## 2 Materials and Methods
### Test Methods and Characterization Techniques  
The chemical composition of the CSA cement, the WPSs and the TTWPSs was evaluated using a X-ray fluorescence apparatus (BRUKER Explorer S4, Bruker Italy, Milan, Italy); a BRUKER D2 PHASER diffractometer (LynxEye detector, Cu K\(\alpha\) radiation and 0.02\({}^{\circ}\)29 s\({}^{-1}\) scanning rate) was used to identify the main CSA cement phases (Table 1) and the principal mineralogical compounds of hydrated pastes, quantitatively estimated using the Rietveld refinement method. The specific surface and the particle size distribution of both CSA cement and TTWPSs were determined using the Blaine apparatus and a laser particle analyzer (Malvern Mastersizer 2000, Malvern-Panalytical Italy, Milan, ITaly), respectively. Three CSA-based binders were investigated: a neat CSA cement (CSAR) and two blended CSA cements, both containing TTWPSs as a partial substitute for CSA cement in concentrations equal to 20% and 35% by mass (CSA20 and CSA35). To obtain expansion/shrinkage (e/s) measurements, eighteen paste samples (15 \(\times\) 15 \(\times\) 78 mm) were prepared using 150 g of binder (b) per system and 97.5 g of distilled water (w) (water/binder mass ratio, w/b, =0.65); the pastes were mechanically stirred for 120 s, placed in stainless-steel molds and covered with plastic foils. The samples were first cured in the air at 20 \({}^{\circ}\)C for 8 h and then demolded. Three samples per system were aged at 20 \({}^{\circ}\)C under tap water; the other three samples were stored at the same temperature in a climatic chamber at 50% relative humidity (R.H.) The length changes were determined as average values of three measurements taken with a length comparator; measurements were taken daily until 56 days of curing. The compressive mechanical strength measurements were carried out on mortars prepared according to EN 196-1 and cured for periods of up to 56 days. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Chemical Composition**} & \multicolumn{3}{c}{**Mineralogical Phase Composition**} \\ \hline  & **CSA Cement** & **WPSs** & **TTWPSs** & **CSA Cement** & **ICDD Ref. Number** & \\ \hline CaO & 44.58 & 4.95 & 6.26 & Ye\({}^{\circ}\)elimite & 30-0256 & 43.0 \\ \hline SiO\({}_{2}\) & 8.95 & 37.71 & 47.66 & \(\upbeta\)-belite & 33-0302 & 21.7 \\ \hline Al\({}_{2}\)O\({}_{3}\) & 22.42 & 27.52 & 34.78 & Celite & 38-1429 & 3.8 \\ \hline Fe\({}_{2}\)O\({}_{3}\) & 1.86 & 2.37 & 3.00 & Anhydrite & 37-1496 & 19.1 \\ \hline TiO\({}_{2}\) & 1.10 & 0.35 & 0.44 & Calcite & 05-0586 & 1.1 \\ \hline K\({}_{2}\)O & 0.30 & 1.01 & 1.28 & Brownmillerite & 30-0256 & 4.5 \\ \hline MnO & 0.08 & 0.33 & 0.42 & Gehlenite & 73-2041 & 1.6 \\ \hline Na\({}_{2}\)O & 0.08 & 0.35 & 0.44 & Others & - & 5.2 \\ \hline MgO & 0.94 & 1.18 & 1.49 & & & \\ \hline Cl & 0.07 & 0.01 & 0.01 & & & \\ \hline SO\({}_{3}\) & 16.85 & 0.53 & 0.67 & & & \\ \hline P\({}_{2}\)O\({}_{5}\) & 0.05 & 1.18 & 1.49 & & & \\ \hline l.o.i \({}^{\ast}\) & 2.16 & 22.12 & 1.56 & & & \\ \hline Total & 99.44 & 99.61 & 99.50 & Total & 100.0 \\ \hline \hline \end{tabular} \({}^{\ast}\) Loss on ignition at 950 \({}^{\circ}\)C \(\pm\) 25 \({}^{\circ}\)C.  
\end{table} 
Table 1: Chemical and mineralogical (only for CSA cement) composition of the used binder components, wt %. For DT-TG, QXRD and MIP analyses, paste samples were prepared according to the same procedure employed for the e/s measurements. The hydration of the pastes was examined from 4 h to 56 days. For each hydration time, 20 g of binder was mixed with distilled water using a w/b mass ratio of 0.65. The pastes were cast into 15 mm high and 30 mm diameter plastic cylindrical models, sealed to minimize CO\({}_{2}\) ingress and cured in a thermostatic bath (at 20 \({}^{\circ}\)C and 95% R.H.). At the end of the fixed aging period, each sample was broken in half: one part was submitted to MIP, the other gently pulverized for DT-TG and QXRD analyses.