Pedro Maiza

Zeolite crystallization in portland cement concrete due to alkali-aggregate reaction

Abstract Concrete used in works and altered by alkali-aggregate reaction was studied in order to identify the reaction products. For this purpose, the methods of petrographic microscopy, XRD and SEM were employed. The crystalline forms observed by SEM were later determined through the petrographic microscope, as being zeolites on the basis of their optical properties and confirmed by XRD. In order to obtain a minimum amount (10 mg) of the reaction product, many thin sections were prepared. The product was isolated under the microscope for XRD analysis, through which it was identified as being a zeolite (heulandite-clinoptilolite group). With the aim of determining the minimum limits capable of being registered by XRD, tests with the addition of 1, 5 and 10 % of a similar natural zeolite (clinoptilolite) were also performed on a concrete sample, showing that 5 % is about the minimum.

Deteriorated pavements due to the alkali–silica reaction: A petrographic study of three cases in Argentina

Abstract Deteriorated concrete pavements from three regions in Argentina were studied. The aim was to evaluate aggregate constituents, especially the presence of deleterious components, determine what reaction products had developed, and find the main causes of the deterioration based on the petrographic study of the concrete. Thin sections were analyzed with a petrographic microscope to evaluate microcracking, characteristics of the aggregate–cement interface, reaction rims, and the development of reaction products. The latter were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDAX). Pavements exhibit widespread microcracking with the development of crystalline materials at the aggregate rims, identified as zeolite-like structures by XRD. From the EDAX analysis, Si, Al, O, Ca, K, and Na were determined. Ettringite is abundant both inside cavities and on crack surfaces within concrete. Its occurrence was confirmed by XRD and EDAX. The aggregate deleterious constituents are mainly glassy vulcanites and volcanic glass, generally altered to argillaceous minerals, and strained quartz, with undulatory extinction. The deterioration of the three pavements studied was due to the development of the alkali–silica reaction (ASR), involving the strained quartz.

Secondary ettringite formation in concrete subjected to different curing conditions

Abstract The large amount of ettringite detected in concrete affected by different failure mechanisms (alkali-silica reaction [ASR], freezing and thawing [FT], and wetting and drying [WD]) in sulfate-free environments has been a matter of concern for many researchers over the past years. Two major lines to approach this issue have been defined. One of them considers ettringite as the main cause of damage and the other assumes that it appears after concrete distress. In order to contribute to the clarification of this phenomenon, research was conducted to cover the above issues. This paper reports on the conclusions arrived at up to date, from studies conducted on concrete affected by different damaging mechanisms: FT, WD, and precracking induced by loading and ASR. Changes in length and mechanical strength of test concrete are reported, as well as the evaluations made by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). Secondary ettringite formation (SEF) is closely linked to pore fluid transport in the mass of concrete. Although it was not possible to define clearly its participation in the damaging processes related to ASR or to FT, secondary ettringite crystallization in concretes subjected to WD cycles seems to be one of the most likely mechanisms to account for the volumetric instability observed in these concretes.

Origin of kaolin deposits in the ‘Los Menucos’ area, Río Negro Province, Argentina

Abstract Kaolinite deposits, hosted by rhyolitic tuffs, are found in the SE of the ‘Los Menucos’ area (Province of Río Negro, Argentina). The most representative examples are from the Blanquita and Equivocada mines. To discover the origin of these deposits, a mineralogical, geochemical (major and trace element) and stable isotope study (O and H) of kaolinite was carried out. Mineralogically, Blanquita mine is characterized by the presence of dickite, kaolinite, alunite and pyrophyllite, whereas in Equivocada mine, kaolinite is accompanied by dickite and traces of alunite (without pyrophyllite). The trace element contents and ratios of kaolin samples (P vs. S, Zr vs. Ti, (Cr + Nb) vs. (Ti + Fe), and (Ce + Y + La) vs. (Ba + Sr)) suggest that they formed from the hydrothermal alteration of the enclosing rhyolites although a possible contribution of kaolinite from residual processes cannot be discounted. δ18O values of kaolinite range from + 4.8 to +10.3‰, and δD varies from - 88 to - 116‰. The presence of pyrophyllite in Blanquita mine suggests temperatures of formation >350°C. The calculated isotopic composition of the fluid in equilibrium with kaolinite at 350°C varies from + 3.6 to + 9.2‰ for O and from - 74 to - 103‰ for H. These values are compatible with fluids of magmatic origin or with fluids of surficial origin isotopically equilibrated with a rhyolitic magma at high temperatures. The isotope composition of kaolinite from the Blanquita and Equivocada mines is clearly different from kaolinite of residual origin from deposits in the Chubut and Santa Cruz provinces. The isotopic signature has proved to be a useful tool in discriminating between different genetic processes in the formation of kaolin deposits.

Statistical analysis of geochemical data: a tool for discriminating between kaolin deposits of hypogene and supergene origin, Patagonia, Argentina

Abstract The numerous kaolin deposits located in Patagonia, Argentina, have been formed by hypogene or supergene processes. The primary origin has been established from O18 and D isotopic composition of the main minerals, kaolinite and/or dickite, and from the behaviour of certain elements during the alteration. The aim of this paper was to find if there is a tool, other than oxygendeuterium data, to establish the origin of the Patagonian kaolin deposits. To handle the large number of variables per sample, a statistical multivariate study was used. The Principal Component method defines, on one hand the variables that better characterize each deposit and, on the other hand, the correlation between them. Fifty seven elements were considered and those that were not explained using these two components (which represent 75% of the total variance of the model) were discarded. As a result, the contents of Fe2O3, P2O5, LOI, Sr, Y, Zr, V, Pb, Hf, Rb, S and REE were used and the results show that the two components separate the deposits into two fields that are consistent with the process of formation. The first component indicates that Fe2O3, Y, Rb, U and HREE are more abundant in the supergene deposits, whereas, Sr, Pb, S and V are more abundant in the hypogene deposits. The second component shows that S, P2O5 and the LREE are enriched in the hydrothermal deposits, whereas Zr is more abundant in those formed under weathering conditions.

The alkali-carbonate reaction and its reaction products an experience with Argentinean dolomite rocks

Abstract Three dolomitic rocks from Argentina were studied under different test conditions (ASTM C 586, ASTM C 227, CSA A23.2–14A, powdered rock samples immersed in strong alkali solutions). X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM) analyses of the various reaction products detected under these conditions are presented. Results are compared with the alkali expansivity of the dolomitic rocks and are also used to discuss the scope and applicability of the different reaction mechanisms proposed in the literature. It has been concluded from this research that the mechanism originally proposed by Hadley is adequate to explain the reaction mechanisms that operate in concrete structures under natural service conditions.

Halloysite in Argentinian deposits: origin and textural constraints

Abstract In Argentina, the only halloysite deposits found so far are located in the southwest of the province of Rio Negro. The areas are named Mamil Choique and Buitrera, separated by 50 km in a W-E direction. The deposits are located in pyroclastic rocks, rhyolitic tuffs and ignimbrites. The aim of this paper is to determine the origin of the alteration, any relationship between the processes in Mamil Choique and Buitrera, and the factors which controlled the halloysite formation. The work was based on field work, mineralogical and geochemical studies, form and distribution of the alteration. Fresh as well as altered rocks were collected. The first were studied by petrographic and chemical methods. In altered samples, the clay mineralogy was determined by XRD and textures by SEM and TEM. Chemical analyses on fresh and altered samples were used to characterize the alteration process and the rock composition. It was concluded that halloysite has been formed by weathering in a time range from Middle Eocene to Middle Oligocene and extended along 50 km in a W-E direction, independent of the source rock. Particle morphology depends on the original texture of the rock. Spheroidal halloysite is related to rocks with low porosity and tubular particles are related to rocks with open spaces.

Alkali silica reaction in basaltic rocks NBRI method

Abstract In Argentina there are large quarries of basaltic rocks that are used as concrete aggregate. Some structures, made with basalts from the quarries in the Northwest, have shown signs of Alkali Silica Reaction (ASR). This paper presents the results of the behavior of this kind of rock applying the test method proposed by van Aardt and Visser (NBRI). The products of the reaction originated in the test are also studied using the optical microscope. Zeolites are the principal material observed. Results indicate that the principal material involved in the ASR is montmorillonite (or smectite) that is disseminated in the mass of the basalt.

Alteration zonation in the Loma Blanca kaolin deposit, Los Menucos, Province of Rio Negro, Argentina

Abstract The Loma Blanca mine is in one of the northwest kaolinized zones of the Los Menucos area (Patagonia, Argentina). The parent rocks are andesites and andesitic tuffs from the Vera Formation, Los Menucos Group (Lower Triassic). Hayase & Maiza (1974) proposed a concentric zonation model. From the parent rock outward, four different alteration patterns were recognized: Zone 1, with sericite, chlorite and montmorillonite; Zone 2, with kaolinite and dickite; Zone 3, with dickite, pyrophyllite and alunite; and Zone 4, with quartz, disseminated sulphides and diaspore. The relationship between the chemical composition of major, minor and trace elements and the mineralogical alteration zonation was evaluated to confirm the genesis of the deposit. Fe2O-, CaO, Na2O and K2O contents decrease from Zone 1 to Zone 3, whereas Al2O3 and LOI increase in the kaolinite-alunite zone. In the chemical composition of alunite, Na > K. Large Ba, Sr, V and Zr contents were observed mainly in Zones 2 and 3. Co, Ni, Cu, Zn and Rb are more common in Zone 1. LREE are more abundant than HREE in Zones 2 and 3. In kaolinites, δ18O values range from 10.8‰ to 13.2‰, and δ D from −83‰ to −85‰. The mineral assemblage (dickite-alunite-pyrophyllite-diaspore), the alteration zonation pattern (laterally concentric), the geochemistry of trace elements, the relation between LREE and HREE and the small δ18O values suggest that the Loma Blanca deposit was formed by hydrothermal processes.

Mineralogy and geochemistry of hydrothermal kaolins from the Adelita mine, Patagonia (Argentina); relation to other mineralization in the area

Abstract The kaolin deposit at the Adelita mine, located in the province of Río Negro (Patagonia, Argentina), was studied. Petrographic studies on thin sections and chemical analyses of major, minor and trace elements on bulk samples were carried out. The kaolin content of the rock ranges from 31% to 65%. The mineralogy of the working front, which is about 45 m thick, varies from the upper zone, where the rock is strongly silicified, stained with iron oxides and carbonated, grading downwards to a kaolinized zone, with a quartz-kaolinite-dickite assemblage with relict lithic particles and a smaller amount of iron oxides, and ending in the deepest zone where dickite, alunite, diaspore, quartz and scarce associated kaolinite occur. The kaolin mineralogy was determined by SEM, XRD, DTA-TG, IR and δ18O and δD isotope analyses. The S, Ba and Sr contents are enriched during hydrothermal alteration, whereas Cr, Nb, Ti and lanthanide elements are concentrated mainly during weathering. The (Ba+Sr) concentrations in the samples studied vary between 600 and 6000 ppm and (Ce+Y+La) between 2 and 150 ppm; (Cr+Nb) remains constant for all the samples, whereas (TiO2+Fe2O3) is below 0.3%. In the hypogene deposits P2O5 is also more abundant and increases with the degree of alteration. Chondrite-normalized rare earth element diagram shows a marked enrichment in LREE relative to HREE, with negative europium anomalies and δ18O values range between 3.8% and 7.7% and δD between -123% and -103%, suggesting that kaolin formed from the hydrothermal alteration of rhyolitic tuffs.