T. MELICHAR et al.: CHANGES IN THE COMPOSITE STRUCTURE AND PARAMETERS AFTER AN EXPOSURE ...
243–249
CHANGES IN THE COMPOSITE STRUCTURE AND
PARAMETERS AFTER AN EXPOSURE TO A SYNERGIC ACTION
OF VARIOUS EXTREME CONDITIONS
SPREMINJANJE STRUKTURE IN PARAMETROV KOMPOZITOV
IZPOSTAVLJENIH SINERGISTI^NI AKTIVNOSTI RAZLI^NIH
EKSTREMNIH POGOJEV
Tomá{ Melichar, Ámos Dufka, Jiøí Byd`ovský
Brno University of Technology, Faculty of Civil Engineering, Institute of Technology of Building Materials and Components,
Veveøí 331/95, 602 00 Brno, Czech Republic
melichar.t@fce.vutbr.cz
Prejem rokopisa – received: 2015-08-14; sprejem za objavo – accepted for publication: 2016-03-01
doi:10.17222/mit.2015.256
The research presented in this paper is aimed at studying the properties of composites designed for a redevelopment of
reinforced concrete structures where it is possible to expect an increased risk of fire, i.e., shock actions of extreme temperatures.
Such conditions may occur, for example, in transport constructions, particularly in tunnels. We have developed two recipes
(formulas) for materials based on a polymer-cement matrix and a porous filler. These materials were subjected to cyclic freezing
and de-freezing in combination with a water action. In terms of a long-term durability, we monitored the characteristics after 50
and 100 cycles. The impact of an increased humidity was not considered in this phase of the research. After testing the frost
resistance, the bodies were dried up. Then, temperature shocks of (400, 600 and 1000) °C followed. The bodies were cooled
down under control, with gradual temperature decreases. The reason for assessing the impact of these two exposure conditions
on the properties of designed materials was mainly the use of the porous filler. This filler has a favourable effect on the
temperature resistance. On the other hand, however, the frost resistance can be negatively affected in combination with water.
Studying the influence of the above two exposures was carried out using the basic physico-mechanical and also
physico-chemical methods. We also utilized analytical methods for assessing the microstructure. The structure was also
examined using an innovative imaging technique allowing a three-dimensional visual assessment, which was primarily aimed at
identifying faults of the structure.
Keywords: composite, polymer-cement matrix, cementitious supplementary material, high temperature, frost resistance,
synergic, microstructure
Namen predstavljene raziskave je {tudij lastnosti kompozitov namenjenih obnovi betonskih zgradb, kjer je mo`no pri~akovati
pove~ano nevarnost po`ara in delovanje ekstremnih temperatur. Taki pogoji se lahko pojavijo, na primer, v prometnih konstruk-
cijah, posebno v tunelih. Razvili smo dva recepta (formuli) materialov, ki temeljijo na me{anici polimer-cement in poroznega
polnila. Ti materiali so bili izpostavljeni cikli~nemu zamrzovanju in odtajanju, v kombinaciji z delovanjem vode. V smislu dolge
zdr`ljivosti, smo pregledali zna~ilnosti po 50 in 100 ciklih. Vpliv pove~anja vla`nosti v tem delu raziskav ni bil obravnavan. Po
preizku{anju odpornosti na mraz, so bila telesa osu{ena. Sledili so temperaturni {oki na (400, 600 in 1000) °C. Telesa so bila
kontrolirano ohlajena, s postopnim zmanj{anjem temperature. Razlog za ocenjevanje u~inka teh dveh pogojev izpostavitve na
lastnosti materiala, je bila predvsem uporaba poroznega polnila. To polnilo ima ugoden vpliv na temperaturno obstojnost. Po
drugi strani pa je lahko odpornost na zmrzal manj{a v kombinaciji z vodo. [tudij vpliva obeh na~inov izpostavitve je bil izveden
z uporabo osnovnih fizikalno-mehanskih in tudi fizikalno-kemijskih metod. Za ocenjevanje mikrostrukture smo uporabili tudi
analiti~ne metode. Struktura je bila preiskana z uporabo inovativne slikovne tehnike, ki omogo~a tridimenzionalno vidno oceno,
katere prvotni namen je bil identifikacija napak v strukturi.
Klju~ne besede: kompozit, me{anica polimer-cement, cementni nadomestni material, visoka temperatura, odpornost na zmrzal,
sinergija, mikrostruktura
1 INTRODUCTION
Durability of building materials is one of the key
aspects of their smooth function in a given structure.
There are many factors that could realistically affect
engineering constructions. These may include exterior
climatic conditions, the presence of aggressive media as
well as accidental exposure to high temperatures. In
practice, consequently, we can even come across situat-
ions where the structure is loaded with cyclic exposures
to water and frost followed by fire. When developed, the
building materials intended for the environments with
the said potential risks of random factors must therefore
be verified in laboratories. The primary reason is the use
of non-traditional raw materials. With regard to the
environmental situation and price, these raw materials
often come from alternative resources. Alternative raw
materials are more or less characterized by the variability
of parameters, including their composition. The choice
of suitable compositions of polymer-cement composites
destined for demanding exposure conditions is one of the
basic prerequisites of their sufficient resistance and the
expected building lifetime.
The development of cement composites for un-
favourable environments was addressed by more authors,
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Materiali in tehnologije / Materials and technology 51 (2017) 2, 243–249 243
UDK 67.017:621.742.48:62-97-022.171 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(2)243(2017)
for example in studies.1–7 Regarding the use of a porous
aggregate for cement composites, very interesting and
significant findings were published in study.8 Here, the
research focuses on the contact zone (or surface
transition zone) of the porous aggregates and the cement
matrix. The issue is dealt with in terms of both experi-
mental research and numerical simulation. It is shown
that this zone is less porous when using a lightweight
aggregate with a smaller thickness than in the case of
conventional dense aggregates. Depending on the water-
cement ratio and the structure of the aggregate surface
layer or aggregate porous system, this matrix/aggregate
transition zone is characterized by different parameters.
For example, this zone disappears in the case of a very
low water-cement ratio and the use of microsilica.
While exploring scientific literature and scientific
articles, we did not find any publications that would pre-
sent a research aimed at the synergistic effects of frost
and subsequent high temperatures (simulating fire) on
the composites containing a lightweight aggregate. The
issue was only addressed separately. Interesting findings
of authors dealing with the effects of high temperatures
on cement composites are presented, inter alia, in stu-
dies.9–11
The parameters of a lightweight aggregate produced
in self-firing processes from secondary energy products
are studied in article.12
2 METHODOLOGY OF THE EXPERIMENTAL
WORK
The research tested two recipes of repair materials
based on a polymer-cement composite matrix. Specific
formulations of recipes are given in the following table
(Table 1).
Table 1: Compositions of tested mixtures
Tabela 1: Sestava preizku{enih me{anic
Component Unit
Mixture
RMS RMA
Cement kg m–3 435 435
Blast furnace slag kg m–3 234 –
Fly ash kg m–3 – 234
Vinyl acetate copolymer % (wcem) 3 3
Microsillica % (wcem) 5 5
Amphibolite 0-1 mm kg m–3 837 837
Porous aggregate 1-2 mm kg m–3 632 632
Polypropylene fibres kg m–3 1,0 1,0
Water kg m–3 187* 187*
* The porous aggregate was saturated with water before preparing the
mixtures. The aggregate has a water-absorption ability of about 35 %.
So, a certain amount of water was leached from the porous aggregate
during the mixing.
The polymeric additive based on a copolymer of
vinyl acetate and ethylene in an amount of 3 % of the
cement weight was used in order to improve the cohe-
sion in the fresh as well as hardened state, and the plasti-
city of the fresh mixture. The filler was an amphibolite-
aggloporite mixture, which is an artificially produced
porous sintered aggregate (hereinafter referred to as
aggloporite).
Since these materials were fine-grained mortars, the
testing was performed on bodies with dimensions of (40
× 40 × 160) mm. The first group of these bodies was
exposed to 50 freezing cycles with a subsequent thermal
load, followed by a definition of the essential charac-
teristics according to 13–15. The second group of the
bodies was exposed to 100 freezing cycles followed by a
thermal load and an assessment of the parameters. The
exposure under the conditions of alternating freezing and
de-freezing was carried out according to 16. Cycling was
implemented so that the tests of the characteristics were
conducted after 70 d or 120 d. In these ages, we also
tested reference bodies that had been only exposed to
extreme temperatures.
The thermal exposure was carried out in steps of
(400, 600 and 1000) °C. The cooling took place
gradually in furnaces with a decreasing gradient of about
1 °C min–1. Laboratory-stored bodies were exposed con-
tinuously to about 22 °C. In addition to the basic
material properties and microstructure, the mortars were
also visually assessed.
3 RESULTS
A comparison of the achieved outputs is shown in the
graphs below (Figures 1 to 6). An emphasis was placed
on the assessment of the bulk density (designated as
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Figure 1: Bulk density and weight change of mixture RMS containing
blast furnace slag (BD – bulk density; W – weight; S70(120)-R – refe-
rence composite after 70 (120) days and thermal exposure; S70(120)-F
– composite after 70 (120) days or 50 (100) frost cycles and thermal
exposure; S70(120)-RF – difference between reference and frost-
exposed specimens)
Slika 1: Gostota osnove in spreminjanje te`e me{anice RMS, ki vse-
buje plav`no `lindro (BD – gostota osnove, W – te`a; S70(120)-R –
referen~ni kompozit po 70 (120) dneh toplotne izpostavitve;
S70(120)-F – kompozit po 70 (120) dnevih ali 50 (100) ciklih zamrzo-
vanja in toplotne izpostavitve; S70(120)-RF – razlika med referen~nim
vzorcem in vzorcem izpostavljenem zamrzovanju)
BD), weight (designated as W) and strength characteris-
tics (designated as fc – compressive strength and ff –
bending tensile strength). The courses of each recipe and
parameter are evaluated separately. Each graph always
contains a comparison of one recipe and the studied
characteristic at the ages of 70 d and 120 d. Courses of
percentage changes (parameters designated as ) of a
given characteristic due to the exposure to the alternating
freezing and de-freezing with a subsequent thermal
shock are plotted on the secondary axis (solid and
dashed curves). Furthermore (shown with a dotted
curve), the graphs indicate differences in the reference
parameters (designated as R) for the frozen (designated
as F) bodies after each temperature exposure (difference
– designated as RF).
Fluctuations of negative temperatures in combination
with a saturation of the material with water and the
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Figure 5: Flexural strength of mixture RMS containing blast furnace
slag (S70(120)-R – reference composite after 70 (120) days and
thermal exposure; S70(120)-F – composite after 70 (120) days or 50
(100) frost cycles and thermal exposure; S70(120)-RF – difference
between reference and frost-exposed specimens)
Slika 5: Upogibna trdnost me{anice RMS, ki vsebuje plav`no `lindro
(S70(120)-R – referen~ni kompozit po 70 (120) dneh toplotne izpo-
stavitve; S70(120)-F – komozit po 70 (120) dneh ali 50 (100) ciklih
zamrzovanja in toplotne izpostavitve; S70(120)-RF – razlika med
referen~nim in zamrzovanju izpostavljenim vzorcem)
Figure 3: Compressive strength of mixture RMS containing blast
furnace slag (S70(120)-R – reference composite after 70 (120) days
and thermal exposure; S70(120)-F – composite after 70 (120) days or
50 (100) frost cycles and thermal exposure; S70(120)-RF – difference
between reference and frost-exposed specimens)
Slika 3: Tla~na trdnost me{anice RMS, ki vsebuje plav`no `lindro
(S70(120)-R – referen~ni kompozit po 70 (120) dneh toplotne
izpostavitve; S70(120)-F – kompozit po 70 (120) dneh ali 50 (100)
ciklih zamrzovanja in toplotni izpostavitvi; S70(120)-RF – razlika
med referen~nim in zamrzovanju izpostavljenim vzorcem)
Figure 4: Compressive strength of mixture RMA containing fly ash
(A70(120)-R – reference composite after 70 (120) days and thermal
exposure; A70(120)-F – composite after 70 (120) days or 50 (100)
frost cycles and thermal exposure; A70(120)-RF – difference between
reference and frost-exposed specimens)
Slika 4: Tla~na trdnost me{anice RMA, ki vsebuje lete~i pepel
(A70(120)-R – referen~ni kompozit po 70 (120) dneh toplotne izpo-
stavitve; A70(120)-F – komozit po 70 (120) dneh ali 50 (100) ciklih
zamrzovanja in toplotne izpostavitve; A70(120)-RF – razlika med
referen~nim in zamrzovanju izpostavljenim vzorcem)
Figure 2: Bulk density and weight change of mixture RMA
containing fly ash (BD – bulk density; W – weight; A70(120)-R –
reference composite after 70 (120) days and thermal exposure;
A70(120)-F – composite after 70 (120) days or 50 (100) frost cycles
and thermal exposure; A70(120)-RF – difference between reference
and frost-exposed specimens)
Slika 2: Gostota osnove in spreminjanje te`e RMA, ki vsebuje lete~i
pepel (BD – gostota osnove, W – te`a; A70(120)-R – referen~ni kom-
pozit po 70 (120) dneh toplotne izpostavitve; A70(120)-F – kompozit
po 70 (120) dneh ali 50 (100) ciklih zamrzovanja in toplotne
izpostavitve; A70(120)-RF – razlika med referen~nim vzorcem in
vzorci po toplotni izpostavitvi)
subsequent thermal load may lead to cracks or micro-
cracks. For this reason, one of the key included analyti-
cal methods was computer tomography (hereinafter
referred to as CT). Figures below present selected ima-
ges of the bodies loaded with a temperature of 1000 °C
including the reference bodies (Figures 7 to 9). Another
substantial analysis was electron microscopy (hereinafter
referred to also as SEM). Here, the attention was focused
on the faults of the matrix itself as well as on any
microscopic cracks, mainly in the matrix-filler interface
(Figures 9 and 10).
4 DISCUSSION
The RMS formula gave us bulk-density values (Fig-
ure 1) of 1810 kg.m–3 and 1830 kg.m–3 after 70 d or 120
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Figure 10: Microstructure of RMS, exposure temperature of 1000 °C
(without freezing), mag. 20.000×; detail of structure degradation
Slika 10: Mikrostruktura RMS, temperature izpostavitve 1000 °C
(brez zamrzovanja), pov. 20,000×; detajl degradacije strukture
Figure 8: CT image – slice of RMA, 120 days, R – reference sample,
100 freezing cycles, exposure to 1000 °C
Slika 8: CT-posnetek rezine RMA, 120 dni, R – referen~ni vzorec po
100 ciklih zamrzovanja, izpostavljen na 1000°C
Figure 7: CT image – slice of RMA, 120 days, R – reference sample
(without freezing cycles), exposure to 1000 °C
Slika 7: CT-posnetek rezine RMA, 120 dni, R – referen~ni vzorec
(brez ciklov zamrzovanja), izpostavljen na 1000 °C
Figure 6: Flexural strength of mixture RMA containing fly ash
(A70(120)-R – reference composite after 70 (120) days and thermal
exposure; A70(120)-F – composite after 70 (120) days or 50 (100)
frost cycles and thermal exposure; A70(120)-RF – difference between
reference and frost-exposed specimens)
Slika 6: Upogibna trdnost me{anice RMA, ki vsebuje plav`no `lindro
(A70(120) – R – referen~ni kompozit po 70 (120) dneh toplotne
izpostavitve; A70(120) – F – kompozit po 70 (120) dneh ali 50 (100)
ciklih zamrzovanja in toplotne izpostavitve; A70(120) – RF – razlika
med referen~nim in zamrzovanju izpostavljenim vzorcem)
Figure 9: CT picture – slice of RMS, 120 days, R – reference sample,
100 freezing cycles, exposure to 1000 °C
Slika 9: CT-posnetek rezine RMS, 120 dni, R – referen~ni vzorec po
100 ciklih zamrzovanja, izpostavljen na 1000 °C
d, respectively. Therefore, an almost negligible growth
was observed. For a proper evaluation (in terms of
requirements of normative documents), the graph (Fig-
ure 1) also contains curves characterizing the weight
loss. The course of the curves indicates that the resis-
tance to high temperatures gradually gently decreased
due to the frost cycles. After 100 cycles and exposure to
an ambient temperature of 1000 °C, we observed a
weight loss of 17.9 % while the reference material
showed a decrease of about 13.3 %. Differences between
the weight losses (RF curve, Figure 1) after 100 frost
cycles were identified as slightly higher. After exposure
to 1000 °C, however, the differences in the weight loss
(RF curve, Figure 1) after 50 and 100 cycles became
equal.
The RMA formula was characterized by bulk-density
values of 1680 kg.m–3 and 1720 kg.m–3 after 70 d and
120 d, respectively (Figure 2). As in the case of the
RMS recipe, this parameter increases very slightly. The
courses of weight decreases are different in comparison
with the RMS formula. The R and F curves can be
characterized by a more uniform and more gradual
decline than in the case of the RMS. Nevertheless, the
weight losses after 100 frost cycles followed by the ther-
mal exposure of 1000 °C are comparable for both recipes
(about 18 %), i.e., the influences of fly ash and slag are
similar (with a negligible difference of 0.3 % in favour of
the slag). The RF curves show a relatively balanced
course.
In comparison with the weight, the declines in
strength characteristics were much more noticeable. In
the case of the RMS recipe, 50 frost cycles led to a de-
crease in the compressive strength by about 21 % (from
the original value of about 47 N.mm–2) and 100 cycles
resulted in a decrease by 26.5 % (from the original value
of 48 N.mm–2; Figure 3). According to the relevant tech-
nical standard,16 the essential criterion for a decrease is
25 %; this criterion was slightly exceeded after 100
cycles. When comparing the R and F curves characte-
rizing the loss of strength due to the thermal stress or
frost stress, it is evident that the influence of the cyclic
frost was manifested by pronounced declines. The
difference between the exposures at 50 or 100 cycles is
not very noticeable. The graph clearly shows that 100
frost cycles followed by a thermal load at the age of 120
d caused a decrease in the compressive strength to
74.6 %, i.e., the residual strength of 24.4 % (or
9 N mm–2). Exposure to the temperature of 1000 °C
resulted in virtually identical residual strengths (Figure
3, RF curves).
In the RMA recipe, the trends of the compressive
strength are not so clear (Figure 4). The values show a
significant increase in the strength owing to a longer
ripening time. This was partly expected due to the nature
of fly ash because of its involvement in the hydration
process occurring after a prolonged period of time. Due
to the frost stress (without the temperature exposure), the
compressive strength decreased by 15.1 % and 27.1 %
after 50 cycles and 100 cycles, respectively. The diffe-
rence is thus slightly greater than for the RMS recipe.
The R and F curves follow a similar pattern; after the
exposure at 1000 °C, it is possible to record almost the
same values of the residual compressive strength, i.e.,
around 30 % (9–10 N.mm–2). Regarding the compressive
strength, therefore, the resistance of the composite
matrix based on fly ash can be evaluated better compared
to the case of using slag.
The bending tensile strength of the RMS recipe
reached 6.9 N.mm–2 and 7.2 N.mm–2 after 70 d and 120
d, respectively (Figure 5). Due to the frost cycles, the
strength decreased by 20 % and 25.8 % after 50 cycles
and 100 cycles, respectively (without the thermal load).
Except for the 70-day exposure to frost with a sub-
sequent thermal load, the residual strengths (after 1000
°C) ranged around the value of 40 %.
The bending tensile strength of the RMA recipe was
around 6.4 N.mm–2 after 50 cycles and 6.7 N.mm–2 after
100 freezing and de-freezing cycles. The residual
strengths after the frost cycles with a subsequent high
temperature load were determined in a range of
33–36 %. The bodies loaded only thermally retained
42–46 % of the bending strength. The results show that
the residual bending tensile strengths in the RMS and
RMA recipes do not differ significantly. Only the
courses of the RF curves are distinctly different.
The CT analysis focused on the structure degra-
dation, both in the individual components and their
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Figure 11: Microstructure of RMS, exposure to 100 freezing cycles
and then the temperature of 1000 °C, mag. 2.000×; detail of a crack
Slika 11: Mikrostruktura RMS, izpostavitev 100 ciklom zamrzovanja
in nato na temperaturi 1000 °C, pov: 2,000×; detajl razpoke
contact zones. It was found that the bodies exposed to
frost and then to high temperatures show a slightly
increased incidence of cracks. In comparison with the
bodies exposed to a high temperature without the
cyclical freezing, however, the difference was not too
pronounced. Identified cracks were located primarily in
the matrix, at the interface of the dense aggregate and the
matrix, and – to a lesser extent – in the porous aggregate
(Figures 7 to 9). As for the incidence of cracks, the
differences between the RMA and RMS recipes were
almost negligible.
The microstructural method was mainly used to
identify the matrices gradually degrading with the in-
creasing temperature (Figures 10 and 11). No diffe-
rences between the bodies exposed and not exposed to
frost were observed. Likewise, there was no significant
difference in the microstructure of the samples after 70 d
and 120 d or after 50 and 100 frost cycles. It is therefore
evident that the frost is more likely to distort the struc-
ture on the "macroscopic" scale without microstructural
changes, while the thermal exposure also supports the
decomposition of hydration complexes and possibly the
emergence of new products. This could particularly
occur in the case of fly ash, which might act as a flux if
the contents of iron or alkalis are increased.
Hydration of fly ash or its involvement in the
hydration reactions during the silica-matrix ripening
requires longer times. According to normative docu-
ments, the influence of fly ash applied to the concrete is
tested after 28 d and 90 d. In the case of a shorter time
period, it is therefore possible that the greater portion of
fly ash could act as a flux without any significant con-
tribution to shaping the silicate-matrix structure. After a
longer period, conversely, the greater portion of fly ash
could hydrate, which would theoretically reduce its
ability as a flux. Alternatively, if the ability as a flux
remained while the participation in hydration reactions
was demonstrable, the positive effect of fly ash would be
clear. In this case, however, it would be necessary to
verify the specific amounts of fly ash depending on its
chemical composition in order to avoid the melting of
the composite at a certain temperature to an extent that
would cause the loss of its carrying capacity. For this
reason, it would be appropriate to supplement the per-
formed analyses with heat microscopy.
5 CONCLUSIONS
With regard to the achieved results, we can say that
both developed recipes are resistant to the action of
extreme temperature conditions, i.e., the combination of
frost and the subsequent high temperatures. However,
this only applies to 50 frost cycles. After an exposure to
100 cycles, the limit criterion of 25 % (the minimum
residual strength of 75 %) was slightly exceeded. Frost
resistance is partially limited by the use of lightweight
porous aggregates. Within the following research, it
would be useful to focus on optimizing the composition
of recipes in terms of a long-term resistance to frost.
Taking into account the conditions of the application of
the developed materials, however, it would also be
possible to consider secondary protection, i.e., surface
treatment by painting. This could increase the resistance
to frost. It is important to find that the temperature resis-
tance was not affected to a striking extent despite the
decline in the strengths in the order of about 15–27 %
due to frost – the trend of the residual strengths.
Higher strengths (without exposures to extreme con-
ditions) were reached in the recipe containing slag, i.e.,
the RMS. In the case of the RMA recipe, a pronounced
incidence of strength characteristics was more apparent
in the longer term. The RMA recipe showed improved
temperature resistance. This is demonstrated by the de-
termined residual strengths, especially the compressive
strengths at 1000 °C, where we observed residual
strengths of almost 30 %. This fact is not so explicit in
the case of bending strengths. The benefit of the pre-
sented research, among other things, is the composition
of the recipes. It was a combination of commercially
produced (i.e., available) primary as well as alternative
raw materials – in terms of both matrix and filler.
To clarify the behaviour of fly ash in the given matrix
under extreme conditions, it would be appropriate to
include other additional analyses. Studying properties of
the developed composites under simultaneous effects of
extreme temperatures and their mechanical stress (com-
pression or tensile bending) seems to be very interesting.
This could prove whether the an increasing temperature
and the related structural changes including degradation
of the matrix or other components lead to a total loss of
the carrying capacity of the respective material before it
becomes cold.
Acknowledgements
This article was made with the financial support of
The Czech Science Foundation (GA^R) project
14-25504S "Research of Behaviour of Inorganic Matrix
Composites Exposed to Extreme Conditions", as well as
under the project No. LO1408 "AdMaS UP – Advanced
Materials, Structures and Technologies", supported by
Ministry of Education, Youth and Sports under the
"National Sustainability Programme I".
6 REFERENCES
1 N. U. Kockal, T. Ozturan, Durability of lightweight concretes with
lightweight fly ash aggregates, Construction and Building Materials,
25 (2011) 3, 1430–1438, doi:10.1016/j.conbuildmat.2010.09.022
2 B. Kucharczyková, Z. Ker{ner, O. Pospíchal, P. Misák, P. Danìk, P.
Schmid, The porous aggregate pre-soaking in relation to the freeze-
thaw resistance of lightweight aggregate concrete, Construction and
Building Materials, 30 (2012) 761–766, doi:10.1016/j.conbuildmat.
2011.12.067
3 H. Garbaliñska, A. Wygocka, Microstructure modification of cement
mortars: Effect on capillarity and frost-resistance, Construction and
Building Materials, 51 (2014), 258–266, 10.1016/j.conbuildmat.
2013.10.091
T. MELICHAR et al.: CHANGES IN THE COMPOSITE STRUCTURE AND PARAMETERS AFTER AN EXPOSURE ...
248 Materiali in tehnologije / Materials and technology 51 (2017) 2, 243–249
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
4 S. Rahman, Z. Grasley, A poromechanical model of freezing con-
crete to elucidate damage mechanisms associated with substandard
aggregates, Cement and Concrete Research, 55 (2014), 88–101,
doi:10.1016/j.cemconres.2013.10.001
5 S. Chandra, L. Berntsson, 10 – Freeze-Thaw Resistance of Light-
weight Aggregate Concrete, in Lightweight Aggregate Concrete,
edited by Satish Chandra and Leif Berntsson, William Andrew
Publishing, Norwich, NY, 2002, 321–368, doi:10.1016/B978-
081551486-2.50013-4
6 M. B. Karakoç, R. Demirboða, Ý. Türkmen, Ý. Can, Modeling with
ANN and effect of pumice aggregate and air entrainment on the
freeze-thaw durabilities of HSC, Construction and Building
Materials, 25 (2011) 11, 4241–4249, doi:10.1016/j.conbuildmat.
2011.04.068
7 S. Chandra, J. Aavik, L. Berntsson, Influence of polymer micro-
particles on freeze-thaw resistance of structural lightweight
aggregate concrete, International Journal of Cement Composites and
Lightweight Concrete, 4 (1982) 2, 111–115, doi:10.1016/0262-
5075(82)90015-X
8 Y. Ke, S. Ortola, A. L. Beaucour, H. Dumontet, Identification of
microstructural characteristics in lightweight aggregate concretes by
micromechanical modelling including the interfacial transition zone
(ITZ), Cement and Concrete Research, 40 (2010) 11, 1590–1600,
doi:10.1016/j.cemconres.2010.07.001
9 J.-P. Won, H.-B. Kang, S.-J. Lee, S.-W. Lee, J.-W. Kang, Thermal
characteristics of high-strength polymer–cement composites with
lightweight aggregates and polypropylene fiber, Construction and
Building Materials, 25 (2011) 10, 3810–3819, doi:10.1016/
j.conbuildmat.2011.03.023
10 F. Koksal, O. Gencel, M. Kaya, Combined effect of silica fume and
expanded vermiculite on properties of lightweight mortars at ambient
and elevated temperatures, Construction and Building Materials, 88
(2015), 175–187, doi:10.1016/j.conbuildmat.2015.04.021
11 S. Aydýn, Development of a high-temperature-resistant mortar by
using slag and pumice, Fire Safety Journal, 43 (2008) 8, 610–617,
doi:10.1016/j.firesaf.2008.02.001
12 V. ^erný, [. Keprdová, Usability of fly ashes from Czech Republic
for sintered artificial aggregate, Advanced Materials Research,
(2014), 805–808, doi:10.4028/www.scientific.net/AMR.887-888.805
13 ^SN EN 12190. Products and systems for the protection and repair
of concrete structures - Test methods - Determination of compressive
strength of repair mortar. ^NI, 1999
14 ^SN EN 196-1. Methods of testing cement - Part 1: Determination of
strength. ^NI, 2005
15 ^SN EN 1504-3. Products and systems for the protection and repair
of concrete structures - Definitions, requirements, quality control and
evaluation of conformity - Part 3: Structural and non-structural
repair. ^NI, 2006
16 ^SN 73 1322, including Z1. Determination of frost resistance of
concrete. ^NI, 2003
T. MELICHAR et al.: CHANGES IN THE COMPOSITE STRUCTURE AND PARAMETERS AFTER AN EXPOSURE ...
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