Fig 1; Fig A2 - Atterberg plastic limit measurements were taken over a range of sodium hydroxide solution concentrations, based on BS 1377-2:1990.

Fig 2; Fig 3; Fig 4; Fig A1; Fig A3  - Powder X-ray diffraction (PXRD) analysis was done to identify phases with a Bruker D8 Advance instrument using monochromatic CuKalpha1 L3 (λ = 1.540598 Å) X-radiation and a Vantec superspeed detector. A step size of 0.016⁰(2θ) and step duration of 0.3 seconds were used.

Fig 7; Fig 8; Fig A5; - Thermogravimetric analysis (TGA) was done to characterise thermal behaviour, using a Setaram Setsys Evolution TGA over a range of 30 to 1000 °C at a heating rate of 10 °C/minute. An air atmosphere was used, with a flow rate of 20 ml/minute. A connected mass spectrometer was used (Pfeiffer Omni) to identify whether evolved gas species contained OH, H2O, CO or CO2. 

Fig 9; Fig 10 - Magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra were measured for 27Al and 29Si to characterise coordination states, using a Varian VNMRS in direct excitation. Standards used were 1M aq. Al(NO3)3 for 27Al and tetramethylsilane for 29Si. Spin rates used were 12 kHz for 27Al and 6 kHz for 29Si, and frequencies used were 104.199 kHz for 27Al and 79.435 MHz for 29Si. Sample holders were 4mm width for 27Al and 6mm width for 29Si. 

Fig 11; Fig A6 - Fourier Transform Infrared Spectroscopy (FTIR) was done to characterise molecular bonding, using a Perkin-Elmer Frontier with a diamond Attenuated Total Reflectance (ATR) head. Spectra were collected over a range of 4000-600 cm-1 using a resolution of 4cm-1 and 5 scans per spectrum.