Estudio termoanalítico y caracterización de los precipitados obtenidos a partir de soluciones FE (III) por alcalinización en medio homogeneo

Tesis - Universidad Complutense de Madrid, 1981.Depto. de Química AnalíticaFac. de Ciencias QuímicasTRUEProQuestpu

Estudio termoanalítico y caracterización de los precipitados obtenidos a partir de soluciones FE (III) por alcalinización en medio homogeneo

Tesis - Universidad Complutense de Madrid, 1981.Depto. de Química AnalíticaFac. de Ciencias QuímicasTRUEProQuestpu

Síntesis hidrotermal de zeolita a partir de ceniza volante tipo F: influencia de la temperatura = Influence of temperature of alkaline hydrothermal treatment on the zeolite conversion of spanish coal class F fly ash

En este trabajo se presenta el papel que juega la temperatura durante el tratamiento hidrotermal en medio alcalino para convertir una ceniza volante de bajo contenido en cal (clase F, según la norma ASTM) en zeolita. Durante este tratamiento a la temperatura de 100 ºC se forma zeolita Na-P1 tipo gismondina (Na6Al6Si10O32.12H2O); al elevar la temperatura a 200 ºC, dicha zeolita se transforma en zeolita analcima C (Na(Si2Al)O6H2O) y en fase sodalita (1.08 Na2O.Al2O3.1.68SiO2.1.8H2O) junto con trazas de tobermorita-11Å (Ca5(OH)2Si6O16.4H2O). A esta temperatura y en estas condiciones se ha conseguido un 100% de reacción. Un estudio equivalente se ha llevado a cabo empleando agua como medio de referencia. La conversión de ceniza volante en zeolita se ha caracterizado mediante técnicas, como difracción de Rayos X (DRX), espectroscopia infrarroja por transformada de Fourier (FTIR) y análisis térmico (TG/ATD); asimismo los cambios en el área superficial se han llevado a cabo mediante la técnica BET-N

Effect of temperature on the durability of class C fly ash belite cement in simulated radioactive liquid waste: Synergy of chloride and sulphate ions

The durability of class C fly ash belite cement (FABC-2-W) in simulated radioactive liquid waste (SRLW) rich in a mixed sodium chloride and sulphate solution is presented here. The effect of the temperature and potential synergic effect of chloride and sulfate ions are discussed. This study has been carried out according to theKoch–Steinegger test, at the temperature of 20 ◦Cand 40 ◦Cduring a period of 180days. The durability has been evaluated by the changes of the flexural strength of mortar, fabricatedwith this cement, immersed in a simulated radioactive liquid waste rich in sulfate (0.5 M), chloride (0.5M) and sodium (1.5M) ions – catalogued like severely aggressive for the traditional Portland cement – and demineralised water, which was used as reference. The reaction mechanism of sulphate, chloride and sodium ions with the mortar was evaluated by scanning electron microscopy (SEM), porosity and pore-size distribution, and X-ray diffraction (XRD). The results showed that the chloride binding and formation of Friedel’s salt was inhibited by the presence of sulphate. Sulphate ion reacts preferentially with the calcium aluminate hydrates forming non-expansive ettringite which precipitated inside the pores; the microstructure was refined and the mechanical properties enhanced. This process was faster and more marked at 40 ◦C

Modifications of the C–S–H gel by hydration at 40 ºC of belite cements from coal fly ash class C

The influence of the temperature on two types of hydrated fly ash belite cement (FABC) pastes were investigated at a nanoscale (1–100 nm) by measuring the specific surface area and pore-size distribution by the sorption isotherms of nitrogen gas and the BET method, and at a microscale from the pore-size distribution measured by mercury intrusion porosimetry. The two belite cements were fabricated by the hydrothermal–calcinations route of fly ash class C in NaOH 1M solution (FABC-2-N) and demineralized water (FABC-2-W). In the case of FABC-2-W, a densification of the C–S–H gel was produced at the temperature of 401C, which favored the formation of pores B3 nm in diameter leading to higher surface area values, compared with the C–S–H gel formed at 201C. At a microscale, the temperature led to an increase of capillary porosity (40.05 lm) at a later age of hydration and, consequently, a decrease of compressive mechanical strength. In the case of FABC-2-N, the densification of the gel was less evident, but the increase of capillary porosity (pores of diameter 40.05 lm) was higher. Significant direct linear quantitative correlations were found among these nanostructure characteristics of the C–S–H gel and macrostructural engineering property such as the compressive mechanical strength, for the two FABC-2-W and FABC-2-N cements under normal conditions. At 401C, the correlations were not so clear probably due to another microstructural factor such as the increase of the larger capillary porosity (40.05 lm)

Cementos Belíticos: caracterización de los productos de hidratación por microscopía electronica de barrido y microanálisis de rayos x

En este trabajo se presenta la caracterización microscópica de dos tipos de cementos belíticos de cenizas volantes (CBCV) y sus productos de hidratación, por medio de microscopía electrónica de barrido, microanálisis cuantitativo por energía dispersa de rayos X y difracción de rayos X. Los cementos se sintetizaron a partir de cenizas volantes de la combustión de carbón, de alto contenido en cal, empleando una ruta de síntesis de baja energía basada en la obtención de fases precursoras del cemento mediante un tratamiento hidrotermal de las cenizas en agua (CBCV-2-A) y una disolución de NaOH 1M (CBCV-2-N). La hidratación ha sido estudiada durante 180 días a la temperatura de 21º C y humedad relativa >95%. Los resultados mostraron una incorporación importante de Al en el gel C-S-H así como otros elementos minoritarios, con una composición cercana a la de la tobermorita sustituida por aluminio. El gel C-S-H formado durante la hidratación del cemento belítico (CBCV-A) es más estable durante el tiempo de hidratación que el gel formado en el caso del cemento CBCV-N. Trazas de Portlandita (Ca(OH)2) se forman durante la hidratación de estos cementos

Mapping of mechanical properties of cement paste microstructures

The presented study is related to the EU 7 th Framework Programme CODICE (COmputationally Driven design of Innovative CEment-based materials). The main aim of the project is the development of a multi-scale model for the computer based simulation of mechanical and durability performance of cementitious materials. This paper reports results of micro/nano scale characterisation and mechanical property mapping of cementitious skeletons formed by the cement hydration at different ages. Using the statistical nanoindentation and micro-mechanical property mapping technique, intrinsic properties of different hydrate phases, and also the possible interaction (or overlapping) of different phases (e.g. calcium-silcate-hydrates) has been studied. Results of the mapping and statistical indentation testing appear to suggest the possible existence of more hydrate phases than the commonly reported LD and HD C-S-H and CH phase

Hydration of C3S, C2S and their Blends. Micro- and Nanoscale Characterization

This study forms part of wider research conducted under a EU 7 th Framework Programme (COmputationally Driven design of Innovative CEment-based materials or CODICE). The ultimate aim is the multi-scale modelling of the variations in mechanical performance in degraded and non-degraded cementitious matrices. The model is being experimentally validated by hydrating the main tri-calcium silicate (T1-C3S) and bi-calcium silicate (β-C2S), phases present in Portland cement and their blends. The present paper discusses micro- and nanoscale studies of the cementitious skeletons forming during the hydration of C3S, C2S and 70 % / 30 % blends of both C3S/C2S and C2S/C3S with a water/cement ratio of 0.4. The hydrated pastes were characterized at different curing ages with 29 Si NMR, SEM/TEM/EDS, BET, and nanoindentation. The findings served as a basis for the micro- and nanoscale characterization of the hydration products formed, especially C-S-H gels. Differences were identified in composition, structure and mechanical behaviour (nanoindentation), depending on whether the gels formed in C3S or C2S pastes. The C3S gels had more compact morphologies, smaller BET-N2 specific surface area and lesser porosity than the gels from C2S-rich pastes. The results of nanoindentation tests appear to indicate that the various C-S-H phases formed in hydrated C3S and C2S have the same mechanical properties as those formed in Portland cement paste. Compared to the C3S sample, the hydrated C2S specimen was dominated by the loose-packed (LP) and the low-density (LD) C-S-H phases, and had a much lower content of the high density (HD) C-S-H phas

Hydraulic activity of belite cement from class C coal fly ash. Effect of curing and admixtures

En este trabajo se discute la influencia del tipo de curado y de un aditivo reductor de la demanda de agua en la actividad hidráulica de un cemento belítico de cenizas volantes de alto contenido en cal denominado (CBCV-2-A). Este cemento ha sido sintetizado por una ruta húmeda hidrotermal con posterior calcinación, empleando ceniza volante de alto contenido en cal (ASTM tipo C) como materia prima. La actividad hidráulica se ha estudiado en la pasta de cemento, durante un periodo de 180 días, por medio del contenido de agua combinada, determinada por análisis termogravimétrico, y el grado de hidratación por difracción de rayos X (DRX). La resistencia mecánica y la porosidad total y distribución de tamaño de poro se han estudiado en probetas equivalentes de mortero.The effect of curing method and a water-reducing additive on the hydraulic activity of high lime content (ASTM type C) fly ash belite cement (FABC-2-W) is reported. A class C fly ash was subjected to hydrothermal treatment and subsequent calcination to synthesize FABC. Hydraulic activity was evaluated in the cement paste over 180 days from the physically bound water content as determined by thermogravimetric analysis and the degree of hydration, in turn found with X-ray diffraction (XRD) analysis. Mechanical strength, porosity and pore size distribution were also studied in equivalent mortar samples.Los autores agradecen la financiación por parte del Ministerio de Ciencia y Tecnología mediante la concesión del proyecto (MAT 2002-04023-CO3) para la realización de estos trabajos; así como a la Central Térmica de Cers (Cataluña) por el suministro de la ceniza volante.Peer reviewe

Actividad hidráulica de un cemento belítico obtenido a partir de cenizas volantes tipo C: influencia del aditivo y tipo de curado

[EN] The effect of curing method and a water-reducing additive on the hydraulic activity of high lime content (ASTM type C) fly ash belite cement (FABC-2-W) is reported. A class C fly ash was subjected to hydrothermal treatment and subsequent calcination to synthesize FABC. Hydraulic activity was evaluated in the cement paste over 180 days from the physically bound water content as determined by thermogravimetric analysis and the degree of hydration, in turn found with X-ray diffraction (XRD) analysis. Mechanical strength, porosity and pore size distribution were also studied in equivalent mortar samples.[ES] En este trabajo se discute la influencia del tipo de curado y de un aditivo reductor de la demanda de agua en la actividad hidráulica de un cemento belítico de cenizas volantes de alto contenido en cal denominado (CBCV-2- A). Este cemento ha sido sintetizado por una ruta húmeda hidrotermal con posterior calcinación, empleando ceniza volante de alto contenido en cal (ASTM tipo C) como materia prima. La actividad hidráulica se ha estudiado en la pasta de cemento, durante un periodo de 180 días, por medio del contenido de agua combinada, determinada por análisis termogravimétrico, y el grado de hidratación por difracción de rayos X (DRX). La resistencia mecánica y la porosidad total y distribución de tamaño de poro se han estudiado en probetas equivalentes de mortero.Peer reviewe