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122 Revista Romnde Materiale / Romanian Journal of Materials 2010, 40(2), 122 - 131

CERCETRI EXPERIMENTALE PENTRU EVALUAREA REZISTENEILA NGHE- DEZGHEA BETONULUI

EXPERIMENTAL RESEARCH FOR THE EVALUATION OF CONCRETE

FREEZE-THAW RESISTANCEDAN GEORGESCU1, ADELINA APOSTU1, GHIULGIAN MIRON2

1Universitatea Tehnicde Construcii Bucureti, B-dul Lacul Tei nr.124, Sector 2, Bucureti, Romnia

2Lafarge Ciment (Romania) S.A.

Articolul prezint rezultatele unor cercetriexperimentale desfurate n premier pe plan naional,n cadrul Laboratorului de Cercetare i ncercri alCatedrei de Construcii din Beton Armat din UniversitateaTehnic de Construcii Bucureti, n vederea studierii

posibilitii de aplicare n Romnia a unor noi criteriieuropene de evaluare a rezistenei la nghe-dezghe abetoanelor preparate cu diferite tipuri de cimenturi.

Rezistena la nghe-dezghea betonului s-a evaluat prinaplicarea unor metode standardizate la nivel european(CEN/TS 12390-9, CEN/TR 15177) care se bazeaz pecalcularea cantitii de material exfoliat i respectiv pedeterminarea valorilor modulului de elasticitate dinamical probelor de beton supuse unor cicluri de nghe-dezghe standardizate. Reducerile masei probelor debeton i respectiv ale modulului de elasticitate dinamicsunt comparate cu valori limit, propuse n funcie dencadrarea ntr-o anumitclasde expunere de tip XF.

The article presents the results of experimentalresearches conducted for the first time in Romania, inthe Research and Testing Laboratory of ReinforcedConcrete from Technical University of Civil EngineeringBucharest, Romania, in order to study the possibility toapply in Romania a new European evaluation criteria ofconcretes freeze-thaw resistance, concrete mixes withdifferent cement types. Concrete freeze-thaw resistance

was evaluated applying the standard methods onEuropean level (CEN/TS 12390-9, CEN/TR 15177)depending on the calculation of the scaled materialquantity and on determination of dynamic elasticmodulus values of concrete samples tested on repeatedstandard freeze-thaw cycles. The mass reducing of theconcrete samples and dynamic elastic modulus arecompared with proposed limit values, depending on thesituation in one of XF exposure class.

Keywords: durability, composite cement, concrete

1. Introducere

Articolul prezint rezuItatele obinute ncadrul unui program de cercetare experimentalelaborat pentru Lafarge Ciment (Romania) S.A. nvederea stabilirii performanelor betoanelorpreparate cu cimentul tip CEM IVB 42,5N [1].

Programul experimental a constat ndeterminarea rezistenei la compresiune a betonuluiavnd diferite compoziii, precum i a rezistenei langhe-dezghet, utiliznd diferite metodestandardizate la nivel naional i european.Rezistena la nghe-dezghe a fost evaluat prin:reducerea rezistenei la compresiune, determinareacantitii de material exfoliat i respectiv reducerea

modulului de elasticitate dinamic.Pe plan european s-au efectuat cercetri

experimentale n vederea stabilirii domeniilor deutilizare a unor diverse tipuri de cimenturi cuadaosuri. Cercetrile experimentale au avut caobiectiv i evaluarea rezistenei la nghe-dezgheabetonului prin aplicarea metodelor standardizate lanivel european. ri europene precum Suedia,Austria i, n special, Germania [2] aplic n modcurent aceste metode, propunnd, de asemenea,criterii de evaluare specifice. Pe plan naional seaplic numai metoda de determinare a reduceriirezistenei betonului dup aplicarea unor cicluri

1. Introduction

The article presents the results obtainedduring an experimental program elaborated forLafarge Cement (Romania) S.A. in order toestablish the performances of concretes mixes withcement type CEM IVB 42,5N [1].

The experimental program consisted indetermination of compressive strength and freeze-thaw resistance for different concrete mixes byusing distinct standard methods on national andEuropean level. The freeze-thaw resistance wasevaluated through: compressive strength reduction,determination of scaled material quantity and byreducing the dynamic elastic modulus.

In Europe were conducted a lot ofexperimental research in order to establish theapplications of different types of blended cements.An important objective was the evaluation of thefreeze-thaw resistance using different Europeanstandard methods. Sweden, Austria and especiallyGermany [2] use currently these methods and theyproposed some evaluation criteria for freeze-thawresistance. In Romania was used until now, onlycompressive strength reduction method and for theobtained values applying this method there are notproposed limits for a particular exposure ofconcrete in XF classes.

Autor corespondent/Corresponding author,Tel.: 0040 21 242 12 91, e-mail: [email protected]


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D. Georgescu, A. Apostu, G. Miron / Cercetri experimentale pentru evaluarea rezistenei la nghe-dezghea betonului 125

1- Temperatura din centrul probei / Temperature range at the centre of the test surface

Fig. 2 Ciclul timp (t) - temperatur(T) n centrul probei de ncercatTime (t) temperature (T) curve in the freezing medium at the centre of the samples

ts,o reprezint timpul de propagare a ultrasuneteloriniial prin fie, n ms;tsn reprezint timpul de propagare a ultrasunetelorprin fie dup aplicarea a n cicluri de nghe-dezghe, n ms.

2.3 Rezultate. Interpretri2.3.1. Caracteristici ale betonului proaspt

n tabelul 2 se prezint unele caracteristicicompoziionale i valorile tasrii i ale densitii

obinute pentru betoanele proaspete, preparate cucimentul de tip IV B 42,5N.

2.3 Presentation and completion of results2.3.1. Fresh concrete characteristics

Table 2 presents some fresh concretecharacteristics, slump and density values obtainedfor fresh concretes prepared with cement type IV B42,5N.2.3.2. Compressive strength

In Table 3 are presented the resultsobtained for concretes compressive strengthprepared with CEM IVB 42,5N with plasticizer and

super plasticizer admixture for 2 and 28 days,samples kept in water until testing date.Tabelul 2

Caracteristicile betoanelor proaspete, preparate cu CEM IVB 42,5N / Characteristics of fresh concretes prepared with CEM IVB 42,5N

Dozaj ciment / Cement dosage(kg/m3)

Aditiv /AdmixtureRaport A/CW/C ratio

Tasare / Slump(mm)

Densitate / Density(kg/m3)

290 plastifiant /plasticizer 0.67 100 2364

336 superplastifiant / superplasticizer 0.55 120 2370

420 superplastifiant / superplasticizer 0.45 105 2366

2.3.2. Rezistena la compresiune

n tabelul 3 se prezint rezultatele obinutepentru rezistena la compresiune a betoanelorpreparate cu CEM IVB 42,5N cu aditiv plastifiant irespectiv superplastifiant, dup 2 i 28 de zile depstrare n ap.

Rezistenele dezvoltate la 28 de zile, ncondiii de pstrare standardizate pentrudeterminarea clasei betonului, au fostcorespunztoare claselor de beton C16/20, pentrudozajul de ciment de 290 kg/m3, C20/25 pentrudozajul de ciment de 336 kg/m3i respectiv C30/37pentru un dozaj de ciment de 420 kg/m3.

Prin meninerea probelor de beton 2 zile n

ap i restul perioadei, pn la 28 de zile, n aers-au obinut rezistene ceva mai reduse (n general

The resistances obtained for 28 days, instandard curing conditions for determination of

concrete class, have been in conformity withconcrete class C16/20, for cement dosage of290 kg/m3, C20/25 for cement dosage of 336kg/m3 and C30/37 with cement dosage of420 kg/m3.

For concrete samples kept for 2 days inwater and between 2 and 28 days in air, theresistances obtained are reduced (generally with 2N/mm2) than the results obtained for concretesamples kept in specific conditions for concreteclass determination. For concrete samples kept for7 days in water and between 7 and testing date inair, the resistances obtained are higher

(approximately 1 N/mm

2

) than the results obtainedfor concrete samples kept in specific conditions forconcrete class determination (figure 3).


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126 D. Georgescu, A. Apostu, G. Miron / Experimental research for the evaluation of concrete freeze thaw resistance

Tabelul 3

Caracteristicile de rezistenale betoanelor preparate cu CEM IVB 42,5N/Resistance characteristics for fresh concretes prepared with CEM IVB 42,5N

AditivAdmixture

Raport A/CW/C ratio

Dozaj cimentCement dosage

(kg/m3)

Rezistena la compresiuneCompressive strength

(N/mm2)

Clasa debeton obinut

Obtainedconcrete

class2 zile

2 days28 zile

28 days

plastifiantplasticizer

0.67 290

12.18

12.13

26.75

26.02 C16/2011.91 25.88

12.31 25.42

superplastifiantsuperplasticizer

0.55 336

15.19

15.82

33.73

33.21 C20/2515.80 33.09

16.46 32.80

superplastifiantsuperplasticizer

0.45 420

24.62

24.11

45.76

45.06 C30/3724.11 44.96

23.60 44.45

0,00

10,00

20,00

30,00

40,00

50,00

60,00

290 336 420

Cement dosage (kg/m3)

Compressivestrength(N/mm

2)

2 days water 28 days water 28 days/ 2 days water 28 days/ 7 days water60 days/ 2 days water 60 days/ 7 days water

Fig.3 Rezistenele la compresiune ale betoanelor preparate cu diferite dozaje de ciment tip IVB, pstrate n condiii diferiteCompressive strength resistances for concretes prepared with different dosages of cement type CEM IVB,

kept in different conditions.

cu 2 N/mm ) dect cele obinute pentru betoanelemeninute n condiiile specifice pentrudeterminarea clasei betonului. Meninerea probelor7 zile n api restul perioadei, pn la vrsta dencercare, n aer, a condus la valori puin crescuteale rezistenelor (cu aproximativ 1 N/mm2) fa devalorile obinute pentru rezistenele betoanelormeninute n condiii specifice pentru determinareaclasei betonului (fig. 3).

Se poate afirma c pstrarea n condiiidiferite nu a influenat mult rezistena lacompresiune a betonului, dup28-60 zile.

Desigur, tratarea betonului (meninerea nstare umed

a betonului dup

turnare) are ns

un

rol decisiv n comportarea n timp a betonului i seefectueazo perioadcare se determinn funcie

It can be declared that the differencesbetween the curing conditions did not have a majorinfluence on the concrete compressive strength,after 28-60 days.

Of course, the cure of concrete (keptconcrete in wet conditions after pouring) has adecisive role in time behavior of concrete and iscompleting for a time period that is determineddepending on the values of the compressivestrength resistance reports for 2 and 28 days andthe exterior temperature.

2.3.3. Freeze-thaw resistanceMethod according to SR 3518. In Table 4

are shown the values obtained for strengthreduction after 50 freeze-thaw cycles.


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de valorile rapoartelor rezistenelor la compresiunela 2 i 28 de zile i de temperatura mediuluiexterior.

2.3.3. Rezistena la nghe-dezghe

Metoda conform SR 3518.n tabelul 4 se

prezint valorile obinute pentru reducerile derezistenla nghe-dezghe, dup50 de cicluri.

The strength reduction obtained after 50freeze-thaw cycles for concrete class C16/20 isrelatively high ( it is situated in 25% maximum limitshown in Romanian standard).

Method according to CEN/TS 12390-9 -cube test. In conformity with this method it wasdetermined the quantity of scaled material for 100

mm cubes edge, for three concrete mixes(Table 5).

Tabelul 4

Reducerea rezistenei la compresiune a betonului dup50 de cicluri de nghe-dezgheCompressive strength reduction after 50 freeze-thaw cycles

Clasa betonConcrete class

Dozaj cimentCement dosage

(kg/m3)

RaportA/C

W/C ratio

Rc martorReference Rc

(N/mm2)

Rc dup50 de cicluri denghe-dezghe

Rc after 50 freeze-thawcycles (N/mm2)

Reducerearezistenei lacompresiune

Strength reduction(%)

C16/20 290 0.67 30.34 25.36 16.43

C20/25 336 0.55 38.48 33.91 11.87C30/37 420 0.45 49.02 45.09 8.02

Tabelul 5

Cantitatea de beton exfoliat dupn cicluri de nghe-dezghe/ Quantity of scaled concrete after n freeze-thaw cycles

Clasa debeton

Concreteclass

MasainiialInitialmass

(g)

Cantitatea de beton exfoliat dupQuantity of scaled concrete after

(g):

Cantitatea totalde beton exfoliatdup56 cicluri

Total quantity ofscaled concrete,

for 56 cycles(g)

Reducereamasei probei

de betonReduction of

concretesample mass

P (%)

P, medieP, medium,

(%)

7 cycles 14 cycles 28 cycles 56 cycles

C16/202342 1.28 2.34 127.30 197.18 328.10 14.01

11.85

2372 3.64 2.00 81.18 202.23 289.05 12.19

2365 1.46 2.76 102.18 193.18 299.58 12.67Masa exfoliatnainte deperiere/ Mass of dried

material before brushing14.42 12.96 147.94 430.10 605.42 8.55

Total 20.80 20.06 458.60 1022.69 1522.15 47.41

C20/252357 0.50 0.68 1.12 12.10 14.40 0.61

1.87

2362 0.78 1.34 4.00 32.48 38.60 1.632365 0.62 0.30 11.86 82.66 95.44 4.04

Masa exfoliatnainte deperiere/ Mass of dried

material before brushing6.00 5.40 8.36 66.08 85.84 1.21

Total 7.90 7.72 25.34 193.32 234.28 7.49

C30/372369 0.44 0.46 0.52 0.34 1.76 0.07

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2360 0.58 0.34 0.54 0.22 1.68 0.072354 0.24 0.04 0.52 0.44 1.24 0.05

Masa exfoliatnainte deperiere/ Mass of driedmaterial before brushing

5.10 2.30 3.36 4.20 14.96 0.21

Total 6.36 3.14 4.4 5.20 19.64 0.41

Reducerea de rezisten dup 50 cicluri denghe-dezghe pentru betonul de clas C16/20este relativ mare (chiar dac se ncadreaz nlimita de maximum 25% indicat n standardulromnesc).

Metoda conform CEN/TS 12390-9 - cubetest. n conformitate cu aceast metod, s-adeterminat cantitatea de material exfoliat, pe cuburicu latura de 100 mm, pentru cele trei compoziii de

beton, datele fiind prezentate n tabelul 5.Pentru aprecierea comportrii betonului langhe-dezghe s-au utilizat criterii de evaluare

For the estimation of concrete behavior forfreeze-thaw were used existing evaluation criteriain some international regulations or technicalspecial literature [9].

The proposed criteria for using this methodare:

- Exposure class XF1: The quantity ofscaled material does not have to producea reduction more than 5% of concrete

sample mass for 56 cycles and respectivemore than 10% for 100 cycles (cementdosage 300 kg/m3and W/C=0.6).


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existente n literatura tehnicde specialitate [9].Criteriile propuse n cazul utilizrii acestei

metode sunt: Clasa de expunere XF1: Cantitatea de

material exfoliat nu trebuie s produc oreducere mai mare de 5% a masei probeide beton dupexpunerea la 56 de cicluri

de nghe-dezghe i respectiv mai marede 10% dup 100 de cicluri de nghe-dezghe (beton cu dozaj de ciment 300kg/m3 i raport A/C=0,6)

Clasa de expunere XF3: Cantitatea dematerial exfoliat nu trebuie s produc oreducere mai mare de 3% a masei probeide beton dupexpunerea la 56 de cicluride nghe-dezghe i respectiv mai marede 5% dup 100 de cicluri de nghe-dezghe (beton cu dozaj de ciment 300kg/m3 i raport A/C=0,6).

Din datele prezentate n tabelul 5 se poateobserva c betonul de clas C16/20, avnd undozaj de ciment de 290 kg/m3 nu ndeplinetecriteriul pentru ncadrarea n clasa XF1, chiar dacdozajul de ciment este relativ apropiat decompoziia standard care se utilizeaz n cazulaplicrii acestui criteriu. Raportul A/C de 0,67 estemai mare dect cel standard de 0,6.

Compoziia de beton corespunztoare claseide beton C20/25 a fost preparatcu un raport A/C= 0,55, deci mai sczut dect al compoziieistandard i un dozaj mai mare de ciment cu 36kg/m3. n acest caz a fost obinut o cantitate dematerial exfoliat, dup

56 de cicluri, sub 2%.

n conformitate cu CP 012/1-2007, pentruclasa de expunere XF1, betonul trebuie s fiepreparat cu un raport A/C de maximum 0,5 i sfiede clasminimde rezistenC25/30.

Metoda conform CEN/TR 15177 - slabtest. Aceast metod presupune determinareamodulului de elasticitate dinamic relativ. Valorileobinute pentru viteza de propagare aultrasunetelor, respectiv pentru modulul deelasticitate dinamic relativ sunt prezentate ntabelele 6 i 7.

Pentru ca betonul s se poat utiliza ncondiii de expunere conform clasei XF3 (dozajciment 320 kg/m3, raport A/C=0,50) trebuiendeplinite urmtoarele criterii:

1. Dupexpunerea la 28 de cicluri de nghe-dezghe, proba de beton nu trebuie s prezinte oreducere a modulului de elasticitate dinamic maimare de 25% (criteriu absolut) [9].

2. Dup expunerea la 56 de cicluri de nghe-dezghe, probele de beton preparate cu cimentulexperimental (care se studiaz n vederea utilizriin betoane rezistente la nghe-dezghe) nu trebuie snregistreze o reducere a modulului de elasticitate

dinamic mai mare de 5% fa de cea nregistratpentru probele preparate cu cimentul etalon, a cruicomportare n timp n condiii reale este cunoscutca

- Exposure class XF3: The quantity ofscaled material does not have to producea reduction more than 3% of concretesample mass for 56 cycles and respectivemore than 5% for 100 cycles (cementdosage 300 kg/m3and W/C=0,6).

From data shown in Table 5 it can be

remarked that the concrete class C16/20, with 290kg/m3dosage cement, is not caring out this criteriafor XF1 class, even if the cement dosage isrelatively closed to standard composition which isused in application of this criteria. The W/C ratio0.67 is higher than the standard 0.6.

The adequate concrete composition forclass C20/25 has a W/C ratio of 0.55, so it is lowerthan the standard composition and has a highercement dosage with 36 Kg/m3. In this case it wasobtained a quantity of scaled material below 2%after 56 cycles.

In conformity with CP 012/1-2007, forexposure class XF1 concrete must have a W/Cratio of maximum 0.5 and a minimum strengthclass C25/30.

Method according to CEN/TR 15177 - slabtest. This method assumes determination ofdynamic elastic modulus. The obtained values forultrasonic pulse speed, respective for dynamicelastic modulus are shown in Tables 6 and 7.

In order to use the concrete in exposureclass XF3 (cement dosage 320 kg/m3, W/C ratio=0.50) have to carry out the next criteria:

1. After 28 freeze-thaw cycles, the concretesample does not have to show a reduction ofdynamic elastic modulus more than 25% (absolutecriteria) [9].

2. After 56 freeze-thaw cycles, the concretesamples prepared with experimental cement type(studied for evaluation of the freeze-thawresistance of concrete) does not have to show areduction of dynamic elastic modulus more than5% beside the value obtained for samplesprepared with standard cement which behavior inspecific circumstance is known as beingappreciative (relative criteria) [10].

From data shown in Table 7 can beremarked that the concrete class C20/25, with W/Cratio higher than 0.5, is not caring out absolutecriteria.

The concrete class C30/37 with a W/C ratioof 0.45 and cement dosage 420 Kg/m3 has adynamic elastic modulus reduction of 21%, closedto limit value, but having improved compositioncharacteristics beside standard concrete samples,and for 56 cycles the reduction of the dynamicelastic modulusis over 45%.

2.3.4 Consideration regarding the applying of the

methods for evaluation of freeze-thawresistance of concrete

The application of the methods involves


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fiind favorabil(criteriu relativ) [10].Din tabelul 7 se observcbetonul de clas

C20/25, avnd dozaj de ciment i raport A/C maimari dect valorile impuse, nu ndeplinete criteriulabsolut.

different number of cycles and time-temperaturecharacteristics. The evaluation of freeze-thawresistance is done by measuring values ofphysical characteristics which vary from onemethod to another.

Tabelul 6

Valorile vitezei ultrasunetelor la n cicluri de nghe-dezghe/ Ultrasonic pulse speed values after n freeze-thaw cyclesClasabetonuluiConcrete

class

Vitezultrasunete / Ultrasonic pulse speed(m/s) Observaii

ObservationsIniialinitial

7 cicluri7 cycles

14 cicluri14 cycles

28 cicluri28 cycles

56 cicluri56 cycles

C16/203971 2920 2375 - -

probe distruse dup28de cicluri

destroyed samples after28 cycles

4182 3557 3459 - -4162 3115 3057 - -

Mediemedium

4105,00 3197,33 2963,67

C20/254289 4170 4047 3524 -

probe distruse dup56cicluri

destroyed samplesafter 56 cycles

4217 4091 3971 3314 -4205 3591 3899 3600 -

Mediemedium

4237,00 3950,67 3972,33 3479,33

C30/37 4389 4205 4089 3839 3214-

4339 4265 4139 4004 31344326 4253 4151 3734 3256

Mediemedium

4351.33 4241.00 4126.33 3859.00 3201.33

Tabelul 7Valorile modulului de elasticitate dinamic relativ al betonelor expuse la n cicluri de nghe-dezghe

The values obtained for dynamic elastic modulus of concrete for n freeze-thaw cycles

ClasabetonuluiConcrete

class

Modulul de elasticitate dynamic relativ RDMUPTT,n ( %), dup:Relative dynamic elastic modulus RDMUPTT,n ( %), after:

7 cicluri7 cycles

14 cicluri14 cycles

Reducere dup14cicluri

Reduction for 14cycles

28 cicluri28 cycles

Reducere dup28cicluri / Reduction

for 28 cycles

56 cicluri56 cycles

Reducere dup56 cicluri

Reduction for56 cycles

C16/20

54.07 35.77 64.23 Probe

distrusedestroyedsamples

-

destroyedsamples

-

72.34 68.41 31.59 - -

56.02 53.95 46.05 - -

Mediemedium

60.81 52.71 47.29

C20/25

94.53 89.03 10.97 67.51 32.49destroyedsamples

-

94.11 88.67 11.33 61.76 38.24 -

72.93 85.98 14.02 73.29 26.71 -

Mediemedium

87.19 87.89 12.11 67.52 32.48

C30/37

91.79 86.80 13.20 76.51 23.49 53.62 46.38

96.62 90.99 9.01 85.15 14.85 52.17 47.83

96.65 92.07 7.93 74.50 25.50 56.65 43.35

Mediemedium

95.02 89.95 10.05 78.72 21.28 54.15 45.85

Betonul de clas C30/37, avnd un raportA/C de 0,45 i un dozaj mare de ciment (420kg/m3), prezint o reducere a modulului deelasticitate de 21%, valoare apropiatde cea limit,caracteristicile compoziionale ale betonului fiindmbuntite fa de cele ale betonului consideratetalon, prin metoda respectiv. Dup56 de cicluride nghe-dezghe, reducerea modulului deelasticitate este de peste 45%.

2.3.4 Consideraii privind aplicarea metodelor deevaluare a rezistenei la nghe-dezghe abetonului

Because is difficult to correlate the results,at the European level are used many methods totest freeze thaw resistance of concrete, taking intoaccount the most unfavorable results.

Applying these methods must take intoaccount the duration of curing, the concrete ageand carbonation [11] which influences in differentways the freeze-thaw resistance of concretesprepared with cement type I, respective blendedcements [12].

The Romanian standard for evaluation offreeze-thaw resistance of concrete does not takeaccount a certain "standard composition of concrete


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Aplicarea metodelor implic efectuareaunor cicluri care difer ca numr i caracteristicitimp - temperatur, iar evaluarea rezistenei langhe-dezghe se face prin msurarea valorilorunor mrimi fizice care difer de la o metod laalta.

Avnd n vedere dificultatea de corelare

ntre metode, pe plan internaional se aplic, ngeneral, mai multe metode/ criterii lundu-se nconsiderare rezultatele cele mai defavorabile.Aceste metode se aplic pentru evaluareaperformanelor la nghe-dezghe a betoanelorpreparate cu anumite tipuri de cimenturi.

Aplicarea acestor metode trebuie s aibn vedere durata pstrrii n ap, vrsta la care seefectueaz ncercarea i carbonatarea [11] careinflueneaz n mod diferit rezistena la nghe-dezghe a betoanelor preparate cu cimenturile detip I, respectiv cu adaosuri [12].

Evaluarea rezistenei la nghe-dezghe abetonului, n conformitate cu actualul standardromnesc, nu ine seama de o anumitcompoziiestandard a betonului, putnd fi aplicatoricare arfi compoziia. Acestcondiie o face greu aplicabilpentru evaluarea performanelor unor anumite tipuride cimenturi n betoane supuse la nghe-dezghe.De altfel, la nivelul reglementrilor naionale nuexist o coresponden ntre un anumit nivel dereducere a rezistenei la compresiune a betonului,dup aplicarea unui anumit numr de cicluri incadrarea ntr-o anumitclasde expunere XF.

4. Concluzii

Rezultatele obinute pentru rezistena lacompresiune i pentru evaluarea rezistenei langhe-dezghe prin aplicarea diferitelor metode dencercare i a unor criterii de evaluare specifice,pentru betoanele preparate cu cimentul tip CEM IVB42,5N conduc la urmtoarele concluzii:

betoanele preparate cu cimentul tipIVB 42,5N pot atinge nivele corespunztoare alerezistenelor la compresiune n cazul respectriicerinelor privind compoziia betonului nconformitate cu CP 012-1/2007;

sensibilitatea la solicitri de nghe-dezghe,

respectiv oportunitatea utilizrii betoanelor nanumite medii, corespunztoare claselor deexpunere XF, sunt dificil de evaluat prin aplicareacriteriilor indicate n actualele standarde romneti;

aplicarea metodelor europene iinterpretarea rezultatelor n spiritul criteriilor indicaten anumite norme europene i din literatura despecialitate, reprezint soluii de viitor n ceea ceprivete stabilirea unor niveluri de performan langhe-dezghei definirea unor domenii de utilizarea betoanelor preparate cu diferite tipuri de cimenturi;

avnd n vedere rezultatele obinute ncadrul cercetrilor experimentale se recomand

corelarea metodelor pentru a se putea evaluarezistena la nghe-dezghea betonului.

and it can be applied whatever the composition is.This condition creates a major difficulty in applyingthis standard for the performance evaluation ofcertain types of cements in concrete subjected tofreeze-thaw cycles. Anyway the method doesntpropose any limits for a particular exposure in aconcrete in XF class.

4. Conclusion

The results obtained for the compressivestrength and evaluation of freeze-thaw resistanceby applying different testing methods and specificevaluation criteria, for concretes prepared withcement type CEM IVB 42,5N are conducting thenext conclusions:

concretes prepared with cement type IVB42,5N can reach adequate compressive strengthin case of requirement of concrete compositionaccording to CP 012-1/2007;

the sensibility for freeze-thaw action,respective the use of concretes in some adequatecircumstances of exposure class XF, is difficult toevaluate applying the shown criteria in actualRomanian standards ;

applying the European methods andinterpretation of results according shown criteria insome European norms and special literaturerepresents a future solution in establishing theperformances levels for freeze-thaw action and todefine some usage domains of concretesprepared with different cement types;

considering the results obtained insideexperimental researches it is recommended tocorrelate the methods in order to evaluate thefreeze-thaw concrete resistance.

REFERENCES

1. xxx, Romanian Standards Association, SR EN 197-1-

Cement composition, specifications and conformity criteria

for common cements.

2. E. Siebel, Frost- und Frost-Tausalz-Widerstand von Beton.

Beton 42 (1992) H. 9, S. 496-501, ebenso Betontechnische

Berichte 1992-94.

3. xxx, Romanian Standards Association, CP 012/1-2007 -

Code of practice for the manufacturing of concrete.

4. xxx, Romanian Standards Association, SR EN 12350-2 -

Testing fresh concrete. Part 2.Slump test.

5. xxx, Romanian Standards Association, SR EN 12390-3 -

Testing hardened concrete. Part 3. Compressive strength of

test specimens.

6. xxx, Romanian Standards Association, SR 3518 -Tests on

concrete for determination of freeze thaw resistance.

7. xxx, European Committee for Standardization, CEN / TS

12390-9 - Testing hardened concrete - Part 9: Freeze-thaw

resistance. Scaling, 2006.

8. xxx, European Committee for Standardization, CEN/TR

15177 - Testing the freeze-thaw resistance of concrete -Internal structural damage, 2006.


10/10


9. C. Muller Durability of concrete with CEM X cements, VDZ

Germany, Dusseldolf, 2008

10. x x x - ONORM- B3303 Betonprfung, 2002

11. M. Gheorghe, A. Andreescu, and D. Voinichi, Aspects

regarding the durability of the concretes based on high blast

furnace slag content cement, Romanian Journal of Materials

2006, 36(1), 29.

12. M. Muntean, N. Noica, L. Radu, I. Ropot, A. Ionescu, and

O. Muntean, Concrete carbonation and its durability,

Romanian Journal of Materials 2008, 38(4) 284.

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MANIFESTRI TIINIFICE / SCIENTIFIC EVENTS

The aim of the conference is to provide an international forum for all concerned with the application of FRPcomposites in civil engineering to exchange and share recent advances in both research and practice. CICE 2010is an official conference of the International Institute for FRP in Construction (IIFC) and is being organized byCentral Research Institute of Building and Construction, MCC Group and Tsinghua University.

Topics FRP Sustainability FRP for Structures in Earthquacke Resistance

Materials and Products

Bond and Interfacial Stresses

Confinement of Concrete in Compression

Hybrid FRP Structures and Concrete Filled FRP Tubes

All FRP Structures

Smart FRP Structures

Strengthening of Concrete Structures, Historic Structures,Masonry Structures, Timber Structures and Metallic Structures

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Fire, Impact and Blast Loading

Durability and Long Term Performance

Inspection and Quality Assurance

Field Applications and Case Studies

Codes, Standards, and Design Guideline

Contact: www.cice2010.net

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CICE 2010

5thInternational Conference on Fibre Reinforced Polymer (FRP)Composites in Civil Engineering

Beijing, China

27 29 September 2010

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