Materials Science Forum Vol. 820

Abstract: Temperature and moisture substantially affect the water elimination procedure, occurring in the drying stage, of ceramic blocks used in building construction. In the present work, a modeling of the thermal gradients and moisture content during the drying process of red clayey ceramic blocks was analyzed using computer simulation by means of Mathematica^® software program. Results of two-dimensional thermal gradients and variation of moisture content were predicted. This revealed that regions next to the vertices of prismatic ceramic blocks are more susceptible to structural damage due to development of cracks and deformations.

Abstract: Concrete mixing technology has spread with the development of water-reducing additives, enabling production of high quality products. Despite the discoveries and important technological advances, occurrences concerning the incompatibility between sealers and additives have been reported. The main incompatibilities occur between additive and cement of different brands, or different batches. This study investigated the influence of a superplasticizer on the properties of two cements of the same class (type CP II E 32), but different manufacturers. Two cements (without the presence of the additive) were characterized by physical, chemical and mechanical tests. The setting times for pastes made ​​from cement, water and superplasticizer mixtures were determined. The results showed a significant difference in physical, chemical and mechanical properties of cements, as well as those related to the hydration process thereof.

Abstract: The use of foundry waste in civil engineering is one of the most discussed issues by several environmental polities. This is caused by the excessive deposition of foundry waste on sanitary landfills. In order to find solutions to overcome this situation, this paper investigates the effect of the foundry powder concentration in the structure of mortars. Experiments were conducted with mortars processed at several concentrations of binders, aggregates and foundry powder. Results indicate that mortars built with foundry waste have water retention above to 75%. This observation indicates that mortars processed with foundry waste can be used in civil construction.

Abstract: The aim of this paper was to investigate the influence of heat treatment on hardness evolution of cement pastes containing silica fume. The specimens were prepared with Ordinary Portland Cement, water/binder ratio of 0,40 and 25% wt. silica fume. The specimens were cast at room temperatures and after 24 hours, they were placed in a furnace for 24 hours, with heat regimes of 100°C, 200°C and 300°C and then submitted to the ultra-microhardness test. The microstructure was analyzed using optical microscopy. The results showed that the silica fume prevents the production of calcium hydroxide and the heat treatment increases the material hardness.

Abstract: Several years ago the study on modification of existing materials that have enhanced properties has gained prominence. In this scenario, the geopolymeric binders, currently widely used in the construction industry have emerged. Thus, this study aimed to evaluate the influence of alumina addition on the mechanical and thermal properties of metakaolin in geopolymer binder. The geopolymers were synthesized from mixtures of metakaolin/alumina and sodium hydroxide, pressed and characterized by diffraction of X-ray and differential thermal analysis and thermogravimetric. Two types of alumina were used in different amounts (14% and 7%) in order to evaluate the effect of the load binder obtained. It can be seen that the incorporation of alumina into the system caused an increase in strength of products obtained as well as a reduction in total mass loss of the sample , especially when the use of fine alumina.

Abstract: The ornamental stone industry in Brazil is a major world producer of marble and granite with a significant amount being destined to foreign countries export. A considerable amount of waste is generated at the several stages of stone processing specially the sawing with the so called diamond wire technique. In the present work a granite waste from a diamond wire sawing was added into conventional mixture of cement, gravel and sand to fabricate concrete used in civil construction. The waste was chemically and mineralogically characterized by X-ray and its pozzolanic activity was evaluated. Concretes with 0, 10 and 20 wt% of waste were tested for the water absorption and mechanical strength as well as environmental behavior. The results indicated that up to 20 wt% addition, the granite waste does not change the concrete performance and attends its environmental requirements.

Abstract: The addition of hollow glass spheres is interesting to reduce the thermal conductivity of the concrete pieces. This work aims to evaluate the concrete with addition of hollow glass microsphere with different combinations of dosage in concrete concerning strength and workability. Slump tests were performed in each dosage of concrete in order to evaluate the effect of glass microspheres in concrete mix. In each age of curing concrete, bodies-specimens underwent ultrasound to estimate the homogeneity of concrete with hollow glass microspheres, and testing of compressive strength. The analysis of the results shows that for some formulations, the addition of hollow glass microspheres imparts high mechanical strength to compressive strength above 30MPa at all analyzed cure periods. The workability of the concrete had to be substantially reduced, showing no workability improvement due to the addition of hollow glass microsphere.

Abstract: The fired-clay ceramic industry generates relatively large amount of wastes mainly bottom ashes remaining in the firing furnaces and broken pieces, known as grog, from inappropriate products. These wastes, if inadequately disposed, may cause pollution associated with environmental degradation as well as health hazards. A viable solution for these wastes is their incorporation in concrete for civil construction, as long as they have pozzolanic activity. Therefore the present work evaluated the pozzolanic activity of three different types of wastes generated at the same ceramic industry. These wastes were a furnace remaining bottom ash from burning wood log, a similar ash from sawdust burning and a grog powder from higher firing temperature broken ceramics. The pozzolanic activity was measured by the electrical conductivity variation method. The results showed that both ashes are not provided with pozzolanic activity while the grog has a moderate activity.

Abstract: The gypsum is a versatile material that shows low thermal conductivity, which makes this material very suitable for application as thermal insulation. The increase of the porosity of gypsum bodies promotes a decrease on the thermal conductivity. This effect optimize the range of applications of gypsum on the thermal insulate field. The present study aimed the numerical modeling of two-dimensional heat conduction by finite differences in a steady state to evaluate the ortotrophy of the thermal conductivity of porous gypsum using the elements of the protected hot plate method. Computer simulations were performed using thermal conductivity of the gypsum equal to 0.35 W/m.K. This value was varied on the x and y directions by 5%, 10% and 15%. The heat flow applied to the numerical simulations were equal 75 W/m2, 100 W/m2 to 125 W/m2.It was possible to produce temperature profiles where is visible the displacement of isotherms as a function of the change in thermal conductivity in the x direction.

Abstract: The objective of this study was to evaluate materials stabilized by solidification after incorporation of oily sludge of oil in a ordinary Portland cement matrix through analysis tests Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The research was divided into two main stages. In the first step the preparation of the specimens composed of cement, sand and oily sludge of oil and the second step was to evaluate the stabilization/solidification material via SEM and XRD analysis. The results of the XRD identified the characteristic peaks of portlandite, calcium silicate and ettringite. The same occurred with the SEM that detected the presence of the main products of the reactions of cement hydration. The results showed that the oily sludge of oil did not interfere with cement hydration reactions.