## 3 Results and Discussion
Compared to the reference system, CSA20-based paste (Figure 7, middle) displayed a trimodal pore size distribution for all the investigated curing times; furthermore, at the shortest and longest curing times, the highest pore widths ranged from 196 nm to 66 nm, while the lowest was below to the detectable apparatus limit (3.6 nm); likewise, its cumulative pore volume lowered of about 40% (passing from 254 mm\({}^{3}\)/g to 149 mm\({}^{3}\)/g) from 4 h to 7 days; after 56 days of curing it further decreased to 131 mm\({}^{3}\)/g. For the CSA35 system (Figure 7, bottom), the cumulative pore volume reduced of about 45% (from 289 mm\({}^{3}\)/g to 160 mm\({}^{3}\)/g) from 4 h to 56 days of curing; in addition, similarly to the CSA20 system, a trimodal pore size distribution at all the investigated curing times was exhibited. Figure 6: Ettringite, ye’elimite and belite concentrations as determined by the Rietveld method at 4 h, 28 and 56 days of curing. Figure 7: _Cont._  
The total porosity percentage (TP) of the investigated systems _vs._ curing time is illustrated in Figure 8; the related curves clearly show a similar trend for all binders whose TP values decrease with an increase in hydration time. In particular, at 4 h and 7 days of hydration, TP was lowest for the plain CSA cement and highest for the blend with 35% by mass of TTWPSs; in this period, the reduction rate of porosity was higher than that exhibited from 7 days to 56 days of curing for the three systems. Finally, at 56 days of curing, the total porosity of CSAR (21.7%) was slightly higher than that of CSA20 (21.1%) and lower than that exhibited by CSA35 (23.4%). Figure 8: Total porosity for CSAR, CSA20 and CSA35 pastes hydrated (w/b = 0.65) for 4 h, 7 and 56 days. Figure 7: Cumulative (left) and derivative (right) Hg volume _vs._ pore radius for CSAR (top), CSA20 (middle) and CSA35 (bottom) pastes hydrated (w/b = 0.65) for 4 h, 7 and 56 days. Environmental Implications of the Manufacture of CSA-Based Cements: Kilin Thermal Requirement and CO\({}_{2}\) Emissions  
The kiln thermal requirement for the manufacture of OPC clinker is about 3450 MJ/t\({}_{\text{clinker}}\), representing the average value of data reported in the scientific literature (3100-3800 MJ/t\({}_{\text{clinker}}\)) [66; 67; 68; 69; 70; 71; 72]. CO\({}_{2}\) specific emissions from the clinker burning process, generated by both limestone calcination (0.54 t\({}_{\text{CO2}}\)/t\({}_{\text{clinker}}\)) and fuel combustion, is estimated at about 0.86 t\({}_{\text{CO2}}\)/t\({}_{\text{clinker}}\); these data represent the average value calculated on the basis of several scientific papers (0.83-0.89 t\({}_{\text{CO2}}\)/t\({}_{\text{clinker}}\)) [66; 73; 74]. The energy consumption associated with CSA clinker manufacture accounts for about 2700 MJ/t\({}_{\text{clinker}}\)[75]; furthermore, the amount of the emitted CO\({}_{2}\) is around 25-35% lower than that generated in the production of OPC clinker (0.86 t\({}_{\text{CO2}}\)/t\({}_{\text{cluster}}\)) [67; 68; 69; 76; 77; 78]. The energy saving and CO\({}_{2}\) emission reduction become higher if we compare an OPC CEM I-type cement (composed by 95% clinker and 5% gypsum) with a CSA binder (constituted by 85% clinker and 15% gypsum); these reductions are even more significant if we blend CSA cements with SCMs, such as TTWPSs. In particular, if flash calcination is employed for the thermal treatment of WPSs, the energy required and the associated CO\({}_{2}\) emissions are 2211 MJ/t\({}_{\text{WPSS}}\) and 0.20 t\({}_{\text{CO2}}\)/t\({}_{\text{WPSS}}\), respectively [79; 80].