## 1 Introduction
The most significant technical properties of CSA cements (e.g., shrinkage compensation/self-stressing behavior, good dimensional stability, high impermeability, rapid hardening) are mainly regulated by the formation of ettrinigite (3 CaO-Al2O3 -3 CaSO4 32H2O) from the hydration of calcium sulfates (belonging and/or added to CSA clinker) and 3 CaO 3 Al2O3 -CaSO4 [28; 29; 30; 31; 32] with or without CaO, according to the following reactions:  
\[\text{3 CaO}\text{-}\text{3 Al}_{2}\text{O}_{3}\text{-}\text{CaSO}_{4}+\text{ 2 CaSO}_{4}+\text{38H}_{2}\text{O}\Longrightarrow\text{3 CaO}\text{-}\text{ \text{Al}}_{2}\text{O}_{3}\text{-}\text{3 CaSO}_{4}\text{-}\text{32H}_{2}\text{O }+\text{2 Al}_{2}\text{O}_{3}\text{-}\text{6H}_{2}\text{O} \tag{1}\]  
\[\text{3 CaO}\text{-}\text{3 Al}_{2}\text{O}_{3}\text{-}\text{CaSO}_{4}+\text{ 8 CaSO}_{4}+\text{6 CaO}+\text{96H}_{2}\text{O}\Longrightarrow\text{3(3 CaO} \text{-}\text{Al}_{2}\text{O}_{3}\text{-}\text{3 CaSO}_{4}\text{-}\text{32H}_{2} \text{O}) \tag{2}\]  
\[\text{Ettrinigite generated in the presence of CaO (Reaction (2)) expands and this behavior can be exploited by special binders such as shrinkage-resistant and self-stressing cements. Ettrinigite produced in Reaction (1) is not expansive and has a high mechanical strength at early ages.  
Furthermore, various other hydration products may occur, such as calcium silicate hydrate (C-S-H) and stratlingite (STR), respectively, according to Reactions (3) and (4):  
\[\text{2 CaO}\text{-}\text{SiO}_{2}+\text{ (1.5+n)H}_{2}\text{O} \Longrightarrow\text{ (1.5+m)CaO}\text{-}\text{SiO}_{2}\text{ (1+m+n)H}_{2}\text{O}+\text{(0.5-m)Ca(OH)}_{2} \tag{3}\]  
\[\text{2 CaO}\text{-}\text{SiO}_{2}+\text{ Al}_{2}\text{O}_{3}\text{-}\text{3H}_{2}\text{O}+\text{5H}_{2}\text{O} \Longrightarrow\text{ 2 CaO}\text{-}\text{Al}_{2}\text{O}_{3}\text{-}\text{SiO}_{2}\text{-}\text{ 8H}_{2}\text{O} \tag{4}\]  
Compared to the OPC manufacturing process, CSA cements exhibit the following environmentally friendly features: (I) reduced limestone requirement (usually <35%), and therefore less kiln thermal input and CO2 generation; (II) lower synthesis temperatures (about 150 \({}^{\circ}\)C-200 \({}^{\circ}\)C) and more friable clinkers (lower grinding energy required); (III) larger clinker dilution with additions of sulfate sources; (IV) greater use of industrial wastes, especially as kiln feed components [33; 34; 35; 36; 37; 38; 39; 40]. To further decrease CO2 emissions, CSA cements can be blended with various SCMs and/or mineral additions [41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60]. Water potabilization sludges (WPSs) are clayish residues produced during the treatment of water for human consumption in conventional water treatment plants (WTPs) [61]. Water potabilization treatments are mainly based on coagulation (generally using an alumina-based coagulant) and flocculation processes; they generate high quantities of sludges which represent about 1-5% of the total untreated water. Huge amounts of WPSs are produced worldwide (~10,000 tonnes/day); consequently, suitable alternatives to landfill need to be explored. Up to now, WPSs have been suggested in the production of bricks, ceramics, lightweight aggregates and for the manufacturing process of cement as an alternative raw material [62]. This paper investigated the possibility of using thermally treated WPSs (TTWPSs) as SCMs in CSA-blended cements; thanks to the thermal treatment, crystalline clay phases were transformed in a predominantly amorphous state (dehydroxylation process). The optimal treatment temperature, namely the one that allows the total sample dehydration [63], is usually in the range 600 \({}^{\circ}\)C-900 \({}^{\circ}\)C for clay-based materials. Two CSA-blended cements, based on TTWPSs, were submitted to physical-mechanical and hydration tests at curing times ranging from 4 h to 56 days. A neat CSA cement was used as a reference term.