Ci a ion: Bílek, V., J .; Kalina, L.;
D oˇ ák, R.; No o ný, R.; Š ec, J.;
Másilko, J.; Šoukal, F. Co ela ing
Hyd a ion o Alkali-Ac i a ed Slag
Modi ied by O ganic Addi i es o he
E olu ion o I s P ope ies. Ma e ials
2023,16, 1908. h ps://doi.o g/
10.3390/ma16051908
Academic Edi o : Hube Rahie
Recei ed: 31 Janua y 2023
Re ised: 17 Feb ua y 2023
Accep ed: 23 Feb ua y 2023
Published: 25 Feb ua y 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/).
ma e ials
A icle
Co ela ing Hyd a ion o Alkali-Ac i a ed Slag Modi ied by
O ganic Addi i es o he E olu ion o I s P ope ies
Vlas imil Bílek, J . 1,* , Lukáš Kalina 1, Richa d D oˇ ák2, Radosla No o ný1, Jiˇ íŠ ec 1, Jiˇ íMásilko 1
and F an išek Šoukal 1
1Ins i u e o Ma e ials Science, Facul y o Chemis y, B no Uni e si y o Technology,
612 00 B no, Czech Republic
2
Ins i u e o Physics, Facul y o Ci il Enginee ing, B no Uni e si y o Technology, 612 00 B no, Czech Republic
*Co espondence: [email p o ec ed]
Abs ac :
This s udy in es iga es he ela ionships be ween he hyd a ion kine ics o wa e glass-
ac i a ed slag and he de elopmen o i s physical-mechanical p ope ies, as well as i s colo change.
To modi y he calo ime ic esponse o alkali-ac i a ed slag, hexylene glycol was selec ed om a ious
alcohols o in-dep h expe imen s. In p esence o hexylene glycol, he o ma ion o ini ial eac ion
p oduc s was es ic ed o he slag su ace, which d as ically slowed down he u he consump ion o
dissol ed species and slag dissolu ion and consequen ly delayed he bulk hyd a ion o he wa e glass-
ac i a ed slag by se e al days. This allowed o show ha he co esponding calo ime ic peak is
di ec ly ela ed o he apid e olu ion o he mic os uc u e and physical-mechanical pa ame e s
and o he onse o a blue/g een colo change eco ded as a ime-lapse ideo. Wo kabili y loss
was co ela ed wi h he i s hal o he second calo ime ic peak, while he mos apid inc ease in
s eng hs and au ogenous sh inkage was ela ed o he hi d calo ime ic peak. Ul asonic pulse
eloci y inc eased conside ably du ing bo h he second and hi d calo ime ic peak. Despi e he
modi ied mo phology o he ini ial eac ion p oduc s, he p olonged induc ion pe iod, and he sligh ly
educed deg ee o hyd a ion induced by hexylene glycol, he o e all mechanism o alkaline ac i a ion
emained unchanged in he long- e m pe spec i e. I was hypo hesized ha he main issue o he use
o o ganic admix u es in alkali-ac i a ed sys ems is he des abilizing e ec o hese admix u es on
soluble silica es in oduced in o he sys em wi h an ac i a o .
Keywo ds:
alkali-ac i a ed slag; calo ime y; mic os uc u e; e a da ion; po e solu ion; o ganic
admix u e; colo change; sh inkage; se ing
1. In oduc ion
Alkali-ac i a ed slag (AAS) belongs o he wide and in e es ing g oup o alkali-
ac i a ed ma e ials (AAMs) and has a conside able po en ial o con ibu e o he sus-
ainabili y o cons uc ion ma e ials [
1
]. Fo he alkaline ac i a ion o slag o o he sui able
aluminosilica es, many ypes o ac i a o [
2
] and hei combina ions can be used a a ious
doses o concen a ions, esul ing in p ac ically unlimi ed complexi y o ma e ials based on
AAS. This, on he one hand, enables ailo ing o AAS p ope ies as equi ed, bu on he
o he hand, esul s in agmen ed esea ch wi h some imes con adic o y o unclea esul s.
The e o e, i is necessa y o look o he ela ionships be ween he measu ed p ope ies and
o be able o es ima e hem om simple obse a ions.
In gene al, he cou se o alkaline ac i a ion consis s o se e al s ages, o which he
s a ing s age is he dissolu ion o he glassy phase. Song and Jennings [
3
] s a ed ha a
pH g ea e han 11.5 is necessa y o e ec i e ac i a ion, as slag below his alue does
no dissol e e ec i ely. Du ing he slag hyd olysis, Ca
2+
and Mg
2+
a e p e e en ially
eleased in o he solu ion ollowed by alumina e species and silica es [
4
]. A e su icien ly
high concen a ions a e eached, new hyd a ion p oduc s o lowe solubili y han he
Ma e ials 2023,16, 1908. h ps://doi.o g/10.3390/ma16051908 h ps://www.mdpi.com/jou nal/ma e ials
Ma e ials 2023,16, 1908 2 o 18
o iginal slag a e o med. The main one is amo phous o poo ly c ys alline pa ially c oss-
linked calcium-alumina e-silica e-hyd a e (C-A-S-H), some imes also w i en as C-N-A-S-H
due o he p esence o an alkali (e.g., sodium) ca ion ha balances he nega i e cha ge
o e ahed al aluminum [
5
]. C-A-S-H is he main s eng h-gi ing phase in AAS, bu a
wide ange o o he p oduc s can be o med, such as hyd o alci e, s ä lingi e, and o he
alumina es [4–6].
The ype and quan i y o hyd a ion p oduc s depend on se e al ac o s, such as slag
and ac i a o composi ion, ac i a o dose o concen a ion, and empe a u e. Powe ul
ools o moni o ing he hyd a ion kine ics a e iso he mal calo ime e s. In he 1990s,
Shi and Day [
7
] desc ibed basic ypes o hea low cu es depending on he ac i a o
na u e and empe a u e and desc ibed s ages o hyd a ion simila o hose o Po land
cemen hyd a ion, i.e., he p e-induc ion pe iod, he induc ion o do man pe iod, he
pe iod o accele a ed and decele a ed hyd a ion, and u he slowing down di usion-
o phase bounda y-con olled s age [
8
]. Fo slag ac i a ion wi h NaOH, wo peaks can
be dis inguished on he hea low cu e. The i s one ha occu s in he p e-induc ion
pe iod is ela ed o he we ing and ini ial eac ions be ween ac i a o and slag g ains,
and a e no o e y sho induc ion pe iod he second peak ha is associa ed wi h
he o ma ion o C-A-S-H akes place [
4
,
7
,
9
]. Fo ac i a ion wi h Na
2
CO
3
and liquid
sodium silica es (wa e glasses), a new addi ional ini ial peak commonly eme ges in he
p e-induc ion pe iod due o he eac ions o anionic g oups o hese ac i a o s. A e his
peak, bo h o hese ac i a o s exhibi a signi ican induc ion pe iod, a e which he hi d
peak o accele a ion/decele a ion hyd a ion occu s, showing he o ma ion o a C-A-S-H
gel [7,10,11].
In addi ion o he composi ion o he ac i a o and p ecu so o empe a u e [
9
,
12
], he
eac ion p ocess o AAS can be conside ably a ec ed by a ious o ganic addi i es. F om
his wide g oup, supe plas icize s a e he mos s udied in o de o con ol he heology [
13
].
Howe e , o he addi i es such as sh inkage- educing admix u es (SRAs) dese e a en ion;
no only o deal wi h he ex ensi e sh inkage o AAS [
14
,
15
], bu also due o hei g ea
e ec on he hyd a ion p ocess [
16
–
20
]. This is inhe en ly ela ed o changes in he e olu ion
o he mic os uc u e and p ope ies. Fo example, he main calo ime ic peak has been
epo ed o be associa ed wi h he highes a e au ogenous sh inkage [
21
,
22
]. In addi ion
o enginee ing p ope ies, he amous colo change o no only AAS bu also o dina y
conc e es con aining slag is well-known. I is belie ed o be somehow ela ed o he
eac ion o slag in hese sys ems [23,24].
Howe e , a comp ehensi e o e iew o he ela ionships be ween he AAS hyd a ion
a e and he e olu ion o i s p ope ies om he esh o well-ha dened s a e suppo ed
by in es iga ions o phase assemblage and mic os uc u e, and i s colo change as well, is
missing. Consequen ly, his is he main objec i e o his pape . Because di e en s ages
o AAS hyd a ion usually mo e o less o e lap, i is necessa y o sepa a e hem o clea ly
obse e he associa ed e ec s. Unlike o he pape s, in which SRAs a e applied o educe
AAS sh inkage [
25
–
27
], we used a ious o ganic subs ances, and pa icula ly hexylene
glycol as a componen o comme cially a ailable SRAs, o in en ionally slow he AAS
hyd a ion p ocess and sepa a e i s di e en s ages. In addi ion, i s ole in AAS hyd a ion is
b ie ly add essed.
2. Ma e ials and Me hods
2.1. Ma e ials and Sample P epa a ion
G ound g anula ed blas u nace slag wi h a Blaine ineness o abou 400 m
2
/kg was
used. Acco ding o he X- ay di ac ion me hod wi h Rie eld analysis using Empy ean
di ac ome e (Mal e n Panaly ical L d., Mal e n, UK), i consis ed mainly o an amo -
phous phase (~87 w . %) and small amoun s o calci e, me wini e, and ake mani e. Calcium
luo ide was used as an in e nal s anda d. I s chemical composi ion de e mined using
X- ay luo escence is gi en in Table 1. Slag was alkali-ac i a ed by wa e glass con aining
Ma e ials 2023,16, 1908 3 o 18
16.1 w . % Na
2
O and 30.7 w . % SiO
2
(silica e modulus o app oxima ely 2.0) dilu ed wi h
wa e o p epa e he s ock solu ion p io o mixing.
Table 1. Chemical composi ion o he used slag de e mined using X- ay luo escence.
SiO2Al2O3Fe2O3CaO MgO SO3K2O Na2O P2O5TiO2Mn2O3S O ZnO Cl LOI
37.2 9.32 0.27 39.1 9.50 1.53 0.43 0.40 0.02 0.03 0.61 0.06 0.02 0.03 1.24
The dose o s ock wa e glass solu ion was adjus ed o 4% Na
2
O wi h espec o
he weigh o he slag and he wa e - o-slag a io (including he wa e om he o iginal
wa e glass) was 0.35. Such plain AAS pas e was modi ied by hexylene glycol (2-me hyl-
2,4-pen anediol) a he doses o 0.5, 1.0 and 2.0% wi h espec o he slag weigh . The
hexylene glycol dose was used o designa ion o he pas es, i.e., Hex-0 o he plain AAS
pas e wi hou hexylene glycol, while Hex-0.5, Hex-1.0, and Hex-2.0 we e used o pas es
con aining hexylene glycol. Hexylene glycol was added o he ac i a ing solu ion and
b ie ly homogenized jus be o e mixing he AAS pas e.
The mixing o he pas es was ca ied ou using a common hand mixe and a beake
in an ai -condi ioned labo a o y a 25
◦
C. The ime o adding he slag o he ac i a ing
solu ion was aken as ime ze o, a e which he mixing p ocess s a ed. The o al mixing
ime was h ee minu es and consis ed o ou in e als: Fi s 60 s o slow mixing, hen 30 s
a maximum mixing a e, 30 s es o sc aping he pas e down in o he ba ch, and inally
60 s a maximum mixing a e. The pas es p epa ed in his manne we e hen used o he
es s desc ibed in he ollowing sec ions.
2.2. Me hods
2.2.1. Iso he mal Hea Conduc ion Calo ime y
Hyd a ion o AAS was moni o ed using a TAM Ai 8-channel calo ime e (TA Ins u-
men s) a 25
◦
C o 28 days. Fo he measu emen , he amoun o pas e co esponding o
4.0 g o slag was placed in a 20 mL PE ial, igh ly sealed wi h a sc ew cap, and inse ed
in o he calo ime e . Reco ding o hea low s a ed i e minu es a e he s a o he mixing.
The ials wi h wa e we e used as a e e ence.
2.2.2. Physical-Mechanical Tes ing
The ini ial and inal se ing ime was es ed using a common Vica needle wi h a
diame e o 1.13 mm. Measu emen was ca ied ou on he basis o EN 196-3 [
28
] bu i
was no made unde wa e . Ins ead, he su ace o he sample was co e ed wi h pa a in
oil o p e en d ying and ensu e au ogenous condi ions, which we e also used in o he
expe imen s. Fu he mo e, he pas es did no ha e no mal consis ency as is p esc ibed
o cemen es ing bu had he same composi ion as in all o he expe imen s (Sec ion 2.1),
i.e., he wa e - o-slag a io o 0.35 and he wa e glass dose o 4% Na
2
O wi h espec o he
slag weigh .
Moni o ing o changes in ul asonic pulse eloci y (UPV) du ing he ongoing hyd a ion
was ca ied ou using a Vikasonic de ice (Schleibinge Ge ä e Teube u. G eim GmbH,
Buchbach, Ge many) wo king wi h a equency pulse o 54 kHz. The measu ing cell had
he same shape as he ing o he se ing ime de e mina ion using a Vica needle (EN
196-3) wi h p obes moun ed in he lowe and uppe base o he pa h leng h o 40 mm. UPV
was au oma ically calcula ed om he pa h leng h and ansi ime. The su aces o he
p obes we e coa ed wi h couplan g ease and sepa a ion oil o p e en di ec con ac o
he p obes wi h he measu ed ma e ial. UPV alues we e eco ded in one-minu e in e als
om he s a o he measu emen in he esh s a e o as long as possible o un il he signal
was dis u bed.
Au ogenous dimensional changes we e de e mined using he hyd os a ic weigh-
ing me hod a 25
◦
C con olled by a ci cula ing he mos a . The pas e was illed in o a
polyu e hane condom and hen app oxima ely 90 g o he pas e was ied wi h a ishing line
Ma e ials 2023,16, 1908 4 o 18
and hung on an analy ical balance wi h eadabili y o 0.1 mg. Fi s , he specimen weigh
in ai was eco ded, hen he specimen was imme sed in pa a in oil and i s weigh was
au oma ically eco ded in one-minu e in e als o a leas 28 days. The ela i e olume
change
∆
V(in olume pe cen ) was calcula ed using he Equa ion (1), whe e m
(ini)
and
m
a e he weigh o he specimen imme sed in oil a he ini ial ime o which sh inkage is
ela ed ( he i s alue in oil in his wo k) and he weigh a a gi en ime o measu emen ,
espec i ely, and mai is he weigh o he sample be o e imme sion in o he oil.
∆V=m (ini)−m
mai −m (ini)
(1)
The comp essi e s eng h was de e mined on cubic specimens wi h nominal edge size
o 25 mm using he DESTTEST 4310 Compac A (Be on Sys em, s. . o.). A e mixing, he
pas es we e cas in o he molds and sealed wi h polye hylene plas ic bags o 23 h, a e
which hey we e demolded and es ed o ob ain 24-h comp essi e s eng h o sealed wi h
s e ch oil and s o ed in a chambe a 25
◦
C un il he ime o es ing, i.e., 2, 3, 7, 10, 14, 21,
and 28 days. A each age, 2 o 3 specimens o each pas e’s composi ion we e used.
2.2.3. Po e Solu ion Composi ion
Fo he isola ion o he po e solu ion, esh AAS pas es we e cas in o he cylind ical
plas ic molds wi h a diame e o 52 mm and a heigh o 60 mm wi h inse ed s e ch oil
o p e en hem om d ying and ca bona ion as well as o acili a e i s demolding. The
po e solu ion o he esh pas es was ob ained by he acuum il a ion using a Büchne
unnel. La e , when he pas e s i ened and se , he oil was emo ed om he samples and
hey we e placed in o a s eel mold o p ess he po e solu ion ou using he hyd aulic de ice
DESTTEST 4310 Compac A (Be on Sys em, s. .o., B no, Czech Republic). The ob ained
po e solu ion was place in a sy inge equipped wi h a nylon il e wi h a po e diame e o
0.45
µ
m and immedia ely dilu ed in a plas ic olume ic lask using demine alized wa e .
The concen a ion o he selec ed elemen s was de e mined by an op ical emission spec-
ome e wi h induc i ely coupled plasma (ICP-OES) Ho iba Jobin Y one, ype Ul ima 2.
The sample was anspo ed using a pe is al ic pump in o a nebulize and u he ca ied
by a gon in o a o ch. The elemen al concen a ion o he po e solu ion was au oma ically
calcula ed on he basis o he calib a ion cu es o s anda d solu ions and he backg ound
ep esen ed by demine alized wa e .
2.2.4. Assessmen o Colo Change
To eco d a well-known bu s ill no ully unde s ood blue/g een colo change in AAS
pas es du ing hyd a ion, samples o he pas es con aining 0, 0.5, 1, and 2% o hexylene
glycol we e illed in o he plas ic cu e es wi h a squa e c oss-sec ion o 10 mm
×
10 mm
and a heigh o 50 mm. To p e en d ying and ai eac ions, he su aces we e co e ed
wi h a pa a in oil. Pho os o hese AAS pas e-con aining cu e es we e con inuously
cap u ed o 28 days e e y 30 min using a digi al came a equipped wi h a mac o lens and
connec ed o a compu e . This expe imen was ca ied ou in an ai -condi ioned oom a
25
◦
C. The ob ained pho og aphs we e hen au oma ically p ocessed in MATLAB so wa e
o sepa a e ou only he a eas o he samples as illus a ed in Figu e 1. Each c opped a ea
o pho o was hen di ided o ed, g een, and blue channel ma ix. Fo each pic u e an
a e age alue o each channel was calcula ed. Because he maximum in ensi y o a pixel in
each channel ma ix has an in ege o 255, we use in e ed alue. Subsequen ly, he colo
change in ime was simply demons a ed as he pas e da kness calcula ed as he sum o he
in e ed in ege s o ed, g een, and blue. The ex ac ed a eas we e also used o make a
ime-lapse ideo.
Ma e ials 2023,16, 1908 5 o 18
Ma e ials 2023, 16, x FOR PEER REVIEW 5 o 17
Figu e 1. Illus a i e example o a pho og aph cap u ed a e 7 days o hyd a ion and ex ac ion o
he a eas o samples o p ocessing o he colo change.
2.2.5. Phase Assemblage
The mic os uc u e and o ma ion o he hyd a ion p oduc s we e assessed using
scanning elec on mic oscopy (SEM), he mog a ime ic analysis (TGA), and X- ay pow-
de di ac ion (XRD). Be o e hese analyses, he hyd a ion eac ions we e s opped using
he sol en exchange me hod by imme sing he b oken pa s (SEM) and c ushed pas e
(TGA, XRD) in he isop opyl alcohol and hen d ying a 40 °C. SEM was pe o med on
bo h ac u e su aces and ionic polished samples embedded in he epoxy esin. F ac u e
su aces we e obse ed using EVO LS 10 (Ca l Zeiss N s, LCC, Peabody, MA, USA) wi h
an accele a ing ol age o 10 kV in he mode o seconda y elec ons, while polished su -
aces we e obse ed using JSM-7600F (JEOL L d., Tokyo, Japan) wi h an accele a ing ol -
age o 5 kV in he mode o backsca e ed elec ons. The TGA was ca ied ou in ai a mos-
phe e wi h a low a e o 100 mL/min wi h a empe a u e amp o 10 °C/min om 40 o
990 °C using a Q600 SDT analyze (TA Ins umen s, New Cas le, DE, USA). XRD was
ca ied ou using Empy ean di ac ome e (Mal e n Panaly ical L d., Mal e n, UK) in
he B agg–B en ano con igu a ion a he ange o 5–90° 2θ wi h s ep o 0.013° 2θ. An X-
ay ube wi h coppe anode, a ol age o 40 kV, and a cu en o 30 mA was used. Da a
we e e alua ed using HighSco e Plus so wa e.
3. Resul s and Thei Discussion
3.1. O e all Cou se o Hyd a ion and Hyd a ion P oduc s
The e ec o hexylene glycol dose on he AAS hyd a ion is gi en in Figu e 2. The
e e ence pas e wi hou hexylene glycol exhibi ed a common ype o calo ime ic cu e
o wa e glass-ac i a ed slag comp ising h ee peaks, which is consis en wi h he li e a-
u e [7,29,30]. The i s o hese peaks occu ing wi hin he i s 30 min is associa ed wi h
he ini ial con ac o ac i a ing solu ion wi h slag g ains, i.e., we ing and dissolu ion o
he slag pa icles and ex e nal mixing. The second one, which eaches maximum a ap-
p oxima ely one hou , was a ibu ed o he gela ion o silica es om ac i a o due o dis-
sol ed species om slag [31–33]. This peak d ama ically dec eased wi h inc easing dose
o hexylene glycol. Finally, he hi d peak occu s, whe e ex ensi e hyd a ion akes place,
esul ing in he o ma ion o he C-A-S-H and o he hyd a es, wi h a maximum hea low
a 21 h o he e e ence pas e. Howe e , he p esence o hexylene glycol and many o he
o ganic addi i es s ongly a ec ed he iming o his ‘peak o he bulk hyd a ion’ [31,32].
I is wo h no ing ha simila e ec can be eached by o he a ious o ganic addi-
i es, as clea ly illus a ed in Appendix A (dose o 2%). The s onges e ec o he sub-
s ances used was obse ed o e hanol, which had he maximum o he hi d peak a ap-
p oxima ely 410 h, o in o he wo ds app oxima ely 20 imes la e when compa ed o he
e e ence pas e. Fu he mo e, Figu e 2 and Appendix A show ha he lowe he gela ion
peak, he mo e delayed he bulk hyd a ion peak.
Figu e 1.
Illus a i e example o a pho og aph cap u ed a e 7 days o hyd a ion and ex ac ion o
he a eas o samples o p ocessing o he colo change.
2.2.5. Phase Assemblage
The mic os uc u e and o ma ion o he hyd a ion p oduc s we e assessed using
scanning elec on mic oscopy (SEM), he mog a ime ic analysis (TGA), and X- ay powde
di ac ion (XRD). Be o e hese analyses, he hyd a ion eac ions we e s opped using he
sol en exchange me hod by imme sing he b oken pa s (SEM) and c ushed pas e (TGA,
XRD) in he isop opyl alcohol and hen d ying a 40
◦
C. SEM was pe o med on bo h
ac u e su aces and ionic polished samples embedded in he epoxy esin. F ac u e
su aces we e obse ed using EVO LS 10 (Ca l Zeiss N s, LCC, Peabody, MA, USA) wi h an
accele a ing ol age o 10 kV in he mode o seconda y elec ons, while polished su aces
we e obse ed using JSM-7600F (JEOL L d., Tokyo, Japan) wi h an accele a ing ol age o
5 kV in he mode o backsca e ed elec ons. The TGA was ca ied ou in ai a mosphe e
wi h a low a e o 100 mL/min wi h a empe a u e amp o 10
◦
C/min om 40 o 990
◦
C
using a Q600 SDT analyze (TA Ins umen s, New Cas le, DE, USA). XRD was ca ied
ou using Empy ean di ac ome e (Mal e n Panaly ical L d., Mal e n, UK) in he B agg–
B en ano con igu a ion a he ange o 5–90
◦
2
θ
wi h s ep o 0.013
◦
2
θ
. An X- ay ube wi h
coppe anode, a ol age o 40 kV, and a cu en o 30 mA was used. Da a we e e alua ed
using HighSco e Plus so wa e.
3. Resul s and Thei Discussion
3.1. O e all Cou se o Hyd a ion and Hyd a ion P oduc s
The e ec o hexylene glycol dose on he AAS hyd a ion is gi en in Figu e 2. The
e e ence pas e wi hou hexylene glycol exhibi ed a common ype o calo ime ic cu e o
wa e glass-ac i a ed slag comp ising h ee peaks, which is consis en wi h he li e a u e [
7
,
29
,
30
].
The i s o hese peaks occu ing wi hin he i s 30 min is associa ed wi h he ini ial con ac
o ac i a ing solu ion wi h slag g ains, i.e., we ing and dissolu ion o he slag pa icles
and ex e nal mixing. The second one, which eaches maximum a app oxima ely one
hou , was a ibu ed o he gela ion o silica es om ac i a o due o dissol ed species
om slag [
31
–
33
]. This peak d ama ically dec eased wi h inc easing dose o hexylene
glycol. Finally, he hi d peak occu s, whe e ex ensi e hyd a ion akes place, esul ing in
he o ma ion o he C-A-S-H and o he hyd a es, wi h a maximum hea low a 21 h o
he e e ence pas e. Howe e , he p esence o hexylene glycol and many o he o ganic
addi i es s ongly a ec ed he iming o his ‘peak o he bulk hyd a ion’ [31,32].

Ma e ials 2023,16, 1908 6 o 18
Ma e ials 2023, 16, x FOR PEER REVIEW 6 o 17
Figu e 2. Calo ime ic esponse o wa e glass-ac i a ed slag con aining 0–2% o hexylene glycol.
I should be no ed ha al hough hexylene glycol g ea ly e a ded he hyd a ion o
AAS, i did no d ama ically change i s o e all mechanism om he long- e m pe spec-
i e. This is sugges ed by he e olu ion in cumula i e hea and u he suppo ed by XRD
a e 28 days (Figu e 3) and by he mog a ime y a e 24 h, 7 days, and 28 days (Figu e
4). No c ys alline phases o med du ing he hyd a ion p ocess we e de ec ed by XRD e-
ga dless o he p esence o hexylene glycol. Only hose o igina ing om he aw slag, i.e.,
calci e, ake mani e, and me wini e we e iden i ied (Figu e 3). This co esponds o p e i-
ous indings [34–36] ha highly amo phous p oduc s a e o med in wa e glass-ac i a ed
slag, mainly C-A-S-H, which is mo e c ys alline in NaOH-ac i a ed slag.
The only no able di e ence in he XRD pa e s is a di e en in ensi y below 8° 2θ,
i.e., in he egion co esponding o he p esence o C-A-S-H [37,38]. Fo he e e ence pas e
(Hex-0), he in ensi y only inc eases e y sligh ly o e ime. On he con a y, he Hex-2
pas e showed iden ically low in ensi ies a e 24 h and 7 days, ollowed by g ea ly in-
c eased in ensi ies a e 28 days. A sligh change also ela ed o he g ea ly inc eased
amoun s o C-A-S-H in Hex-2 pas e a e 28 days is also isible as an inc eased back-
g ound be ween 29 and 30° 2θ. Un o una ely, he di ac ions o C-A-S-H in his egion
[37,38] canno be clea ly seen due o he p esence o ake mani e and pa icula ly calci e.
In addi ion, he issue o poo isibili y o C-A-S-H in hese XRD ou pu s is i s al eady
men ioned highly amo phous s uc u e. The di e en e olu ion o he XRD pa e n o
Hex-0 and Hex-2 pas e co esponds o hei di e en a e o eac ion (Figu e 2), because
conside able amoun s o C-A-S-H can be expec ed in Hex-0 pas e e en a e 24 h, while
he onse o he bulk hyd a ion peak o Hex-2 pas e occu ed a e one week.
Figu e 3. XRD pa e ns o wa e glass-ac i a ed slag wi h 0 and 2% o hexylene glycol a e 28 days
o hyd a ion.
The mog a ime y (Figu e 4, Table 2) con i med a g ea e ec o hexylene glycol on
amoun s o hyd a es o e ime, as indica ed by weigh loss in he empe a u e ange o
40–550 °C. I is mainly ela ed o he dehyd a ion and dehyd oxyla ion o C-A-S-H, bu
Figu e 2. Calo ime ic esponse o wa e glass-ac i a ed slag con aining 0–2% o hexylene glycol.
I is wo h no ing ha simila e ec can be eached by o he a ious o ganic addi i es,
as clea ly illus a ed in Appendix A(dose o 2%). The s onges e ec o he subs ances
used was obse ed o e hanol, which had he maximum o he hi d peak a app oxima ely
410 h, o in o he wo ds app oxima ely 20 imes la e when compa ed o he e e ence pas e.
Fu he mo e, Figu e 2and Appendix Ashow ha he lowe he gela ion peak, he mo e
delayed he bulk hyd a ion peak.
I should be no ed ha al hough hexylene glycol g ea ly e a ded he hyd a ion o
AAS, i did no d ama ically change i s o e all mechanism om he long- e m pe spec i e.
This is sugges ed by he e olu ion in cumula i e hea and u he suppo ed by XRD a e
28 days (Figu e 3) and by he mog a ime y a e 24 h, 7 days, and 28 days (Figu e 4). No
c ys alline phases o med du ing he hyd a ion p ocess we e de ec ed by XRD ega dless
o he p esence o hexylene glycol. Only hose o igina ing om he aw slag, i.e., cal-
ci e, ake mani e, and me wini e we e iden i ied (Figu e 3). This co esponds o p e ious
indings [
34
–
36
] ha highly amo phous p oduc s a e o med in wa e glass-ac i a ed slag,
mainly C-A-S-H, which is mo e c ys alline in NaOH-ac i a ed slag.
Ma e ials 2023, 16, x FOR PEER REVIEW 6 o 17
Figu e 2. Calo ime ic esponse o wa e glass-ac i a ed slag con aining 0–2% o hexylene glycol.
I should be no ed ha al hough hexylene glycol g ea ly e a ded he hyd a ion o
AAS, i did no d ama ically change i s o e all mechanism om he long- e m pe spec-
i e. This is sugges ed by he e olu ion in cumula i e hea and u he suppo ed by XRD
a e 28 days (Figu e 3) and by he mog a ime y a e 24 h, 7 days, and 28 days (Figu e
4). No c ys alline phases o med du ing he hyd a ion p ocess we e de ec ed by XRD e-
ga dless o he p esence o hexylene glycol. Only hose o igina ing om he aw slag, i.e.,
calci e, ake mani e, and me wini e we e iden i ied (Figu e 3). This co esponds o p e i-
ous indings [34–36] ha highly amo phous p oduc s a e o med in wa e glass-ac i a ed
slag, mainly C-A-S-H, which is mo e c ys alline in NaOH-ac i a ed slag.
The only no able di e ence in he XRD pa e s is a di e en in ensi y below 8° 2θ,
i.e., in he egion co esponding o he p esence o C-A-S-H [37,38]. Fo he e e ence pas e
(Hex-0), he in ensi y only inc eases e y sligh ly o e ime. On he con a y, he Hex-2
pas e showed iden ically low in ensi ies a e 24 h and 7 days, ollowed by g ea ly in-
c eased in ensi ies a e 28 days. A sligh change also ela ed o he g ea ly inc eased
amoun s o C-A-S-H in Hex-2 pas e a e 28 days is also isible as an inc eased back-
g ound be ween 29 and 30° 2θ. Un o una ely, he di ac ions o C-A-S-H in his egion
[37,38] canno be clea ly seen due o he p esence o ake mani e and pa icula ly calci e.
In addi ion, he issue o poo isibili y o C-A-S-H in hese XRD ou pu s is i s al eady
men ioned highly amo phous s uc u e. The di e en e olu ion o he XRD pa e n o
Hex-0 and Hex-2 pas e co esponds o hei di e en a e o eac ion (Figu e 2), because
conside able amoun s o C-A-S-H can be expec ed in Hex-0 pas e e en a e 24 h, while
he onse o he bulk hyd a ion peak o Hex-2 pas e occu ed a e one week.
Figu e 3. XRD pa e ns o wa e glass-ac i a ed slag wi h 0 and 2% o hexylene glycol a e 28 days
o hyd a ion.
The mog a ime y (Figu e 4, Table 2) con i med a g ea e ec o hexylene glycol on
amoun s o hyd a es o e ime, as indica ed by weigh loss in he empe a u e ange o
40–550 °C. I is mainly ela ed o he dehyd a ion and dehyd oxyla ion o C-A-S-H, bu
Figu e 3.
XRD pa e ns o wa e glass-ac i a ed slag wi h 0 and 2% o hexylene glycol a e 28 days
o hyd a ion.
Ma e ials 2023,16, 1908 7 o 18
Table 2.
Weigh losses (%) o wa e glass-ac i a ed slag pas es wi h 0 and 2% o hexylene glycol
e alua ed in a ious empe a u e anges.
Sample 40–550 ◦C 270–470 ◦C 550–720 ◦C 720–860 ◦C 550–990 ◦C 40–990 ◦C
Hex-0: 24 h 6.64 1.67 1.45 0.39 1.87 8.51
Hex-0: 7 d 9.13 2.50 1.61 0.28 1.98 11.1
Hex-0: 28 d 12.1 2.36 1.51 0.32 1.97 14.1
Hex-2: 24 h 4.03 0.71 1.30 0.31 1.48 5.51
Hex-2: 7 d 4.35 0.80 1.34 0.31 1.53 5.88
Hex-2: 28 d 10.1 2.05 1.58 0.53 2.24 12.4
Ma e ials 2023, 16, x FOR PEER REVIEW 7 o 17
some con ibu ion o he hyd o alci e-like phase is also possible, pa icula ly in he ange
o 270–470 °C [39–41]. Fo he e e ence pas e, he amoun o hyd a es (40–550 °C) g adu-
ally inc eased o e ime. Dis inc i ely di e en beha io was obse ed o Hex-2 pas e,
o which he weigh loses o he Hex-2 pas e almos did no changes be ween 24 h and 7
days, while g ea ly inc eased be ween 7 and 28 days. This co ela es well wi h he e a d-
ing e ec o hexylene glycol appa en om calo ime ic ou comes (Figu e 2).
Figu e 4. Changes in weigh (A) and hei empe a u e de i a i e (B) o wa e glass-ac i a ed slag
pas es wi h 0 and 2% o hexylene glycol du ing he i s 28 days o hyd a ion wi h highligh ed
anges ha we e e alua ed (see Table 2).
Weigh loss in he ange o 550–990 °C was no signi ican ly a ec ed by hexylene
glycol (Figu e 4, Table 2). In his ange, wo di e en s eps can be dis inguished. The i s
ook place be ween 600 and 700 °C and was ela ed o he decomposi ion o calci e o igi-
na ing om slag, while he second egion a ound 800 °C is usually assigned o he decom-
posi ion o C-A-S-H along wi h he c ys alliza ion o wollas oni e [39,42]. Mo eo e , i is
e y likely o be a ec ed by s opping hyd a ion using he sol en exchange me hod be-
cause o ganic sol en s g ea ly modi y TGA ou comes in his empe a u e ange also o
Po land cemen sys ems [43].
Table 2. Weigh losses (%) o wa e glass-ac i a ed slag pas es wi h 0 and 2% o hexylene glycol
e alua ed in a ious empe a u e anges.
Sample 40–550 °C 270–470 °C 550–720 °C 720–860 °C 550–990 °C 40–990 °C
Hex-0: 24 h 6.64 1.67 1.45 0.39 1.87 8.51
Hex-0: 7 d 9.13 2.50 1.61 0.28 1.98 11.1
Hex-0: 28 d 12.1 2.36 1.51 0.32 1.97 14.1
Hex-2: 24 h 4.03 0.71 1.30 0.31 1.48 5.51
Hex-2: 7 d 4.35 0.80 1.34 0.31 1.53 5.88
Hex-2: 28 d 10.1 2.05 1.58 0.53 2.24 12.4
3.2. Co ela ions du ing he Gela ion S ages o AAS Hyd a ion
Figu e 5 co ela es he al eady showed e ec o hexylene glycol on he gela ion peak
(Figu e 2) wi h he e olu ion o ea ly mechanical p ope ies ep esen ed by he Vica nee-
dle es and UPV. In addi ion, he changes in he po e solu ion composi ion o e ime a e
also included.
Despi e i s g ea e ec on AAS hyd a ion, hexylene glycol did no ha e signi ican
e ec s on ini ial and inal se ing imes de e mined using he Vica needle, as i emained
a ound 35 and 55 min, espec i ely, ega dless o he dose o hexylene glycol. A he same
ime, he onse o UPV was no a ec ed by he p esence o hexylene glycol, while i s sub-
sequen inc ease slowed sligh ly. All hese phenomena co ela ed well wi h he po e so-
lu ion composi ion, which was oughly he same o he Hex-0 and Hex-2 pas es du ing
he i s 30 min: The concen a ions o Si and Na in oduced in o he sys em mainly wi hin
Figu e 4.
Changes in weigh (
A
) and hei empe a u e de i a i e (
B
) o wa e glass-ac i a ed slag
pas es wi h 0 and 2% o hexylene glycol du ing he i s 28 days o hyd a ion wi h highligh ed anges
ha we e e alua ed (see Table 2).
The only no able di e ence in he XRD pa e s is a di e en in ensi y below 8
◦
2
θ
,
i.e., in he egion co esponding o he p esence o C-A-S-H [
37
,
38
]. Fo he e e ence pas e
(Hex-0), he in ensi y only inc eases e y sligh ly o e ime. On he con a y, he Hex-2
pas e showed iden ically low in ensi ies a e 24 h and 7 days, ollowed by g ea ly inc eased
in ensi ies a e 28 days. A sligh change also ela ed o he g ea ly inc eased amoun s o
C-A-S-H in Hex-2 pas e a e 28 days is also isible as an inc eased backg ound be ween
29 and 30
◦
2
θ
. Un o una ely, he di ac ions o C-A-S-H in his egion [
37
,
38
] canno be
clea ly seen due o he p esence o ake mani e and pa icula ly calci e. In addi ion, he
issue o poo isibili y o C-A-S-H in hese XRD ou pu s is i s al eady men ioned highly
amo phous s uc u e. The di e en e olu ion o he XRD pa e n o Hex-0 and Hex-2 pas e
co esponds o hei di e en a e o eac ion (Figu e 2), because conside able amoun s
o C-A-S-H can be expec ed in Hex-0 pas e e en a e 24 h, while he onse o he bulk
hyd a ion peak o Hex-2 pas e occu ed a e one week.
The mog a ime y (Figu e 4, Table 2) con i med a g ea e ec o hexylene glycol on
amoun s o hyd a es o e ime, as indica ed by weigh loss in he empe a u e ange o
40–550
◦
C. I is mainly ela ed o he dehyd a ion and dehyd oxyla ion o C-A-S-H, bu
some con ibu ion o he hyd o alci e-like phase is also possible, pa icula ly in he ange o
270–470
◦
C [
39
–
41
]. Fo he e e ence pas e, he amoun o hyd a es (40–550
◦
C) g adually
inc eased o e ime. Dis inc i ely di e en beha io was obse ed o Hex-2 pas e, o
which he weigh loses o he Hex-2 pas e almos did no changes be ween 24 h and 7 days,
while g ea ly inc eased be ween 7 and 28 days. This co ela es well wi h he e a ding e ec
o hexylene glycol appa en om calo ime ic ou comes (Figu e 2).
Weigh loss in he ange o 550–990
◦
C was no signi ican ly a ec ed by hexylene
glycol (Figu e 4, Table 2). In his ange, wo di e en s eps can be dis inguished. The
i s ook place be ween 600 and 700
◦
C and was ela ed o he decomposi ion o calci e
o igina ing om slag, while he second egion a ound 800
◦
C is usually assigned o he
Ma e ials 2023,16, 1908 8 o 18
decomposi ion o C-A-S-H along wi h he c ys alliza ion o wollas oni e [
39
,
42
]. Mo eo e ,
i is e y likely o be a ec ed by s opping hyd a ion using he sol en exchange me hod
because o ganic sol en s g ea ly modi y TGA ou comes in his empe a u e ange also o
Po land cemen sys ems [43].
3.2. Co ela ions du ing he Gela ion S ages o AAS Hyd a ion
Figu e 5co ela es he al eady showed e ec o hexylene glycol on he gela ion peak
(Figu e 2) wi h he e olu ion o ea ly mechanical p ope ies ep esen ed by he Vica needle
es and UPV. In addi ion, he changes in he po e solu ion composi ion o e ime a e
also included.
Ma e ials 2023, 16, x FOR PEER REVIEW 8 o 17
he ac i a o emained a ound 3 M, while he concen a ions o o he elemen s o igina ing
om he dissol ing slag, such as Ca, Mg, and Al, g adually inc eased. The maximum con-
cen a ion o Ca was a ound 0.4 M i espec i e o he p esence o hexylene glycol, while
he maximum concen a ions o Mg and Al we e lowe by app oxima ely one o de o
magni ude compa ed o hose o Ca. A e he i s 30 o 45 min, he concen a ions o all
elemen s s a ed o d op qui e apidly, pa icula ly o he e e ence Hex-0 pas e; and un il
he 118 h minu e, hey dec eased as much as by an o de o magni ude compa ed o hei
maximum alues. The de e mined alues as well as he obse ed end o he e olu ion
o he po e solu ion composi ion o e ime co ela e well wi h a ecen ly published s udy
[26], in which a sligh ly highe dose o wa e glass (5% Na2O) wi h a somewha lowe sili-
ca e modulus (1.2) was used o ac i a e he mix u e o slag/ ly (50/50).
Figu e 5. Co ela ions o he calo ime ic esponse o wa e glass-ac i a ed slag wi h i s po e solu ion
composi ion, he ul asonic pulse eloci y and he se ing ime ( e ical lines show a e age alues
o he ini ial and inal se ing ime, shaded a ea a ound hem shows he se ing pe iod including he
sample’s s anda d de ia ion).
Figu e 5.
Co ela ions o he calo ime ic esponse o wa e glass-ac i a ed slag wi h i s po e solu ion
composi ion, he ul asonic pulse eloci y and he se ing ime ( e ical lines show a e age alues o
he ini ial and inal se ing ime, shaded a ea a ound hem shows he se ing pe iod including he
sample’s s anda d de ia ion).
Ma e ials 2023,16, 1908 9 o 18
Despi e i s g ea e ec on AAS hyd a ion, hexylene glycol did no ha e signi ican
e ec s on ini ial and inal se ing imes de e mined using he Vica needle, as i emained
a ound 35 and 55 min, espec i ely, ega dless o he dose o hexylene glycol. A he
same ime, he onse o UPV was no a ec ed by he p esence o hexylene glycol, while i s
subsequen inc ease slowed sligh ly. All hese phenomena co ela ed well wi h he po e
solu ion composi ion, which was oughly he same o he Hex-0 and Hex-2 pas es du ing
he i s 30 min: The concen a ions o Si and Na in oduced in o he sys em mainly wi hin
he ac i a o emained a ound 3 M, while he concen a ions o o he elemen s o igina ing
om he dissol ing slag, such as Ca, Mg, and Al, g adually inc eased. The maximum
concen a ion o Ca was a ound 0.4 M i espec i e o he p esence o hexylene glycol, while
he maximum concen a ions o Mg and Al we e lowe by app oxima ely one o de o
magni ude compa ed o hose o Ca. A e he i s 30 o 45 min, he concen a ions o all
elemen s s a ed o d op qui e apidly, pa icula ly o he e e ence Hex-0 pas e; and un il
he 118 h minu e, hey dec eased as much as by an o de o magni ude compa ed o hei
maximum alues. The de e mined alues as well as he obse ed end o he e olu ion o
he po e solu ion composi ion o e ime co ela e well wi h a ecen ly published s udy [
26
],
in which a sligh ly highe dose o wa e glass (5% Na
2
O) wi h a somewha lowe silica e
modulus (1.2) was used o ac i a e he mix u e o slag/ ly (50/50).
In he case o he e e ence pas e, he simul aneous sha p inc ease in mechanical p op-
e ies and high concen a ions o elemen s o igina ing om slag in he po e solu ion a e
30 o 45 min poin o he concu en o ma ion o new solid p oduc s and he con inuing
dissolu ion o slag. A la e s ages, he dissol ed species a e consumed apidly. Conside -
ably slowed down consump ion o dissol ed species was obse ed o Hex-2 pas e, which
co ela es wi h less hea gene a ed a his s age and wi h a sligh ly slowe inc ease in he
UPV eloci y.
This beha io is likely ela ed o he e ec o hexylene glycol on mic os uc u al e olu-
ion in hese e y ea ly s ages o eac ion, as shown in Figu e 6. Du ing he i s 5 h, a highly
po ous bu o he wise homogeneous ma ix o he ini ial eac ion p oduc s was o med
among he slag g ains in he e e ence pas e (Figu e 6A,C). No e ha a simila mic os uc-
u e has al eady been obse ed by Sun e al. [
44
] and was a ibu ed o he gela ion o he
ac i a o , e en i he slag was eplaced by qua z, due o he p epa a ion o he c yogenic
sample. These simila i ies suppo he heo y ha he addi ional ini ial calo ime ic peak o
he wa e glass-ac i a ed slag is ela ed o he gela ion o he ac i a o [31,32].
In con as o he e e ence, no bulk ma ix can be ound in he pas e wi h 2% hexlyene
glycol (Figu e 6B,D). Ins ead, a hin laye o he eac ion p oduc s co e s he slag g ains
and binds hem oge he h ough he adjacen su aces, enough o indica e se ing by he
Vica needle es o an inc ease in UPV. Simul aneously, i shows ha he g ea educ ion in
he gela ion peak does no lead o a signi ican p olonga ion o he wo kabili y pe iod. To
each i , he gela ion peak should be delayed, as in he case o ci ic acid [45].
The da ke g ay shade o he o med laye compa ed o ha o he slag pa icle means
ha he o me is composed o ligh e elemen s. The mo e de ailed image gi en in Figu e 7
e eals ha he hickness o his laye can each app oxima ely 200 o 300 nm and is qui e
dense, al hough he esolu ion is limi ed. The line scan o he elemen al composi ion gi en
in he same igu e showed ha hese p oduc s a e ich in Na and Si, which con i ms ha
he laye o igina es mainly om he gela ion o he ac i a o . The con en o o he elemen s
such as Ca and Mg is also possible and, wi h espec o he e olu ion o he composi ion o
he po e solu ion o e ime, e en p obable (see Figu e 5), bu hei signal is limi ed by a
low accele a ing ol age.
Ma e ials 2023,16, 1908 16 o 18
Ma e ials 2023, 16, x FOR PEER REVIEW 15 o 17
Figu e A2. E ec o polyp opylene glycol molecula weigh on he calo ime ic esponse o wa-
e glass-ac i a ed slag.
Figu e A3. E ec o selec ed alcohols on he calo ime ic esponse o wa e glass-ac i a ed slag.
Re e ences
1. P o is, J.L. Alkali-ac i a ed ma e ials. Cem. Conc . Res. 2018, 114, 40–48. h ps://doi.o g/10.1016/j.cemcon es.2017.02.009.
2. Shi, C.; K i enko, P.V.; Roy, D. Alkali-Ac i a ed Cemen s and Conc e es; Taylo & F ancis: London, UK, 2006.
3. Song, S.; Jennings, H.M. Po e solu ion chemis y o alkali-ac i a ed g ound g anula ed blas - u nace slag. Cem. Conc . Res. 1999,
29, 159–170. h ps://doi.o g/10.1016/S0008-8846(98)00212-9.
4. Zuo, Y.; Ye, G. P elimina y In e p e a ion o he Induc ion Pe iod in Hyd a ion o Sodium Hyd oxide/Silica e Ac i a ed Slag.
Ma e ials 2020, 13, 4796. h ps://doi.o g/10.3390/ma13214796.
5. Mye s, R.J.; Be nal, S.A.; San Nicolas, R.; P o is, J.L. Gene alized s uc u al desc ip ion o calcium-sodium aluminosilica e
hyd a e gels: The c oss-linked subs i u ed obe mo i e model. Langmui 2013, 29, 5294–5306. h ps://doi.o g/10.1021/la4000473.
6. Lo henbach, B.; G usko njak, A. Hyd a ion o alkali-ac i a ed slag: The modynamic modelling. Ad . Cem. Res. 2007, 19, 81–92.
h ps://doi.o g/10.1680/adc .2007.19.2.81.
Figu e A3. E ec o selec ed alcohols on he calo ime ic esponse o wa e glass-ac i a ed slag.
Re e ences
1. P o is, J.L. Alkali-ac i a ed ma e ials. Cem. Conc . Res. 2018,114, 40–48. [C ossRe ]
2. Shi, C.; K i enko, P.V.; Roy, D. Alkali-Ac i a ed Cemen s and Conc e es; Taylo & F ancis: London, UK, 2006.
3.
Song, S.; Jennings, H.M. Po e solu ion chemis y o alkali-ac i a ed g ound g anula ed blas - u nace slag. Cem. Conc . Res.
1999
,
29, 159–170. [C ossRe ]
4.
Zuo, Y.; Ye, G. P elimina y In e p e a ion o he Induc ion Pe iod in Hyd a ion o Sodium Hyd oxide/Silica e Ac i a ed Slag.
Ma e ials 2020,13, 4796. [C ossRe ] [PubMed]
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