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S uc u al In eg i y P ocedia 00 (2024) 000–000
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Pee - e iew unde esponsibili y o NICOM8 Chai pe sons
In e na ional Symposium on Nano echnology in Cons uc ion Ma e ials NICOM8
Co osion Sensing P ope ies o Ca bon Black-Based Cemen i ious
Sma Coa ings
Gab iele Milonea,b
*
, Ma ia C uz Alonsob, Ch is os Vlachakisa, Jean-Ma c Tullianic and
Abi Al-Tabbaaa
aDepa men o Enginee ing, Uni e si y o Camb idge, T umping on S ee , Camb idge CB2 1PZ, UK
bEdua do To oja Ins i u e o Cons uc ion Sciences (IETCC), Spanish Na ional Resea ch Council, C. de Se ano Gal ache, 4, Mad id 28033,
Spain
cDepa men o Applied Science and Technology, INSTM R.U. Lince Labo a o y, Poli ecnico di To ino, Co so Duca degli Ab uzzi 24, Tu in
10129, I aly
Abs ac
This esea ch explo es he sensing capabili ies o ca bon black (CB)-based cemen i ious coa ings o de ec ing de o ma ions a ising
om ein o cemen co osion. The in es iga ion ocused on a chlo ides-con amina ed ein o ced mo a elemen subjec ed o
con olled accele a ed co osion. The objec i e is o u ilize sma coa ings' sensing p ope ies o es ablish a link be ween
elec ochemical a acks and he mechanical e ec s induced by co osion. Di e en ly om hei mo e equen applica ion in he
li e a u e, his ype o s udy ocused on a chemical a ack a he han physical. The senso s we e employed o quan i y he inc ease
in in e nal s ess and s ain due o oxide o ma ion and p opaga ion wi hin he ma ix.
The senso s exhibi good sensi i i y o co osion p og ession iden i ying a ack pene a ion on he ein o cemen and c ack
o ma ion on he su ace. The esea ch was ini ia ed wi h he implemen a ion o a p o ocol designed o e icien ly accele a e
co osion in ein o ced mo a beams, conside ing a ying eba exposu e. Subsequen ly, a co ela ion was es ablished be ween he
elec omechanical esponse o he sma coa ings and he ongoing co osion in he subs a e, culmina ing in su ace ac u e
de elopmen . Posi ioned ans e sally o he beam's longi udinal di ec ion, all senso s consis en ly p o ided accu a e c ack
p opaga ion measu emen s up o an a e age wid h o 116 ± 45 μm. Addi ionally, he senso s demons a ed he abili y o p o ide
c ack de elopmen measu emen s also when posi ioned a a ying dis ances om he di ec ly a ec ed eba sec ions. This s udy
expands he use o sma ca bon-based coa ings, posi ioning hem as mul i unc ional sys ems beyond adi ional s uc u al
applica ions.
* Co esponding au ho .
E-mail add ess: [email protected]
2 G. Milone e al./ S uc u al In eg i y P ocedia 00 (2024) 000–000
© 2024 The Au ho s. Published by ELSEVIER B.V.
This is an open access a icle unde he CC BY-NC-ND license (h ps://c ea i ecommons.o g/licenses/by-nc-nd/4.0)
Pee - e iew unde esponsibili y o NICOM8 Chai pe sons
Keywo ds: co osion sensing; sma ma e ials; ca bon-based cemen i ious senso s; s uc u al heal h moni o ing
1. In oduc ion
Rein o ced conc e e (RC) is he mos widely used cons uc ion ma e ial in he wo ld (Gagg, 2014). By combining
conc e e's abili y o wi hs and comp ession wi h s eel's duc ili y o ension, his ma e ial is an ideal composi e o all
ypes o s uc u es (Fehling, Leu beche , and Roede , 2011; Wigh , 2016). Howe e , as conc e e is p one o c acking
(Sa iuddin e al., 2018), one o he main challenges o RC s uc u es e ol es a ound ein o cemen co osion (Popo ,
2023). The co osion o s eel eba s wi hin conc e e is ini ia ed h ough he pene a ion o chlo ides o ca bona ion,
educing he alkalini y o conc e e and, consequen ly, b eaking he na u al passi a ion o s eel (Zhu e al., 2016). This
leads o he p og essi e weakening o he eba ’s c oss-sec ional a ea and ad e sely a ec ing he bond be ween s eel
and conc e e (Syll and Kanakubo, 2022), which is c ucial o he s uc u al pe o mance o ein o ced conc e e
elemen s (Coccia, Impe a o e, and Rinaldi, 2016).
The epai and main enance o co oded s uc u es lead o en i onmen al issues and high cos s, equi alen o hal
o he yea ly cons uc ion budge spen on eno a ion o exis ing s uc u es o ex end hei se ice li e (Cailleux and
Polle , 2009). Hence, he de elopmen o e ec i e p e en ion and p o ec ion echniques aims a limi ing co osion o
main aining sa e y and se iceabili y le els o exis ing s uc u es (Angs , 2018; Abbas and Sha iee, 2020). Di e en
s a egies include co osion inhibi o s, al e na i e ein o cemen ma e ials, coa ings, and elec ochemical me hods
(Goyal e al., 2018). Despi e he a ie y o echniques a ailable, each co osion moni o ing me hod is cha ac e ized
by di e en e iciencies and limi a ions, such as in asi eness, cos , and he inabili y o p o ide ea ly wa ning signs
(Koma y e al., 2023). Fo ins ance, while elec ochemical me hods p o ide p ecise co osion a es, hey equi e di ec
access o he s eel (Popo a and P ošek, 2022). Simila ly, ibe B agg g a ing (FBG) based acous ic emission, hough
capable o eal- ime moni o ing, s uggles wi h backg ound noise and in e p e ing da a accu a ely (Jinachand an and
Rajan, 2021). In a ed he mog aphy o e s a non-des uc i e me hod o co osion assessmen . I s accu acy, howe e ,
can be a ec ed by ex e nal he mal a ia ions and he placemen o he ein o cemen wi hin conc e e (Kobayashi and
Ban hia, 2011).
The eme gence o sel -sensing cons uc ion ma e ials o e s a no el solu ion o o e come he limi a ions o
adi ional co osion de ec ion in ein o ced conc e e, by in eg a ing sensing capabili ies di ec ly in o cons uc ion
ma e ials (Han, Ding, and Yu, 2015). These sma ma e ials a e cemen sys ems, such as pas es, mo a o conc e e,
ha ha e been doped wi h a single o a combina ion o elec ically conduc i e ille s o enhance hei sensing p ope ies
(Ding e al., 2019; Tian e al., 2019). Moni o ing is made possible h ough he analysis o elec ical changes in
elec ical esis ance o hese conduc i e based ma e ial unde ex e nal s imuli such as s ain, damage, empe a u e and
mois u e (Chung, 2023). Sel -sensing ma e ials also de ec and moni o co osion, add essing some o he issues
associa ed wi h mo e adi ional me hods, as a consequence o he de o ma ion and c acking induced in he conc e e
co e due o he gene a ion o i on oxides. Jin e al. (2017) explo ed how he inco po a ion o a ious chlo ide ion
con en s a ec s he elec ical esponse o ca bon-based cemen i ious composi es. They ound ha he p esence o ions
suppo ed g aphene ille s in c ea ing addi ional conduc i e ne wo ks wi hin he ma ix. Al e na i ely, ca bon-based
cemen i ious binde s can be used as a pseudo e e ence elec ode which, embedded in conc e e, allows o moni o he
di e en co osion s a es o s eel (Jin e al., 2019). None heless, he me hodology o hese applica ions – gene ally
e e ed o as “bulk” – p esen signi ican limi a ions, i.e., in asi eness, due o he subs i u ion o conc e e wi h he
conduc i e ma e ial, and cos , associa ed wi h he la ge ille amoun needed o enhance he conduc i i y o an en i e
s uc u al elemen . Mo eo e , his me hodology does no ep esen gene al co osion obse a ions since ca bon-based
pa icles may ac as p o ec i e laye s on s eel which supp ess bo h me al oxida ion and oxygen educ ion, limi ing he
o e all eba co osion (Coa ing, 2012).
Al e na i ely, cemen -based sys ems can be applied as ex e nal senso s – “coa ings” – which ha e he po en ial o
moni o co osion de elopmen on a ein o ced subs a e. Hence, his esea ch aims a explo ing he po en ial o ca bon
black (CB)-based cemen i ious coa ings as sma , mul i unc ional sys ems o ea ly co osion de ec ion and moni o ing
G. Milone e al./ S uc u al In eg i y P ocedia 00 (2024) 000–000 3
in ein o ced conc e e s uc u es. Coa ings p o ide g ea e lexibili y in e ms o deploymen o new and exis ing
in as uc u e, and also in ab ica ion due o hei smalle size and hus lowe cos s (Chung, 2023; Ding e al., 2019).
The co osion moni o ing capabili y o hese sensing coa ings, simila o con en ional gauges, was achie ed by
measu ing he subs a e’s inne s a e o s ain and ela ing i wi h he mo emen s o co osion p oduc s be ween he
eba and he cemen i ious ma ix (G a an e al., 2009; Rou oulas and Ba is, 1999). Di e en ly om he adi ional
echniques men ioned abo e, his co osion sensing me hod has he po en ial o moni o b oade a eas while p ese ing
he subs a e s uc u e.
The esea ch me hodology in ol es he sensing capabili ies o sma coa ings in chlo ide-induced co osion
scena ios. To emula e such co oding condi ions in a b ie amoun o ime, an accele a ed co osion es was pu sued
on all ein o ced mo a specimens (Mi ó e al., 2021). This es spanned 24 days and pe mi ed he de elopmen o
co osion app oxima ely 53 imes as e han na u al se ings. By employing CB-based sma coa ings, a link be ween
elec ochemical a acks and he mechanical e ec s induced by co osion was es ablished. Senso s we e u ilized as
high-p ecision gauges o quan i y he inc ease in in e nal s ess and s ain due o oxide o ma ion and p opaga ion
wi hin he ma ix (And ade, Alonso, and Molina, 1993). Visual analysis p oceeded in pa allel o qu ali a i ely assess
he oxides’ p opaga ion and hei in luence on he mo a ’s inne s a e o s ess. This sensing capabili y was measu ed
in bo h ee and pa ially con ined eba scena ios, showing he e sa ili y o he coa ings unde di e en s uc u al
condi ions. This wo k se es as a s a ing poin o cemen i ious coa ings in co osi e en i onmen s, se ing he s age
o u he explo a ion o mul i unc ional senso s.
2. Ma e ials and me hods
2.1. Ma e ials
The sma coa ings used in his s udy we e o mula ed by combining Po land cemen (CEM I – 52.5N, supplied
by Hanson Cemen , UK), con o ming o BS EN 197-1, wi h conduc i e ca bon black powde , as ou lined in Table 1
(sou ced om Al a Aesa , US). To ensu e uni o mi y and op imal wo kabili y ac oss di e en ca bon black
concen a ions, Mas e Glenium C315 (BASF, UK) was u ilized as a supe plas icize by weigh o ca bon black.
Table 1. Ca bon black p ope ies as pe he manu ac u e .
Appea ance (colou )
Black
Fo m
Powde
Ash (%)
≤0.50
Elec ical esis i i y (Ω∙cm)
≤0.25
pH
7.6
Mois u e (%)
0.12
A e age pa icle size (nm)
42
Su ace a ea (m2/g)
75
Bulk densi y (g/L)
170-230
These senso s had dimensions equal o 7.5 mm × 3 mm × 30 mm and embedded wo coppe wi es (20 mm in
leng h, 1 mm in hickness), p ocu ed om RS Componen s, UK. Thei applica ion was aided by he use o small
pince s ha con olled he posi ion o he elec odes and p e en ed mo emen du ing cas ing and cu ing. To ensu e
ha he hickness o he senso s was in line wi h hei nominal alue, i e hickness measu emen s we e ob ained o
all coa ings along hei longi udinal di ec ion by means o a calipe . The esis i i y was calcula ed on his basis o
p e en geome ical a iabili y in he samples. Table 2 displays he mix design used o cas ing he senso coa ings
o elec omechanical es ing.
Table 2. Mix design o he coa ing composi ion es ed in his s udy (kg/m3).
Name
Cemen
Wa e
Ca bon
black
Dispe san
CB dosage
[w %]
CB dosage
[ ol%]
4 G. Milone e al./ S uc u al In eg i y P ocedia 00 (2024) 000–000
CB3
2906.8
1327.5
85.9
8.6
3.0
15.7
Fo he subs a e p epa a ion, he ein o ced mo a was designed in iew o he co osion es . The mo a mix
comp ised cemen CEM I – 42.5R (supplied by Cimen s molins, Spain), s anda dized sand (p oduced a IETcc) as pe
UNE EN 196-1, and wa e , wi h a wa e -cemen a io main ained a 0.5 o all samples. To simula e chlo ide-induced
co osion en i onmen s, 2% o NaCl by weigh o cemen was added di ec ly in o he mixing wa e un il i s
dissolu ion. The ein o ced ba s, ype D500SD (p o ided by I u ino suminis os indus ials, Spain), we e 6 mm in
diame e . Some s eel eba s we e coa ed wi h a p o ec i e wo-phase epoxy esin o limi he co osion sp ead wi hin
p ede e mined sec ions o he ba . Finally, he senso s we e ins alled on he mo a ’s su ace using a di e en wo-
phase apid-ha dening epoxy esin, om Hun sman Ad anced Ma e ials (US) and supplied by RS componen s (UK).
2.2. Sample p epa a ion
The mo a beams subjec ed o accele a ed co osion had s anda d dimensions o 40 mm × 40 mm × 160 mm. They
inco po a ed one s eel eba , ensu ing a co e dep h o 4.8 mm om he su ace o acili a e a ge ed c ack
de elopmen . This co e - o-diame e a io (c/ϕ = 0.8) was c i ical in di ec ing c ack p opaga ion along he mo a
beam's su ace, aiming o simula e eal-wo ld s uc u al deg ada ion pa e ns unde accele a ed co osion condi ions.
The eba s we e ei he ully exposed o co osion o pa ially limi ed h ough epoxy coa ing. Hence, he co osion es
included specimens wi h bo h con ined and uncon ined eba s subjec ed o accele a ed co osion, as speci ied in Table
3.
Table 3. Types o eba se ing subjec ed o accele a ed co osion es and ela ed co osion moni o ing senso s applied.
S eel exposu e
Senso no.
Epoxy con inemen o
s eel [cm]
Senso dis ance om
exposed eba [mm]
Applied senso s
Uncon ined
#1, #2, #3
0
4.8
X, Y, Z
Con ined
#4
4
36.3
Y
#5
8
76.2
#6
12
116.1
In ag eemen wi h UNE EN 196-1:2005, he mo a p isms we e cu ed unde con olled condi ions (a 22 ± 2°C,
RH = 98%) o 7 days. Such a sho cu ing pe iod was selec ed o gi e su icien ime o he cemen i ious ma ix o
ha den and o limi i s na u al co osion de elopmen . A e wa ds, ully cu ed cemen -based senso s we e applied on
op o 7-days old mo a p ism. Figu e 1 shows he senso s' encapsula ion and subsequen applica ion on he op
su ace o he subs a e p ism. These coa ings we e posi ioned ans e sally o he longi udinal axis o he eba , each
spaced 40 mm om he o he (Figu e 2), ensu ing s able adhe ence and ope a ional in eg i y h oughou he co osion
es ing phase. In uncon ined eba es s, he h ee senso s we e named X, Y, and Z acco ding o hei dis ance om
he eba side di ec ly connec ed o he co osion equipmen (Figu e 2b).
G. Milone e al./ S uc u al In eg i y P ocedia 00 (2024) 000–000 5
Figu e 1. Visual ep esen a ion o sensing coa ing p epa a ion and ins alla ion: (a) epoxy esin mixing; (b) senso encapsula ion; and (c) sen so
applica ion on mo a su ace.
Figu e 2. (a) Schema ic and (b) pho og aphic ep esen a ion o sensing coa ings on o mo a subs a e. Final con igu a ion o h ee senso s X, Y
and Z along he ans e sal di ec ion o he p ism ac oss he eba axis. Iden ical con igu a ion o samples #1, #2 and #3 .
Selec ed eba s we e coa ed wi h epoxy esin, a ying he leng h o encapsula ion ac oss specimens o s udy he
e ec o con inemen on co osion sp ead and senso esponse. The eba sec ions we e encapsula ed symme ically
in he middle, wi h encapsula ion ex ending o e 4, 8, and 12 cm, as shown in Figu e 3a. Fo pa ially con ined eba s,
a single sensing coa ing (senso Y) was applied o he middle sec ion o he beam (Figu e 3b). The p ima y objec i e
o his s udy was o assess he co osion sensing capabili ies o a sma ca bon black (CB)-based coa ing ins alled a
a ying dis ances om he co osion-a ec ed sec ion; speci ically, a 36.3, 76.2, and 116.1 mm om he uncon ined
s eel.
6 G. Milone e al./ S uc u al In eg i y P ocedia 00 (2024) 000–000
Figu e 3. Visual ep esen a ion o (a,c,e) mould con igu a ion and (b,d, ) mo a p isms wi h pa ially con ined eba s o samples #4, #5 and #6:
(a,b) encapsula ion ex ending 4 cm and senso dis anced 36.3 mm om uncon ined s eel; (c,d) encapsula ion ex ending 8 cm and senso dis anced
76.2 mm om uncon ined s eel; (e, ) encapsula ion ex ending 12 cm and senso dis anced 116.1 mm om uncon ined s eel.
2.3. Expe imen al p og am
2.3.1. Accele a ed co osion es
The co osion es equi ed a unique se up o induce accele a ed co osion wi hin he mo a specimens, ocusing
on elec ochemical a ack kine ics. The sensing p ope y capabili y o sma coa ings was ela ed o he mechanical
e ec induced by he co osi e elec ochemical a ack in he s eel/cemen in e ace. P io o ini ia ing he accele a ed
co osion, he depasi a ion s a e o he eba , as a consequence o he addi ion o NaCl o he mo a , was assessed
h ough he measu emen o elec ochemical me hods, o e ing insigh s in o he ini ial co osion s a us o he s eel
eba s. This was based on he linea pola iza ion es (Rp) which elies on he linea i y o pola iza ion cu es a ound
he co osion po en ial (i.e., Eco ± 20 mV) (S e n, 1958). By applying a small ampli ude h ough an al e na ing signal
o he wo king elec ode (i.e., s eel eba ), he co osion cu en (Ico ) was de e mined using he S e n-Gea y equa ion
(S e n and L.G., 1957):
Ico =B/Rp (1)
The cons an B can be de e mined om Ta el slopes o he ca hodic and anodic pola iza ion cu es (Song, 2000;
Kouřil, No ák, and Bojko, 2006), and i was assumed equal o 26 mV in his in es iga ion (And ade and Alonso,
1996). The esul an alue was adjus ed o accoun o he ohmic d op be ween he wo king and e e ence elec odes.
The ob ained ou pu (Ico ) was compa ed wi h he s anda ds – UNE 112072:2011 – o ob ain an unde s anding o he
sys em’s co osion le el. Following he ini ial 7-day cu ing o he mo a p isms (be o e senso applica ion), such a
G. Milone e al./ S uc u al In eg i y P ocedia 00 (2024) 000–000 7
alue was expec ed no o be excessi ely high; none heless, due o he p esence o NaCl in he ma ix, he co osion
cu en was no negligible and, he e o e, i s measu emen was equi ed o he subsequen co osion accele a ion.
The applica ion o a cons an co osion cu en , acili a ed by a TG 97 Gal anos a (Bank Elek onik, Ge many),
s anda dized he a e o oxide o ma ion ac oss specimens, ensu ing a con olled en i onmen o s udying he
co osion's mechanical impac and he subsequen esponse o he sma coa ings. Figu e 4 displays he se up used in
his s udy whe e a s ainless-s eel shee wo ked as he coun e elec ode (ca hode) connec ed o he eba which became
he wo king elec ode (anode). The gal anos a ic o ced pola iza ion ensu ed ha he ca hode beha ed as he nega i e
elec on dono and he posi i e anode was he co oded eba (Shi, Jia, and A ens, 2012). Bo h he c ack elonga ion
and he oxide p opaga ion wi hin he ma ix we e isually assessed wi h a manual op ical mic oscope (RS PRO USB
digi al mic oscope 5M, RS componen s, Spain).
Figu e 4. (a) Schema ic and (b) g aphical desc ip ion o se up employed o applying cons an cu en o an uncon ined eba embedded in a
40 mm × 40 mm × 160 mm mo a p ism in o de o accele a e i s co osion p opaga ion.
The mo a samples we e all connec ed o he gal anos a – as speci ied in Figu e 4b – which, in u n, was linked
in se ies wi h a 500 Ω esis o . This se up p o ided a cons an co osion cu en o 3016 μA which, assuming a
cylind ical geome y o he eba , esul ed in Ico = 100 μA/cm² o all mo a beams. Such a alue was chosen in
8 G. Milone e al./ S uc u al In eg i y P ocedia 00 (2024) 000–000
ag eemen wi h he li e a u e o ensu e apid co osion p og ess wi hin he mo a sample (And ade, Alonso, and
Molina, 1993; Ca é and Raha inai o, 2007). This esul ed in a cons an mass loss o he s eel eba wi h an a ack
pene a ion (A.P.) o ~4.74 μm/day, acco ding o equa ion 2 (Rod iguez and And ade, 1990).
ϕ( )=ϕi-0.023·Ico · (2)
This es was conduc ed o app oxima ely 24 days un il he ex eme co osion o all samples p oduced c acks wi h
a wid h abo e ~500 μm. Fo pa ially con ined eba s, he co oded sec ion was smalle han i s uncon ined
coun e pa . Thus, a cons an cu en o 2.3, 1.5, and 0.75 mA o samples wi h a eba con inemen o 4, 8, and 12 cm,
espec i ely. These cu en alues we e de e mined by conside ing he exposed a ea o he eba when applying he
ixed co osion cu en o 100 μA/cm².
2.3.2. Co osion sensing measu emen
Du ing he a o emen ioned accele a ed co osion es , he sma coa ings we e used as ex e nal senso s o assess
he p og ess o he co osion in he mo a subs a es (Table 3). Via he 2-p obe me hod (Miccoli e al., 2015), he
applica ion o al e na e cu en was implemen ed daily using a po en ios a PGSTAT204 (Me ohm, Swi ze land) o
minimize he pola iza ion e ec in he sys em (20 Hz – 300 kHz; U = 0.5 V; 9 poin s pe decade). The bulk esis ance,
ob ained by decon olu ing he impedance spec um, can be used o de ine he e ec i e conduc i i y, de ined by
equa ion 3:
1
Rbulk (L
A)=σbulk (3)
whe e Rbulk is he esis ance alue co esponding o he ionic conduc ion o he in e connec ed po es in pa allel
wi h he elec onic conduc ion h ough he conduc i e ille (Wang and Pang, 2019) [Ω], L is he dis ance be ween he
pai o chosen elec odes o gauge leng h [m] and A is he c oss-sec ion o he coa ing senso s [m²].
The co osion measu emen o uncon ined eba s was ob ained om h ee iden ical sensing coa ings applied
pe pendicula ly o he eba di ec ion and, he e o e, o he c ack expansion (Figu e 5). The senso s, dis anced 40 mm
om one ano he , wo ked as bo h s ain and damage moni o ing de ices. The elec ical ou pu was gi en om he
Nyquis plo ob ained a di e en co osion imes and he damage was assessed ia a po able mic oscope o measu e
c ack wid h along he eba on each su ace. Once he co osion es inished a e 24 days o accele a ed co osion,
he samples we e ans e sally cu wi h an elec ic saw and subsequen ly manually spli open o isualize he oxide
p oduc ion and p opaga ion om he eba o he su ace unde s udy.
Figu e 5. G aphical ep esen a ion o ully co oded ein o ced beam and senso loca ion pe pendicula o ac u e loca ion.
G. Milone e al./ S uc u al In eg i y P ocedia 00 (2024) 000–000 9
3. Resul s and discussion
3.1. Accele a ed co osion
The accele a ed co osion es s, acili a ed by he inclusion o 2% NaCl by weigh o cemen in he mo a mix,
we e employed o simula e a chlo ide-con amina ed en i onmen o s eel eba co osion. Ini ial co osion
assessmen s ia elec ochemical measu emen s e ealed ha despi e achie ing mode a e o high co osion le els, as
pe UNE 112072:2011 s anda d, he ac ual a e o co osion was insu icien o achie e ele a ed oxides p oduc ion
wi hin a sho ime. Indeed, wi h a na u al co osion cu en o 0.630 ± 0.044 μA/cm², he samples ollowed an
es ima ed a ack pene a ion a e o ~0.09 μm/day. The e o e, he gal anos a ic app oach was employed, ensu ing a
consis en and p edic able a e o oxide p oduc ion (i.e., 4.74 μm/day in ag eemen wi h equa ion 2).
To empi ically assess he e ec i eness o he heo e ical a ack pene a ion (equa ion 2), he diame e o ully
co oded eba s was measu ed ia s e eoscope. Figu e 6 depic s he di e ence be ween non-co oded and co oded
eba , ea ed wi h a solu ion o hyd ochlo ic acid and hexame hylene e amine o s eel co osion p e en ion, o
emo e he oxides on he eba s’ su ace while limi ing any u he oxida ion o he eba in he acid. A e applying
Ico = 100 μA/cm² o 24 days, he heo e ical a ack pene a ion (A.P.) eached ~114 μm. The eba diame e a e
co osion can be app oxima ed o ~5.85 mm, esul ing in an empi ical A.P. o 150 ± 55 μm, sligh ly highe bu s ill
analogous o he heo e ical alue.
Figu e 6. Visual ep esen a ion o diame e o (a) unco oded and (b) co oded beam a e applying I co = 100 μA/cm2 o 24 days.
A c i ical aspec in alida ing he accele a ed co osion p o ocol in ol es he ela ionship be ween ac u e wid h
on he mo a ’s su ace and oxides p oduc ion and mo emen . Fo eba s posi ioned 4.8 mm below he su ace, he
i s isible c ack eme ged o an a ack pene a ion o 24 μm (wi hin 5/6 days). Despi e a sligh ly highe empi ical
A.P. (Figu e 6b), he sys ems expe ienced he i s c ack occu ence on he su ace a a slowe a e han wha was
expec ed by heo y (Alonso e al., 1996). Indeed, when cu en s d i e chemical eac ions, he e iciency o accele a ed
co osion is ypically less han 100%, mainly due o simul aneous hea gene a ion (Alonso e al., 1996; Dzhioe ,
Koso , and Von Oppen, 2013). Consequen ly, highe a ack pene a ions we e necessa y o achie e speci ic c ack
wid hs, when applying high co osion a es (i.e., Ico = 100 μA/cm²), and o compensa e o he oxide di usion h ough
he po es o he co e (Alonso e al., 1996). Hence, bo h longi udinal and ans e sal c oss-sec ions o he co oded
specimens a e p esen ed in Figu e 7 and Figu e 8, p o ing he signi ican ole o oxide p opaga ion in in luencing
c ack o ma ion on he sys em’s su ace. Mo eo e , Figu e 7 e eals ha oxides, o igina ing om he eba , exhibi a
andom mo emen owa d any o he ou su aces pa allel o he ein o cemen .
16 G. Milone e al./ S uc u al In eg i y P ocedia 00 (2024) 000–000
By employing CB-based sma coa ings, a link be ween elec ochemical a acks and he mechanical e ec s induced
by co osion was es ablished. Senso s we e u ilized o quan i y he inc ease in in e nal s ess and s ain due o oxide
o ma ion and p opaga ion wi hin he ma ix. This capabili y was e idenced in bo h ee and pa ially con ined eba
scena ios, showcasing he coa ings' e sa ili y ac oss di e en s uc u al condi ions. Fo uncon ined eba , he coa ings
p o ided accu a e acking o c ack de elopmen and p og ession up o an a e age wid h o 116 ± 45 μm,
demons a ing hei po en ial as ea ly wa ning sys ems o s uc u al in eg i y. Fu he mo e, in con igu a ions
in ol ing con ined eba , he coa ings we e cha ac e ized by good sensi i i y o he de elopmen o co osion, e en
when posi ioned a la ge dis ances om he di ec ly a ec ed eba sec ions.
In conclusion, his esea ch unde sco ed he impo ance o sma cons uc ion ma e ials in enhancing he du abili y
and sa e y o ci il in as uc u e. The s udy ex ended he applica ion o CB-based coa ings beyond adi ional uses,
highligh ing hei po en ial as a mul i unc ional ma e ial. Thei success ul implemen a ion o co osion sensing
ep esen s an ini ial p omising s ep owa ds he p oduc ion o sma e and mo e esilien in as uc u e. Fu u e wo k
will ocus on be e aming he p oduc ion and p opaga ion o he oxides wi hin he co oded ma ix, using a ying
accele a ion a es o co osion, and co ela ing hem wi h he elec ical esponse o hese senso s. Indeed, co osion
de elopmen has been p o en o be signi ican in he in e p e a ion o s uc u al heal h moni o ing sys ems. Hence,
u he co oding se ups need o be in es iga ed wi h he use o sma coa ings, explo ing hei scalabili y and
in eg a ing eal- ime moni o ing o accomplish he comp ehensi e p edic i e main enance o ci il s uc u es.
Acknowledgemen s
This p ojec has ecei ed unding om he Eu opean Union’s Ho izon 2020 esea ch and inno a ion
p og amme unde he Ma ie Skłodowska-Cu ie g an ag eemen No 860006.
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