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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). [ABSTRACT FROM AUTHOR]

The mixture of activated paper sludge and fly ash can successfully be used as pozzolans for the manufacture of a more ecological portland cement. The saturation indexes and the mineral stability fields of a pozzolanic reaction are studied at 1, 3, 7, 28, 90, and 360 days into the reaction. The system is formed of a pozzolanic mix (activated clay waste and fly ash) and a saturated solution of Ca(OH) 2 at 40°C. The behavior of the reactions is predicted in this study by means of a thermodynamic model running on a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations. The concentration of soluble species in the aqueous solution is determined by inductively coupled plasma mass spectrometry. The evolution of the hydrated phases formed in this study and the mineral stability fields are evaluated with the geochemical programs PHREEQC and SUPCRT92. The hydrated phases produced during the pozzolanic reactions were C-S-H gels, C4AH13 (calcium aluminate hydrate), C4AcH12 (calcium monosulfoaluminate), and layered double hydroxide (LDH)-type structures or hydrotalcite are anionic clays. The saturation index values indicate that the LDH-type structures (phyllosilicate/carbonate) are the most thermodynamically stable phase in the activated clay/fly ash-Ca(OH) 2 system after 7 days of reaction. Mineral stability fields situate all the samples among the LDH-type structures (phyllosilicate/carbonate). [ABSTRACT FROM AUTHOR]

One of the problems to affect Portland cement matrices is low resistance to aggressive agents, due principally to the presence of a high content of portlandite in the hydrated cements. Pozzolanic materials have, for decades, played an important role in improving the durability of cement-based materials. This work studies the behaviour of cement mortar matrices blended with 10% calcined paper sludge (source for metakaolin, MK) and exposed to different environmental conditions (marine and tableland environments). The results obtained using X-ray diffraction and scanning electron microscopy/energy-dispersive X-ray analyser techniques show that the ions present speed of different penetration as well as various phases and/compounds in the matrices following exposure over 1 year. [ABSTRACT FROM AUTHOR]

The article focuses on the study which aims to determine the effect of calcined paper sludge as an environmentally friendly source of metakaolin for manufacture of cementitious materials. In the process, various chemical, mineralogical and pozzolanic characteristics were evaluated in order to provide a manufacture of blended cements. The result of the study indicates that the thermal conditions have a major influence on the properties of the calcined sludge as well as the pozzolanic behavior.

Abstract: This paper presents for the first time the influence of mixing different thermally activated paper sludges (APS) and fly ash (FA) on the pozzolanic reaction kinetics in APS–FA–Ca(OH)2 systems as a previous step to manufacture the future commercial ternary blended cements. In this study, two paper sludge wastes from different origins and activation conditions (laboratory (LS) and industrial (IS) scale) have been investigated, once mixed with fly ash at a ratio of 1:1 by weight. The results indicated that binary blends of pozzolans exhibited a high pozzolanic activity, showing that the hydrated phases produced during the pozzolanic reaction depend on the origin and activation conditions of clay wastes. At all times of reaction, the predominant phase turn out to be the LDH structures when LS pozzolan was used; meanwhile for the IS pozzolan the along with the LDH were the main phases during the first 28days. [Copyright &y& Elsevier]

Abstract: The hydraulic activity of ternary Portland cements containing different proportions of commercial thermally activated paper sludge (APS(I)) and fly ash (FA) from coal combustion was evaluated from the textural characterization of the C–S–H gels formed during hydration. The study was accomplished by means of the specific surface area (SSA) and pore-size distribution (PSD), which were measured by the sorption isotherms of nitrogen gas and the BET method. The microstructure was characterized by scanning electron microscopy (SEM). The incorporation of such admixtures (APS and FA) clearly revealed an increase in both porosity and SSA. This effect decreased with the progress of hydration, together with a refinement of the nano-porous structure of C–S–H. In addition, high correlations were found between nano-structural characteristics of the C–S–H gel and mechanical compressive strengths. [Copyright &y& Elsevier]