Papers by Author: Joao A. Labrincha

Abstract: One of the key characteristics of fresh mortars is their rheological behaviour since it determines the material workability and has a clear influence on the hardened product final properties. Indeed, mortars rheological properties are extremely important since several factors, related with placement, consolidation, durability and strength depend on the flow properties of the mortar paste. In this work, the effect of ageing time on the rheological properties of fresh aerial lime-based mortars was investigated. Mortars having a 1/3 binder/aggregate volume ratio were studied as a function of ageing time. The influence of a water retaining agent (0.1 wt. %) addition in these mortars was also analysed. Mixing and ageing have a clear influence in the water intake process ruling over the rheological behaviour of this type of mortars.

Abstract: Alumina and alumina-mullite based refractory ceramic materials were produced from formulations based on an industrial Al-rich sludge derived from the wastewater treatment of the aluminium anodising process. Other ceramic raw materials like diatomite was also added, which can be consider as a by-product. Cylindrical samples processed by uniaxial dry pressing were sintered at different temperatures (between 1400-1650°C, 1 hour soaking) to study the ceramic properties evolution. The performance of fired materials was evaluated (firing shrinkage, water absorption, bending strength, thermal expansion coefficient, refractoriness and SEM microstructure) and demonstrated that optimal properties were obtained at 1650°C for alumina and 1450°C for alumina-mullite.

Abstract: The preparation of ceramic pigments using industrial waste, a galvanizing sludge from the Cr/Ni plating process, as primary source is here reported. The ceramic pigments were prepared using the common solid state reaction process, investigating the optimal formulation, milling and firing conditions. The main focus will be given on the synthesis of chrome-tin red malayaite Ca(Cr,Sn)SiO5 pigment that was fully characterised and then tested in a standard ceramic glaze. Typical working conditions and colour development will be also reported.

Abstract: This work describes the studies carried out with various industrial wastes and natural byproducts based on the SiO2-Al2O3-CaO system, aimed at extruding ceramic products of industrial interest. Four waste materials were selected and characterised, namely, (i) Al-rich anodising sludge (A-sludge), (ii) sludge from the filtration/clarification of potable water (W-sludge), (iii) sludge generated in marble sawing processes (M-sludge), and (iv) foundry sand (F-sand). Two different formulations were prepared and bodies were shaped by extrusion, after its detailed optimisation. Screw extruded rods were then fired at several temperatures and characterised in terms of relevant functional properties (shrinkage, density and mechanical strength). Their electrical insulating properties were assessed by impedance spectroscopy. The design of interesting technological properties, such as high electrical and mechanical resistance, refractoriness, etc, was found to be easily achievable by controlling the initial batch formulation and/or the sintering schedule.

Abstract: Al-rich sludge produced from industrial anodising and surface treatment processes had been tested in the fabrication of mullite-based materials, by using unidirectional dry pressing as shaping technique. Mixture with common natural silica and magnesium-containing materials, like ball clay, kaolin and diatomite were prepared in order to achieve interesting final fired refractory and/or electrical insulating materials. Microstructural changes upon sintering and crystalline phase evolution are detailed and their relationship with the electrical behaviour is also studied, by the use of impedance spectroscopy. Finally, different models were used to fit the experimental electrical resistivity values and to estimate the percolation limit of the bi-phase material.