*2.2. Methods*

The thermal behaviour of the acid-activated geopolymers obtained in this study was evaluated through differential thermal analysis (DTA) combined with thermogravimetric analysis (TGA). Moreover, X-ray diffraction (XRD) was involved to analyse the phase transition following the geopolymerisation reaction.

### 2.2.1. X-ray Diffraction

The mineralogical composition of the acid-activated geopolymers was analysed by XRD using X'Pert Pro MPD equipment (Malvern Panalytical Ltd., Eindhoven, The Netherlands). The CuKα radiation was recorded in the range of 5◦ and 60◦ 2θ using a single channel detector. The radiation was collected at a step size of 0.013◦, while the copper X-ray tube was operated at a 40 mA current intensity and a 45 kV voltage.

The XRD analysis was performed on samples in a powder form, which were grounded after the curing period.

#### 2.2.2. Simultaneous Thermal Analysis

The transformations of phases and weight evolution was evaluated in the 25–600 ◦C temperature range using STA PT–1600 equipment (Linseis, Selb, Germany). The heating was performed in a static air atmosphere on samples lighter than 50 mg at a rate of 10 ◦C/min.
