11 research outputs found
Comparative study on the preparation of belite cement from nano-silicas extracted from different agricultural wastes with calcium carbide residue
No full textBelite cement was prepared using nano-silicas extracted from three different agricultural wastes–black rice husk ash (BRHA), bagasse ash (BA), and palm oil fuel ash (POFA)–which were reacted at 1200 − 1400 °C with CaC2 residue as calcium source. The product was compared with that from CaCO3. Nano-silica extracted from BRHA was of very fine particle size (surface area 312.4 m2/g and V/S ratio 0.35 × 106 cm) and being highly reactive, forms β-C2S at lower firing temperatures; however, at higher temperatures, less-desirable γ-polymorphs are formed. Nano-silica extracted from POFA contains Na2O, Al2O3, and K2O impurities, which stabilize the β and α-forms and delay the transformation to γ-phase. This is reflected in relatively high compressive strength at firing temperature above 1200 °C, compared to other mixtures. Thus, these results indicate that the best combination of these waste materials for the preparation of belite cement phases is POFA ash and CaC2 residue
Avaliação da fixação de metais pesados em matrizes cimentícias
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Civil, Florianópolis, 2008Com o aumento na produção de resíduos industriais, é crescente a preocupação com tratamento e disposição final destes. Um método desenvolvido é o tratamento pela incorporação dos resíduos em matrizes à base de cimento Portland, que age tanto como barreira física quanto química para os poluentes concentrados no resíduo. A investigação da segurança deste método é feita por meio de ensaios de lixiviação, dentre outros. Um deles é o ensaio de tanque, adequado para amostras monolíticas, conforme a norma holandesa NEN 7345. O objetivo deste trabalho foi analisar a fixação de metais pesados na matriz cimentícia por meio do ensaio de tanque em amostras previamente contaminadas com os metais Cd, Cr III, Cr VI, Pb e Zn, na concetração de 100 ppm. As amostras analisadas consistiam em argamassas nas quais a cinza pesada (CZP) oriunda de uma usina termelétrica e o agregado reciclado de entulho (RCD) originário de uma unidade de beneficiamento substituíam a areia, em volume. As amostras de referência foram confeccionadas com areia normal IPT, com granulometria similar a CZP e RCD. Foram utilizados dois tipos de cimento: CP I S e CP V ARI. O lixiviante utilizado no ensaio de tanque foi água destilada e deionizada com pH alterado para 4 através da adição de HNO3. A renovação do lixiviante ocorreu após 6 horas, 1; 2,25; 4; 9; 16; 36 e 64 dias. A cada renovação, o líquido extraído era filtrado, tinha seu pH e condutividade elétrica medidos e era submetido à análise semiquantitativa de energia dispersiva por raios-X (EDX). Os ensaios evidenciaram que é possível avaliar o potencial de liberação de metais pesados das matrizes cimentícias e estimar o tempo de liberação dos poluentes. A técnica semiquantitativa por EDX demonstrou-se adequada na avaliação da inética de liberação do Cd, Cr III, Cr VI, Pb e Zn.Along with the increase in the generation of industrial wastes, the concern with their treatment and final disposal has been growing. A developed method is the treatment by the incorporation of wastes into Portland cement based matrices, which acts as a physical barrier as well as a chemical one for the pollutants concentrated in the waste. The investigation of the safety of this method is done through leaching tests, among others. One of them is the tank leach test, adequate for monolithic samples, according to the Dutch standard NEN 7345. The aim of this research was to assess the retention of heavy metals in the cementitious matrix through the tank test in samples previously contaminated with Cd, Cr III, Cr VI, Pb and Zn, at the concentration of 100 ppm. The samples analyzed consisted of mortars in which the bottom ash (CZP, coming from a thermoelectric plant and the recycled aggregates from debris (RCD), coming from a recycling plant, replaced the sand in volume. The reference samples were produced with standard sand IPT, with grain-size composition similar to CZP and RCD. Two types of cement were used: CP I S and CP V ARI. The leachant used for the tank leach test was distilled and deionized water with its pH altered to 4 through the addition of HNO3. The renewal of the leachant occurred after 6 h, 1; 2,25; 4; 9; 16; 36 and 64 days. After each renewal, the liquid extracted was filtered, it had its pH and electrical conductivity measured and was submitted to semi-quantitative analyses through Energy Dispersive X-ray (EDX). The tests showed that it is possible to assess the potential heavy metals release from the cementitious matrices and to estimate the time of the pollutants release. The semi-quantitative technique through EDX showed to be adequate for the assessment of the release kinetics of Cd, Cr III, Cr VI, Pb and Zn
Avaliação dos parâmetros de lixiviação de metais pesados em matriz de cimento Portland por meio da condutividade elétrica
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Civil, Florianópolis, 2013.Esta pesquisa analisou a condutividade elétrica como alternativa à obtenção de parâmetros de lixiviação de metais pesados em materiais cimentícios. Utilizaram-se corpos de prova cilíndricos de argamassas produzidas nos moldes recomendados para ensaios de resistência do cimento (NBR 7215:1997). O cimento escolhido foi do Tipo V e o agregado miúdo foi areia padrão. A contaminação das amostras se deu a partir de nitratos de metal pesado, por esta ser uma forma mais solúvel e susceptível à lixiviação. Foram utilizados nitratos de cromo, chumbo e zinco nas dosagens de 250 mg/kg, 500 mg/kg, 750 mg/kg e 1000 mg/kg. Os testes de lixiviação foram realizados de acordo com os procedimentos da norma holandesa NEN 7375:2004, na sua versão mais recente, no qual o extrato utilizado é a água deionizada. Trabalhou-se com tempos de cura variando de 28, 60 e 100 dias, para averiguação dessa influência sobre as taxas de liberação. As medidas da condutividade elétrica da solução lixiviada fazem parte dos procedimentos normalizados e servem para indicação da presença de elementos solubilizados. A condutividade elétrica da amostra monolítica foi tomada nos intervalos da troca do extrato a partir de eletrodos de cobre pressionados nas extremidades do corpo cilíndrico. Os equipamentos elétricos utilizados para leitura da condutividade do material consistiram de um gerador de tensão alternada e um medidor de corrente, posicionados em série. A tensão gerada foi fixada em 30 V e a frequência de 60 Hz, conforme a rede local. Os resultados mostraram existir semelhanças no comportamento à lixiviação das espécies e a condutividade elétrica, medida tanto na solução quanto no sólido. As correlações observadas permitiram a estimativa da concentração máxima de uma espécie qualquer disponível para liberação e, também, do tempo máximo decorrido até o seu esgotamento. Este procedimento pode substituir a realização dos ensaios prévios para determinação da disponibilidade de elementos susceptíveis à lixiviação. Os resultados parecem indicar não haver alteração na cinética de transporte das espécies iônicas ao longo do tempo e nem influência da concentração nesse movimento. Abstract : This research examined the electrical conductivity as an alternative to obtaining parameters of metal leaching in cementitious materials. Cylindrical specimens of mortars produced in the manner recommended for testing the compressive strength of cement were used (NBR 7215:1997). The chosen cement was Type V, and the fine aggregate was default standard sand. The contamination of the samples occurred from heavy metal nitrates, as this is more soluble and susceptible form to leaching. Nitrates of chromium, lead and zinc in doses of 250 mg/kg, 500 mg/kg, 750 mg/kg and 1000 mg/kg were used. The leaching tests were performed according to standard procedures of the Dutch NEN 7375:2004, in its latest version, in which the liquid solvent used is deionized water. The cure times ranged from 28, 60 and 100 days to investigate its influence on rates of release. The measurements of the electrical conductivity of the leach solution are part of the standard procedures and serve to indicate the presence of solubilized elements. The electrical conductivity of monolithic sample was taken at the intervals of exchange of the liquid solvent from pressed copper electrodes at the ends of the cylindrical specimens. The electrical equipment used for reading the conductivity of the material consisted of an alternating voltage generator and a current meter positioned in series. The generated voltage was set at 30 V and the frequency of 60 Hz, according to the mains. The results showed similarities in the leaching behavior of the species and the electrical conductivity, measured both in solution and in the solid. The observed correlations allowed the estimation of the maximum concentration of any species available for release and also the maximum time elapsed until its exhaustion. This procedure can replace the prior tests for determining the availability of elements susceptible to leaching. The results seem to indicate there is neither change in the kinetics of transport of ionic species over time nor influence of the concentration in this movement
Effect of different high surface area silicas on the rheology of cement paste
No full text[ES] Efecto de diferentes sílices de alta área superficial sobre la reología de pastas de cemento. Este tra¬bajo estudia el efecto de la nanosílice (NS) sobre la reología de pastas de cemento por comparación con sílices de alta área superficial: humo de sílice (SF) y pirosílice (PS). Las pastas fueron fabricadas con diferentes rela¬ciones agua-material cementante y sustituciones sólidas de sílice. Fueron ejecutados ensayos de demanda de agua, tiempo de fraguado y reología. Se encontró que la NS y SF disminuyen la viscosidad plástica, mientras que la PS la aumenta. Solo la PS tuvo efecto sobre el límite elástico. La NS presentó mayor disminución de la viscosidad, independientemente de su alta demanda de agua. Se concluyó que el comportamiento de las pastas con NS y SF es gobernado por el efecto de ¿rodamiento¿ de la sílice, por su grado de aglomeración y por su impacto en la fracción de sólidos. El comportamiento de las pastas con PS es gobernado por su capacidad de absorber agua.[EN] This work studies the effect of nanosilica (NS) on the rheology of cement paste by comparing it with two high specific surface area silicas: silica fume (SF) and pyrogenic silica (PS). Portland cement pastes were produced with different water-to-cementing material ratios and different solid substitutions of cement by silica. Water demand, setting time, and rheology tests were performed. Results showed that NS and SF decreased plastic viscosity, while PS increased it. Only PS was found to have an effect on yield stress. NS showed the most decreasing effect on viscosity, regardless of its higher water demand. It was concluded that the behavior of pastes containing NS and SF is governed by the "ball-bearing" effect from silica particles, by their agglomeration degree, and their impact on the solid volume fraction. The behavior of pastes containing PS is governed by its ability to absorb a portion of the mixing water.Tobón, J.; Mendoza, O.; Restrepo, O.; Borrachero Rosado, MV.; Paya Bernabeu, JJ. (2020). Effect of different high surface area silicas on the rheology of cement paste. Materiales de Construcción. 70(340):1-9. https://doi.org/10.3989/mc.2020.15719S19703401. Kwan, A.K.H.; Li, Y. (2013) Effects of fly ash microsphere on rheology, adhesiveness and strength of mortar. Constr. Build. Mater. 42, 137-145.2. Jal, P.K.; Sudarshan, M.; Saha, A.; Patel, S.; Mishra, B.K. (2004) Synthesis and characterization of nanosilica prepared by precipitation method. Coll. Surf. A Physicochem. Eng. Asp. 240 [1-3], 173-178.3. El Sokkary, T. M.; Assal, H. H.; Kandeel, A. M. (2004) Effect of silica fume or granulated slag on sulphate attack of ordinary portland and alumina cement blend. Ceram. Int. 30 [2], 133-138.4. Gutsch, A.; Krämer, M.; Michael, G.; Mühlenweg, H.; Pridöhl, M.; Zimmermann, G. (2002) Gas-Phase production of nanoparticles. KONA Powder Part. J. 20, 24-37.5. Singh, L.P.; Karade, S.R.; Bhattacharyya, S.K.; Yousuf, M.M.; Ahalawat, S. (2013) Beneficial role of nanosilica in cement based materials - A review. Constr. Build. Mater. 47, 1069-1077.6. Björnström, J.; Martinelli, A.; Börjesson, L.; Panas, I.; (2004) Accelerating effects of colloidal nano-silica for beneficial calcium-silicate-hydrate formation in cement. Chem. Phys. Lett. 392 [1-3], 242-248.7. Mendoza Reales, O.A.; Silva, E.C.C.M.; Paiva, M.D.M.; M.; Duda, P.; Toledo Filho, R.D. (2017) The role of surface area and compacity of nanoparticles on the rheology of cement paste 25.3. ACI Symp. Pub. 320, 25.1-25.14. https://www.concrete.org/publications/internationalconcreteabstractsportal/m/details/id/51701063.8. Tobón, J. I.; Mendoza Reales, O.; Retrepo, O.J.; Borrachero, M.V. (2018) Effect of pyrogenic silica and nanosilica on Portland cement matrices. J. Mater. Civ. Eng. 30 [10], 1-10.9. Mehdipour, I.; Khayat, K.H. (2018) Understanding the role of particle packing characteristics in rheo-physical properties of cementitious suspensions: A literature review. Constr. Build. Mater. 161, 340-353.10. Boukendakdji, O.; Kadri, E.H.; Kenai, S. (2012) Effects of granulated blast furnace slag and superplasticizer type on the fresh properties and compressive strength of selfcompacting concrete. Cem. Concr. Compos. 34 [4], 583-590.11. Park, C.K.; Noh, M.H.; Park, T.H. (2005) Rheological properties of cementitious materials containing mineral admixtures. Cem. Concr. Res. 35 [5], 842-849.12. Deng, H.; Li, H. (2018) Assessment of self-sensing capability of carbon black engineered cementitious composites. Constr. Build. Mater. 173, 1-9.13. Mendoza-Reales, O.A.; Arias Jaramillo, Y.P.; Ochoa Botero, J.C.; Delgado, C.A.; Quintero, J.H.; Toledo Filho, R.D. (2018) Influence of MWCNT/surfactant dispersions on the rheology of Portland cement pastes. Cem. Concr. Res. 107, 101-109.14. Quercia, G.; Hüsken, G.; Brouwers, H.J.H. (2012) Water demand of amorphous nano silica and its impact on the workability of cement paste. Cem. Concr. Res. 42 [2], 344-357.15. Norhasri, M.S.M.; Hamidah, M.S.; Fadzil, A.M. (2017) Applications of using nano material in concrete: A review. Constr. Build. Mater. 133, 91-97.16. Bowen, P. (2002). Particle size distribution measurement from millimeters to nanometers and from rods to platelets. J. Dispers. Sci. Technol. 23 [5], 631-662.17. Staiger, M.; Bowen, P.; Ketterer, J.; Bohonek, J. (2002) Particle size distribution measurement and assessment of agglomeration of commercial nanosized ceramic particles. J. Dispers. Sci. Technol. 23 [5], 619-630.18. Hidalgo, A.; Petit, S.; Domingo, C.; Alonso, C.; Andrade, C. (2007) Microstructural characterization of leaching effects in cement pastes due to neutralisation of their alkaline nature. Part I: Portland cement pastes. Cem. Concr. Res. 37 [1], 63-70.19. Srinivasan, S.; Barbhuiya, S.A.; Charan, D.; Pandey, S.P. (2010) Characterising cement-superplasticiser interaction using zeta potential measurements. Constr. Build. Mater. 24 [12], 2517-2521.20. de Larrard, F. (1999) Concrete mixture proportioning a scientific approach, E. & F.N. Spon, London.21. Banfill, P.F.G. (2006) Rheology of fresh cement and concrete. Rheol. Reviews 2006. 61-130.22. Burneau, A.; Barres, O.; Gallas, J.P.; Lavalley, J.C. (1990) Comparative Study of the Surface Hydroxyl Groups of Fumed and Precipitated Silicas. 2. Chatracterization by infrared spectroscopy of the interacctions with water. Langmuir. 6 [8], 1364-1372.23. Xie, X-L.; Liu, Q-X.; Li, R.K-Y.; Zhou, X-P.; Zhang, Q-X.; Yu, Z-Z.; Mai, Y-W. (2004) Rheological and mechanical properties of PVC/CaCO3 nanocomposites prepared by in situ polymerization. Polymer. 45 [19], 6665-6673.24. Asavapisit, S.; Fowler, G.; Cheeseman, C.R. (1997) Solution chemistry during cement hydration in the presence of metal hydroxide wastes. Cem. Concr. Res. 27 [8], 1249-1260
Performance of electrical spectroscopy using a RESPER probe to measure salinity and water content of concrete and terrestrial soil
No full text<p>This paper discusses the performance of electrical spectroscopy using a RESPER probe to measure the salinity <em>s</em> and volumetric content <em>θ<sub>W</sub></em> of the water in concrete or terrestrial soil. The RESPER probe is an induction device for spectroscopy which performs simultaneous and non invasive measurements of the electrical RESistivity <em>1/σ</em> and relative dielectric PERmittivity <em>ε<sub>r</sub></em> of a subjacent medium. Numerical simulations establish that the RESPER can measure <em>σ </em>and <em>ε</em> with inaccuracies below a predefined limit (<em>10%</em>) up to the high frequency band (HF). Conductivity is related to salinity and dielectric permittivity to volumetric water content using suitably refined theoretical models which are consistent with the predictions of Archie’s and Topp’s empirical laws. The better the agreement, the lower the hygroscopic water content and the higher <em>s</em>; so closer agreement is found with concrete containing almost no bonded water molecules provided these are characterized by a high <em>σ</em>. A novelty of the present paper is the application of a mathematical–physical model to the propagation of errors in the measurements, based on a sensitivity functions tool. The inaccuracy of salinity (water content) is the ratio (product) between the conductivity (permittivity) inaccuracy, specified by the probe, and the sensitivity function of salinity (water content) relative to conductivity (permittivity), derived from the constitutive equations of the medium. The main result is the model’s prediction that the lower the inaccuracy for the measurements of <em>s </em>and <em>θ<sub>W</sub></em> (decreasing by as much as an order of magnitude from <em>10%</em> to <em>1%</em>), the higher <em>σ</em>; so the inaccuracy for soil is lower. The proposed physical explanation is that water molecules are mostly dispersed as <em>H<sup>+</sup></em> and <em>OH<sup>-</sup></em> ions throughout the volume of concrete but are almost all concentrated as bonded <em>H<sub>2</sub>O</em> molecules only at the surface of soil.</p>
Zeolites synthesis intensification from microparticulate mining residues through use of microwaves as a non-Conventional energy supply technology
No full textilustraciones, graficasLa actividad minera desarrollada por la empresa Agregados Cantarrana S.A.S., ubicada
en la ciudad de Bogotá - Colombia, genera un residuo sólido que se caracteriza por la alta
presencia de óxidos de silicio en su composición, lo que lo convierte en materia prima
potencial para la cristalización de zeolitas por medio de activación hidrotérmica, objetivo
del presente trabajo de investigación. Fueron llevados a cabo procesos de conversión
directa encaminados a la producción de un donor de silicatos acuoso a partir del residuo
sólido minero, el cual, junto con el donor de aluminatos solubles, se utilizó en la síntesis
hacia la obtención del material zeolítico. La zeolitización involucró la cristalización
hidrotérmica del hidrogel precursor, donde el calentamiento fue realizado por microondas
a temperaturas entre los 65 °C y 90 °C, intensificando el proceso de reacción permitiendo
tiempos de síntesis más cortos. Variables como la temperatura de reacción y el tiempo se
controlaron automáticamente. Para la determinación de los tipos de zeolitas obtenidos,
fueron realizados procesos de caracterización del material cristalizado. La Difracción de
Rayos X (DRX) permitió establecer zeolitas tipo A, Na – X, y sodalita resultados de la
síntesis, la Microscopía Electrónica de Barrido (MEB) permitió dilucidar la morfología de
las partículas y agregados de estas zeolitas y la Fluorescencia de Rayos X (FRX) permitió
establecer la composición química del material, especialmente la relación [Si / Al] (donor
de silicatos / donor de aluminatos). Las zeolitas Na – X fueron evaluadas en la remoción
de plomo de soluciones acuosas mediante contacto de equilibrio durante un tiempo de 15
horas. La interpretación de los resultados se efectuó mediante la isoterma de adsorción
de Langmuir. (Texto tomado de la fuente)The mining activity carried out by the Agregados Cantarrana SAS company, located in
Bogotá - Colombia, generates a solid residue that is characterized by the high presence of
silicon oxides in its composition, which makes it a potential raw material for the
crystallization of zeolites by hydrothermal activation medium, which was the objective of
this research work. Direct conversion processes were carried out aimed at the production
of an aqueous silicate donor from the solid mining residue, which, together with the soluble
aluminate donor, was used in the synthesis to obtain the zeolitic material. Zeolitization
involved hydrothermal crystallization of the precursor hydrogel, where the heating was
carried out by microwaves at temperatures between 65 °C and 90 °C, intensifying the
reaction process, allowing shorter synthesis times. Variables such as reaction temperature
and time were automatically controlled. To determine the types of zeolites obtained,
characterization processes of the crystallized material were carried out. X – Ray Diffraction
(XRD) allowed to establish A, Na – X and Sodalite zeolites types for synthesis results,
Scanning Electron Microscopy (SEM) allowed to elucidate the morphology of the particles
and aggregates of these zeolites and the X – Ray Fluorescence (XRF) allowed to establish
the chemical composition of the material, especially the [Si / Al] ratio (silicate donor /
aluminate donor). The Na – X zeolites were evaluated in the removal of lead from aqueous
solutions by equilibrium contact for a time of 15 hours. The interpretation of the results was
carried out using the Langmuir adsorption isotherm.MaestríaMagíster en Ingeniería - Materiales y ProcesosAprovechamiento de residuos sólidos minero
Valorización de cascarilla de arroz en diferentes sectores industriales
No full textLa cascarilla de arroz (CA) es un residuo de alta generación que junto con sus cenizas (CCA) en Colombia y el mundo y por sus características físicas y químicas, ha sido de gran interés académico e industrial. En este capítulo se identifican y analizan los principales usos de la CA y la CCA para crear nuevos materiales o mejorar productos en varios sectores industriales. Se resaltan sectores como el de la construcción, donde se han usado estos residuos para la fabricación de cemento, como materia prima alternativa del concreto y los ladrillos de arcilla cocida, también como material para la estabilización de suelos. En procesos de obtención de nuevos materiales, se ha usado principalmente CCA para obtener cerámica avanzada y como materia prima en la producción de sílice, así como la CA en la obtención de carbón activado. En el sector energético, a partir de la CA ha sido posible la producción de combustible sólido y su aprovechamiento como
combustible alternativo, también con resultados menos prometedores en la generación de biogás y bioetanol. Por último, se analizaron usos importantes de la CA para el acondicionamiento de suelos y las CCA adsorbente de diversos contaminantes para la descontaminación de aguas residuales y purificación de agua. Es indispensable continuar en búsqueda de soluciones que permitan valorizar estos residuos en procesos industriales actuales y en la obtención de nuevos productos, buscando hacer parte del modelo de economía circular.1.era ed
