Mineralogical Characterization of Dolomitic Aggregate Concrete: the Camarasa Dam (Catalonia, Spain)
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minerals 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]. Minerals 2020, 10, 117; doi:10.3390/min10020117 www.mdpi.com/journal/minerals Minerals 2020, 10, 117 2 of 13 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. Minerals 2019, 9, x FOR PEER REVIEW 4 of 13 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.