## 2 Materials and Methods  
The material used in this study was a carbonate-high illite clay (LCR) mined in the region of Apulia, Lucera, FG, Italy. Based on earlier findings [21], this clay was pre-treated mechanically (15 min at 1800 rpm in a Retsch MM 400 mixer mill) and thermally (700 \({}^{\circ}\)C for 1 h) to yield a clay here labelled MA157. Table 1 gives the chemical compositions of the original and pre-treated clays as found on a Panalytical AXOS-Advanced XRF spectrometer fitted with an X SST-mAX (Rh anode) X-ray source. The table also lists the XRD (Rietveld method)-determined mineralogical composition for the clays [21].  
Figure 1 shows the particle size distribution for clay MA157 dispersed via ultrasound in a DOLAPIX CE64 1/100 ethanol and dispersion medium, as determined on a SYMPATEC laser sizer with a measuring range of 0.05 to 875 \(\upmu\)m.  
MA157 clay pastes were prepared with 4, 6 and 8 M solutions of NaOH at an alkaline solution/clay (S/B) ratio of 0.55, previously found to be the most suitable to ensure good paste workability. The pastes were subsequently poured into prismatic (\(1\times 1\times 6\) cm\({}^{3}\)) moulds and cured at ambient temperature and relative humidity \(>90\%\) in a climate chamber. They were removed from the moulds 20 h later and stored in the climate chamber until the 2 and 28 days test ages, when six samples at each age were tested for compressive strength on an IBERTEST(r) test frame (six specimens per test age and material were tested).  
The reaction products were analysed by X-ray Powder Diffraction analysis (XRPD) with a Bruker AXS D8 Advance Cu-K\(\alpha\) radiation diffractometer operating at 30 mA and 40 kV across a 2\(\uptheta\) range of 5\({}^{\circ}\) to 60\({}^{\circ}\) and scanning at 0.0197\({}^{\circ}\) (20) steps. They were likewise characterised Fourier-transform infrared spectroscopy (FTIR), on KBr pellets (1 mg of sample in 200 mg of KBr) with a Nicolet Thermo FTIR spectrometer, recording 64 scans per sample at 4000 to 400 cm\({}^{-1}\). Lastly, the products were analysed along the sputter-coated fracture surfaces of the samples under Scanning Electron Microscopy - Energy Dispersive X-ray spectroscopy (SEM/EDX) a JEOL JSM 5400 SEM equipment fitted with an Oxford  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multicolumn{6}{c}{**Chemical Composition (wt\%) XRF**} & \multicolumn{3}{c}{**Mineralogical Composition (wt\%, 3\(\sigma\))**} \\ \hline \multicolumn{2}{c}{**Untreated Clay**} & \multicolumn{2}{c}{**MA157 1**} & \multicolumn{2}{c}{**Untreated Clay**} & \multicolumn{2}{c}{**MA157 1**} \\ \hline
**SiO2** & 35.67 & 43.05 & **Quartz** & 16.3 (0.7) & 20.6 (1.4) \\
**Al2O3** & 11.47 & 13.14 & **Calcite** & 31.2 (1.3) & 5.4 (1.1) \\
**CaO** & 21.15 & 29.97 & **Illite/Muscovite** & 3.8 (0.5) & 3.5 (1.0) \\
**K2O** & 1.73 & 2.28 & **R0 illite(0.3)/smectite** & 24.5 (2.9) & - \\  & & & **mixed layers 2** & 24.5 (2.9) & - \\
**Na2O** & 0.34 & 0.36 & **Kaolinite** & 5.9 (1.0) & - \\
**Fe2O3** & 6.67 & 9.34 & **K-feldspar** & 4.2 (1.0) & 10.6 (1.7) \\
**MgO** & 1.91 & 2.22 & **Albite** & 3.2 (0.5) & 3.4 (0.8) \\
**MnO** & 0.15 & 0.21 & **Goethite** & 1.7 (0.2) & - \\
**TiO2** & 0.53 & 0.73 & **Hematite** & - & 2.8 (0.5) \\
**P2O5** & 0.07 & 0.09 & **Dolomite** & 1.0 (0.2) & - \\
**LoI** & 20.32 & 0.61 & **Chlorite** & 1.0 (0.3) & - \\  & & & **Amorphous matter** & 7.1 (6.3) & 53.9 (3.6) \\  & & & **Tot C.M.** & 35.2 (3.7) & 3.5 (1.0) \\ \hline \end{tabular}
\end{table}
Table 1: Bulk chemical composition and mineralogical content of the original untreated clay and pre-treated MA157.  
Figure 1: MA157 particle size distribution.  
Link-ISIS-EDX spectrometer, collecting the images with secondary electrons (SE) at a working distance of 15 mm and a 20 kV accelerating voltage. The EDX (point) analyses were conducted with a 20 \(\upmu\)m beam, also at a 20 kV accelerating voltage and a working distance of 15 mm. Acquisition time was 30 s per point analysis.