The alkaline reaction of FEBEX bentonite: a contribution to the study of the performance of bentonite/concrete engineered barrier system

Desde 1997, el desarrollo de dos proyectos de la Unión Europea, Effects of Cement On CLAY barrier performance (ECOCLAY, 1997-2000) y ECOCLAY phase II (2000-2003), ha permitido abordar la investigación del efecto de la pluma alcalina inducida por la lixiviación del hormigón sobre la bentonita. Ambos materiales forman parte de un concepto de barrera compuesta de hormigón y bentonita, en el contexto del almacenamiento de residuos a una profundidad dada. El grupo de geoquímica aplicada a las arcillas de la Universidad Autónoma de Madrid (UAM) ha participado en ambos proyectos, y ha conseguido aportar experiencia y cono¬cimiento al estudio del comportamiento de la bentonita de referencia española (FEBEX) bajo condiciones de elevada alcalinidad. Este artículo ofrece una síntesis del trabajo desarrollado, mencionando las lecciones aprendidas sobre la reactividad alcalina de la bentonita, y su enfoque práctico hacia el análisis del comportamiento de uno de los conceptos de referencia, el almacenamiento de residuos en formaciones arcillosas. Se han seleccionado las principales contribuciones científicas a este respecto, a juicio de los autores: (1) la naturaleza particular de los productos generados en la reacción alcalina de la bentonita FEBEX (zeolitas, arcillas magnésicas y geles de silicato aluminato cálcico hidratado (CASH)); (2) la aproximación mediante mineralogía cuantitativa al ritmo de reacción de la montmorillonita FEBEX a pHs elevados, y (3) la validación experimental de la reactividad alcalina de la bentonita a partir de experimentos en columna

Mineral phases in metakaolin-portlandite pastes cured 15 years at 60 °C. New data for scientific advancement

One of the problems addressed by the scientific community in connection with cement matrix hydration is the evolution of hydrated phases under certain, primarily temperature-related, curing conditions. Such conditions are of utmost importance when the cement generates metastable hydrated phases that develop into stable phases, inducing substantial physical-mechanical changes in the matrix. One such instance arises during the pozzolanic reaction between metakaolinite and calcium hydroxide at 60 °C when metastable hexagonal phases co-exist with cubic stable phases. Such processes are well understood in the short and medium term (<5 years). Evolution at longer curing times has not been studied, however. This paper describes the evolution of the initial (stable and metastable) mineral phases in the metakaolinite / Ca(OH) reaction toward a zeolite-like phase after 15 year curing at 60 °C. An understanding of such mineralogical changes is scientifically significant, given their direct impact on the engineering properties of cement-based matricesThe authors thank the Spanish Ministry of Science, Innovation and Universities and the European Regional Development Fund (ref: RTI2018-097074-B-C21/C22

The deterioration and environmental impact of binary cements containing thermally activated coal mining waste due to calcium leaching

Calcium-leaching processes can potentially degrade the structure of a concrete matrix. This problem is studied here through the progressive dissolution of Ca2+ in both ordinary Portland cement pastes (C-0) and binary cement blends (C-20) containing 20% thermally Activated Coal Mining Waste (ACMW).1 A series of accelerated tests are conducted that involve the immersion of these cement pastes in a 6 M ammonium nitrate solution at a temperature of 20  C for 7 and for 21 days. A rise in paste porosity was observed, due to increased capillary pore sizes of between 5 and 0.1 μm. In the case of the 20% ACMW pastes (C-20), calcium leaching decreased, probably as a consequence of the pozzolanic effect of the ACMW, while potassium and magnesium leaching increased, due to the presence of the phyllosilicates in the ACMW. The paste compounds most affected by leaching were Ca(OH)2, C6AS3H32, and C4AC¯H12. In general terms, it can be concluded that the incorporation of ACMW into binary cements slightly reduces the calcium leaching phenomena. Concerning the environmental impact assessment, the substitution of 20% OPC by ACMW reduced CO2 emissions by as much as 12% and improved energy efficiency by using approximately 19% fewer fossil resources.This research was developed in the framework of the MATCON Associated Unit (CSICTecnalia, Madrid, Spain) with the support of the Spanish Ministry of Economy and Competitiveness (Project Ref. MAT2012-37005-CO3-01/02/03) and the European Regional Development Fund (MINECO/FEDER) (Project Ref.BIA2015-65558-C3- 1,2,3-R. The authors are also grateful to the Sociedad Anónima Hullera Vasco-Leonesa and to the Spanish Cement Institute (IECA) for providing us with raw materials

Characterization of dolia from the Guadalquivir valley and found in the southern Lusitanian sites (Algarve, Portugal)

info:eu-repo/semantics/publishedVersio

Nuevos materiales ecoeficientes a partir de residuos de la industria papelera como adiciones activas para la fabricación de cementos portland

El desarrollo industrial lleva asociado la generación de grandes volúmenes de subproductos y residuos industriales que, en la mayoría de los casos, terminan en los vertederos, perdiendo su potencial como materias primas para otros sectores industriales. El sector cementero, por sus características de fabricación de clinker, es uno de las principales industrias que liberan más gases con efecto invernadero. Una de las prioridades de este sector, es la búsqueda de cementos más ecoeficientes y respetuosos con el medioambiente. Para ello, los esfuerzos se dirigen hacia la fabricación de cementos con mayores contenidos de adiciones activas. En esta línea de investigación, el presente trabajo recopila la experiencia llevada a cabo sobre la valorización de residuos de lodos de papel como fuente alternativa para obtener metacaolinita reciclada como adición activa en la fabricación de cementos comerciales. Mediante un proceso de activación térmica, la caolinita presente se transforma en metacaolinita, conocida por su alta actividad puzolánica. La obtención de esta puzolana reciclada, y no a través de un proceso natural, representa una línea innovadora con repercusión directa en el desarrollo sostenible. Los resultados expuestos muestran la viabilidad científica, técnica y medioambiental de reciclar estos residuos de lodos de papel los cuales, una vez activados bajo condiciones óptimas a 650-700ºC durante 2 horas, se pueden aprovechar como adiciones activas para la fabricación de cementos portland.Proyectos nacionales refs:MAT2003-06479-C03, CTM2006-12551-C03/TECNO y MAT2009-10874-C03), y a la empresa Holmer Paper Madrid y al IECAPeer reviewe

Coal Mining Waste as a Future Eco-Efficient Supplementary Cementing Material: Scientific Aspects

The stockpiling of tailings around coal mines poses a major environmental problem. Nonetheless, this clay mineral (kaolinite)-based waste can be reused as a supplementary cementitious material (recycled metakaolinite) in the manufacture of future eco-efficient cements. This paper explores the most significant scientific questions posed in connection with the conversion of this waste into pozzolans, such as the variation in product mineralogy depending on the sintering temperature and its effect on reaction kinetics in the pozzolan/Ca(OH)2 system over a period of 365 days. The findings show that the optimal sintering temperature is 600 °C, such that the cementitious properties of the activated product are determined solely by the conversion of kaolinite into metakaolinite and are unaffected by the other clay minerals (micas). The presence of 20% activated coal waste favors the formation of larger amounts of aluminous phases such as C4AH13 and C4AcH12 than in the reference paste and enhances C–S–H gel polymerization.This research was funded by the Spanish Ministry of the Economy and Competitiveness under coordinated projects MAT2012-37005-CO3-01, BIA2015-65558-C3-1-2-3R (MINECO/FEDER). We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

From coal-mining waste to construction material: a study of its mineral phases

The study from the recycling of coal mining waste from NW of Spain as pozzolans materials in cement industry is the scope of this present study. The thermal activation of coal-mining wastes, the formation of their hydrated phases and their evolution are analyzed, over pozzolanic reactions at 1, 7 and 28 days following activation. The coal-mining waste showed good pozzolanic activity, following thermal activation at 600 and 900 °C for 2 h. Total destruction of kaolinite is produced after treatment at 600 °C/2 h retention in the oven. This temperature and time are best suited for activation of the best environmental way. The compounds arising during the pozzolanic reaction in coal-mining waste activated at 600° and 900° in a Ca(OH)2 system were C–S–H gels, stratlingite (C2ASH8), tetracalcium aluminate hydrate (C4AH13), layered double hydroxides and monosulfoaluminate. When the temperature is 600 °C appeared layered double hydroxides via the metastable phase is favored during the first 7 days of reaction, while stratlingite is present as the major crystalline phase at 28 days into the pozzolanic reaction.Peer reviewe

Estériles de carbón como fuente de obtención de puzolanas base metacaolinita

XIV Congreso Nacional de Materiales; Gijón, 8 al 10 de junio de 2016; http://sociemat.es/index.php/es/congresos-sociemat/96-congresos-nacionales/xiv-congreso-nacional-de-materiales-gijon-2016/436-cnmat-gijon-2016Uno de los problemas sociales y medioambientales de la industria cementera es la explotación de canteras naturales para la obtención tanto de materias primas como para algunas de las adiciones activas recogidas en la normativa vigente de la fabricación de cementos comerciales. Sin embargo, en el supuesto del metacaolin (MK), producto calcinado con altas propiedades puzolánicas, se abre una alternativa en el suministro de MK empleando un residuo industrial procedente de la industria del carbón. Dicho residuo, por su naturaleza, requiere de un proceso de activación térmica que transforme este residuo inerte y contaminante, en materia prima secundaria utilizada en la elaboración de cementos eco-eficientes e innovadores. En este trabajo se analiza la naturaleza de dos estériles de carbón (obtenidos en los procesos de extracción y lavado) logrados en una explotación minera a cielo abierto, perteneciente a la Sociedad Anónima Hullera Vasco-Leonesa, localizada en Santa Lucía (León, España), abordando tanto los aspectos científicos como sus propiedades puzolánicas. El estudio se completa con el desarrollo de la cinética de reacción en diferentes sistemas cementantes, tales como estéril de carbón activado /Ca(OH)2 y estéril de carbón activado/cemento a 90 días de reacción.Los autores agradecen al MINECO su financiación económica (Proyecto Ref. MAT2012-37005-CO3-01/02/03). También, a la Sociedad Anónima Hullera Vasco-Leonesa y al IECA por su ayuda técnica.Peer Reviewe

Sodium chloride effect on durability of ternary blended cement. Microstructural characterization and strength

This work is a continuation of a previous durability study of ternary Portland cements (TPCs), containing thermally activated paper sludge and fly ash, in the main expansive salts present in the sea water. The same experimental methodology was applied in the present case, but with a sodium chloride solution. The study was carried out by testing the flexural strength of blended pastes immersed in sodium chloride (24,530 ppm), and demineralised water as a reference, at 18 C over a period of 180 days. The reaction mechanism of chloride ions with the paste was evaluated by scanning electron microscopy (SEM), porosity and pore-size distribution, and X-ray diffraction (XRD). The results showed that ternary blended cement was stable against chloride attack. The enhancement of mechanical properties was a result of the formation of non-expansive Friedel’s salt inside the pores and an alkaline activation of the pozzolanic reaction of the additions promoted by the ingress of chloride and secondary related reactions; accordingly, the microstructure was refined.Peer reviewe

Influence of ZnO on the activation of kaolinite-based coal waste: Pozzolanic activity and mineralogy in the pozzolan/lime system

One inconvenience presented by the thermal activation of kaolinite-based wastes is their low content of metakaolinite, a highly pozzolanic product listed in current standards for the manufacture of commercial cements. The addition of a chemical activator during the thermal activation process is a priority line of research to increase the reactivity of the recycled metakaolinite. In this paper, an additional chemical activator, ZnO, is studied and its effect on both pozzolanic properties and the evolution of mineralogical phases in the thermal activation of coal waste with a reaction time of up to 90 days in the pozzolan/lime system. To do so, activation temperatures of between 550 °C/650 °C were selected and additions of chemical activator (ZnO) in percentages of between 0.0% and 3.0% by weight of coal waste, because it is an activator with a positive effect on a 100% natural kaolinite. The results showed that the incorporation of ZnO inhibited the reactivity of the recycled metakaolinite and in consequence, the capacity of the metakaolinite to react with the surrounding lime; even more so when the content of added chemical activator was raised, albeit with some exceptions, in the samples activated at 550 °C and 650 °C with 0.5% of chemical activator. In none of the cases under analysis was the chemical activator able to improve the properties of the metakaolinite in comparison with the properties of the reference sample activated only with temperature. The hydrated phases that appeared in the pozzolanic reaction were tetracalcium aluminate hydrate, stratlingite, monosulfoaluminate hydrate and LDH (phyllosilicate/carbonate)The authors wish to express their gratitude and sincere appreciation to the Spanish Ministry of the Economy and Competitiveness under coordinated projects MAT2012-37005-CO3-01, BIA2015-65558-C3-1-2-3R (MINECO/FEDER) for financing this research work and grateful to the Sociedad Anónima Hullera Vasco-Leonesa (Spain) and to the Spanish Cement Institute (IECA) for their assistance with this researc