure 3: Preparation of the RMC based concrete samples. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Mix** & **RMC (kg)** & **Fly Ash (kg)** & **Slag (kg)** & **Aggregate (kg)** & **Water (kg)** \\ \hline M1 & 1000 & - & - & 1500 & 400 \\ M2 & 500 & 500 & - & 1500 & 400 \\ M3 & 500 & - & 500 & 1500 & 400 \\ \hline \hline \end{tabular}
\end{table}