THE DEVELOPMENT OF NEW TYPES OF SECONDARY PROTECTION FOR CONCRETE STRUCTURES ... - IMTmit.imt.si/izvodi/mit173/dufka.pdf · 2017. 6. 6. · 533–540 the development of new types

A. DUFKA et al.: THE DEVELOPMENT OF NEW TYPES OF SECONDARY PROTECTION ...533–540

THE DEVELOPMENT OF NEW TYPES OF SECONDARYPROTECTION FOR CONCRETE STRUCTURES EXPOSED TO

EXTREME CONDITIONS

RAZVOJ NOVIH VRST SEKUNDARNE ZA[^ITE BETONSKIHKONSTRUKCIJ IZPOSTAVLJENIH EKSTREMNIM POGOJEM

Amos Dufka, Tomá{ Melichar, Jiøí Byd`ovský, Jan VanìrekBrno University of Technology, Faculty of Civil Engineering, Institute of Building Materials and Components, Veveøí 95,

602 00 Brno, Czech [email protected]

Prejem rokopisa – received: 2015-08-07; sprejem za objavo – accepted for publication: 2016-06-09

doi:10.17222/mit.2015.249

During their use reinforced concrete structures are exposed to external influences. Nowadays, the reducing effect of theseinfluences is usually ensured by secondary (barrier) protection. At present, coatings based on organic substances are commonlyused. However, these types of secondary protection show substantial limits under extreme conditions. A method that has consi-derable potential to eliminate these disadvantages includes the application of secondary protection based on alkali-activatedmaterials or geopolymers. This paper is focused on the development and optimisation of secondary protection (coating, plaster)based on alkali-activated materials intended for reinforced concrete structures to be exposed to highly chemically aggressiveenvironments.

Keywords: coatings, alkali-activated substances, extreme conditions, agressive environment, durability of structures

Med uporabo so armirane betonske konstrukcije izpostavljene zunanjim vplivom. Danes se zmanj{anje vpliva teh u~inkovzagotovi z uporabo sekundarne za{~ite (prepreka). Obi~ajno se uporabljajo premazi na osnovi organskih snovi. Vendar pa so tevrste sekundarne za{~ite precej omejene pri ekstremnih pogojih. Metoda s potencialom da odpravi te pomanjkljivosti, vklju~ujeuporabo sekundarne za{~ite na osnovi alkalno-aktiviranih materialov ali geopolimerov. ^lanek obravnava razvoj in optimiranjesekundarne za{~ite (premaz, omet) na osnovi alkalno aktiviranega materiala, namenjenega za armirane betonske konstrukcije, kibodo izpostavljene kemijsko mo~no agresivnemu okolju.

Klju~ne besede: premazi, alkalno-aktivirane snovi, ekstremni pogoji, agresivno okolje, zdr`ljivost konstrukcij

1 INTRODUCTION

The conditions of exploitation are a key factor thatlimits the service life of building structures. Theseinclude both physico-mechanical influences (especiallythe synergistic effect of moisture and frost, increasedtemperature, etc.) and physico-chemical influences(aggressive substances, biotic agents, etc.). In principle,the resistance of building structures to negativeinfluences can be ensured by several approaches, i.e., bystructural design and the resistance of the materials used(i.e., by primary protection) and, especially, by havingthe negative influences of external environment onto thestructure eliminated by a barrier protection. In particular,this includes coatings, sheets, etc. (i.e., secondaryprotection). Presently, a wide range of coating materialsto protect reinforced concrete structures is available. Ingeneral terms, it comprises high-quality materials that,under standard conditions and withadequate mainten-ance, contribute considerably to the increased service lifeof the structure. This, however, only applies to buildingsexposed to normal conditions.

If, however, the building structures are exposed toextreme conditions, a different situation will occur. In

some types of chemically aggressive environments, forexample, the coating materials based on organic sub-stances feature distinct limits. The situation is even moredistinctive in the buildings exposed to increased tem-peratures. This primarily applies to cases when thetemperature changes are associated with a conspicuousgradient. Under such conditions, stresses may occur inthe coating-substrate interface due to the differentthermal coefficients of expansion as well as due tochanges in the microstructure of the polymer matrix, andresult in the separation of the coating from the substrate,cracking, etc.

The development of coating materials with a matrixbased on alkali-activated substances, or geopolymers,seems to be a very viable material basis making itpossible to solve the above problems. The coating basedon alkali-activated slag presented in this article shallhereinafter be referred to as AAM coating.

The unique properties of alkali-activated materialsprovide assumptions for the development of new secon-dary protections intended for reinforced concrete con-structions operated in extreme conditions (for instance,in environments of synergistic actuation of highertemperature and chemically aggressive substances, etc.).

Materiali in tehnologije / Materials and technology 51 (2017) 3, 533–540 533

MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS

UDK 624.012.44:620.1:621.7.016 ISSN 1580-2949Professional article/Strokovni ~lanek MTAEC9, 51(3)533(2017)

The alkali activated slag material being representedherein is intended as a secondary protection for rein-forced concrete constructions. On that basis the pro-perties of the developed AAM material are comparedwith an acrylate co-polymer-based coating intended justfor the constructions exploited in chemically aggressiveenvironments. In addition, the effect of the selectedaggressive environment type is monitored on cementconcrete without any secondary protection for compa-rison.

The developed material based on alkali-activated slagis not developed as repair mortar in this case but assecondary protection. Within this context the comparisonof the properties of the secondary protection based onalkali-activated slag with a polymeric coating cantherefore be considered as relevant.

2 SPECIFICATION OF THE COATINGS BEINGDEVELOPED

In general terms, we can say that the coatings basedon alkali-activated materials are made by the poly-condensation of aluminosilicates at temperatures up to100 °C. The polymerisation includes the chemical reac-tions of aluminosilicates (Al3+ in tetrahedral coordina-tion) and alkaline polysilicates forming polymericbindings Si–O–Al. As a result, a solid and compactstructure forming a dominant component of the matrix ofthe composite, or coating system, is created.1,2

This paper deals with the development of a coatingsystem based on alkali-activated substances to be usedfor the protection of reinforced concrete structuresexposed to extreme conditions. A typical examplerepresenting such extreme conditions includes the jointeffect of chemically aggressive environments and in-creased temperature. For example, the structures formingan integral part of process lines for the production ofchemicals and the like may be subject to such exposure.Due to the specifics of the above productions, thereinforced concrete structures are frequently loaded by acyclic effect of increased temperatures for long periodsand exposed, on practically a continuous basis, to theeffects of aggressive chemicals. The above-mentionedfacts have been taken into account during the develop-ment of the coating system.

3 EXPERIMENTAL PART

The previous researches made in this field have beenfollowed by the development of an alkali-activatedcoating. In terms of the service life and functionality ofthe coating system being developed, its adhesion to thesubstrate represents one of key parameters. With regardto this fact, the alkali-activated matrix was modified by apolymer dispersion. The coating composition obtainedby the optimisation process is shown in Table 1. Theoptimisation process for AAM-based coating develop-

ment follows the research presented in 1–4. For instance,the effect of the water glass silicate module is examinedin this case in relation to the slag chemical composition,further to the glass-phase content in it, etc. Optimizingthe granulometry and the amount of filler used, forexample, was based on data provided in 5,6.

Table 1: Composition of AAM coatingTabela 1: Sestava AAM premaza

Coating component Content of component (w/%)Water glass 16

Polymer dispersion 2Slag 31

Filler – silica sand, fractionof 0.45 mm 44

Water 7

For the water glass used, a silicate modulus of 1.7was applied. Primarily, the water glass silicate moduledrew from the findings presented in 1,4,5. The chemicalcomposition of the water glass is shown in Table 2.

Table 2: Chemical composition of water glassTabela 2: Kemijska sestava vodnega stekla

Component of water glass Content of component (w/%)SiO2 21.41 %Na2O 12.81 %K2O 0.62 %CaO 0.02 %

The polymer dispersion used was based on vinylacetate ethylene copolymer. For the chemical compo-sition of the slag, please refer to Table 3.

Table 3: Chemical composition of slagTabela 3: Kemijska sestava `lindre

Component of slag Content of component (w/%)CaO 35.9SiO2 40.1Fe2O3 6.9Al2O3 8.2Na2O 2.1K2O 0.9P2O5 1.4MgO 2.1MnO 0.3

The experiments were aimed at the development of acoating to be resistant as much as possible to extremeconditions, i.e., to the synergistic effect of highlychemically aggressive environments and increasedtemperature. In particular, the coating was exposed to thesaturated solution of ammonium sulphate with a part ofammonia sulphate not already dissolved in the suspen-sion. The solution temperature was 50 °C. The testsamples were prepared so that the developed coating wasapplied to the concrete substrate using a roller (concreteclass C30/37 was used). In order to assess the resistance

A. DUFKA et al.: THE DEVELOPMENT OF NEW TYPES OF SECONDARY PROTECTION ...

534 Materiali in tehnologije / Materials and technology 51 (2017) 3, 533–540


of the AAM coating in an impartial manner, a com-mercially available coating based on acrylate copolymerwas exposed to the same type of aggressive environment.We used a coating designed by its manufacturer toprotect the surface of the reinforced concrete structuresexploited in chemically aggressive environments. Hereagain, test samples were prepared so that the coating wasapplied on the substrate consisting of concrete, classC30/37. The coating was applied in accordance with theapplicable product’s technical data sheet (i.e., especiallyin regard to the coating consumption and the method ofapplication). Furthermore, the effect of the test environ-ment was tested directly on the uncoated concrete; again,concrete class C30/37 was used. For both coating types(i.e., the developed AAM coating and the commerciallyavailable coating based on acrylate copolymer) as well asfor the uncoated concrete, two sets of test specimenswere prepared. The samples of the first set were keptunder laboratory conditions for the entire period of theexperiment (i.e., t = 20±2 °C, % = 50±5 %). The valuesfound in these specimens were considered as a reference.The test samples of the second set were exposed to thesaturated solution of ammonium sulphate at increasedtemperature for periods of 3 months and 6 months. Thetest solution was prepared with an excessive amount ofammonium sulphate that remained unsolved. The solu-tion temperature was maintained at 50 °C. Test samplesaged for 28 d were placed in this aggressive environ-ment.

In order to assess the effect of the test environment,individual test samples were then subject to the follow-ing determinations after the 3-month and 6-monthexposures:

• Visual evaluation – the condition of coatings wasprimarily assessed in terms of the potential occur-rence of cracks (^SN EN ISO 4628-4) and blistering(^SN EN ISO 4628-2). For the uncoated concrete,the appearance of the concrete surface layers wasassessed;

• Determination of the coating thickness (^SN EN ISO2808);

• Determination of the coating adhesion to the sub-strate (^SN EN ISO 4624). For the uncoated con-crete, the tensile strength of the concrete surfacelayers was observed (^SN 73 1318). During this testa disk with a 50-mm diameter is glued on the surfaceof the concrete being evaluated and it is cut to clearlydefine the loaded area. During this test the definedarea is loaded by tensile force up to the breakagelimit of the tested material;

• Determination of the water-tightness of coatings(^SN 73 2578). This test proves the coating system’sability to hold water in the liquid state. The test resultis expressed as the amount of water that passedthrough the coating in the screeding materials(without any actuation of the hydrostatic pressure)within 30 min; the unit is therefore 1 litre of waterrelated to 1 m2 of the tested surface;

• Analyses of the microstructure using a scanningelectron microscope (methodological procedure No.30-33/1 by Brno University of Technology, Facultyof Civil Engineering).The mentioned complex of the experiments followed

de facto the stipulations of the standards involved inquestions of the rehabilitation of reinforced concreteconstructions ^SN EN 1504-1 and ^SN EN 1504-2.

4 RESULTS

4.1 Visual evaluation

Attention was primarily paid to the evaluation of thecondition of the surface layers of the tested samples. Inthe sample with the developed AAM coating, it wasfound that even the 6-month exposure to the test envi-ronment did not cause any changes to the coating thatwould prove its degradation due to aggressive sub-stances. Even after the completion of the experiment, thecoating structure remained practically identical. This




Figure 2: Macroscopic view of the structure of developed AMMcoating after a 6-month exposure to ammonium sulphateSlika 2: Makroskopski izgled konstrukcije z AMM premazom po{estih mesecih izpostavitve amonijevemu sulfatu

Figure 1: Macroscopic view of the structure of developed AMMcoating prior to its exposure to aggressive environmentsSlika 1: Makroskopski izgled konstrukcije z AMM-premazom predizpostavitvijo agresivnemu okolju

situation is documented in the following photographs(Figures 1 and 2):

It was concluded that even a 6-month exposure of theAAM coating would not cause any significant change inthe structure of the surface layers of the AAM coating. Inaddition, the visual evaluation did not reveal any evidentpresence of cracks or any other defects. Yet, a differentsituation was found in the coating based on acrylatecopolymer. In this case, a 6-month exposure to the solu-tion of ammonium sulphate and an increased tempera-ture resulted in the coating’s degradation. This fact isdocumented in the following photographs (Figures 3 and 4).The evident destruction of the surface layers of thecoating is shown in Figure 3. The destroyed surfacelayers of the coating film (i.e., flaking of the coating)and cracks are shown in Figure 4.

Furthermore, it was proven that the effect of the testenvironment on the concrete without secondary pro-tection caused a significant degradation of the cementmatrix. The visual evaluation revealed a change in thecolour of surface layers, and especially the occurrence ofcracks and local separations of surfaces layers (i.e., of

concrete up to a depth of approx. 5 mm) from thesubstrate (Figure 5).

4.2 Determination of coating thickness

Coating thickness is one of the key factors deter-mining the protective function of the coating. Besides, itis a parameter, the monitoring of which, or monitoring ofchanges in coating thickness, makes it possible tocarefully assess the development of the coating degra-dation due to the aggressive environment. The coatingthickness was measured prior to placing the individualsamples in the aggressive environment (the samples were28 d old) and then after 3-month and 6-month exposuresto aggressive environments. The coating thickness wasmeasured using a cutting method and procedureaccording to the ^SN EN ISO 2808 standard. For theresults of the coating thickness measurements, pleaserefer to Table 4. The shown values represent anarithmetic mean of ten measurements.

Table 4: Coating thicknessTabela 4: Debelina premaza

Type of coating PlacementExposure time

28 d 3 months 6 months

DevelopedAAM coating

Laboratoryenvironment 520 μm 510 μm 515 μm

Aggressiveenvironment — 500 μm 490 μm

Commerciallyavailable coat-ing based onacrylate copo-lymer

Laboratoryenvironment 410 μm 415 μm 410 μm

Aggressiveenvironment — 350 μm 290 μm

Evaluation

It was proven that even a 6-month exposure wouldnot cause any significant change of the thickness of theAMM coating. Yet, a different situation occurred in thecommercially available coating. In this coating, the




Figure 4: A 6-month exposure to the test environment caused thedegradation of the coating based on copolymer acrylateSlika 4: [estmese~na izpostavljenost preizkusnemu okolju je povzro-~ila degradacijo premaza na osnovi kopolimernega akrilata

Figure 5: A 6-month exposure to the test environment caused amassive degradation of surface layers of uncoated concreteSlika 5: [estmese~na izpostavljenost preizkusnemu okolju je povzro-~ila mo~no degradacijo povr{ine betona brez premaza

Figure 3: View of the macrostructure of coating based on acrylatecopolymer after a 6-month exposure to the test environmentSlika 3: Izgled makrostrukture premaza na osnovi akrilatnega poli-mera po {estih mesecih izpostavljenosti preizkusnemu okolju

effect of the aggressive environment resulted in athickness reduction by approximately 30 %. This findingis in full compliance with the visual evaluation thatrevealed a degradation of the coating based on acrylatecopolymer (i.e., especially fissures, separations ofsurface layers of the coating, etc.). This degradation ofthe surface layers of the coating film, in particular, hasthen become the dominant cause of thickness reductionfor the commercially available coasting.

4.3 Determination of coating adhesion to a substrate

Adhesion to a substrate is another parameter that isquite critical in terms of the protective function andservice life of the coating. Coating-substrate adhesionwas determined in accordance with the applicableprovisions of the ^SN EN ISO 4624 standard. Inaddition, the effect of concentrated ammonium sulphateand increased temperature was tested in the uncoatedconcrete. The concrete was subjected to pull-off testing,and the tensile strength of the surface layers was deter-mined using the procedure according to the ^SN 731318 standard.

For the results of the determination of coasting-substrate adhesion, or a determination of the tensilestrength of the concrete surface layers, please refer toTable 5. The values shown represent an arithmetic meanof five measurements.

Table 5: Determination of coating-substrate adhesionTabela 5: Dolo~anje adhezije premaz-podlaga

Type ofmaterial Placement

Exposure time28 d 3 months 6 months

DevelopedAAM coating

Laboratoryenvironment 2.1 MPa 2.4 MPa 2.6 MPa

Aggressiveenvironment — 2.2 MPa 2.0 MPa

Commerciallyavailablecoating basedon acrylatecopolymer



Uncoatedconcrete



Evaluation

It was concluded that the test environment caused adegradation of the uncoated concrete, which resulted, forexample, in a distinct decrease in the tensile strength ofthe surface layers. A significant decrease in the coating-substrate adhesion after the exposure to the test environ-ment was found for the coating based on acrylatecopolymer. The coating material itself, not the coating-substrate interface, was the area in which the defectswere mainly revealed after pull-off testing. The smallestdecrease in adhesion to the substrate was detected in theAMM coating. In this type of coating, a 6-month

exposure to the test environment caused only a decreaseof approximately 25 %. The AAM coating-substrateinterface was the area with the most frequent occurrenceof defects.

4.4 Determination of coating water-tightness

The water-tightness of the coatings was determinedusing the procedure according to the ^SN 73 2578standard. For the test results, please refer to Table 6; thevalues represent an arithmetic mean of five measure-ments.

Table 6: Coating water-tightnessTabela 6: Vodotesnost premaza

Type of coating PlacementExposure time

28 d 3 months 6 months

Developed AAMcoating

Laboratoryenvironment 0.9 l.m–2 0.9 l.m–2 0.8 l.m–2

Aggressiveenvironment — 1.0 l.m–2 1.1 l.m–2

Commerciallyavailable coatingbased on acrylate

copolymer

Laboratoryenvironment 0.2 l.m–2 0.2 l.m–2 0.2 l.m–2

Aggressiveenvironment — 0.6 l.m–2 0.9 l.m–2

Evaluation

The testing shows that the water-tightness of thedeveloped AAM coating is lower when compared to theacrylate coating. In terms of water-tightness, the AAMcoating satisfied the requirements for vapour-permeablecoatings, while the coating based on acrylate copolymerhas, in terms of this parameter, satisfied the requirementsfor vapour-tight coatings. However, it was proven thatthe water-tightness of the coating based on acrylatecopolymer rapidly decreased when exposed to the testenvironment. A 6-month exposure to the test environ-ment caused a more than four times lower water-tight-ness of the coating based on the acrylate copolymer. In




Figure 6: View of the microstructure of AAM-based coating. Thecoating structure is compact. 100× magnificationSlika 6: Izgled makrostrukture premaza na osnovi AAM. Strukturapremaza je kompaktna. Pove~ava 100×

this case, the decrease in water-tightness is associatedwith the impaired compactness of the coating due todefects (occurrence of microcracks, etc.). In the AAMcoating, the changes due to the test environment were notso distinct.

4.5 Analysis of microstructure with the electron micro-scope

Using the electron microscope, the microstructure ofindividual materials and, in particular, the changescaused by the effects of an aggressive environment wereanalysed. Hence, this method was primarily consideredas comparative; it means that the samples were primarilycompared prior to and after the exposure to laboratoryconditions.

Evaluation

The analysis of the microstructure with the electronmicroscope confirmed and further extended our knowl-edge obtained during the previous determinations. Theresistance of the AAM coating to the effects of the testenvironment was confirmed. The fact that the structureof AAM coating is relatively compact is shown inFigure 6. To increase the adhesion to the substrate,AAM coating was modified with a polymer dispersion.This fact resulted in a partial increase in the porosity ofthe coating structure (Figure 7). Pseudomorphs of cal-cium hydrosilicate gels represent a dominant componentof AAM-based coating (Figure 8). Calcium hydrosili-cate phases are still dominant components ofAAM-based coating also after a 6-month exposure to thetest environment (Figure 9). Special attention wasfocused on the analysis of the interface AAM paint/con-




Figure 10: View of the AAM coating/concrete substrate interfaceafter a 6-month exposure to the test environment. 600× magnificationSlika 10: Izgled stika AAM premaza/betonska podlaga po izpostavitvi{est mesecev preizkusnemu okolju. Pove~ava 600×

Figure 8: Pseudomorphs of calcium hydrosilicate gels in AAM-basedcoating – a sample placed at laboratory conditions. 5000× magni-ficationSlika 8: Psevdomorfija kalcijevega hidrosilikatnega gela v premazu naosnovi AAM – vzorec izpostavljen laboratorijskim pogojem. Pove~ava5000×

Figure 9: View of the microstructure of AAM-based coating after a6-month exposure to the test environment. 5000× magnificationSlika 9: Izgled mikrostrukture premaza na osnovi AAM, po {estmese~ni izpostavitvi preizkusnemu okolju. Pove~ava 5000×

Figure 7: To increase the adhesion to the substrate, AAM coating wasmodified with polymer dispersion. 100× magnificationSlika 7: Za pove~anje adhezije na podlago, je bil AAM premazmodificiran z disperzijo polimera. Pove~ava 100×

crete. It was found that the interface structure is compact.The absence of any corrosive new formations both in thecoating and in the substrate is evident (Figures 10 and11).

Conversely, the surface layers of the concrete pro-tected with the coating based on acrylate copolymer haveproven that the exposure to an aggressive environmentcause negative changes in the microstructure of thesurface layers of the concrete substrate. It was found thatthe microstructure of this concrete has been subject tonegative changes – new formations of ettringite andgypsum have been created (Figures 12 and 13).

The degradation due to the test environment hasshown itself to an extreme degree in the concrete thatwas not protected with any coating during the exposure.




Figure 14: View of the structure of uncoated concrete after a three-month exposure to the test environment. The creation of corrosiveproducts (gypsum pseudomorphs) in the microstructure is evident.4200× magnificationSlika 14: Izgled zgradbe iz neza{~itenega betona po treh mesecihizpostavitve preizkusnemu okolju. Viden je nastanek korozijskih pro-duktov (psevdomorfija mavca). Pove~ava 4200×

Figure 11: Detailed view of the AAM coating/concrete substrateinterface after a 6-month exposure to the test environment. 1000×magnificationSlika 11: Detajl izgleda stika AAM premaz/betonska podlaga, poizpostavitvi {est mesecev preizkusnemu okolju. Pove~ava 1000×

Figure 15: Detailed view of corrosive new formations (gypsum) in themicrostructure of cement matrix after a 6-month exposure to the testenvironment. 4500× magnificationSlika 15: Detajl korozijskih produktov (mavec) v betonski osnovi poizpostavitvi {est mesecev preizkusnemu okolju. Pove~ava 4500×

Figures 12 and 13: View of the structure of surface layers of theconcrete that was protected with acrylate copolymer-based coatingand exposed to an aggressive environment for a period of 6 months.4200× magnificationSliki 12 in 13: Izgled zgradbe povr{inske plasti betona, ki je bilza{~iten s prematom na osnovi akrilatnega polimera in izpostavljenegaagresivnemu okolju za dobo {est mesecev. Pove~ava 4200×

12)

13)

In that case, the development of corrosive new forma-tions (mainly of gypsum) was essential (Figures 14 and15).

5 CONCLUSIONS

The performed experiments have confirmed that thesynergistic effect of the concentrated solution ofammonium sulphate and the increased temperatureresults in a significant degradation of the coating basedon acrylate copolymer. In this type of coating, the utilityparameters have decreased despite the fact that thecoating is designed for chemically aggressive environ-ments. It is just the synergistic effect of chemicals and,in particular, of increased temperatures that can bedesignated as the primary cause of such a negative effectof the test environment.

In turn, positive results have been achieved with thecoating based on alkali-activated slag using appropriatetypes of modifying additives. It has been confirmed thatthis type of coating is able to effectively withstand thejoint effect of chemically aggressive substances andincreased temperature. For any of the parametersobserved, no decrease greater than 25 % has been found.The listed findings unambiguously confirm the potentialfor the use of material based on alkali-activated sub-stances for the secondary protection of reinforcedconcrete structures exposed to extreme conditions. Thedevelopment of this type of coating has not been com-pleted yet, but it is still ongoing. In the following stages,attention will be paid, for example, to the possibility ofhaving the autogenous shrinkage limited using nano-sized reinforcements, to the application of modifyingadditives; hence, the analysis of the AAM coating/con-crete substrate interface, etc. will become an importantresearch area.

Acknowledgements

This research was conducted with the financial helpof project GA^R 14-25504S Research of Behaviour ofInorganic Matrix Composites Exposed to Extreme Con-ditions and the project No. LO1408 AdMaS UP– Advanced Materials, Structures and Technologies,supported by Ministry of Education, Youth and Sportsunder the National Sustainability Programme I.

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