matricea cimentului cu fibra de sticla

8/12/2019 Matricea Cimentului Cu Fibra de Sticla

1/11

Revista Romnde Materiale / Romanian Journal of Materials 2013, 43(2), 139 149 139

CARACTERISTICILE MECANICE ALE UNOR MATRICE MINERALEDIN CIMENT I SULFAT DE CALCIU ANHIDRU RECICLAT

ARMATE CU FIBRE DE STICLMECHANICAL CHARACTERISTICS OF GLASS FIBRE REINFORCED

COMPOSITES WITH CEMENT AND RECYCLED ANHYDRITE MATRIX

GEORGE RANU, IRINA LUNGU, NICOLAE RANU, MIHAI BUDESCUUniversitatea TehnicGheorghe Asachi din Iai, B-dul. Mangeron nr. 43, Iai 700050, Romnia

Materialele compozite cu matrice mineralarmatecu fibre din sticlsunt utilizate n prezent att la elementede construcii noi ct i la consolidarea structurilordeteriorate. Utilizarea acestor compozite este condiionat

de cunoaterea caracteristicilor de rezisteni de rigiditatenecesare proiectrii.n cadrul unui program experimental complex

desfurat la Facultatea de Construcii i Instalaii aUniversitii Tehnice Gheorghe Asachi din Iai au fostanalizate posibilitile de utilizare ale compozitelor cumatrice mineral la elemente de construcii uzuale, pentrumodule tip necesare n situaii de urgen. Programul acuprins studii i cercetri privind utilizarea unei matriceecologice armate, obinute prin nlocuirea parial acimentului cu un liant obinut din deeuri industriale.

Din determinrile experimentale efectuate pe diversereete i fraciuni volumetrice de fibr s-au stabilitrezistenele mecanice i modulii de elasticitatecorespunztori la solicitri axiale curente. Rezultateleobinute confirm eficiena utilizrii acestor tipuri de

compozite la elemente structurale pentru construcii.

Composite materials made of glass fibrereinforced mineral matrices are nowadays utilized in both

new construction elements and in strengthening solutionsof deteriorated civil engineering structures. The use of such

materials requires a good knowledge of their strength andstiffness properties for the corresponding design works.An extensive experimental program has been

carried out at the Faculty of Civil Engineering and BuildingServices of the Gheorghe Asachi Technical University ofIasi to reveal the usage possibilities of mineral matrixcomposites, relating to regular construction elements andto specialized modules in emergency conditions. Theresearch program has included theoretical andexperimental studies regarding the utilization of ecologicalreinforced matrix, obtained by partial substitution of theordinary Portland cement by a hydraulic bindermanufactured from industrial wastes. The mechanicalstrengths and the elastic moduli from composites withvarious mixes and fibre volume fractions experimentallyestablished confirm the suitability of these materials to

structural members subjected mainly to axial loading.

Keywords:mineralmatrix composites, glass fibre mesh, mechanical strength, elastic modulus, structural response

1. Introducere

Programele de cercetare-dezvoltarereferitoare la materialele compozite, desfurate nultimele decade, au condus la rezultate importanteprivind utilizarea acestora la construcii noi i lareabilitarea sistemelor structurale deteriorate [1].

Lucrrile de cercetare iniiale referitoare la matriceleminerale adecvate formrii compozitelor armate cufibre din sticl au demarat n anii 1960 prinutilizarea gipsului [2]. Mai trziu, cimentul Portlandobinuit (OPC) a fost de asemenea introdus ca osoluie alternativ pentru matricele minerale pebaz de ciment, armate cu fibre din sticl [3-6].Soluiile compozite bazate pe matrice mineralearmate cu fibre de sticl au fost concepute astfelnct s devin alternative viabile la materialele deconstrucii tradiionale precum lemnul, zidria saubetonul [7, 8]. Aceste soluii alternative noi aucondus la elemente de construcii mai eficiente

1. Introduction

Research and development programscarried out in the recent decades relating tocomposite materials have led to important resultsconcerning their use in new construction andstrengthening of the deteriorated framing

systems.[1]. The initial research works on a mineralmatrix capable of forming a composite materialreinforced with glass fibres begun in the 1960s withthe utilization of gypsum [2]; later on, the OrdinaryPortland Cement (OPC) has also been introducedto another solution for cementitious mineralmatrices reinforced with glass fibres. [3-6].Composite solutions based on glass fibrereinforced mineral matrices have been conceivedso that they become viable alternatives totraditional building materials such as wood,masonry or concrete [7, 8]. These new alternativesolutions have led to more cost-effective construc-

Autor corespondent/Corresponding author,

Tel.:+40 0232 232 219;e-mail: [email protected]


2/11

140 G. ranu, I.Lungu, N. ranu, M. Budescu / Mechanical characteristics of glass fibre reinforced compositeswith cement and recycled anhidrite matrix

economic i cu rapoarte mbuntiterigiditate/greutate, respectiv rezisten/greutate icu caracteristici termicesuperioare. Cteva analizenumerice cu MEF au fost realizate pe panouri deperete i pe o structur complet a unei caseprototip. Un model prototip a fost de asemeneatestat pe platforma seismic la o accelera ie

maxim de 0,4g (mai mare dect valoarea maxim posibil pe teritoriul rii noastre) ceea ce a condusla o valoare maxim a tensiunilor din compresiunede 3 [N/mm2] i din ntindere de 5 [N/mm2]. Acestevalori pot fi considerate ca valori minime necesareprivind caracteristicile de rezisten. Productorulmaterialului care este de asemenea i deintorulpatentului [9], garanteaz caracteristicile privinddurabilitatea acestui material, similare cu cele aleOPC.

n cadrul lucrrii se prezint rezultateleexperimentale ale unui program de cercetarecomplex desfurat la Facultatea de Construcii iInstalaii a Universitii Tehnice Gheorghe Asachidin Iai. Programul a fost iniiat pentru atragerea npiaa materialelor de construcii a unor produsereciclabile din reziduuri industriale [10] i pentru aevidenia calitile unei matrice ecologice cucaracteristici favorabile utilizrii n construcii.Aceast matrice este ob inut combinnd OPC cusulfat de calciu n forma anihindrid III.Conform patentului produsului [9], gipsul camaterial de baz este disponibil n stare natural sau artificial. n starea artificial se g sete nspecial sub form de fosfogips i gips desulfurat.Fosofgipsul este un reziduu al fosfatului dinindustria fertilizatorilor. Gipsul desulfurat este unprodus similar, folosit la desulfurarea gazelor, nparticular a gazelor de ardere din centraleletermoelectrice. Aspectul ecologic al materialuluiderivdin reciclarea reziduurilor industriale. Acestprodus pe baz de sulfat de calciu n forma anhidrid III s-a ob inut n urma unor procesechimice la temperaturi de sub 750C [9].

Principalul beneficiu studiat n timpulprogramului de cercetare s-a dovedit a filucrabilitatea acestui nou liant capabil de a fi turnatn spaii cu dimensiuni mici. Acest produs s-a

folosit pentru a concepe, proiecta i executaelemente speciale de tip sandvi alc tuite dinstraturi exterioare rezistente i rigide, separate deun strat intermediar termoizolator din polistiren.Straturile exterioare au fost realizate din matriceaecologic mineral armat cu plase din fibre dinsticl. Acest eco-material este complet reciclabil iarprin introducerea n diferite amestecuri au rezultatdiverse produse cu utilizare n domeniulconstruciilor cum ar fi ape autonivelante, mortare,adezivi sau aditivi. n urma unor cercetri efectuatede alte echipe [11] rezultate experimentale obinuteau reliefat posibilitatea utilizrii acestuia ca liant

sau ca nlocuitor parial al cimentului Portlandobinuit. Domeniul construciilor ofer o larg varietate de aplicaii ale materialului (fig. 1).

tion elements with improved stiffness/weight andstrength/weight ratios and enhanced thermalcharacteristics. Some numerical simulations withFEM have been performed on wall panels and alsoon a complete structural model of a prototypehouse. The prototype has also been tested on ashake table with a maximum ground acceleration

equal to 0.4g (larger than any possible value withinour country) leading to a maximum requiredcompressive stress of 3 [N/mm2] and a maximumtensile stress equal to 5 [N/mm2]. These valuescan be considered as minimum strengthrequirements. The supplier of the material who isalso the owner of the product patent [9]guarantees that the durability characteristics of thisproduct are at least equal to those of OPC.

The paper presents experimental results ofa comprehensive research program performed atthe Faculty of Civil Engineering and BuildingServices of the Gheorghe Asachi TechnicalUniversity of Iasi. The program was initiated toattract recyclable materials from industrial wastes[10] in the building material market and to provethe qualities of an ecological mineral matrix withconvenient characteristics in construction. Thismatrix is obtained combining OPC with calciumsulphate anhydrite form III '. According to theproduct patent [9] gypsum as a basic material isavailable in natural and synthetic form. In syntheticform is available mainly as phosphogypsum anddesulfogypsum. Phosphogypsum is a by-productof the phosphate fertilizer industry. Thedesulfogypsum is itself such a product for thedesulphurisation of gases, in particular flue gas ofpower plants. The ecological features of thestudied material are ensured by the recycling ofindustrial wastes. This product based on calciumsulphate in the -anhydrite III' form has beenobtained as a result of chemical processes attemperatures below 750C [9].

The main benefit explored during theresearch program proved to be the workability ofthis new binder leading to a mineral matrix capableof being moulded into small spaces. This producthas been utilized to conceive, design and

manufacture special types of sandwich elementsmade of strong and stiff external layers separatedby an intermediate layer of thermally insulatingpolystyrene. The external layers have been madeof the ecological mineral matrix reinforced withfibreglass mesh. This eco-material is fullyrecyclable and, by utilizing different mixes, variouscompounds result to be introduced in theconstruction production such as self-levellingscreeds, mortars, adhesives and additives. Fromthe research work conducted by other researchteams [11] the experimental results have revealedthe possibility of its use as a binder or as a partial

replacement of the OPC. The construction industryoffers a wide range of applications (Fig. 1).


3/11

G. ranu, I.Lungu, N. ranu, M. Budescu / Caracteristicile mecanice ale unor matrice minerale din ciment 141i sulfat de calciu anhidru reciclat armate cu fibre de sticl

Fig. 1 Aplicaii cu material compozit mineral/ Mineral composite materials applications.

n cadrul programului experimental s-aurmrit realizarea unui amestec compus dinsulfatul de calciu n forma anhidrid III i OPC,amestecul avnd rolul unui liant compatibil cunisipul i constituind o matrice mineral adecvat armrii cu fibre din sticlrezistente la alcalii, pentruelemente de construcii compozite.

2. Programul experimental

2.1. MaterialePrin utilizarea matricei minerale i a

armturilor din plase de fibr de sticl bidirecionale s-au putut realiza cteva elementestratificate de nchidere i compartimentare. ncadrul programului experimental s-au confecionati elemente tip grind la care s-a urm ritmbuntirea comportrii la sarcini transversale.Pentru realizarea matricei minerale s-au utilizatnisip cuaros, splat i frimpurit i, cu granulaiade pn la 1mm, ciment Portland tip CEM II/B-V32,5 R i sulfatul de calciu n form anhidrid III.Caracteristicile de baz ale cimentului sunt celespecificate de productor pe site-ul acestuiaconform SR ENV 197-1 [12].

Armtura sub form de plase din fibre desticl E rezistent la alcalii, utilizat la ranforsareaprobelor din programul experimental este de tipulunei reele ortogonale de 3,5 x 3,8 mm [13].Caracteristicile plaselor din fibr de sticl suntprezentate n tabelul 1.

2.2. Pregtirea amestecurilor i epruvetelorn cadrul programului experimental s-au

confecionat epruvete prismatice cu dimensiunile160x40x40mm pentru determinareacaracteristicilor mecanice. Testarea s-a efectuatpentru stabilirea rezistenei la ntindere din

The experimental program aimed toachieve an admixture of anhydrous calciumsulphate in the -anhydrite III' form with OPC; thismixture acts as a binder compatible with sand andthat may form a mineral matrix capable of beingreinforced with alkali resistant glass fibres forcomposite construction elements.

2. The experimental program

2.1. MaterialsClosing and dividing layered elements

made of mineral matrix and bidirectional glass fibremesh reinforcement have been manufactured. Inaddition, beam type elements with improvedbehaviour under transverse loading have beenmade as well. To achieve the mineral matrix, thequartz sand washed and free of impurities with agrain size up to 1 mm, Portland cement type CEMII / BV 32.5 R and the calcium sulfate III 'anhydride form have been utilized. Thecharacteristics of the Portland cement are

specified by the manufacturer according to SRENV 197-1 [12].The reinforcement made of alkali resistant E

glass fibre mesh 3.5 x 3.8 mm orthogonallyarranged has been used to strengthen theexperimental samples [13]. The fibre glass meshcharacteristics are presented in Table 1.

2.2. Mixtures and specimens preparationThe prismatic specimens 160x40x40mm

have been prepared to be tested for theexperimental evaluation of mechanicalcharacteristics. Tensile strength from bending and

compressive strength have been analyzed. Thepercentage of the mix components was set involumetric dry parts; several trials have been


4/11


Tabelul 1Caracteristicile plaselor din fibrde sticl E/ E fibre glass mesh characteristics

Caracteristici/ Characteristics Unitate demsur/ Units

Plasdin fibre de sticl / Fibre glass mesh

Urzeal/ warp B ttur/ weft

Dimensiunea ochiurilor reelei / Slot mesh [mm] 3.5 x 3.8

Grosimea reelei / Slot thickness [mm] 0.52

Densitatea reelei / Mesh density [g/m ] 160

Rezistena la intindere / Tensile strength [N/mm ] 2000

Modul de elasticitate la ntindere / Tensile modulus [N/mm ] 72413

Tratamentul chimic al fibrei/ Fibre chemical treatment rezistent alcalin f remolient cumpiedicarea desfacerii firelor/ alkali resistant

without emolient obstructing yarn drifting

Tabelul 2

Compoziii de mortare armate cu plase din fibrde sticl i fraciunile volumetrice utilizate/ Mortars mixes reinforced with glassfibre meshes and the corresponding fibre volume fractions

Etichetamestec / Mixture label Nisip /Sand (%)

CimentPortlandPortland

cement(%)

sulfat de calciu anhidridIII / -

anhydrite III'

calcium sulphate (%)

Raportul apliant / Water

binder ratio

Fraciunevolumetricdefibre din sticl

Glass fibrevolume fraction

(%)NCK 50/25/25 matrice

nearmat/ unreinforced matrix50 25 25 0.40

0

NCK 2GF 50/25/25 matricearmat/ reinforced matrix

50 25 25 0.402


50 25 25 0.405


50 25 25 0.4010

ncovoiere i a rezistenei la compresiune.Componenii amestecurilor au fost stabilii n privolumetrice n stare uscat. Proporiile acestora aufost stabilite n urma unor ncercri pentrurealizarea unor amestecuri convenabile [14, 15]tabelul 2. Turnarea, ntrirea i ncercareaepruvetelor s-a efectuat conform SR EN 196-1:2006 [16].

Epruvetele cilindrice pentru ncercarea lacompresiune, cu diametrul d= 50 mm i nlimeah =100 mm (fig. 2a,c) s-au turnat din materialeleindicate n tabelul 2, n matrie din PVC, cte 5probe din fiecare categorie. n matrie au fostintroduse plasele de armare cu 3, 6 i 12 rnduri(fig. 2b), cu firul de btturdispus circumferen ial

performed to establish the most convenient mixes[14, 15], Table 2. The mix preparation and theprismatic samples casting, curing and testing werecarried out according to SR EN 196-1:2006 [16].

The cylindrical specimens for compressiontesting, with a diameter d= 50 mm and the heighth = 100 mm (Fig. 2a,c) have been cast from thematerials described in Table 2, in PVC moulds, tensamples for each material type. The reinforcingmeshes with 3, 6 and 12 rows (Fig. 2b) have beenarranged with the weft circumferentially orientedand the warp disposed longitudinally. The fibrevolume fractions are identical with those utilized forthe prismatic samples.

a b c

Fig. 2 Alctuirea probelor cilindrice / The cylindrical specimens: (a) - dimensiunile probei / the specimen dimensions;

(b) - introducerea plaselor de armare / the insertion of the reinforcing mesh; (c) epruvetele turnate / the cast specimens.


5/11


a

b

Fig. 3 Probe tip fie pentru ncercarea la traciune / The strip type specimens for the tensile testing: - (a) dimensiunile epruvetei / thesample dimensions;- (b) epruvetele turnate i sistemul de armare/ the cast samples and the reinforcing system.

iar firul de urzeal n direc ie longitudinal,fraciunile volumetrice de fibr fiind cele utilizate ila epruvetele prismatice.

Caracteristicile la ntindere axial au fostdeterminate pe epruvete tip fie nearmate iarmate cu dimensiunile de 400x30x10mm (fig.3a),cte zece din fiecare tip. Probele s-au turnat nmatrie paralelipipedice, cele armate fiindprevzute cu 1, 2 i 4 straturi de plase de fibr dinsticl cu firul de urzeal n direc ie longitudinal(fig.3b). Fraciunile volumetrice de fibr, n cazulepruvetelor armate au fost de 2%, 5% i 10%.

2.3. Testarea epruvetelorEpruvetele prismatice nearmate i armate au

fost testate la ncovoiere sub aciunea unei foreconcentrate aplicatla mijlocul deschiderii (fig. 4a).

Testarea s-a efectuat la 28 de zile conform

prescripiilor SR EN 196-1:2006 [16].Viteza deaplicare a sarcinii concentrate pentru solicitarea lancovoiere a fost de 50 N/s pnn momentul ruperii,produs prin dep irea rezistenei la ntindere dinncovoiere a materialului din epruvet, figura 4a.Testarea la compresiune s-a desfurat pe semi-prisme aplicndu-se o rat de nc rcare egal cu2400 N/s, constantpn la rupere (fig. 4b).

Ten strip specimens of 400x30x10 mm (Fig. 3a)made of unreinforced matrix and of reinforcedmatrix have been cast for testing under axial loadto determine the tensile characteristics. Thesamples have been poured in parallelepipedicmoulds; the reinforced specimens have beenstrengthened with 1, 2 and 4 layers of fibreglassmesh having the wrap yarns arranged in thelongitudinal direction (Fig. 3b). The fibre volumefractions achieved in case of reinforced sampleswere 2%, 5% and 10%.

2.3. Testing of specimensThe prismatic specimens both unreinforced

and reinforced have been subjected to bendingunder a three point loading scheme. (Fig. 4a). The28-days tests have been performed according toSR EN 196-1:2006 [16]. Loading rates equal to 50N/s and 2400 N/s, for the bending tests and for thecompression tests respectively have been selecteduntil the rupture of samples occurred, Figure 4a, b.The bending failure occurred when the concretetensile strength was reached and the half prismsresulted from this test were utilized in thecompression test (Fig. 4b).

a b

Fig. 4 - ncercarea probelor prismatice / Testing of prismatic samples: (a) - la ncovoiere / in bending;(b) - la compresiune pe semi-prism/ in compression on half-prism.

Probele cilindrice au fost ncercate lacompresiune centric, urmrindu-se stabilirearezistenei la compresiune i a modulului deelasticitate la aceast solicitare. Test rile s-au

efectuat cu o main universal de tipZWICK/ROELL de 1000 kN, prevzut cu

The cylindrical samples have been testedunder axial compression to determine thecompressive strength and the elastic modulus. AUniversal Testing Machine type ZWICK/ROELL

having a load capacity 1000 kN, with an automaticcontrol system operated by the dedicated software


6/11


a b c

Fig. 5 - ncercarea la compresiune pe epruvete cilindrice / Compression test on cylindrical samples: (a) epruveta cilindricechipat cuextensometru / the cylindrical specimen equipped with extensometer; (b) cedarea la compresiune a epruvetei nearmate /compressive failure of a unreinforced specimen; (c) - cedarea la compresiune a epruvetei armate / compressive failure of areinforced specimen.

a bFig. 6 ncercarea la traciune a fiilor din matrice mineral / Tensile testing of mineral matrix strips: (a)- montajul experimental /

experimental set-up; (b)- cedarea f iei armate cu 10% fraciune volumetricde fibr / failure of the 10% fibre volume fractionreinforced strip.

sistem automat de control, prin softul dedicat,Test/Expert versiunea 2.0. n timpul ncerc rii s-aaplicat o vitez de nc rcare egal cu 0,255N/mm2s. nregistrarea deformaiilor s-a realizat cutraductorii din dotarea mainii i cu unextensometru montat ca n figura 5a; ncrcareaprobelor a continuat pn la cedarea acestora (fig.5b, c).

n cazul probelor tip fie solicitate lantindere axial testarea s-a efectuat cu aceea imain universal , instrumentarea probelor cuextensometrul realizndu-se ca n figura 6a.

Msurarea deformaiilor realizate prin alungireaprobei s-a efectuat cu o precizie de 0,002% dinlungimea de calcul L0 stabilit de 50 mm n zonacentral (fig. 6a). Detalii privind modul de rupere alepruvetelor armate tip fie se prezint n figura6b.

2.4. Calculul caracteristicilor mecanice

Caracteristicile mecanice au fostdeterminate cu relaiile prezentate n tabelul 3.

Test/Expert 2.0. A loading rate equal to 0.255N/mm2s has been applied throughout the testingprocess. The deformations were recorded with themachines transducers and with an extensometermounted as shown in Figure 5a; the loading of thetest samples continued until their failure, (Fig.5b,c).

Testing of the strip type specimenssubjected to axial tension has been carried outusing the same testing machine, and theextensometer has been mounted as shown inFigure 6a. A base length L0 equal to 50 mm has

been selected and marked on the central portion ofthe sample, (Fig 6a), where the deformations havebeen measured with a precision of 0.002%. Detailson the failure mode of the reinforced strip areillustrated in Figure 6b.

2.4. Calculations

The mechanical characteristics weredetermined using the equations presented in Table3.


7/11


Tabelul 3Relaiile de calcul pentru determinarea caracteristicilor mecanice/ The mechanical characteristics evaluation formula

Caracteristica mecanicMechanical characteristic

Rezistena la ntindereTensile strength

(N/mm2)

Rezistena lacompresiune

Compressive strength (N/mm2)

Modul de elasticitate/ Elastic modulus(N/mm2)

Relaia de calculFormula

PrismePrismatic

specimens 3

1 5 =

fct

F lf

b

1600

= ucF

f

CilindriiCylindricalspecimens 1962 5

= ucF

f,

( )( )

0 50 20

2

20 50

4c,cyl

L F FE

d L L

=

Fii/ Stripspecimens 300

= uct

Ff

( )

( )

( )

( )50 20 0 50 20

50 20 50 20

t

L F FE

ab L L

= =

unde:- Ff este for a la rupere aplicat n mijlocul

prismei, n N, l este distan a dintre reazemelegrinzii prismatice, n mm, iarb reprezint laturaseciunii ptrate a prismei, n mm.

- Fu este for a maxim n momentul ruperii la

compresiune a probelor semi-prismatice, n N,iar 1600 mm2 reprezint aria sec iuniitransversale a epruvetei comprimate, avndlatura de 40mm (fig. 4b).

- Fu este for a maxim n momentul ruperii lacompresiune a probelor cilindrice, n N, iar1962,5 mm2 este aria sec iunii transversale aepruvetei, 300 mm2 este aria sec iuniitransversale a fiei solicitat la trac iune.

- L0este lungimea de calcul ( L0= 50 mm), F50 iF20 reprezint nc rcrile axialecorespunztoare fraciunilor de 50%, respectiv20% din fora maxim de compresiune Fu a

epruvetei, iar L50 i L20 sunt lungimile cecorespund ncrcrilor menionate anterior.- a este grosimea f iei, iar b l imea acesteia,

n mm.Valorile modulilor de elasticitate determinai

pe epruvetele cilindrice solicitate la compresiuneEc,cyl, n N/mm

2, au fost calculate cu diferen adintre valorile de pe curbele tensiuni-deforma iispecifice stabilite la 50% i 20% din ncrcareaaxial maxim . Valorile modulilor de elasticitatedeterminai pe epruvetele tip fie solicitate latraciune Et, n N/mm

2, au fost calculate n modsimilar [17], pentru mrimile corespunztoare

nregistrate la 50% i 20% din ncrcarea axialmaxim, pe curbele de tensiuni i deformaiispecifice:

3. Rezultate experimentale i discuii

Cu mrimile rezultate din ncercrileexperimentale pe epruvetele matricelor nearmatei armate, utiliznd relaiile din tabelul 3, au fostdeterminate valorile rezistenelor mecanice lasolicitri uzuale precum i modulii de elasticitatecorespunztori tipurilor de epruvete i naturiincrcrilor. O sintez a rezultatelor ob inute este

prezentat n tabelele 4 i 5.Rezistenele mecanice la compresiune,determinate experimental pe matrice nearmat

where:- Ff is the fracture load applied at the

midspan of the specimen, in N, l is thespan of the bent sample, in mm, while b isthe side of the prismatic square section, inmm.

- Fu is the maximum force at failure of thesemi-prismatic specimens, in N, while1600 mm2 is the contact surface betweenthe loading plate of the machine and the40mm sample side (fig. 4b).

- Fu is the maximum force at failure of thecylindrical specimens, in N, while 1962.5mm2 is the cross-sectional area of thesample, 300 mm2 is the cross-sectionalarea of the tensioned sample.

- L0is the base length ( L0= 50 mm), F50andF20 representing the axial loads at 50%,and 20% respectively from the ultimate

compressive force Fuon the sample, whileL50 and L20 are the corresponding lengthsassociated with the above mentionedloads.

- a is the strip thickness and b its width, inmm.

The elastic modulus values determined onthe compressed cylindrical samples Ec,cyl, inN/mm2, have been calculated from thecorresponding magnitude differences recorded onthe stress-strain curves at 50% and 20% from theultimate compressive load. The modulus valuesestablished on the strip type samples loaded in

tension, Et, in N/mm2

, have been also evaluated ina similar manner [17], utilizing the appropriatemagnitude differences recorded on the stress-strain curves at 50% and 20% from the ultimatetensile load.

3. Experimental results and discussionsThe mechanical strengths under current

loading schemes as well as the elastic modulicorresponding to the tested sample types havebeen determined utilizing the experimentalrecordings and the formulas presented in Table 3.A synthesis of the obtained results is given in

Tables 4 and 5.The compressive strengths experimentallydetermined on unreinforced matrix (Table 4),


8/11


(tabelul 4), prezint diferen e mici ntre valorileindividuale; coeficientul de variaie este 2,30% ncazul probelor prismatice i 2,60% pentru celecilindrice. Valorile modulului de elasticitate lacompresiune, stabilit pe probe cilindrice, au deasemenea o mprtiere redus, caracterizatprintr-o abatere standard egal cu 203 N/mm 2 i un

coeficient de variaie de 2,29%. Valoarea relativredus a modulului de elasticitate la compresiunese datoreazalc tuirii matricei nearmate, care esteformat doar din particule fine, lipsind agregatul cudiametrul mare, care reprezintscheletul betonuluiclasic. Armarea matricei minerale cu plase din fibredin sticl contribuie nesemnificativ la cre terearezistenei la compresiune. Diferenele dintreprobele nearmate i respectiv cele armate (tabelele4 i 5) cu 2%, 5% i 10% au rezultat n mbuntiriale acestei rezistene egale cu 4,35%, 6,57% i11,89%.

reveal small differences between individual values;the coefficient of variation is 2.30% for prismaticsamples and 2.60% for the cylindrical ones. Thecompressive modulus values determined oncylindrical samples, also have a reduced scatteringcharacterized by a standard deviation equal to 203N/mm2and a coefficient of variation of 2.29%. The

relatively low value of the compressive elasticmodulus is explained by the structure of theunreinforced matrix, consisting of fine particlesonly and lacking large diameter aggregates,existing in the classic concrete skeleton.

The reinforcing of the mineral matrix withglass fibre meshes does not significantly contributeto the increase of the compressive strength.Differences between the unreinforced andreinforced samples (Tables 4 and 5) with fibrevolume fractions of 2%, 5% and 10% resulted in

Tabelul 4

Rezultatele testelor experimentale pe amestecul NCK 50/25/25 matrice nearmatExperimental test results for the mix NCK 50/25/25 unreinforced matrix

Prisme / Prismaticsamples

Cilindrii / Cylindric samples F ii / Strip type samples

fcta fc fc

c Ec,cil / Ec,cyl fcte Et

Valoare medie /Average value

[N/mm2]

7.28 31.29 25.72 8840 1.13 9259

Abatere standard / Standard

deviation [N/mm2]

0.18 0.72 0.67 203 0.024 246

Coeficientul de variaie /

Coefficient of variation[%]2.47 2.30 2.60 2.29 2.12 2.65

Tabelul 5Rezultatele testelor experimentale pe amestecul NCK 50/25/25 matrice armat/ Experimental test results for the mix NCK

50/25/25 reinforced matrix

Armare/ GFR - 2% Armare/ GFR - 5% Armare/ GFR - 10%Cilindrii

Cylinders Fii / Strips Cilindrii

CylindersFii / Strips Cilindrii

CylindersFii / Strips

fcc)

[N/mm2]

Ec,cil /Ec,cyl

d)[N/mm2]

fcte)

[N/mm2]

Etf)

[N/mm2

fcc)

[N/mm2]

Ec,cil /Ec,cyl

d)

[N/mm2]

fcte)

[N/mm2]

Etf)

[N/mm2]

fcc)

[N/mm2]

Ec,cil /Ec,cyl

d)

[N/mm2]

fcte)

[N/mm2]

Etf)

[N/mm2]Valoare medie /

Average value

[N/mm2]

26.84 9007 4.87 39175 27.41 9250 5.73 42933 28.78 9836 6.24 45595

Abatere standard/

Standard

deviation

[N/mm

2

]

0.53 217 0.18 962 0.63 231 0.21 1167 0.92 275 0.22 1241

Coeficientul de

variaie/

Coefficient ofvariation[%]

1.97 2.40 3.69 2.45 2.29 2.49 3.66 2.71 3.01 2.79 3.52 2.72

a) Rezistena la ntindere din ncovoiere a probelor prismatice / Tensile strength from bending of the prismatic samples b) Rezistena la compresiune pe semi-prisme / Compressive strength on half-prisms c) Rezistena la compresiune pe cilindrii / Compressive strength on cylindrical samples d) Modulul de elasticitate la compresiune pe cilindrii / Compressive elastic modulus on cylindrical samples e) Rezisten a la traciune pe fii / Tensile strength on strips f) Modulul de elasticitate la trac iune pe fii / Tensile elastic modulus on strips

Modulul de elasticitate la compresiune peepruvete cilindrice a nregistrat creteri ca urmarea ranforsrii cu plasele de armare. Creterile

valorilor acestei caracteristici mecanice reprezint1,9%, 4,63% i respectiv 11,2%, pentru matricelearmate cu fraciuni volumetrice de fibr egale cu

improvements of this strength equal to 4.35%,6.57% and 11.89%.

The compressive modulus established on

cylindrical samples has risen as a result ofreinforcing with glass fibre meshes. The magnitudeincreases of this modulus are 1.9%, 4.63% and


9/11


2%, 5% i 10%.Rspunsul structural la compresiune a

probelor cilindrice este exemplificat n figura 7, princurbele medii tensiuni-deformaii specifice,calculate pentru seturi de 10 epruvete. Se observc alura diagramelor caracteristice i valorile limitale deformaiilor specifice liniare sunt similare cu

cele de la betonul simplu cu agregat mrunt.n ceea ce privete comportarea probelor

solicitate la compresiune axial s-a constatat c epruvetele nearmate au cedat brusc, prindespicare (fig. 5b) n timp ce ranforsarea cu plasinduce o cedare lin i continu (fig. 5c).

Rezistenele la ntindere din ncovoiere aprobelor prismatice nearmate (tabelul 4) suntrelativ omogene, avnd un coeficient de variaieegal cu 2,47%. n cazul probelor tip fie,nearmate, rezultatele indic o mpr tiere deasemenea redus, caracterizat printr-un coefi-cient de variaie egal cu 2,12%. Prin ranforsarea

11.2%, for matrices reinforced with 2%, 5% and10% fibre volume fractions.

The structural response of cylindricalsamples subjected to compression is illustrated inFigure 7, by the average stress-strain curves,plotted for sets of 10 samples. It can be noticedthat the shape of the characteristic diagrams and

the limit strain values are similar to those of plainconcrete with small aggregates.

The cylindrical unreinforced specimenloaded in axial compression had suddenly failed bysplitting of samples (Fig. 5b) while the meshreinforcing had induced a smooth and continuousfailure (Fig. 5c).

The tensile strengths determined by thethree point loading test of the unreinforcedprismatic samples (Table 4) are relativelyhomogeneous, with a coefficient of variation equalto 2.47%. When unreinforced strip type samplesare loaded in tension, the experimental results also

fiilor, rezistenele cresc n raport cu matricelenearmate, dup cum urmeaz : la fraciuneavolumetric de fibr egal cu 2%, cre terearezistenei la traciune a fost de 331%; la 5%fraciune volumetric de fibr , rezistena latraciune a sporit cu 407%, iar la fraciuneavolumetric maxim de armare, egal cu 10%,creterea rezistenei a fost de 806%. Coeficieniide variaie ai rezistenelor la traciune pentruprobele armate au fost de 3,69% (pentru 2%armare), 3,66% (pentru 5% armare), respectiv3,41% (pentru 10%), indicnd o omogenitateremarcabil a valorilor.

Fig. 7 Curbe caracteristice cu valori medii tensiuni-deforma iispecifice la compresiune pe probe cilindrice / Theaverage stress-strain diagrams in compression oncylindrical samples.

Din tabelul 5 se poate constata o creteresubstan

ial a valorii modulului de elasticitate la

traciune (323%), pe probele tip fie armate cu2% fraciune volumetric de fibr , iar pentru

Fig. 8 Curbe caracteristice cu valori medii tensiuni-deformaiispecifice la traciune pe epruvete tip fie / The averagestress-strain diagrams in tension on strip specimens.

indicate a small scattering, characterized by a

coefficient of variation equal to 2.12%. Byreinforcing the strips, significantly increased tensilestrengths have been obtained: a 331%increasehas been determined for samples with 2% fibrevolume fraction; for 5% fibre volume fraction, thetensile strength increased with 407% and themaximum volume fraction of reinforcement, equalto 10%, lead to an increase of 806%. Thecoefficients of variation of tensile strengths forreinforced samples were 3.69% (for 2%reinforcement), 3.66% (for 5% reinforcement) or3.41% (for 10%), indicating a remarkablehomogeneity of the strength values.

It can be noticed from Table 5, that asubstantial increase of the tensile modulus value,


10/11


celelalte procente de armare creterile relative suntmai reduse, respectiv de 363% pentru fraciuneavolumetric de 5% i 392% pentru fraciuneavolumetric de fibr egal cu 10%, p strndu-seomogenitatea rezultatelor experimentale.

Rspunsul structural al probelor tip fie,nearmate i armate, solicitate la traciune, este

ilustrat prin curbele caracteristice tensiuni deformaii specifice, din figura 8. Cedarea s-aprodus prin apariia unor fisuri transversale laintervale cvasi uniforme, de aproximativ 20mm nvecintatea flcilor de prindere ale mainii dencercat; ntr-o faz ulterioar de solicitare, fibrelede sticl din zona central au preluat integralefortul axial de ntindere. n final cedarea probei s-a produs prin ruperea succesiv a fibrelor dearmtur i smulgerea acestora din matrice ndirecia efortului axial. n figura 6b este prezentatmodul de cedare al fiei armate cu 10% fraciunevolumetricde fibr .

4. Concluzii

n cadrul unor programe de cercetare-dezvoltare de la Facultatea de Construcii iInstalaii din Iai s-a studiat posibilitatea utilizrii nconstrucii a unei matrice minerale ecologicerealizat prin nlocuirea par ial a cimentuluiPortland cu un liant obinut din deeuri industriale.

Direciile de folosire preconizate se refer ladezvoltarea unor module tip din matrice mineralranforsat cu plase din fibre de sticl i la utilizareaacestor materiale la soluiile de reabilitarestructurala elementelor din materiale tradi ionale.

Utilizarea eficient a acestor compozite cumatrice mineraleste condi ionat de cunoa tereacaracteristicilor de rezisten i de rigiditatenecesare proiectrii; de aceea a fost conceput irealizat un program cuprinztor de ncercriexperimentale.

Determinrile experimentale s-au efectuatpe probe din matrice nearmat i pe epruvetearmate cu fraciuni volumetrice de fibr cuprinsentre 2% i 10%.

ncercrile au fost concepute i realizate peprobe pstrate n condiii de laborator timp de 28de zile n vederea determinrii caracteristicilor derezisten i de rigiditate specifice destinaieianticipate a materialului.

Determinrile s-au efectuat pe epruveteprismatice n vederea stabilirii rezistenei lantindere din ncovoiere, ct i a rezistenelor lacompresiune pe semi-prisme; caracteristicile derezisten i rigiditate la compresiune s-au stabilitpe probe cilindrice, iar caracteristicile de rezisteni rigiditate la ntindere axial s-au studiat peepruvete paralelipipedice de tip fie.

Matricea ecologic i compozitul mineral au

o lucrabilitate bun asigurnd formarea f rdificultate a probelor experimentale i aelementelor prototip.

namely 323%, has been obtained on the strip typespecimens reinforced with 2% fibre volumefraction; for the other fibre reinforcing ratios therelative increase were 363% for the 5% fibrevolume fraction, and 392% for 10% reinforcingratio, maintaining the homogeneity of theexperimental results.

The structural response of the unreinforced andreinforced strip type samples loaded in tension isillustrated by the stress-strain characteristicdiagrams, Figure 8. Failure occurred initially by thedevelopment of quasi - uniform transverse cracksspaced at about 20mm near the clamping grips ofthe testing machine; later on as loadingprogressed, the glass fibres in the gauge lengthtook over the total axial load. Eventually, thesample failure occurred by successively fracturingthe reinforcing fibres along the axial force directionand a visible pull-out. Figure 6b presents thefailure mode of the 10% fibre volume fractionreinforced strip.

4. Conclusions

The possibility of usage of a green mineralmatrix achieved by partial replacement of Portlandcement with a binder from industrial waste inconstruction have been extensively studied insome research and development programs carriedout at the Faculty of Civil Engineering of Iasi.

The intended use directions relate to thedevelopment of modular type units made ofmineral matrix reinforced with fibreglass meshes

and the utilization of these materials to structuralrehabilitation of the load bearing elements fromtraditional building materials.

However the efficient use of these mineralmatrix composites depends on a thoroughknowledge of the strength and stiffnesscharacteristics required for the design process;therefore a comprehensive experimental programhas been designed and performed.

The experimental determinations havebeen carried out on samples made of unreinforcedmatrix and of reinforced matrix with fibre volumefractions between 2% and 10%.

The tests have been conceived andperformed on samples kept in laboratory for 28days to determine the particular strength andstiffness characteristics required by the destinationof the material.

The experimental values have beenrecorded on prismatic specimens to determine thetensile strength from bending under the three pointloading test and the compressive strength on thesemi-prisms; the compressive strength andstiffness characteristics have been established oncylindrical samples while the tensile strength andstiffness properties under axial loading have beenstudied on strip type rectangular specimens.

The ecological matrix and the


11/11


Rezultatele astfel obinute reliefeazomogenitatea materialelor studiate reflectat prinvalorile reduse ale abaterilor standard i alecoeficienilor de variaie.

Influena armrii cu plase din fibre de sticleste favorabil pentru rezisten ele la traciuneobinute att pe prisme ct i pe epruvetele tip

fie; aceast influen este semnificativ i ncazul modulilor de elasticitate a fiilor ntinse.Fibrele pot fi orientate astfel nct direciileacestora s coincid cu cele ale tensiunilorprincipale. Experimentele realizate pe elementeportante i pe modelul structural, au confirmateficiena acestor soluii.

Armarea nu modificesen ial caracteristicilede rezisten i rigiditate la compresiune darmbuntete rspunsul structural i caracterulcedrii.

Mulumiri

NOT: Aceast lucrare a beneficiat de suport financiarprin proiectul Dezvoltarea i susinerea de programepostdoctorale multidisciplinare n domenii tehnice prioritare alestrategiei naionale de cercetare - dezvoltare - inovare 4D-POSTDOC, contract nr. POSDRU/89/1.5/S/52603, proiectcofinanat din Fondul Social European prin ProgramulOperaional Sectorial Dezvoltarea Resurselor Umane 2007-2013.

REFERENCES

1. N. ranu, G. Oprian, I. Entuc, M. Budescu, V.Munteanu, and G. Taranu, Composite and hybrid solutionsfor sustainable development in civil engineering,Environmental Engineering and Management Journal,2012, 11(4), 783.

2. A. J. Majumdar, Glass fibre reinforced cement and gypsumproducts, Proceedings of the Royal Society (Series A)Composites, 1971, 319(3), 6.

3. J. A. G. Thomas, Fibre composites as constructionmaterials, Composites, 1972, 3(2), 2.

4. A. M. Brandt, Present trends in the mechanics of cementbased fibre reinforced composites, Construction andBuilding Materials, 1987, 1(1), 11.

5. T. Ando, T. Ikeda, H. Sakai, H. Otaguro, and T.Sawanobori, Fibre reinforced cement mortar product, 23,Composites, Japan, Pat. No. 1, 1992

6. D. Feldman, Fibre reinforced cementitious composites,Canadian Journal of Civil Engineering, 1993, 20(2), 10.

7. M. Singh and M. Garg, Gypsum-based fibre-reinforcedcomposites: an alternative to timber, Construction andBuilding Materials, 1994, 8(3), 5.

8. M. Barbu, N. ranu and M. Harja, Wastes used inobtaining polymer composites, Environmental Engineeringand Management Journal, 2009, 8(5), 1145.

9. C. Baux, Process for the industrial manufacture ofcompositions based on anhydrous calcium sulphate in theb-anhydrite iii' form, and corresponding compositions andbinders, France, Pat. No. WO/2010/003827, 2010.

10. M. Barbu, M. Harja and D. Babor, Concrete polymer withfly ash. Morphologic analysis based on scanning electronmicroscopic observations,, Romanian Journal of Materials,2010, 40(1), 3.

corresponding mineral matrix composite have agood workability enabling the casting of theexperimental samples and of the prototypecomponents.

The experimentally determined resultsreveal the material homogeneity reflected by lowvalues of the standard deviations and of the

variation coefficients.It has been noticed that reinforcing with

fibreglass meshes is beneficial to the tensilestrengths obtained on both prismatic and strip typespecimens; this favourable influence is alsonoticeable on the elastic tensile moduli. The fibrescan be oriented in such a way that theycorrespond to the principal stresses. Theexperiments carried out on load bearing elementsand on the structural module confirmed theefficiency of these solutions.

Reinforcing does not significantly influencethe essential compression characteristics but itimproves the structural response and the failuremode.

AcknowledgmentsThis paper was supported by the project "Develop and

support multidisciplinary postdoctoral programs in primordialtechnical areas of national strategy of the research -development - innovation" 4D-POSTDOC, contractPOSDRU/89/1.5/S/52603, project co-funded from EuropeanSocial Fund through Sectorial Operational Program HumanResources 2007-2013.

**********************************************************

11. B. Aranda, O. Guillou, C. Lanos, C. Tessier, and F. Le

Dret, Synthese dun liant vert capable de concurrencer leciment Portland, in Journe des doctorants, Comunicationorale, 2011, Universit de Rennes, France.

12. *** Ordinary Portland cement for concrete,http://www.lafarge.ro/CEM_II_-_B-V_32.5R.pdf.

13. *** Render Reinforcing Mesh GMESH/R131/1000/50,http://www.fibreglassmesh.co.uk/wp-content/uploads/2011/03/Texile-Technologies-160gm-Medum-Weight-Render-Mesh1.pdf.

14. G. ranu, I. O. Toma, R. Pleu and I. Grdinariu,Evaluation of Mechanical Properties of Cement andCalcium Sulphate Mineral Matrix, Bulletin of thePolytechnic Institute of Iasi. Construction and ArchitectureSection, 2011, LVII (LXI)(2), 131.

15. I. O. Toma, G. ranu, A.-M. Toma and M. Budescu,Influence of Cement and Sand Type on the Strength

Characteristics of Mortars with Various Contents of GreenBinder, Procedia Engineering, 2011, 21, 196.16. *** SR EN 196-1:2006 - Methods of Testing Cement - Part

1: Determination of Strength, 2006.17. N. ranu, C. Banu, G. Oprian, M. Budescu, V.

Munteanu, and O. Ioni, Tensile Characteristics of GlassFibre Reinforced Polymeric Bars, Romanian Journal ofMaterials, 2010, 40(4), 323.

*****************************************************************************************************************

matricea cimentului cu fibra de sticla

Documents