Effect of Na versus Ca Sulfate Salts on the Hydration of Calcium Sulfoaluminate Clinker

Ci a ion: Padilla-Encinas, P.; Palomo, A.; Fe nández-Jiménez, A. E ec o Na e sus Ca Sul a e Sal s on he Hyd a ion o Calcium Sul oalumina e Clinke . Molecules 2023,28, 7651. h ps://doi.o g/ 10.3390/molecules28227651 Academic Edi o : Hom Na h Dhakal Recei ed: 7 Oc obe 2023 Re ised: 8 No embe 2023 Accep ed: 16 No embe 2023 Published: 18 No embe 2023 Copy igh : © 2023 by he au ho s. Licensee MDPI, Basel, Swi ze land. This a icle is an open access a icle dis ibu ed unde he e ms and condi ions o he C ea i e Commons A ibu ion (CC BY) license (h ps:// c ea i ecommons.o g/licenses/by/ 4.0/). molecules A icle E ec o Na e sus Ca Sul a e Sal s on he Hyd a ion o Calcium Sul oalumina e Clinke Pila Padilla-Encinas, Angel Palomo and Ana Fe nández-Jiménez * Edua do To oja Ins i u e o Cons uc ion Science, Na ional Resea ch Council (iETcc-CSIC), 28033 Mad id, Spain; [email p o ec ed] (P.P.-E.); [email p o ec ed] (A.P.) *Co espondence: [email p o ec ed] Abs ac : This pape examined how he amoun (5% o 20%) and ype (CaSO 4 o Na 2 SO 4 ) o sulpha e sal a ec he hyd a ion o calcium sulphoalumina e clinke (KCSA). The mechanical beha io o he pas es was de e mined a 1, 3, 28, and 90 days, he hea low and o al hea we e measu ed wi h iso he mal conduc ion calo ime y, and he eac ion p oduc s we e cha ac e ized using X- ay di ac ion (XRD), di e en ial he mal analysis/ he mog a ime y (DTA/TG) and scanning elec on mic oscopy (SEM). The esul s ob ained indica ed ha bo h he amoun o sulpha e sal (5% o 20%) and i s ype (CaSO 4 o Na 2 SO 4 ) a ec he hyd a ion kine ics, ype o eac ion p oduc s o med, and de elopmen o mechanical s eng h. The inco po a ion o CaSO 4 has a posi i e e ec on he de elopmen o he mechanical s eng h o KCSA. Howe e , Na 2 SO 4 can also p oduce ad e se side e ec s a olde ages. The p esence o Na 2 SO 4 inc eases pH alues, which pa ly des abilizes he e ingi e o med, he eby a o ing ca bona ion and hena di e p ecipi a ion, which can cause he specimens o c ack and b eak. Keywo ds: calcium sul oalumina e clinke ; alkaline sal s; mic os uc u e; calo ime y 1. In oduc ion The p esence o a high alkali con en du ing KCSA hyd a ion has a nega i e e ec on he de elopmen o mechanical s eng h. Con e sely, a ela i ely low alkali con en (0.1, 1 M) can ha e a posi i e e ec . This pape in es iga es how he p esence o solid chemical alkali ac i a o s (Na 2 SO 4 ype sal s) a ec s KCSA hyd a ion. The in e es in knowing how his sal a ec s KCSA hyd a ion s ems om he possibili y o p oducing hyb id alkaline cemen s (HACs) [ 1 – 3 ], in which hese ypes o sal s a e used o inc ease he eac i i y o he mine al addi ions ( ly ash, slag) [4–6]. Du ing he p oduc ion o Po land-cemen -based HACs, his neu al sal (Na 2 SO 4 ) in e ac s wi h he Ca(OH) 2 (p oduced by hyd a ion o he Po land cemen ) o gene a e alkalini y in si u (see Equa ion (1)), which inc eases he eac i i y o he mine al addi ions. Ca(OH)2+ Na2SO4+2H2O→CaSO4·2 H2O (s) + 2 Na+OH−(aq) (1) In he hyd a ion o KCSA o calcium sul oalumina e (CSA), he o ma ion o Ca(OH) 2 is no a o ed, so we assume ha his eac ion does no ake place. The e o e, i is impo an o know how he p esence o Na2SO4can a ec KCSA hyd a ion. Many pape s [ 7 – 10 ] in he li e a u e ha e s udied he e ec o calcium sul a e on KCSA hyd a ion. The p esence o calcium sul a e (anhyd i e o gypsum) leads o he o ma ion o e ingi e and aluminum hyd oxide. Thus, i is es ima ed ha 15–25% by mass is he app op ia e amoun o gypsum and/o anhyd i e o be added o calcium sul oalumina e clinke o op imize he se ing ime, de elopmen o mechanical s eng h and olume s abiliza ion and o ob ain a CSA. In he hyd a ion p ocess o KCSA wi h calcium sul a e, Jansen e al. [ 11 ] dis inguished he o ma ion o wo di e en ypes o e ingi e: (i) i s -gene a ion e ingi e, oge he wi h Molecules 2023,28, 7651. h ps://doi.o g/10.3390/molecules28227651 h ps://www.mdpi.com/jou nal/molecules Molecules 2023,28, 7651 2 o 20 o he compounds such as CAH 10 , amo phous AH 3 and monosul a e, which co esponded o he i s peak and induc ion pe iod in he hea low cu es o iso he mal conduc ion calo ime y; and (ii) second-gene a ion e ingi e, oge he wi h a mic ocys alline AH 3 , which co esponded o he main peak in he hea low cu es o iso he mal conduc ion calo ime y. The p esence o di e en shoulde s in he hea low cu es was a ibu ed by he au ho s o he ec ys alliza ion p ocesses o mic oc ys alline AH 3 and he inal adjus men o he wa e con en o he aluminum hyd oxide owa ds AH3. Howe e , e y ew s udies ha e in es iga ed he e ec o Na 2 SO 4 on he hyd a ion o KCSA o CSA. Sánchez-He e o e al. [ 12 ] analyzed he e ec o adding 4% Na 2 SO 4 and 8% Na 2 SO 4 on he hyd a ion o C 3 A. They obse ed ha he addi ion Na 2 SO 4 a o ed he p ecipi a ion o he U-phase (C 4 A s NH 16 ), which is mo phologically simila o calcium monosul oalumina e. The same au ho s [ 13 ] s udied he e ec o 4% Na 2 SO 4 on he hyd a ion o syn he ic ye’elimi e. They obse ed he o ma ion o he U-phase, which sligh ly a o s he de elopmen o mechanical s eng h since he U-phase has he capaci y o densi y he ma e ial. Rega ding he e ec o hese sal s on he hyd a ion o CSA, Palou e al. [ 14 ] obse ed ha he hyd a ion o CSA is as e in he p esence o 1, 2, and 3% Na 2 SO 4 han wi h wa e . This beha io is associa ed wi h he o ma ion o a p ima y e ingi e, p obably on he su ace o he ye’elimi e. Du lo e al. [ 15 ] s udied he e ec o 5% Na 2 SO 4 on he hyd a ion o CSA cemen . They obse ed wo opposi e e ec s: in he sho e m, he hyd a ion o ye’elimi e is accele a ed, while in he long e m, he e is ep ecipi a ion o hena di e, p ecipi a ion o gypsum and ca bona ion o he e ingi e. To de e mine he e ec o Na 2 SO 4 on he hyd a ion o KCSA, wo doses o his sal (5% and 20%) ha e been selec ed o his s udy. The i s dose (5%) is he dosage no mally used in Po land-cemen -based HACs [ 16 – 18 ] and he second (20%) is chosen o enable compa ison wi h he CaSO 4 dosage used in CSAs [ 9 , 10 ]. CaSO 4 is used a he same dosage (5% and 20%) o p o ide a e e ence, and some o he es s also included comme cial CSA cemen as a con ol ma e ial. 2. Resul s 2.1. Iso he mal Conduc ion Calo ime y The hyd a ion kine ics o he calcium sul oalumina e clinke we e analyzed using iso he mal conduc ion calo ime y in he p esence o 5% and 20% Na 2 SO 4 and CaSO 4 ( e e ence). This sec ion also includes he hyd a ion o a comme cial CSA ha should be conside ed a con ol ma e ial. The liquid (wa e )/solid a io used in all cases was 0.5. The hea elease a e esul s a e shown in Figu e 1. The hea elease a e cu e o he wa e -hyd a ed KCSA pas e (KCSA-H) shows ou peaks, occu ing, espec i ely, a 30 min, 1.4 h, 6.5 h, and 11 h (see Figu e 1). The cu e o he wa e -hyd a ed cemen (CSA-H) also shows ou peaks [ 15 ]. The i s o hese, which occu s a 30 min, is common o all he pas es. A e ha , wo peaks and one shoulde a e o med, eaching hei highes alues a 1.7 h, 3.4 h, and 5.3 h, espec i ely. Compa ison o he wo pas es (KCSA-H and CSA-H) shows ha cemen hyd a ion gene a es ema kable hea elease o app oxima ely 20 h; du ing KCSA hyd a ion, he hea elease con inues o a ound 30 h. While no induc ion pe iod is e iden in he cemen (CSA-H), he clinke pas e (KCSA-H) p esen s an induc ion pe iod o 3 h. When 5% CaSO 4 is added o he KCSA (KCSA-5CS), i e peaks a e o med (Figu e 1a). The i s o hese occu s a 30 min, ollowed by wo peaks a 1.4 h and 4.1 h. A 13 h induc ion pe iod is ollowed by one peak (22 h) and one shoulde (28 h). Inc easing he calcium sul a e concen a ion o 20% (KCSA-20CS) esul s in h ee peaks and one shoulde . The i s is common o all he p e ious pas es and is ollowed by wo peaks ha each hei maximum alues a 1.5 h and 2.2 h, espec i ely. A e ha , one shoulde is o med a 4 h. When compa ing he hea elease a e cu es o he ou pas es (CSA-H, KCSA-H, KCSA-5CS, KCSA-20CS), he main di e ence lies in he p esence o an induc ion pe iod be o e he hi d and ou h peaks in he pas es ha ha e ei he ze o calcium sul a e (KCSA- H) o a low calcium sul a e con en (KCSA-5CS). Howe e , all ou pas es ha e a i s peak Molecules 2023,28, 7651 3 o 20 ha appea s a a ound 30 min, ollowed by a second peak ha also appea s a simila imes in all o hem (be ween 1.4 and 1.7 h). These esul s co obo a e hose ob ained by o he au ho s [ 9 , 10 ], who indica e ha he p esence o CaSO 4 con en close o he s oichiome ic a io (20–22%) accele a es he hyd a ion eac ion o he KCSA. Molecules 2023, 28, x FOR PEER REVIEW 3 o 21 pas es (KCSA-H and CSA-H) shows ha cemen hyd a ion gene a es ema kable hea elease o app oxima ely 20 h; du ing KCSA hyd a ion, he hea elease con inues o a ound 30 h. While no induc ion pe iod is e iden in he cemen (CSA-H), he clinke pas e (KCSA-H) p e- sen s an induc ion pe iod o 3 h. When 5% CaSO4 is added o he KCSA (KCSA-5CS), i e peaks a e o med (Figu e 1a). The i s o hese occu s a 30 min, ollowed by wo peaks a 1.4 h and 4.1 h. A 13 h induc ion pe iod is ollowed by one peak (22 h) and one shoulde (28 h). Inc easing he calcium sul a e concen a ion o 20% (KCSA-20CS) esul s in h ee peaks and one shoulde . The i s is com- mon o all he p e ious pas es and is ollowed by wo peaks ha each hei maximum alues a 1.5 h and 2.2 h, espec i ely. A e ha , one shoulde is o med a 4 h. When compa ing he hea elease a e cu es o he ou pas es (CSA-H, KCSA-H, KCSA-5CS, KCSA-20CS), he main di e ence lies in he p esence o an induc ion pe iod be o e he hi d and ou h peaks in he pas es ha ha e ei he ze o calcium sul a e (KCSA-H) o a low calcium sul a e con en (KCSA-5CS). Howe e , all ou pas es ha e a i s peak ha ap- pea s a a ound 30 min, ollowed by a second peak ha also appea s a simila imes in all o hem (be ween 1.4 and 1.7 h). These esul s co obo a e hose ob ained by o he au ho s [9,10], who indica e ha he p esence o CaSO4 con en close o he s oichiome ic a io (20–22%) ac- cele a es he hyd a ion eac ion o he KCSA. When sodium sul a e is added ins ead o calcium sul a e, ou signals a e ob ained o he KCSA-5NS pas e, and i e a e ob ained o he KCSA-20NS pas e (Figu e 1b). The i s wo peaks eme ge a simila imes o hose in he pas es hyd a ed wi h wa e (a e 30 min and be ween 1.4 and 1.8 h). In he pas e con aining 20% Na2SO4 (KCSA-20NS), he peak o med a 1.8 h is ollowed by a small shoulde a 2.9 h. The hyd a ion p ocess o he pas es con aining he sal is hen slowed by a long induc ion pe iod, which is g ea es in he KCSA-5NS pas e. The las peaks appea a 15 h and 25.7 h in he KCSA-5NS and a 10 h and 13 h in he KCSA- 20NS. These esul s show ha he sul a e ype and concen a ion signi ican ly a ec he induc- ion pe iod and he hi d and ou h peaks o he hea elease a e cu es. Rela i ely low sul a e sal concen a ions delay he hi d and ou h signals while high concen a ions accele a e hem. The i s and second peaks, howe e , which, acco ding o he li e a u e [11,19], a e as- socia ed wi h he o ma ion o a p ima y e ingi e, do no appea o be se iously a ec ed. Figu e 1. (a) Hea elease a e o he pas es con aining 5% and 20% CaSO4; (b) hea elease a e o he pas es con aining 5% and 20% Na2SO4. Figu e 1. ( a ) Hea elease a e o he pas es con aining 5% and 20% CaSO 4 ; ( b ) hea elease a e o he pas es con aining 5% and 20% Na2SO4. When sodium sul a e is added ins ead o calcium sul a e, ou signals a e ob ained o he KCSA-5NS pas e, and i e a e ob ained o he KCSA-20NS pas e (Figu e 1b). The i s wo peaks eme ge a simila imes o hose in he pas es hyd a ed wi h wa e (a e 30 min and be ween 1.4 and 1.8 h). In he pas e con aining 20% Na 2 SO 4 (KCSA-20NS), he peak o med a 1.8 h is ollowed by a small shoulde a 2.9 h. The hyd a ion p ocess o he pas es con aining he sal is hen slowed by a long induc ion pe iod, which is g ea es in he KCSA-5NS pas e. The las peaks appea a 15 h and 25.7 h in he KCSA-5NS and a 10 h and 13 h in he KCSA-20NS. These esul s show ha he sul a e ype and concen a ion signi ican ly a ec he induc ion pe iod and he hi d and ou h peaks o he hea elease a e cu es. Rela i ely low sul a e sal concen a ions delay he hi d and ou h signals while high concen a- ions accele a e hem. The i s and second peaks, howe e , which, acco ding o he li e a u e [11,19] , a e associa ed wi h he o ma ion o a p ima y e ingi e, do no appea o be se iously a ec ed. Figu e 2shows he o al hea as a unc ion o ime. I demons a es ha o he i s wo hou s, all he sys ems sha e e y simila cu es. O e longe ime pe iods, he wa e -hyd a ed clinke wi h no added sul a es (KCSA-H) eleases he mos o al hea . The KCSA-5CS and KCSA-5NS pas es elease he leas ini ial hea due o hei delayed eac ion a e, bu a ad anced ages, he hea eleased, al hough less han ha eleased by he KCSA-H, is highe han ha eleased by he pas es wi h a 20% sul a e con en (KCSA-20CS and KCSA-20NS). The samples wi h he g ea es calcium sul a e con en s (CSA-H and KCSA-20CS) elease he mos hea ini ially, which is consis en wi h he accele a ion o he eac ion p ocess obse ed in Figu e 1. Al hough he KCSA-20NS pas e ini ially eleases sligh ly less hea han he o he pas es, i beha es simila ly o hem a ad anced ages. The lowe amoun s o hea eleased by hese samples (CSA-H, KCSA-20CS, and KCSA-20NS) a ad anced ages may be pa ly due o a dilu ion e ec . Molecules 2023,28, 7651 4 o 20 Molecules 2023, 28, x FOR PEER REVIEW 4 o 21 Figu e 2 shows he o al hea as a unc ion o ime. I demons a es ha o he i s wo hou s, all he sys ems sha e e y simila cu es. O e longe ime pe iods, he wa e - hyd a ed clinke wi h no added sul a es (KCSA-H) eleases he mos o al hea . The KCSA-5CS and KCSA-5NS pas es elease he leas ini ial hea due o hei delayed eac ion a e, bu a ad anced ages, he hea eleased, al hough less han ha eleased by he KCSA- H, is highe han ha eleased by he pas es wi h a 20% sul a e con en (KCSA-20CS and KCSA-20NS). The samples wi h he g ea es calcium sul a e con en s (CSA-H and KCSA- 20CS) elease he mos hea ini ially, which is consis en wi h he accele a ion o he eac- ion p ocess obse ed in Figu e 1. Al hough he KCSA-20NS pas e ini ially eleases sligh ly less hea han he o he pas es, i beha es simila ly o hem a ad anced ages. The lowe amoun s o hea eleased by hese samples (CSA-H, KCSA-20CS, and KCSA-20NS) a ad anced ages may be pa ly due o a dilu ion e ec . Figu e 2. To al hea o he e e ence samples (KCSA-H and CSA-H) and o he pas es con aining 5% and 20% CaSO4 and Na2SO4. 2.2. Mechanical Beha io Figu e 3 shows he comp essi e s eng h alues o he pas es a 1, 3, 28, and 90 days. As can be seen, he KCSA-5CS pas e p esen s s eng h alues close o hose ob ained by he KCSA-H, while he KCSA-20CS pas e p esen s highe s eng h alues a all ages, sim- ila o hose ob ained by he cemen (CSA-H). Figu e 3. Comp essi e s eng h o he pas es con aining 5% and 20% sal concen a ions; (a) CaSO4; (b) Na2SO4. 010 20 30 40 50 60 70 80 0 50 100 150 200 250 300 350 400 0 2 4 6 8 10 12 14 16 18 20 22 24 0 50 100 150 200 250 300 350 400 0 2 4 6 8 10 12 14 16 18 20 22 24 0 50 100 150 200 250 300 350 400 Hea eleased (J/g) Time (h) H2O CSA 5% CaSO4 20% CaSO4 5% Na2SO4 20% Na2SO4 KCSA-H CSA-HKCSA-20CS KCSA-5CS KCSA-5NS KCSA-20NS Hea eleased (J/g) Time (h) H2O CSA 5% CaSO4 20% CaSO4 5% Na2SO4 20% Na2SO4 KCSA-H CSA-H KCSA-20CS KCSA-5CS KCSA-5NS KCSA-20NS Hea eleased (J/g) Time (h) H2O CSA 5% CaSO4 20% CaSO4 5% Na2SO4 20% Na2SO4 KCSA-H CSA-H KCSA-20CS KCSA-5CS KCSA-5NS KCSA-20NS Figu e 2. To al hea o he e e ence samples (KCSA-H and CSA-H) and o he pas es con aining 5% and 20% CaSO4and Na2SO4. 2.2. Mechanical Beha io Figu e 3shows he comp essi e s eng h alues o he pas es a 1, 3, 28, and 90 days. As can be seen, he KCSA-5CS pas e p esen s s eng h alues close o hose ob ained by he KCSA-H, while he KCSA-20CS pas e p esen s highe s eng h alues a all ages, simila o hose ob ained by he cemen (CSA-H). Molecules 2023, 28, x FOR PEER REVIEW 4 o 21 Figu e 2 shows he o al hea as a unc ion o ime. I demons a es ha o he i s wo hou s, all he sys ems sha e e y simila cu es. O e longe ime pe iods, he wa e - hyd a ed clinke wi h no added sul a es (KCSA-H) eleases he mos o al hea . The KCSA-5CS and KCSA-5NS pas es elease he leas ini ial hea due o hei delayed eac ion a e, bu a ad anced ages, he hea eleased, al hough less han ha eleased by he KCSA- H, is highe han ha eleased by he pas es wi h a 20% sul a e con en (KCSA-20CS and KCSA-20NS). The samples wi h he g ea es calcium sul a e con en s (CSA-H and KCSA- 20CS) elease he mos hea ini ially, which is consis en wi h he accele a ion o he eac- ion p ocess obse ed in Figu e 1. Al hough he KCSA-20NS pas e ini ially eleases sligh ly less hea han he o he pas es, i beha es simila ly o hem a ad anced ages. The lowe amoun s o hea eleased by hese samples (CSA-H, KCSA-20CS, and KCSA-20NS) a ad anced ages may be pa ly due o a dilu ion e ec . Figu e 2. To al hea o he e e ence samples (KCSA-H and CSA-H) and o he pas es con aining 5% and 20% CaSO4 and Na2SO4. 2.2. Mechanical Beha io Figu e 3 shows he comp essi e s eng h alues o he pas es a 1, 3, 28, and 90 days. As can be seen, he KCSA-5CS pas e p esen s s eng h alues close o hose ob ained by he KCSA-H, while he KCSA-20CS pas e p esen s highe s eng h alues a all ages, sim- ila o hose ob ained by he cemen (CSA-H). Figu e 3. Comp essi e s eng h o he pas es con aining 5% and 20% sal concen a ions; (a) CaSO4; (b) Na2SO4. 010 20 30 40 50 60 70 80 0 50 100 150 200 250 300 350 400 0 2 4 6 8 10 12 14 16 18 20 22 24 0 50 100 150 200 250 300 350 400 0 2 4 6 8 10 12 14 16 18 20 22 24 0 50 100 150 200 250 300 350 400 Hea eleased (J/g) Time (h) H2O CSA 5% CaSO4 20% CaSO4 5% Na2SO4 20% Na2SO4 KCSA-H CSA-HKCSA-20CS KCSA-5CS KCSA-5NS KCSA-20NS Hea eleased (J/g) Time (h) H2O CSA 5% CaSO4 20% CaSO4 5% Na2SO4 20% Na2SO4 KCSA-H CSA-H KCSA-20CS KCSA-5CS KCSA-5NS KCSA-20NS Hea eleased (J/g) Time (h) H2O CSA 5% CaSO4 20% CaSO4 5% Na2SO4 20% Na2SO4 KCSA-H CSA-H KCSA-20CS KCSA-5CS KCSA-5NS KCSA-20NS Figu e 3. Comp essi e s eng h o he pas es con aining 5% and 20% sal concen a ions; ( a ) CaSO 4 ; (b) Na2SO4. The p esence o sodium sul a e (Figu e 3b) esul s in low s eng h alues a all ages in he s udy, wi h he KCSA-20NS pas e e en ually ac u ing a 90 days. Figu e 3includes a pho og aph o he c acked pas e specimen a 90 days o which, due o he ac u e, i was no possible o de e mine he mechanical s eng h. Simila esul s we e ob ained in ano he s udy [ 20 ], in which KCSA clinke was hyd a ed wi h an 8 M NaOH solu ion, and also in he pape s published by Tamba a e al. [ 15 ] on he hyd a ion o a CSA wi h Na 2 SO 4 , and by Sánchez e al. [21] on he hyd a ion o ye’elimi e wi h 8 M NaOH. Cemen pas e is a chao ic sys em wi h a e y complex s uc u e in which, in addi ion o he size and olume o po es, he e a e geome ic cha ac e is ics ha a e di icul o quan i y, i egula po e shapes and diso de ed spa ial dis ibu ions o po es. The s uc- u e o he po es can be p edic ed indi ec ly h ough compu a ional models, applying Molecules 2023,28, 7651 5 o 20 he concep s o ac al me hodology [ 22 ] o he modynamics. I can also be measu ed di ec ly h ough expe imen al echniques such as nuclea magne ic esonance, ni ogen adso p ion/deso p ion and me cu y in usion po osime y (MIP). In his wo k, he la e me hod has been used. Al hough wi h his echnique he e a e pa ame e s ha a e no aken in o accoun , such as he o uosi y o he sys em, i is conside ed ha he in o ma ion ob ained may be su icien o he desi ed objec i e. Figu e 4shows he po osi y alues and po e size dis ibu ion o he pas es con aining 5% and 20% CaSO 4 and Na 2 SO 4 a 1 and 28 days o hyd a ion. The i s obse a ion is ha , in e e y case, he po osi y dec eases wi h an inc ease in he hyd a ion ime. The igu e also shows ha he pas es con aining CaSO 4 clea ly p esen lowe po osi y alues and po e sizes han hose ob ained wi h Na 2 SO 4 . Based on he po e diame e in a ha dened cemen pas e, po es can be classi ied as ollows: gel po es (<0.01 µ m), small capilla y po es (0.01–0.1 µ m), la ge capilla y po es (0.1–1 µ m), and ai po es (>1 µ m) [ 23 ]. The numbe o capilla y po es depends on he wa e /binde (w/b) a io and he deg ee o eac ion o he pas e, which ends o dec ease as he deg ee o hyd a ion inc eases. The pas es con aining calcium sul a e gene ally ha e a highe pe cen age o small capilla y po es (0.01–0.1 µ m), while la ge capilla y po es (0.1–1 µm) p edomina e in pas es con aining sodium sul a e. Molecules 2023, 28, x FOR PEER REVIEW 5 o 21 The p esence o sodium sul a e (Figu e 3b) esul s in low s eng h alues a all ages in he s udy, wi h he KCSA-20NS pas e e en ually ac u ing a 90 days. Figu e 3 includes a pho og aph o he c acked pas e specimen a 90 days o which, due o he ac u e, i was no possible o de e mine he mechanical s eng h. Simila esul s we e ob ained in ano he s udy [20], in which KCSA clinke was hyd a ed wi h an 8M NaOH solu ion, and also in he pape s published by Tamba a e al. [15] on he hyd a ion o a CSA wi h Na2SO4, and by Sánchez e al. [21] on he hyd a ion o ye’elimi e wi h 8M NaOH. Cemen pas e is a chao ic sys em wi h a e y complex s uc u e in which, in addi ion o he size and olume o po es, he e a e geome ic cha ac e is ics ha a e di icul o quan i y, i egula po e shapes and diso de ed spa ial dis ibu ions o po es. The s uc- u e o he po es can be p edic ed indi ec ly h ough compu a ional models, applying he concep s o ac al me hodology [22] o he modynamics. I can also be measu ed di ec ly h ough expe imen al echniques such as nuclea magne ic esonance, ni ogen adso p- ion/deso p ion and me cu y in usion po osime y (MIP). In his wo k, he la e me hod has been used. Al hough wi h his echnique he e a e pa ame e s ha a e no aken in o accoun , such as he o uosi y o he sys em, i is conside ed ha he in o ma ion ob ained may be su icien o he desi ed objec i e. Figu e 4 shows he po osi y alues and po e size dis ibu ion o he pas es con aining 5% and 20% CaSO4 and Na2SO4 a 1 and 28 days o hyd a ion. The i s obse a ion is ha , in e e y case, he po osi y dec eases wi h an inc ease in he hyd a ion ime. The igu e also shows ha he pas es con aining CaSO4 clea ly p esen lowe po osi y alues and po e sizes han hose ob ained wi h Na2SO4. Based on he po e diame e in a ha dened cemen pas e, po es can be classi ied as ollows: gel po es (<0.01 μm), small capilla y po es (0.01–0.1 μm), la ge capilla y po es (0.1–1 μm), and ai po es (>1 μm) [23]. The numbe o capilla y po es depends on he wa e /binde (w/b) a io and he deg ee o eac ion o he pas e, which ends o dec ease as he deg ee o hyd a ion inc eases. The pas es con aining calcium sul a e gene ally ha e a highe pe cen age o small capilla y po es (0.01–0.1 μm), while la ge capilla y po es (0.1–1 μm) p edomina e in pas es con aining sodium sul a e. Figu e 4. Po osime y esul s a 1 and 28 days o he hyd a ed pas es con aining 5% and 20% CaSO4 and Na2SO4. 2.3. Mine alogical Cha ac e iza ion: Con inuous X- ay Di ac ion (XRD) Figu e S1 shows he con inuous XRD (e e y 30 min) di ac og ams ob ained om he hyd a ed pas es (KCSA-5NS, KCSA-5CS, KCSA-20NS, KCSA-20CS) in he i s 24 h. 5CS 1d 5CS 28d 20CS 1d 20CS 28d 5NS 1d 5NS 28d 20NS 1d 20NS 28d 0 5 10 15 20 25 30 35 40 32.23% 28.53% 34.31% 33.83% 11.05% 16.93% 15.66% 19.53% Po osi y (%) P<0.01 0.1>P>0.01 1>P>0.1 10>P>1 100>P>10 P>100 Figu e 4. Po osime y esul s a 1 and 28 days o he hyd a ed pas es con aining 5% and 20% CaSO 4 and Na2SO4. 2.3. Mine alogical Cha ac e iza ion: Con inuous X- ay Di ac ion (XRD) Figu e S1 shows he con inuous XRD (e e y 30 min) di ac og ams ob ained om he hyd a ed pas es (KCSA-5NS, KCSA-5CS, KCSA-20NS, KCSA-20CS) in he i s 24 h. Di e en colo s a e used in he di ac og ams depending on he ime in e als es ablished o each signal ob ained du ing calo ime y (Figu e 1). The educ ion in he in ensi y o he peaks associa ed wi h he ye’elimi e is g ea e in he calcium sul a e pas es (KCSA-5CS and KCSA-20CS (Figu e S1a,b) han in he sodium sul a e pas es (Figu e S1c,d). The in ensi y o he peaks associa ed wi h he e ingi e, meanwhile, is g ea e . As ega ds he sul a e con en , g ea e ye’elimi e consump ion appea s o occu in he pas es wi h 20% sul a e con en (KCSA-20CS and KCSA-20NS) han in he pas es wi h 5% sul a e con en (KCSA-5CS and KCSA-5NS). This con i ms he esul s obse ed using calo ime y, whe e he pas es wi h 20% sul a e con en begin o eac ea lie han hose wi h 5% sul a e con en did. Fo a clea e ep esen a ion o pas e hyd a ion, Figu e 5shows he con inuous XRD di ac og ams selec ed as a unc ion o he ime a which he peaks we e ob ained using calo ime y (Figu e 1). The o ma ion o small e ingi e peaks was obse ed a 30 min in all Molecules 2023,28, 7651 6 o 20 ou pas es (Figu e 5). In he pas es con aining calcium sul a e (Figu e 5a,b), he in ensi y o he e ingi e peaks inc eases om 1.5 h onwa ds. In he KCSA-5CS pas e, e ingi e becomes he main p oduc om 22 h onwa ds, while in he KCSA-20CS pas e, in addi ion o e ingi e being o med a 1.5 h, small peaks co esponding o AH 3 a e also obse ed. These peaks o AH 3 also s a o eme ge a e 4.1 h in he pas e con aining 5CS. In addi ion, he KCSA-5CS pas e shows small peaks co esponding o calcium ca boalumina e (C 4 A c H 11 ). Molecules 2023, 28, x FOR PEER REVIEW 7 o 21 Figu e 5. Con inuous XRD di ac og ams as a unc ion o calo ime y ime. Legend: Y: ye’elimi e; a: anhyd i e; b: beli e; B: b ediggi e; P: pe iclase; A: AH3; e: e ingi e; o: C4A𝑐H11; d: CAH10; L: mi a- bili e (Na2SO4 · 10 H2O). 2.4. Mine alogical Cha ac e iza ion: Discon inuous XRD Figu e 6 shows a po ion o he di ac og ams (zone spanning alues 2–5 a 30°) o he clinke and hyd a ed pas es (KCSA-5CS, KCSA-20CS, KCSA-20NS, and KCSA- 5NS) a 1, 3, 28, and 90 days. In bo h he clinke and he calcium sul oalumina e cemen , ye’elimi e (C4A3S) p e- sen s as he main phase. In addi ion, he cemen also con ains anhyd i e and, in bo h ma- e ials, beli e (C2S) and b ediggi e (Ca7Mg(SiO4)4), gehleni e (Al2Ca2O7Si), C3A, and pe i- clase (MgO) p esen as seconda y phases. The di ac og ams o he pas es con aining calcium sul a e (KCSA-5CS and KCSA- 20CS, Figu e 6) show ha as he hyd a ion ime inc eases, he in ensi y o he peaks asso- cia ed wi h he ye’elimi e and anhyd i e dec eases. The main hyd a ion p oduc , alongside AH3 and calci e, is e ingi e. In he pas e wi h 5% con en (KCSA-5CS), calcium ca boalu- mina e (C4AcH11) also p esen s a 90 days. In he pas e wi h 20% con en (KCSA-20CS), he p esence o calcium ca boalumina e is de ec ed a e 24 h alongside small peaks a - ibu able o calcium monosul oalumina e. Figu e 5. Con inuous XRD di ac og ams as a unc ion o calo ime y ime. Legend: Y: ye’elimi e; a: anhyd i e; b: beli e; B: b ediggi e; P: pe iclase; A: AH 3 ; e: e ingi e; o: C 4 A c H 11 ; d: CAH 10 ; L: mi abili e (Na2SO4·10 H2O). In he case o he pas es con aining sodium sul a e (Figu e 5c,d), he di ac og ams show ha e ingi e becomes he main hyd a ion p oduc om 1.5–2 h onwa ds, wi h he peaks being mos in ense in he KCSA-20NS pas e. The o ma ion o peaks o AH 3 and small peaks co esponding o calcium alumina e (CAH 10 ) is also obse ed a e 24 h in he KCSA-5NS pas e. Meanwhile, in he KCSA-20NS pas e, he o ma ion o small peaks iden i ied as co esponding o he mi abili e (Na 2 SO 4· 10 H 2 O) is obse ed om 30 min onwa ds, inc easing in in ensi y wi h ime [24]. I all he con inuous di ac og ams o he pas es con aining calcium sul a e a e ana- lyzed, he main phase in bo h pas es (KCSA-5CS and KCSA-20CS) is e ingi e, wi h he mos in ense peaks appea ing o be hose gene a ed by he 5% sample. In he di ac og ams o he pas es con aining sodium sul a e (KCSA-5NS and KCSA- 20NS), he o ma ion o e ingi e as he main eac ion p oduc is also obse ed in he 5% and 20% samples. Bo h pas es also show peaks co esponding o AH 3 ha inc ease in in ensi y wi h an inc ease in he hyd a ion ime om 15 h onwa ds. 2.4. Mine alogical Cha ac e iza ion: Discon inuous XRD Figu e 6shows a po ion o he di ac og ams (zone spanning alues 2–5 Φ a 30 ◦ ) o he clinke and hyd a ed pas es (KCSA-5CS, KCSA-20CS, KCSA-20NS, and KCSA-5NS) a 1, 3, 28, and 90 days. Molecules 2023,28, 7651 7 o 20 Molecules 2023, 28, x FOR PEER REVIEW 8 o 21 Figu e 6. Di ac og am o he KCSA pas e con aining he di e en p opo ions o sal s: (a) 5% CaSO4, (b) 20% CaSO4, (c) 5% Na2SO4, (d) 20% Na2SO4 a 1, 3, 28, and 90 days. Legend: Y: Ye’elimi e (C4A3𝑠, PDF-33-0256); b: beli e (C2S PDF-86-0398); e: e ingi e (C6A𝑠3H32 PDF-41-1451); A: AH3 (AH3 PDF-74-1775); T: hena di e (Na2SO4 PDF-37-1465); o: C4A𝑐 H 11 (C4A𝑐 H11 PDF-87-0493); c: calci e (CaCO3 PDF-86-2334); d: CAH10 (CAH10 PDF-12-0408); m: calcium monosul oalumina e (C4A𝑠H12 PDF- 83-1289); a: anhyd i e (C𝑠 PDF-72-0916). In he case o he pas es con aining sodium sul a e (Figu e 6), he in ensi y o he ye’elimi e also dec eases wi h an inc ease in he hyd a ion ime. In he KCSA-5NS pas e, he main p oduc o med is e ingi e, which inc eases in in ensi y up o 28 days be o e dec easing a 90 days, he age a which he p esence o o he phases such as AH3, C4A𝑐H11, and calci e is obse ed along wi h small peaks o CAH10. In he KCSA-20NS pas e, he p esence o C4A𝑐H11 is also obse ed a 90 days, while he AH3 and calci e a e obse ed a 3 days and 1 day, espec i ely. In his pas e (KCSA-20NS), CAH10 is no de ec ed. One impo an inding o no e in he KCSA-20NS pas e is ha , a 1 day, he p esence o Na2SO4 was no obse ed, no was i obse ed in he con inuous XRD analyses (see Figu e 5). Howe e , his phase was de ec ed a mo e ad anced ages, indica ing ha so- dium sul a e dissolu ion ollowed by e-p ecipi a ion in he o m o hena di e occu s. The peaks associa ed wi h he p esence o hena di e inc ease in in ensi y wi h an inc ease in he hyd a ion ime. A his poin , i should be no ed ha hese pas es exhibi ed signi ican mechanical s eng h losses (and e en c acking) be ween 28 and 90 days (see Figu e 3). 2.5. Di e en ial The mal Analysis and The mog a ime y (DTA/TG) Figu e 7 p esen s he DTA/TG esul s o he hyd a ed KCSA pas es con aining 5% and 20% CaSO4 and Na2SO4 a 1, 3, 28, and 90 days. Figu e 6. Di ac og am o he KCSA pas e con aining he di e en p opo ions o sal s: ( a ) 5% CaSO 4 , ( b ) 20% CaSO 4 , ( c ) 5% Na 2 SO 4 , ( d ) 20% Na 2 SO 4 a 1, 3, 28, and 90 days. Legend: Y : Ye’elimi e (C 4 A 3s , PDF-33-0256); b : beli e (C 2 S PDF-86-0398); e: e ingi e (C 6 A s3 H 32 PDF-41-1451); A : AH 3 (AH 3 PDF-74-1775); T : hena di e (Na 2 SO 4 PDF-37-1465); o : C 4 A c H 11 (C 4 A c H 11 PDF-87-0493); c : calci e (CaCO 3 PDF-86-2334); d : CAH 10 (CAH 10 PDF-12-0408); m : calcium monosul oalumina e (C4AsH12 PDF-83-1289); a: anhyd i e (CsPDF-72-0916). In bo h he clinke and he calcium sul oalumina e cemen , ye’elimi e (C 4 A 3 S) p esen s as he main phase. In addi ion, he cemen also con ains anhyd i e and, in bo h ma e ials, beli e (C 2 S) and b ediggi e (Ca 7 Mg(SiO 4 ) 4 ), gehleni e (Al 2 Ca 2 O 7 Si), C 3 A, and pe iclase (MgO) p esen as seconda y phases. The di ac og ams o he pas es con aining calcium sul a e (KCSA-5CS and KCSA- 20CS, Figu e 6) show ha as he hyd a ion ime inc eases, he in ensi y o he peaks associa ed wi h he ye’elimi e and anhyd i e dec eases. The main hyd a ion p oduc , alongside AH 3 and calci e, is e ingi e. In he pas e wi h 5% con en (KCSA-5CS), calcium ca boalumina e (C 4 A c H 11 ) also p esen s a 90 days. In he pas e wi h 20% con en (KCSA- 20CS), he p esence o calcium ca boalumina e is de ec ed a e 24 h alongside small peaks a ibu able o calcium monosul oalumina e. In he case o he pas es con aining sodium sul a e (Figu e 6), he in ensi y o he ye’elimi e also dec eases wi h an inc ease in he hyd a ion ime. In he KCSA-5NS pas e, he main p oduc o med is e ingi e, which inc eases in in ensi y up o 28 days be o e dec easing a 90 days, he age a which he p esence o o he phases such as AH 3 , C 4 A c H 11 , and calci e is obse ed along wi h small peaks o CAH 10 . In he KCSA-20NS pas e, he p esence o C 4 A c H 11 is also obse ed a 90 days, while he AH 3 and calci e a e obse ed a 3 days and 1 day, espec i ely. In his pas e (KCSA-20NS), CAH10 is no de ec ed. One impo an inding o no e in he KCSA-20NS pas e is ha , a 1 day, he p esence o Na 2 SO 4 was no obse ed, no was i obse ed in he con inuous XRD analyses (see Figu e 5). Howe e , his phase was de ec ed a mo e ad anced ages, indica ing ha sodium sul a e dissolu ion ollowed by e-p ecipi a ion in he o m o hena di e occu s. The peaks Molecules 2023,28, 7651 8 o 20 associa ed wi h he p esence o hena di e inc ease in in ensi y wi h an inc ease in he hyd a ion ime. A his poin , i should be no ed ha hese pas es exhibi ed signi ican mechanical s eng h losses (and e en c acking) be ween 28 and 90 days (see Figu e 3). 2.5. Di e en ial The mal Analysis and The mog a ime y (DTA/TG) Figu e 7p esen s he DTA/TG esul s o he hyd a ed KCSA pas es con aining 5% and 20% CaSO4and Na2SO4a 1, 3, 28, and 90 days. Molecules 2023, 28, x FOR PEER REVIEW 9 o 21 Figu e 7. Di e en ial he mal analysis (DTA) and he mog a ime ic (TG) analysis o he KCSA pas es con aining di e en sal s. The DTA cu es show he p esence o a se ies o signals ha co espond o he de- composi ion o he di e en phases men ioned abo e and iden i ied using XRD. The i s signal (signal 1), a a ound 100 °C, co esponds o he p esence o e ingi e. In he KCSA- 20NS pas e, his signal (signal 1) is de ec ed a ~95 °C and spli s, c ea ing ano he signal (signal 5) a a ound 65 °C o he pas es a 1, 3, and 28 days. Al hough signal 5 is no longe de ec ed a 90 days, ano he signal (signal 2) is obse ed a 125 °C. Signal 5 may be due o he decomposi ion o he calcium ca boalumina e while signal 2 may be due o he decom- posi ion o he hyd a ed calcium alumina e, which is no clea ly obse ed in he KCSA- 20NS pas e using XRD [25]. A hi d signal (signal 3) hen appea s a close o 245 °C and shi s o 267 °C as he hyd a ion ime inc eases. This signal is associa ed wi h he decomposi ion o he alumi- num hyd oxide phase (AH3) p e iously obse ed wi h XRD. In he KCSA-20NS pas e, a 28 days, signal 3 spli s in wo, s anding a 247 °C and 261 °C, espec i ely. In he KCSA- Tempe a u e Tempe a u e Figu e 7. Di e en ial he mal analysis (DTA) and he mog a ime ic (TG) analysis o he KCSA pas es con aining di e en sal s. The DTA cu es show he p esence o a se ies o signals ha co espond o he decomposi ion o he di e en phases men ioned abo e and iden i ied using XRD. The i s signal (signal 1), a a ound 100 ◦ C, co esponds o he p esence o e ingi e. In he KCSA-20NS pas e, his signal (signal 1) is de ec ed a ~95 ◦ C and spli s, c ea ing ano he signal (signal 5) a a ound 65 ◦ C o he pas es a 1, 3, and 28 days. Al hough signal 5 is no longe de ec ed a 90 days, ano he signal (signal 2) is obse ed a 125 ◦ C. Signal 5 may be due o he decomposi ion o he calcium ca boalumina e while signal 2 may be due o he decomposi ion o he hyd a ed calcium alumina e, which is no clea ly obse ed in he KCSA-20NS pas e using XRD [25]. Molecules 2023,28, 7651 9 o 20 A hi d signal (signal 3) hen appea s a close o 245 ◦ C and shi s o 267 ◦ C as he hyd a ion ime inc eases. This signal is associa ed wi h he decomposi ion o he aluminum hyd oxide phase (AH 3 ) p e iously obse ed wi h XRD. In he KCSA-20NS pas e, a 28 days, signal 3 spli s in wo, s anding a 247 ◦ C and 261 ◦ C, espec i ely. In he KCSA-5CS and KCSA-20CS pas es, a simila spli occu s a 3 days and 28 days, espec i ely [ 23 ]. The signal de ec ed a 250 ◦C in he KCSA-20CS pas e is associa ed wi h his phase (AFm). Finally, a alues abo e 600 ◦ C, he signal (signal 4) ob ained co esponds o he loss o he CO 2 in he calcium ca boalumina e and he calci e, wi h he peak a 650 ◦ C being a ibu able o he C4AH11 and he peak a a ound 720 ◦C being a ibu able o he calci e. Rega ding he TG cu es in he 50–200 ◦ C in e al (co esponding o he phases C 4 A s3 H 32 , CAH 10 , C 4 A c H 11 and C 4 A s H 12 ), i can be obse ed how, in all he pas es, he wa e loss inc eases up o 28 days and dec eases a 90 days; mo eo e , his wa e loss inc eases as he concen a ion o he sal s inc eases. Fo he nex in e al (200–400 ◦ C), whe e he AH 3 phase is ound, he weigh loss inc eases wi h an inc ease in he hyd a ion ime and dec eases wi h inc easing CaSO 4 concen a ion, while in he case o he Na 2 SO 4 sal , he wa e loss is g ea e han 20%. The ange (600–800 ◦ C) is associa ed wi h he loss o CO2 om he ca boalumina es and calci e. 2.6. Scanning Elec on Mic oscopy (SEM/EDX) The KCSA pas es con aining he di e en sal s a 5% and 20% concen a ions we e analyzed a 3 and 90 days using SEM (Figu es 8–11). Molecules 2023, 28, x FOR PEER REVIEW 11 o 21 Figu e 8. SEM mic og aphs o KCSA con aining CaSO4; (a) KCSA-5CS a 3 days; (b) KCSA-5CS a 90 days; (c) KCSA-20CS a 3 days; (d) KCSA-20CS a 90 days. Figu e 9. High- esolu ion iew o he mic og aphs showing e ingi e in he KCSA-CS pas es. SEM analysis o he pas es con aining di e en concen a ions o sodium sul a e like- wise e eals e ingi e needles (Figu e 10a) and aluminum hyd oxide pla es (Figu e 10b) in he pas e con aining 5% (KCSA-5NS). When he concen a ion o sodium sul a e (KCSA-20NS) inc eases, in addi ion o he abo e-men ioned phases, p isma ic pa icles co esponding o hena di e (Figu e 10c) a e de ec ed. A 90 days, in addi ion o he he- na di e, calcium ca bona e pla es a e also de ec ed (Figu e 10d). The p esence a 90 days Figu e 8. SEM mic og aphs o KCSA con aining CaSO 4 ; ( a ) KCSA-5CS a 3 days; ( b ) KCSA-5CS a 90 days; (c) KCSA-20CS a 3 days; (d) KCSA-20CS a 90 days. Molecules 2023,28, 7651 16 o 20 e ec becomes less isible a 28 and 90 days and e en diminishes. As ega ds AH 3 , he da a show how i s p esence inc eases sligh ly wi h an inc ease in he hyd a ion ime. The ma e ials con aining sodium sul a e a e highly po ous (see Figu e 4), howe e , and la ge capilla y po es (0.1–1 µ m) a e clea ly p edominan , which explains he low mechanical s eng h alues. This g ea e po osi y is pa ly associa ed wi h nonhyd a ed a eas and pa ly wi h he c acks c ea ed by he o ma ion o c ys alline phases in he ha dened pas e. The c ys alliza ion (see he SEM mic og aphs, Figu es 10 and 11) causes he samples o expand, leading o c acking. Ano he impo an aspec o highligh in he KCSA-20NS pas es is he appa en dec ease in e ingi e a ad anced ages, a o ing he o ma ion o calci e and, abo e all, hena di e. The c acking o he specimens a 90 days is ela ed o he in e nal s ess caused by p ecipi a ion o calci e and hena di e in he ma ix and he appa en decomposi ion o he e ingi e. The beha io obse ed in he KCSA-20NS pas es closely esembles ha o he hyd a ed pas es wi h high alkali con en s (KCSA-4M and KCSA-8M) [ 36 ]. This sugges s ha he high sodium sul a e con en eleases sul a e ions ha eac o o m AF , as well as eleasing Na + ions ha may con ibu e o he inc ease in pH le el. When he pH inc eases, he e ingi e’s s abili y dec eases, a o ing ca bona ion [ 15 , 21 ]. As e ingi e is uns able a high pH le els, i b eaks down and eleases sul a e ions, which, wi h he Na + p esen in he medium, e-p ecipi a e in he o m o hena di e. SEM (Figu e 10) analysis shows a high p esence o hena di e and calcium ca bona e (calci e) pla es when he hyd a ion ime o he KCSA-20NS pas e inc eases om 3 o 90 days. This combina ion o des abiliza ion and c ys alliza ion o sul a e sal s (Na 2 SO 4 ) is esponsible o he change in he olume o he ma e ial and i s subsequen c acking [37]. As ega ds he pH le el o he po ous solu ion o a KCSA o CSA pas e, his alue is known o be a ound 11, clea ly lowe han ha o a Po land cemen pas e (pH le el o ~12.5). A his poin , an addi ional s udy was conduc ed o de e mine how he pH o he KCSA-20NS pas e e ol ed in he i s 24 h. Fo his pu pose, pas es we e p epa ed in a 2:1 a io and he liquid phase was ex ac ed using a acuum pump. This liquid phase was la e used o measu e he pH alue [ 38 , 39 ]. The esul s ob ained a e shown in Table 1. I can be seen ha in he i s 24 h, he pH ises o alues g ea e han 13. Table 1. pH alues o he aqueous phase o he KCSA-20NS pas e. pH MEASUREMENTS 30 min 1 h 2 h 5 h 7 h 24 h KCSA-20NS 11.39 11.40 11.64 12.42 12.51 13.19 The s abili y ange o e ingi e as a unc ion o pH emains unde deba e. Based on s udies conduc ed on di e en ypes o cemen s, se e al au ho s [ 15 , 21 , 36 ] indica e ha e ingi e is s able a pH le els be ween 9 and 13. I has been obse ed how, in syn he ic sys ems and a high pH le els (>13), he mo phology o he AF changes om needle o sphe ical o m. This beha io is e y simila o ha obse ed in he KCSA-20NS pas es (see Figu e 11). A highe pH alues, he e ingi e becomes uns able [33]. In sho , he p esence o sodium sul a e a ec s he hyd a ion o KCSA clinke di - e en ly depending on he sal concen a ion. A 5%, he mechanical s eng h is lowe han ha ob ained wi h ei he he e e ence ma e ial (H 2 O) o calcium sul a e. In addi- ion, he a e o hyd a ion slows and he main hyd a ion p oduc is e ingi e, ollowed by AH 3 and hena di e. A a 20% sal con en , he a e o hyd a ion inc eases bu he mechanical s eng h dec eases, p oducing specimen ac u e a 90 days due o he inc eased p ecipi a ion o hena di e. Molecules 2023,28, 7651 17 o 20 4. Ma e ials and Me hods 4.1. Ma e ials In his s udy, a calcium sul oalumina e cemen clinke (KCSA) and an indus ial calcium sul oalumina e cemen (CSA)—ma ke ed by i. ech ALI PRE GREEN (supplied by Heidelbe g Cemen Hispania)—we e used. Table 2shows he chemical composi ion de e mined using X- ay luo escence and he mine alogical composi ion ob ained using X- ay di ac ion, including quan i a i e analysis using he Rie eld me hod in he Topas applica ion. Table 2. Chemical and mine alogical analysis o he KCSA clinke . Chemical Composi ion Mine alogical Composi ion Oxides KCSA CSA 2ICDD PDF KCSA CSA CaO 40.82% 41.50% Ye’elimi e, C4A3s, (PDF = 33-0256) 68.4 ±0.9% 52.6 ±0.4% SiO29.51% 8.14% B ediggi e, Ba0.293Ca13.467Mg1.81Mn0.43O32Si8 (PDF = 36-399) 7.40 ±0.4% 5.0 ±0.5% Al2O329.37% 23.20% Beli e, C2S, (PDF = 86-0398) 16.90 ±1.0% 14.9 ±0.4% Fe2O31.32% 1.05% Pe iclase, MgO, (PDF = 4-829) 3.67 ±0.2% 2.8 ±0.3% MgO 4.13% 3.22% Gehleni e, Al2Ca2O7Si, (PDF = 35-755) 1.90 ±0.4% 1.6 ±0.5% Na2O 1.06% 0.86% C3A, (PDF = 70-0839) 1.75 ±0.4% 1.0 ±0.2% K2O 0.47% 0.44% Anhyd i e, CaSO4(PDF = 72-0916) 22.1 ±0.4% TiO20.39% 0.32% SO39.92% 18.36% O he s 1.70% 1.35% 1LOI 1.31% 1.45% C ys allog aphy Open Da abase 1Loss on igni ion; 2In e na ional Cen e o Di ac ion Da a. Figu e S2 shows he g anulome ic analyses o he calcium sul oalumina e clinke (KCSA) and he calcium sul oalumina e cemen (CSA). These lase di ac ion analyses we e pe o med using a COULTER LS 130 g anulome ic analyze wi h a measu emen ange o 0.1–900.0 µ m. In o al, 90% o he pa icles in he KCSA we e smalle han 35 µ m; in he CSA, 90% o he pa icles we e smalle han 11.51 µ m. The clinke had a densi y o 2.83 g/mL and he cemen had a densi y o 2.90 g/mL. The Blaine inenesses we e 408.82 m2/kg and 474.6 m2/kg o he KCSA and CSA, espec i ely. 4.2. P ocedu e To he KCSA, 5 and 20% Na 2 SO 4 and CaSO 4 we e inco po a ed ia solid subs i u ion. To de e mine he e olu ion o he mechanical s eng h, pas es we e p epa ed om solid mix u es o KCSA wi h he abo emen ioned sal s, wi h a cons an wa e /binde a io o 0.5. A p isma ic mold (6 es specimens o 1 × 1 × 6 cm 3 ) was hal - illed and 60 s okes we e gi en on he shaking able so ha he pas e was dis ibu ed homogeneously and no po es we e le in he es specimen. The mold was hen illed and he 60 s okes we e epea ed. Once he molds we e illed, he pas e was cu ed in a clima ic chambe o 24 h a 21 ◦ C wi h a 95% ela i e humidi y. The es specimens we e hen demolded, labelled and s o ed again in he clima ic chambe un il he es age (1, 3, 28 and 90 days). A he selec ed age, he specimens we e b oken using comp ession. The equipmen used o his was an Ibe es p ess (Au o es -200/10-SW). A e b eaking he specimens, pa o he ma e ial ob ained was g ound in an aga e mo a and mixed wi h isop opanol o hal he hyd a ion p ocess. The mix u e was hen shaken o 3 min and il e ed unde acuum. Nex , o emo e he le o e isop opanol, he mix u e was d ied in a acuum desicca o o 3 days, a e which i was cha ac e ized using XRD, DTA/TG, and MRI. Some o he ung ound pieces we e imme sed in a ja o isop opanol o 7 days o la e use in SEM mic os uc u al analysis and me cu y in usion po osime y. The po osime y equipmen used was a MICROMERITICS Au opo e IV 9500 capable o eaching p essu es o up o 3200 Psi, he equi alen o a po e size o 0.0067 µm. Molecules 2023,28, 7651 18 o 20 The con inuous XRD equipmen used was a BRUKER D8 ADVANCE made up o a 3 kW high- ol age gene a o , an X- ay ube wi h a coppe anode (Cu K α1,2 adia ion, 1.540 Å) ha usually ope a es a 40 kV and 50 mA, and a Lynxeye de ec o wi h a 3 mm an isca e sli and a Ni K-be a (0.5%) il e wi hou a monoch oma o (does no emo e K α2 ). The KCSA and sal mix u e was shaken o 3 min and he sample holde was illed and co e ed wi h Kap on. Sample eadings we e aken e e y 30 min in a 5–45◦ ange a a ime/s ep o 0.9 s wi h a s ep size o 0.01973◦. Discon inuous XRD analysis was pe o med using he same equipmen as o con in- uous XRD. Analysis was pe o med using a 6 mm a iable di e gence sli in a 5–60 ◦ 2 θ ange a a ime/s ep o 0.5 s wi h a s ep size o 0.02◦. DTA/TG was pe o med using a TA SDT Q 600. The eco ding condi ions we e as ollows: hea ing om oom empe a u e o 1000 ◦ C a a a e o 10 ◦ C/min in a pla inum c ucible unde a ni ogen a mosphe e. The measu emen sensi i i y was 0.001 ◦ C o DTA and 0.1 µg o TG. Scanning elec on mic oscopy and ene gy-dispe si e X- ay (SEM/EDX) we e pe - o med using a HITACHI S-4800 mic oscope. The scanning mic oscope employed a ield emission gun (FEG) wi h a esolu ion o 1.4 nm. This de ice was equipped wi h a backsca e ed scanning elec on mic oscope (BSEM), a BRUKER X- ay de ec o , QUAN- TAX 400 mic oanalysis so wa e and i e moni o ed axes. The samples we e acuum-d ied and me allized wi h cha coal. The hea elease a e and he o al hea associa ed wi h he hyd a ion eac ions we e also analyzed using iso he mal conduc ion calo ime y, employing a THERMOMETRIC TAM AIR de ice ope a ing a 25 ◦ C. To his end, pas es wi h he same 0.5 wa e /binde a io we e p epa ed. Measu es o 10 g o he cemen ing mix u e and 5 g o wa e we e mixed ex si u o 3 min. A 7.5 g sample o his mix u e was inse ed in he calo ime e . Fo he e e ence ma e ial, dis illed wa e was used. 5. Conclusions This pape analyzes he e ec o alkaline sal s (Na 2 SO 4 ) and alkali ea h (CaSO 4 ) on he hyd a ion o comme cial calcium sul oalumina e clinke (KCSA) a 1, 3, 28, and 90 days. The esul s a e compa ed wi h he e e ence clinke and e e ence calcium sul oalumina e cemen , bo h hyd a ed wi h wa e . The gene al conclusions ha can be d awn om his pape a e summa ized below. The sul a e sal ype (CaSO 4 o Na 2 SO 4 ) and quan i y (5% o 20%) a ec he hyd a ion kine ics, ype o eac ion p oduc s o med, and de elopmen o mechanical s eng h. Low sul a e concen a ions (~5%) accele a e p ima y AF o ma ion bu slow seconda y AF o ma ion. Howe e , highe quan i ies (20%) sligh ly delay he o ma ion o p ima y AF and accele a e he o ma ion o seconda y AF . These phenomena a e complex and equi e mo e de ailed s udy. Ne e heless, i is belie ed ha hey may be ela ed o he ype and mo phology o he AF ini ially o med. Hyd a ion o he KCSA in he p esence o calcium sul a e leads o he o ma ion o e ingi e as he main hyd a ion p oduc , along wi h o he phases such as C 4 A c H 11 , AH 3 , CAH 10 , and calci e. Hyd a ion o KCSA con aining sodium sul a e also induces he o ma ion o e ingi e, alongside o he p oduc s such as AH 3 and calci e. Inc easing he hyd a ion ime as a unc ion o added Na 2 SO 4 con en causes pa o he AF o b eak down o o m hena di e and calci e. The inco po a ion o calcium sul a e sal s has a posi i e e ec on he de elopmen o mechanical s eng h in KCSA. Adding sodium sul a e, howe e , has less posi i e o e en ad e se e ec s, especially a ad anced ages. This beha io is la gely associa ed wi h he ac ha he p esence o Na 2 SO 4 inc eases he pH alue, which pa ly des abilizes he AF o med, a o ing ca bona ion and he p ecipi a ion o hena di e, which can cause he specimens o c ack and b eak. Molecules 2023,28, 7651 19 o 20 Supplemen a y Ma e ials: The ollowing suppo ing in o ma ion can be downloaded a : h ps:// www.mdpi.com/a icle/10.3390/molecules28227651/s1, Figu e S1: Con inuous XRD di ac og ams o he KCSA pas es wi h each o he sal s; Figu e S2: KCSA pa icle size. Au ho Con ibu ions: Concep ualiza ion, A.F.-J. and A.P.; me hodology, P.P.-E. and A.F.-J.; alida- ion, A.P. and A.F.-J.; o mal analysis, P.P.-E.; in es iga ion, P.P.-E. and A.F.-J.; esou ces, A.F.-J.; da a cu a ion, P.P.-E.; w i ing—o iginal d a p epa a ion, P.P.-E.; w i ing— e iew and edi ing, A.F.-J., P.P.-E. and A.P.; p ojec adminis a ion, A.F.-J.; unding acquisi ion, A.F.-J. All au ho s ha e ead and ag eed o he published e sion o he manusc ip . Funding: Thanks o he suppo o he Minis y o Science and Inno a ion and Uni e si ies and FEDER unds ha subsidize he P ojec BIA2016-76466-R and he aid BES-2017-082022. Also hanks o he P ojec PID 2019-111464RB-I00/AEI/10.13039/501100011033. 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[C ossRe ] Disclaime /Publishe ’s No e: The s a emen s, opinions and da a con ained in all publica ions a e solely hose o he indi idual au ho (s) and con ibu o (s) and no o MDPI and/o he edi o (s). MDPI and/o he edi o (s) disclaim esponsibili y o any inju y o people o p ope y esul ing om any ideas, me hods, ins uc ions o p oduc s e e ed o in he con en .