Sivaldo Leite Correia

Assessment of the recycling potential of fresh concrete waste using a factorial design of experiments

Recycling of industrial wastes and by-products can help reduce the cost of waste treatment prior to disposal and eventually preserve natural resources and energy. To assess the recycling potential of a given waste, it is important to select a tool capable of giving clear indications either way, with the least time and work consumption, as is the case of modelling the system properties using the results obtained from statistical design of experiments. In this work, the aggregate reclaimed from the mud that results from washout and cleaning operations of fresh concrete mixer trucks (fresh concrete waste, FCW) was recycled into new concrete with various water/cement ratios, as replacement of natural fine aggregates. A 3(2) factorial design of experiments was used to model fresh concrete consistency index and hardened concrete water absorption and 7- and 28-day compressive strength, as functions of FCW content and water/cement ratio, and the resulting regression equations and contour plots were validated with confirmation experiments. The results showed that the fresh concrete workability worsened with the increase in FCW content but the water absorption (5-10 wt.%), 7-day compressive strength (26-36 MPa) and 28-day compressive strength (32-44 MPa) remained within the specified ranges, thus demonstrating that the aggregate reclaimed from FCW can be recycled into new concrete mixtures with lower natural aggregate content.

Effect of quartz sand replacement by agate rejects in triaxial porcelain

The ceramics industry, given the high volume of materials processed, stands as one of the largest consumers of natural raw materials but has also the capacity and potential to make significant contributions to solving environmental problems associated with other industries rejects. This work investigates the effects of quartz sand replacement by agate rejects (scrap) in a traditional triaxial porcelain composition. The study was carried out using the design of experiments (DoE) method. Characterization results were used to calculate statistically significant and valid regression equations, relating dried and fired body properties with clay, feldspar and agate scrap contents in the unfired mixture. The regression models were then discussed against X-ray diffraction and scanning electron microscopy results and used simultaneously to delimit the combinations of those three raw materials most adequate to produce a porcelainized stoneware floor tile with specified properties. Thus, an alternative use of an otherwise waste material is proposed, which can be translated into economic benefits and an important and welcome relief on environmental and waste disposal concerns.

Effects of Raw Materials on the Technological Properties of Brick Compositions Using a Statistical Design Approach

The simultaneous effect of raw materials (A, B and C) on physical and technological properties of brick compositions was studied. This investigation was carried out using the statistical design of mixture experiments. Ten mixtures of three raw materials were selected and used in the experiments design. Those mixtures were processed under conditions similar to those found in the ceramics industry. Fired body characterisation results were then used to iteratively calculate statistically significant and valid regression equations (trace plots), relating linear firing shrinkage, open porosity, fired bending strength and water absorption with the proportions of raw materials. The microstructures of some selected samples were studied using scanning electron microscopy. Mixtures with high clay B contents were most adequate to produce, under constant processing conditions, a brick with specified properties. The microstructures are characterized by a low closed porosity and absence of vitreous phase.

Clays from Southern Brazil: Physical, Chemical and Mineralogical Characterization

Fore knowledge of the characteristics of ceramic raw materials is of utmost importance during the development, processing and production stages of any ceramic product. This work describes the characterization of clays commonly used in the ceramics industry. Two different clays were selected: clay A, from Tubarão-SC and clay B, from Porto Alegre-RS. Their chemical composition was obtained by X-ray fluorescence and their mineralogy by X-ray diffraction, coupled with numerical rational analysis. Their thermal behaviour was studied by differential thermal analysis and thermogravimetry. Their particle size distribution and plasticity were also determined. Clay A showed circa 47.5 % quartz (by weight), 40.2 % kaolinite and 9.9 % muscovite mica. Clay B showed a high kaolinite content (circa 72 wt.%), accompanied by montmorillonite (circa 10 %) and potash feldspar (circa 10 % microcline). Clay B was found to be much more plastic than clay A, and both are suitable for pottery, tiles and brick making.

An Optimisation of Scrap Agate Powder Contents in Triaxial Ceramic Bodies Using Mathematical and Statistical Strategies

In the present study, the waste scrap agate, obtained as a by-product of rock agate beneficiation as decorating ends and media for wet grinding was used as inert filler in a traditional triaxial red stoneware tiles composition. The effects on the technological properties have been investigated. The study has been carried out using the mixtures experiments method for the experimental design. Characterization results were used to calculate statistically significant and valid regression equations, relating dried and fired body properties with clay, feldspar and scrap agate contents in the unfired mixture. The regression models were then used simultaneously to delimit the combinations of those three raw materials most adequate to produce a ceramic body with specified properties. The use of mathematical optimisation shown that, for the particular raw materials under consideration, there is a rather forgiving composition range of clay (20-68 wt.%), feldspar (17-50 wt.%) and scrap agate (15-45 wt.%) contents within which it is possible to simultaneously specify the technological requirements for triaxial red stoneware tiles bodies, not only of the fired products but also of the intermediate materials at important stages of the processing.

Using Experiments Design to Model the Effect of Raw Materials on the Sintering and Technological Properties of Brick Compositions

Mixtures of clays are often used in the manufacture of bricks. In industrial practice, it is desirable to be able to predict, in an expeditious way, what the effects of a change in raw materials or the proportions thereof might be in the various processing steps towards the final product. When the property of interest is basically determined by the combination of raw materials, an optimisation methodology specific to the design of mixture experiments can be successfully used. In the present study, fired bending strength and linear firing shrinkage were selected as the properties to model. Ten formulations of three different clays were selected and used in the experiments design. Those formulations were wet processed, uniaxially pressed, and then fired at 1000 °C for 2 h.. From the experimental results, regression models were calculated, relating each technological property with the proportions of raw materials. The regression models were then used simultaneously to define which combination of those three raw materials was most adequate to produce, under constant processing conditions, a brick with specified properties.

Using Experiments Design to Model Linear Firing Shrinkage of Triaxial Ceramic Bodies

In the development and manufacture stages of floor and wall ceramic tiles, firing shrinkage is basically determined by the combination of raw materials and frequently used as quality control parameters. This configures the ideal scenario to apply the techniques of experiments design, often used in various other areas, to model those properties of such ceramics bodies. In this work, ten formulations of three different raw materials, namely a clay mixture, potash feldspar and quartz (triaxial compositions) were selected and processed under conditions similar to those used in the ceramics industry. With the experimental results, a regression model was calculated, relating linear shrinkage with composition. After statistical analysis and verification experiments, the significance and validity of the model was confirmed. The regression model can then be used to select the best combination of those three raw materials to produce a ceramic body with specified properties.

Characterisation of Refractory Ceramic Pressed Body Containing Industrial Waste

This study investigates the use of an industrial refractory brick waste in the refractory based silica and alumina ceramic body. From the characterization of the waste, a mixture containing a clay, silica, alumina and waste was processed via wet route and sintered at 1400 °C. The specimens were evaluated in dry (density) and after sintering (linear shrinkage, density and modulus of rupture).Microstructural characterization by scanning electron microscopy (secondary electron) revealed a microstructure unevenly and a presence of big porous which shows also small amounts of vitreous phase, which can be related to sintering process not fully finished. The results for the linear shrinkage (about 6 %) and modulus of rupture at three points (about 63 MPa) showed that the mixture containing the refractory brick waste and the processing conditions were satisfactory for obtaining a suitable refractory material for the manufacture of bricks for melting furnaces.

Characterisation of Geopolymer Cements Obtained from Different Sources of Metakaolin

In the present study metakaolin and clay brick waste (CBW) were used as a source of silica and alumina along with precursors aiming to obtain geopolymer cements, which were characterised via scanning electron microscopy (SEM) and X-ray diffraction (XRD). The CBW was obtained from rejected clay brick industrial manufacturing process. The precursors were activated by using of 5.0, 10.0 and 15.0 [mol.L-1] KOH solutions, which was added to K2SiO3 solution at 1:1 weight ratio. To obtain the geopolymer cements the weight ratio of precursor and activators were changed at levels of 0.6, 1.0 and 1.4. The samples were prepared and cured at room temperature for 7 days. The geopolymer cement obtained from metakaolin at 15 mol.L-1 level of KOH concentration and KOH/K2SiO3 ratio of 1:1.4 provided the best cement which can be estimated by the largest reduction and dissolution of crystalline phases in the activation reaction.

Property Optimisation of EPDM Rubber Composites Using Mathematical and Statistical Strategies

This paper describes a study in which EPDM-based rubber composites were investigated aiming at developing formulations subjected to restrictions on cost and the properties of the material. The contents of components other than calcium carbonate, paraffinic oil, and CBS vulcanising accelerator, as well as additives and processing conditions, were kept constant. Fractional factorial design coupled with computational numerical optimisation was used to minimise the number of mixtures. The results demonstrate that statistical design of experiments and particle swarm optimisation (PSO) algorithms are promising methods to design composition variables. Mixture costs as low as 1.92 US