# Fracture Behaviour of Concrete with Reactive Magnesium Oxide as Alternative Binder
## 2 Materials and Methods
### Experimental Procedure
#### 2.1.2 Mix Design  
The mixes' composition was based on the methodology proposed by [PERSON] et al. [34], taking into account the following parameters: C30/37 strength class, XC3 exposure class, and S2 slump in accordance with the EN 206 standard [35]. The materials' contents of the mixes, in volume, are provided in Table 2. All the mixes were designed based on the same composition, with different w/c ratios required to keep all mixes within the target slump.  
Concrete production was done in three phases with a total mixing time of 10 min. The first phase lasted 4 min and the coarse aggregates were mixed with 2/3 of the total mixing water. In the second phase, the fine aggregates were added and mixing lasted two minutes. The third phase consisted of adding the cement with the remaining 1/3 of the water in the mix for four minutes. The replacement of cement with reactive MgO was made by mass at 5%, 10%, and 20%. These percentages were defined according to the results obtained in a previous investigation [22]. There, the mechanical and durability behavior of mortars with reactive MgO was studied, using replacement ratios of 0%, 5%, 10%, 15%, 20%, and 25% by mass. The mixes were named as follows: RC for the reference concrete without any reactive MgO, concrete with partial replacement of reactive MgO from Spain and without grinding treatment was named S0, concrete with reactive MgO and with one-hour grinding treatment was named S1, and concrete with MgO's from Australia and Canada was named A and C, respectively. To designate the MgO incorporation ratio in the mixes, the nomenclature that designates first the amount of substitution and then the origin, was used, e.g., C5:C describes a concrete with 5% MgO from Canada.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **MgO-S0** & **MgO-S1** & **MgO-C** & **MgO-A** & **Cement** \\ \hline \hline Purity (\%) & 85.0 & 86.3 & 96.0 & 98.8 & - \\ Specific surface (m\({}^{2}\)/g) & 4.9 & 3.0 & 47.9 & 51.2 & 2.8 \\ Reactivity (s) & 3544 & 1460 & 16 & 14 & - \\ Skeletal density (kg/m\({}^{3}\)) & 3071 & 3111 & 3371 & 3584 & 3110 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics of the various reactive MgO’s and cement.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Mixes Name** & **Quantity of** & **Quantity of** & **Quantity of** & **Quantity of Fine** & **Quantity of Coarse** & **Fresh-State** \\  & **Water** & **Cement** & **MgO** & **Aggregates** & **Aggregates** & **Density** \\ \hline RC & 174 & 300 & 0 & 883 & 997 & 2427.5 \\ C5:C & 179 & 285 & 15 & 883 & 997 & 2455.0 \\ C10:C & 182 & 270 & 30 & 883 & 997 & 2372.8 \\ C20:C & 188 & 240 & 60 & 883 & 997 & 2363.1 \\ C5:S0  
Table 2 also shows the results of the fresh-state density of concrete. It shows that the density remains constant as the MgO incorporation ratio increases.  
By increasing the incorporation ratio of reactive MgO, the consistency of the mixes tended to decrease. Therefore, it was necessary to increase the water/binder ratio in the mixes as reactive MgO increased to maintain the target consistency, as observed in Figure 1a. Figure 1b shows that all mixes are within the S2 consistency range as the content of reactive MgO increases.