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The transformation process of the natural kaolinite into metakaolinite for its use as a cement addition was very much known long time ago. However, environmental policies prioritize the waste recycling as raw material by its environmental benefits. This article reports, for the first time, the scientific aspects related to the recycling of three Spanish coal mining wastes of different nature and origin, as an alternative source to obtain future pozzolans based on metakaolinite. The effect of activation conditions on the mineralogy, as well as the formation and evolution of hydrated phases formed during the pozzolanic reaction, was analyzed using different instrumental techniques such as X‐ray fluorescence, X‐ray diffraction, thermogravimetric analysis, infrared spectroscopy, and scanning electron microscopy. The results showed that all activated coal mining wastes exhibited high pozzolanic activity. The identification and evolution of hydrated phases with the hydration time in activated kaolin/Ca(OH)2 system were directly related to the origin and nature of the starting coal mining waste and not to the activation temperature itself. Finally, the coal mining wastes are suitable for being used as future pozzolans.

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The replacement of natural aggregates by recycled aggregates in the concrete manufacturing has been spreading worldwide as a recycling method to counteract the large amount of construction and demolition waste. Although legislation in this field is still not well developed, many investigations demonstrate the possibilities of success of this trend given that concrete with satisfactory mechanical and durability properties could be achieved. However, recycled aggregates present a low quality compared to natural aggregates, the water absorption being their main drawback. When used untreated in concrete mix, the recycled aggregate absorb part of the water initially calculated for the cement hydration, which will adversely affect some characteristics of the recycled concrete. This article seeks to demonstrate that the technique of pre-saturation is able to solve the aforementioned problem. In order to do so, the water absorption of the aggregates was tested to determine the necessary period of soaking to bring the recycled aggregates into a state of suitable humidity for their incorporation into the mixture. Moreover, several concrete mixes were made with different replacement percentages of natural aggregate and various periods of pre-saturation. The consistency and compressive strength of the concrete mixes were tested to verify the feasibility of the proposed technique.

RESUMENEn este estudio se plantea la posibilidad de reutilizar los residuos cerámicos de sanitarios como árido grueso sustituyendo de forma parcial (15, 20 y 25%) al árido grueso natural. Para ello, se llevó a cabo la caracterización del árido cerámico reciclado y posteriormente se procedió a establecer los parámetros de dosificación y fabricación de los distintos hormigones. Finalmente, se realizó sobre los mismos unos ensayos de caracterización de las propiedades físicas y mecánicas, y un estudio de las fases cristalinas. Los resultados indican que a medida que se aumenta el porcentaje de sustitución se ven mejoradas las propiedades mecánicas de éstos, mientras que las propiedades físicas se mantienen prácticamente constantes. A la vista de estos resultados se puede concluir que es posible la utilización de este tipo de residuo cerámico como árido grueso en la elaboración de hormigones con fines estructurales.Palabras clave: árido, cerámica, hormigón, caracterización, propiedades mecánicas. SUMMARYThis study examined the possibility of reusing the ceramic wastes of sanitary ware as coarse aggregate, in partial substitution (15, 20 y 25%) of natural coarse aggregates. Firstly, the characterization of recycled coarse ceramic aggregate was carried out subsequently proceeded to establish the parameters of dosage and manufacture of different concretes. Lastly, tests were conducted using these mixes to characterize physical and mechanical, and a study was carried out to identify the crystalline phases. Results showed that as the substitution proportion increased, the mechanical properties of the concrete improved, whilst physical properties remained practically constant. In view of these results, we conclude that it is possible to use this type of ceramic waste as coarse aggregate when mixing concrete destined for structural purposes. Keywords INTRODUCCIÓNEl desarrollo industrial y económico se ha incrementado notablemente en las últimas décadas incidiendo en la mejora de la calidad de vida y el bienestar de los ciudadanos, no obstante, conviene tener presente que todo sistema productivo origina subproductos y residuos que pueden producir alteraciones sobre el medio ambiente. Estas alteraciones pueden producirse en cualquier fase del ciclo de vida del producto: en la fase inicial de obtención de materias primas, en la fase de producción y transformación, en la distribución de los productos o, por último, cuando el poseedor tiene que desprenderse de los productos no validos.España es el líder mundial de mercado de materiales cerá-micos sanitarios. Este tipo de industria produce más de 7 millones de piezas al año (2008), según datos proporcionados por los propios fabricantes se generan en torno a 24 t de residuos al mes que van directamente al vertedero.En el proceso de su fabricación se genera de forma inevitable, independientemente de las mejoras que tengan lugar en los procesos de fabricación, un porcentaje de producto no apto para su comercialización, y por lo tanto de rechazo, como consecuencia de dos razones pr...

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