Augusto Cesar da Silva Bezerra

The effect of calcination conditions on the physical and chemical characteristics of sugar cane bagasse ash

The effect of calcination temperature and air flow on the content of organic material, morphology of particles, degree of crystallinity and the reactivity with lime solution of the sugar cane bagasse ash is evaluated. The results show that the long fibers of the bagasse and organic material are retained when calcination occurs without sufficient air flow. Calcining with forced air-flow breaks the fibers, removes organic material and produces fine particles at a temperature of 600oC. The non-organic material observed in the ash displays a high degree of crystallinity. Experiments show that the crystalline structure observed in the ashes is due to adhered sand which was not previously washed away. The reduction on the conductivity in lime solution and X-rays diffraction pattern suggest that amorphous silica is formed at temperatures lower than 600 o C and cristobalite is formed at higher temperatures.

Sterile Clay Pozzolans from Phosphate Mining

The work presents the characterization of clays from sterile mining of the concentrated phosphatic materials of Araxa in Minas Gerais as pozzolanic materials. Three clays of distinct tones, namely, yellow (YC), red (RC), and intermediate (IC) clays, were used at different levels of excavation depth. The clays were calcined at three temperatures (680, 760, and 840 °C) in a muffle-type electric oven. The pozzolanic activity levels of the calcined clays was measured through the conductivity change in saturated Ca(OH)2 solutions and also from the result of the compressive failure load achieved by mortars with 35% of the Portland cement replaced with the calcined material. The results indicated that the calcined clays showed a high level of pozzolanic activity and can be used as a partial substitute for Portland cement, thus suggesting the possibility of recovering this sterile material.

Iron Ore Tailing as Addition to Partial Replacement of Portland Cement

The manufacture of Portland cement used in the production of concrete emits large amounts of CO2 into the atmosphere, contributing to the increase of the greenhouse effect. The environmental impact generated by the mineral exploration activity is a problem of easy verification, especially in open pit mines. The present work evaluated the possibility of using iron ore tailing as an addition to the partial replacement of the cement in mortars. The iron ore tailings were processed by drying in oven (48h at 105oC) and milling in a planetary mill (10min at 300RPM), obtaining medium grain size of 14,13 μm. For the characterization, laser granulometry, X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal and thermogravimetric analysis (DTA / TGA) were performed. The sample is composed predominantly by quartz, hematite, goethite and gibbsite. After the characterization, the waste was used in the preparation of test specimens, with 10, 20 and 30% weight substitution of the cement. The composites were submitted to compression tests, with ages of 3, 7 and 28 days, using a strength rate of 0,25MPa/s. The mortars with 10, 20 and 30% of substitution presented resistance of 41.65, 36.26 and 31.64 MPa, being able to be characterized as category of Portland cement of resistance 40, 32 and 25 respectively. Considering the reduction of cement in the mortars produced, the results of compressive strength were relevant for the substitutions. The cements produced with the substitutions according to the Brazilian standards under the mechanical aspect can be classified as Portland cement.

Adsorption of Caffeine on Activated Carbon Obtained from Green Coconut Waste

In this study activated carbon was produced using green coconut shell as the carbon source. Furthermore, caffeine adsorption behavior in the produced material was studied, as a function of temperature, through the adsorption isotherms and their thermodynamic parameters. For this, the green coconut shell powder was subjected to the activation process, involving impregnation with phosphoric acid solution followed by pyrolysis in a muffle furnace. The adsorption experiments at four temperatures, 25, 35, 45 and 55°C, were studied with five aqueous solutions of different caffeine concentrations maintaining the same agitation rate (150 rpm). Langmuir and Freundlich equations were employed for thermodynamic equilibrium, the data adjusting better to the Langmuir model. The thermodynamic parameters such as entropy change, enthalpy change and Gibbs free energy variation were calculated from the linear equation of the Van’t Hoff. The results showed that caffeine adsorption in the activated carbon is a spontaneous and exothermic process, and the amount of caffeine adsorbed increases according to the concentration at a constant temperature, reaching values close to 170 mg g-1. The results demonstrated the potential of green coconut waste material as feedstock to obtain activated carbon, as well as for the treatment of wastewater containing emerging contaminants.

Evaluation of Sample Preparation Parameters in the Compressive Strength of Cementitious Composites

This paper presents an experimental evaluation of how variations in proposed parameters interfere with compressive strength resistance of mortar and concrete specimens. The results were obtained through laboratory tests in which samples were tested under varying conditions. These conditions were as follows: speed of load application (0.25, 0.50, 0.75, and 1.00 MPa/s), environmental conditions (saturated, 2 h dried, and 24 h dried specimens), curing (dry and wet), and specimen ends preparation (sulphur, neoprene, rectification, and without regularization). Comparisons were made on the basis of the compression strength resistance results and the coefficient of variation in order to analyse the homogeneity and dispersion among variables. It was found that in the case of capping, the best results were obtained by the rectification of concrete specimens. In the case of loading speed, the best results were obtained at a speed of 1 MPa/s. Dry curing showed the best results, even though not resulting in the highest resistance. The results for specimen conditions were in accordance with the expectations, with lower dispersion for saturated specimens.

Post-fire Behavior of Ordinary Concrete Reinforced with Short Steel Fibers

Concrete is a widely used material in civil construction and may be submitted to high working temperatures under various circumstances. Many factors influence the behavior of this material at high temperatures, which usually leads to the evaporation of the hydrated cement. The dehydrated cement undergoes a contraction, simultaneously with the thermal expansion of the inert fraction of the material. As a consequence of these conflicting expansions and contractions, the material cracks and its strength and modulus of elasticity decrease significantly. On the other hand, the addition of short metallic fibers to the material increases its toughness, probably due to its action on the cracking behavior of the composite. It is thus expected that a concrete containing metallic fibers should maintain its original properties even after exposure to elevated temperatures. This paper presents an evaluation of the influence of steel fibers on the microstructure and toughness of concretes submitted to high temperatures. The bending behavior, under strain rate control, of concretes with a strength of 30 MPa and containing short steel fibers, submitted to a previous treatment at 500 °C, was analyzed. It was observed that, after both heat treatments, the addition of metallic fibers to concrete was able to maintain the pseudo-ductility and load-carrying capacity of this composite material.

EUCALYPTUS CHIP ASHES IN CEMENTITIOUS COMPOSITES

The Alto Paranaiba and Triângulo Mineiro mesoregion in the state of Minas Gerais and the State of São Paulo have a number of industries with eucalyptus chip fired boilers that produce great amounts of ash. Since thermoelectric ashes generally have good pozzolanic activity, this paper studied the mechanical behavior of cementitious composites made with raw eucalyptus chip ash as a partial replacement for Portland cement and processed under two different conditions. The mechanical behavior of the composites was measured from tests on specimens for their compressive strength, tensile strength to diametral stress and to bending. Results show ashes could be used as mineral additives.

Propriedades mecânicas de compósitos cimentícios produzidos com lodo de estação de tratamento de efluentes da indústria de batata pré-fritas

The large volume of industrial solid waste generated by the pre-fried potato industry and the high cost of its management encouraged researchers to find solutions best suited to its final destination. This study characterized the solid residue (sludge) from the effluents pre-fried potatoes industrys treatment station. The sludge was processed by drying, grinding and sieving. Laser particle size, scanning electron microscopy (SEM) with X-ray spectrometer dispersive energy (EDS), X ray diffraction, differential thermal analysis (DTA), thermogravimetric (TGA) and loss on ignition were used to characterize the sludge. After characterization, cement was made using 3, 5, 7 and 10 percentages of the sludge to replace the cement. The composites were tested to obtain the compressive strength and dynamic elasticity modulus. Based on the result of the loss on ignition, the use of sludge as pozzolan was discarded. Based on the mechanical property tests carried out, it was noted that the addition of sludge as a partial replacement of cement is negatively impacted, with only the results of the cement composites of 3% and 5% being satisfactory.

The influence of specimen capping on the results of compression strength tests of cementitious composites

Cementitious composites are commonly evaluated considering their workability, level of incorporated air, elasticity modulus and compression strength. Data from compression testing commonly present a high dispersion, which has been attributed to effects of the specimen geometry, dimensions and of the degree of material compaction, as well as to problems in the specimen end-faces, such as their parallelism, orthogonality in relation to the compression axis and surface regularity. Specimen end-face regularization has been achieved through various techniques, such as adhering or non-adhering capping with various materials, mechanical grinding and systems involving special moulds. The regularization methods utilized more frequently employ sulfur mortar capping, neoprene cushions and surface grinding. The present work covers the experimental compression tests of cementitious composites of different classes of strength employing sulfur mortar capping and neoprene cushions. It was concluded that there is a strong influence of the chosen regularization technique on the measured compression strengths.