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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.

The correct assessment of industrial by-products and waste materials requires an in-depth knowledge of their characteristics. In thermally activated products, the calcining conditions have an important influence on the properties and later behaviour of cementitious matrices. The present study was carried out to determine the effect of calcining conditions (2-5 h at 700-8008C) on the properties of treated paper sludge. Various chemical, physical, morphological, mineralogical and pozzolanic characteristics were evaluated in order to provide a complete understanding of the properties of the calcined sludge and the possibility of using them in the manufacture of blended cements. The results showed that the thermal conditions have a major influence on the properties of the calcined sludge, primarily the mineralogical and morphological properties, as well as the pozzolanic behaviour.

In recent years, agro-industrial residues are focusing attention worldwide as a new source of pozzolans; in Brazil one of the wastes generated from agro-industrial activities comes from elephant grass that is cultivated as biomass for energy cogeneration. The goal of this paper is to analyze the influence of elephant grass, once activated at 700 C for 1 h in electric furnace, on the evolution of the hydration reaction as well as physical and mechanical properties in blended cement elaborated with 20% of elephant grass ash. For the present study, different instrumental techniques of characterization and methodologies (XRF, XRD, TG/DTG, mercury porosimetry, isothermal calorimetry and mechanical strength) were used. The results obtained in the present work show, that due to its high pozzolanic activity, the elephant grass ash activated at 700 C can be used as an alternative pozzolan in the blended cement manufacture. Additions of 20% of ash confirm the formation of CSH gels and hexagonal C 4 AH 13 as main products from hydration as well as pozzolanic reaction. The 20% ash blended cement showed lower heat evolution than OPC and similar to the 20% silica fume blended cement, a 12% of reduction of compressive strength and an important reduction of pore sizes below 50 nm.

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