Combining mixture design of experiments with phase diagrams in the evaluation of structural ceramics containing foundry by-products

This work compares the effects of the incorporation of foundry by-products (foundry sand dust and Waelz slag) on the technological properties of three different ceramic products fabricated with different clays and fired at different temperatures: wall bricks (850 degrees C), roof tiles (950 degrees C) and face bricks (1050 degrees C). To this aim, the mixture design of experiments (M-DoE) methodology was used to define the minimum number of mixtures necessary to model and predict the technological properties (water absorption, flexural strength, open porosity, linear firing shrinkage, weight loss and apparent density) in terms of raw materials contents: clay, foundry sand dust and Waelz slag. The results obtained were interpreted in terms of the chemical and mineralogical compositions of the final products, which showed the importance of combining the M-DoE methodology with the phase equilibrium predictions to better understand the development of the fired products final properties. (C) 2014 Elsevier B.V. All rights reserved

Using mixture design of experiments to assess the environmental impact of clay-based structural ceramics containing foundry wastes

This work describes the leaching behavior of potentially hazardous metals from three different clay-based industrial ceramic products (wall bricks, roof tiles, and face bricks) containing foundry sand dust and Waelz slag as alternative raw materials. For each product, ten mixtures were defined by mixture design of experiments and the leaching of As, Ba, Cd, Cr, Cu, Mo, Ni, Pb, and Zn was evaluated in pressed specimens fired simulating the three industrial ceramic processes. The results showed that, despite the chemical, mineralogical and processing differences, only chrome and molybdenum were not fully immobilized during ceramic processing. Their leaching was modeled as polynomial equations, functions of the raw materials contents, and plotted as response surfaces. This brought to evidence that Cr and Mo leaching from the fired products is not only dependent on the corresponding contents and the basicity of the initial mixtures, but is also clearly related with the mineralogical composition of the fired products, namely the amount of the glassy phase, which depends on both the major oxides contents and the firing temperature. (C) 2015 Elsevier B.V. All rights reserved

Granite waste and coffee husk ash synergistic effect on clay-based ceramics

Brazil produces massive amounts of granite sawing waste and coffee husk ash and their inadequate and, often, illegal disposal causes enormous environmental problems. In the past decade, these and other industrial wastes have been intensively studied aiming at determining their potential as alternative raw materials, particularly for the ceramic industry. This work describes research carried out on the joint incorporation of those wastes in ceramic roof tile formulations. The results indicated that the simultaneous use of both materials translates into a very forgivable industrial working range, both composition- and temperature-wise, which, given the technological properties values observed after firing at 1100 degrees C, enables industrial up-grade to wall tile production. As collateral benefits, the use of granite waste and coffee husk ash as alternative raw materials in the manufacture of clay-based products will relieve the stress on feldspars consumption and attenuate waste disposal concerns

Setting behaviour of waste-based cements estimated by impedance spectroscopy and temperature measurements

Este trabajo describe el estudio del desarrollo de fases durante el fraguado de diferentes formulaciones de clinker preparados con residuos industriales o subproductos, denominados barros (generados en los procesos de recubrimientos industriales por anodizado de Al, en procesos de filtración/depuración de agua potable y en procesos de corte de mármol) y arenas de fundición. Con el objeto de comparar, se prepararon formulaciones similares a partir de materias primas comerciales de alta pureza y procesadas en idénticas condiciones. Para sortear las restricciones experimentales de inherentes a la aguja de Vicat (esto es, grandes cantidades de material), se realizaron medidas de resistividad eléctrica en corriente alterna (a.c.) de espectroscopía de impedancia para seguir el proceso de hidratación y fraguado. Durante el fraguado, la evolución de la temperatura de las pastas de agua/cemento se registró. Los estudios de espectroscopía de impedancia mostraron ser un método fiable y en algunos casos, pueden emplearse como técnica sensible para detectar el inicio de las reacciones de hidratación

Increased added value reuse of construction waste in clay based building ceramics

This paper illustrates a new way to explore reuse alternatives for construction and demolition waste, seeking higher added value applications for the reclaimed waste. Additions (up to 50 wt-%) of a clean construction waste were made to a red clay brick mixture, and sintered samples (950-1150 degrees C, 1 h) were characterised (X-ray diffraction and fluorescence, thermal analysis, firing shrinkage, water absorption and flexural strength). The results show that waste additions below similar to 10 wt-% result in no significant change in bricks properties; waste additions above similar to 20 wt-% and a slightly higher firing temperature enable the manufacture of higher grade building products (tiles). The waste changes roles from inert to fluxing at 10-20 wt-% owing to the change of compatibility triangles in the phase diagram. Such large usages of clean construction wastes in applications other than the usual low grade ones demonstrate the importance of selective waste collection programmes

Untreated coffee husk ashes used as flux in ceramic tiles

The agro-industrial activities are responsible for the production of large amounts of solid wastes, which, so far, have found scarce reuse alternatives. Among the former, coffee bean beneficiation generates an equal amount of coffee husks whose highest reuse potential is as fuel. The resulting ashes are frequently an object of illegal covert disposal and a serious source of environmental impact. However, coffee husk ashes (CHA) are particularly rich in alkaline and alkaline-earth metals, and might be adequate to replace the traditional feld-spars, which are used in high content as fluxes in clay-based ceramic formulations but are becoming scarce and costly. In this work, the fluxing effect of CHA additions to an industrial clay-based mixture was evaluated. Based on the characterization results and the mullite-silica-leucite phase diagram, additions of 5 to 20 wt.% CHA were made to the clay-based mixture and the resulting compositions were evaluated after sintering at temperatures between 1100 and 1200 degrees C (60 min soaking time). The results obtained show that firing temperatures near 1180 degrees C and similar to 10 wt.% CHA addition lead to linear shrinkage, water absorption and flexural strength values that fall within the range specified by floor tile standards (NBR 13817, EN 176 and ISO 13006), requiring no significant changes in processing parameters. Coffee husk ashes can thus advantageously replace feldspars in the role of fluxing material, with the potential to reduce not only natural ceramic raw material consumption, but also production and landfill costs as well as waste disposal area requirements. (C) 2013 Elsevier B.V. All rights reserved

Influence of fired clay brick waste additions on the durability of mortars

The use of metakaolin is known to help improve properties of Portland cement-based mortars. The presumed similarities between the characteristics of metakaolin and those of a powdered (<45 mu m) fired clay brick clean waste (CBW) led to the investigation of the effect on the durability of mortars of partial replacement (10, 25 and 40 wt.%) of Portland cement by CBW. Properties such as 28 and 90 days-compressive strength, water absorption, apparent porosity, absorption by capillarity, chloride retention, carbonation depth and sulphate resistance were evaluated. The CBW-containing cured mortars showed improved strength and density, as the result of combined physical and pozzolanic pore filling effect of added CBW. However, CBW-free mortar exhibited larger spreading and, being more porous, higher sulphate resistance and ability to absorb chlorides. Optimum performance was found for the 40 wt.% CBW mortar whose compressive strength can be up to 130% higher than that of the CBW-free mortar. (C) 2015 Elsevier Ltd. All rights reserved

Mullite formation from bentonites containing kaolinite: Effect of composition and synthesis parameters

Mullite (3Al(2)O(3)center dot 2SiO(2)) is rare in nature and not so easy to synthesize, but its unique ceramic properties explain the continuous search for alternative synthesis methods and precursors. Suggested precursors include other naturally occurring aluminosilicates, among which bentonites, and alternative methods include fast microwave heating, which might accelerate mullite nucleation kinetics and crystal growth. Thus, the aim of this work was to study the effect of bentonite composition and microwave exposure time (15-25 min) on the amount of formed phase and the morphology of mullite grains, which were characterized by X-ray diffraction and electron microscopy. Despite the short firing cycles, mullite formation and growth were found to closely follow the changes in fluxing oxide content and the estimates provided by the phase equilibrium diagram of the relevant system. The elongated grain morphology was promoted by impurities soluble in the mullite structure. (C) 2013 Elsevier B.V. All rights reserved