Mineralogical Characterization of Dolomitic Aggregate Concrete: the Camarasa Dam (Catalonia, Spain)

Article Mineralogical Characterization of Dolomitic Aggregate Concrete: The Camarasa Dam (Catalonia, Spain)

Encarnación Garcia 1 , Pura Alfonso 2,* and Esperança Tauler 3 1 Departament d’Enginyeria Electrònica, Escola d’Enginyeria de Barcelona Est (EEBE), Universitat Politècnica de Catalunya Barcelona Tech, Av. d’Eduard Maristany 16, E-08019 Barcelona, Spain; [email protected] 2 Departament d’Enginyeria Minera, Industrial i TIC, Universitat Politècnica de Catalunya Barcelona Tech, Av. Bases de Manresa 61-63, 08242 Manresa, Barcelona, Spain 3 Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona, Carrer Martí i Franquès s/n, 08028 Barcelona, Spain; [email protected] * Correspondence: [email protected]; Tel.: +34938777292

Received: 31 December 2019; Accepted: 26 January 2020; Published: 29 January 2020

Abstract: The Camarasa Dam was built in 1920 using dolomitic aggregate and Portland cement with two different compositions: type A (dolomite and Portland cement) and type B (dolomite and sand-cement). The sand cement was a finely powdered mixture of dolomite particles and clinker of Portland cement. The mineralogy of concrete was studied by optical microscopy, scanning electron microscopy, and x-ray powder diffraction. Reaction of dedolomitization occurred in the two types of concrete of the Camarasa Dam, as demonstrated by the occurrence of calcite, brucite, and/or absence of portlandite. In the type A concrete, calcite, brucite, and a serpentine-group mineral precipitated as a rim around the dolomite grains and in the paste. The rims, a product of the dedolomitization reaction, protected the surface of dolomite from the dissolution process. In type B concrete, in addition to dolomite and calcite, quartz and K-feldspar were present. Brucite occurred in lower amounts than in the type A concrete as fibrous crystals randomly distributed in the sand-cement paste. Although brucite content was higher in the type A concrete, type B showed more signs of loss of durability. This can be attributed to the further development of the alkali-silica reaction in this concrete type.

Keywords: dolomite; sand-cement; concrete; dedolomitization reaction

1. Introduction Concrete made of dolomite aggregate, has been the source of problems such as expansion and cracking [1–7]. Traditionally, these deterioration problems were associated with the alkali-carbonate reaction (ACR) [8,9], which is produced when dolomitic rocks with clay minerals are used as aggregates or as a result of the reaction of dolomite with cryptocrystalline quartz [10]. Several dams, built with carbonate aggregates, exhibit signs of deterioration such as the Bimont Dam in France, constructed with dolomitic limestones [11], and the Chickamagua Powerhouse Dam in Tennessee [12]. Dolomite aggregate in the presence of hydrated Portland cement paste produces the dedolomitization Reaction (1):

CaMg(CO ) + Ca(OH) 2CaCO + Mg(OH) 3 2 2 → 3 2 (1) dolomite portlandite calcite brucite

Dolomite reacts with the portlandite of the cement paste to produce calcite and brucite. The kinetics of this reaction have been studied in diﬀerent alkaline media, temperatures, and silica content [13–16].

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The occurrence of the ACR can be checked using a combination of different techniques. Petrographic study is a preliminary test to evaluate the reactive potential of the aggregates and to identify the location of the chemical reactions [17]. The morphological characteristics of the aggregate particles and their textures have an important role in the properties and durability of concrete [18–20]. The effective reactive surface area is a critical parameter to the kinetics and depends on the surface morphology, surface roughness, and internal structure (dislocation density, impurities, point defects) of the mineral representing highly localized dissolution [21]. For this, accelerated testing of mortar specimens is usually used to determine the reactive aggregates [22,23]. However, the study of dolomitic concrete from old constructions could be a real study case that contributes with data to understand this reaction. At the beginning of the 20th century, several dams were built with a new agglomerate called sand-cement. Sand-cement was patented in Copenhagen in 1893, and consisted of 45 wt% of siliceous particles and 55 wt% of clinker of Portland cement, powdered up to less than 0.1 mm in size [24]. The concrete performed with this new product was largely investigated in the USA, where good mechanical properties were reported: impermeability, low drying shrinkage because of the short increase of temperature, and low setting time [25]. Other advantages of the sand-cement were that it was cheaper than the Portland cement and was obtained in the manufacturing plant of the dam. The new agglomerate was used to construct dams such as Arrowrock in 1915 and Elephant Butte in 1916, in the USA and Camarasa in 1920 and Tranco de Beas in 1934 in Spain. The Camarasa water reservoir is used for water storage and the production of hydroelectric power. It is a 92 m high gravity dam. When it was constructed between 1917 and 1920 [26], it was the first in Europe and the fourth in the world in height. The Camarasa concrete was made with a binder material used for building several dams at that time named sand-cement. This was constituted by dolomitic fine particle aggregates. In the present work, the petrography and mineralogical composition of concrete from the Camarasa Dam was studied, a hundred years after its construction, to assess the development of the ACR and thus, the concrete durability. The Camarasa Dam can be considered as a natural laboratory to study the reaction of dedolomitization in concrete. The characterization of this concrete can illustrate the behavior of an ancient hydraulic construction made of dolomitic aggregate and of sand-cement composed of a high fraction of very small particles of dolomite, which, in an alkaline media, are highly reactive.

2. Materials and Methods

2.1. Materials The Camarasa Dam was constructed with Portland cement and dolostones in its vicinity. It is located on the Noguera-Pallaresa channel river, just before the conﬂuence with the Segre River (Figure1). This area is constituted of Jurassic carbonated rocks of the Mesozoic Tremp Basin in the marginal Sub-Pyrenean Zone (Spain). The dam is hosted in dolomitic rocks constituted by massive dark beds, with abundant dissolution cavities ﬁlled of calcite crystals, up to one cm in size [27]. The raw dolostones exhibit a sparitic texture with dolomite subhedral crystals of up to 1.0 mm in size. They are composed of almost pure dolomite, with less than 1 wt% of calcite (Figure2). Calcite is not homogenously distributed; it constitutes interstitial cement or is located in the rims around the dolomite crystals; occasionally dolomite crystals are surrounded by calcite crystals formed by a dedolomitization process. The raw rocks were crushed and selected according its grain size at the manufacturing plant located beside the dam, at a higher level to transport the materials by gravity. Several blocks of dolostones (15% of the total volume of concrete), were deposited in the basis and in the inner parts of the dam in order to increase the whole density and make the structure more stable [26]. According to the dose, two types of concrete, A and B, were used for the construction of the Camarasa Dam (Figure1b). The basis of the dam was built with 32.559 m 3 of type A concrete, composed of 9 wt% of Portland cement and 91 wt% of dolomitic aggregate. Minerals 2019, 9, x FOR PEER REVIEW 3 of 13

According to the dose, two types of concrete, A and B, were used for the construction of the Minerals 2020, 10, 117 3 of 13 Camarasa Dam (Figure 1b). The basis of the dam was built with 32.559 m3 of type A concrete, composed of 9 wt% of Portland cement and 91 wt% of dolomitic aggregate.

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The x-ray powder diffraction (XRPD, Siemens AG, Munich, Germany) was used to determine the mineral phases present in the concrete. Measurements were performed in a Bragg-Brentano θ2θ Siemens D-500 diffractometer (radius = 215.5 mm) with Cu Kα radiation, selected by means of a secondary graphite monochromator. The divergence slit was 1° and the receiving slit of 0.15°. The step size was 0.05° 2θ and the measuring time was 10 seconds per step. For the calculation of the mineral phase contents, the quantitative Rietveld analysis method with the FULLPROF program [28] was used. The analyses were made at the CCiTUB. Figure 1. ((a)) View of the Camarasa Dam; ( b), sketch with the distribution of the two concrete types 3. Results(modified(modiﬁed from [[26]26] andand thethe locationlocation ofof thethe corescores (black(black lines)lines) andand samplessamples (red)).(red)).

Later, in order to reduce the costs, the Portland cement was substituted by the sand-cement 3.1. RawLater, Dolostones in order to reduce the costs, the Portland cement was substituted by the sand-cement mixture, and 183.839 m3 of type B concrete were used to ﬁnish building the dam [27]. The total mixture, and 183.839 m3 of type B concrete were used to finish building the dam [27]. The total compositionThe rocks of used this concreteas aggregates consisted were of mainly 5.2 wt% consti of Portlandtuted by cement dolomite and up 94.8 to 89 wt% wt% of dolomite.and calcite The up composition of this concrete consisted of 5.2 wt% of Portland cement and 94.8 wt% of dolomite. The sand-cementto 11 wt% (Figure used 2). in The this occurrence dam was a of homogeneous calcite is the mixtureresult of ofthe 55 dedolomitization wt% of clinker of process Portland of the cement raw sand-cement used in this dam was a homogeneous mixture of 55 wt% of clinker of Portland cement anddolostones 45 wt% before of dolomite being poundedexploited. together Brucite upwas to been less thanobserved 0.13 mm in any in size. case. The composition of the two and 45 wt% of dolomite pounded together up to less than 0.13 mm in size. The composition of the concreteUnder types the ismicroscope, presented inthe Table dolomite1. crystals exhibited a turbid appearance due to the content of two concrete types is presented in Table 1. abundantThe concrete internal was inclusions studied forming in ten drill dark cores and of clear 55 mm bands, in diameter, or a zebra obtained texture in 1998(Figure by the3). electricCalcite The concrete was studied in ten drill cores of 55 mm in diameter, obtained in 1998 by the electric powerconstituted company, the interstitial owner of cement the dam. or was located in the rims around the dolomite crystals (Figure 3b) poweror in grains company, of dolomite owner inof the naturaldam. process of dolomitization forming path textures.

Table 1. Composition of type A and type B concrete [26].

Component Particle Size (mm) Type A (wt%) Type B (wt%) Dolomitic aggregate 10–150 - 66 Dolomitic aggregate 10–70 62 - Dolomitic aggregate 1–10 13 12 Dolomitic aggregate 0.1–1 12.2 10.8 Dolomitic aggregate <0.1 3.8 6 Portland cement 9.0 5.2

2.2. Analytical Methods Thin sections were made from the cores with non-aqueous polishing fluids and epoxy resin adhesives to prevent the dissolution of mineral phases. Several thin sections were stained with Alizarin Red S+ Potassium to evaluate the composition of carbonate minerals. ThinFigure sections 2. XRPD were (X-ray(x-ray studied powder powder by diffraction) di electronicﬀraction) pattern micros ofcopy the dolostones with x-ray used energy as aggregates dispersive to spectroscopy make the (SEMCamarasa + EDS); images concrete. and qualitative analyses were produced using a Leika Stereoscan 360, an ESEM Quanta 200 FEI, XTE 325/D8395 and a field emission scanning electron microscope JEOL JSM-7001F at the Serveis Científics i Tecnològics de la Universitat de Barcelona (CCiTUB).

Figure 3. Textures of raw dolomitic rocks: (a) The most abundant dolomite aggregates with a zebra texture. (b) The dolomite rock dyed with a solution of Alizarin Red S + 0.9g showed natural dedolomitization; the red matrix is calcite.

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Table 1. Composition of type A and type B concrete [26].

Minerals 2019, 9, x FOR PEER REVIEW 4 of 13 Component Particle Size (mm) Type A (wt%) Type B (wt%) The x-rayDolomitic powder aggregate diffraction (XRPD, 10–150 Siemens AG, Munich, -Germany) was used 66 to determine the mineralDolomitic phases present aggregate in the concrete. 10–70 Measurements were performed 62 in a Bragg-Brentano - θ2θ Siemens D-500Dolomitic diffractometer aggregate (radius = 215.5 1–10 mm) with Cu Kα 13 radiation, selected 12 by means of a secondaryDolomitic graphite monochromator. aggregate The divergence 0.1–1 slit was 1° 12.2 and the receiving 10.8 slit of 0.15°. The Dolomitic aggregate <0.1 3.8 6 step size was 0.05° 2θ and the measuring time was 10 seconds per step. For the calculation of the Portland cement 9.0 5.2 mineral phase contents, the quantitative Rietveld analysis method with the FULLPROF program [28] was used. The analyses were made at the CCiTUB. 2.2. Analytical Methods 3. Results Thin sections were made from the cores with non-aqueous polishing fluids and epoxy resin adhesives3.1. Raw to preventDolostones the dissolution of mineral phases. Several thin sections were stained with Alizarin Red S+ Potassium to evaluate the composition of carbonate minerals. The rocks used as aggregates were mainly constituted by dolomite up to 89 wt% and calcite up Thin sections were studied by electronic microscopy with x-ray energy dispersive spectroscopy to 11 wt% (Figure 2). The occurrence of calcite is the result of the dedolomitization process of the raw (SEMdolostones+ EDS); images before being and qualitative exploited. Brucite analyses was were been producedobserved in using any case. a Leika Stereoscan 360, an ESEM Quanta 200Under FEI, the XTE microscope, 325/D8395 the and dolomite a field crystals emission exhibi scanningted a turbid electron appearance microscope due to JEOL the content JSM-7001F of at the Serveisabundant Cient internalíficsi inclusions Tecnològics forming de la Universitatdark and clear de bands, Barcelona or a (CCiTUB).zebra texture (Figure 3). Calcite Theconstituted x-ray powderthe interstitial diffraction cement (XRPD,or was located Siemens in the AG, rims Munich, around Germany)the dolomite was crystals used (Figure to determine 3b) the mineralor in grains phases of dolomite present in in the the natural concrete. process Measurements of dolomitization were forming performed path textures. in a Bragg-Brentano θ2θ Siemens D-500 diffractometer (radius = 215.5 mm) with Cu Kα radiation, selected by means of a secondary graphite monochromator. The divergence slit was 1◦ and the receiving slit of 0.15◦. The step size was 0.05◦ 2θ and the measuring time was 10 seconds per step. For the calculation of the mineral phase contents, the quantitative Rietveld analysis method with the FULLPROF program [28] was used. The analyses were made at the CCiTUB.

3. Results

3.1. Raw Dolostones The rocks used as aggregates were mainly constituted by dolomite up to 89 wt% and calcite up to 11 wt% (Figure2). The occurrence of calcite is the result of the dedolomitization process of the raw dolostones before being exploited. Brucite was been observed in any case. Under the microscope, the dolomite crystals exhibited a turbid appearance due to the content of abundant internal inclusions forming dark and clear bands, or a zebra texture (Figure3). Calcite constituted the interstitial cement or was located in the rims around the dolomite crystals (Figure3b) Figure 2. XRPD (x-ray powder diffraction) pattern of the dolostones used as aggregates to make the or in grainsCamarasa of dolomite concrete. in the natural process of dolomitization forming path textures.

FigureFigure 3. Textures3. Textures of of raw raw dolomitic rocks: rocks: (a) (Thea) Themost most abundant abundant dolomite dolomite aggregates aggregates with a zebra with a zebratexture. texture. (b) ( bThe) The dolomite dolomite rock rock dyed dyed with with a solution a solution of Alizarin of Alizarin Red RedS + S0.9g+ 0.9g showed showed natural natural dedolomitization;dedolomitization; the the red red matrix matrix is is calcite. calcite.

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Minerals 2020, 10, 117 5 of 13 3.2. Concrete Petrography and Mineralogy MineralsType 2019 A, 9 ,and x FOR type PEER B concreteREVIEW can be distinguished by the color of the cement paste: type A is5 light of 13 3.2. Concrete Petrography and Mineralogy grey, whereas type B is dark brown (Figure 4). The visual inspection showed significant differences 3.2.between ConcreteType the A and Petrographytype type A and B concrete and type Mineralogy B canconcrete. be distinguished Type A looked by the more color compact of the cement and was paste: more type resistant A is light to grey,abrasion,Type whereas whereas A and type type the B is Btype darkconcrete B brownconcrete can (Figure be was distinguished more4). The disa visualgreeable. by the inspection color It was of expected, the showed cement significant then, paste: that type the di ffAbehaviorerences is light betweengrey,of the whereas dedolomitization the type type A B and is darkreaction type brown B concrete.would (Figure be Typecons 4). iderablyThe A looked visual different moreinspection compact in the showed two and concrete wassignificant more types. resistantdifferences to abrasion,betweenAggregate whereasthe type particles theA and type fromtype B concrete Bthe concrete. Camarasa was moreType Dam disagreeable.A lookedexhibited more Itan was equantcompact expected, and and angular then,was more that shape, the resistant behavior and did to ofabrasion,not the look dedolomitization weathered.whereas the The type reaction most B concrete abundant would was be aggregatesmore considerably disagreeable. were diff erentgrey-brown It was in the expected, twopartic concreteles then, constituted that types. the behavior of pure of the dedolomitization reaction would be considerably different in the two concrete types. Aggregate particles from the Camarasa Dam exhibited an equant and angular shape, and did not look weathered. The most abundant aggregates were grey-brown particles constituted of pure dolomite grains.

FigureFigure 4.4.FragmentsFragments of of cores cores from from the the Camarasa Camarasa Dam. Dam. (a) ( Typea) Type A concrete; A concrete; (b) type(b) type B concrete; B concrete; (c) core (c) section:core section: the left the half left ishalf made is made up of up type of Btype concrete B concrete and the and right the right half is half type is A. type A.

Aggregate particles from the Camarasa Dam exhibited an equant and angular shape, and did FigureUnder 4.the Fragments microscope, of cores the from type the A Camarasaand type Dam.B co ncrete(a) Type showed A concrete; a random (b) type distribution B concrete; ( cof) the not look weathered. The most abundant aggregates were grey-brown particles constituted of pure differentcore particlesection: thesize left fractions half is made of dolomitic up of type part B concreteicles (Figure and the 5a). right Unconnecte half is typed A.porosity was randomly dolomitedistributed grains. in the paste. The thin sections stained with red alizarin show red rims in the contact betweenUnderUnder the thethe cement microscope,microscope, paste and thethe the typetype particles AA andand of typetype the dolomitic BB concreteconcrete aggregate showedshowed a(Figurea randomrandom 5b). distributiondistribution ofof thethe didifferentﬀerent particleparticle sizesize fractionsfractions ofof dolomiticdolomitic particlesparticles (Figure(Figure5 a).5a).Unconnected Unconnected porosityporosity waswas randomly randomly distributeddistributed inin thethe paste.paste. The thin sections stainedstained with red alizarin show red rimsrims inin thethe contactcontact betweenbetween thethe cementcement pastepaste andand thethe particlesparticles ofof thethe dolomiticdolomitic aggregateaggregate (Figure(Figure5 b).5b).

Figure 5. Microscope image of the Camarasa type A concrete. (a) General view; (b) sample stained with red alizarin that shows a red rim of calcite in the contact dolomite aggregate-paste. dol, dolomite; cal, calcite. FigureFigure 5.5. MicroscopeMicroscope imageimage ofof thethe CamarasaCamarasa typetype AA concrete.concrete. ((aa)) GeneralGeneral view;view; ((bb)) samplesample stainedstained Dolomite and calcite are the major components in the paste of both concrete types. Other withwith redred alizarinalizarin thatthat showsshows aa redred rimrim ofof calcite in the contact dolomite aggregate-paste. dol, dolomite; crystalline phases detected were different in them (Table 2). In order to evaluate the reactions cal,cal, calcite.calcite.

Dolomite and calcite are the major components in the paste of both concrete types. Other crystalline phases detected were different in them (Table 2). In order to evaluate the reactions

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Minerals 2019, 9, x FOR PEER REVIEW 6 of 13 Dolomite and calcite are the major components in the paste of both concrete types. Other crystallineproduced in phases the Camarasa detected were Dam di aggregates,fferent in them we (Tabledescribe2). Inthe order differences to evaluate found the in reactions the chemical produced and inmineralogical the Camarasa characteristics Dam aggregates, of the we two describe concrete the types. differences found in the chemical and mineralogical characteristics of the two concrete types. Table 2. Mineralogical composition of the paste from type A (convectional) and type B concrete (with Tablesand-cement). 2. Mineralogical composition of the paste from type A (convectional) and type B concrete (with sand-cement).Type Sample Calcite Dolomite Quartz Brucite Microcline A Type5bi-1 Sample 35 Calcite Dolomite 52 Quartz - Brucite 13 Microcline - A A5bi-2 5bi-1 27 35 66 52 - - 13 7 - - A AP5bc 5bi-2 56 27 40 66 - 2 7 2 - - B A4a P5bc 16 5666 40 211 2 1 - 6 B 4a 16 66 11 1 6 B B13a 13a 18 1859 59 1515 1 1 7 7 B BP4a P4a 18 1867 67 1111<1 <1 4 4 B BP6a P6a 19 1965 65 1111<1 <1 4 4 B P10a1 18 65 12 <1 5 B BP10a1 P10a2 18 2665 55 1312 1 <1 5 5 B P10a2 26 55 13 1 5 3.2.1. Type A Concrete 3.2.1. Type A Concrete XRPD and SEM show that in the type A cement paste, in addition to dolomite and calcite, a significantXRPD amountand SEM of bruciteshow that and in portlandite the type A was cement also presentpaste, in (Figure addition6). to dolomite and calcite, a

Figure 6. XRPD pattern of the cement paste of type A concrete.

EDS analyses of dolomite crystals reveal approximately 25 25 µmµm wide compositional rims rims (Figure (Figure 77).). The chemical composition composition of of mineral mineral phases phases from from th theseese rims rims in in the the contact contact with with the the cement cement paste paste is isMg, Mg, Al, Al, Si-rich Si-rich and and indicates indicates that that their their mineralogy mineralogy is is constituted constituted by by brucite brucite and and a a member member of of the serpentine group mineralsminerals (Figure7 7).). Minerals 2020, 10, 117 7 of 13 Minerals 2019, 9, x FOR PEER REVIEW 7 of 13

Figure 7. (a) Image of a thinthin sectionsection of typetype AA concreteconcrete stainedstained with red alizarin,alizarin, where calcitecalcite is redred stained and dolomitedolomite is notnot stained.stained. (b) BSC-SEM Image ofof twotwo selectedselected zoneszones withwith aggregateaggregate dolomitedolomite particles showingshowing greygrey rims rims of of reaction reaction between between aggregate aggregate particles particles and and cement cement paste; paste; (c) Zoom(c) Zoom of the of rimthe rim on topon top (c,d ()c,d with) with the the mineral mineral phases phases identified identified by by SEM-EDS, SEM-EDS, dolomite dolomite (dol), (dol), calcite calcite (Cal), (Cal), serpentineserpentine d group mineral (Srp-g); (d) zoomzoom ofof thethe imageimage c,c, brucitebrucite (Brc)(Brc) isis detecteddetected byby SEM-EDSSEM-EDS formingforming radialradial aggregates of fibrous crystals or elongated crystals maximum 6 µm; (e,f) Zoom of other rim of dolomite, aggregates of fibrous crystals or elongated crystals maximum 6 µm; (e,f) Zoom of other rim of dolomite, where elongated brucite crystals appears in contact with a cryptocrystalline serpentine-group mineral where elongated brucite crystals appears in contact with a cryptocrystalline serpentine-group mineral and calcite crystals with irregular borders. and calcite crystals with irregular borders. 3.2.2. Type B Concrete 3.2.2. Type B Concrete The XRPD of the paste in the type B concrete indicates that the crystalline phases were mainly dolomite,The XRPD calcite, of brucite, the paste quartz, in the and type K-feldspar. B concrete In thisindicates type ofthat concrete, the crystalline portlandite phases was were not detected mainly anddolomite, the contents calcite, of brucite, brucite werequartz, significantly and K-feldspar. lower than In inthis the type type of A concreteconcrete, (Table portlandite2). The presencewas not ofdetected quartz and and the K-feldspar contents was of brucite probably were due significan to the additiontly lower of sandthan in from the the type channel A concrete river and(Table from 2). CretaceousThe presence sandstones of quartz ofand the K-feldspar area during was the probably manufacturing due to the process addition of the of sand-cement. sand from the The channel SEM river and from Cretaceous sandstones of the area during the manufacturing process of the sand- cement. The SEM observations confirm the presence of brucite crystals up to 10 µm in size, with platelets or fibrous habit (Figure 8).

Minerals 2020, 10, 117 8 of 13 observations conﬁrm the presence of brucite crystals up to 10 µm in size, with platelets or ﬁbrous habit Minerals 2019, 9, x FOR PEER REVIEW 8 of 13 (FigureMinerals8 2019). , 9, x FOR PEER REVIEW 8 of 13

Figure 8. (a) Image of a thin section of type B concrete stained with red alizarin; (b,c) SEM images of FigureFigure 8. 8.( a(a)) Image Image of of a a thin thin section section of of type type B B concrete concrete stained stained with with red red alizarin; alizarin; ( b(b,c,c)) SEM SEM images images of of the dolomite- and-cement paste contact in type B concrete with the development of fibrous brucite. thethe dolomitedolomite- and-cement and-cement paste paste contact contact in in type type B B concrete concrete with with the the development development of of ﬁbrous fibrous brucite. brucite. InIn addition,addition, the SEM SEM observations observations also also showed showed th thee occurrence occurrence of ofettringite ettringite and and belite. belite. Some Some illite In addition, the SEM observations also showed the occurrence of ettringite and belite. Some illite illiteelongated elongated crystals crystals were were detected detected by SEM-EDS, by SEM-EDS, and andnests nests of belite, of belite, “bunch “bunch of grapes”, of grapes”, with withdark elongated crystals were detected by SEM-EDS, and nests of belite, “bunch of grapes”, with dark darkhydration hydration rims rims dispersed dispersed in the in the interstitial interstitial comp componentonent or or paste paste could could occa occasionallysionally bebe observedobserved hydration rims dispersed in the interstitial component or paste could occasionally be observed (Figure(Figure9 a),9a), indicating indicating that that the the hydration hydration of of cement cement was was not not complete. complete. Unconnected Unconnected porosity porosity was was (Figure 9a), indicating that the hydration of cement was not complete. Unconnected porosity was randomlyrandomly distributeddistributed inin thethe paste.paste. MostMost cavitiescavities exhibitedexhibited recrystallizationrecrystallization rimsrims oror werewere totallytotally oror randomly distributed in the paste. Most cavities exhibited recrystallization rims or were totally or partiallypartially ﬁlled filled of of calcite, calcite, ettringite, ettringite, or or portlandite portlandite (Figure (Figure9b). 9b). partially filled of calcite, ettringite, or portlandite (Figure 9b).

FigureFigure 9. 9.Backscattered-Scanning Backscattered-Scanning ElectronElectron MicroscopyMicroscopy imageimage ofof typetype BB concrete. concrete. (a(a)) Elongated Elongated illite illite Figure 9. Backscattered-Scanning Electron Microscopy image of type B concrete. (a) Elongated illite crystalcrystal showingshowing exfoliationexfoliation planes,planes, nodulesnodules ofof belite, belite, and and dolomite dolomite particles particles showing showing rhombohedral rhombohedral crystal showing exfoliation planes, nodules of belite, and dolomite particles showing rhombohedral exfoliationexfoliation imbibed imbibed in in the the cement cement paste; paste; ( b(b)) regular regular distribution distribution of of dolomite dolomite particle particle of of aggregate aggregate and and exfoliation imbibed in the cement paste; (b) regular distribution of dolomite particle of aggregate and ﬁbrousfibrous crystals crystals of of ettringite ettringite ﬁlling filling a a pore pore imbibed imbibed in in the the cement cement paste. paste. fibrous crystals of ettringite filling a pore imbibed in the cement paste. 4. Discussion 4. Discussion 4. Discussion The absence of brucite in the dolomitic rocks and its occurrence in the two types of concrete The absence of brucite in the dolomitic rocks and its occurrence in the two types of concrete indicatesThe thatabsence the dedolomitization of brucite in the reaction dolomitic took rocks place and in theits concreteoccurrence from in thethe Camarasatwo types Dam. of concrete In the indicates that the dedolomitization reaction took place in the concrete from the Camarasa Dam. In typeindicates A concrete, that the the dedolomitization reaction occurred reaction on the surface took place of the in dolomite the concrete aggregates, from the whereas Camarasa in the Dam. type BIn the type A concrete, the reaction occurred on the surface of the dolomite aggregates, whereas in the concrete,the type theA concrete, reaction the mainly reaction took occurred place in theon sand-cementthe surface of pastethe dolomite and in the aggregates, dolomite whereas grain borders, in the type B concrete, the reaction mainly took place in the sand-cement paste and in the dolomite grain althoughtype B concrete, Blanco etthe al. reaction [29] attributed mainly a took geological place in origin the sand-cement to the occurrence paste of and brucite in the in dolomite the Camarasa grain borders, although Blanco et al. [29] attributed a geological origin to the occurrence of brucite in the Damborders, concrete. although Blanco et al. [29] attributed a geological origin to the occurrence of brucite in the Camarasa Dam concrete. CamarasaIn the reactionDam concrete. of dedolomitization, two processes are involved: the dissolution of dolomite and In the reaction of dedolomitization, two processes are involved: the dissolution of dolomite and portlanditeIn the andreaction the precipitation of dedolomitization, of new phases two processe of brucites are and involved: calcite. The the reaction dissolution of dedolomitization of dolomite and portlandite and the precipitation of new phases of brucite and calcite. The reaction of dedolomitization portlandite and the precipitation of new phases of brucite and calcite. The reaction of dedolomitization proceeds until the consumption of portlandite [15]. The dissolution rate of dolomite depends on the proceeds until the consumption of portlandite [15]. The dissolution rate of dolomite depends on the mineral surface, which, in turn, depends on the particle sizes, and controls the kinetics of the reaction mineral surface, which, in turn, depends on the particle sizes, and controls the kinetics of the reaction [14,20]. The most reactive dolomite aggregate was the finest fraction, <0.13 mm in the concrete of the [14,20]. The most reactive dolomite aggregate was the finest fraction, <0.13 mm in the concrete of the

Minerals 2020, 10, 117 9 of 13 proceeds until the consumption of portlandite [15]. The dissolution rate of dolomite depends on theMinerals mineral 2019, 9 surface,, x FOR PEER which, REVIEW in turn, depends on the particle sizes, and controls the kinetics of9 of the 13 reaction [14,20]. The most reactive dolomite aggregate was the ﬁnest fraction, <0.13 mm in the concrete ofCamarasa the Camarasa Dam. Dam.The two The types two types of concrete of concrete exhibited exhibited differences diﬀerences in the in thecontent content of ofthis this fraction fraction of ofdolomite dolomite aggregates. aggregates. In Inthe the type type B Bconcrete, concrete, all all of of the the dolomite dolomite particles particles of this fractionfraction werewere constituentsconstituents ofof thethe sand-cementsand-cement andand werewere dispersed dispersed in in the the Portland Portland cement. cement. InIn thethe typetype AA concrete,concrete, thethe occurrenceoccurrence ofof portlanditeportlandite inin thethe pastepaste indicatesindicates thatthat thisthis reactionreaction cancan 22++ − stillstill taketake place.place. TheThe MgMg removed from dolomitedolomite waswas accomplishedaccomplished withwith thethe OHOH− from portlandite,portlandite, andand brucitebrucite precipitatesprecipitates asas aa rimrim aroundaround the the partially partially dissolved dissolved dolomite dolomite grains grains (Figure (Figure 10 10).).

Figure 10. (a) Image of a thin section of the type B concrete stained with red alizarin; (b) SEM images Figure 10. (a) Image of a thin section of the type B concrete stained with red alizarin; (b) SEM images of type B concrete that show the development of calcite and a rim of a serpentine group mineral; (c,d) of type B concrete that show the development of calcite and a rim of a serpentine group mineral; (c,d) details of this rim; (e) development of brucite in the sand-cement paste. details of this rim; (e) development of brucite in the sand-cement paste. In addition to the precipitation of brucite, the dissolution of the Si, Al-rich phases of the cement In addition to the precipitation of brucite, the dissolution of the Si, Al-rich phases of the cement paste removes the aluminum and silicon that substitute the Mg2+ from brucite. In this case, in order 2+ paste removes the aluminum and silicon that substitute the Mg from brucite.2 In this case, in order to balance the electrical charges, a coupled substitution of OH− by CO3 − and a Mg rich rim is to balance the electrical charges, a coupled substitution of OH− by CO32− and a Mg rich rim is formed formed [30,31]. This rim constitutes a barrier that makes the dissolution of the dolomite aggregates [30,31]. This rim constitutes a barrier that makes the dissolution of the dolomite aggregates difficult, difficult, as a result, the reaction of dedolomitization slows down [14,32,33]. as a result, the reaction of dedolomitization slows down [14,32,33]. 2 2+ In the reaction of dedolomitization, calcite is formed from the CO3 − and one Ca provided by In the reaction of dedolomitization, calcite is formed from the CO32− and one Ca2+ provided by the dissolution of dolomite, and another Ca2+ provided by portlandite located in the cement paste. the dissolution of dolomite, and another Ca2+ provided by portlandite located in the cement paste. Then, most calcite is formed, not in direct contact with the dolomite aggregate, but in the contact Then, most calcite is formed, not in direct contact with the dolomite aggregate, but in the contact point between the brucite rim and cement paste. A similar distribution of the products of the reaction point between the brucite rim and cement paste. A similar distribution of the products of the reaction of dedolomitization was obtained in experiments performed with a dolomite crystal immersed in of dedolomitization was obtained in experiments performed with a dolomite crystal immersed in an an alkaline portlandite-rich solution [14]. In that case, brucite precipitated attached to the dolomite alkaline portlandite-rich solution [14]. In that case, brucite precipitated attached to the dolomite surface while most calcite precipitated in the solution. surface while most calcite precipitated in the solution. In the type B concrete, the reaction of dedolomitization took place early, due to the high reactive In the type B concrete, the reaction of dedolomitization took place early, due to the high reactive surface of dolomite particles in the sand-cement paste. In this concrete, portlandite is dissolved and the surface of dolomite particles in the sand-cement paste. In this concrete, portlandite is dissolved and OH anions are quickly trapped by the Mg2+ provided by dolomite in the sand-cement paste. Thus, the− OH− anions are quickly trapped by the Mg2+ provided by dolomite in the sand-cement paste. Thus, brucite precipitates as fibrous crystals distributed in the sand-cement paste. The reaction consumes all brucite precipitates as fibrous crystals distributed in the sand-cement paste. The reaction consumes available portlandite, and then, the coarser particles of dolomite aggregate will not be affected by the all available portlandite, and then, the coarser particles of dolomite aggregate will not be affected by dedolomitization reaction. This process was also suggested for the dedolomitization reaction in batch the dedolomitization reaction. This process was also suggested for the dedolomitization reaction in experiments of dolomite dispersion in alkaline media [14]. batch experiments of dolomite dispersion in alkaline media [14]. Although the dedolomitization reaction occurred in both types of concretes, the visual inspection showed slight differences between types A and B, where A looked more compact than type B. The matrix of type B appeared more disaggregated and more fragile. However, the dedolomitization reaction was more extended in the conventional, or type A aggregate, as

Minerals 2020, 10, 117 10 of 13

Although the dedolomitization reaction occurred in both types of concretes, the visual inspection showed slight differences between types A and B, where A looked more compact than type B. The matrix of type B appeared more disaggregated and more fragile. However, the dedolomitization reaction was more extended in the conventional, or type A aggregate, as demonstrated by the higher proportion of calcite and brucite, which in turn decreased the binding properties and alkalinity of the matrix. The compression resistance of the cores from Camarasa confirmed these observations. Cabrera Vélez [34] reported mean values of 279.3 kg/cm2 for the concrete of Portland cement and from 148.5 to 220.1 kg/cm2 for concrete made with sand-cement. The parent density of both types of concrete [29] also showed that the alteration in the area that constituted of sand-cement was higher. Brucite has been considered as one of the main factors responsible for the loss of concrete durability [35]. However, in other cases, the highest expansion and loss of durability was attributed to the alkali-silica reaction (ASR) produced by the reactions due to the presence of quartz in the concrete matrix, which can accompany the dolomitic aggregates [36,37]. It can be considered that the concrete of the dam contains an excess of dolomite, whereas the amount of Portland cement, on the other hand, is significantly lower and therefore a limited amount of portlandite and silica gel will be produced. The pore solution in contact with these phases is subsatured in dolomite and CHS, which are thermodynamically unstable in this medium and will be dissolved. The dissolution of these phases produces two basic processes: (1) a dedolomitization reaction, which produces secondary calcite and brucite, and (2) between dolomite and the cement paste, a calcium silicate gel (CHS) gel is present, which reacts with brucite to produce a Mg-silicate gel that crystallizes in a serpentine group mineral. The formation of this mineral phase has also been reported in other concretes of dolomite aggregates [7,36,38].

H Ca Si O + 3Mg(OH) = Mg (Si O )(OH) + Ca(OH) + H O 6 3 2 10 2 3 2 5 4 2 2 (2) CSH brucite serpentine group mineral portlandite

The kinetics of the dedolomitization reaction is controlled by the dissolution of the dolomite and the amount of portlandite available in the system. The reaction occurs very quickly for the smallest particles. For this reason, the mineralogical evolution of the system is qualitatively and quantitatively different in each of the concretes used for the construction of the dam. The use of a concrete made with sand-cement contributes to the system with a particle size fraction of dolomite with an enormous reactive surface that confers to the reaction of dedolomitization a very fast kinetics. This reaction is completed in the sand-cement matrix by replacing the sand-cement paste in the surface, formed by dolomite and portlandite, with a mixture constituted of calcite and brucite. The agglomerating properties of brucite are not good enough and therefore the properties of the mechanical strength of the concrete are slightly diminished, as confirmed by the resistance behavior of the concrete made with sand-cement. Once the dolomite of the paste is consumed, a small fraction of portlandite remains undissolved and is susceptible to react with the larger grain size fractions of particles in the aggregate. In the case of Portland concrete, the proportion of dolomitic aggregates with a reactive surface equivalent to that of the sand-cement dolomite particles was significantly lower. It was observed that the dedolomitization was produced by forming a reaction rim of less than 25 µm in thickness around the dolomite particles, consisting mainly of brucite, calcite, and a gel phase, and that a significant proportion of portlandite remained in the matrix of the concrete. The formation of a reaction rim around the aggregate hinders the dissolution of the dolomite, therefore the reaction occurs very slowly. The gel phase is unstable in the system and evolves in the presence of Mg, forming hydrotalcite and serpentine group mineral, which are more stable in the system. Reaction (2) describes how the gel reacts with brucite, which is the product of the dedolomitization reaction, to form serpentine group mineral. Studies carried out on concretes attacked by magnesium sulfates show that serpentine group minerals have a low binder capacity with an appearance similar to that of the final stages of Minerals 2020, 10, 117 11 of 13 concrete deterioration [30]. In the case of the Camarasa concrete, the magnesium source comes from the dissolution of dolomite and the presence of magnesium sulfate is not necessary. Concrete constituted initially of dolomite and gel of the Portland cement in the appropriate ratios will evolve until reaching the equilibrium state with the formation of calcite and serpentine group mineral. The concrete of the Camarasa Dam has a large excess of dolomite that will not react. Given the reduced agglomerating properties of the serpentine group mineral, its difficulty of formation is rather beneficial, since it allows the gel life of the Portland to be extended. On the other hand, the formation of reaction rims on the surface of the dolomite is also an important factor in delaying the reactions that will produce the degradation of the concrete [39].

5. Conclusions The concrete of the Camarasa Dam is made of aggregates mainly composed of dolomite. According to the dose, two type of concrete are distinguished: type A (dolomite and Portland cement) and type B (dolomite and sand-cement). The ACR occurs in both concrete types of the Camarasa Dam, forming calcite and brucite from the dissolution of dolomite in an alkaline media. In type A concrete, the dedolomitization reaction takes place on the surface of the aggregate particles and stops early, preserving the portlandite of the cement paste. In contrast, in the type B concrete, the reaction occurred in the sand-cement paste and all portlandite available was consumed very early by the dedolomitization reaction. Although the brucite content was higher in type A concrete, type B showed more signs of loss of durability. This can be attributed to the greater development of the ASR in this concrete type. In order to prevent the ACR, it is proposed that fractions smaller than 1 mm of the dolomite aggregate in the concrete are avoided completely.

Author Contributions: P.A. and E.T. wrote the paper; E.G. did the analytical work. All authors contributed to data interpretation and discussion. All authors have read and agreed to the published version of the manuscript. Funding: This research was sponsored by the CICYT Spanish research project MAT2002-3345 and contract RED99-57. We thank ENDESA for providing the samples. The research was supported by the SGR-198 and SGR-707 of the Generalitat de Catalunya. Acknowledgments: The SEM and electron microprobe analyses were performed at the Serveis Científico-Tècnics (SCT) de la Universitat de Barcelona with the assistance of R. Fontarnau, A. Domingo, and X Llovet. X-ray diffraction analyses were performed at the X-ray unit at the SCT (X. Alcobé). E. Garcia acknowledges the receipt of a FPU fellowship from the Spanish Ministerio de Educación y Cultura. Conflicts of Interest: The authors declare no conflicts of interest.

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