Valorização de resíduos industriais como fonte alternativa mineral : composições cerâmicas e cimentíceas

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

This present work describes studies of valorization of wastes as alternative raw materials. Different industrial wastes, based on the SiO2-Al2O3-CaO system and classified as non-hazardous, were selected: Al-rich anodizing sludge, sludge from the filtration/clarification of potable water, sludge generated in ornamental stone-cutting processes, and foundry sand. The full characterization of the waste materials is reported, including physical and chemical parameters and thermal behaviour. Based on the observed valorization potential, four possible applications were selected and, for each, various mixtures were prepared and experimentally processed: (i) clinkers/cements, (ii) refractory ceramics (iii) lightweight aggregates, and (iv) retardants and workability-aids in rendering/plastering mortars. The clinker formulations were characterized by conventional and advanced techniques, such as: 27Al and 29Si magic-angle spinning nuclear magnetic resonance (NMR-MAS), differential scanning calorimetry (DSC) and powder Xray diffraction (XRD). Using those experimental techniques, phase formation and development kinetics during the clinker thermal processing could be followed. The major cement compounds found in common formulations (C2S, C3S, C3A e C4AF) were also synthesized and used as reference. The extrusion of ceramic refractory formulations was also studied. The plastic behaviour was characterised by stress-strain curves. After adjusting the plasticity level, samples were extruded in different conditions of ram speed and pressure. Using those conditions and the Benbow model for paste extrusion, the processing conditions were optimized and so were the properties of the fired samples, which were also characterized. The processing of a new lightweight aggregate, based on the sludge generated in granite cutting and polishing processes, was investigated. The study was aimed at improving the samples mechanical strength with minimum sacrifice (increase) of the apparent density, which results from the aggregate microstructure, consisting of internal closed pores and a partially vitrified surface layer. Changes in microstructure were evaluated by scanning electron microscopy and the expansive behaviour was studied by hot stage microscopy. The effect of the relevant thermal processing variables on the samples properties was studied and, in this way, the process could be optimized and the understanding of the phenomena causing the expansion could be furthered. Finally, studies are described on the use of the sludge generated in potable water filtration/cleaning operations as set retardant and workability-aid in a rendering/plastering industrial mortar, instead of commercial bentonite. The waste material was enriched with sodium phosphate, which is the set retarding active agent in cement pastes, and was used as transference matrix for the active agent. The fresh mortars were characterized in terms of consistency throughout the setting period, from the onset of setting until full hardenining. The mortars workability also was accompanied by rheological measurements using a special viscometer. This study demonstrates the potential of the wastes various valorization routes, which can thus be upgraded to alternative raw materials to natural mineral resources.

ASSUNTO(S)

materiais nao metalicos mortars cimentos argamassas agregados leves valorization of wastes lightweight aggregates cerâmica ceramics valorização de resíduos cements resíduos industriais

ACESSO AO ARTIGO

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