universitat politÈcnica de catalunya -...

SPECIAL WORKSHOP“CHEMICAL EXPANSION OF CONCRETE IN DAMS AND HYDRO-

ELECTRIC PROJECTS”

UNIVERSITAT POLITÈCNICA DE CATALUNYAEscuela Técnica Superior de Canales, Caminos y Puertos de BarcelonaDepartamento de Ingeniería de la Construcción

Antonio AguadoGeorgia Serafim

Servando ChinchónCarlos María López

Luis Agulló

Granada, October 18, 2007

INTERNAL SULPHATE ATTACK IN INTERNAL SULPHATE ATTACK IN DAMS DAMS

IntroductionIntroduction

MicroMicro--structuralstructural

--Reactions andReactions andexpansive expansive productsproducts--Expansive Expansive

modelmodel--Experimental Experimental

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ConclusionsConclusions

Abnormal Abnormal behaviorbehavior

Levels ofLevels ofstudystudy

MesoMeso--structuralstructuralMacroMacro--

structuralstructural--NumericalNumericalstudiesstudies--MovementsMovements

Structures such as Structures such as damsdams require special attention to be paid to the require special attention to be paid to the material, especially the material, especially the aggregate aggregate whichwhich may contain minerals that are may contain minerals that are potentially unstablepotentially unstable and which can react with cement components to give and which can react with cement components to give rise to rise to expansive compounds.expansive compounds.

This presentation describes the This presentation describes the methodology developedmethodology developed to to evaluate evaluate concrete expansionconcrete expansion and the consequent and the consequent abnormal behavior in gravity abnormal behavior in gravity dams dams suffering from suffering from internal sulfate attackinternal sulfate attack (ISA). (ISA).

Sulfate attackSulfate attack is a is a chemical processchemical process between between sulfate ionssulfate ions and the and the components of hardenedcomponents of hardened concrete which results in its concrete which results in its deteriorationdeterioration. .

AGGREGATEAGGREGATE


IntroductionIntroduction In structures such as In structures such as concrete gravity damsconcrete gravity dams, the , the internal expansioninternal expansion due due to the to the oxidation of sulfide minerals in the aggregateoxidation of sulfide minerals in the aggregate is characterized by:is characterized by:

Change in concrete Change in concrete surface surface colorcolorMapped cracksMapped cracks

Operational Operational problemsproblems

Displacement in the Displacement in the upstream directionupstream direction




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The The macro abnormal behaviormacro abnormal behavior in the concrete dams is a reflection of the in the concrete dams is a reflection of the material expansionmaterial expansion. To obtain . To obtain satisfactory conclusions,satisfactory conclusions, the studies need to the studies need to integrate the distinct levels integrate the distinct levels and and the the results from one levelresults from one level can be used as can be used as datadata for the for the followingfollowing..

The study concentrates in:The study concentrates in:••Reactions and kinetics Reactions and kinetics ••Products formedProducts formed••Maximum expansionMaximum expansion

MICROSCALEMICROSCALE

••The structure is The structure is modeledmodeledby FEMby FEM

••The displacements are The displacements are analyzed by a analyzed by a mathematical modelmathematical model

MACROSCALEMACROSCALE

The study concentrates in the The study concentrates in the micromicro--cracking caused by the cracking caused by the increase in the internal increase in the internal tension by a numerical tension by a numerical modellingmodelling

MESOSCALEMESOSCALE

[Aguado, [Aguado, et alet al., 1996]., 1996]

This methodology of study is a This methodology of study is a global approachglobal approach that can be applied to that can be applied to any any typetype of of internal expansive reactions in damsinternal expansive reactions in dams..






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The The expansionexpansion induced by the oxidation of the iron sulfide mineral in the induced by the oxidation of the iron sulfide mineral in the concrete mass has concrete mass has two stepstwo steps::




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MesoMeso--structuralstructural


Primary reaction:Primary reaction: the iron sulfide, in the presence of oxygen and humidity, the iron sulfide, in the presence of oxygen and humidity, oxidizes to form alteration compounds like oxidizes to form alteration compounds like sulfatessulfates and and hydroxide hydroxide and aand adecrease of the alkalinity decrease of the alkalinity of the systemof the system::

iron iron sulfidesulfide oxygenoxygen waterwater ironiron

hydroxidehydroxideiron iron

sulfatesulfate HH+++ → ++ +

iron iron sulfatesulfateportlanditeportlandite waterwater secondary secondary

ettringiteettringitetricalciumtricalciumaluminatealuminate

+ →+ +

Secondary reaction:Secondary reaction: the alteration compounds react with the products of the alteration compounds react with the products of the hardened cement paste to produce the the hardened cement paste to produce the internal sulfate attackinternal sulfate attack with the with the formation of the formation of the expansiveexpansive secondary ettringite:secondary ettringite:

[Casanova, [Casanova, et alet al., 1996]., 1996]




MacroMacro--structuralstructural

--NumericalNumericalstudiesstudies--MovementsMovements

The products formed in the The products formed in the oxidationoxidation and in the and in the sulfate attacksulfate attack have have greater greater volumesvolumes than their respective original compounds.than their respective original compounds.




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By applying a chemical kinetic model it was possible to obtain tBy applying a chemical kinetic model it was possible to obtain the he maximum expansionmaximum expansion at reaction completion for both at reaction completion for both sulfide oxidationsulfide oxidation and and sulfate attack.sulfate attack. [Casanova, [Casanova, et alet al., 1996]., 1996]

172,19 cm3 per mole of sulfateSecondary: SULFATE ATTACK

6,04 cm3 per mole of sulfidePrimary: SULFIDE OXIDATION

A A numerical modelnumerical model that allows calculation of the that allows calculation of the maximum expansion maximum expansion and and itsits velocityvelocity was developed.was developed.

Graphical expression of the numerical modelGraphical expression of the numerical model

Aspects to highlight:Aspects to highlight:••The stabilization of the The stabilization of the

expansion with time.expansion with time.••The exponential shapeThe exponential shape






To determine the To determine the main causemain cause of the abnormal behaviour of the of the abnormal behaviour of the structure a structure a chemical and mineralogical analysischemical and mineralogical analysis using different using different

laboratory testslaboratory tests was carried out.was carried out.1 1 -- Characterization of the aggregateCharacterization of the aggregate

Typical rock sample with Typical rock sample with the sulfide bands.the sulfide bands.




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To identify the To identify the crystalline compoundscrystalline compounds in the in the rockrock (a)(a) an an XX--ray diffractionray diffraction(XRD) was used.(XRD) was used.

The The difractogramdifractogramreveals that the reveals that the rockrock is composed is composed of of quartzquartz, , micamicaand an and an apparently apparently nonnon--expansive expansive type of claytype of clay..

Rock sample collected in Rock sample collected in Torán Dam zone.Torán Dam zone.






To To detect and quantify other compounds,detect and quantify other compounds, a sample of a sample of rockrock with with sulfide bands sulfide bands was chemically analyzed by was chemically analyzed by XX--ray fluorescence (XRF)ray fluorescence (XRF)::

It can be observed the It can be observed the elements of the rockelements of the rock componentscomponents

S SOS SO33 2.0322.032

These compounds must be from the These compounds must be from the iron sulfidesiron sulfides contained incontained inthe the schistsschists..

1 1 -- Characterization of the aggregate [cont]Characterization of the aggregate [cont]

These These large quantity of sulfurlarge quantity of sulfur in the aggregate can in the aggregate can oxidizeoxidize and form and form expansive productsexpansive products as explained before.as explained before.

and a and a percentage of percentage of sulfur sulfur that was that was not expectednot expected to find. to find.




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2 2 -- Characterization of the iron sulfideCharacterization of the iron sulfide

During the preparation for the experimental work, it was observeDuring the preparation for the experimental work, it was observed d that the sample could be that the sample could be attracted by a magnetattracted by a magnet, that is a , that is a characteristic of the characteristic of the pyrrhotitepyrrhotite crystals. crystals.

This is a This is a first signfirst sign that the sample of iron sulfide contains a that the sample of iron sulfide contains a significant quantity of significant quantity of pyrrhotitepyrrhotite..




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2 2 -- Characterization of the iron sulfide [cont]Characterization of the iron sulfide [cont]

To characterize the iron sulfide an To characterize the iron sulfide an XX--ray diffraction (XRD)ray diffraction (XRD) and the and the Scanning Electron Microscope (SEM) with microanalysis (EDAX)Scanning Electron Microscope (SEM) with microanalysis (EDAX)were used.were used.

In the XDR In the XDR difractogramdifractogram the peaks corresponding to the peaks corresponding to pyritepyrite and and pyrrhotitepyrrhotite, , and theand the minerals of the rock minerals of the rock that accompany the iron that accompany the iron sulfide sample can be observed.sulfide sample can be observed.




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2 2 -- Characterization of the iron sulfide [cont]Characterization of the iron sulfide [cont]

To identify the To identify the predominant iron sulfidepredominant iron sulfide the sample was studied the sample was studied by scanning electron microscope (SEM) and the by scanning electron microscope (SEM) and the constituent constituent elementselements were identified by Xwere identified by X--ray spectrometer.ray spectrometer.

Image, spectrum and microImage, spectrum and micro--analysisanalysis

Sulfur to iron ratio = 0.62Sulfur to iron ratio = 0.62

The The magnetismmagnetism and the and the sulfur to iron ratio sulfur to iron ratio indicate that the indicate that the predominant iron sulfide in the analysed rock sample of Torán predominant iron sulfide in the analysed rock sample of Torán Dam is Dam is pyrrhotitepyrrhotite..

The sulfur to iron ratioThe sulfur to iron ratio of the of the samplesample isis closer closer to the sulfur to iron to the sulfur to iron ratio ofratio of pyrrhotitepyrrhotite (0.65) (0.65) than to the sulfur to iron ratio ofthan to the sulfur to iron ratio of pyrite pyrite (1.15).(1.15).




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3 3 -- Characterization of the compounds formed in the oxidation Characterization of the compounds formed in the oxidation of the iron sulfide.of the iron sulfide.

To determine the To determine the products generated products generated by alteration of the aggregate, by alteration of the aggregate, the rock samples were analysed by the rock samples were analysed by XX--ray diffractionray diffraction (XRD) and by (XRD) and by scanning electron microscopescanning electron microscope (SEM)(SEM)..

The results indicate that the predominant The results indicate that the predominant iron hydroxideiron hydroxide in the in the sample is sample is goethite, goethite, FeO(OHFeO(OH).).MicroMicro--

structuralstructural--Reactions andReactions andexpansive expansive productsproducts--Expansive Expansive


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3 3 -- Characterization of the compounds formed in the oxidationCharacterization of the compounds formed in the oxidationof the iron sulfide [cont].of the iron sulfide [cont].

The presence of The presence of potassiumpotassium in the microanalysis indicate that the in the microanalysis indicate that the jarositejarosite, KFe, KFe33(SO(SO44))22(OH)(OH)66, is the predominant , is the predominant iron sulfateiron sulfate in the in the analysed sample.analysed sample.




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4 4 -- Characterization of the products of the sulfate attackCharacterization of the products of the sulfate attack

Once the Once the oxidation products in the aggregate oxidation products in the aggregate were identified its were identified its necessary to determine if these products do indeed necessary to determine if these products do indeed react with the react with the cement paste compoundscement paste compounds..

The optical microscopy technique can reveal important details abThe optical microscopy technique can reveal important details about out the concrete dam samples:the concrete dam samples:

No oxidized Iron sulfideNo oxidized Iron sulfide Oxidized edge of aggregateOxidized edge of aggregate

Needle shape crystal in poresNeedle shape crystal in poresNeedle shape crystal in interface Needle shape crystal in interface and cracksand cracks




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4 4 -- Characterization of the products of the sulfate attack [cont]Characterization of the products of the sulfate attack [cont]

The The needle shape crystalneedle shape crystal was analysed by was analysed by scanning electron scanning electron microscope microscope (SEM) with (SEM) with microanalysismicroanalysis (EDAX) and identified as (EDAX) and identified as ettringite,ettringite, 3CaO.Al3CaO.Al22OO33.3CaSO.3CaSO4431H31H22O,O, confirming the confirming the internal sulfate internal sulfate attackattack..

In the In the ISAISA the sulfide oxidation leads to the sulfide oxidation leads to iron hydroxides and sulfateiron hydroxides and sulfatethat, once inside the concrete mass, react with the cement pastethat, once inside the concrete mass, react with the cement pastecompounds to form the compounds to form the expansive secondary ettringiteexpansive secondary ettringite..




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Considering physicalConsidering physical--chemical aspects and the maximum expansion of the chemical aspects and the maximum expansion of the primary and secondary reactions, the approximate increase in theprimary and secondary reactions, the approximate increase in the volume volume due to both expansions is due to both expansions is ∆∆V/V = 0,0146V/V = 0,0146. [Aguado . [Aguado et alet al., 1998]., 1998]

The The expansion expansion due to the deterioration process, generate an due to the deterioration process, generate an increase in the internal tensionincrease in the internal tension that can cause that can cause micromicro--crackingcracking..

To evaluate the effects, a To evaluate the effects, a 2D numerical2D numerical model in the model in the mesoscalemesoscale was was developed based on the developed based on the finite element methodfinite element method (FEM) considering (FEM) considering constitutive lawsconstitutive laws for the for the aggregateaggregate, the , the cement matrixcement matrix and the and the interfaceinterface..[[LópezLópez, 1999], 1999]

SampleSample Original meshOriginal mesh Deformed meshDeformed mesh

If the phenomenon is isotropic (If the phenomenon is isotropic (εεxx = = εεyy = = εεzz) the deformation has an ) the deformation has an approximate value of approximate value of 4,87 mm/m4,87 mm/m. [. [LópezLópez, 1999, 1999]]

This This mesomeso--structural numerical model was structural numerical model was able to representable to represent the the real real cracking observed in the damcracking observed in the dam..










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To To develop the oxidationdevelop the oxidation, the iron sulfide needs , the iron sulfide needs oxygen and oxygen and humidityhumidity. The immediate consequence in a dam is that the . The immediate consequence in a dam is that the reactions reactions will havewill have different velocities different velocities in thein the upstream upstream and in theand in the downstream downstream

faceface..

Since the Since the upstream faceupstream face is is submerged submerged for long periods of time, the for long periods of time, the availability of oxygen availability of oxygen is muchis much lower lower than thethan the downstreamdownstream..

The The distribution of the deformationdistribution of the deformation caused by the expansion will be caused by the expansion will be nonnon--linear linear that leads to the appearance of anthat leads to the appearance of an internal selfinternal self--equilibrated equilibrated

stressesstresses..

In concrete gravity dams, the In concrete gravity dams, the more intensemore intense expansionexpansion in the in the downstreamdownstream face will lead to an face will lead to an upstream displacementupstream displacement..








With the With the deformationsdeformations, resulting of the previous , resulting of the previous mesostructuralmesostructuralstudy, the study, the crest displacementcrest displacement in a cross section of the Torán Dam in a cross section of the Torán Dam

was analysed by the was analysed by the Finite Element MethodFinite Element Method, in , in plain deformationplain deformation and and elastic linealelastic lineal conditions. conditions.

For the structural analysis a For the structural analysis a 2D2D or or 3D3D and a and a linearlinear or or nonnon--linearlinearanalysis can be made. The results must be considered from a analysis can be made. The results must be considered from a

technical,technical, scientificscientific and and economicaleconomical point of view.point of view.

In this case was not possible contrast the In this case was not possible contrast the obtained displacementobtained displacement with with the real movements but it the real movements but it correlatescorrelates with the movements observed in with the movements observed in

similar dams affected by ISA.similar dams affected by ISA.




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To analyze the To analyze the observed displacementobserved displacement a a mathematical modelmathematical model was was used. used.

−+=

−

p

Ct

eBAy 1

The equation The equation proposedproposed has the following has the following exponentialexponential formform: :

A A -- initial value of the movements initial value of the movements B B -- maximum predicted movementmaximum predicted movementC C -- abscissa of the inflection point (the expansion begins to abscissa of the inflection point (the expansion begins to

stabilize)stabilize)t t -- time in monthstime in monthsp p -- parameter that influences the shape of the curveparameter that influences the shape of the curve

[Aguado [Aguado et alet al., 1998]., 1998]




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The function was The function was adjustedadjusted to obtain the parameters for to obtain the parameters for distinct distinct stabilization timestabilization time (C) for the movements observed in (C) for the movements observed in GrausGraus and and

TavascánTavascán dams.dams.

Analyzing the results of the various adjusted curves, the curve Analyzing the results of the various adjusted curves, the curve with with inflection point near inflection point near 350 months350 months is the one that is the one that best represents the best represents the

movements observedmovements observed. .

The The adjusted curvesadjusted curves provide a provide a highly satisfactory representation.highly satisfactory representation.





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The The mathematical modelmathematical model enables enables predictionprediction of the of the maximum maximum expected movementsexpected movements and the and the stabilization of the movementsstabilization of the movements..

This function not only This function not only representsrepresents the the exponential behavior exponential behavior of theof thedisplacement observeddisplacement observed in the structure, but also in the structure, but also the equation the equation thatthat

dictates dictates thethe material expansionmaterial expansion for the for the ISA.ISA.

Since the Since the alkalialkali--aggregate reactionaggregate reaction has a has a microstructuralmicrostructural behavior behavior with a with a similar approachsimilar approach, as verified by a , as verified by a thermodynamically based thermodynamically based

modelmodel and and experimental workexperimental work of of LariveLarive [1998],[1998], the the proposed proposed mathematical modelmathematical model can be can be appliedapplied to study the to study the structural behaviorstructural behavior

of of damsdams affected by AARaffected by AAR..

The mathematical model The mathematical model was applied in dams was applied in dams

affectedaffected by the by the AAR AAR and and the the adjusted curveadjusted curve

represents the observed represents the observed displacements.displacements.

The The differencedifference to the dams suffering from to the dams suffering from ISAISA is the is the kinetics, kinetics, with the with the stabilization timestabilization time around 500 months.around 500 months.--NumericalNumerical

studiesstudies--MovementsMovements




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From the various From the various existing internal sulfate sourcesexisting internal sulfate sources that can that can deteriorate the deteriorate the concrete of the damsconcrete of the dams, the presence of , the presence of iron sulfide iron sulfide

minerals in the aggregateminerals in the aggregate is one of the is one of the most commonmost common..

In consequence the structures present superficial signs like In consequence the structures present superficial signs like mapped mapped crack and change of concrete colorcrack and change of concrete color, , operational problemsoperational problems and and

permanent displacement.permanent displacement.

Since the abnormal structure behavior is a consequence of the material behavior it is necessary integrate the three levels of study.

A A correct understandingcorrect understanding of the reactions of the expansive of the reactions of the expansive phenomenon and a phenomenon and a diagnosisdiagnosis based on the available laboratory based on the available laboratory techniques are very important to techniques are very important to obtain the maximum expansionobtain the maximum expansion

that will be the data for the numerical studies.that will be the data for the numerical studies.

As a consequence of the consumption of the potentially reactive As a consequence of the consumption of the potentially reactive minerals, minerals, the expansion of the materialthe expansion of the material and the and the displacementsdisplacements

stabilize with timestabilize with time..

The phenomenon occurs in The phenomenon occurs in two stagestwo stages, both with formation of , both with formation of expansive productsexpansive products..




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SPECIAL WORKSHOP“CHEMICAL EXPANSION OF CONCRETE IN DAMS AND HYDRO-

ELECTRIC PROJECTS”

UNIVERSITAT POLITÈCNICA DE CATALUNYAEscuela Técnica Superior de Canales, Caminos y Puertos de BarcelonaDepartamento de Ingeniería de la Construcción

Antonio AguadoGeorgia Serafim

Servando ChinchónCarlos María López

Luis Agulló

Granada, October 18, 2007

INTERNAL SULPHATE ATTACK IN INTERNAL SULPHATE ATTACK IN DAMS DAMS

Internal sulfate attack J.S. CHINCHON, C. AYORA, A. AGUADO y F. GUIRADO Influence of Weathering of Iron Sulphides Contained in Aggregates on Concrete. Durability. Rev. Cement and Concrete Research. Vol. 25. Issue. 5. Agosto 1995. pp. 1264-1272. http://www.sciencedirect.com/science/journal/00088846 I. CASANOVA, L. AGULLO and A. AGUADO Aggregate Expansivity Due to Sulfide Oxidation - I. Reaction System and Rate Model. Rev. Cement and Concrete Research. Vol. 26. nº 7. Agosto 1996. pp. 993-998. http://www.sciencedirect.com/science/journal/00088846 I. CASANOVA., A. AGUADO y L. AGULLÓ Aggregate expansivity due to sulfide oxidation, II.- Physico- chemical modeling of sulfate attack. Rev. Cement and Concrete Research, Vol. 27, nº 11. Nov. 1997. pp. 1627-1632. http://www.sciencedirect.com/science/journal/00088846 C. AYORA, S. CHINCHÓN, A. AGUADO, F. GUIRADO Weathering of Iron Sulfides and Concrete Alteration: Thermodynamic Model and Observation in Dams From Central Pyrenees, Spain. Rev. Cement and Concrete Research, Vol. 28, nº 9, 1998. pp. 1223-1235 http://www.sciencedirect.com/science/journal/00088846 G. S. ARAUJO, A. AGUADO, L. AGULLÓ, y C. Mª. LÓPEZ Análise do comportamento estructural do concreto: Do micro a macro estructura. Aplicacao ao caso do barragens. Revista Internacional Construlink. Vol 4. nº 11. pp.: 4-16. Febrero 2006. I.S.S.N.: 1645-5576. http://www.construlink.com/ J. SEGARRA, J. M. BUIL and A. AGUADO Analysis of the possibilities of using reactive aggregates in the construction of new concrete dams. Proceedings of the International Symposium on Dams and Reservoirs, Societies and Environment in the 21st Century. ICOLD - SPANCOLD. Barcelona. 18th June 2006. Ed. By L. Berga et al. Balkema. ISBN-10: 0-415-40240-9 pp.: 515-520 http://www.balkema.nl/ G. S. ARAUJO, S. CHINCHÓN and A. AGUADO, Evaluation of the behavior of concrete gravity dams suffering from internal sulfate attack. Accepted IBRACON Materials Journal - Instituto Brasileiro do Concreto http://www.ibracon.org.br/publicacoes/revistas_ibracon/rev_materiais/ingles/index.html Numerical models of concrete. Meso-structural studies Carlos María LÓPEZ GARELLO Análisis microestructural del hormigón utilizando elementos finitos de interfase. E.T.S. Ingenieros de Caminos, Canales y Puertos. U.P.C. 28 de junio de 1999. Directores de tesis: Ignacio CAROL y Antonio AGUADO.

C. Mª LOPEZ, I. CAROL AND A. AGUADO Meso-structural study of concrete fracture using interface elements. I: Numerical model and Tensile behavior. Accepted Cement and Concrete Research. http://www.sciencedirect.com/science/journal/00088846 C. Mª LOPEZ, I. CAROL AND A. AGUADO Meso-structural study of concrete fracture using interface elements. II: Compression, Biaxial and Brazilian test. Accepted Cement and Concrete Research. http://www.sciencedirect.com/science/journal/00088846 A. AGUADO, A. RODRÍGUEZ-FERRAN y I. CASANOVA Funciones de ajuste del comportamiento de expansiones en hormigón de presas. Congreso Internacional de Conservación y Rehabilitación de Presas. Sociedad Española de presas y Embalses. SEPREM. Madrid. De 11 a 13 de Noviembre 2002. Publicado en DAM MAINTENANCE & REHABILITATION. Llanos et al. (eds). 2003 A. A. Balkema Publishers, Lisse, pp.: 137-143. ISBN 90 5809 534 7. http://www.balkema.nl/ A. AGUADO, A. RODRÍGUEZ-FERRAN, I. CASANOVA y L. AGULLÓ Modeling time evolution of expansive phenomena in concrete dams as a decision making tool. XXI Congrès des Grands Barrages MONTREAL. ICOLD. R.72 Tomo II. Quest. 82. pp.1219-1228. 13 a 18 junio 2003. ISSN 0254-0703. http://www.icold-cigb.org/

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