## 3 Results and Discussion
### MIP Results  
In Figure 7 the plots of the porosimetric tests for the pastes of the four examined cements are reported; its left and right sides, respectively, represent the derivative and cumulative pore volume (CPV) curves related to the intruded mercury for the calcium sulfoaluminate-based cements towards the pore radius for the aging periods ranging from 16 h-56 days. For the C_R sample (Figure 7a), all the derivative plots displayed unimodal distributions. According to [100; 101], MIP curves do not depict the actual distribution of pore sizes in hydrated cement paste systems. In fact, large internal pores (LIPs), communicating with the outside often only through smaller pores (SPs), cannot be filled until higher pressures, which are necessary for the mercury intrusion into the SPs, are reached. Consequently, nearly all the volumes of LIPs are erroneously assigned to the sizes of the SPs. In addition, measured porosity does not coincide with actual total porosity to the extent that (a) isolated pores, entirely sealed against intrusion, may exist as well, and (b) the finest pores  
Figure 7: Derivative (**right**) and cumulative (**left**) mercury intruded volume vs. pore radius for the C_R (a), C_15 (b), C_25 (c), and C_35 (**d**) samples hydrated for 16 h and 2, 28, and 56 days. to be intruded require pressure values higher than the maximum available pressure of commercial porosimeters. Nevertheless, to compare the four investigated systems, the derivative volume coupled with the CPV could be taken as a useful indicator of the process of space-filling and of pore refinement [102]. Over the aging period, the CPV as well as the threshold pore radius slightly decreased (from 142 to 123 mm\({}^{3}\)/g and from nearly 25 to 16 nm, respectively). Compared to the C_R sample, the TTRSBT-based cements showed similar behaviours; in fact, unimodal pore size distributions could be observed at any examined aging period. Moreover, for the C_15 sample, the CPV decreased nearly 30%, passing from 201 (at 16 h) to 140 mm\({}^{3}\)/g (after 2 days); at longer aging times, it was further reduced (to approximately 100 mm\({}^{3}\)/g after 56 days of hydration). Similarly, the pore widths ranged from 274 (at 16 h) to 120 nm (at 56 days). For the C_25 and C_35 samples, the CPVs decreased approximately 39% and 16%, respectively (going from 207 to 118 mm\({}^{3}\)/g and from 190 to 160 mm\({}^{3}\)/g, respectively), in the same time interval. In comparison with the C_15 sample, the C_25, and C_35 samples exhibited pore size distributions oriented towards higher radii at all the investigated curing times, being in the 315-160 nm and 400-240 nm intervals, respectively. As a consequence of the fast hydration product generation for the C_R (revealed by both the XRD and DT-TGa analyses), a region of lower porosity was quickly established; therefore, the hydration products lowered and separated the inner space. At longer aging periods, the porosity developed gradually to the extent that the hydration had approximately stopped. Due to the lack of phases (e.g., calcium hydroxide) able to react with the thermally treated reservoir sediments the investigated blended cements, in comparison with the C_R sample, they always displayed higher pore size distributions. The total porosity percentage (TP) results vs. the aging period related to the four investigated cements are displayed in Figure 8, where the histograms show an evidently comparable trend for all the cement pastes such that their TP values decreased as the curing time increased. In particular, at all the hydrations periods, the plain CSA showed the lowest TP values; moreover, it was found that the higher the CSA cement substitution, the higher the TP value. At 2 and 56 days of curing, the TP values for the C_R sample were 21.1% and 16.8%, respectively; at the same hydration periods, the TP values for the C_15, C_25, and C_35 samples were, respectively, 14.2%, 26.4%, and 29.2%, and these were 6.5%, 22.0%, and 38.0% higher, respectively, than those for the plain CSA.