Abstract The use of supplementary cementitious materials (SMCs) is one of the three essential factors for the sustainability of the cement industry. To reduce CO2 emissions, several studies have introduced new methods for the utilization of industrial wastes such as the addition into cementitious materials. The objectives of this study were to chemically and physically characterize refractory ceramic industry waste and determine its viability as an SMC. The pozzolanic characteristics or SMC characteristics of the refractory waste were investigated using standard tests. The results revealed that the refractory waste was mainly composed of Al2O3 and SiO2. The mineralogical analysis revealed that the mullite was the major phase of the waste, followed by small amounts of cristobalite and quartz phases. The results of the modified Chapelle test and pozzolanic activity index with lime after 7 days indicated that the waste did not meet the minimum pozzolanicity required by the standard. However, the waste improved the mechanical resistance of the cement specimens containing the waste after 28 days compared with the reference sample, indicating the promising potential of the material for this application. This result indicated that the refractory waste shows a filler type effect, and thus, can be employed as an SCM.

Resumo Bentonita é um tipo de argila composta principalmente de montmorilonita. Possui excelentes propriedades de adsorção e como principais características a alta capacidade de troca catiônica, capacidade de inchamento, grande área superficial e baixa condutividade hidráulica. A bentonita é utilizada como matéria-prima em mais de 40 aplicações industriais. O processo de liofilização consiste na secagem de um produto, passando pela etapa de sublimação, para remoção da água contida utilizando baixa pressão e impedindo qualquer atividade biológica e reações químicas. Ele é eficiente em características como contração do produto, perda de voláteis, decomposição térmica, ações enzimáticas e desnaturação de proteínas, se comparado com outros meios de desidratação, ou seja, mantém a integridade do produto. Neste trabalho, foi avaliado o comportamento e realizada a caracterização de bentonita sódica mais ativa e sódica menos ativa, antes e após o processo de liofilização. Considerou-se como mais ativa a bentonita que apresentou maior capacidade de troca catiônica - CTC relacionada aos íons sódio (Na+). Foram feitas análises químicas e mineralógicas, de capacidade de troca catiônica, análise microbiológica, FTIR e capacidade de inchamento. Observou-se um incremento de aproximadamente 32% na capacidade de inchamento da bentonita mais ativa após a liofilização.

Abstract Bentonite is a type of clay composed mainly of montmorillonite, shows excellent properties of adsorption and, as main features, high cation exchange capacity, swelling capacity, large surface area and low hydraulic conductivity. Bentonite is used as a raw material in over 40 industrial applications. The lyophilization process is a drying process of a product through a sublimation step for removing water using low pressure. This process prevents any biological activity and chemical reactions. The lyophilization process is effective in product shrinkage, loss of volatiles, thermal decomposition, enzymatic activities and protein denaturation as compared to other drying means, as it maintains the integrity of the product. This study evaluated the behavior and characterized the more and less active sodium bentonites, before and after the lyophilization process. It was considered as more active the bentonite that presented more cation exchange capacity related to sodium ions (Na+). Chemical and mineralogical analyzes, cation exchange capacity, microbiological analysis, FTIR and swelling capacity were evaluated. An increment on swelling capacity of the more active freeze-dried bentonite of approximately 32% in comparison to the standard was observed.

AbstractSingle-cycle firing is currently the most widespread method used for the production of ceramic tile. The productivity is directly related to the performance of the constituent materials of the ceramic piece during thermal cycling. Numerical tools which allow the prediction of the material behavior may be of great help in the optimization of this stage. This study addressed the mathematical modeling of the temperature profile within a ceramic tile, together with the sintering kinetics, to simulate the effect of the thermal cycle on the final size. On the laboratory scale, 80 mm x 20 mm specimens with thicknesses of 2.3 mm and 7.8 mm were prepared in order to determine the kinetic constants and validate the model. The application was carried out on an industrial scale, with 450 mm x 450 mm pieces that were 8.0 mm thick. These results show that the model was capable of predicting the experimental results satisfactorily.

A produção de revestimentos cerâmicos pelo processo monoqueima é atualmente o mais difundido entre as empresas de cerâmica. O processo de queima está em constante evolução e adaptação à novos parâmetros, devido ao crescimento tecnológico e à diversificação dos produtos cerâmicos. É necessário entender o mecanismos envolvidos na queima de placas cerâmicas utilizando fornos a rolos, principalmente o desempenho térmico do equipamento e características técnicas dos revestimentos cerâmicos. Neste trabalho, um modelo matemático e um procedimento experimental foram aplicados para determinar a cinética de retração. Os parâmetros cinéticos foram determinados experimentalmente, utilizando pó industrial para obter corpos-de-prova de 80 x 20 x 2,3 mm³ queimados em forno elétrico laboratorial a rolo. A energia de ativação, Ea =178041 J/mol, o expoente do tempo "n" que determina o mecanismo de sinterização, n = 0,26285 e fator de freqüência, k0 = 44768 s-1 foram determinados depois de distintas condições de queima em 30, 40 e 50 min de frio a frio e as temperaturas entre 1000 a 1150 °C (com passos de 30 °C).

The firing process is the core of the tiles production, currently the single-cycle firing is the most widespread method in ceramic industries. Moreover, the increasing demand of technological improvements and technical diversifications of ceramic products, leads the firing process to continuously adapt to new operative conditions. The physical mechanisms that occur in roller kilns have to be understood, mainly those involving thermal performance of the equipment and technical characteristics of the ceramic tiles. In this work, a mathematical model and an experimental procedure has been applied to determine the shrinkage kinetics. The kinetic parameters have been experimentally determined using industrial powder to obtain test pieces of 80 x 20 x 2.3 mm³ fired in laboratory electrical roller kiln. Activation energy, Ea=178 kJ/mol, parameter "n", n=0.26285 and frequency factor, k0=44768 s-1 were determined after several firing conditions 30, 40 and 50 min cold-to-cold and temperatures from 1000 to 1150 ºC (steps of 30 ºC).