72 research outputs found

    Productos de neoformaci贸n identificados en prismas y barras de mortero realizados con agregados p茅treos de la provincia de C贸rdoba

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    Los productos de neoformaci贸n vinculados a la reacci贸n 谩lcali-s铆lice, desarrollados en prismas de hormig贸n y barras de mortero, presentan morfolog铆as y composiciones muy variables. Esas variabilidades dependen de un gran n煤mero de factores como el tipo de soluci贸n utilizada, el tiempo de ensayo, el tipo de roca que ha participado en la reacci贸n y las caracter铆sticas microestructurales de la s铆lice presente en estos agregados, la disponibilidad de espacio para la nucleaci贸n y crecimiento de los productos de neoformaci贸n y su interacci贸n con la pasta de cemento, etc. En el presente trabajo se estudian productos de neoformaci贸n desarrollados en barras de mortero (IRAM 1674) y prismas de hormig贸n (IRAM 1700) realizados con triturados p茅treos de la provincia de C贸rdoba a fin de avanzar sobre qu茅 factores influyen en esas variabilidades y de qu茅 manera lo hacen. Las probetas post ensayo fueron estudiadas mediante estereomicroscop铆a, microscop铆a de polarizaci贸n sobre secciones delgadas y microscop铆a electr贸nica de barrido acoplada con espectr贸metro de energ铆a dispersiva (SEM-EDS).Neoformation products associated with alkalisilica reaction, developed in concrete prisms and mortar bars, show variable morphologies and compositions. Those variabilities depend on many factors like the type of solution used, the test time, the rock type that has participated in the reaction and the microestructural characteristics of silica present in these aggregates, the availability of space for nucleation and growth of the neoformation products and their interaction with the cement paste, etc. In this work neoformation products developed in mortar bars (IRAM 1674) and concrete prisms (IRAM 1700) made with crushed stones from the province of C贸rdoba are studied to advance about what factors influence in those variabilities and how they do it. Posttest samples were studied by stereomicroscopy, polarized light microscopy in thin sections and scanning electron microscopy coupled with energy dispersive spectrometer (SEM-EDS)

    Dedolomitization and alkali-silica reactions in low-expansive marbles from the province of C贸rdoba, Argentina

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    Marbles from the province of C贸rdoba (Argentina) have been used as aggregates in concrete; however, there is little information about their potential reactivity and interaction with the cement paste. Recently, the alkali-carbonate reactivity of dolomitic to calcitic marbles from this province was determined by standardized methods (ASTM C1293, ASTM C586, CSA A23.2-26A) and a modification of the Chinese Accelerated Mortar Bar Method (M-CAMBT) using a single aggregate size fraction (2.5鈥5.0 mm). Although all samples behaved as non-reactive some expansion was recorded, especially in the M-CAMBT method. In this work microstructural and chemical studies were carried out by stereomicroscopy, polarizing microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) on mortar bars tested by the M-CAMBT method. Dedolomitization was detected in all dolomitic and calc-dolomitic marbles being more accentuated in the samples with more dolomite. This process is characterized by the development of different zones in the cement鈥揳ggregate interface that differ in texture and chemical composition and are similar to the zones described by other authors in dolomitic limestones typically associated with the so-called alkali鈥揷arbonate reaction. Therefore, the presence and distribution of dedolomitization appears not to be related to the texture of the aggregates but to the amount of dolomite in the rock. The low expansions recorded were associated with relict strained quartz and possibly with fine-grained phlogopite in the matrix of the rocks, which have acted as silica sources for the development of secondary silicates of variable composition (卤Ca 卤 Na 卤 K 卤 Mg 卤 Al) and microfissures as a result of the alkali鈥搒ilica reaction rather than the non-expansive dedolomitization process

    Estudio qu铆mico y microestructural sobre barras de mortero realizadas con m谩rmoles de la provincia de C贸rdoba ensayadas por el m茅todo M-CAMBT

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    En un trabajo previo se estudi贸 la potencial reactividad de m谩rmoles de la provincia de C贸rdoba frente a la reacci贸n 谩lcali-carbonato (RAC) utilizando diferentes m茅todos de ensayo (IRAM 1700, ASTM C586, CSA A23.2-26A y M-CAMBT). Si bien todos los agregados se clasificaron como no reactivos, se registraron algunas expansiones, especialmente en el m茅todo M-CAMBT. A fin de determinar las causas de este comportamiento, se realizaron estudios qu铆micos y microestructurales sobre las barras de mortero post ensayo, mediante estereomicroscop铆a, microscop铆a 贸ptica de polarizaci贸n, microscop铆a electr贸nica de barrido (MEB) y microsonda de electrones (ME). A nivel macrosc贸pico las barras no evidenciaron deterioro. En sectores muy localizados se observ贸 el desarrollo de materiales de neoformaci贸n en cavidades y en microfisuras en la pasta y en la interfase agregado-mortero. A nivel microsc贸pico se observ贸 el desarrollo de bordes de reacci贸n en todos los m谩rmoles dolom铆ticos y calco-dolom铆ticos y fisuras rellenas, asociadas principalmente a agregados con cuarzo tensionado. Los estudios de MEB y ME permitieron asociar los bordes de reacci贸n a procesos de dedolomitizaci贸n (en los m谩rmoles dolom铆ticos y calco-dolom铆ticos) sin evidencias de expansi贸n, siendo m谩s acentuado este proceso cuanto mayor es el contenido de dolomita en la roca. Por otro lado, las fisuras rellenas con materiales de neoformaci贸n, se vinculan a procesos asociados a la reacci贸n 谩lcali-s铆lice (RAS), causados por la inestabilidad del cuarzo tensionado contenido en las mismas. Estos estudios apoyan la teor铆a que las expansiones atribuidas a la RAC son una combinaci贸n de procesos de dedolomitizaci贸n no expansivos y expansiones por RAS producto de la s铆lice reactiva contenida en la matriz de las rocas carbon谩ticas

    Microstructural and chemical study on an expansive dolostone from Argentina

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    An Argentinian fine-grained dolostone has proved to react deleteriously with alkalis following a mechanism similar to ACR. As this reaction is very controversial, the rock was reassessed for going deeper into the knowledge of its reactivity. The effect of the aggregate grain size on mortar expansion was evaluated by comparing RILEM AAR-2麓s test results with those from Lu et al. test method. The inhibiting effect of a high-level replacement of low-calcium fly ash was also tested. The influence of rock porosity was studied on rock and concrete prisms, stored under conditions similar to ASTM C586 and RILEM AAR-3, respectively. Microstructural and chemical studies (mercury porosimetry, polarizing microscopy, XRD, SEM-EDS) were carried out on fresh and tested rock samples. The amount of alkali-silica gel observed was very low to explain mortar or concrete expansion. Fly ash failed to inhibit mortar expansion. The only correlation observed was between concrete expansion and degree of dedolomitization

    Sustainable use of concrete aggregates in Argentina

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    C贸rdoba province (Argentina) produces important quantities of aggregates, especiallyfor concrete structures. Low quality materials can decrease structure鈥檚 Ufe and increment environmental liabilities and the use of quartz- bearing rocks can develop alkali-silica reactions (ASR) which affect concrete durability. Rocks reactivityfrom C贸rdoba was evaluated through standardized methods showing good behaviour due to their favorable textural and microstructural characteristics

    Zeolita, estudio de aptitud como una puzolana natural aplicada a hormig贸n estructural

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    Nowadays, concrete is one of the most widely used construction materials due to its low price, appropriate mechanic characteristics and durability. Also, due to its ease to adopt diverse forms and sizes (Najimi et al., 2012). Owing to the importance in the use of concrete as a structural material and to its impact in the environment as a consumer of great quantities of natural resources and emitter of CO2 in the concrete industry, it is necessary to develop, from the science of materials, mixtures that support the growth of the construction industry and that consider the environment. Therefore, it becomes necessary to develop energetically efficient materials. A natural zeolite was studied as a material with potential pozzolanic activity and as partial replacement in different percentages of Portland cement in structural concrete. The results of the mechanic trials in concrete samples prove the feasibility of using this element as pozzolanic material.En la actualidad, el hormig贸n es uno de los materiales de construcci贸n m谩s ampliamente utilizados debido a su bajo precio, apropiadas caracter铆sticas mec谩nicas y de durabilidad, as铆 como por su facilidad de adoptar diversas formas y tama帽os (Najimi et al., 2012). Debido a la importancia del uso del hormig贸n como material estructural de construcci贸n y a su impacto ambiental como consumidor de grandes cantidades de recursos naturales y emisor de CO2 en la industria del cemento, es necesario desarrollar, desde la ciencia de materiales, mezclas que acompa帽en el crecimiento de la industria de la construcci贸n considerando el medioambiente; es decir, desarrollar materiales energ茅ticamente eficientes. Se estudi贸 una zeolita natural como un material con potencial actividad puzol谩nica y como reemplazo parcial en distintos porcentajes del cemento p贸rtland en hormigones estructurales. Los resultados de ensayos mec谩nicos en hormigones evidencian la factibilidad de utilizar esta adici贸n como material puzol谩nico.Fil: Raggiotti, Barbara Belen. Universidad Tecnol贸gica Nacional. Facultad Regional C贸rdoba. Grupo de Investigaci贸n En Tecnolog铆as de Materiales y Calidad; ArgentinaFil: Positieri, Mar铆a Josefina. Universidad Tecnol贸gica Nacional. Facultad Regional C贸rdoba. Grupo de Investigaci贸n En Tecnolog铆as de Materiales y Calidad; ArgentinaFil: Locati, Francisco. Consejo Nacional de Investigaciones Cient铆ficas y T茅cnicas. Centro Cient铆fico Tecnol贸gico Conicet - C贸rdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de C贸rdoba. Facultad de Ciencias Exactas F铆sicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Murra, Juan Alberto F茅lix. Consejo Nacional de Investigaciones Cient铆ficas y T茅cnicas. Centro Cient铆fico Tecnol贸gico Conicet - C贸rdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de C贸rdoba. Facultad de Ciencias Exactas F铆sicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Marfil, Silvina Andrea. Consejo Nacional de Investigaciones Cient铆ficas y T茅cnicas. Centro Cient铆fico Tecnol贸gico Conicet - C贸rdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de C贸rdoba. Facultad de Ciencias Exactas F铆sicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentin

    Hormig贸n liviano estructural extruido (HLEE): comportamiento de arenas volc谩nicas frente a la reacci贸n 谩lcali-s铆lice

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    En un trabajo previo se estudi贸 la factibilidad de producir un Hormig贸n Liviano Estructural (densidad promedio de ~ 2000 Kg/m3) con arena volc谩nica, colocado mediante m谩quinas extrusoras, desarrollado en el departamento de calidad de la empresa Astori Estructuras S.A. Se moldearon losas alveolares mediante m谩quinas de alto rendimiento las cuales evidenciaron condiciones f铆sico-mec谩nicas aceptables tanto en estado fresco como endurecido. Las losas fueron acopiadas sin ninguna protecci贸n y expuestas a los agentes clim谩ticos durante aproximadamente 3 a帽os. Los agregados livianos utilizados corresponden a fragmentos de pumitas (piedra p贸mez), compuestas por vidrio volc谩nico, un material potencialmente reactivo frente a la reacci贸n 谩lcali-s铆lice (RAS) por ser metaestable y de r谩pida velocidad de reacci贸n. A su vez los agregados gruesos utilizados poseen un alto porcentaje de cuarzo tensionado en su composici贸n. Teniendo en cuenta esto y que los elementos premoldeados podr铆an ser utilizados en sectores expuestos a la intemperie, se llevaron a cabo estudios para establecer posibles deterioros asociados a la RAS. Se realiz贸 una inspecci贸n ocular de los elementos estructurales y luego se extrajeron muestras de diferentes sectores que fueron estudiadas con estereomicroscopio y microscopio 贸ptico de polarizaci贸n sobre secciones delgadas. Finalmente, se determin贸 la densidad del hormig贸n (IRAM 1567) y la resistencia a la flexi贸n (IRAM 11598) de las losas. El hormig贸n se encuentra en buen estado a nivel macrosc贸pico y microsc贸pico, reconoci茅ndose solo escasas microfisuras. Los valores de densidad son similares a los determinados inicialmente y se observ贸 un mejoramiento de la resistencia en los ensayos de flexi贸n. Seg煤n las observaciones realizadas, hasta el momento las losas no presentan deterioros asociados a la RAS posiblemente por el efecto puzol谩nico del material v铆treo de grano fino. La incorporaci贸n de este material habr铆a contribuido no solo en la generaci贸n de elementos estructurales livianos, sino a mejorar las prestaciones del hormig贸n

    Na2O, K2O, SiO2 and Al2O3 release from potassic and calcic鈥搒odic feldspars into alkaline solutions

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    The potential release of elements from potassic and calcic鈥搒odic feldspars into the concrete pore solution was evaluated by ICP-MS using 1 N NaOH and KOH solutions at 80 掳C in accordance with the conditions set in the chemical test method. Materials were characterized by petrography, XRD and by XRF analysis. The influence of textural and microstructural characteristics on the leaching process was also analyzed by immersing polished plates of each mineral in 1 N NaOH at 80 掳C for 7 days. Optical microscope and SEM observations indicate that microstructural characteristics, such as cleavage zones, twins, grain鈥揼rain contact and the finer and less abundant phases in perthites, play a key role in the leaching process under alkaline conditions. Na2O, K2O, SiO2 and Al2O3 are supplied by hydrolysis, although the participation of other processes cannot be ruled out

    Characterization of ASR products in a 40-year-old highway

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    The majority of crushed aggregates utilized in Argentina come from the Sierras Pampeanas of C贸rdoba, (Province of C贸rdoba). Many of the exploited lithologies are quartz-rich and have undergone deformation processes affecting their texture and producing internal microstructures. Previous studies have shown that those characteristics make rocks potentially alkali reactive. In order to compare those results with performance of aggregates in concrete structures, an important highway that links C贸rdoba and Villa Carlos Paz cities was studied. Preliminary results showed that this deterioration could be interpreted as a normal aging of concrete, accelerated by humidity problems and ASR development. In this work, further studies on reaction products were carried out through a stereomicroscope, a polarized light microscope, powder XRD and SEM-EDS analyses. Calcium silicates with variable contents of sodium and potassium, associated with ettringite, were identified in fissures, mortar, in the mortar-aggregate interface and filling air voids

    Use of natural zeolites as ASR inhibitor in basaltic rocks

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    The capacity of a natural zeolite from the province of La Rioja (Argentina) to inhibit the alkali-silica reaction (ASR) was studied. The pozzolanic material corresponds to a mixture of clinoptilolite zeolite with minor gypsum, quartz and feldspar discarded in spoil heaps in a quarry. An alkali-reactive basaltic aggregate from a quarry in the Argentine Mesopotamia region was used for the study. Two series of tests according to the accelerated mortar bar method (IRAM 1674) were carried out. One set with 0% (control specimen), 10%, 15% and 20% replacement of cement by natural zeolite and another with the same percentages but using milled zeolite. To monitor the reaction process, mortar bars were studied after the test by stereomicroscopy, polarizing microscopy and SEM-EDS. After 16 days of testing, a reduction in expansion (~42 %) was detected in the mortars with 20% replacement by natural zeolite. However, their behaviour was still reactive. On the other hand, the mortars with 20% replacement by milled zeolite produced a 90% reduction in expansion at 16 days, below the limit prescribed by the standard. A simple milling process transforms this material into a good pozzolanic material inhibiting the alkali-reactivity of basaltic aggregates
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