Ac a Geodyn. Geoma e ., Vol. 12, No. 1 (177), 79–89, 2015
DOI: 10.13168/AGG.2015.0009
jou nal homepage: h p://www.i sm.cas.cz/ac a
ORIGINAL PAPER
ANALYSIS OF INNER STRUCTURE CHANGES OF CONCRETES EXPOSED TO HIGH
TEMPERATURES USING MICRO X-RAY COMPUTED TOMOGRAPHY
Libo SITEK 1)*, Lenka BODNÁROVÁ 2), Kamil SOUČEK 1),
Lubomí STAŠ 1) and Lucie GURKOVÁ 1)
1) Ins i u e o Geonics o he CAS, . . i., S uden ská 1768, 708 00 Os a a, Czech Republic
2) B no Uni e si y o Technology, Facul y o Ci il Enginee ing, Ve eří 331/95, 602 00 B no, Czech Republic
*Co esponding au ho ‘s e-mail: libo .si [email p o ec ed]as.cz
ABSTRACT
The X- ay Compu ed Tomog aphy (X- ay CT) ep esen s a p og essi e non-des uc i e me ho
d
o analysing he inne s uc u e o ma e ials. The me hod was used o moni o ing changes in
inne s uc u e o conc e e samples o di e en composi ion be o e and a e hei exposu e o
a ious he mal loads. Eigh ypes o conc e e samples we e p epa ed which di e ed by cemen
and agg ega e ypes. We in en ionally used such composi ion o conc e e mix u es which
inc eased hei esis ance o high empe a u es. The inne s uc u e o samples was analysed
using he mic o X- ay CT be o e he he mal loading and a e exposu e o samples o
empe a u es o 600 °C o 900 °C. Damages and cha ac e o changes in he inne s uc u e
caused by high empe a u es we e in luenced by he cha ac e o cemen and agg ega e we used.
The analysis o ob ained esul s is p esen ed in he pape .
ARTICLE INFO
A
icle his o y:
Recei ed 6 No embe 2014
Accep ed 16 Feb ua y 2015
A ailable online 2 Ma ch 2015
K
eywo ds:
Conc e e
Cemen pas e
Agg ega e
High empe a u e
in he inne s uc u e o conc e e a e he he mal
exposu e is o cu a sample and p o ide consequen
mac oscopic and mic oscopic analyses. As i is
impossible o e alua e changes in he same sample in
unloaded s a e and in s a e a e he he mal load wi h
adi ional me hods, we used he mic o X- ay
Compu ed Tomog aphy (mic o X- ay CT) o he
quan i a i e and quali a i e analyses o he inne
s uc u e o conc e e. The majo ad an age o his
p ocedu e is i s non-des uc i i y du ing he 3D
isualiza ion and analyses o he s udied ma e ials.
USE OF THE X-RAY COMPUTED TOMOGRAPHY
IN INDUSTRIAL APPLICATIONS
Recen ly, p og essi e me hods o analysing
a ious ypes o ma e ials ha e been inc easingly
applied. One o hem is he X- ay Compu ed
Tomog aphy which was o iginally used o he
pu poses o medical diagnos ics. Based on success ul
and apid de elopmen o his diagnos ic me hod
encou aged by esea ch and de elopmen o he X- ay
Compu ed Tomog aphy sys ems du ing he 1980s, i
b
egins o be used o indus ial applica ions in
ma e ials enginee ing, including he esea ch in o
b
eha iou o bioma e ials, as epo ed by O ani
(2004). In his ield o esea ch, i is especially
ad an ageous o use he 2D/3D X- ay Compu ed
Tomog aphy sys ems wi h high- esolu ion imaging
( he so-called mic o X- ay CT) based on he mic o
ocal X- ay sou ce and app op ia e line and a ea (2D)
de ec o s o X- ays which enable o esol e indi idual
p
ic u e elemen s o a CT slice, o olume elemen s
( oxels), small as uni s and ens o mic ome es in
INTRODUCTION
Conc e e has many ad an ageous p ope ies, e.g.
in lammabili y o low empe a u e conduc i i y.
Howe e , when a conc e e cons uc ion is exposed o
high empe a u es, i loses i s load-
b
ea ing capaci y,
especially in su ace laye s which a e loaded a mos .
Se ious p oblem is he so-called explosi e spalling
which is caused by he combina ion o inc easing
p essu e in inne po es and inne comp essi e s esses
o igina ing om ma e ial expansion a highe
empe a u es. Spalling o a conc e e laye leads o
weakening o he conc e e c oss-sec ion o a e-
in o ced cons uc ion and, in some cases, e en o he
exposu e o s eel ein o cemen o empe a u es abo e
he c i ical le el. De ec s can be so se ious ha he
comple e cons uc ion ge s des oyed. Design o
a conc e e mix u e wi h esis ance o he mal exposu e
o a ce ain pe iod o ime has been al eady classi ied
among he passi e i e p o ec ion me hods. Basic
composi ion o cemen conc e e can be p oblema ic,
as i is a composi e ma e ial consis ing o wo
ma kedly di e en componen s, i.e. he cemen pas e
and agg ega e. When exposed o high empe a u es,
bo h componen s beha e di e en ly and hei
physical, chemical and mechanical p ope ies change.
Expe imen al esea ch in o he a o emen ioned
ield o s udy consis s o p epa a ion o es samples
acco ding o he p elimina y concep o he conc e e
mix u e composi ion and hei es ing a high
empe a u es o du ing di ec lame impingemen . The
nex s ep is he p ope ies diagnos ics o samples
which can be based on a wide ange o es s and
measu emen s. The only way how o examine changes
L. Si ek e al.
80
Kodu , 2008; Xing a al., 2011 and Scheyd e al.,
2012).
A
GGREGATE
When p epa ing he he mal- esis an conc e e
mix u e, we used he basal agg ega e which shows
a long- e m esis ance o high empe a u es due o i s
cha ac e and o igin. In addi ion, we also used he
ligh weigh a i icial agg ega e om he expanded
clay (see Eu opean S anda ds EN 13055-1,
EN 14063-1 and EN ISO 9001).
Agg ega e om expanded clay has sui able
p ope ies in e ms o olume s abili y when exposed
o empe a u es up o 1050 °C. (Technical guide -
Liapo ). This agg ega e is p oduced in o a y kiln a
a empe a u e o 1100°C o 1200°C. Wa e abso p ion
o expanded clay agg ega e anges om 2 o 7 % (by
weigh ) a e 30 min and om 7 o 9 % a e 24 hou s
o ull imme sion in wa e (Technical guide - Liapo ).
Beha iou o conc e e wi h his agg ega e is
signi ican ly a ec ed by he so-called mois u e
con en . The mois u e con en in conc e e is a basic
ac o which can cause c acks and explosi e spalling
du ing he he mal loading (e.g. Kopinga and Pel,
1994). Due o he e apo a ion o wa e om expanded
clay, po es in conc e e a e loaded by some addi ional
p
essu e. I he p essu e o apou is highe han he
lexu e s eng h o cemen pas e, he cemen pas e
b
eaks and mic oc acks o explosi e spalling a e
o med ( an de Heijden a al., 2007). In e ms o i e
and hea esis ance o ligh weigh conc e e, he wo
mos impo an ac o s a e he mixing p ocedu e and
condi ions o which he cons uc ion is exposed. The
wo possibili ies o how o dose expanded clay
agg ega es in o conc e e mix u e a e he ollowing:
 in soaked s a e, wi h posi i e e ec s on
wo kabili y o conc e e and in e nal cu ing.
Highe mois u e con en is b ough in o conc e e
s uc u e and con inuously eleased du ing he
cu ing o conc e e. The ime necessa y o wa e
elease depends on en i onmen al condi ions.
This echnological p ocess is especially sui able
o eady-mix conc e e, high pe o mance
ligh weigh conc e e and applica ions in oad
cons uc ions. Ligh weigh conc e e p epa ed by
his echnological p ocess has he mois u e
con en up o 20 % a e 28 days o cu ing;
 in d y s a e. This echnological p ocess is
especially used in p e ab ica ion, as he moulding
o conc e e is as (wi hin 10 minu es). The e is
no ime o he agg ega e o soak up mixing
wa e ; howe e , his p ocedu e educes he
wo kabili y o ligh weigh conc e e. Ligh weigh
conc e e p epa ed by his echnological p ocess
has much lowe mois u e con en ( om 3 o 5 %
a e 28 days o cu ing).
Conc e e es specimens wi h expanded clay
agg ega es we e p epa ed acco ding o he i s
p
ocess. The agg ega es we e s o ed in wa e o
size. Al hough any speci ic di e ence be ween he
X- ay CT and mic o X- ay CT has no been speci ied,
i can be de ined in ela ion o he space esolu ion o
oxel o he limi alue o app oxima ely 200 μm
which he medical X- ay CT scanne s canno usually
each. The size o a sample examined wi h he mic o
X- ay CT me hod anges om app oxima ely 40 cm
(la ge samples) o a ew mic ome es (small samples).
Fo geosciences and cons uc ion ma e ials esea ch,
s anda d samples o he mic o X- ay CT a e o one
millime e o 5 cen ime es in size (Cnudde and
Boone, 2013).
The applica ion o he X- ay CT me hod o
quan i a i e and quali a i e analyses o beha iou o
di e en kinds o geoma e ials and o he ela ed
ma e ials, such as ocks, soil, cons uc ion ma e ials,
ce amic ma e ials and geocomposi es (Ščučka and
Souček, 2007), is g adually inc easing. This non-
des uc i e me hod o in es iga ions o geoma e ials
b
eha iou is also sui able o he 4D isualiza ion and
analysis o changes in objec s exposed o ex e nal
ac o s ( o example, s ess, he mal exposu e,
deg ada ion changes o ma e ials, s udy o liquid- low
in ma e ials, e c. – see Des uess e al., 2006).
E
SSENTIALS OF COMPUTED TOMOGRAPHY
Indus ial mic o X- ay Compu ed Tomog aphy
u ilizes he di e ences o X- ays p ope ies du ing he
in e ac ion wi h he mass o a s udied ma e ial. In case
o he X- ay CT, i is especially he abili y o X- ays
o pene a e a ious kinds o ma e ials wi h di e en
le els o hei a enua ion in ela ion o p ope ies o
analysed objec s, especially objec densi y. I is
necessa y o ob ain se ies o 2D adiog aphs o each
de e mined o a ion angle du ing he scanning p ocess
o he analysed objec wi h o a ion o 360° o he
consequen econs uc ion o he CT olume
consis ing o indi idual oxels. The 2D adiog aph
p ojec ions a e ealized using he X- ays a ea de ec o
wi h he de e mined numbe o pixels. The adiog aph
is a 2D map o pixels which shows he in ensi y o
a enua ion o X- ay signals passing h ough he
s udied objec . Di e en g ey le els (g ey le el scales
a e de e mined by he ype o de ec o and i s bi scale
- 8-bi , 16-
b
i , e c.) co espond o a ious in ensi ies
o a enua ion. Based on su icien numbe o
p
ojec ions, he CT olume o he objec is
econs uc ed using algo i hm calcula ions (e.g. he
Radon ans o ma ion, he in e se Radon ans-
o ma ion o Fil e ed Back-P ojec ion Me hod as
epo ed by Kak and Slaney, 1987).
EXPERIMENTAL PROCEDURE
P epa a ion o a mixing concep ion o conc e es
loaded by high empe a u es o i e is no an easily
sol able p oblem. P epa a ion o ou samples was
b
ased on ou own expe iences and ecommenda ions
o o he au ho s which ha e been occupied in ensi ely
b
y he simila p oblem (e.g. Khou y, 1992; Vyd a e
al., 2001; Mindeguia e al., 2013; Sa a e al., 2005,
ANALYSIS OF INNER STRUCTURE CHANGES OF CONCRETES EXPOSED TO HIGH …
.
81
Table 1 Composi ion o mix u es wi h basal agg ega e.
Mix u e componen  Quan i y pe m3
Cemen 350 kg
Wa e 175 kg
Agg ega e 0-4 mm basal 1070 kg
Agg ega e 4-8 mm basal 1050 kg
Supe plas i ie Mape luid N2006.3 kg
Table 2 Composi ion o mix u es wi h basal and expanded clay agg ega e.
Mix u e componen  Quan i y pe m3
Cemen 375 kg
Wa e 125 kg
Expanded clay agg ega e 0-4/5000.24 m3
Expanded clay agg ega e 4-8/6000.4 m3
Agg ega e 0-4 mm basal 500 kg
Supe plas i ie Mape luid N2004.5 kg
Table 3 Types o cemen used in mix u es.
Po land cemen CEM I 42.5 R 
Po land composi e cemen wi h limes oneCEM II/B-M (S-LL) 32.5 R 
Po land slag cemen CEM II/B-S 32.5 R 
Blas u nace cemen CEM III/B 32.5 N-SV 
a numbe o cylind ical co es, wi h a diame e o
22 mm and heigh o abou 40 mm, we e d illed.
Then, he con igu a ion o he used X- ay
omog aph was op imised o ob ain he bes possible
quali y o indi idual CT slices. Acco ding o he size
o analysed es ed objec s, he size o a oxel ( he
b
asic composi ion elemen o he econs uc ed
omog aphy olume) was abou 0.025 mm. The inne
s uc u e o cylind ical samples was u he scanned
wi h he mic o X- ay CT. Subsequen ly, samples we e
exposed o he he mal s ess o 600 °C o 900 °C.
Samples we e hea ed in acco dance wi h he s anda d
empe a u e cu e ISO 834 (see ISO 834-1) and las ed
a he de e mined empe a u e o he pe iod o
60 minu es. The s anda d empe a u e- ime cu e ISO
834 (also known as he Cellulosic cu e o he
s anda d nominal i e cu e) ep esen s a bu ning a e
o ully de eloped i e in a compa men . I shows ha
empe a u e inc eases wi h ime a a cons an a e (see
Fig. 1). The cu e is de ined by he ollowing
equa ion:


0345 8 1log



gT
whe e

g
is he empe a u e o gases in compa men
i e (°C), T0 ep esen s he empe a u e in
compa men i e be o e i e ou b eak (°C) and is he
du a ion o he i e (min). A e hea ing a he desi ed
empe a u e, he samples we e cooled a he labo a o y
48 hou s p io o manu ac u ing; expanded clay
agg ega es we e used in he soaked s a e. The
mois u e con en o he conc e e wi h expanded clay
agg ega es was 12 %, while he mois u e con en o
he conc e e wi h basal agg ega es only 4 %.
CEMENTS
In e ms o a ious le els o he mal esis ance,
ou ypes o cemen s we e chosen as binde o
cemen mix u e p epa a ion, i.e. he Po land cemen ,
he Po land composi e cemen wi h limes one, he
Po land slag cemen and, inally, he Blas u nace
cemen . The Po land cemen is he mos commonly
used ype o cemen in conc e e mixing. I was he
eason why o he cemen s we e compa ed wi h his
ype o cemen . E en hough, due o low esis ance o
he mal loads, his cemen is no gene ally used o
p epa a ion o he mally s able conc e es.
Fi s ly, 8 di e en conc e e mix u es we e
p
epa ed using a ious ypes o cemen s and
agg ega es. Fou mix u es we e composed o he
b
asal agg ega e; hey di e ed by he used cemen . In
case o o he ou mix u es, he mix u e o he basal
agg ega e and he a i icial agg ega e om he
expanded clay was used. The Table 1 and Table 2
show he composi ion o all es ed mix u es. The ypes
o used cemen a e speci ied in Table 3.
Secondly, es ing beams o dimensions o abou
400x100x100 mm3 we e p epa ed om each conc e e
mix u e. F om each analysed ype o conc e e,
L. Si ek e al.
82
Fig. 1 The s anda d empe a u e- ime cu e ISO 834.
Fig. 2 De ini ion o he es ed space in a conc e e sample o de ec ion
o he inc emen in po e space a e hea ing (le - sample be o e
he mal exposu e, igh - sample a e he mal exposu e).
ANALYSIS OF INNER STRUCTURE CHANGES OF CONCRETES EXPOSED TO HIGH …
.
83
Fig. 3 Example o he analysis o changes in he olume o po e space in one o he CT slices o a
conc e e es sample be o e and a e he he mal exposu e.
Table 4 Speci ica ion o XT H 225 indus ial mic o X- ay CT sys em used du ing expe imen .
Max. accele a ion ol age and powe o he X- ay sou ce ( e lec ion
mode)
225kV / 225W
Max. accele a ion ol age and powe o he X- ay sou ce ( ansmission
mode)
180kV / 20W
Size o he X- ay ube ocus ( e lec ion mode / ansmission mode) <3 µm / <1 µm
Max. weigh , diame e and heigh o scanned objec s 50 kg / app ox. 0.5 m / 0.5 m
Max. omog aphy hickness o analysed ma e ials 237 kg.m-2
Senso o he X- ay adia ion (16-bi dep h) – a ea de ec o 200 µm pe pixel,
No. o pixels - 2000 x 2000
newly o med due o hea ing. The di e ence be ween
hese wo olumes indica es, in a ce ain way, he a e
o esis ance o he analysed conc e e mix u e agains
he he mal loading. Based on he analysis o
econs uc ed olumes, changes in po es space we e
de e mined again using he mic o X- ay CT. Po es
space was analysed in he ollowing s eps:
 A es ed space o app oxima ely equal olume
(abou 3300 mm3) o he analysis o changes i
n
he olume o po es space on an iden ical sample
b
e o e and a e hea ing was de ined (see Fig. 2).
The es ed space was posi ioned in he middle
p
a o he es ed sample o elimina e he
in luence o ex e nal bounda y condi ions.
Resul s om he sample edge can be in luence
d
b
y an excessi e loss o he agg ega e and cemen
binde caused by hea ing. Thus, i can nega i ely
a ec he alue o po e space inc emen .
 Analysis o he olume o po e space was ca ie
d
ou in he es ed space o all es samples b
y
de e mina ion o a h eshold which enabled he
di e en ia ion be ween he po e space and he
empe a u e o 20 °C. Once indi idual es ed objec s
we e cooled, compa a i e CT scans o he
co esponding conc e e samples we e pe o med o
he consequen e alua ion o e ec s o he he mal
load on hei in eg i y. Using he VGS udio Max
so wa e, sepa a e econs uc ed CT olumes o
analysed samples we e isualised. Co esponding CT
olumes, scanned be o e and a e he he mal
exposu e, we e dimensionally o ien ed in a way ha
he omog aphic c oss-sec ions wi h iden ical posi ion
could be simul aneously compa ed. On so-
p
osi ioned
and isualised c oss-sec ions, e ec s o high
empe a u es we e e alua ed.
Fo p ecise quan i a i e e alua ion o ailu e a e
o empe ed conc e e mix u es, olume o po es space
in iden ical sample be o e and a e hea ing a he
desi ed empe a u e we e compa ed. The olume o
p
o e space o he sample analysed be o e hea ing is
ep esen ed mainly by ai bubble po es ha a ise om
he echnological p ocessing o conc e e mix u es
du ing sample p epa a ion. A e hea exposu e, he
olume o po es space is ep esen ed no only by ai
b
ubbles, bu also by c acks in he cemen ma ix

L. Si ek e al.
84
Table 5 Se ings o pa ame e s o mic o X-Ray CT.
X- ay sou ce se ings
X- ay pene a ion [kV] 150
X- ay In ensi y [µA] 300 - 400
X- ay il e Aluminium, hickness 2.25mm
Se ings o CT scanning
No. o p ojec ions [--] 2 800 -3 000
No. o ames pe p ojec ion [--] 8
P ojec ion exposu e [ms] 354
Scanning ime [h] app ox. 2.5
Recons uc ion
Voxel esolu ion [µm] 20 - 30
No. o oxels in CT olume app ox. 1.5 E9
econs uc ion ime [min] app ox. 10
oxel bi dep h / g ey le els 8-bi / 255
EXPERIMENTAL EQUIPMENT AND CONDITIONS
Fo he s udy o s uc u al changes o conc e e
es samples exposed o he mal loads, he
N
ikon
Me ology XT H 225 indus ial mic o X- ay CT
sys em was used. I is a ully au oma ed appa a us
wi h a o a ing scanning sys em equipped wi h a mic o
ocal X- ay sou ce which gene a es cone-shaped
beams. The used sys em is speci ied in Table 4.
S udied olumes we e econs uc ed using CT P o 3D
and CT P o 2D so wa e (by Nikon Me ology NV).
Visualiza ion was p o ided by a VGS udio Max
so wa e (by Volume G aphics), e sion 2.2, wi h
addi ional modules o p ope image analysis.
Se ings o pa ame e s o he mic o X- ay CT
sys em used o scanning he inne s uc u e o
conc e e ma e ials a e p esen ed in de ail in Table 5.
Tes samples we e hea ed o he desi ed
empe a u e using an elec ically hea ed labo a o y
es ing u nace Classic 1013L wi h inne space
dimensions o abou 800 x 800 x 800 mm3. The
u nace (Fig. 4) enables o each and sus ain he
empe a u e up o 1100°C acco ding o a ious
empe a u e cu es. Cu en empe a u e was
moni o ed and eco ded using a da a logge Tes o
174-T4 wi h ex e nal empe a u e p obes connec ion.
Tempe a u e cu e o es ing ollowed he s anda d
ISO 834 cu e.
ANALYSIS OF RESULTS
Resul s o s uc u al changes in es samples a e
he he mal load a e g aphically p esen ed as ollows.
Example o wo iden ical omog aphic c oss-sec ions
o one sample be o e and a e he exposu e o he
he mal load o 900 °C is shown in Figu e 5. I
demons a es how easily indi idual g ains o
agg ega e, ai po es, c acks in cemen pas e, e c. can
be iden i ied on a pa icula CT slice. Fo an easie
compa ison o bo h inne s uc u es, some ypical
c acks and hei a e age wid hs a e highligh ed in
s uc u es a e he mal exposu e.
Fig. 4 Tes ing u nace Classic 1013L and da a
logge Tes o 174-T4 wi h ex e nal
empe a u e p obe connec ions o
eco ding eal empe a u e cu e.
es o conc e e ma e ial (agg ega es and cemen
binde ). Example o he inc ease in he olume
o po e space in one o he es sample sec ions
be o e and a e hea ing is shown in Figu e 3.
 Finally, he inc ease in he olume o po e space,
caused by hea ing a ious conc e e mix u es up o
a empe a u e o 600 °C and 900 °C, was
calcula ed and e alua ed.
ANALYSIS OF INNER STRUCTURE CHANGES OF CONCRETES EXPOSED TO HIGH …
.
85
Fig. 5 Changes in he inne conc e e s uc u e a e he exposu e o he mal load (le – s uc u e
be o e he mal exposu e, igh – he same s uc u e a e he mal exposu e).
Fig. 6 Conc e e wi h he Po land composi e cemen , basal agg ega e and ligh weigh agg ega e
om expanded clay be o e and a e he exposu e o a he mal load o 900°C (wid hs o
selec ed c acks a e indica ed in millime es).
he cemen ma ix (see Fig. 9) we e p e ailing in
s uc u es o cemen s exposed o he he mal load. I
was gene ally ue ha ex ensi e c acks in he cemen
ma ix occu ed especially in he ma ix consis ing o
he Blas u nace cemen and he Po land slag cemen
( o example, Fig. 9). Sepa a ion c acks along
agg ega e g ains we e mo e common in he cemen
ma ix p epa ed om he Po land cemen and he
Po land composi e cemen (see Fig. 6 and Fig. 11).
The inne s uc u e o he conc e e wi h expanded clay
was usually mo e damaged due o agg ega e
p ope ies – mo e wa e was used in he p epa a ion
I was p o ed ha he ype o used agg ega e, as
well as he ype o cemen pas e, in luenced he inne
s uc u e o s udied samples exposed o a he mal
load. The mally loaded conc e e samples wi h
expanded clay we e much mo e damaged (especially
b
y c acks along clay g ains) han he conc e e samples
consis ing only o basal agg ega e (compa e Fig. 6
and Fig. 7).
Na u e o occu ed damages we e signi ican ly
in luenced by he ype o used cemen . I de e mined
whe he sepa a ion c acks along he agg ega e g ains
(especially along expanded clay – Fig. 6) o c acks in
L. Si ek e al.
86
Fig. 7 Conc e e wi h he Po land composi e cemen and basal agg ega e be o e and a e he
exposu e o a he mal load o 900°C (wid hs o selec ed c acks a e indica ed in millime es).
Fig. 8 Conc e e wi h he Blas u nace cemen wi h basal agg ega e and ligh weigh agg ega e o
m
expanded clay be o e and a e exposu e o a he mal load o 600°C (wid hs o selec ed
c acks a e indica ed in millime es).
Fig. 9 Conc e e wi h he Blas u nace cemen wi h basal agg ega e and ligh weigh agg ega e o
m
expanded clay
b
e o e and a e exposu e o a he mal load o 900°C (wid hs o selec ed
c acks a e indica ed in millime es).
ANALYSIS OF INNER STRUCTURE CHANGES OF CONCRETES EXPOSED TO HIGH …
.
87
Fig. 10 Conc e e wi h he Po land cemen wi h basal agg ega e and ligh weigh agg ega e o
m
expanded clay be o e and a e exposu e o a he mal load o 600°C (wid hs o selec ed
c acks a e indica ed in millime es).
Fig. 11 Conc e e wi h he Po land cemen wi h basal agg ega e and ligh weigh agg ega e o
m
expanded clay be o e and a e exposu e o a he mal load o 900°C (wid hs o selec ed
c acks a e indica ed in millime es).
The mal esis ance was isually e alua ed (in
e ms o numbe , size and cha ac e o occu ed
c acks) on es samples o all es ed conc e e mix u es
hea ed o 600 °C and 900 °C. Mo eo e , he inc ease
in po e space in he es ed olume o each sample
b
e o e and a e hea ing was e alua ed quan i a i ely.
This can be in e p e ed as a o ma ion o new c acks
and/o an inc ease in he olume o exis ing c acks.
This dependence is illus a ed in Figu e 12. I is
ob ious ha inc ease in he empe a u e loading o
a sample also leads o a g ow h o he olume o
c acks. Gene ally, samples wi h added expanded clay
agg ega e a e mo e damaged by c acks (expansion o
he po e space up o 8 %), which is appa en om he
p
ocess due o he p esence o po es in he clay
agg ega e (see abo e). Consequen ly, he cemen
ma ix s uc u e was damaged by he wa e
e apo a ing om he agg ega e.
As expec ed, he inne conc e e s uc u e was
mo e damaged a he highe empe a u e (900 °C) han
a he lowe one (600 °C). C acks occu ed in he
cemen ma ix mo e equen ly and hey we e wide
(compa e Fig. 8 and Fig. 9). Sepa a ion c acks along
he expanded clay agg ega e only de eloped when he
sample was hea ed o 900 °C. A a empe a u e o
600°C, any o samples did no exhibi ed c acks along
he expanded clay (compa e, o ins ance, Fig. 10 and
Fig. 11).