Daniel Véras Ribeiro

Potential use of natural red mud as pozzolan for Portland cement

Red mud, the main waste generated in aluminum and alumina production by the Bayer process, is considered hazardous due to its high pH, according to the Brazilian standard NBR 10004/2004, and worldwide generation of this waste exceeds 117 million tons/year. In this work, non-calcined red mud was used, thus requiring less energy and time and reducing costs, which is the ideal condition for reusing wastes. Mortars containing 30 wt. (%) of cement substituted by red mud showed higher strength of hardened products. The pozzolanic activity index was evaluated based on physical and mechanical parameters (Brazilian NBR 5751 and NBR 5752 standards) and on a chemical analysis (European EN 196-5 standard). A comparison of the reference mixture (without red mud) and the results obtained with red mud confirm the potential of non-calcined red mud for use a as pozzolanic additive in cementitious materials. The setting time (according to the MERCOSUL NM 65 standard) tends to increase but workability remains almost unchanged.

Uso da Espectroscopia de Impedância Eletroquímica (EIE) para monitoramento da corrosão em concreto armado

Entre as tecnicas mais utilizadas para a avaliacao e estudo da corrosao em concreto armado estao as tecnicas eletroquimicas, entre elas a espectroscopia de impedância eletroquimica (EIE). A EIE e uma tecnica poderosa para a caracterizacao de uma grande variedade de sistemas eletroquimicos e para a determinacao da contribuicao de processos individuais de eletrodo ou eletrolito nestes sistemas. A analise dos resultados de EIE em amostras de concreto armado e de alta complexidade, devido a sobreposicao de arcos provenientes de fenomenos simultâneos e a ruidos da medida, associados, evidentemente, a heterogeneidade das amostras e que dificultam de forma consideravel esta analise. Assim, o presente trabalho propoe uma nova forma de analise, baseada na frequencia angular de relaxacao caracteristica, w, de cada fenomeno e associando as capacitâncias e frequencias tipicas.

Chloride diffusivity in red mud-ordinary portland cement concrete determined by migration tests

Red mud, which is a solid waste produced in the alumina production process, is classified as dangerous due to its high pH. In this work, the concentration of chlorides was monitored by measuring the conductivity of the anolyte, which initially was distilled water. The steady and nonsteady-state chloride diffusion coefficients were estimated from the “time lag” and “equivalent time” between diffusion and migration experiments. The capillary water absorption, apparent porosity and pore size distribution of concretes were also analyzed. The addition of red mud apparently ensured lower chloride diffusion in the tested mixtures due to its superfine particle-size distribution and its “filler” effect. Red mud lengthened the service life of the concrete to 35 years (double that of the reference concrete). This finding is very positive since it indicates a delay in the onset of the rebar corrosion process caused by the migration of chloride ions.

Performance Analysis of Magnesium Phosphate Cement Mortar Containing Grinding Dust

Magnesium phosphate cement materials are formed by reacting magnesium oxide with water-soluble phosphates such as monoammonium dihydrogen phosphate (ADP), which solidifies at ambient temperature through the formation of hydrated phases in the material. Cylindrical specimens of magnesium phosphate cement were molded and varying amounts (0 to 30% weight) of grinding dust were added to the ceramic matrices. The influence of the addition of grinding dust on the characteristics of the mortars in terms of microstructure (SEM), mechanical strength and capillary water absorption was verified. The results obtained proved very satisfactory for the use of this waste as an additive in magnesium phosphate mortars.

Effect of Calcination Temperature on the Pozzolanic Activity of Brazilian Sugar Cane Bagasse Ash (SCBA)

This study evaluated the feasibility of using sugar cane bagasse ash (SCBA), a by-product of the sugar cane ethanol industry, obtained under controlled calcination as a partial replacement for Portland cement in mortars. Materials with pozzolanic characteristics may be used to partially replace cement in mortars or concrete and are known to provide durability to the products. Initially, TG/DTA curves of the sugar cane bagasse were conducted to define suitable calcination temperatures (500oC, 600oC and 700oC), and tests were conducted to characterize the physical-chemical parameters of the SCBA and the pozzolanic activity according to NP EN 196-5. The results showed the technical feasibility of using the SCBA as a pozzolanic material in construction, which would provide an alternative to proper disposal for this waste while providing products with high technical performance.

Effect of Chemically Treated Leather Shaving Addition on characteristics and microstructure of OPC mortars

The growing concern with environmental issues in tanneries and the search for a technological solution to their wastes are evaluated in this study. The leather shaving was chemically treated aiming the immobilization of the chromium ion on ordinary Portland cement (OPC) matrix. Cementitious mortars were obtained by adding different proportions of waste treated solutions (5 and 10% compared to the cement mass) and after 28 days, the samples were evaluated in relation to their physical properties, axial compressive strength and, for the most promising compositions, microstructural characterization analyses tests were realized. Results showed that the alternatives used for the pretreatment were effective for the leather shaving dissolution; but the results analysis describes little change in pH values when the treated waste is added in three different media. The best axial compressive strength after 28 days age were obtained by addition of diluted phosphoric acid solution at low concentration, although this addition minimize the Portlandite formation and favor the calcium phosphate formation.

Effect of Calcined Red Mud Addition on the Hydration of Portland Cement

The red mud (RM) is a solid waste derived from the processing of bauxite ore to produce alumina and it is considered a hazardous waste due to its high pH. This paper describes the use of mud untreated and after calcination at distinct temperatures (450, 650, and 1000°C) attempting to improve its reactivity. The Portland cement was replaced up to 30 wt% red mud, and its addition changed the hydration process, evaluated by calorimetric studies of early hydration and setting time. By comparing with the reference mixture (without red mud), the obtained results confirm the potential of the red mud to be used as pozzolanic additive to cementitious materials. Temperature of hydration was monitored by a quasi-adiabatic calorimeter (Langavant). The hydration temperature increases with RM addition, particularly if calcined in the same interval (450-650°C). In this condition, the hydration process is accelerated.

Efeito da eletrodeposição de Zinco e da liga Zinco-Níquel na corrosibilidade das armaduras de concreto armado

O presente trabalho avaliou os parâmetros de corrosao das barras de aco revestidas com Zinco (Zn) e com a liga Zinco-Niquel (Zn-Ni), por eletrodeposicao, comparando-as com as tradicionalmente utilizadas, sem revestimento. Para isso, utilizaram-se amostras de concreto armado que foram submetidas a ensaios acelerados de corrosao por acao de cloretos (câmara de nevoa salina – “salt spray” e ciclos de imersao e secagem). O potencial de corrosao das armaduras foi medido para monitoramento qualitativo do processo e, apos o fim dos ensaios, estimaram-se as taxas de corrosao das barras, atraves da perda de massa, para analise quantitativa. As barras revestidas com Zn e Zn-Ni se mostraram mais resistentes a corrosao, quando comparadas com as barras convencionais, em ambientes com forte acao de cloretos e o envelhecimento por ciclos se mostrou muito mais eficiente na aceleracao do processo de corrosao.

Synthesis and Sintering of LaCo1-XFexO3 Ceramics: Microstructure Analysis

This work intends to show the effect of the iron ion doping in LaCoO3 perovskite, both in powders and in sintered samples obtained from combustion reaction route. The phase formation and particle morphology and particle size distribution of the powders were analysed by XRD, SEM and sedimentation techniques, respectively. Relative density, microstructure (secondary phases and grain size) and pore size distribution of LaCo1-xFexO3 sintered ceramics have been investigated by SEM/EDS and Hg porosimetry analysis. Although LaCo1-xFexO3 powders obtained from combustion reaction exhibited smaller grain sizes when sintered at high temperatures, they showed higher volume fraction of secondary phases. The presence of these crystalline phases in addition to the desired perovskite affected the microstructure acting as grain growth inhibitors by grain boundary pinning. It is believed by observing three grain junction pores that LaFeO3 phase has a smaller dihedral angle than LaCoO3. This fact would explain why LaFeO3 presented a smaller driving force for sintering with higher tendency of pore and inclusion coarsening at higher temperatures (1400°C).

Evaluation of the Incorporation of Waste Generated from Titanium Dioxide Manufacturing in Red Ceramics

Rotary-vacuum-filter mud (RVFM) is waste generated during the manufacturing process of titanium dioxide. In this work, RVFM and ceramic bricks containing different ratios of this waste are investigated. The mud samples were characterized using thermal analysis (TG/DTG). The aim of the present work was to determine the effect of adding RVFM on the ceramic properties of clay, such as apparent porosity, water absorption, linear shrinkage and flexural strength, used to produce red ceramics (bricks and roofing tiles). Samples were dried out at 110°C and fired at 800°C, 950°C and 1100°C. The addition of RVFM tends to increase the apparent porosity and water absorption and to decrease the flexural strength of the ceramic specimens. Based on the results, ceramic specimens with 20% RVFM content that are burned at 800oC can not be used as bricks, and ceramic specimens with 20% RVFM content that are fired at 800oC and 950°C can not used as roofing tiles, according to Brazilian standards.